CN102639737A - Steel material exhibiting excellent fatigue-crack progress resistance and corrosion resistance, and production method for same - Google Patents

Abstract

Disclosed is a steel material exhibiting excellent fatigue-crack progress resistance and corrosion resistance which has a chemical composition including, by mass%, 0.01-0.14% C, 0.04-0.6% Si, 0.5-2.0% Mn, 0.01% or less P,0.003% or less S, less than 0.2% Cu, more than 0.0007% but not more than 0.005% B, less than 0.05% Al, less than 0.007% N, 0.003% O, and 0.03-0.50% Sn, with the remainder being Fe and impurities, and the Cu/Sn ratio being 1 or less, and which is characterised in that the Bq value is 0.003 or less, the Ceq value is 0.15-0.35, and the oxide number in the region which is 2mm or less from the surface layer is 5x104 per 1 square mm. Furthermore, one more of the following may also be included: Mo, V, Nb, Ni, Cr, Ti, Ca, and Mg.

Description

The steel of fatigue cracking extended attribute and excellent corrosion resistance and method of manufacture thereof

Technical field

The present invention relates to be suitable for steel and method of manufacture thereof that hull, civil construction thing, construction implement, hydraulic pressure iron pipe, oceanic tectonic thing, pipeline etc. require the welding structure thing etc. of fatigue cracking extended attribute and erosion resistance.

Background technology

In recent years, the tendency that the welding structure thing maximizes is remarkable day by day, expectation high strength and lightweight.But, because stress rises when using plow-steel, therefore, be easy to produce fatigure failure from weld part, being easy to becomes important problem from the improvement of weld part generation fatigure failure.In constructing with Plate Steels such as steel, implement welding procedure usually, therefore, might produce fatigue cracking from weld part.Thereby, as long as the fatigue cracking that produces, expands from weld part is trapped in the steel, just help to prolong the fatigue lifetime of structure.Therefore, the various steel that the fatigue cracking expansion suppresses effect that have have been proposed.

A kind of such technology has for example been proposed in patent documentation 1: if through make full use of identical temperature then intensity be lower than the ferritic phase of austenite phase, reduce hot strength and relax the welding residual stress in the welding joint.That is and since weld part after welding by quenching, therefore, the TR of austenite one phase is wider, along with the unrelieved stress of the thermal contraction of welding base metal generation higher level.Therefore, in patent documentation 1 described invention, in steel, contain 0.5%～2.0% Al, in 800 ℃～600 ℃ TR, generate ferritic, make low intensive ferritic viscous deformation, thereby relax unrelieved stress as the ferritic generting element.

In patent documentation 2, also proposed such technology: the tissue that makes the welding heat affected zone (HAZ) of the high-tensile steel of tensile strength 490MPa～780MPa is main body with the bainite; The grain boundary ferrite that inhibition generates from austenite grain boundary, thus fatigue strength improved.In this technology, in order to suppress the generation of grain boundary ferrite, add 0.0005%～0.01% B, and, contain bainite and martensitic whole tissue in order to strengthen, the qualification of carbon equivalent (Ceq) is set.

On the other hand, the weldsteel structure mostly by the sea the area, be scattered with under the more environment of the salt amounts of wafting such as area of snow melt salt, and in the shipbuilding field, use under seawater spittle environment.

Usually, when being exposed to the weathering resistance steel in the atomospheric corrosion environment, be formed with rusty scale, the Corrosion Of Steel after suppressing with protectiveness on its surface.Therefore, the weathering resistance steel are as not application and the minimum steel of safeguarding that can open ground use are used for structures such as bridge.

But; Not only regional by the sea; Even and in the more area of the salt amount of as also be scattered with snow melt salt, frostproofer regional in landlocked portion, wafting, be difficult to be formed with rusty scale with protectiveness on the surface of weathering resistance steel, be difficult to performance and suppress the corrosive effect.Therefore, in these areas, can't use exposed weathering resistance steel, it is normal conditions that the application that ordinary steel is implemented the ordinary steel that application uses is used.But, use in application under the situation of this ordinary steel, cause the deterioration of filming by corrosion, needs carry out application in per approximately 10 years again, and therefore, the expense of keeping administrative institute's need is very big.

