CN101050507A - Steel with excellent corrosion resistance for shipping - Google Patents

Abstract

The present invention provides a kind of steels for ship with excellent anti-caustic, the characteristics of which is that it contains C 0.01~0.3%, Si 0.01~2%, Mn 0.01~2%, Al 0.005~0.1%, Cu 0.01~1% and Cr 0.01~1%,the allowance is Fe and the unavoidable impurity, the Fe is most component, the amount of the bainite and/or martensite is under 30%(including 0%).

Description

The steel for ship of excellent corrosion resistance

Technical field

The present invention relates in the boats and ships of oil tanker, goods ship, semi-cargo ship, passenger boat, warship etc. the steel for ship that uses as main structural wood.The present invention in detail, exposed to the open air under even relate to from the salinity of seawater and hot and humid highly corrosive environments, also demonstrate the steel for ship of excellent erosion resistance, the steel of the excellent corrosion resistance that uses as the crude oil basin base plate (being designated hereinafter simply as " crude oil basin base plate ") of the oil tanker that is used to preserve crude oil or former greasy filth, and the steel (particularly Plate Steel) that are attached to the excellent corrosion resistance that uses on the ballast tank (ballast tank) on the boats and ships for the stability that improves boats and ships.Steel for ship of the present invention can be used for the structural wood of ballast tank and cruise etc. according to its embodiment, is particularly useful for crude oil basin base plate etc.The present invention also provides a kind of boats and ships in addition, and it has the ballast tank of the excellent in te pins of durability that is made of steel plate of the present invention.

Background technology

The steel that in described various boats and ships, use as main structural wood (for example: outside plate, ballast tank, crude oil basin etc.) and since be exposed to from the salinity of seawater and hot and humid in, thereby be subjected to corrosion damage mostly.

Specifically, the ballast tank of cabin carries out the injection and the discharge of seawater according to the variation of loading state etc., therefore in the corrosive environment that employed steel can be in the impregnation state of seawater repeatedly and the moistening atmosphere that contains salt is extremely harsh like this.In addition, to upperdeck, be high temperature in the ballast tank owing to sun exposure is arranged, but because hull by cooled with seawater, so brought temperature gradient to the anticorrosive coating film in the cabin.If bring temperature gradient to anticorrosive coating film, then owing to the pressure of soaking into of temperature difference generation, moisture will invade steel at an easy rate by filming, the corrosion under promoting to film, therefore if compare, for anticorrosive coating film harsh environment in the ballast tank then with common atmospheric environment.

Conspicuous problem is on crude oil basin base plate, because the moisture (retained water) that is detained becomes to grade with Sulfur from crude oil at the bottom of high density contains muriatic crude oil basin, steel are subjected to the intensive local corrosion and produce hole.

Because such corrosion might cause the sinking accident of boats and ships and from the oil spill disaster of oil tanker, therefore be necessary steel are implemented various anti-corrosion measures.Up to now the anti-corrosion measure of being carried out is at present known (a) application and (b) electric protection etc.

Be in the application of representative with the recoat dress wherein, the possibility height that paint film defect exists because the collision in the manufacturing process etc. also have the situation that causes damage to filming, therefore has basic steel to expose more.At such steel exposed division, can be locally and concentrated area corrosion steel, this will cause the early stage leakage of the crude oil of being accommodated.Though can confirm to produce effect by antirust/anticorrosion protection ratio that brings steel, the same with application, the such problem of corrosion of the steel exposed portions serve that can't avoid sheet scar portion is also arranged.

Electric protection is for very effective by the position of thorough impregnation in the high aqueous electrolyte liquid of electric conductivitys such as seawater.But the gas phase portion on crude oil basin and ballast tank top because there is not aqueous electrolyte liquid, does not bring into play preservative effect so can not form electric loop.In addition, because on crude oil basin base plate, play the retained water of aqueous electrolyte liquid effect insufficient (retained water thin thickness), so the distance that sacrificial anode works is unsuitable for electric protection for a short time.The galvanic anode of this external anticorrosion usefulness consumes unusually and comes off and when disappearing, have fierce corrosion at once and advance.

Among the described measure; open in the flat 06-322477 communique the spy; disclose by add among Cu, Cr, Ni and the Mo more than a kind; erosion resistance is improved; again by add among Nb, Ti and the V more than a kind; can make ferrite grain grain refined and reinforcement, be reduced in the be full of cracks advance rate of ferrite intragranular progress.Open in the 2004-190123 communique the spy, the chemical constitution that discloses with general steel for welded structures serves as basic, do not add Cr in fact, and with any one or both sides and an amount of compound interpolation of Cu of Mo, the W of specified quantitative, and limit as the P of impurity, the addition of S, can make thus at ordinary times and improve for the corrodibility under the environment in the crude oil tank deck (deck) of gas phase portion.Open in the 2003-82435 communique the spy, disclose, the erosion resistance of steel is improved by suitable adjustment chemical ingredients, inclusion and tissue.

Open in the 2005-97709 communique the spy, disclose, particularly make Ni content an amount of, and increase N content, thereby make of the anti-local corrosion raising of crude oil basin base plate with steel by adjusting chemical ingredients.Open in the 2004-204344 communique the spy, the chemical constitution that discloses with general steel for welded structures serves as basic, do not add Cr in fact, and with any one or both sides and an amount of compound interpolation of Cu of Mo, the W of specified quantitative, and limit as the P of impurity, the addition of S, and add Al, alleviate the local corrosion damage of steel for crude oil tank thus.Open in the 2006-9128 communique the spy, disclose the Co and the Mg that make specified amount and contain together, and suitably adjust chemical ingredients and form, thereby the corrodibility of steel for ship is improved.

Open in the 2000-17381 communique erosion resistance steel that also propose to have adjustment by chemical ingredients etc. that the erosion resistance of steel self is improved the spy.Open in the 2005-171332 communique the spy in addition, also proposing has by chemical ingredients adjustment and zinc rich primer steel (zinc rich primer) and that be used for improving erosion resistance.This external spy opens in the flat 7-34196 communique, also proposes to have the technology of combination corrosion-resistant steel and resin-coated raising weather resistance.

Open in the 2004-169048 communique the spy, disclose a kind of unrefined oil tank steel, optimizings such as chemical composition of steel is formed by making for it, the composition of the sulfide-based inclusion in the steel and oxide-based inclusion, size, number, improve the erosion resistance in the environment in the unrefined oil tank, and improved HAZ (welding heat affected zone) toughness under the high heat energy welding.

Summary of the invention

Utilize these improving technologies,, then can reach the state that the sort of erosion resistance is guaranteed if compare with existing material.But, can constantly require the raising of erosion resistance for steel for ship.Therefore, the purpose of this invention is to provide a kind of steel for ship that demonstrates more excellent erosion resistance.

In first grown form of the present invention, can reach the steel for ship that the above-mentioned purpose steel for ship is an excellent corrosion resistance, it is characterized in that, contain:

C:0.01～0.3% (meaning of quality %, as follows),

Si：0.01～2％、

Mn：0.01～2％、

Al：0.005～0.1％、

Cu：0.01～1％、

Ni:0.01～1%, and

Cr：0.01～1％，

Surplus is Fe and unavoidable impurities,

And ferrite is a maximum tissue, and bainite and/or martensite total were lower than for 30% (containing 0).Also have first grown form of the present invention to comprise first embodiment described later～the 3rd embodiment.

In second grown form of the present invention (the 4th embodiment), can reach the steel for ship that the above-mentioned purpose steel for ship is an excellent corrosion resistance, it is characterized in that, contain:

C：0.01～0.30％、

Si：0.01～2.0％、

Mn：0.01～2.0％、

Al：0.005～0.10％、

Below the S:0.010%,

And contain: a group element (from Mg, Ca, Sr, Ba, select more than a kind): 0.0005～0.020%; With

B group element (from Ti, Zr, Hf, select more than a kind): 0.005～0.20%,

And ratio S (a)/S (b) of the total content S (a) of above-mentioned a group element and the total content S (b) of b group element is in 0.01～1 scope, surplus is Fe and unavoidable impurities, in addition, satisfy the sulfide-based inclusion of following prerequisite and the median size of oxide-based inclusion and be respectively 1～10 μ m, and it is at the every 1mm of rolling direction ²Section in respectively have 200～2000.

Sulfide-based inclusion: in total amount contain described a group element 1～30% and/or in total amount contain described b group element 1～30%, equivalent circle diameter is the sulfuration type impurity more than the 0.5 μ m,

Oxide-based inclusion: in total amount contain described a group element 1～30% and/or in total amount contain described b group element 1～30%, equivalent circle diameter is the oxide-based inclusion more than the 0.5 μ m.

Except suitable adjustment chemical ingredients was formed, by suitable control metal structure and/or non-metallic inclusion, discovery can access the steel for ship of excellent corrosion resistance.

Description of drawings

Fig. 1 is an example of the sulfide-based inclusion of expression the 3rd embodiment of the present invention, and last figure is its SEM photo, and figure below is the EDX spectrum of the arrow portion of last figure.

Fig. 2 is the secondary electron image that produced by SEM of the sulfide-based inclusion in the steel of expression the 4th embodiment of the present invention and the chart of representing the EDX analytical results of this inclusion.

Fig. 3 is the secondary electron image that produced by SEM of the oxide-based inclusion in the steel of expression the 4th embodiment of the present invention and the chart of representing the EDX analytical results of this inclusion.

Fig. 4 is the face shaping explanatory view of the test film A of use among expression embodiment 1 and the embodiment 2.

Fig. 5 is the face shaping explanatory view of the test film B of use among expression embodiment 1 and the embodiment 2.

Fig. 6 is the face shaping explanatory view of the test film C of use among expression embodiment 1 and the embodiment 2.

Fig. 7 is the face shaping explanatory view of the test film D of use among expression embodiment 1 and the embodiment 2.

Fig. 8 is the graphic representation of the relation of anti-general corrosion and pearlitic long-width ratio in steel No.7～34 that make among the expression embodiment 1.

Fig. 9 is the graphic representation of the relation of anti-general corrosion and S (c)/S (a) value in steel No.40～61 that make among the expression embodiment 2.

Figure 10 is the graphic representation of the relation of anti-crevice corrosion and S (c)/S (b) value in steel No.40～61 that make among the expression embodiment 2.

Figure 11 is the explanatory view of the face shaping of the test film E of use among the expression embodiment 3.

Figure 12 is the explanatory view of the face shaping of the test film F (having formed cut channel) of use among the expression embodiment 3.

Figure 13 illustrates the corrosion test method of embodiment 3, expression be maintaining a high position as the synthetic sea water of experimental liquid, make that test film is whole to submerge wherein, in this way the figure of the state of She Zhiing.

Figure 14 illustrates the corrosion test method of embodiment 3, expression be being maintained at low level as the synthetic sea water of experimental liquid, making test film be exposed to the water surface, in this way the figure of the state of She Zhiing.

Figure 15 is the explanatory view of the face shaping of the test film G of use among the expression embodiment 4 and 5.

Figure 16 is the explanatory view of the face shaping of the test film H of use among the expression embodiment 4 and 5.

Figure 17 is the explanatory view of the face shaping of the test film I of use among the expression embodiment 4 and 5.

Figure 18 is the graphic representation that demonstrates with the relation of comprehensive erosion resistance for the ratio (S (a)/S (b)) of the total content S (b) of the total content S (a) of a group element of examination steel and b group element that arrangement obtains among the embodiment 4 and 5.

Embodiment

Steel for ship of the present invention consists of feature suitably to control chemical ingredients in order to improve erosion resistance.Below at first form and describe with regard to chemical ingredients.

Steel for ship of the present invention contains C, Si, Mn and Al as basal component.C is used to guarantee the necessary element of the strength of materials.But contain as if making it excessive, then the toughness deterioration.Si and Al are used for deoxidation and guarantee the needed element of intensity.But contain as if making it excessive, then the weldability deterioration.Mn is the same with Si to be to be used for deoxidation and to guarantee the needed element of intensity.But contain as if making it excessive, then the toughness deterioration.Therefore in steel of the present invention, the C amount is 0.01～0.3%, the Si amount is 0.01～2%, the Mn amount be 0.01～2% and the Al amount be in 0.005～0.1% the scope.

Steel of the present invention contain unavoidable impurities such as P and S.But P and S are the elements that makes deteriorations such as toughness and weldability, and P in the preferred steel of the present invention and the amount of S are low as much as possible, recommend respectively below 0.01%.

In steel of the present invention, level according to desired erosion resistance, also can contain element, for example: Ca, Mg, Sr, Ba, Ti, Zr, Hf, Ni, Co, Cu, Cr, La, Ce, Nd, Sm, Se, Sb, Bi and/or Te with the effect of raising erosion resistance.These erosion resistances improve the content of elements in addition, suit to adjust according to the desired characteristic of steel to get final product.

The effect that Ca, Mg, Sr and Ba have is to suppress because of corrosion dissolved Fe owing to add the pH reduction that water decomposition causes.Under this effect, can suppress to film/pH that the clearance portion of steel interface and structure is difficult to take place the part of hydrogen ion diffusion like this reduces, and the erosion resistance (particularly anti-crevice corrosion) of this part is improved.In addition, if Mg and Co coexistence, the then significant effect of performance on corrodibility improves.But if excessive containing, then processibility and weldability deterioration.When therefore containing Ca, Mg, Sr and Ba in steel of the present invention, amount separately should be controlled at below 0.020%.Have again in the embodiments of the present invention,, determine that in more detail Ca, Mg, Sr and Ba also have the content of each following element according to desired performance.

The effect that Ti, Zr and Hf have is to make formed surface rust tunicle stabilization in corrosive environment, is through still making for a long time the corrosion inhibition effect from surface rust tunicle be manifested the aspect effective elements.But, excessive if their quantitative change gets, weldability and processibility (particularly hot workability) deterioration then.Therefore Ti, Zr and Hf are contained sometimes, amount separately should be controlled at below 0.2%.

Ni and Co have the effect that fine and close surface rust tunicle is formed, and are the elements that manifests the corrosion inhibition effect that surface rust tunicle brings.But excessive if their quantitative change gets, then weldability and hot workability deterioration.Therefore Ni and Co are contained sometimes, amount separately should be controlled at below 5.0%.

The effect that Cu and Cr have is to help to be highly advantageous to the formation of the surface scale film of the densification that erosion resistance improves, and is to improve the environment barrier property and element that erosion resistance is improved.Proper C r can improve toughness effectively in addition.But if make their excessive containing, then weldability and hot workability deterioration.Therefore Cu and Cr are contained sometimes, amount separately should be controlled in 0.01～5.0% the scope.

La, Ce, Nd, Sm and Se have the effect of further raising erosion resistance, and the pH that particularly helps to be brought by Ca etc. reduces the stabilization effect of the surface rust tunicle that suppresses effect and brought by Ti etc.But if make their excessive containing, then processibility and weldability deterioration.Therefore they are contained sometimes, the amount of La, Ce, Nd and Sm should be controlled at respectively below 0.01%, and the Se amount should be controlled at below 0.1%.

Sb, Bi and Te be help from the rust densification of Cu etc. as and improve the element of erosion resistance.But if make their excessive containing, then processibility and weldability deterioration.Therefore they are contained sometimes, Sb and Bi amount should be controlled at respectively below 0.2%, and the Te amount should be controlled at below 0.1%.

Steel of the present invention also can contain the element that improves steel characteristics except above-mentioned element, for example B, V, Nb and Ta etc.B and V are improving (especially B improves hardenability) effective elements on the intensity.Ta is the element that helps to reduce the ferrite particle diameter by crystal grain miniaturization effect.Nb has their two sides' effect (intensity improves and crystal grain miniaturization effect).But excessive if their quantitative change gets, toughness deterioration then.Therefore they are contained sometimes, the B amount should be controlled at below 0.01%, and V, Nb and Ta amount should be controlled at below 0.5% respectively.

In these external steel of the present invention,, can further improve the erosion resistance of steel by the ratio of components of suitable control chemical ingredients.In more detail, make surperficial Ti, Zr and the Hf that becomes rusty the tunicle stabilization effect be categorized as b group as if being categorized as a group having the pH of inhibition reduction effect Ca, Mg, Sr and Ba, having, Co and Ni are categorized as c group, and then a that effect is different～c group element acts on with complementing each other.Thereby, can further improve erosion resistance by suitably controlling the ratio of the total content of a group element, b group element and c group element.

Specifically, be made as S (a) % (meaning of quality % at total content with a group element, as follows), the total content of b group element is made as S (b) %, when the total content of c group element is made as S (c) %, from the viewpoint of comprehensive erosion resistance, recommend to adjust as follows these elements: preferred 20≤S (c)/S (a)≤350, more preferably 50≤S (c)/S (a)≤170.From the viewpoint of anti-crevice corrosion, recommending the adjustment mode is preferred 1.00≤S (c)/S (b)≤60, more preferably 10≤S (c)/S (b)≤30 in addition.Have in order to improve comprehensive erosion resistance, recommending the adjustment mode is preferred 0.01≤S (a)/S (b)≤1, more preferably 0.02≤S (a)/S (b)≤0.8 again.

Steel for ship in first grown form of the present invention is adjusted in the proper range by chemical ingredients is formed, thereby is realized excellent erosion resistance.Therefore, at first form and describe with regard to the chemical composition of steel of first grown form of the present invention.

(C：0.01～0.3％)

From the above-mentioned viewpoint of guaranteeing intensity and toughness deterioration, the C of first grown form of the present invention amount is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.04%, but below 0.3%, be preferably below 0.28%, more preferably below 0.26%.

(Si：0.01～2％)

From above-mentioned deoxidation with guarantee intensity and the viewpoint of weldability deterioration, the Si of first grown form of the present invention amount is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.05%, below 2%, be preferably below 1.8%, more preferably below 1.6%.

(Mn：0.01～2％)

From above-mentioned deoxidation with guarantee intensity and the viewpoint of toughness deterioration, the Mn of first grown form of the present invention amount is more than 0.01%, is preferably more than 0.05%, more preferably more than 0.10%, but below 2%, be preferably below 1.8%, more preferably below 1.6%.

(Al：0.005～0.1％)

From above-mentioned deoxidation with guarantee intensity and the viewpoint of weldability deterioration, the Al of first grown form of the present invention amount is more than 0.005%, is preferably more than 0.010%, more preferably more than 0.015%, but below 0.1%, be preferably below 0.09%, more preferably below 0.08%.

(Cu：0.01～1％)

From above-mentioned raising erosion resistance (particularly helping fine and close surface scale film to form), and the viewpoint of weldability and hot workability deterioration sets out, and the Cu amount of first grown form of the present invention is more than 0.01%, is preferably more than 0.05%, but, be preferably below 0.9% below 1%.

(Ni：0.01～1％)

From above-mentioned raising erosion resistance (the particularly formation of Zhi Mi surface scale film), and the viewpoint of weldability and hot workability deterioration sets out, and the Ni amount of first grown form of the present invention is more than 0.01%, is preferably more than 0.02%, but, be preferably below 0.9% below 1%.

(Cr：0.01～1％)

Improve from above-mentioned raising erosion resistance (particularly encouraging fine and close surface scale film forms) and toughness, and the viewpoint of weldability and hot workability deterioration is set out, the Cr amount of first grown form of the present invention is more than 0.01%, be preferably more than 0.05%, but, be preferably below 0.8% below 1%.

The basal component of the steel for ship of first grown form of the present invention such as above-mentioned, surplus are made of iron and unavoidable impurities (for example P, S, O, N, H, Mo, W etc.) in fact.But the amount of unavoidable impurities need be in the degree that does not hinder steel characteristics.In the steel of first grown form of the present invention, except mentioned component, can also make the element that uses in aftermentioned the 1st～the 3rd embodiment contain also effective as required in addition as selecting element.

Steel for ship in first grown form of the present invention except the adjustment that chemical ingredients is formed, also can improve erosion resistance by suitable control metal structure.In detail, be exactly with ferrite as maximum tissue, bainite and/or martensite add up to and were lower than for 30% (containing 0), can further improve erosion resistance thus.

In the steel for ship in first grown form of the present invention, ferrite has maximum area occupation ratio.Ferrite weldability and excellent in workability, the susceptibility of the stress corrosion cracking that causes for muriate is little in addition, therefore preferred its tissue as the structural member that uses under the such chloride environment of seawater.

On the other hand, bainite and martensite are intensity and the flexible tissues that is used to improve steel effectively.But if excessively have bainite and/or martensite in ferrite, then the corrosion of bainite and/or martensite portion is promoted, erosion resistance reduces.In order to prevent that this erosion resistance from reducing, recommend bainite+martensitic area occupation ratio to add up to and be lower than for 30% (comprising that bainite, martensitic any one party or both sides are 0 situation).

In the present invention, the employing of area occupation ratio of tissue is as follows: under the thickness of steel is situation more than the 6mm, be at the position that reaches 3mm from the surface deeply, thickness at steel is lower than under the situation of 6mm, it is 1/2 position at the thickness of steel, with the observation multiplying power of 400 times of principles and the above field of view observation by light microscope of 150 μ m * 200 μ m, the mean value of the area occupation ratio of in 30 visuals field arbitrarily, obtaining.Also have the so-called surface that becomes the benchmark of the degree of depth, refer to face by the steel of the rolling power of applying.