In recent years, as NaCl 0.05mg/dm is arranged in the salt amount of wafting ²In area more than the/day (0.05mdd), the for example riviera; Utilize the standardized climate-resistant steel of JIS (JIS) (JIS G 3114: welding structure is used the weathering resistance hot-strip) bigger because of producing the amounts of being corroded such as squamous rust, stratiform rust; Therefore, can't under the situation of no application, use (building association with reference to build economizing building institute, (company) steel social hall, (company) Japanese bridge: be applied to the design and construction main points that the relevant joint research report (XX) of bridge-nothing is coated with the weathering resistance bridge (change edition-1993.3)) with climate-resistant steel.

Like this, under the more environment of salt such as area, usually common iron is carried out application and handle by the sea.But present situation is: build near the river mouth riviera, spread in the road of intermountain portion etc. of snow melt salt the bridge corrosion significantly, no longer application.For these again application to spend great workload, therefore, strong request can not have the steel that application ground uses.

Recently, developed that a kind of to add the Ni that about 1%～3% Ni forms be the high weather resistance steel.But, can clearly in the area of salt amount of wafting, under the situation of only adding this Ni, be difficult to be applied to not have the steel that application ground uses greater than 0.3mdd～0.4mdd.

Owing to the corrosion of steel becomes along with the salt amount of wafting increases acutely, therefore, consider the weathering resistance steel that need form based on the salt amount of wafting from the aspect of erosion resistance and economy.In addition, even bridge, according to the place of using, the difference at position, the corrosive environment of steel is also different.For example, in the crossbeam outer exposed in rainfall, dew with in sunshine.On the other hand, though be exposed in the dew, can not be caught in the rain in crossbeam inside.Usually, in the more environment of the salt amount of wafting, we can say that the inner corrosion of crossbeam is outside more violent than crossbeam.

In addition, on road, spread in the environment of snow melt salt, frostproofer, this salt is rolled by the car in going, and on the bridge attached to the supporting road, therefore, becomes harsh corrosive environment.And, also be exposed under the harsh salt damage environment away from the eaves of seashore are inferior slightly, in this area, becoming the salt amount of wafting is the above harsh corrosive environment of 1mdd.

In order to tackle this problem, the corrosive steel under the more environment of a kind of salt amount that prevents to waft had been developed in the past.

For example, the weathering resistance steel that a kind of increase chromium (Cr) amount forms have been proposed in patent documentation 3, and, the weathering resistance steel that a kind of increase nickel (Ni) amount forms have been proposed in patent documentation 4.

Patent documentation 1: TOHKEMY 2004-211150 communique

Patent documentation 2: TOHKEMY 2003-171731 communique

Patent documentation 3: japanese kokai publication hei 9-176790 communique

Patent documentation 4: japanese kokai publication hei 5-118011 communique

But steel that fatigue cracking expansion suppresses the steel of effect and have the erosion resistance that kind that is described below that has of above-mentioned proposition has problem points.

The technology that patent documentation 1 proposes exists in wider TR in order to make ferritic phase, with the Al that adds high density as prerequisite.But though Al helps ferritic phase to generate, Al makes as structure with the significantly reduced element of the toughness of one of desired fundamental characteristics of steel.Therefore, employing should technology, though suppress the unrelieved stress of weld part, can expect to improve fatigue strength, and the toughness itself of resisting static load is with regard to deficiency.Not only consider, consider, also must carry out the shape of building material, the design of size, in the technology that patent documentation 1 proposes, can't improve the intensity viability evenly from the aspect of the anti-brittle rupture of opposing static load from the aspect of fatigue strength.

In the technology that patent documentation 2 proposes, can in crystal boundary, improve hardening capacity through adding, suppress the B of grain boundary ferrite efficiently, suppress grain boundary ferrite and generate.But,, therefore to note the use of B because B is the flexible element that reduces welding heat affected zone.In welded-joint, the fatigue characteristic of being not only the opposing repeated load are important, and owing to will prevent the brittle rupture that static load causes, therefore guarantee that toughness also is important.Particularly, the major part of scantling is decided by the latter's toughness, and for the part of necessity, in the Fatigue Design system of the present situation of the fatigue survey of confirming anti-fatigure failure, toughness and fatigue characteristic equally also are important.In this looks like, also consider the situation of welding conditions, the change of for example weld heat input, we can say that it is very difficult only utilizing the such method of interpolation B that grain boundary ferrite generation and welding heat affected zone toughness are set up simultaneously.

In addition; The increase chromium (Cr) that above-mentioned patent documentation 3 proposes though the zone of the waft salt amount of weathering resistance steel below to a certain degree that form of amount in can improve weathering resistance; But, make the weathering resistance deterioration on the contrary surpassing under the harsh salt environment of this degree.

Under the situation of the weathering resistance steel that increase nickel (Ni) amount that above-mentioned patent documentation 4 proposes forms, though weathering resistance improves to a certain extent, the cost of steel self raises, and is very expensive as the material that is used for purposes such as bridge.For fear of this point, when reducing the Ni amount, how weathering resistance is not improved, under the more situation of the salt amount of wafting, be created in steel surface generate lamellatedly peel off rust, corrode remarkable, be unable to undergo the such problem of life-time service.

And in the weldsteel structure that under the more environment of the salt amount of wafting, uses, the separability of anti-the application becomes very big problem.Promptly; As noted above, in the environment that has coastal environment that a large amount of muriates wafts, is scattered with Snow Agent or frostproofer, even implement application; Also exist application to peel off very soon and corrode such problem, need every several years～more than ten years to implement the brushing again of application.In addition, when implementing the brushing again of application,, need implement sandblasting once more, therefore will spend great cost having corroded assembling scaffolding on the bridge once as its preceding operation.And even also be difficult to remove under the situation of derusting fully implementing sandblasting once more, even can't remove application once more on the steel that derust fully, the application life-span also significantly shortens.Depend under the most situation of the separability of anti-the application that the corrosion resistance of steel that comprises as substrate is in interior characteristic.

Thereby strong expectation prolongs the life-span of application and will study for a second time courses one has flunked overlay painting interval and draw longlyer.That is, in needing the ship domain of application, bridge field, the requirement of product life minimization of cost is also higher, and on the basis of the product-life-management of considering bridge, it also is very important prolonging the application life-span.

Summary of the invention

The problem that invention will solve

The present invention promptly makes in order to address this problem, and its purpose is to provide steel and the method for manufacture thereof that does not contain infringement flexible element, fatigue cracking extended attribute and excellent corrosion resistances such as Al, B in a large number.

At this, the meaning of above-mentioned erosion resistance is meant erosion resistance in the perchloride environment (comprise application do not peel off and suppress the corrosion of painting defect portion and weathering resistance when keeping erosion resistance (separability of anti-the application) and not having application).

The scheme that is used to deal with problems

The inventor etc. in order to achieve the above object; At first carried out being conceived to the research of fatigue characteristic with the correlationship of the degree of cleaning that are present in the inclusion in the steel of welding joint, learnt between degree of cleaning and the joint fatigue characteristic in the whole cross section of steel to have no correlationship.

Therefore, be conceived to the more steel surface of addendum modification, carry out after the more detailed investigation, clear and definite joint fatigue characteristic largely depend on the characteristic of steel surface, but through improving the degree of cleaning lifting sub fatigue characteristic of steel surface.More particularly, with inclusion analysis be limited to from surface of steel plate along the thickness of slab direction to the zone of the 2mm degree of depth, obtain degree of cleaning to each steel plate, after investigation and the correlationship of joint fatigue characteristic, conclude to have extremely strong correlationship.As the reason of concluding this correlationship, the addendum modification of being commonly considered as steel surface is big and be easy to become the originating end of fatigue cracking.