Secondly, explain first embodiment～the 3rd embodiment that is comprised in first grown form of the present invention.At first be that first embodiment of the present invention is a kind of steel, it is characterized in that, contain:

C：0.01～0.3％、

Si：0.01～2％、

Mn：0.01～2％、

Al：0.005～0.1％、

P:0.01% following (not containing 0%),

S:0.005% following (not containing 0%),

Cu：0.01～1％、

Ni:0.01～1%, and

Cr：0.01～1％，

Surplus is Fe and unavoidable impurities,

And the constituting in area occupation ratio and comprise of tissue: perlite: 5～25%, bainite: be lower than 20%, martensite: be lower than 10%, surplus is a ferrite,

And the ferrite particle diameter is below the 15 μ m, and pearlitic long-width ratio is 3.0～20.

In the steel for ship of first embodiment of the present invention, contain again as inferior element as required also effective,

(1) at least a kind of element selecting of the mass selection that constitutes from following element: (do not contain 0%) Ca:0.005% below, (do not contain 0%) below the Mg:0.005%, (do not contain 0%) below the Sr:0.005%, (do not contain 0%) below the Ba:0.005%, (do not contain 0%) below the La:0.005%, (do not contain 0%) below the Ce:0.005%, (do not contain 0%) below the Nd:0.005%, (do not contain 0%) below the Sm:0.005%, reach and (do not contain 0%) below the Se:0.1%;

(2) at least a kind of element selecting of the mass selection that constitutes from following element: (do not contain 0%) Ti:0.2% below, (do not contain 0%) below the Zr:0.2%, reach and (do not contain 0%) below the Hf:0.2%;

(3) at least a kind of element selecting of the mass selection that constitutes from following element: (do not contain 0%) Sb:0.2% below, (do not contain 0%) below the Bi:0.2%, reach and (do not contain 0%) below the Te:0.1%;

(4) Co:1% following (not containing 0%);

(5) Nb:0.5% following (not containing 0%) and/or Ta:0.5% following (not containing 0%); Perhaps

(6) B:0.01% following (not containing 0%) and/or V:0.5% following (not containing 0%) according to the kind of the composition that contains, can further improve steel characteristics.The steel for ship of first embodiment of the present invention, also can satisfy simultaneously (1)～in the prerequisite of (6) more than 2.

The steel for ship of first embodiment of the present invention, suitably adjust the chemical ingredients composition and (II) suitably control metal structure by (I), even thereby under harsh corrosive environment, also can demonstrate excellent erosion resistance, through also guaranteeing weather resistance for a long time.Below at first form and be illustrated with regard to the chemical composition of steel of first embodiment of the present invention.

(C：0.01～0.3％)

Guarantee and the viewpoint of toughness deterioration that from above-mentioned intensity the C amount of first embodiment of the present invention is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.04%, but below 0.3%, be preferably below 0.28%, more preferably below 0.26%.

(Si：0.01～2％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of weldability deterioration, the Si of first embodiment of the present invention amount is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.05%, but below 2%, be preferably below 1.8%, more preferably below 1.6%.

(Mn：0.01～2％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of toughness deterioration, the Mn of first embodiment of the present invention amount is more than 0.01%, is preferably more than 0.05%, more preferably more than 0.10%, but below 2%, be preferably below 1.8%, more preferably below 1.6%.

(Al：0.005～0.1％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of weldability deterioration, the Al of first embodiment of the present invention amount is more than 0.005%, is preferably more than 0.010%, more preferably more than 0.015%, but below 0.1%, be preferably below 0.09%, more preferably below 0.08%.

(P:0.01% following (not containing 0%))

In first embodiment of the present invention, be below 0.01%, to be preferably below 0.005% to toughness and the deleterious P amount of weldability as above-mentioned recommendation.

(S:0.005% following (not containing 0%))

In first embodiment of the present invention, be below 0.005%, to be preferably below 0.004% to toughness and the deleterious S amount of weldability as above-mentioned recommendation.

(Cu：0.01～1％)

Improve the viewpoint of the deterioration of (particularly helping fine and close surface scale film to form) and weldability and hot workability from above-mentioned corrodibility, the Cu amount of first embodiment of the present invention is more than 0.01%, be preferably more than 0.05%, but, be preferably below 0.9% below 1%.

(Ni：0.01～1％)

Improve the viewpoint of the deterioration of (particularly fine and close surface scale film forms) and weldability and hot workability from above-mentioned corrodibility, the Ni amount of first embodiment of the present invention is more than 0.01%, be preferably more than 0.02%, but, be preferably below 0.9% below 1%.

(Cr：0.01～1％)

Improve (particularly helping fine and close surface scale film to form) and toughness raising from above-mentioned corrodibility, and the viewpoint of the deterioration of weldability and hot workability is set out, the Cr amount of first embodiment of the present invention is more than 0.01%, be preferably more than 0.05%, but, be preferably below 0.8% below 1%.

The basal component of the steel for ship of first embodiment of the present invention as mentioned above, surplus comes down to iron and unavoidable impurities (for example O, N, H, Mo, W etc.).But the amount of unavoidable impurities need be for not hindering the degree of steel characteristics.In addition in the steel of first embodiment of the present invention, except mentioned component, containing as required that following being chosen to grade also is effectively again, according to the kind of contained composition, can further improve steel characteristics.

(at least a kind of element that the mass selection that constitutes from following element is selected: below the Ca:0.005%, below the Mg:0.005%, below the Sr:0.005%, below the Ba:0.005%, below the La:0.005%, below the Ce:0.005%, below the Nd:0.005%, below the Sm:0.005% and below the Se:0.1%)

Ca, Mg, Sr, Ba, La, Ce, Nd, Sm and Se (being preferably Ca, Mg, La, Ce and Se) improve erosion resistance aspect effective choice element.As mentioned above, for erosion resistance is improved, particularly reduce in order to suppress pH, recommendation makes in the steel of first embodiment of the present invention and contains Ca, Mg, Sr and Ba, is preferably the amount more than 0.0001% respectively, more preferably the amount more than 0.0005%, contain La, Ce, Nd and Sm and be preferably amount more than 0.0001% respectively, the amount more than 0.0003% more preferably contains Se and is preferably amount more than 0.001%, the more preferably amount more than 0.002%.On the other hand, they are contained sometimes, viewpoint from the deterioration of above-mentioned processibility and weldability, recommendation is adjusted to Ca, Mg, Sr, Ba, La, Ce, Nd and Sm amount below 0.005% respectively, preferably adjust to below 0.004%, the Se amount is adjusted to below 0.1%, preferably adjusted to below 0.05%.

(at least a kind of element that the mass selection that constitutes from following element is selected: below the Ti:0.2%, below the Zr:0.2% and below the Hf:0.2%)

Ti, Zr and Hf are improving effective choice element on the erosion resistance.As mentioned above, improve,, recommend to make in the steel of first embodiment of the present invention and contain Ti, Zr and Hf, be preferably respectively more than 0.005%, more preferably more than 0.008% particularly in order to make surface rust tunicle stabilization in order to make erosion resistance.On the other hand, the viewpoint from the deterioration of above-mentioned weldability and processibility contains sometimes them, recommends Ti, Zr and Hf amount are adjusted to respectively below 0.2%, preferably adjusts to below 0.15%.

(at least a kind of element that the mass selection that constitutes from following element is selected: below the Sb:0.2%, below the Bi:0.2% and below the Te:0.1%)

Sb, Bi and Te are improving effective choice element on the erosion resistance.As mentioned above, for erosion resistance is improved, particularly in order to encourage the effect of Cu etc., recommendation makes in the steel of first embodiment of the present invention and contains Sb and Bi, it is preferably the amount more than 0.005% respectively, the amount more than 0.008% more preferably contains Te and is preferably amount more than 0.001%, the more preferably amount more than 0.002%.On the other hand, the viewpoint from the deterioration of above-mentioned processibility and weldability contains sometimes them, recommendation is adjusted to the amount of Sb and Bi below 0.2% respectively, preferably adjust to below 0.15%, the Te amount is adjusted to below 0.1%, preferably adjust to below 0.05%.

(Co:1% is following)

Co is improving effective choice element on the erosion resistance.As mentioned above, improve,, recommend to make in the steel of first embodiment of the present invention and contain Co, be preferably more than 0.01%, more preferably more than 0.02% particularly in order to form fine and close surface rust tunicle in order to make erosion resistance.On the other hand, from the viewpoint of the deterioration of weldability and processibility, contain and recommend sometimes the Co amount is adjusted to below 1%, preferably adjust to below 0.8%.

(Nb:0.5% is following and/or Ta:0.5% is following)

Nb and Ta have crystal grain miniaturization effect as mentioned above, are the selection elements that helps to reduce the ferrite particle diameter.The result who further reduces the ferrite particle diameter by these effects can further improve erosion resistance.From the viewpoint of crystal grain miniaturization effect, recommend to make in the steel of first embodiment of the present invention and contain Nb and Ta, be preferably respectively more than 0.003%, more preferably more than 0.005%.On the other hand,, recommend sometimes Nb and Ta amount is adjusted to respectively below 0.5% containing, preferably adjust to below 0.4% from the viewpoint of above-mentioned toughness deterioration.

(B:0.01% is following and/or V:0.5% is following)

B and V are improving effective elements on the intensity.From the viewpoint that intensity improves, to recommend to make the steel of first embodiment of the present invention contain B and/or V, the amount of B is preferably more than 0.0001%, and more preferably more than 0.0003%, the amount of V is preferably more than 0.01%, more preferably more than 0.02%.On the other hand,, contain and recommend sometimes the B amount is adjusted to below 0.01%, preferably adjust to below 0.009%, the V amount is adjusted to below 0.5% from the viewpoint of above-mentioned toughness deterioration.

The steel for ship of first embodiment of the present invention, for erosion resistance is improved metal structure is suitably controlled, this tissue of one of its feature is in area occupation ratio specifically, comprise: perlite: 5～25%, bainite: be lower than 20%, martensite: be lower than 10%, surplus is a ferrite.Also have, organize the meaning of area occupation ratio and measuring method same as described above.

In the steel of first embodiment of the present invention, ferrite has the maximum area rate.This be because as above-mentioned, ferrite is preferred as being organized as of the structural member that uses in the such chloride environment of seawater.

Perlite is necessary for the desired intensity of the steel that obtain first embodiment of the present invention.In addition, if the perlite area occupation ratio is too small, then perlite demonstrates the tendency that locality point distributes, and the tendency that produces the local corrosion of pitting attack and crevice corrosion etc. becomes big.From the viewpoint of intensity and anti-local corrosion, in first embodiment of the present invention, the perlite area occupation ratio is decided to be more than 5%.But pearlitic increase is except meeting causes the deterioration of toughness and weldability, also can work as the negative electrode position (cathode site) of corrosion reaction, thus the erosion resistance of making (anti-general corrosion) deterioration.Therefore the perlite area occupation ratio is decided to be below 25%.The preferred scope of perlite area occupation ratio is 8～20%.

Bainite such as above-mentioned erosion resistance is had detrimentally affect particularly makes anti-local corrosion reduction.Therefore the bainite area occupation ratio in first embodiment of the present invention is recommended as and is lower than 20%, preferably is lower than 18%.

Martensite such as above-mentionedly erosion resistance is caused the detrimentally affect except meeting also damages toughness and weldability.Therefore, the martensite area occupation ratio in first embodiment of the present invention is recommended as and is lower than 10%, preferably is lower than 8%.

One of its feature of steel for ship of first embodiment of the present invention is, for erosion resistance is improved the ferrite particle diameter is controlled at below the 15 μ m, and pearlitic long-width ratio is controlled at 3.0～20.

The ferrite particle diameter of first embodiment of the present invention value adopted be thickness at steel be 6mm when above at the position that reaches 3mm apart from the surface deeply, when the thickness of steel is lower than 6mm at 1/2 position of the thickness of steel, with the observation multiplying power of 400 times of principles and the above field of view observation by light microscope of 150 μ m * 200 μ m, the mean value of the ferritic equivalent circle diameter of in 30 visuals field arbitrarily, obtaining.Equivalent circle diameter can be tried to achieve by suitable image analysis apparatus and software.Preferably the sample of observing is carried out the suitable etching of nital etc. in addition.

What the so-called pearlitic long-width ratio in first embodiment of the present invention defined is, with reference to JISH7402 (the long-width ratio test method of the staple fibre in the fibre-strengthened metal), maximum distance between two points on the periphery of establishing the perlite profile is perlite major diameter: Lp, report to the leadship after accomplishing a task with pearlitic major diameter direction and to meet at right angles, the distance of being distinguished by the perlite profile on the line of the mid point by the perlite major diameter is as the perlite minor axis: during Dp, and the value that calculates by Lp/Dp.What the value of the pearlitic long-width ratio among the present invention adopted is, at the thickness of steel is that 6mm is when above, at the position that reaches 3mm apart from the surface deeply, when the thickness of steel is lower than 6mm, 1/2 position at the thickness of steel, with the observation multiplying power of 400 times of principles and the above field of view observation by light microscope of 150 μ m * 200 μ m, the mean value of the Lp/Dp that in 10 visuals field arbitrarily, obtains.

If dwindle the ferrite particle diameter, then therefore the uniformity height of corrosion reaction can make erosion resistance, particularly anti-local corrosion raising.In addition,, crystal boundary is increased, reduced the crystal boundary concentration of this impurity, therefore can reach higher erosion resistance by dwindling the ferrite particle diameter though cause dysgenic P and S etc. strong in the tendency of grain boundary segregation to erosion resistance.In order to give full play to such effect, recommending the ferrite particle diameter is below the 15 μ m, more preferably below the 10 μ m.

By increasing pearlitic long-width ratio erosion resistance is improved in addition.Though this principle is still indeterminate, be estimated as if perlite/ferrite interface is increased, then the impurity concentration in the interface segregation reduces, and erosion resistance improves thus.But the present invention is not limited thereto and infers.In order to improve erosion resistance, recommending pearlitic long-width ratio is more than 3.0, is preferably more than 6, more preferably more than 12.On the other hand, according to the anisotropic viewpoint of material, be defined as 20 on the pearlitic long-width ratio.

The steel for ship of first embodiment of the present invention for example can be according to following method manufacturing.At first, by the common melting method of converter, electric stove etc., adjust chemical ingredients and form to satisfy described scope, carry out melting simultaneously, the castmethod common by Continuous casting process, ingot casting method etc. forms steel ingot.In order to reduce the gaseous constituent of O, N, H etc., preferably carry out the external refining of this vacuum outgas method etc. of so-called DH method and RH method as required.In addition for deoxidation, from the viewpoint of mechanical characteristics and weldability, recommend the preferred deoxidized steel (killed steel) that uses, from the viewpoint of erosion resistance, the Al deoxidized steel of the reduced in segregation of detrimental impurity such as P and S more preferably.

Secondly, carry out hot rolling after preferably resulting steel ingot being heated to 1000～1200 ℃ temperature field, thereby become the ideal size shape.If the Heating temperature before rolling is lower than 1000 ℃, then the solid solubility step-down of Si, Mn, Ni, P and S etc. is consequently organized the heterogeneity that becomes, and causes local corrosion easily.On the other hand, if Heating temperature surpasses 1200 ℃, then thickization of austenite grain is difficult to obtain the following ferrite particle diameter of 15 μ m.

Guarantee toughness in order to suppress thickization of austenite that is caused by the recrystallize in rolling, preferred hot rolling final temperature is controlled at 750～850 ℃.By the total draft of hot rolling rate is adjusted to 80～97% scope, can make pearlitic long-width ratio be in 3.0～20.

Be controlled at 0.5～15 ℃/second scope by hot rolling being stopped the back to 500 ℃ speed of cooling, can form as undertissue: perlite: 5～25%, bainite: be lower than 20%, martensite: be lower than 10%, surplus is a ferrite.In addition, if this speed of cooling is lower than 0.5 ℃/second, then the generation of carbide is remarkable, and the negative electrode position under the corrosion reaction increases, the erosion resistance deterioration.On the other hand, if this speed of cooling surpasses 15 ℃/second, then the toughness deterioration brought of martensitic transformation might become big.

The steel for ship of first embodiment of the present invention can expose (non-processor) to be used because of excellent corrosion resistance, but also can implement application, plating or change into the surface treatment of processing etc. and use.When steel of the present invention were used as the structural wood of the oil cargo tank (cargo oil tank) of oil tanker, preferred inboard crude oil basin side exposed (non-processor) was used, and the ballast tank side application in the outside is used.But also can implement with initial stage antirust in crude oil basin side as required is the processing of the zinc-rich paint (zinc rich paint) of purpose and shop primer (shop primer) etc.Coating as the ballast tank side can be enumerated: tar epoxy (tar epoxy) cold coating, sex change epoxypaint or representational heavy-duty coating in addition etc.In addition, steel of the present invention also can and be used with other anti-corrosion methods of electric protection (galvanic anode method, external power source method) etc.

The steel for ship of first embodiment of the present invention, even under harsh corrosive environment, still demonstrate excellent erosion resistance, and, therefore be suitable for structural wood as the outside plate in the boats and ships of oil tanker, goods ship, semi-cargo ship, passenger boat, warship etc., ballast tank, crude oil basin etc. through still guaranteeing weather resistance for a long time.

Next describe second embodiment of the present invention in detail.Second embodiment of the present invention relates in the steel for ship, the special employed steel of crude oil basin base plate.The corrosive environment that this crude oil basin base plate is exposed to the open air is very harsh, for this just constantly requires further to improve erosion resistance (especially anti-local corrosion) to employed steel.In the oil tanker of double-skin (double hull) structure, the oil tank bottom plate outside becomes the ballast tank side, normally uses under the state of having implemented applications such as epoxy resin coating in addition.This ballast tank side be because can fill seawater when zero load, thus can stand the corrosive nature that this salinity produces, on the other hand, because when Crude Oil Transportation, can be subjected to from the how wet corrosive naturees of high temperature, so require that excellent application erosion resistance is arranged.Therefore, on the crude oil basin base plate of double-skin structure, just require the both sides of anti-local corrosion (medial surface) and application erosion resistance (ballast tank side) all excellent.Therefore the purpose of second embodiment of the present invention is, all excellent crude oil basin base plate steel of both sides of a kind of anti-local corrosion (inner face side that contacts with crude oil) and application erosion resistance (with the ballast tank side of contact with sea water) are provided.

Second embodiment of the present invention that can reach above-mentioned purpose is a kind of crude oil basin base plate steel, it is characterized in that, contains:

C：0.01～0.3％、

Si：0.01～2％、

Mn：0.01～2％、

Al：0.005～0.1％、

Cu：0.01～1％、

Cr：0.01～1％、

Ca：0.0001～0.005％、

Ti:0.005～0.2%, and

Ni：0.01～1％，

Surplus is Fe and unavoidable impurities,

And the formation of tissue comprises in area occupation ratio: perlite: 5～25%, bainite: be lower than 20%, martensite: be lower than 10%, surplus is a ferrite,

And the number that equivalent circle diameter surpasses the non-metallic inclusion per unit area of 20 μ m is 0.20/mm ²Below.

At the crude oil basin base plate of second embodiment of the present invention with in the steel, contain again as inferior element as required also effective,

(1) at least a kind of element from the group that following element constitutes, selecting: (do not contain 0%) below the Mg:0.005%, (do not contain 0%) below the Sr:0.005% and (do not contain 0%) below the Ba:0.005%; (2) Zr:0.2% following (not containing 0%) and/or Hf:0.2% following (not containing 0%); (3) Co:1% following (not containing 0%); (4) at least a kind of element selecting of the mass selection that constitutes from following element: (do not contain 0%) La:0.01% below, (do not contain 0%) below the Ce:0.01%, (do not contain 0%) below the Nd:0.01%, (do not contain 0%) below the Sm:0.01%, reach and (do not contain 0%) below the Se:0.1%; (5) Sb:0.2% following (not containing 0%), Bi:0.2% following (not containing 0%) and Te:0.1% following (not containing 0%); (6) at least a kind of element selecting from the mass selection of following element formation: (do not contain 0%) below the B:0.01%, (do not contain 0%) below the V:0.5% and (do not contain 0%) below the Nb:0.5%; Perhaps (7) Ta:0.5% following (not containing 0%) according to the kind of the composition that contains, can further improve the characteristic of crude oil basin base plate with steel.The crude oil basin base plate steel of second embodiment of the present invention, also can satisfy simultaneously in the prerequisite of this (1)～(7) more than 2.

Use in the steel at the crude oil basin base plate of second embodiment of the present invention, Ca, Mg and Sr are categorized as a group, Ti, Zr and Hf are categorized as b group, Co and Ni are categorized as c group, if the total content of a group element is S (a) % (meaning of quality %, as follows), the total content of b group element is S (b) %, when the total content of c group element is S (c) %, preferably adjust the total content of a～c group element in the mode that satisfies following formula (1) and (2).

20≤S(c)/S(a)≤350...(1)

1.00≤S(c)/S(b)≤60...(2)

The crude oil basin base plate steel of second embodiment of the present invention are because the both sides of anti-local corrosion and application erosion resistance are all excellent, so especially preferably use as the crude oil basin base plate of the oil tanker of double-skin structure.

Second embodiment of the invention, suitably adjusting chemical ingredients by (I) forms, especially contain the Ni etc. that has the Ca etc. that suppresses pH and reduce effect, has the Ti that makes surface rust tunicle stabilization effect etc. and have the effect that forms fine and close surface rust tunicle with appropriate amount, (II) suitably control metal structure, and (III) be suppressed at the non-metallic inclusion that exists in the steel, just can realize all excellent crude oil basin base plate steel of both sides of anti-local corrosion and application erosion resistance.Below, at first the chemical composition of steel composition with regard to first embodiment of the present invention describes.

(C：0.01～0.3％)

Guarantee and the viewpoint of toughness deterioration that from above-mentioned intensity the C amount of second embodiment of the present invention is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.04%, but below 0.3%, be preferably below 0.28%, more preferably below 0.26%.

(Si：0.01～2％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of weldability deterioration, the Si of second embodiment of the present invention amount is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.05%, but below 2%, preferred below 1.8%, more preferably below 1.6%.

(Mn：0.01～2％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of toughness deterioration, the Mn of second embodiment of the present invention amount is more than 0.01%, is preferably more than 0.05%, more preferably more than 0.10%, but below 2%, be preferably below 1.8%, more preferably below 1.6%.

(Al：0.005～0.1％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of weldability deterioration, the Al of second embodiment of the present invention amount is more than 0.005%, is preferably more than 0.010%, more preferably more than 0.015%, but below 0.1%, be preferably below 0.09%, more preferably below 0.08%.

(Cu：0.01～1％)

Improve the viewpoint of the deterioration of (particularly helping fine and close surface scale film to form) and weldability and hot workability from above-mentioned erosion resistance, the Cu amount of second embodiment of the present invention is more than 0.01%, be preferably more than 0.05%, but, be preferably below 0.9% below 1%.

(Cr：0.01～1％)

Improve (particularly helping fine and close surface scale film to form) and toughness raising from above-mentioned erosion resistance, and the viewpoint of the deterioration of weldability and hot workability is set out, the Cr amount of second embodiment of the present invention is more than 0.01%, be preferably more than 0.05%, but, be preferably below 0.8% below 1%.

(Ca：0.0001～0.005％)

Improve (particularly suppressing pH reduces) and toughness raising from above-mentioned erosion resistance, and the viewpoint of the deterioration of processibility and weldability is set out, the Ca amount of second embodiment of the present invention is more than 0.0001%, be preferably more than 0.0005%, but, be preferably below 0.004% below 0.005%.

(Ti：0.005～0.2％)

Improve (stabilization of surface rust tunicle) and toughness raising from above-mentioned erosion resistance, and the viewpoint of the deterioration of weldability and processibility sets out, and the Ti amount of second embodiment of the present invention is more than 0.005%, is preferably more than 0.008%, but, be preferably below 0.15% below 0.2%.

(Ni：0.01～1％)

Improve the viewpoint of the deterioration of (particularly helping fine and close surface scale film to form) and weldability and hot workability from above-mentioned erosion resistance, the Ni amount of second embodiment of the present invention is more than 0.01%, be preferably more than 0.02%, but, be preferably below 0.9% below 1%.

The crude oil basin base plate of second embodiment of the present invention with the basal component of steel as above, surplus is made of iron and unavoidable impurities (for example P, S, O, N, Mo, W etc.) in fact.But the amount of unavoidable impurities need be in the degree of the characteristic that does not hinder steel.In addition in the steel of second embodiment of the present invention, except mentioned component, can also contain following being chosen to as required and grade also effectively, the kind of the composition that correspondence contains will further be improved the characteristic of steel.

(at least a kind of element that the mass selection that constitutes from following element is selected: Mg:0.005% below, below the Sr:0.005%, reach below the Ba:0.005%)

Mg, Sr and Ba are being the effective choice elements aspect the raising erosion resistance.As mentioned above, in order to improve erosion resistance, particularly reduce in order to suppress pH, be recommended in the steel of second embodiment of the present invention and contain Mg, Sr and Ba, its content is preferably more than 0.0001%, more preferably more than 0.0005%.On the other hand, the viewpoint from the deterioration of above-mentioned processibility and weldability is containing sometimes, recommends Mg, Sr and Ba amount are adjusted to respectively below 0.005%, preferably adjusts to below 0.004%.

(Zr:0.2% is following and/or Hf:0.2% is following)

Zr and Hf are being the effective choice element aspect the erosion resistance raising.,, be recommended in the steel of second embodiment of the present invention and contain Zr and Hf particularly in order to make surface rust tunicle stabilization in order to improve erosion resistance as above-mentioned, its content is preferably respectively more than 0.005%, more preferably more than 0.008%.On the other hand, the viewpoint from the deterioration of above-mentioned weldability and processibility is containing sometimes, recommends Zr and Hf amount are adjusted to respectively below 0.2%, preferably adjusts to below 0.15%.

(Co:1% is following)

Co is being the effective choice element aspect the erosion resistance raising.,, be recommended in the steel of second embodiment of the present invention and contain Co particularly for fine and close surface rust tunicle is formed in order to improve erosion resistance as above-mentioned, its content is preferably more than 0.01%, more preferably more than 0.02%.On the other hand, the viewpoint from the deterioration of weldability and hot workability is containing sometimes, recommends the Co amount is adjusted to below 1%, preferably adjusts to below 0.8%.

(at least a kind of element that the mass selection that constitutes from following element is selected: (do not contain 0%) La:0.01% below, below the Ce:0.01%, below the Nd:0.01%, below the Sm:0.01%, reach below the Se:0.1%)

La, Ce, Nd, Sm and Se all are effective choice elements on erosion resistance improves.As mentioned above in order to improve erosion resistance, particularly in order to help the effect of Ca or Ti etc., be recommended in the steel of second embodiment of the present invention and contain La, Ce, Nd and Sm, its content is preferably more than 0.0001% respectively, more preferably more than 0.0005%, recommend be preferably more than 0.001%, more preferably the amount more than 0.002% contains Se.On the other hand, the viewpoint from the deterioration of above-mentioned processibility and weldability is containing sometimes, recommendation is adjusted to La, Ce, Nd and Sm amount below 0.01% respectively, preferably adjust to below 0.008%, recommend the Se amount is adjusted to below 0.1%, preferably adjust to below 0.05%.

(at least a kind of element that the mass selection that constitutes from following element is selected: Sb:0.2% below, below the Bi:0.2%, reach below the Te:0.1%)

Sb, Bi and Te are effective choice elements aspect the erosion resistance raising.The explanation of content about them is identical with above-mentioned first embodiment of the present invention.

(at least a kind of element that the mass selection that constitutes from following element is selected: B:0.01% below, below the V:0.5%, reach below the Nb:0.5%)

B, V and Nb all are effective elements aspect the intensity raising.Be recommended in for intensity is improved in the steel of second embodiment of the present invention and contain B, V and Nb, the amount of B is preferably more than 0.0001%, more preferably more than 0.0003%, the amount of V is preferably more than 0.01%, more preferably more than 0.02%, the amount of Nb is preferably more than 0.003%, more preferably more than 0.005%.On the other hand, viewpoint from above-mentioned toughness deterioration, containing sometimes, recommendation is adjusted to the B amount below 0.01%, more preferably adjust to below 0.009%, recommend the V amount is adjusted to below 0.5%, more preferably adjust to below 0.45%, recommendation is adjusted to the Nb amount below 0.5%, preferably adjusts to below 0.45%.

(Ta:0.5% is following)

Ta is an effective choice element aspect the crystal grain miniaturization.Explanation about its content is identical with first embodiment of the invention described above.

Can be listed below as preferred selection element: from the group that Mg and Sr constitute, select at least a kind; From the group that Zr and Hf constitute, select at least a kind; Co; From the group that La, Ce, Nd, Sm constitute, select at least a kind; From the group that B, V and Nb constitute, select at least a kind.

The crude oil basin base plate of this external second embodiment of the present invention is with in the steel, ratio of components by suitable control chemical ingredients, suitably control S (c)/S (a) ratio and S (c)/S (a) ratio specifically as described above, the erosion resistance of steel is improved.The explanation of the S of second embodiment of the present invention (c)/S (a) ratio and S (c)/S (a) ratio is the same.

The crude oil basin base plate steel of second embodiment of the present invention, one of its feature is, suitably controls the metal structure area occupation ratio in order to improve erosion resistance.About the explanation of the area occupation ratio of the metal structure of second embodiment of the present invention, identical with the first above-mentioned embodiment.

The crude oil basin base plate steel of second embodiment of the present invention, one of its feature is, in order to improve erosion resistance the non-metallic inclusion that exists in the steel is controlled.This non-metallic inclusion can become the starting point of local corrosion.Here the what is called " non-metallic inclusion " in second embodiment of the present invention, the meaning are sulfide-based, the Al of MnS etc. ₂O ₃And SiO ₂Deng oxide compound and the nitride-based inclusion of TiN etc.

In the environment of crude oil basin base plate, the big non-metallic inclusion that equivalent circle diameter surpasses 20 μ m is harmful especially, and recommending to make the quantity of this inclusion is 0.20/mm ²Below, 0.10/mm more preferably ²Below.

In second embodiment of the present invention, the employing of number of per unit area that surpasses the non-metallic inclusion of 20 μ m is, at the thickness of steel is that 6mm is when above, at the position that reaches 3mm apart from the surface deeply, when the thickness of steel is lower than 6mm, at 1/2 position of the thickness of steel, with the observation multiplying power and the above field of view observation by light microscope of 150 μ m * 200 μ m of 400 times of principles, the mean value of the quantity of the per unit area of this inclusion that in 30 visuals field arbitrarily, obtains.There is what is called to become the surface of depth datum again, refers to face by the steel of the rolling power of applying.The observational technique of opticmicroscope is followed " the micrographic test method of the non-metallic inclusion of steel " that JIS G 0555 is put down in writing in addition.

The crude oil basin base plate steel of second embodiment of the present invention can be according to for example following method manufacturing.At first, adjust the chemical ingredients composition and carry out melting simultaneously, make steel ingot with the common castmethod of Continuous casting process, ingot casting method etc. to satisfy above-mentioned scope by the common melting method of converter, electric stove etc.Also have as the deoxidation form, recommend preferably to adopt deoxidized steel based on the viewpoint of mechanical characteristics and weldability, more preferably the Al deoxidized steel.At this, by carrying out the external refining of such vacuum outgas method of for example DH method and RH method etc., the number that can reach the per unit area of the non-metallic inclusion that makes equivalent circle diameter surpass 20 μ m reduces to 0.20/mm ²Below.

Secondly, carry out hot rolling after preferably the steel ingot that obtains being heated to 1100～1200 ℃ temperature field, thereby form the ideal size shape.At this moment by the hot rolling final temperature is controlled at 750～850 ℃, stop back to 500 ℃ speed of cooling from hot rolling and be controlled at 0.5～15 ℃/second scope, just can access the steel that have as undertissue: perlite: 5～25%, bainite: be lower than 20%, martensite: be lower than 10%, surplus is ferrite.

The crude oil basin base plate of second embodiment of the present invention is all excellent because of the both sides of its anti-local corrosion and application erosion resistance with steel, so as the basin base plate of the oil tanker of double-skin structure and use, especially be preferably crude oil basin side exposed (non-processor), the ballast tank side is implemented application.But also can implement with initial stage antirust in crude oil basin side as required is the processing of the zinc-rich paint of purpose and shop primer etc.Coating as the ballast tank side can be enumerated: tar epoxy class coating, sex change epoxypaint or representational heavy-duty coating in addition etc.In addition, also can and be used for using crude oil basin base plate steel of the present invention with other anti-corrosion methods of electric protection (galvanic anode method, external power source method) etc.

Next describe the 3rd embodiment of the present invention in detail.The 3rd embodiment of the present invention relates in steel for ship, particularly the employed steel of ballast tank.The purpose of the 3rd embodiment of the present invention is, provides a kind of ballast tank with steel and ballast tank, and it helps to reduce the loss that prolongs the economy that (losing time) wait during the maintenance cost of boats and ships and the harbour, and helps the security of shipping raising.A kind of ballast tank steel and ballast tank are provided in the 3rd embodiment of the present invention in addition, near high temperature such as the heating part of its upperdeck inboard, loading and the engine electric protection inoperative when water ballast is arranged (even also not submergence seawater), as the harsh position of corrosion-resistant environment, weather resistance is effective for improving.

The ballast tank steel that the 3rd embodiment of the present invention that can reach above-mentioned purpose is an excellent corrosion resistance is characterized in that, contain:

C：0.01～0.30％、

Si：0.01～2.0％、

Mn：0.01～2.0％、

Below the P:0.01%,

S：0.0005～0.005％、

Al：0.005～0.10％、

Cu：0.1～1.0％、

Ni：0.01～1.0％、

Cr：0.01～0.5％，

Surplus is Fe and unavoidable impurities,

And have based on ferrite, add up to the tissue that is lower than 30% (containing 0) in area occupation ratio bainite and/or martensite, the median size of sulfide-based inclusion is 0.5～10 μ m.

Use in the steel at the ballast tank of the 3rd embodiment of the present invention, except mentioned component, contain as inferior element also effective as required again: the mass selection that (1) constitutes from following element select more than a kind or 2 kinds: Mg:0.0001～0.005%, Ca:0.0001～0.005%, Sr:0.0001～0.005%, Ba:0.0001～0.005%, La:0.0001～0.005%, Ce:0.0001～0.005%, Nd:0.0001～0.005%, Sm:0.0001～0.005%, and Se:0.001～0.1%; (2) mass selection that constitutes from following element select more than a kind or 2 kinds: Co:0.005～0.20%, Ti:0.005～0.20%, Zr:0.005～0.20%, and Hf:0.005～0.20%; (3) mass selection that constitutes from following element select more than a kind or 2 kinds: Sb:0.005～0.2%, Bi:0.005～0.2%, and Te:0.001～0.1%; (4) mass selection that constitutes from following element select more than a kind or 2 kinds: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%; Or (5) Ta:0.003～0.5%, the corresponding kind that contains composition will further be improved the characteristic of steel.The ballast tank of the 3rd embodiment of the present invention also can satisfy more than 2 of prerequisite of this (1)～(5) simultaneously with steel.

Among the ballast tank of the 3rd embodiment of the present invention is used steel, preferably anticorrosive coating film directly is formed at steel surface.Also provide a kind of boats and ships in addition in the 3rd embodiment of the present invention, it has the ballast tank that is made of with steel above-mentioned ballast tank.

What present inventors studied repeatedly with keen determination found that, except compositions such as C, Si, Mn, Al, suitably adjust the interpolation element of Cu, Ni etc. again, except the state optimizing that makes tissue and inclusion, further direct painting anticorrosion coating on these steel can be reached the described purpose of the 3rd embodiment of the present invention thus.

During the corrosive chemical substance that causes moisture, salinity and oxygen etc. was impregnated into and films, Corrosion Of Steel took place filming down, and the deterioration of anticorrosive coating film just begins thus.Under the ballast tank environment, pass through to adopt the steel of the 3rd embodiment of the present invention, can be suppressed at the Corrosion Of Steel that takes place under the anticorrosive coating film effectively, therefore the turgor pressure of comparing corrosion product with existing steel diminishes, the expansion of anticorrosive coating film will be difficult to take place, thereby bring the life-span of anticorrosive coating film to prolong.In addition, even on anticorrosive coating film, have the defective of bubble etc. and flaw and when having steel to expose, because the corrosion advance rate of its exposed division of steel of the 3rd embodiment of the present invention is slow, so can not cause great corrosion damages such as steel plate perforation.Below describe with regard to the qualification reason of the composition range of the steel of this 3rd embodiment that has.

(C：0.01～0.30％)

C is that the intensity that is used for material is guaranteed needed element.In order to ensure as the minimum intensity of the structural member of petroleum-type basin (wall thickness that depends on steel, but probably be about 400MPa), need make it to contain more than 0.01%.Guarantee and the viewpoint of above-mentioned toughness deterioration that from this intensity the C amount of the 3rd embodiment of the present invention is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.04%, but below 0.30%, be preferably below 0.28%, more preferably below 0.26%.

(Si：0.01～2.0％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of weldability deterioration, the Si of the 3rd embodiment of the present invention amount is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.05%, but below 2.0%, be preferably below 1.8%, more preferably below 1.6%.

(Mn：0.01～2.0％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of toughness deterioration, the Mn of the 3rd embodiment of the present invention amount is more than 0.01%, is preferably more than 0.05%, more preferably more than 0.10%, but below 2.0%, be preferably below 1.80%, more preferably below 1.60%.

(P:0.01% is following)

P is the element that sea water resistance is improved by adding.But P also is the element that makes toughness and weldability deterioration, preferably suppresses its content as far as possible.The 3rd embodiment of the present invention is paid attention to toughness and weldability and is not used the sea water resistance of P to improve effect, thereby the permission upper limit of P is terminated in 0.01%.

(S：0.0005～0.005％)

S also is the element that makes toughness and weldability deterioration, preferably suppresses its content as far as possible.The permission upper limit of S terminates in 0.005%, then can not guarantee as the weldability of ballast tank with steel if surpass.Therefore in the 3rd embodiment of the present invention, the S amount is below 0.005%.

(Al：0.005～0.10％)

From above-mentioned deoxidation with guarantee intensity and the viewpoint of weldability deterioration, the Al amount of the 3rd embodiment of the present invention is more than 0.005%, be preferably more than 0.010%, more preferably more than 0.015%, but below 0.10%, be preferably below 0.090%, more preferably below 0.080%.

(Cu：0.01～1.0％)

Cu is improving effective elements on the erosion resistance.Cu has the effect that is suppressed under the anticorrosive coating film corrosion reaction that takes place, and is the paint blister that the incidental corrosion down of filming causes that grades of the film section in application is had the element that suppresses effect.In addition, also have and when the steel of paint film defect portion are subjected to corroding, make the effect that generates the rust densification, find that it is an effective elements aspect the effect of the corrosion progress of the flaw portion that suppresses to film.In order to bring into play these effects, the Cu amount of the 3rd embodiment of the present invention is more than 0.01%, to be preferably more than 0.05%.On the other hand, in order to prevent the above-mentioned weldability and the deterioration of hot workability, the Cu amount is below 1.0%, to be preferably below 0.90%.

(Ni：0.01～1.0％)

Ni improves erosion resistance effectively.Ni is the same with Cu to be the element with following effect: the corrosion progress that suppresses to film down and corrode the paint blister that causes and suppress to film flaw portion.Ni prevents because of adding the needed element of red shortness that Cu brings in addition.In order to bring into play such effect, the Ni amount of the 3rd embodiment of the present invention is more than 0.01%, to be preferably more than 0.05%.On the other hand, in order to prevent the above-mentioned weldability and the deterioration of hot workability, the Ni amount is below 1.0%, to be preferably below 0.90%.

(Cr：0.01～0.5％)

Cr is an effective elements aspect the raising erosion resistance.Cr has and suppresses the effect that anticorrosive coating film priming paint (primer) down consumes, and finds that in addition it is an effective elements aspect the effect of making progress of the corrosion in the flaw portion that suppresses to film.Proper C r can improve toughness effectively in addition, also is to be used for obtaining as the needed element of the needed mechanical characteristics of the former material of ballast tank.In order to bring into play these effects, the Cr of the 3rd embodiment of the present invention amount is for being more than 0.01%, to be preferably more than 0.05%.On the other hand, in order to prevent the above-mentioned weldability and the deterioration of hot workability, the Cr amount is below 0.5%, to be preferably below 0.45%.

, also effective according to following selection component is contained except mentioned component at the ballast tank of the 3rd embodiment of the present invention with in the steel, will further improve the characteristic of steel according to the kind of ingredient.

(mass selection that constitutes from following element select more than a kind or 2 kinds: Mg:0.0001～0.005%, Ca:0.0001～0.005%, Sr:0.0001～0.005%, Ba:0.0001～0.005%, La:0.0001～0.005%, Ce:0.0001～0.005%, Nd:0.0001～0.005%, Sm:0.0001～0.005%, and Se:0.001～0.1%)

Mg, Ca, Sr, Ba, La, Ce, Nd, Sm and Se are effective choice elements aspect the erosion resistance raising.Their effects of bringing into play are to suppress pH to reduce the corrosion acceleration that brings, thereby suppress paint blister effectively.Therefore recommend to make in the steel of the 3rd embodiment of the present invention and contain Mg, Ca, Sr, Ba, La, Ce, Nd and Sm, its content is preferably more than 0.0001%, more preferably more than 0.0005%, recommend be preferably more than 0.001%, more preferably the amount more than 0.002% makes and contains Se in the steel.On the other hand, viewpoint from the deterioration of above-mentioned processibility and weldability, they are contained sometimes, recommendation is adjusted to the amount of Mg, Ca, Sr, Ba, La, Ce, Nd and Sm below 0.005%, preferably adjust to below 0.004%, recommendation is adjusted to the Se amount below 0.1%, preferably adjusts to below 0.05%.

(mass selection that constitutes from following element select more than a kind or 2 kinds: Co:0.005～0.20%, Ti:0.005～0.20%, Zr:0.005～0.20%, and Hf:0.005～0.20%)

Co, Ti, Zr and Hf are effective choice elements aspect the raising erosion resistance.Be exactly in detail in the chloride corrosion environment, Co has the effect of the rust densification of the generation of making, and Ti, Zr and Hf have the effect that makes the rust stabilization, and they all are to suppress to film the element of corrosion progress of flaw portion.Therefore recommend to make in the steel of the 3rd embodiment of the present invention and contain Co, its content is preferably more than 0.005%, more preferably more than 0.02%, recommends to make to contain Ti, Zr and Hf in the steel, its content is preferably more than 0.005%, more preferably more than 0.008%.On the other hand, from the viewpoint of the deterioration of above-mentioned weldability and processibility, recommend sometimes the Co amount is adjusted to below 0.20%, preferably adjust to below 0.18% in that they are contained, recommendation is adjusted to Ti, Zr and Hf amount below 0.20%, preferably adjusts to below 0.15%.