But the hardness of inclusion is higher, therefore, even can not be out of shape down heavily stressed yet.On the other hand, because the addendum modification of steel surface is bigger, therefore, it is generally acknowledged in the interface of inclusion and substrate tissue, to produce be full of cracks, fatigue characteristic deterioration.Thereby it is the thickness of slab central part at steel usually mostly that the degree of cleaning of inclusion become problem, but about fatigue characteristic, the spatter property of steel surface becomes problem.

On the other hand, the inventor etc. study the corrosion under the more environment of the salt amount of wafting, and the result finds: under such environment, and FeCl ₃The dried wet of solution is corrosive essence condition repeatedly, utilizing Fe ³⁺Hydrolysis make under the state that pH reduces, and pass through Fe ³⁺Play the effect of oxygenant and corrosion is quickened.

The corrosion reaction of this moment is as follows.

As cathodic reaction, reaction below main the generation.

Fe ³⁺+ e ^-→ Fe ²⁺(Fe ³⁺Reduction reaction)

And, except that this reaction, the cathodic reaction below also taking place simultaneously.

2H ₂O＋O ₂＋2e ^－→4OH ^－，

2H ^＋＋2e ^－→H ₂

On the other hand, with respect to above-mentioned Fe ³⁺Reduction reaction, the anodic reaction below taking place.

Anodic reaction: Fe → Fe ²⁺+ 2e ^-(solubilizing reaction of Fe)

Thereby, corrosive combined reaction such as following (1) formula.

2Fe ³⁺+ Fe → 3Fe ²⁺(1) formula

Utilize the Fe of the reaction generation of above-mentioned (1) formula ²⁺Utilize atmospheric oxidation and be oxidized to Fe ³⁺, the Fe of generation ³⁺Play the effect of oxygenant once more, accelerated corrosion.At this moment, Fe ²⁺The speed of response of atmospheric oxidation slower usually under low pH environment, but in dense thick chloride soln, be accelerated, be easy to generate Fe ³⁺Owing to be the reaction of such round-robin, therefore, can be clearly under the environment of salt amount more than very of wafting, sustainable supply Fe all the time ³⁺, the corrosion of steel is quickened, the remarkable deterioration of erosion resistance.

The inventor etc. study for the influence of weathering resistance various alloying elements based on the Corrosion Mechanism in this salt environment, and the result has drawn the opinion shown in following (a)～(c).

(a) Sn is as Sn ²⁺Dissolving utilizes 2Fe ³⁺+ Sn ²⁺→ 2Fe ²⁺+ Sn ^{4 +}Reaction make Fe ³⁺Concentration reduce, thereby suppress the reaction of (1) formula.Sn also has the such effect of the anode dissolution of inhibition.

(b) Cu was the basic element that in the more environment of the salt amount of wafting, improves effect as erosion resistance in the past, in long environment of moistening time, manifested erosion resistance and improved effect.But, under the environment can be clearly bigger, that the local decline of pH is such at chloride concentration, thus for example adhering to through salt humidity change do wet repeatedly and generate under the so more dried environment of β-FeOOH, Cu on the contrary promotes corrosion.

(c) like this, the steel that contain Sn energetically and suppressed the Cu amount can be expected higher erosion resistance.And, because erosion resistance is higher, therefore, even steel are carried out application; The application that is caused by Corrosion Of Steel is peeled off also less, suppresses the corrosion of painting defect portion, and also can expect the anticorrosion ability of filming; Therefore, under the situation of application, can expect the effect of higher erosion resistance.Thereby, except that erosion resistance, also have life-span that can prolong application, will study for a second time courses one has flunked overlay painting interval draw long effect.Particularly bring into play effect in the improvement of the separability of anti-application the in ship domain, bridge field.