(mass selection that constitutes from following element select more than a kind or 2 kinds: Sb:0.005～0.2%, Bi:0.005～0.2%, and Te:0.001～0.1%)

Sb, Bi and Te are effective choice elements aspect the raising erosion resistance.The explanation of amount about them is identical with above-mentioned first embodiment of the present invention.

(mass selection that constitutes from following element select more than a kind or 2 kinds: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%)

B, V and Nb are effective choice elements aspect the raising of mechanical characteristics (intensity).For intensity is improved, recommendation makes in the steel of the 3rd embodiment of the present invention and contains B, V and Nb, B content is preferably more than 0.0001%, more preferably more than 0.0003%, V content is preferably more than 0.01%, more preferably more than 0.02%, Nb content is preferably more than 0.003%, more preferably more than 0.005%.On the other hand,, make it to contain sometimes, recommending the B amount is adjusted to below 0.010%, preferably adjusting to below 0.0090%, recommending V and Nb amount are adjusted to respectively below 0.50%, preferably adjusting to below 0.45% from the viewpoint of above-mentioned toughness deterioration.

(Ta：0.003～0.5％)

Ta is an effective choice element aspect the crystal grain miniaturization.Explanation about its content is identical with first embodiment of the present invention.

Can be listed below as preferred selection element: more than a kind or 2 kinds of selection from the group of Mg, Ca and Sr formation; More than a kind or 2 kinds of selection from the group of Co, Ti and Zr formation; More than a kind or 2 kinds of selection from the group of B, V and Nb formation.

The ballast tank of the 3rd embodiment of the present invention with the composition of steel as mentioned above, surplus is made of iron and unavoidable impurities.As unavoidable impurities, can enumerate for example O, N, H, Mo, W etc., preferably it is no more than 0.1%, further recommends to be no more than 0.01%.

(tissue)

The tissue of the steel of the 3rd embodiment of the present invention is preferably based on the ferrite (is more than 50% with area occupation ratio integral body) of weldability and excellent in workability.In addition, because the susceptibility of the stress corrosion cracking that ferrite causes for muriate is little, so have advantage as the structural member under the such chloride environment of seawater.In addition steel of the present invention need to control bainite and/or martensitic area occupation ratio based on ferrite.Also have, steel of the present invention also allow the tissue beyond these ferrites, bainite and the martensite, for example situation about containing as the part of its formation such as perlite.

Because of bainite and/or martensite erosion resistance is caused detrimentally affect as above-mentioned, so in third embodiment of the invention, recommend to make bainite+martensitic area occupation ratio be lower than for 30% (comprising that bainite, martensitic any one party or both sides are 0 situation).The meaning of area occupation ratio and assay method and with above-mentioned in a organized way again.

(sulfide-based inclusion)

As non-metallic inclusion, the inclusion of sulfide-based, oxide-based, nitride-based or carbon compound etc. exists in steel.Wherein, because the sulfide-based inclusion of MnS etc. becomes the corrosive starting point, therefore on the viewpoint of erosion resistance, it is with the most deleterious inclusion of steel as ballast tank.When the size of the sulfide-based inclusion of attempt control and quantity, reduce number if find increased in size, then cause with this as the starting point significant local corrosion to take place and perforation etc. in early days.Increase number on the contrary if reduce size, then the corrosion starting point under the anticorrosive coating film becomes many and quickens the expansion generation of anticorrosive coating film.Except in steel making working procedure, using suitable desulfurizer, also can make above-mentioned detrimentally affect minimization by adjusting its size to reduce the sulfide-based inclusion.Specifically, be 0.5～10 μ m by the median size (equivalent circle diameter) that makes sulfide-based inclusion, just can make its hazardous property minimization.

The sulfide-based inclusion of the 3rd embodiment defined of the present invention, can be by for example when secondary refining, except adjusting to the mentioned component scope, be more than 10 with the ratio of Mn/ (S+Mg+Ca+Sr) again and be lower than 700 mode and carry out the composition adjustment, implement to utilize the bubbling (bubbling) of the rare gas element of Ar etc. simultaneously, stir molten steel fully and obtain.Mn has the caryogenic effect that suppresses sulfide-based inclusion, and S, Mg, Ca, Sr have the effect of the generation that promotes this inclusion on the contrary.For this reason, the ratio of Mn/ (S+Mg+Ca+Sr) the just size with sulfide-based inclusion is relevant, if this ratio is big, then the karyogenesis of sulfide-based inclusion is suppressed, and the inclusion of generation has the tendency of thickization.So, can control the median size of sulfide-based inclusion by adjusting this ratio.

In the 3rd embodiment of the present invention, the employing of the median size of sulfide-based inclusion is that the thickness at steel is under the situation more than the 6mm, at the position that reaches 3mm apart from the surface deeply, thickness at steel is lower than under the situation of 6mm, at 1/2 position of the thickness of steel, measure the equivalent circle diameter of any 30 sulfide inclusion things and the mean value that obtains.The mensuration of the equivalent circle diameter of sulfide-based inclusion can have been carried out the sample of mirror ultrafinish with scanning electronic microscope (SEM) observation, and carried out image analysis under the suitable multiplying power about 1000～5000 times, try to achieve thus.

So-called sulfide-based inclusion in the 3rd embodiment of the present invention as illustrated in Fig. 1, in EDX spectrum (spectrum), relatively is equivalent to the intensity of the peak value of S, O, N and C, the peak strength maximum of S be called sulfide-based inclusion.Can when the SEM that is used for median size mensuration observes, carry out EDX and analyze, thereby confirm sulfide-based inclusion.

(manufacture method)

The steel of the 3rd embodiment of the present invention can pass through for example following method manufacturing.Use the RH vacuum degasser, comprise the secondary refining that composition adjustment/temperature is adjusted for the molten steel that is poured into from converter or electric stove the ladle, in order to control the sulfuration type impurity, need when secondary refining, implement to utilize the bubbling of rare gas elementes such as Ar, and fully stir molten steel.By common castmethods such as Continuous casting process, ingot casting methods make it become steel ingot thereafter.Also have as the deoxidation form, recommend preferably to adopt deoxidized steel based on the viewpoint of mechanical characteristics and weldability, more preferably the Al deoxidized steel.

Then, carry out hot rolling after preferably the steel ingot that obtains being heated to 1100～1200 ℃ temperature field, thereby form the ideal size shape.At this moment by the hot rolling final temperature is controlled at 700～850 ℃, stop the scope that back to 500 ℃ speed of cooling is controlled at 0.1～15 ℃/second, just can access the tissue of regulation from hot rolling.

(protective system)

During the coating protective system of delivering from steel mill, usually be coated with the priming paint of zinc-rich paint etc. for preventing the purpose that steel get rusty.Before the coating of protective system, cause purposes such as dysgenic rust that produces in the priming paint defective part and oil content for removing to application, general using wire brush (wirebrush) and sand paper etc. are coated the purification of face.The ballast tank steel of the 3rd embodiment of the present invention, before the application of the protective system of epoxy resin, remove above-mentioned priming paint and remaining casting skin (oxide skin), coating is coated directly onto on the steel, directly act on corrosion reaction to improving the effective alloying element of erosion resistance thus, therefore can access and further improve application erosion resistance effect.As the method for removing priming paint etc., consider operability etc. and the suitable methods such as sandblast, shot-peening, grinding of selecting.

As the ballast tank of coating the 3rd embodiment of the present invention with the protective system on the steel, the epoxy resin coating of preferred tar epoxy class coating and sex change epoxypaint etc., but as indicated in its action effect, even when adopting the coating of urethanum (urethane) resene and vinylformic acid (acrylic) resinoid etc., can find that also the life-span of filming prolongs effect.In addition, also can with can not damage electric protection (galvanic anode method, external power source method) etc. other anti-corrosion methods action effect with it and use.

Next describe second grown form of the present invention (the 4th embodiment) in detail.The situation of the 4th embodiment special concern of the present invention is, the contact part of foreign matter and steel and have so-called crevice corrosion to expand rapidly in " slit " portion that produces owing to damage of constructional reason and anticorrosive coating film etc., thereby the life-span is significantly shortened, but existing aseptic technic still can't satisfy for such corrosion erosion resistance partly.Therefore, the purpose of the 4th embodiment of the present invention is to provide a kind of steel for ship, even it does not carry out anticorrosive coating and electric protection, but under high corrosive environment, still demonstrate other erosion resistance of utility grade, particularly for the excellent in te pins of durability of crevice corrosion, even and adhere to and, still demonstrate the protection against corrosion weather resistance of excellence in the face of the salinity that causes because of seawater owing to the corrosion that produces repeatedly at moist environment.A kind of steel for ship wherein also is provided,, when using, still demonstrates excellent erosion resistance as the structural wood of the basin that directly contacts with the oil fuel of former wet goods etc. even it is as the former material of oil tanker of the oil fuel of conveying crude oil etc.

The so-called steel for ship that can reach the 4th embodiment of the present invention of above-mentioned purpose contains:

C：0.01～0.30％、

Si：0.01～2.0％、

Mn：0.01～2.0％、

Al：0.005～0.10％、

Below the S:0.010%,

And contain:

A group element (select among Mg, Ca, Sr, the Ba more than a kind): 0.0005～0.020%; With

B group element (select among Ti, Zr, the Hf more than a kind): 0.005～0.20%,

And ratio S (a)/S (b) of the total content S (a) of above-mentioned a group element and the total content S (b) of b group element is in 0.01～1 scope, surplus is Fe and unavoidable impurities, have again, satisfying the sulfide-based inclusion of following prerequisite and the median size of oxide-based inclusion is 1～10 μ m, and it is at the every 1mm of rolling direction ²Section in respectively have 200～2000.

Sulfide-based inclusion: be contain in the described a group element of total amount 1～30% and/or in the described b group element of total amount 1～30%, equivalent circle diameter is the sulfide-based inclusion more than the 0.5 μ m,

Oxide-based inclusion: be contain in the described a group element of total amount 1～30% and/or in the described b group element of total amount 1～30%, equivalent circle diameter is the oxide-based inclusion more than the 0.5 μ m.

The above-mentioned steel for ship of the 4th embodiment of the present invention can also contain as follows as other element: (1) at least a kind of selecting from the group that following element constituted: Cr:0.01～5.0%, Cu:0.01～5.0%, Ni:0.01～5.0%, and Co:0.01～5.0%; (2) from following element constituted group, select at least a kind: La:0.0001～0.005%, Ce:0.0001～0.005%, Nd:0.0001～0.005%, Sm:0.0001～0.005%, and Se:0.001～0.1%; (3) from following element constituted group, select at least a kind: Sb:0.005～0.2%, Bi:0.005～0.2%, and Te:0.001～0.1%; (4) from following element constituted group, select at least a kind: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%, perhaps (5) Ta:0.003～0.5%.The steel for ship of the 4th embodiment of the present invention also can satisfy more than 2 of prerequisite of this (1)～(5) simultaneously.

The steel for ship of the 4th embodiment of the present invention then shows excellent erosion resistance, particularly can be as the former material of crude oil basin of oil tanker and the utmost point is applied flexibly effectively.

Steel for ship according to the 4th embodiment of the present invention, be grouped into by the one-tenth of suitably adjusting steel, a group element (the Mg that particularly contains regulation in right amount, Ca, Sr, more than a kind of Ba) and b group element (Ti, Zr, more than a kind of Hf), and adjust it and contain ratio, have again and will contain the size and the number control specialized range of the sulfide-based inclusion and the oxide-based inclusion of these a group elements and b group element, even a kind of steel for ship that anticorrosive coating and electric protection still demonstrate sufficient erosion resistance of not implementing just can be provided, particularly can provide a kind of steel for ship, it can realize the raising at the weather resistance of crevice corrosion, even and the salinity that causes because of seawater adhere to and the harsh corrosive environment that causes repeatedly at moist environment under, still bringing into play excellent non-corrosibility.The steel for ship that possesses the 4th embodiment of the present invention of such characteristic is suitable for the former material as the outside plate of the boats and ships of oil tanker, freighter, semi-cargo ship, passenger boat, warship etc. and ballast tank etc., wherein extremely is suitable for the former material as the crude oil basin.

Present inventors are research with keen determination repeatedly in order to reach previous illustration purpose.Its result is known, if contain reduction restraining effect with pH and a group element (more than a kind of Mg, Ca, Sr, Ba) and the b group element (more than a kind of Ti, Zr, Hf) that generates the static stabilization of rust in right amount, suitably control their ratio that contains, then can adjust the sulfide-based inclusion that contains these elements and the size and the number of oxide-based inclusion well, obtain to solve the high performance steel for ship of above-mentioned problem, thereby finish the 4th embodiment of the present invention.

In the 4th embodiment of the present invention, in order to satisfy the basic characteristic as steel, basal component such as C, Si, Mn, Al also need suitably to adjust, and at first illustrate the qualification reason of these basal component in addition.

(C：0.01～0.30％)

C is the important element that is used to guarantee the structural strength of steel, in order to ensure as the MIN intensity of the structural member of boats and ships (wall thickness that depends on steel, but probably be about 400MPa), C is contained more than 0.01%.Guarantee and the viewpoint of above-mentioned toughness deterioration that from this intensity the C amount of the 4th embodiment of the present invention is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.04%, but below 0.30%, be preferably below 0.28%, more preferably below 0.26%.

(Si：0.01～2.0％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of weldability deterioration, the Si of the 4th embodiment of the present invention amount is more than 0.01%, is preferably more than 0.02%, more preferably more than 0.05%, but below 2.0%, be preferably below 1.5%, more preferably below 1.0%.

(Mn：0.01～2.0％)

From above-mentioned deoxidation with intensity is guaranteed and the viewpoint of toughness deterioration, the Mn of the 4th embodiment of the present invention amount is more than 0.01%, is preferably more than 0.05%, more preferably more than 0.10%, but below 2.0%, be preferably below 1.80%, more preferably below 1.60%.

(Al：0.005～0.10％)

From above-mentioned deoxidation with guarantee intensity and the viewpoint of weldability deterioration, the Al amount of the 4th embodiment of the present invention is more than 0.005%, be preferably more than 0.010%, more preferably more than 0.015%, but below 0.10%, be preferably below 0.050%, more preferably below 0.040%.

(S:0.010% is following)

In the 4th embodiment of the present invention, will adjust to below 0.010% for toughness and the deleterious S amount of weldability as above-mentioned recommendation, preferably adjust to below 0.008%.

(a group element (select among Mg, Ca, Sr, the Ba at least a kind): 0.0005～0.020%)

In the 4th embodiment of the present invention, improve the viewpoint of the deterioration of (particularly suppressing pH reduces) and shaping processability and weldability from above-mentioned erosion resistance, the content of these elements that a group is contained adds up to more than 0.0005%, be preferably more than 0.0008%, but, be preferably below 0.015% below 0.020%.

(b group element (select among Ti, Zr, the Hf at least a kind): 0.005～0.20%)

In the 4th embodiment of the present invention, improve the viewpoint of the deterioration of (the particularly stabilization of surface rust tunicle) and processibility and weldability from above-mentioned erosion resistance, the content of these elements that b group is contained adds up to more than 0.005%, be preferably more than 0.008%, but, be preferably below 0.15% below 0.20%.

In the 4th embodiment of the present invention, the pH that is brought by above-mentioned a group element for collaborative performance reduces restraining effect and the static stabilization of the surface scale film that brought by the b group element, and the ratio of total content S (b) of suitably controlling the total content S (a) of a group element and b group element is very important.In order to improve comprehensive erosion resistance, the S (a) in the 4th embodiment of the present invention/S (b) is preferably more than 0.02, but below 1, is preferably below 0.8 than being more than 0.01 as above-mentioned.

The necessary of the steel for ship of the 4th embodiment of the present invention constitutes element as above, surplus is the iron-smelting raw material (iron ore and auxiliary material, slag etc.) and the impurity (for example P, O, N, W, Mo etc.) of sneaking into inevitably from manufacturing process etc., but their only allow to contain with the limit trace of the characteristic that do not hinder steel.But if these allow compositions too much, then will cause detrimentally affect, therefore be at most below 0.5%, more preferably should be suppressed at below about 0.1% to toughness etc.

In the 4th embodiment of the present invention, contain selection element shown below more energetically as other elements, can realize that further rerum natura is improved.Below, select element and additive effect to remark additionally with regard to these.

(from following element constituted group, select at least a kind: Cr:0.01～5.0%, Cu:0.01～5.0%, Ni:0.01～5.0%, and Co:0.01～5.0%)

Cr, Cu, Ni and Co all are the selection elements that help the erosion resistance raising of steel.As above-mentioned for erosion resistance is improved, particularly in order to form fine and close surface scale film,, recommend to make in the steel of the 4th embodiment of the present invention and contain Cr, Cu, Ni and Co perhaps in order to help it to form, its content is preferably respectively more than 0.01%, more preferably more than 0.05%.On the other hand, the viewpoint from the deterioration of above-mentioned weldability and hot workability makes it to contain sometimes, recommends Cr, Cu, Ni and Co amount are adjusted respectively below 5.0%, preferably adjusts to below 4.50%.

(from following element constituted group, select at least a kind: La:0.0001～0.005%, Ce:0.0001～0.005%, Nd:0.0001～0.005%, Sm:0.0001～0.005%, and Se:0.001～0.1%)

La, Ce, Nd, Sm and Se are effective choice elements aspect the erosion resistance raising.About their explanation of content, identical with above-mentioned first embodiment of the present invention.

(from following element constituted group, select at least a kind: Sb:0.005～0.2%, Bi:0.005～0.2%, and Te:0.001～0.1%)

Sb, Bi and Te are effective choice elements aspect the erosion resistance raising.About their explanation of content, identical with above-mentioned first embodiment of the present invention.

(from following element constituted group, select at least a kind: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%)

B, V and Nb all are the selection elements that help intensity further to improve.For such intensity improves, recommendation makes in the steel of the 4th embodiment of the present invention and contains B, V and Nb, B content is preferably more than 0.0001%, more preferably more than 0.0003%, V content is preferably more than 0.01%, more preferably more than 0.02%, Nb content is preferably more than 0.003%, more preferably more than 0.005%.On the other hand, viewpoint is arranged, make it to contain sometimes, recommend the B amount is adjusted to below 0.010%, preferably adjust to below 0.0090%, recommend respectively V and Nb amount to be adjusted to below 0.50%, preferably adjust to below 0.45% from above-mentioned toughness deterioration.

(Ta：0.003～0.5％)

Ta is an effective choice element aspect the crystal grain miniaturization.Explanation about its content is identical with above-mentioned first embodiment of the present invention.

As preferred selection element, can enumerate at least a kind that selects the group who constitutes from Cr, Cu, Ni and Co; From B, V and Nb constituted group, select at least a kind.

It more than is qualification reason about chemical ingredients, but in the 4th embodiment of the present invention, the a group element and the b group element that make sulfide-based inclusion in the steel and oxide-based inclusion contain afore mentioned rules, and suitably control its size and number, this is very important on the erosion resistance that obtains excellence.Below describe with regard to these inclusiones.

In containing the water system environment of chloride ion, sulfide-based inclusion is dissolved in water gradually and becomes the corrosive starting point.Contain above-mentioned a group element and b group element as if making in the sulfide-based inclusion with specified amount, then the dissolving of the sulfide-based inclusion in containing the water system environment of chloride ion is suppressed as can be known.In addition, under the corrosive environment that contains sulphur composition (element shape sulphur and hydrogen sulfide etc.) from petroleum-type, contain above-mentioned a group element and b group element if make in the oxide-based inclusion with specified amount, but the then dissolving of promotes oxidn thing type impurity promotes them to be dissolved in water and the pH of water system environment is risen.Its results verification arrives, and the local anodic of dissolved that iron takes place adds pH that the water decomposition reaction causes to be reduced and suppressed, thereby has suppressed corrosion reaction, helps the raising of erosion resistance.

Therefore in the 4th embodiment of the present invention, suitably contain element contained among above-mentioned a group and the b group by making in sulfide-based inclusion and the oxide-based inclusion, the dissolving of sulfide-based inclusion suppresses and dissolving the pH rising that causes and the effect of corrosion inhibition that accompanies with it of oxide-based inclusion are able to corresponding performance, has increased substantially erosion resistance.

In order to bring into play such effect effectively, make contain respectively in sulfide-based inclusion and the oxide-based inclusion above-mentioned a group element total amount be 1～30% and/or b group element total amount be 1～30%, and among these sulfide-based inclusiones and oxide-based inclusion, though equivalent circle diameter is more than the 0.5 μ m, median size and number need be controlled in the proper range.Promptly, in the 4th embodiment of the present invention, in sulfide-based inclusion that contains above-mentioned a group element and/or b group element in right amount and oxide-based inclusion, though equivalent circle diameter is more than the 0.5 μ m, but median size is respectively 1～10 μ m, and makes their every 1mm in the steel cross section ²Have 200～2000 respectively, this brings into play on the high-caliber erosion resistance very important effectively bringing into play above-mentioned two characteristics.

Moreover, about above-mentioned sulfide-based and oxide-based inclusion, for example use diamond paste (diamond paste) etc. to carrying out mirror ultrafinish up to about 1 μ m for the cross section of examination steel, observe the ground sample face of minute surface with scanning electronic microscope (SEM), disperse the ultimate analysis of shape X-ray analysis (EDX) to confirm the composition that contains of these inclusiones through energy, contained S in this inclusion, O, S (sulphur) content is maximum among the N amount is accredited as sulfide-based inclusion (for example with reference to Fig. 2), and O (oxygen) content is maximum is accredited as oxide-based inclusion (for example with reference to Fig. 3).