The present invention promptly is based on such opinion and accomplishes, and its purport is the steel of fatigue cracking extended attribute shown in following (1)～(6) and excellent corrosion resistance and the method for manufacture that following (7) reach the steel of fatigue cracking extended attribute shown in (8) and excellent corrosion resistance.

(1) steel of a kind of fatigue cracking extended attribute and excellent corrosion resistance is characterized in that, have such chemical constitution; Promptly; By quality %, contain below C:0.01%～0.14%, Si:0.04%～0.6%, Mn:0.5%～2.0%, P:0.01%, below the S:0.003%, Cu: less than 0.2%, B: greater than 0.0007% and 0.005% below, Al: less than 0.05%, reach Sn:0.03%～0.50% below the N:0.007%, below the O:0.003%, remainder is made up of Fe and impurity; And the Cu/Sn ratio is below 1; And the Bq value of being obtained by following (1) formula is below 0.003, and the Ceq value of being obtained by following (2) formula is 0.15～0.35; And, be 5 * 10 apart from top layer 2mm with the per 1 square of mm of the oxide compound number in the interior zone ⁴Below individual.

$\mathrm{Bq}=B-\frac{10.8}{14.1}\×(N-\frac{\mathrm{Ti}}{3.4})---\left(1\right)$

$\mathrm{Ceq}=C+\frac{1}{24}\mathrm{Si}+\frac{1}{6}\mathrm{Mn}+\frac{1}{40}\mathrm{Ni}+\frac{1}{5}\mathrm{Cr}+\frac{1}{4}\mathrm{Mo}+10B---\left(2\right)$

Wherein, each symbol of element in the above-mentioned formula is meant the amount (quality %) of each element.In addition, be substitution 0 (zero) under the situation of impurity levels at the amount of each element.

(2) according to the fatigue cracking extended attribute of above-mentioned (1) and the steel of excellent corrosion resistance; It is characterized in that; By quality %, these steel also contain below Mo:1.0%, below the V:0.1%, and below the Nb:0.1% the element more than a kind of selection.

According to the fatigue cracking extended attribute of above-mentioned (1) or (2) and the steel of excellent corrosion resistance, it is characterized in that (3) by quality %, these steel also contain below the Ni:1.5%.

According to each the fatigue cracking extended attribute and the steel of excellent corrosion resistance in above-mentioned (1)～(3), it is characterized in that (4) by quality %, these steel also contain below the Cr:1.2%.

According to each the fatigue cracking extended attribute and the steel of excellent corrosion resistance in above-mentioned (1)～(4), it is characterized in that (5) by quality %, these steel also contain below the Ti:0.05%.

(6) according to each the fatigue cracking extended attribute and the steel of excellent corrosion resistance in above-mentioned (1)～(5), it is characterized in that, by quality %, these steel also contain below the Ca:0.003% and below the Mg:0.003% in a kind of or two kinds.

(7) method of manufacture of the steel of a kind of fatigue cracking extended attribute and excellent corrosion resistance is characterized in that, comprises following operation A～D, and the backheat temperature amplitude after the cooling of step D is finished is below 70 ℃,

Operation A: the operation that under the condition that satisfies following (3) formula, in molten steel, is blown into non-active gas;

Process B: the molten steel to obtaining casts continuously, obtains having the operation of the steel billet of each chemical constitution in above-mentioned (1)～(6);

Operation C: the steel billet that obtains being heated to after 900 ℃～1180 ℃, is to implement the operation that hot rolling obtains hot-finished material under 650 ℃～1000 ℃ the condition in the precision work temperature;

Step D: the average cooling rate in 620 ℃～500 ℃ TR is under 5 ℃/second～50 ℃/second the condition; The hot-finished material that obtains is quickened cooling from 620 ℃～950 ℃ TR; In the TR below 500 ℃, finish the refrigerative operation

$\frac{G_1\×H_1\×t_1}{S_1\×D_1}\≥2.0---\left(3\right)$

Wherein, the definition of the symbol in above-mentioned (3) formula is described below.