The contained above-mentioned a group element and the content of b group element are lower than respectively at 1% o'clock in these sulfide-based inclusiones and the oxide-based inclusion, the sort of other erosion resistance of level of being pursued in the 4th embodiment of the present invention improves effect and can't bring into play, in addition, if it becomes excessive above 30% respectively, then the mechanical characteristics of steel becomes badly, so contained a group element and the content of b group element are decided to be 1～30% scope respectively in these inclusiones.Preferred content is below 2%, below 28%, more preferably more than 3%, below 25%.

If the particle diameter of sulfide-based inclusion is too small, then fine sulfide-based inclusion sheet disperses and general corrosion takes place easily, and erosion resistance reduces.Opposite particle diameter as if sulfide-based inclusion is excessive, then the mechanical characteristics variation of steel.In addition if the particle diameter of oxide-based inclusion is too small, then it is insufficient to the pH effect of increasing that the dissolving of water system atmosphere produces, the pH reduction that causes is reacted in the water decomposition that adds that can not be suppressed at the local anode portion of dissolved that causes iron, is difficult to bring into play gratifying erosion resistance and improves effect.Otherwise if the particle diameter of oxide-based inclusion is excessive, then the situation with sulfide-based inclusion is identical, the characteristic variation of the machinery of steel.Because like this, sulfide-based inclusion and its median size of oxide-based inclusion (mean value of equivalent circle diameter) should be adjusted to the scope of 1～10 μ m, the more preferably scope of 2.0～9.0 μ m.

The particle diameter that also has these sulfide-based inclusiones and oxide-based inclusion, be to carrying out mirror ultrafinish (for example using diamond paste up to about 1 μ m) afterwards for the cross section of examination steel, (SEM) takes pictures to this abrasive surface with scanning electronic microscope, select to be considered to equivalent circle diameter among each inclusion by image analysis and be approximately any 100 inclusiones more than the 0.5 μ m, try to achieve their equivalent circle diameter, with its mean value as median size.

Then, about the number of these inclusiones, if the number of sulfide-based inclusion is very few, then each sulfide-based inclusion becomes excessive and the mechanical characteristicies infringement steel, and its number itself is too much in addition, can make the mechanical characteristics deterioration of steel too.In addition, if the number deficiency of oxide-based inclusion, the then previously described pH effect of increasing that dissolving brings in the water system environment reduces, the local anode of dissolved of iron takes place and adds pH that the water-dispersion reaction brings to reduce restraining effect insufficient, the erosion resistance deficiency, in addition if number is too much, the mechanical characteristics deterioration of steel then.So in the 4th embodiment of the present invention, every 1mm in the arbitrary section of steel ²The sulfide-based inclusion of viewed above-mentioned size (equivalent circle diameter is more than the 0.5 μ m) and the number of oxide-based inclusion are decided to be 200～2000 respectively.Preferred number is 500～1500.

The number of said here sulfide-based inclusion and oxide-based inclusion, be to carrying out mirror ultrafinish (for example using diamond paste up to about 1 μ m) afterwards for the cross section of examination steel, observe abrasive surfaces by scanning electron microscope (SEM) with 400 times of multiplying powers, try to achieve as mean value respectively by the sulfide-based inclusion of viewed above-mentioned size (equivalent circle diameter is more than the 0.5 μ m) in 10 visuals field arbitrarily and the number of oxide-based inclusion.

The steel for ship of the 4th embodiment of the present invention, as above-mentioned except suitable adjustment chemical ingredients is formed, by (I) adjust a group element in the steel and b group element contain ratio S (a)/S (b) and (II) control contain the size and the number of the sulfide or the oxide-based inclusion of a group element and b group element with specified amount, can reach excellent erosion resistance.The 4th embodiment of the present invention for this reason, the steel for ship of second grown form promptly of the present invention, different with the steel of above-mentioned first grown form of the present invention, unqualified for metal structure.

Next the manufacture method with regard to the above-mentioned steel for ship of the 4th embodiment of the present invention describes.The steel of the 4th embodiment of the present invention can be by following such method manufacturing.That is,, adopt the RH vacuum degasser to comprise the secondary refining that composition adjustment and temperature are adjusted for according to conventional methods by converter and electric stove melting and be poured into molten steel in the ladle.In the 4th embodiment of the present invention, a group element and the b group element that constitute above-mentioned sulfide-based inclusion and oxide-based inclusion add when this secondary refining, adjust with the method that the one-tenth that becomes regulation is grouped into.In the secondary refining operation, can utilize the S that takes off of LF (ladle refining) to handle etc. as required, also can adopt the device beyond the RH to handle.As the deoxidation form in the secondary refining, from the viewpoint of the steel that obtain mechanical characteristics and welding property excellent, preferably use deoxidized steel, more preferably use the Al deoxidized steel.After the secondary refining, make steel ingot by common castings such as Continuous casting process and ingot casting methods.

Carry out hot rolling after the steel ingot that obtains being heated to 1100～1200 ℃ temperature field, form the size shape of wishing.At this moment preferred hot rolling final temperature is 750～850 ℃, and hot rolling is stopped the back is controlled at 0.1～15 ℃/second to the speed of cooling of 500 ℃ temperature field scope.

When stating manufacture method on the implementation, particularly in order to adjust to aforesaid optimum range with becoming the above-mentioned sulfide-based inclusion of important integrant and the size and the number of oxide-based inclusion in the 4th embodiment of the present invention, interpolation a group element and b group element are very important when secondary refining.If when secondary refining, add these elements, and adjusting addition makes the ratio of a group element and b group element be in specialized range, can make and contain a group element and b group element in sulfide-based inclusion and the oxide-based inclusion, the size and the number of inclusion is controlled at proper range.If interpolation a group element and b group element carry out the composition adjustment before secondary refining, then inclusion formation element becomes too much, generates thick inclusion easily, can not bring the size and the number of inclusion into aforesaid proper range.

In addition, the steel billet before the hot rolling (steel ingot) Heating temperature is heated to 1100～1200 ℃ very important.If Heating temperature surpasses 1200 ℃, even if then chemical ingredients is suitable, but the change of the number of inclusion is many, still can not reach the purpose of the 4th embodiment of the present invention.

The steel for ship of the 4th embodiment of the present invention, because above-mentioned characteristic, basically the unreal dress that applies, steel itself are also being brought into play excellent erosion resistance, but as required, also can with being other antisepsises such as various heavy anti-corrosion paints, zinc rich primer, shop primer, electric protection of representative and using shown in the embodiment as described later with sex change epoxypaint etc.When having implemented such anticorrosive coating, shown in the embodiment, the erosion resistance of coated film itself (the flaw portion erosion resistance of filming) is also excellent as described later.

[embodiment]

Below enumerates embodiment and be described more specifically the present invention, but the present invention is not limited by the following examples, the scope that can be fit to the forward and backward aim of stating in addition suitably change can implement certainly, these all are included in technical scope of the present invention.Also have in aftermentioned embodiment " % " unless special mark is the meaning of " quality % ".

Embodiment 1 (example of the present invention and the comparative example of first embodiment of the present invention)

(for the making of examination material)

After carrying out the converter melting, make the steel billet of the chemical ingredients composition that has shown in following table 1 and the table 2 by Continuous casting process.According to the condition shown in table 3 and the table 4 these steel billets are carried out hot rolling and make steel plate.In table 3 and table 4, Heating temperature before the hot rolling is recorded and narrated and is " Heating temperature ", the record of hot rolling final temperature is " finishing temperature ", adds up to draft to record and narrate through hot rolled and is " draft ", and the speed of cooling record that is terminated to 500 ℃ from hot rolling is " speed of cooling ".

[table 1]

Steel No.	Chemical composition of steel is formed (unit: quality %)
											C	Si	Mn	Al	P	S	Cu	Ni	Cr	Other
	1	0.18	0.18	1.05	0.038	0.008	0.009
2											0.16	0.22	1.09	0.045	0.008	0.005	0.05	0.12	0.05
	3	0.15	0.22	1.12	0.039	0.008	0.004	0.09	0.11	0.06
4											0.16	0.25	1.22	0.058	0.007	0.005	0.11	0.11	0.11
	5	0.15	0.29	1.07	0.019	0.009	0.005	0.10	0.09	0.10
6											0.14	0.09	0.91	0.021	0.007	0.004	0.11	0.09	0.004
	7	0.28	0.30	0.99	0.034	0.008	0.004	0.15	0.11	0.09
8											0.30	0.11	0.98	0.005	0.009	0.005	0.22	0.09	0.007	B：0.0008
	9	0.11	0.22	0.92	0.008	0.009	0.004	0.33	0.34	0.09											Ca：0.0012
10											0.13	0.15	0.99	0.015	0.008	0.004	0.02	0.58	0.23	Mg：0.0024，V：0.011
	11	0.13	0.24	1.97	0.028	0.008	0.004	0.11	0.79	0.21											La：0.0019
12											0.09	0.25	1.28	0.019	0.009	0.004	0.12	0.15	0.11	Ca：0.0002，Mg：0.0019
	13	0.11	0.24	1.22	0.059	0.008	0.004	0.09	0.19	0.12											Ca：0.0028，Ce：0.0011
14											0.06	0.17	0.95	0.094	0.008	0.005	0.32	0.34	0.14	Ti：0.011
	15	0.12	0.21	1.24	0.019	0.007	0.004	0.29	0.22	0.06											Ti：0.005，Zr：0.029， B：0.0002
16											0.09	0.18	1.21	0.015	0.007	0.004	0.19	0.48	0.51	Ti：0.023，Hf：0.018
	17	0.12	0.20	1.12	0.018	0.008	0.004	0.49	0.44	0.07											Sb：0.005

[table 2]

Steel No.	Chemical composition of steel is formed (unit: quality %)
											C	Si	Mn	Al	P	S	Cu	Ni	Cr	Other
	18	0.12	0.22	1.19	0.009	0.007	0.004	0.12	0.21	0.12											Zr：0.008，Sb：0.027， Bi：0.009
19											0.14	1.99	1.04	0.028	0.003	0.002	0.80	0.92	0.01	Ce：0.0001，Ti：0.018， Hf：0.009，B：0.0099
	20	0.15	0.96	1.27	0.043	0.004	0.003	0.49	0.02	0.81											Ca：0.0025，La：0.0005， Zr：0.005
21											0.04	0.48	1.00	0.027	0.004	0.001	0.30	0.08	0.19	Mg：0.0033，La：0.0019， Ti：0.022，Sb：0.052
	22	0.18	0.16	1.45	0.059	0.004	0.002	0.17	0.38	0.03											Ca：0.0019，Mg：0.0002， La：0.0014，Ti：0.028 Zr：0.049，Hf：0.096， Sb：0.11
23											0.08	0.19	0.02	0.040	0.008	0.004	0.31	0.11	0.13	Co：0.02
	24	0.17	0.18	0.99	0.099	0.009	0.005	0.99	0.28	0.09											Ta：0.019
25											0.12	0.21	0.95	0.048	0.009	0.004	0.19	0.21	0.28	Mg：0.0019，Ce：0.0049， Nb：0.018
	26	0.10	0.52	1.13	0.037	0.008	0.004	0.25	0.48	0.13											La：0.0001，Ce：0.0029， Co：0.12，Se：0.099
27											0.11	0.13	1.28	0.049	0.009	0.004	0.02	0.34	0.09	Ca：0.0032，Co：0.18， V：0.498
	28	0.19	0.12	1.07	0.053	0.008	0.004	0.23	0.43	0.05											Ti：0.023，Sb：0.019， Te：0.099
29											0.09	0.38	0.90	0.020	0.010	0.005	0.28	0.33	0.02	Zr：0.011，Sb：0.13，Co：0.33
	30	0.11	0.26	1.09	0.042	0.008	0.005	0.12	0.56	0.08											Bi：0.005，Ta：0.003
31											0.22	0.02	1.09	0.035	0.008	0.004	0.44	0.99	0.99	Ca：0.0008，Mg：0.0021， La：0.0033， Ce：0.028，Sb：0.05， Nb：0.003
	32	0.09	0.27	1.56	0.087	0.002	0.002	0.18	0.02	0.09											Ca：0.0049，Ce：0.0007， Ti：0.082，Hf：0.005 Sb：0.199，Bi：0.014， Ta：0.499
33											0.13	0.18	1.6	0.028	0.003	0.002	0.12	0.19	0.25	Mg：0.0050，Zr：0.199， Hf：0.015，Se：0.002
	34	0.12	0.22	1.15	0.032	0.003	0.003	1.00	0.34	0.18											La：0.0049，Ti：0.019， Sb：0.015，Te：0.002

[table 3]

Steel No.	Heating temperature (℃)	Finishing temperature (℃)	Draft (%)	Speed of cooling (℃/second)	Organize area occupation ratio (%) *1			Ferrite particle diameter (μ m)	Pearlitic long-width ratio
										P	B	M
					1	1100	760							85	10	15	8	0	14	5.1
2	1150	760	85	0.1				26	5	0	13	4.8
					3	1150	760						85	18	7	21	9	12	3.9
4	1250	860	85	10				15	9	0	16	5.5
					5	1150	760						78	10	17	5	0	14	2.8
6	1150	760	85	10				15	8	0	14	3.8
					7	1150	750						80	8	20	0	0	13	3.2
8	1200	750	80	8				10	10	2	15	5.1
					9	1150	770						80	3	20	5	0	12	6.0
10	1150	780	80	5				14	10	2	14	6.7
					11	1150	780						85	0.5	25	0	0	13	8.0
12	1150	800	85	5				10	0	0	12	10.5
					13	1150	800						85	5	12	0	0	13	9.9
14	1150	800	85	0.8				20	0	0	13	10.3
					15	1150	760						85	8	16	18	5	11	9.2
16	1050	800	87	5				13	10	0	10	9.7
					17	1050	800						87	5	12	12	0	9.8	10.5

^{* 1}P: perlite, B: bainite, M: martensite, surplus portion: ferrite

[table 4]

Steel No.	Heating temperature (℃)	Finishing temperature (℃)	Draft (%)	Speed of cooling (℃/second)	Organize area occupation ratio (%) *1			Ferrite particle diameter (μ m)	Pearlitic long-width ratio
										P	B	M
					18	1050	800						90	5	14	10	0	8.7	9.3
19	1100	820	92	10				8	18	7	10	16.3
					20	1100	820						87	8	10	12	0	11	18.6
21	1000	800	85	8				6	8	0	5.2	12.1
					22	1050	800						80	2	20	4	0	6.5	11.3
23	1050	800	80	2				4	0	0	5.8	11.4
					24	1000	800						90	1	12	0	0	3.9	10.5
25	1100	800	92	8				9	2	0	3.2	16.1
					26	1100	780						92	8	15	3	0	2.7	16.6
27	1100	800	90	15				5	10	9	3.3	13.2
					28	1050	800						90	5	11	5	0	3.2	17.8
29	1050	850	97	5				7	17	6	2.5	19.8
					30	1050	850						97	15	8	18	5	3.8	17.5
31	1050	800	95	15				5	19	8	2.8	19.2
					32	1050	800						95	0.5	15	12	4	1.9	19.2
33	1050	800	95	1				12	11	3	2.7	18.6
					34	1100	820						90	1	10	10	2	3.3	18.1

^{* 1}P: perlite, B: bainite, M: martensite, surplus portion: ferrite

The steel plate that as above obtains is like this cut and surface grinding, make the test film A of 300 * 300 * 10 (mm) size thus.The face shaping of test film A shows in Fig. 4.In addition as shown in Figure 5, the big test film (identical with above-mentioned test film A) of 4 of 60 * 60 * 5 (mm) small test sheets and 300 * 300 * 10 (mm) contact, making has formed the test film B of clearance portion.The steel of the chemical ingredients composition that the small test sheet that the formation gap is used is identical with big test film employing, surface working is also identical with big test film A.Offer the hole of 10mm  then at the center of small test sheet, be opened in base material side (big test film side), fix by M8 plastics screw-making.

Make again and implemented in full denaturation loop epoxy resins application (average film thickness: the test film that test film C (Fig. 6) conduct 50 μ m) is used in the simulated environment of ballast tank.In addition, for anticorrosive coating film being paid the corrosion progress degree of damage when exposing with investigation blank steel, also made test film D (Fig. 7), it is (long: 300mm, wide: about 0.5mm) by cutting knife has formed through blank on above-mentioned test film C 1 cut channel.On the test face of these test films C and D, be the pure zinc metal sheet that the mode of 20mm is installed 20mm  * 10mm with the distance of the end of the center of zinc metal sheet and test film, implement electrocorrosion.The face (test face) of estimating corrosion condition in addition in test film arbitrarily all has only one side, the face beyond the test face by silicone sealant (silicone sealant) lining to prevent corrosion.

(corrosion test)

(I) test of the simulated environment of crude oil basin

Mixing of former greasy filth that will extract from oil tanker and the natural sea-water that extracts in Bingku county Gu Chuan city 1: 1 by volume, horizontal dip test sheet A and B in such crude oil mimic solvent, in intrinsic standoff ratio with 5%O ₂-0.5%H ₂S-10%CO ₂(surplus is N ₂) mixed gas import in the Thoughs.The number of test film is that test film A and B are 10 respectively, and test period is 1 year.After off-test,, test film A is removed the corrosion product of iron rust etc. by the katholysis in the diammonium hydrogen citrate aqueous solution (JIS K8284).Take off for test film B in addition and form the small test sheet that the gap is used, also remove corrosion product with same method.

With proof test film A and B in this simulated environment, according to the anti-general corrosion of the benchmark evaluation shown in the table 5, corrosion homogeneity and anti-crevice corrosion.Show the corrosion test result in the table 6 and 7.

(II) test under the simulated environment of ballast tank

Test film C and D are vertically set in the airtight corrosion test groove, " the seawater impregnation state " during the importing seawater in ballast tank with hypothesis, make with the lift-launch crude oil of hypothesis " humid tropical condition " during empty in the ballast tank, per respectively two weeks repeat once.At this moment the seawater of Shi Yonging is the natural sea-water that extracts from Bingku county Jia Guchuan city, and seawater temperature remains on 30 ℃.Under humid tropical condition, carry out temperature regulation and humidification with 40 ℃ of atmosphere temperatures, mode more than the humidity 90%RH.The number of test film is that test film C and D are 10 respectively, and adding up to test period is 1 year.

With proof test film C and D in this simulated environment, according to the anti-paint blister of the benchmark evaluation shown in the table 5 and the flaw portion erosion resistance of filming.Show the corrosion test result in the table 6 and 7.

(1) anti-general corrosion and corrosion homogeneity

Use test film A, the quality change before and after the test is converted into average thickness of slab reduction Dave (mm), calculate the mean value of 10 test films, estimate each anti-general corrosion for the examination material.In addition, use the contact pin type 3 d shape testing device, try to achieve the maximum depth of erosion Dmax (mm) of test film A, calculate Dmax/Dave, estimate the corrosion homogeneity.

(2) anti-crevice corrosion

Use test film B, use the contact pin type 3 d shape testing device, measure the crevice corrosion degree of depth of big test film side, the maximum value of 10 test films as maximum clearance depth of corrosion Dcrev (mm), is estimated anti-crevice corrosion.

(3) anti-paint blister

Use test film C, suit to observe, calculating to measure has the time (day) of taking place by the visual expansion that can confirm on filming, estimate anti-paint blister.

(4) the flaw portion erosion resistance of filming

Use test film D,, the maximum value of 10 test films is calculated as the maximum swelling width gauge, estimate the flaw portion erosion resistance of filming with the paint blister width (mm) on vernier callipers mensuration and the cut channel vertical direction.