G ₁: be blown into the non-active gas flow (NL/min) in the molten steel

H ₁: be blown into the distance (m) of the top of nozzle from non-active gas to liquid steel level

t ₁: non-active gas is blown into the time (min)

S ₁: casting ladle molten steel amount (ton)

D ₁: casting ladle internal diameter (m).

(8) method of manufacture of the steel of a kind of fatigue cracking extended attribute and excellent corrosion resistance is characterized in that, comprises following operation A1～D, and the backheat temperature amplitude after the cooling of step D is finished is below 70 ℃,

Operation A1: under the condition that satisfies following (4) formula, molten steel is carried out the vacuum refinement treatment procedures;

Process B: the molten steel to obtaining casts continuously, obtains having the operation of the steel billet of each chemical constitution in above-mentioned (1)～(6);

Operation C: the steel billet that obtains being heated to after 900 ℃～1180 ℃, is to implement the operation that hot rolling obtains hot-finished material under 650 ℃～1000 ℃ the condition in the precision work temperature;

Step D: the average cooling rate in 620 ℃～500 ℃ TR is under 5 ℃/second～50 ℃/second the condition; The hot-finished material that obtains is quickened cooling from 620 ℃～950 ℃ TR; In the TR below 500 ℃, finish the refrigerative operation

$\frac{{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="HDA00001656895900011.png"\; state="\{\{state\}\}">G</figure-callout>}}_2\&times;{{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="HDA00001656895900011.png"\; state="\{\{state\}\}">D</figure-callout>}}_2}^2\&times;t_2}{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="HDA00001656895900011.png"\; state="\{\{state\}\}">S</figure-callout>}}_2}\&GreaterEqual;5.5---\left(4\right)$

Wherein, the definition of the symbol in above-mentioned (4) formula is following.

G ₂: the molten steel employed non-active gas flow (NL/min) that refluxes

D ₂: soaking tub internal diameter (m)

t ₂: vacuum processing time (min)

S ₂: casting ladle molten steel amount (ton).

The effect of invention

Therefore the fatigue cracking extended attribute and the excellent corrosion resistance of steel of the present invention, are suitable for hull, civil construction thing, construction implement, hydraulic pressure iron pipe, oceanic tectonic thing, line pipe etc. and require welding structure thing of fatigue cracking extended attribute etc.

Description of drawings

Fig. 1 is the figure of the shape and size of expression connector test body.

Embodiment

A. chemical constitution of steel of the present invention etc.

At first, chemical constitution of steel of the present invention etc. is described.In following explanation, " % " relevant with amount is meant " quality % ".

C：0.01％～0.14％

C is in order to ensure the required element of intensity.Less than 0.01% o'clock, can't guarantee required intensity at its amount.But greater than 0.14% o'clock, welding heat affected zone (HAZ), mother metal all were difficult to guarantee toughness under the situation of welding at its amount.Thereby the amount of C is 0.01%～0.14%.The preferred of C amount is limited to 0.03% down, is limited to 0.10% on preferably.

Si：0.04％～0.6％

Si has desoxydatoin, and, also help to promote the intensity of steel.In order to obtain these effects, need contain the Si more than 0.04%.But, greater than 0.6% o'clock, can cause toughness to reduce at its amount.Thereby the amount of Si is 0.04%～0.6%.

Mn：0.5％～2.0％

Mn has the effect of the hardening capacity that improves steel, is to guaranteeing the effective composition of intensity.Less than 0.5% o'clock, hardening capacity was not enough, can't obtain desired intensity and toughness at its amount.But, containing sometimes greater than 2.0% ground at Mn, segregation increases, and hardening capacity is too high, and welding heat affected zone, the equal toughness of mother metal reduce when welding.Thereby the amount of Mn is 0.5%～2.0%.