[table 5]

Test film	Estimate characteristic	The mensuration project	Judge
							×	△	○	◎
			A	Anti-general corrosion	Dave (mm)	3.00 more than					0.50 it is above, be lower than 3.00	0.10 more than be lower than 0.50	Be lower than 0.10
The corrosion homogeneity	Dmax/ Dave	5.0 more than					2.0 more than low dried 5.0	1.5 more than be lower than 2.0	Be lower than 1.5
				B	Anti-crevice corrosion	Dcrev (mm)				3.00 more than	0.50 more than be lower than 3.00	0.10 more than be lower than 0.50	Be lower than 0.10
C	Anti-paint blister	Expansion time of origin (day)	Be lower than 30				Be lower than 60 more than 30	Be lower than 180 more than 60	More than 180
				D	The flaw portion erosion resistance of filming	Maximum swelling width (mm)				More than 5	Be lower than 5 more than 2	Be lower than 2 more than 1	Be lower than 1

[table 6]

Steel No.	Crude oil basin side			The ballast tank side		Synthetic determination
							Anti-general corrosion	The corrosion homogeneity	Anti-crevice corrosion	Anti-paint blister	The flaw portion erosion resistance of filming
	1	×	×	×	×							×	×
2						×	△	×	△	×	×
	3	△	×	△	×							△	×
4						△	×	△	×	△	×
	5	×	△	×	△							×	×
6						△	△	△	×	×	×
	7	△	△	△	△							△	△
8						△	△	△	△	△	△
	9	○	△	○	○							○	△～○
10						○	△	○	○	○	△～○
	11	○	△	○	○							○	△～○
12						○	△	○	○	○	△～○
	13	○	△	○	○							○	△～○
14						○	○	○	○	○	○
	15	○	○	○	○							○	○
16						○	○	○	○	○	○
	17	○	○	○	○							○	○

[table 7]

Steel No.	Crude oil basin side			The ballast tank side		Synthetic determination
							Anti-general corrosion	The corrosion homogeneity	Anti-crevice corrosion	Anti-paint blister	The flaw portion erosion resistance of filming
	18	○	○	○	○							○	○
19						◎	◎	◎	◎	◎	◎
	20	◎	◎	◎	◎							◎	◎
21						◎	◎	◎	◎	◎	◎
	22	◎	◎	◎	◎							◎	◎
23						○	○	○	○	○	○
	24	○	○	○	○							○	○
25						◎	◎	◎	◎	◎	◎
	26	◎	◎	◎	◎							◎	◎
27						◎	◎	◎	◎	◎	◎
	28	◎	○	○	○							○	○～◎
29						◎	○	○	○	○	○～◎
	30	◎	○	○	○							○	○～◎
31						◎	◎	◎	◎	◎	◎
	32	◎	◎	◎	◎							◎	◎
33						◎	◎	◎	◎	◎	◎
	34	◎	◎	◎	◎							◎	◎

Steel No.1～6 erosion resistances of the prerequisite of first embodiment of discontented unabridged version invention are insufficient.Steel No.1 is the existing steel that does not contain Cu, Ni and Cr in detail, and the result of the whole projects of corrosion test is all bad.Contained steel No.2 its corrosion homogeneity and the paint blister property improvement of Cu, Ni and Cr, but the result of other project is bad.This is estimated to be is because the perlite area occupation ratio is excessive.The result of its corrosion homogeneity of steel No.3 and anti-paint blister is bad.This is estimated to be is because the bainite area occupation ratio is excessive.The result of steel No.4 corrosion homogeneity and anti-paint blister is bad.This is estimated to be is because the ferrite particle diameter is excessive.The result of its anti-general corrosion of steel No.5, anti-crevice corrosion and the flaw portion erosion resistance of filming is bad.This is estimated to be is because pearlitic long-width ratio is too small.The result of its anti-paint blister of steel No.6 and the flaw portion erosion resistance of filming is bad.This is estimated to be is because the Cr amount is very few.

With respect to this, satisfy steel No.7～34 of the prerequisite of first embodiment of the present invention fully, crude oil basin and ballast tank all demonstrate excellent erosion resistance under simulated environment as can be known, and it is preferably as steel for ship.Relevant for No.7～34, represent that the graphic representation of the relation of anti-general corrosion and pearlitic long-width ratio shows in Fig. 8 again.As table 3,4,6 and 7 shown in Figure 8 in addition, if pearlitic long-width ratio is more than 3, then in anti-general corrosion, can access good result (△), if then can access excellent result (zero) more than 6, if then can access extremely excellent result (◎) more than 12.

Embodiment 2 (example of the present invention and the comparative example of second embodiment of the present invention)

(for the making of examination material)

With the steel of the chemical ingredients shown in converter melting table 8 and 9, will be heated to by the steel billet that Continuous casting process is made and carry out hot rolling after 1150 ℃ and make steel plate.Hot rolling final temperature when the steel tissue is made by making and be terminated to 500 ℃ speed of cooling from hot rolling and change and adjust.Equivalent circle diameter surpasses the quantity of the non-metallic inclusion of 20 μ m, utilizes the degassing treatment time of RH method to adjust by increase and decrease.

In table 10, it is " finishing temperature " that the hot rolling final temperature is recorded and narrated, being terminated to 500 ℃ speed of cooling from hot rolling records and narrates and to be " speed of cooling ", the area occupation ratio of steel tissue is recorded and narrated and is " tissue area occupation ratio ", and the equivalent circle diameter quantity that surpasses the non-metallic inclusion of 20 μ m is recorded and narrated and is " non-metallic inclusion ".In table 10, also put down in writing the value of S (c)/S (a) and S (c)/S (b) in addition.

[table 8]

Steel No.	Chemical composition of steel is formed (unit: quality %)
										C	Si	Mn	Al	Cu	Cr	Ca	Ti	Ni
	35	0.18	0.23	1.54	0.049	-	-	-	-										-
36										0.18	0.22	1.55	0.050	0.15	0.004	0.0021	0.012	0.05
	37	0.28	0.23	1.55	0.049	0.15	0.14	0.0018	0.009										0.04
38										0.15	0.23	1.58	0.049	0.18	0.15	0.0013	0.011	0.11
	39	0.16	0.23	1.54	0.095	0.15	0.12	0.0020	0.012										0.09
40										0.12	0.24	1.52	0.039	0.31	0.18	0.0049	0.092	0.09
	41	0.09	0.24	2.00	0.039	0.01	0.09	0.0028	0.052										0.06
42										0.23	0.18	1.49	0.037	0.25	0.05	0.0002	0.056	0.06
	43	0.30	0.29	1.22	0.047	0.24	0.14	0.0045	0.021										0.07
44										0.17	1.99	1.35	0.022	0.18	0.99	0.0045	0.021	0.07
	45	0.16	0.32	1.29	0.005	0.06	0.12	0.0032	0.009										0.55
46										0.17	0.13	0.99	0.055	0.29	0.11	0.0004	0.028	0.29
	47	0.14	0.05	0.98	0.029	0.09	0.01	0.0033	0.005										0.16
48										0.11	0.18	1.58	0.028	0.99	0.47	0.0038	0.028	0.01
	49	0.12	0.22	1.49	0.046	0.33	0.22	0.0023	0.012										0.11
50										0.24	0.32	1.51	0.038	0.24	0.16	0.0014	0.005	0.56
	51	0.19	0.24	1.40	0.019	0.22	0.19	0.0022	0.19										0.79
52										0.18	0.27	1.39	0.033	0.15	0.12	0.0027	0.007	0.12
	53	0.18	0.24	1.50	0.012	0.012	0.09	0.0025	0.017										0.99
54										0.18	0.23	1.48	0.029	0.22	0.18	0.0034	0.009	0.18
	55	0.10	0.22	1.22	0.099	0.33	0.10	0.0043	0.023										0.49
56										0.05	0.22	1.42	0.027	0.79	0.06	0.0023	0.028	0.14
	57	0.11	0.29	1.29	0.039	0.31	0.09	0.0016	0.041										0.33
58										0.15	0.01	1.52	0.049	0.28	0.08	0.0009	0.006	0.15
	59	0.15	0.21	0.94	0.043	0.33	0.12	0.0019	0.022										0.49
60										0.14	0.10	0.89	0.011	0.27	0.06	0.0038	0.019	0.26
	61	0.13	0.23	0.01	0.032	0.32	0.09	0.0012	0.007										0.27

[table 9]

Steel No.	Chemical composition of steel is formed (unit: quality %)
							Mg	Sr	Zr	Hf	Co	そ he
	35	-	-	-	-	-
36							-	-	-	-	-
	37	-	-	-	-	-
38							-	-	-	-	-
	39	-	-	-	-	-
40							-	-	-	-	-
	41	0.0029	-	-	-	0.05
42							-	-	0.005	-	-
	43	-	-	-	0.011	-							Nb：0.003
44							0.0001	0.0002	-	-	0.02
	45	0.0021	0.0005	0.008	-	0.48							V：0.05
46							0.0003	0.0015	0.20	0.014	0.49	B：0.0002
	47	-	-	-	-	-							B：0.0099
48							0.0043	-	-	-	0.19
	49	-	0.0022	-	-	-
50							-	0.0018	0.005	-	-	V：0.49
	51	-	0.0001	0.009	0.023	-							Nb：0.49
52							0.0009	-	-	0.005	0.01
	53	0.0012	0.0035	0.018	0.19	0.09
54							-	-	-	-	-	La：0.0002 V：0.011
	55	-	-	-	-	-							Ce：0.0001 Nd：0.0008
56							0.0019	-	-	-	0.39	Sm：0.0002
	57	0.0022	-	-	-	0.28							La：0.0021 Ce：0.0098
58							-	-	0.006	-	-	La：0.0099
	59	-	0.0029	-	0.013	-							Nd：0.0097
60							0.0049	-	-	0.026	0.99	Sm：0.0096
	61	0.0023	0.0048	-	0.025	0.17							La：0.0038 Nd：0.0098

[table 10]

Steel No.	S(c)/ S(a)	S(c)/ S(b)	Finishing temperature (℃)	Speed of cooling (℃/second)	Organize area occupation ratio (%) *1			Non-metallic inclusion is (individual/mm 2)
									P	B	M
					35	-	-					770	10	12	15	0	0.19
36	23.8	4.2	770	10				22	7	0	0.19
					37	22.2	4.4					750	0.1	26	18	0	0.19
38	84.6	10.0	770	26				5	20	8	0.19
					39	45.0	7.5					770	10	19	18	5	0.23
40	18.4	0.98	760	10				15	15	3	0.14
					41	19.3	2.1					790	4	14	9	0	0.19
42	300	0.98	770	2				19	5	0	0.19
					43	15.6	2.2					760	0.5	25	5	0	0.14
44	18.8	4.3	850	5				10	15	5	0.19
					45	177.6	60.6					790	5	14	5	0	0.19
46	354.5	3.2	790	15				5	19	7	0.19
					47	48.5	32.0					770	10	13	5	0	0.09
48	24.7	7.1	840	15				8	16	9	0.14
					49	24.4	9.2					770	15	16	0	0	0.14
50	175.0	56.0	770	1				22	3	0	0.14
					51	343.5	3.6					750	10	14	5	3	0.09
52	36.1	10.8	770	15				10	8	2	0.09
					53	150.0	4.8					770	10	14	5	0	0.09
54	52.9	20.0	750	3				20	4	4	0.09
					55	114.0	21.3					770	10	11	5	0	0.09
56	126.2	18.9	770	5				5	5	0	0.19
					57	160.5	14.9					780	10	16	5	0	0.14
58	166.7	12.5	770	15				12	10	7	0.14
					59	102.1	14.0					770	5	18	4	2	0.14
60	143.7	27.8	820	1				19	4	0	0.14
					61	53.0	13.8					800	3	16	5	0	0.14

^{* 1}P: perlite, B: bainite, M: martensite, surplus portion: ferrite

Make the test film A (Fig. 4) of 300 * 300 * 25 (mm) size, except thickness was 25mm, other were identical with embodiment 1.Adopting thickness is the described test film A of 25mm, makes the test film B (Fig. 5) that has formed clearance portion in mode similarly to Example 1.Also make in addition and implemented in full denaturation loop epoxy resins application (average film thickness: test film C (Fig. 6) 50 μ m), and the test film D (Fig. 7) that has formed 1 cut channel (long: 300m, wide 0.5mm), except thickness was 25mm, other all similarly to Example 1.Also have, at the test face of test film C and D, installing with it, thickness matches, size is for the pure zinc metal sheet of 20mm  * 25mm and implement electrocorrosion.

(corrosion test)

(I) test of the simulated environment of crude oil basin

The test of the simulated environment of crude oil basin is identical with embodiment 1, estimates its above-mentioned anti-general corrosion, corrosion-resistant homogeneity and the (criterion: above-mentioned table 5) of anti-crevice corrosion for test film A and B.Table 11 shows the result of corrosion test.

(II) test under the simulated environment of ballast tank

Test under the simulated environment of ballast tank is identical with embodiment 1, estimates its above-mentioned anti-paint blister and films (the criterion: above-mentioned table 5) of flaw portion erosion resistance for test film C and D.Table 11 shows the result of corrosion test.

[table 11]

Steel No.	Crude oil basin side			The ballast tank side		Synthetic determination
							Anti-general corrosion	The corrosion homogeneity	Anti-crevice corrosion	Anti-paint blister	The flaw portion erosion resistance of filming
	35	×	×	×	×							×	×
36						△	×	×	△	△	×
	37	×	△	△	×							△	×
38						△	×	△	×	△	×
	39	△	△	×	×							△	×
40						△	○	△	○	○	△～○
	41	△	◎	○	◎							◎	△～◎
42						○	○	△	○	○	△～○
	43	△	○	○	○							○	△～○
44						△	◎	○	◎	◎	△～◎
	45	○	◎	△	◎							◎	△～◎
46						△	◎	○	◎	◎	△～◎
	47	○	○	○	○							○	○
48						○	◎	○	◎	◎	○～◎
	49	○	○	○	○							○	○
50						○	○	○	○	○	○
	51	○	○	○	○							○	○
52						○	◎	◎	◎	◎	○～◎
	53	◎	◎	○	◎							◎	○～◎
54						◎	◎	◎	○	○	○～◎
	55	◎	◎	◎	○							○	○～◎
56						◎	◎	◎	◎	◎	◎
	57	◎	◎	◎	◎							◎	◎
58						◎	◎	◎	○	○	○～◎
	59	◎	◎	◎	○							○	○～◎
60						◎	◎	◎	◎	◎	◎
	61	◎	◎	◎	○							○	○～◎

Steel No.35 is the existing steel that does not contain Cu, Cr, Ca, Ni and Ti, all presents bad result in the whole projects of corrosion test.Steel No.36 compares with No.35, and anti-general corrosion and paint blister have improvement slightly, but because the specified amount of the second embodiment defined of the discontented unabridged version invention of Cr amount, so be bad result in other project.Though No.37 and 38 satisfies the prerequisite that the chemical ingredients of the second embodiment defined of the present invention is formed, because perlite area occupation ratio and bainite area occupation ratio surpass prescribed value respectively, so the improvement of erosion resistance is insufficient.Though No.39 also satisfies the prerequisite that the chemical ingredients of second embodiment of the present invention is formed, because do not satisfy the prerequisite of non-metallic inclusion quantity, so anti-crevice corrosion and anti-paint blister are bad.

With respect to this, all satisfy steel No.40～61 of the prerequisite of second embodiment of the present invention, under any simulated environment of crude oil basin and ballast tank, all demonstrate excellent erosion resistance as can be known, it is preferably as crude oil basin base plate steel.About these steel No.40～61, represent the graphic representation of relation of the value of the relation of value of its anti-general corrosion and S (c)/S (a) and anti-crevice corrosion and S (c)/S (b), in Fig. 9 and Figure 10, show.

As table 10 and 11 and shown in Figure 9, in the scope of 20≤S (c)/S (a)≤350, anti-general corrosion is good result (zero), is extremely good result (◎) in the scope of 50≤S (c)/S (a)≤170.As table 10 and 11 and shown in Figure 10, in 1.00≤S (c)/S (b)≤60 scope, anti-crevice corrosion is good result (zero), is extremely good result (◎) in 10≤S (c)/S (b)≤30 scope in addition.So, erosion resistance (especially anti-general corrosion and anti-crevice corrosion) is improved by suitably controlling S (c)/S (a) and S (c)/S (b).

Embodiment 3 (example of the present invention and the comparative example of the 3rd embodiment of the present invention)

(for the making of examination material)

Adopt the RH vacuum degasser, implement to utilize the bubbling of Ar gas, stir molten steel and carry out the composition adjustment simultaneously and become the composition shown in the table 12, make steel ingot by Continuous casting process for water the molten steel that outpours by converter.The deoxidation form is the Al deoxidized steel.The steel ingot that obtains is heated to 1150 ℃ carries out hot rolling afterwards, make the steel plate of thick 19mm.At this moment the hot rolling final temperature reaches from hot rolling termination back as shown in table 13 to 500 ℃ speed of cooling.The area occupation ratio of the bainite+martensite of the steel that obtain (B+M) and the median size of sulfide-based inclusion are also as shown in table 13.Also have, all based on ferrite (F) (counting more than 50% with area occupation ratio), another part contains other perlite (P) with the tissue of the surplus of steel.

[table 12]

Chemical composition of steel (quality %)

No	C	Si	Mn	Al	P	S	Cu	Ni	Cr	Mg	Ca	Sr	Co	Ti	Zr	Other
																	62	0.18	0.18	1.05	0.038	0.008	0.0092	-	-	-	-	-	-	-	-	-	-
63	0.18	0.18	1.05	0.038	0.008	0.0092	-	-	-	-	-	-	-	-	-	-
																	64	0.16	0.24	1.42	0.045	0.008	0.0043	0.04	0.23	0.12	-	-	-	-	-	-	-
65	0.13	0.19	1.39	0.051	0.007	0.0049	0.21	0.25	0.004	-	-	-	-	-	-	-
																	66	0.14	0.28	0.9	0.033	0.007	0.0048	0.26	0.31	0.11	-	-	-	-	-	-	-
67	0.15	0.24	0.05	0.021	0.008	0.0051	0.19	0.33	0.08	-	-	-	-	-	-	-
																	68	0.11	0.32	1.00	0.034	0.008	0.0054	0.15	0.11	0.09	-	-	-	-	-	-	-
69	0.11	0.32	1.00	0.034	0.008	0.0054	0.15	0.11	0.09	-	-	-	-	-	-	-
																	70	0.11	0.32	1.00	0.034	0.008	0.0054	0.15	0.11	0.09	-	-	-	-	-	-	-
71	0.12	0.22	0.91	0.008	0.009	0.0008	0.11	0.34	0.25	0.0034	-	-	-	-	-	-
																	72	0.21	0.15	0.99	0.015	0.008	0.0005	0.39	0.38	0.23	-	0.0019	-	-	-	-	-
73	0.21	0.15	0.99	0.015	0.008	0.0005	0.39	0.38	0.23	-	0.0019	-	-	-	-	-
																	74	0.08	0.24	1.98	0.028	0.008	0.0045	0.47	0.99	0.21	-	-	0.0028	-	-	-	B：0.0002
75	0.12	0.25	1.28	0.019	0.009	0.0044	0.19	0.25	0.11	0.0002	0.0037	-	-	-	-	-
																	76	0.19	0.21	1.09	0.099	0.005	0.0039	0.33	0.19	0.08	-	0.0002	0.0015	-	-	-	V：049
77	0.11	0.19	0.14	0.072	0.006	0.0048	0.64	0.34	0.26	0.0016	0.0023	0.0049	-	-	-	-
																	78	0.30	0.22	0.81	0.019	0.005	0.0026	0.33	0.38	0.49	-	-	-	0.053	-	-	-
79	0.11	0.25	0.95	0.066	0.007	0.0039	0.39	0.22	0.33	-	-	-	-	0.019	-	Nb：049
																	80	0.11	0.25	0.95	0.066	0.007	0.0039	0.39	0.22	0.33	-	-	-	-	0.019	-	Nb：049
81	0.10	0.12	1.55	0.085	0.007	0.0026	0.48	0.50	0.26	-	-	-	-	-	0.089	-
																	82	0.14	1.99	1.24	0.058	0.008	0.0040	0.29	0.41	0.05	-	-	-	0.006	0.056	-	-
83	0.15	0.22	1.11	0.019	0.007	0.0042	0.99	0.29	0.15	-	-	-	-	0.199	0.008	-
																	84	0.14	0.33	1.04	0.005	0.002	0.0033	0.19	0.32	0.01	0.0042	-	-	0.099	0.005	0.021	Nb：0.003
85	0.15	0.26	1.27	0.047	0.004	0.0035	0.35	0.02	0.81	0.0024	-	0.0028	-	-	0.005	-
																	86	0.11	0.28	1.00	0.022	0.008	0.0028	0.32	0.29	0.19	-	0.0033	0.0019	0.20	-	0.018	-
87	0.11	0.28	1.00	0.022	0.008	0.0021	0.32	0.29	0.19	-	0.0033	0.0019	0.20	-	0.018	-
																	88	0.18	0.26	0.99	0.055	0.005	0.0022	0.14	0.32	0.14	0.0019	0.0002	0.0014	0.12	0.022	0.199	-

[table 13]

No.	Mn/ (S+Mg+Ca+Sr) compare	Hot rolling termination temperature (℃)	Speed of cooling (℃/s)	M+B area occupation ratio (%)	The median size of sulfide-based inclusion (μ m)
						62	114.1	800	10	12	3.4
63	114.1	800	10	12	3.4
						64	330.2	800	10	15	4.5
65	283.7	800	10	14	4.2
						66	187.5	770	20	32	2.8
67	9.8	780	10	14	0.43
						68	185.2	820	10	15	2.5
69	185.2	820	10	15	2.5
						70	185.2	820	10	15	2.5
71	216.7	800	15	28	3.8
						72	412.5	750	8	11	8.2
73	412.5	750	8	11	8.2
						74	271.2	780	5	10	5.6
75	154.2	780	1	8	2.8
						76	194.6	780	10	21	3.2
77	10.3	780	5	10	0.48
						78	311.5	820	0.1	0	5.9
79	243.6	800	1	3	5.2
						80	243.6	800	1	3	5.2
81	596.2	780	5	8	9.9
						82	310.0	850	5	7	7.8
83	264.3	820	5	8	6.9
						84	138.7	780	10	18	2.3
85	146.0	700	12	25	2.4
						86	125.0	720	10	19	2.1
87	137.0	720	10	18	2.1
						88	173.7	780	8	15	3.0

Downcut the test film of 100 * 100 * 10 (mm) size from the steel plate that obtains.(pouncing paper #600) carries out smooth grinding to the whole face of test film with the wet type grindstone, after washing and acetone (acetone) cleaning, with average film thickness is 15 μ m (± 3 μ m) coating zinc rich primer, makes it dry more than 24 hours in moisture eliminator (desiccator).Then as shown in table 13, carry out pre-treatment, (airless spray) is coated with various protective systems by Airless spraying.Also have, the scratch brushing of implementing as the application processing is to be used to remove the refuse of the face of being coated, the processing of dust.In addition, sandblast should proceed to until zinc rich primer and disappear.

The face shaping of the test film E that so obtains as shown in figure 11.In test, corrosion progress degree when exposing the blank steel with flaw in order to investigate anticorrosive coating film, use-testing sheet F (Figure 12) also, its test face side (high temperature side during corrosion test) by cutting knife formed 1 long: 100mm, wide: the cut channel of the through blank of about 0.5mm.

(corrosion test method)

Laboratory evaluation method in the simulation ballast tank is as follows.In the Thoughs of having filled with as the synthetic sea water of experimental liquid, test film E and F are set vertically, the temperature of the test face side of test film is adjusted to 40 ℃, its back temperature is adjusted to 10 ℃, anticorrosive coating film is paid temperature gradient.Also have, the test film F of band cut channel is provided with test film in the mode that its cut channel is in high temperature side.As shown in figure 13, so that test film integral body there is not the state (the ballast tank state that simulation is unloaded) in the entry to keep two time-of-weeks, thereafter, the discharging synthetic sea water, and as shown in figure 14 so that the state that test film surfaces (simulation loading state) keeps 1 time-of-week.Also have, under the state of Figure 14, make with the test film in the Thoughs and compare the remaining synthetic sea water in bottom, keep the temperature gradient of test film by the temperature difference of gas phase portion.When applying temperature gradient, promote the moisture of filming to permeate to low temperature side from high temperature side.Therefore the significant high temperature side of corrosion (40 ℃) of filming down is test face (evaluation face).In evaluation test, the state of Figure 13 and Figure 14 adds up to last till for 24 weeks (168 days) repeatedly.The number E, the F that supply with the test film of test are 5 respectively.

In test film E, measure to reach and film/time that paint blister that the turgor pressure by corrosion product at steel interface causes takes place, estimate anti-paint blister.Reaching the time that paint blister takes place is, observes by 1 time on the 1st the visual outward appearance of carrying out, and within 5 test films of examination any one is arranged up to confirming each time of paint blister.

In test film F, after being determined at off-test with vernier callipers (through 24 week the back) expansion amplitude (with the expansion amplitude on the cut channel vertical direction) of anticorrosive coating film, according to each for the maximum value (maximum swelling amplitude) within 5 test films of examination the evaluation flaw portion erosion resistance of filming.

(corrosion test result)

Corrosion test result is as shown in table 14.The both who forms the anti-paint blister of No.62 (△) that the denaturation loop epoxy resins of 250 μ n of standard films and the flaw portion erosion resistance (*) of filming as common anticorrosive coating film is poor, suppose the part that anticorrosive coating film is thin No.63 both all be *, non-constant.The prescribed value of the 3rd embodiment of the discontented respectively unabridged version invention of No.64 and 65 its Cu content and Cr content, so the improvement of application erosion resistance is insufficient, is not suitable as the ballast tank steel.Though the composition range that respectively adds element of No.66 and 67 the 3rd embodiments of the present invention satisfies prescribed value in addition, but because the median size of its bainite+martensitic area occupation ratio and sulfide-based inclusion does not satisfy regulation, so it is not too abundant that the application erosion resistance is improved, can not satisfy as the needs of ballast tank with steel.

With respect to this, (No.68～88) that are controlled at the composition range of the 3rd embodiment of the present invention show that all erosion resistance brings up to the level more than zero.Particularly remove shop primer and protective system is directly coated (No.69, No.73, No.80, No.87) on the steel, have (No.68, No.72, No.79, the No.86) of shop primer to compare, improve erosion resistance effect height as can be known with remaining.In addition, the raising effect of application erosion resistance is to obtain in denaturation loop epoxy resins and the tar epoxy confirming at anticorrosive coating, can both confirm in thickness is any thickness of 50 and 250 μ n.

[table 14]

No.	Coating process			Corrosion test result
						Pre-treatment	Coating	Thickness (μ m)	Anti-paint blister * 1	The solidity to corrosion * of flaw portion 2 films
	62	Scratch brushing	The denaturation loop epoxy resins	252	△						×
63						Scratch brushing	The denaturation loop epoxy resins	50.3	×	×
	64	Scratch brushing	The denaturation loop epoxy resins	50.1	×						△
65						Scratch brushing	The denaturation loop epoxy resins	49.9	△	×
	66	Scratch brushing	The denaturation loop epoxy resins	50.2	△						○
67						Scratch brushing	The denaturation loop epoxy resins	50.1	△	○
	68	Scratch brushing	The denaturation loop epoxy resins	50.4	○						○
69						Sandblast → scratch brushing	The denaturation loop epoxy resins	50.3	◎	○
	70	Scratch brushing	The denaturation loop epoxy resins	253	◎						○
71						Scratch brushing	The denaturation loop epoxy resins	50.9	◎	○
	72	Scratch brushing	Tar epoxy	50.4	◎						○
73						Sandblast → scratch brushing	Tar epoxy	50.2	◎	◎
	74	Scratch brushing	The denaturation loop epoxy resins	49.2	◎						○
75						Scratch brushing	The denaturation loop epoxy resins	50.3	◎	○
	76	Scratch brushing	The denaturation loop epoxy resins	50.4	◎						○
77						Scratch brushing	The denaturation loop epoxy resins	50.0	◎	○
	78	Scratch brushing	The denaturation loop epoxy resins	49.9	○						◎
79						Scratch brushing	The denaturation loop epoxy resins	49.6	○	◎
	80	Sandblast → scratch brushing	The denaturation loop epoxy resins	50.2	◎						◎
81						Scratch brushing	The denaturation loop epoxy resins	50.1	○	◎
	82	Scratch brushing	The denaturation loop epoxy resins	49.5	○						◎
83						Scratch brushing	The denaturation loop epoxy resins	50.2	○	◎
	84	Scratch brushing	The denaturation loop epoxy resins	50.3	◎						◎
85						Scratch brushing	The denaturation loop epoxy resins	50.1	◎	◎
	86	Scratch brushing	The denaturation loop epoxy resins	49.4	◎						◎
87						Sandblast → scratch brushing	The denaturation loop epoxy resins	50.2	◎◎	◎
	88	Scratch brushing	The denaturation loop epoxy resins	49.4	◎						◎

* 1 expansion time of origin, *: be lower than 7, △: be lower than more than 7 days more than 14 days, zero: 14 day and be lower than 21, ◎: be lower than 84 more than 42 days, ◎ ◎: more than 84 days

* 2 maximum swelling width, *: above, the △ of 20mm: be lower than 20mm, 10mm above, zero: be lower than that 10mm, 5mm are above, ◎: be lower than 5mm

As above, the steel of the 3rd embodiment of the present invention are its application excellent corrosion resistance as can be known, can make the deterioration of filming that begins from paint blister obtain postponing, the corrosion progress of steel exposed divisions such as being derived from paint film defect and flaw portion is suppressed, thereby preferably as the ballast tank steel.Therefore, distinguish easily also that the ballast tank that is made of the steel of third embodiment of the invention possesses excellent weather resistance.

Embodiment 4 (example of the present invention and the comparative example of the 4th embodiment of the present invention)

(for the examination material)

Follow the interpolation period of a group element shown in the table 17, b group element, the steel that the chemical ingredients shown in following table 15 and 16 is formed carry out the converter melting, carry out dephosphorization and desulfurization by secondary refining after, make steel billet by continuous casting.Then, the steel billet that obtains is carried out hot rolling after with the Heating temperature reheat shown in the table 17, obtain containing the sulfide-based inclusion of median size shown in the table 18 and number and the steel plate of oxide-based inclusion thus.

After the diamond paste that uses 1 μ m carries out mirror ultrafinish for the rolling direction cross section of examination steel to each, 5000 times of multiplying powers) and EDX (energy disperse shape fluorescent x-ray analyzer) utilization SEM (scanning electron microscope:, observe size and number and affirmation for sulfide-based inclusion contained in the examination material and oxide-based inclusion.

Promptly, measure the chemical constitution of each inclusion by EDX in optional 5 positions, for the sulfide-based inclusion and the oxide-based inclusion of the content of a group element that satisfies regulation and b group element, observe by SEM and to try to achieve its median size (mean value of equivalent circle diameter; Lave) and every 1mm ²The mean value that has number (N).In Fig. 2, an example of EDX analysis chart that shows the arrow portion of the SEM binary electronic image of sulfide-based inclusion and this electronic image is in addition in Fig. 3, an example of EDX analysis chart that shows the arrow portion of the SEM binary electronic image of oxide-based inclusion and this electronic image.

In addition, each steel plate that obtains is cut off, carry out the test film G (Figure 15) of final 100 * 100 * 25 (mm) of the making size of surface grinding, in addition as shown in figure 16, the big test film (identical with above-mentioned test film G) of the small test sheet and 100 * 100 * 25 (mm) of 4 20 * 20 * 5 (mm) is contacted, make the test film H that has formed between the gap.The gap forms the small test sheet of usefulness and the steel that big test film uses identical chemical ingredients composition, and surface working is also identical with test film G carries out surface grinding.Wear the hole of diameter 5mm then at the center of small test sheet, offer screw in base material side (big test film side) and also fix with the plastics screw-making.

In addition, use-testing sheet I (Figure 17) also, its with whole of the test film of test film G same size on implemented the denaturation loop epoxy resins application (base paint: zinc rich primer) of mean thickness 250 μ m.At the single face of this test film I, be used for that rot-resistant causes damage on filming and corrosion progress degree when having the blank steel to expose in order to investigate, with cutting knife also form the cut channel that reaches blank deeply (long: 100mm, wide: about 0.5mm).

Use each 5 respectively of above-mentioned test film G, H and I, carry out corrosion test by following method.

(etching test X: the ocean simulated environment)

The ocean environment of at first simulating boats and ships and being exposed to the open air carries out the compound cycle corrosion test repeatedly of sea water spray mist test and constant temperature and humid test.In sea water spray mist test, will (each test film G～I) be arranged in the Thoughs from the angle of horizontal tilt to 60 °, with the synthetic sea water (salt solution of Cl concentration 2%) of 35 ℃ of vaporific continuous injections for trying material.At this moment spray amount is adjusted in advance, and horizontally disposed area is 80cm in Thoughs ²Circular ware in, the per at an arbitrary position synthetic sea water that can collect 1.5 ± 0.3mL in 1 hour.Constant temperature and humid test in addition is to be adjusted into temperature: 60 ℃, and humidity: in 95% the Thoughs, each is carried out from the angle setting of horizontal tilt to 60 ° for test portion.Sea water spray mist test: 4 hours, constant temperature and humid test: with 4 hours be 1 circulation, it hockets with corrosion mutually for the examination material.Test period altogether is 6 months.

(1) anti-general corrosion and corrosion homogeneity

Estimate the method for anti-general corrosion and corrosion homogeneity, replace 10 test film A except adopting 5 test film G, all identical with embodiment 1.Also have, weight determination after the test and measurement of plate thickness are that the corrosion product of removing iron rust etc. by katholysis (JIS K8284) in 10% the diammonium hydrogen citrate aqueous solution carries out afterwards.

(2) anti-crevice corrosion

Estimate the method for anti-crevice corrosion, replace 10 test film B except adopting 5 test film H, all identical with embodiment 1.Also have, maximum clearance depth of corrosion Dcrev (mm) is to remove corrosion product by above-mentioned katholysis, adopts the contact pin type 3 d shape testing device " SE3500 " of platelet institute system to measure.

(3) the flaw portion erosion resistance of filming

The film method of flaw portion erosion resistance of evaluation replaces 10 test film D except adopting 5 test film I, and is all identical with embodiment 1.

Shown in the following statement 19 of judgement criteria of above-mentioned anti-general corrosion (Dave), corrosion homogeneity (Dmax/Dave), anti-crevice corrosion (Dcrev), the flaw portion erosion resistance of filming (maximum swelling amplitude).The result shows in table 20 and 21 with aftermentioned embodiment 5.

[table 15]

Chemical ingredients for the examination material

No.	Chemical ingredients (mass%)
														C	Si	Mn	Al	S	The a group element	The b group element	Cr	Cu	Ni	Co	Other	S(a)/S(b)
	89	0.20	0.21	1.01	0.021	0.008	-	-	-	-	-	-	-														-
90														0.19	0.25	0.93	0.019	0.008	Ca：0.0008	Ti：0.150	-	-	-	-	-	0.005
	91	0.10	0.22	0.93	0.020	0.009	Ca：0.0180	Ti：0.008	-	-	-	-	-														2.25
92														0.21	0.19	0.94	0.021	0.006	Mg：0.0004	Zr：0.010	-	-	-	-	-	0.04
	93	0.15	0.23	1.02	0.022	0.004	Ca：0.0028	Ti：0.003	-	-	-	-	-														0.933
94														0.13	0.21	1.00	0.035	0.009	Ca：0.0015	Ti：0.100 Zr：0.020	-	-	-	-	-	0.013
	95	0.15	0.30	0.95	0.015	0.005	Mg：0.0020	Zr：0.100 Hf：0.050	-	-	-	-	-														0.013
96														0.14	0.25	0.99	0.008	0.009	Ca：0.0009	Ti：0.014	-	-	-	-	-	0.064
	97	0.09	0.21	1.89	0.027	0.009	Mg：0.0006	Ti：0.010 Zr：0.006	-	-	-	-	-														0.038
98														0.03	0.25	0.93	0.020	0.009	Ca：0.0010	Ti：0.016 Hf：0.015	4.95	-	-	-	-	0.032
	99	0.14	0.05	0.94	0.021	0.008	Mg：0.0004 Ca：0.0004	Ti：0.016	-	0.33	-	-	V：023														0.05
100														0.10	0.21	0.10	0.035	0.008	Ca：0.0009	Ti：0.006	-	-	3.01	-	-	0.15
	101	0.21	0.23	0.96	0.048	0.008	Ca：0.0009	Ti：0.016	-	-	-	0.22	-														0.056
102														0.18	0.23	0.97	0.063	0.008	Ca：0.0010 Sr：0.0005	Ti：0.010 Zr：0.004	0.20	0.15	-	-	-	0.107
	103	0.19	0.21	0.98	0.028	0.008	Sr：0.0005 Ba：0.0005	Zr：0.015	0.03	-	0.30	-	-														0.067
104														0.10	0.25	0.97	0.046	0.008	Ca：0.0010	Ti：0.017	-	0.36	-	4.96	-	0.059
	105	0.18	0.22	0.97	0.020	0.008	Ca：0.0005 Ba：0.0003	Ti：0.010 Zr：0.006	-	0.32	3.16	-	-														0.05
106														0.15	0.19	0.98	0.096	0.009	Ca：0.0009	Ti：0.011	0.32	4.98	0.36	-	-	0.082

[table 16]

Chemical ingredients for the examination material

No.	Chemical ingredients (mass%)
														C	Si	Mn	Al	S	The a group element	The b group element	Cr	Cu	Ni	Co	Other	S(a)/S(b)
	107	0.13	0.23	0.98	0.019	0.008	Ca：0.0015 Sr：0.0010 Ba：0.0005	Ti：0.181	-	-	0.03	1.34	-														0.017
108														0.14	0.21	0.91	0.036	0.007	Ca：0.0180	Ti：0.030	0.20	0.15	-	-	-	0.60
	109	0.10	0.25	0.96	0.028	0.008	Mg：0.0005 Ca：0.0004	Ti：0.006 Zr：0.004 Hf：0.004	-	-	0.33	-	-														0.064
110														0.18	0.22	1.56	0.033	0.007	Ca：0.0015	Ti：0.016	-	0.36	-	0.45	-	0.094
	111	0.15	0.22	0.98	0.039	0.008	Ca：0.0010	ri：0.062	2.54	0.02	-	-	B：0.0062														0.016
112														0.10	0.22	0.94	0.031	0.008	Ca：0.0010 Sr：0.0009	Ti：0.004 Zr：0.004 Hf：0.004	0.32	0.38	0.36	0.20	Nb：0.252	0.158
	113	0.19	0.19	0.93	0.038	0.008	Ca：0.0008	Ti：0.013	-	-	0.18	0.02	V：0.23														0.062
114														0.15	0.23	0.86	0.025	0.008	Mg：0.0004 Ca：0.0005	Ti：0.010 Hf：0.005	-	0.15	-	0.45	V：0.30	0.06
	115	0.10	0.21	0.96	0.028	0.008	Ca：0.0190	Ti：0.010 Hf：0.010	-	-	0.55	-	B：0.0009														0.85
116														0.21	0.19	0.95	0.021	0.006	Mg：0.0020 Ca：0.0015 Sr：0.0015	Ti：0.191	-	0.36	-	0.51	Nb：0.326	0.026
	117	0.13	0.22	0.95	0.034	0.007	Ca：0.0010	Ti：0.020	-	0.32	4.98	-	V：0.15 Nb：0.2 12														0.05

[table 17]

For creating conditions of examination material

No.	The interpolation period of a group, b group element	Heating temperature [℃]
			89	-	1150
90	During secondary refining	1120
			91	During secondary refining	1160
92	During secondary refining	1120
			93	During secondary refining	1195
94	During secondary refining	1140
			95	During secondary refining	1150
96	During secondary refining	1250
			97	During secondary refining	1190
98	During secondary refining	1165
			99	During secondary refining	1135
100	During secondary refining	1170
			101	During secondary refining	1140
102	During secondary refining	1185
			103	During secondary refining	1175
104	During secondary refining	1160
			105	During secondary refining	1150
106	During secondary refining	1170
			107	During secondary refining	1135
108	During secondary refining	1110
			109	During secondary refining	1195
110	During secondary refining	1120
			111	During secondary refining	1100
112	During secondary refining	1195
			113	During secondary refining	1150
114	During secondary refining	1135
			115	During secondary refining	1160
116	During secondary refining	1170
			117	During secondary refining	1185

[table 18]

Inclusion for the examination material

No.	Sulfide-based inclusion		Oxide-based inclusion
					Lave (μm)	N is (individual/mm 2)	Lave (μm)	N is (individual/mm 2)
	89	-	-	-					-
90					15.3	250	18.4	300
	91	3.1	2630	2.0					2400
92					15.8	180	15.3	250
	93	1.3	560	9.5					180
94					13.3	1430	7.5	1508
	95	12.9	1540	14.1					1460
96					5.6	2381	12.3	2095
	97	8.5	1305	3.5					314
98					5.7	1298	3.7	859
	99	2.8	857	3.3					541
100					1.6	1159	6.9	751
	101	4.1	1460	4.9					1305
102					3.9	751	2.8	1298
	103	5.9	314	4.9					857
104					4.3	859	4.1	1159
	105	3.3	863	3.9					1460
106					2.8	1325	9.6	1054
	107	6.8	1235	3.5					1038
108					1.9	1082	7.3	986
	109	4.5	751	3.1					824
110					6.3	859	4.9	1307
	111	5.3	863	4.9					865
112					7.2	985	4.1	1268
	113	3.3	859	3.9					869
114					4.5	541	3.7	963
	115	3.3	751	3.5					749
116					3.1	1305	3.2	965
	117	2.8	1298	3.1					875

[table 19]

Corrosion test result's metewand (corrosion test method X: the ocean simulated environment)

Test film	Estimate characteristic	The mensuration project	Judge
							×	△	○	◎
			G	Anti-general corrosion	Dave(mm)	0.50 more than					0.10 more than be lower than 0.50	0.05 more than be lower than 0.10	Be lower than 0.05
The corrosion homogeneity	Dmax/Dave	2.5 more than					2.0 more than be lower than 2.5	1.5 more than be lower than 2.0	Be lower than 1.5
				H	Anti-crevice corrosion	Dcrev(mm)				0.50 more than	0.10 more than be lower than 0.50	0.05 more than be lower than 0.10	Be lower than 0.05
I	The flaw portion erosion resistance of filming	Maximum swelling width (mm)	More than 5				Be lower than 5 more than 2	Be lower than 2 more than 1	Be lower than 1

[table 20]

Corrosion test result

No.	Corrosion test method X (ocean simulated environment)				Corrosion test is Y (crude oil storage tank simulated environment) as a result				Synthetic determination
										Comprehensively	Homogeneous	The gap	Application	Comprehensively	Homogeneous	The gap	Application
	89	×	×	×	×	×	×	×										×	×
90									△	×	△	△	△	×	×	△	×～△
	91	△	×	×	△	△	×	×										△	×～△
92									△	×	×	×	△	×	×	×	×～△
	93	△	×	△	×	△	×	△										×	×～△
94									△	△	△	△	△	△	△	△	△
	95	△	△	△	△	△	△	△										△	△
96									△	△	○	△	△	△	○	○	△～○
	97	○	○	○	○	○	○	○										○	○
98									◎	○	○	○	◎	○	○	○	○～◎
	99	◎	○	○	○	◎	○	○										○	○～◎
100									○	○	○	◎	○	○	○	◎	○～◎
	101	○	◎	○	○	○	◎	○										○	○～◎
102									◎	○	◎	○	◎	○	◎	○	○～◎
	103	◎	○	○	○	○	○	○										○	○～◎

[table 21]

Corrosion test result

No.	Corrosion test method X (ocean simulated environment)				Corrosion test is Y (crude oil storage tank simulated environment) as a result				Synthetic determination
										Comprehensively	Homogeneous	The gap	Application	Comprehensively	Homogeneous	The gap	Application
	104	◎	◎	○	○	◎	◎	○										○	○～◎
105									◎	○	○	◎	◎	○	○	◎	○～◎
	106	◎	○	○	◎	◎	○	○										◎	○～◎
107									○	◎	◎	○	○	◎	◎	○	○～◎
	108	◎	○	○	○	◎	○	○										○	○～◎
109									○	○	○	○	○	○	○	○	○
	110	○	◎	○	○	○	◎	○										○	○～◎
111									○	○	◎	○	○	○	◎	○	○～◎
	112	◎	◎	◎	◎	◎	◎	◎										◎	◎
113									○	○	○	○	○	○	○	○	○
	114	○	◎	○	○	○	◎	○										○	○～◎
115									○	○	○	○	○	○	○	○	○
	116	◎	◎	◎	○	◎	◎	◎										○	○～◎
117									◎	◎	◎	◎	◎	◎	◎	◎	◎

Can do following investigation by above-mentioned result of experiment.A group element (the Mg of regulation, Ca, Sr, more than a kind of Ba) and b group element (Ti, Zr, (No.90～93) of the content more than a kind of Hf) and the regulation prerequisite of the 4th embodiment that contains the discontented unabridged version invention of ratio, though perhaps satisfy the content of a group element of regulation and b group element and contain ratio, but owing to before secondary refining, add a group element and b group element, or billet heating temperature surpasses proper temperature, thereby (No.94～96) of the prescribed value of the 4th embodiment of the discontented unabridged version invention of median size of sulfide-based inclusion and oxide-based inclusion (Lave) and number (N), (No.89) compares with existing steel, its anti-general corrosion is all slightly improved in each corrosion test, but can not think has the sufficient effect of improving on corrosion homogeneity and anti-crevice corrosion, insufficient as the erosion resistance of steel for ship.

With respect to this, regulation according to the 4th embodiment of the present invention, the content of Gui Ding a group element and b group element and ratio thereof are suitably as can be known, and the confession examination material (No.97～117) that median size of sulfide-based inclusion and oxide-based inclusion (Lave) and number (N) are suitably controlled, (No.89) compares with existing steel, all demonstrate excellent erosion resistance, as boats and ships corrosion-resistant steel excellence.

In addition, make the raising erosion resistance element that contains Cu, Cr, Ni, Co etc. in the steel in right amount, can notify the erosion resistance of further raising steel.Among this, added in the steel grade (for example No.98,99 etc.) of Cu and Cr and can confirm that anti-general corrosion increases substantially.In addition, in the steel grade that has added an amount of Ni (for example No.105,106 etc.), the flaw portion erosion resistance of filming significantly improves.In this external steel grade that adds Co (for example No.101,104 etc.), the corrosion homogeneity significantly improves.

As above, except the adjustment of chemical ingredients, if contain a group element and the b group element of specified amount with adequate rate, suitably control contains a group element and the sulfide-based inclusion of b group element and the size and the number of oxide-based inclusion of regulation, then can access the significantly excellent steel for ship of anti-corrosive durability.

Embodiment 5 (example of the present invention and the comparative example of the 4th embodiment of the present invention)

(for the examination material)

According to the method same with previous embodiment 4, make contain that the chemical ingredients shown in above-mentioned table 15 and 16 is formed and table 18 shown in the steel of inclusion.Then cut and surface grinding, make test film G, H and the I of Figure 15～17 similarly to Example 4, each respectively 5 use for corrosion test.At this moment etching test is as follows.

(corrosion test method Y: Simulation of Crude Oil basin environment)

Carry out the corrosion test under the simulated environment of crude oil basin, except replacing test film A with test film G, replace test film B with test film H, replace beyond the test film C with test film I, all the other are all identical with implementation column 1.

Use-testing sheet G～I estimates anti-general corrosion, corrosion homogeneity, anti-crevice corrosion and the flaw portion erosion resistance of filming similarly to Example 4.The judgement criteria of anti-general corrosion (Dave), corrosion homogeneity (Dmax/Dave), anti-crevice corrosion (Dcrev), the flaw portion erosion resistance of filming (maximum swelling amplitude) is shown in following table 22.

[table 22]

Corrosion test result's metewand (corrosion test method Y: the crude oil storage tank simulated environment)

Test film	Estimate characteristic	The mensuration project	Judge
							×	△	○	◎
			G	Anti-general corrosion	Dave(mm)	3.00 more than					0.50 more than	0.10 more than	Be lower than 0.10
Be lower than 3.00	Be lower than 0.50
		The corrosion homogeneity					Dmax/Dave	5.0 more than	2.0 more than	1.5 more than	Be lower than 1.5
Be lower than 5.0	Be lower than 2.0
				H	Anti-crevice corrosion	Dcrev(mm)			3.00 more than	0.50 more than		0.10 more than	Be lower than 0.10
Be lower than 3.00	Be lower than 0.50
		I	The flaw portion erosion resistance of filming				Maximum swelling width (mm)	More than 10		More than 2	More than 1	Be lower than 1
Be lower than 10	Be lower than 2

(corrosion test result)

Corrosion test result such as above-mentioned table 20 and 21 are concentrated expression.Regulation according to the 4th embodiment of the present invention, a group element (Mg, Ca, Sr, more than a kind of Ba) and b group element (Ti, Zr, more than a kind of Hf) content is than suitably not adjusted, though with ratio suitably but content does not satisfy (No.90～93) of regulation prerequisite, though perhaps the content of a group element and b group element ratio and content satisfy the regulation prerequisite, but before secondary refining, add a group element and b group element, or billet heating temperature surpasses proper range, thereby median size of sulfide-based inclusion and oxide-based inclusion (Lave) and number (N) do not satisfy (No.94～96) of regulation prerequisite, (No.89) compares with existing steel, although anti-general corrosion is slightly improved, but can not think has the effect of improvement on corrosion homogeneity and anti-crevice corrosion, insufficient as the erosion resistance of steel for ship.

With respect to this, regulation according to the 4th embodiment of the present invention, the content of a group element and b group element and content are than suitable as can be known, and median size of sulfide-based inclusion and oxide-based inclusion (Lave) and number (N) are in (No.97～117) of proper range, compare the erosion resistance that all demonstrates excellence with existing steel (No.89), as boats and ships corrosion-resistant steel excellence.

In addition, make the erosion resistance that contains Cu, Cr, Ni, Co etc. in the steel in right amount improve element, can further improve the erosion resistance of steel.Wherein, added in right amount in the steel (for example No.98,99 etc.) of Cu and Cr, anti-general corrosion increases substantially.In addition, in the steel that added Ni (for example No.105,106 etc.), the significantly raising of the flaw portion erosion resistance of can confirming to film.In these external steel that add Co (for example No.101,104 etc.), it is high that the corrosion homogeneity is significantly carried ground.

As above, as can be known except the adjustment of chemical ingredients, if contain a group element and the b group element of regulation, and make its ratio suitable, and control a group element and the sulfide-based inclusion of b group element and the size and the number of oxide-based inclusion that contains specified amount, then can access the higher steel for ship of weather resistance.

Figure 18 is to be benchmark with the foregoing description 4 and 5 results, the ratio (S (a)/S (b)) of the total content S (a) of a group element of each steel of arrangement expression and the total content S (b) of b group element and the comprehensive graphic representation of the relation of erosion resistance.Promptly, transverse axis is S (a)/S (b) ratio, the longitudinal axis is the synthetic determination (judging that 2 markers of leap betwixt) of erosion resistance, S (a)/S (b) does not satisfy 0.01～1.0 be expressed as " ◇ ", S (a)/S (b) though ratio in 0.01～1.0 scope, but the size of two inclusiones and number any one party are expressed as " " outside the prerequisite of regulation, and the embodiment of prerequisite that all satisfies the regulation of the 4th embodiment of the present invention is expressed as " zero ".

Graphic representation satisfies the example of the present invention of prerequisite of the regulation of the 4th embodiment of the present invention as can be known thus, all can access the good result more than zero in the comprehensive evaluation of erosion resistance.

Claims (42)

1. the steel for ship of an excellent corrosion resistance is characterized in that, % contains in quality:

C：0.01～0.3％、

Si：0.01～2％、

Mn：0.01～2％、

Al：0.005～0.1％、

Cu：0.01～1％、

Ni:0.01～1%, and

Cr：0.01～1％，

Surplus is Fe and unavoidable impurities,

And ferrite is a maximum tissue, and bainite and/or martensite add up to and is lower than 30% and comprise 0.

2. the steel for ship of excellent corrosion resistance according to claim 1 is characterized in that, % contains in quality:

C：0.01～0.3％、

Si：0.01～2％、

Mn：0.01～2％、

Al：0.005～0.1％、

P:0.01% following but do not contain 0%,

S:0.005% following but do not contain 0%,

Cu：0.01～1％、

Ni:0.01～1%, and

Cr：0.01～1％，

Surplus is Fe and unavoidable impurities,

And have as undertissue: in area occupation ratio, perlite: 5～25%, bainite: be lower than 20%, martensite: be lower than 10%, surplus is a ferrite,

The ferrite particle diameter is below the 15 μ m, and pearlitic long-width ratio is 3.0～20.

3. the steel for ship of excellent corrosion resistance according to claim 2, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: Ca:0.005% below but do not contain 0%, below the Mg:0.005% but do not contain 0%, below the Sr:0.005% but do not contain 0%, below the Ba:0.005% but do not contain 0%, below the La:0.005% but do not contain 0%, below the Ce:0.005% but do not contain 0%, below the Nd:0.005% but do not contain 0%, below the Sm:0.005% but do not contain 0%, reach below the Se:0.1% but do not contain 0%.

4. the steel for ship of excellent corrosion resistance according to claim 2, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: Ca:0.005% below but do not contain 0%, below the Mg:0.005% but do not contain 0%, below the La:0.005% but do not contain 0%, below the Ce:0.005% but do not contain 0%, reach below the Se:0.1% but do not contain 0%.

5. the steel for ship of excellent corrosion resistance according to claim 2, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: Ti:0.2% below but do not contain 0%, below the Zr:0.2% but do not contain 0%, reach below the Hf:0.2% but do not contain 0%.

6. the steel for ship of excellent corrosion resistance according to claim 2, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: Sb:0.2% below but do not contain 0%, below the Bi:0.2% but do not contain 0%, reach below the Te:0.1% but do not contain 0%.

7. the steel for ship of excellent corrosion resistance according to claim 2 is characterized in that, in quality %, it is following but do not contain 0% also to contain Co:1%.

8. the steel for ship of excellent corrosion resistance according to claim 2 is characterized in that, in quality %, also contain Nb:0.5% following but do not contain 0% and/or Ta:0.5% following but do not contain 0%.

9. the steel for ship of excellent corrosion resistance according to claim 2 is characterized in that, in quality %, also contain B:0.01% following but do not contain 0% and/or V:0.5% following but do not contain 0%.

10. the steel for ship of excellent corrosion resistance according to claim 2 is characterized in that, in quality %, also contains:

At least a kind of element from the group that following element constitutes, selecting: Ca:0.005% below but do not contain 0%, below the Mg:0.005% but do not contain 0%, below the La:0.005% but do not contain 0%, below the Ce:0.005% but do not contain 0%, reach below the Se:0.1% but do not contain 0%;

At least a kind of element from the group that following element constitutes, selecting: Ti:0.2% below but do not contain 0%, below the Zr:0.2% but do not contain 0%, reach below the Hf:0.2% but do not contain 0%;

At least a kind of element from the group that following element constitutes, selecting: Sb:0.2% below but do not contain 0%, below the Bi:0.2% but do not contain 0%, reach below the Te:0.1% but do not contain 0%;

Co:1% is following but do not contain 0%;

Nb:0.5% following but do not contain 0% and/or Ta:0.5% following but do not contain 0%; With

B:0.01% following but do not contain 0% and/or V:0.5% following but do not contain 0%.

11. the crude oil basin base plate steel of an excellent corrosion resistance is characterized in that % contains in quality:

C：0.01～0.3％、

Si：0.01～2％、

Mn：0.01～2％、

Al：0.005～0.1％、

Cu：0.01～1％、

Cr：0.01～1％、

Ca：0.0001～0.005％、

Ti:0.005～0.2%, and

Ni：0.01～1％，

Surplus is Fe and unavoidable impurities,

And have as undertissue: in area occupation ratio, perlite: 5～25%, bainite: be lower than 20%, martensite: be lower than 10%, surplus is a ferrite,

Equivalent circle diameter is 0.20/mm above the number of the per unit area of the non-metallic inclusion of 20 μ m ²Below.

12. crude oil basin base plate steel according to claim 11, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: below the Mg:0.005% but do not contain 0%, below the Sr:0.005% but do not contain 0% and below the Ba:0.005% but do not contain 0%.

13. crude oil basin base plate steel according to claim 11 is characterized in that, in quality %, also contain Mg:0.005% following but do not contain 0% and/or Sr:0.005% following but do not contain 0%.

14. crude oil basin base plate steel according to claim 11 is characterized in that, in quality %, also contain Zr:0.2% following but do not contain 0% and/or Hf:0.2% following but do not contain 0%.

15. crude oil basin base plate steel according to claim 11 is characterized in that, in quality %, it is following but do not contain 0% also to contain Co:1%.

16. crude oil basin base plate steel according to claim 11, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: La:0.01% below but do not contain 0%, below the Ce:0.01% but do not contain 0%, below the Nd:0.01% but do not contain 0%, below the Sm:0.01% but do not contain 0%, reach below the Se:0.1% but do not contain 0%.

17. crude oil basin base plate steel according to claim 11, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: La:0.01% below but do not contain 0%, below the Ce:0.01% but do not contain 0%, below the Nd:0.01% but do not contain 0%, reach below the Sm:0.01% but do not contain 0%.

18. crude oil basin base plate steel according to claim 11, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: Sb:0.2% below but do not contain 0%, below the Bi:0.2% but do not contain 0%, reach below the Te:0.1% but do not contain 0%.

19. crude oil basin base plate steel according to claim 11, it is characterized in that, in quality %, also contain at least a kind of element from the group that following element constitutes, selecting: B:0.01% below but do not contain 0%, below the V:0.5% but do not contain 0%, reach below the Nb:0.5% but do not contain 0%.

20. crude oil basin base plate steel according to claim 11 is characterized in that, in quality %, it is following but do not contain 0% also to contain Ta:0.5%.

21. crude oil basin base plate steel according to claim 11 is characterized in that, in quality %, also contain:

Mg:0.005% following but do not contain 0% and/or Sr:0.005% following but do not contain 0%;

Zr:0.2% following but do not contain 0% and/or Hf:0.2% following but do not contain 0%;

Co:1% is following but do not contain 0%;

At least a kind of element from the group that following element constitutes, selecting: La:0.01% below but do not contain 0%, below the Ce:0.01% but do not contain 0%, below the Nd:0.01% but do not contain 0%, reach below the Sm:0.01% but do not contain 0%; With

At least a kind of element from the group that following element constitutes, selecting: B:0.01% below but do not contain 0%, below the V:0.5% but do not contain 0%, reach below the Nb:0.5% but do not contain 0%.

22. crude oil basin base plate steel according to claim 21, it is characterized in that, Ca, Mg and Sr are categorized as a group, Ti, Zr and Hf being categorized as b group, Co and Ni are categorized as c group, is S (a) % in quality % at the total content of establishing a group element, the total content of b group element is S (b) %, when the total content of c group element is S (c) %, satisfy following formula (1) and (2)

20≤S(c)/S(a)≤350 ...(1)

1.00≤S(c)/S(b)≤60 ...(2)。

23. according to each described crude oil basin base plate steel in the claim 11～22, it is characterized in that, be used to the storage tanker base plate of the oil tanker of double-skin structure.

24. the ballast tank steel of an excellent corrosion resistance is characterized in that % contains in quality:

C：0.01～0.30％、

Si：0.01～2.0％、

Mn：0.01～2.0％、

Below the P:0.01%,

S：0.0005～0.005％、

Al：0.005～0.10％、

Cu：0.1～1.0％、

Ni：0.01～1.0％、

Cr：0.01～0.5％，

Surplus is Fe and unavoidable impurities,

And have based on ferrite, bainite and/or martensite add up in area occupation ratio and are lower than 30% and comprise 0 tissue,

The median size of sulfide-based inclusion is 0.5～10 μ m.

25. the ballast tank steel of excellent corrosion resistance according to claim 24, it is characterized in that, in quality %, also contain from the group that following element constitutes, select more than a kind or 2 kinds: Mg:0.0001～0.005%, Ca:0.0001～0.005%, Sr:0.0001～0.005%, Ba:0.0001～0.005%, La:0.0001～0.005%, Ce:0.0001～0.005%, Nd:0.0001～0.005%, Sm:0.0001～0.005%, and Se:0.001～0.1%.

26. the ballast tank steel of excellent corrosion resistance according to claim 24, it is characterized in that, in quality %, also contain from the group that following element constitutes, select more than a kind or 2 kinds: Mg:0.0001～0.005%, Ca:0.0001～0.005%, and Sr:0.0001～0.005%.

27. the ballast tank steel of excellent corrosion resistance according to claim 24, it is characterized in that, in quality %, also contain from the group that following element constitutes, select more than a kind or 2 kinds: Co:0.005～0.20%, Ti:0.005～0.20%, Zr:0.005～0.20%, and Hf:0.005～0.20%.

28. the ballast tank steel of excellent corrosion resistance according to claim 24, it is characterized in that, in quality %, also contain from the group that following element constitutes, select more than a kind or 2 kinds: Co:0.005～0.20%, Ti:0.005～0.20%, and Zr:0.005～0.20%.

29. the ballast tank steel of excellent corrosion resistance according to claim 24, it is characterized in that, in quality %, also contain from the group that following element constitutes, select more than a kind or 2 kinds: Sb:0.005～0.2%, Bi:0.005～0.2%, and Te:0.001～0.1%.

30. the ballast tank steel of excellent corrosion resistance according to claim 24, it is characterized in that, in quality %, also contain from the group that following element constitutes, select more than a kind or 2 kinds: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%.

31. the ballast tank steel of excellent corrosion resistance according to claim 24 is characterized in that, in quality %, also contain Ta:0.003～0.5%.

32. the ballast tank steel of excellent corrosion resistance according to claim 24 is characterized in that, in quality %, also contain:

From the group that following element constitutes, select more than a kind or 2 kinds: Mg:0.0001～0.005%, Ca:0.0001～0.005%, and Sr:0.0001～0.005%;

From the group that following element constitutes, select more than a kind or 2 kinds: Co:0.005～0.20%, Ti:0.005～0.20%, and Zr:0.005～0.20%; With

From the group that following element constitutes, select more than a kind or 2 kinds: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%.

33. the ballast tank steel of excellent corrosion resistance according to claim 32 is characterized in that, make anticorrosive coating film directly be formed at steel surface.

34. the boats and ships with ballast tank is characterized in that, this ballast tank is made of with steel each described ballast tank in the claim 24～33.

35. the steel for ship of an excellent corrosion resistance is characterized in that, in quality %, contains:

C：0.01～0.30％、

Si：0.01～2.0％、

Mn：0.01～2.0％、

Al：0.005～0.10％、

Below the S:0.010%,

And, contain:

From Mg, the Ca of a group element, Sr, Ba, select more than a kind: 0.0005～0.020%; With

From Ti, the Zr of b group element, Hf, select more than a kind: 0.005～0.20%,

And ratio S (a)/S (b) of the total content S (a) of above-mentioned a group element and the total content S (b) of b group element is in 0.01～1 scope, surplus is Fe and unavoidable impurities, in addition, satisfy the sulfide-based inclusion of following prerequisite and the median size of oxide-based inclusion and be respectively 1～10 μ m, and these inclusiones are at the every 1mm of rolling direction ²Section in have 200～2000 respectively,

Sulfide-based inclusion: be in total amount contain 1～30% described a group element and/or contain in total amount 1～30% described b group element, equivalent circle diameter is the sulfuration type impurity more than the 0.5 μ m,

Oxide-based inclusion: be in total amount contain 1～30% described a group element and/or contain in total amount 1～30% described b group element, equivalent circle diameter is the oxide-based inclusion more than the 0.5 μ m.

36. the steel for ship of excellent corrosion resistance according to claim 35, it is characterized in that, described steel, in quality %, also contain at least a kind that selects the group who constitutes from following element: Cr:0.01～5.0%, Cu:0.01～5.0%, Ni:0.01～5.0%, and Co:0.01～5.0%.

37. the steel for ship of excellent corrosion resistance according to claim 35, it is characterized in that, described steel, in quality %, also contain at least a kind that selects the group who constitutes from following element: La:0.0001～0.005%, Ce:0.0001～0.005%, Nd:0.0001～0.005%, Sm:0.0001～0.005%, and Se:0.001～0.1%.

38. the steel for ship of excellent corrosion resistance according to claim 35, it is characterized in that, described steel in quality %, also contain at least a kind that selects the group who constitutes from following element: Sb:0.005～0.2%, Bi:0.005～0.2%, and Te:0.001～0.1%.

39. the steel for ship of excellent corrosion resistance according to claim 35, it is characterized in that, described steel, in quality %, also contain at least a kind that selects the group who constitutes from following element: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%.

40. the steel for ship of excellent corrosion resistance according to claim 35 is characterized in that, described steel in quality %, also contain Ta:0.003～0.5%.

41. the steel for ship of excellent corrosion resistance according to claim 35 is characterized in that, described steel in quality %, also contain:

From following element constituted group, select at least a kind: Cr:0.01～5.0%, Cu:0.01～5.0%, Ni:0.01～5.0%, and Co:0.01～5.0%; With

From following element constituted group, select at least a kind: B:0.0001～0.010%, V:0.01～0.50%, and Nb:0.003～0.50%.

42. the steel for ship according to each described excellent corrosion resistance in the claim 35～41 is characterized in that, it is used as the former material of storage tanker of oil tanker.

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