Below the P:0.01%

P is present in the steel as impurity inevitably., not only can segregate in the crystal boundary and toughness is reduced greater than 0.01% o'clock at its amount, and when welding, cause heat cracking.Thereby the amount of P need be limited in below 0.01%.P is fewer unreasonablely to be thought.

Below the S:0003%

S is present in the steel as impurity inevitably.When its amount is too much, encourage center segregation, perhaps generate the MnS that extend in a large number, make the mechanical properties deterioration of mother metal and welding heat affected zone.Thereby the amount of S need be limited in below 0.003%.S is fewer unreasonablely to be thought.

Cu: less than 0.2%

Cu as the fundamental element that improves weathering resistance, adds in all beach climate-resistant steels, the corrosion-resistant steel, but in the more dried environment under height is wafted salinity, on the contrary reduces erosion resistance usually.In addition, if coexist, then when rolling, crack with Sn.Therefore, need less contain Cu.Even contain as impurity, the Cu amount also need be less than 0.2%.Preferably less than 0.1%.

B: greater than below 0.0007% and 0.005%

B has the element that promotes hardening capacity and improve the effect of intensity.In order to obtain this effect, need contain greater than 0.0007% ground.But, at its amount greater than 0.005% o'clock, the fatigue characteristic deterioration.Thereby the amount of B is greater than below 0.0007% and 0.005%.

Al: less than 0.05%

Al is the element with desoxydatoin.But, be 0.05% when above at its amount, mainly toughness is easy to deterioration in welding heat affected zone.It is generally acknowledged that its reason is, be easy to form the alumina type inclusion particle of thick pencil.Thereby the Al amount is less than 0.05%.But the Si that has desoxydatoin in utilization carries out also can not containing especially under the situation of deoxidation.In addition, in order to play consistently the desoxydatoin of Al, preferably contain more than 0.001%.

Below the N:0.007%

N is present in the element in the steel inevitably as impurity.Under its a large amount of situation about existing, can become the reason of the toughness deterioration of mother metal and welding heat affected zone.Thereby the amount of N is below 0.007%.N is fewer unreasonablely to be thought.

Below the O:0.003%

O (oxygen) is present in the element in the steel inevitably as impurity.Greater than 0.003% o'clock, can produce detrimentally affect at its amount to the ductility of base metal tenacity and elongation pull and stretch etc.Thereby the O amount is limited in below 0.003%.

Sn：0.03％～0.50％

Sn becomes Sn ²⁺And dissolve, have the suppressor factor that utilizes in the acid chloride solution and be used for suppressing the corrosive effect.In addition, Sn has the Fe of making ³⁺Reduce, reduce Fe rapidly as oxygenant ³⁺The effect of concentration, thus Fe suppressed ³⁺The corrosion promoter action, therefore, promote the weathering resistance in the high salt time-sharing environment of wafting.In addition, Sn exists the anode dissolution that suppresses steel to react and the effect of lifting erosion resistance.And,, can bring into play the effect that in the more environment of the salinity of wafting, also can promote the weathering resistance of Cr through containing Sn.These effects obtain through the Sn that contains more than 0.03%, and these amounts that act on Sn are saturated greater than 0.50% o'clock.Thereby the amount of Sn is 0.03%～0.50%.The preferred range of Sn amount is 0.03%～0.20%.

Cu/Sn ratio: below 1

Under the situation of the steel that contains Sn, cause erosion resistance significantly to reduce because of containing Cu.In addition, when making steel, also can cause rolling crack because of containing Cu.Therefore, need make Cu/Sn than, be the Cu amount and the ratio of Sn amount is below 1.

Steel of the present invention have above-mentioned chemical constitution, and remainder is made up of Fe and impurity.At this, the meaning of impurity is meant when in industry, making steel because the composition that a variety of causes of manufacturing process is mainly sneaked into from such raw materials such as ore, waste materials is can not produce the composition of being allowed in the dysgenic scope to the present invention.

In steel of the present invention, can contain more than a kind of composition of at least 1 group selection from following the 1st group～the 5th group as required.Below, the composition that belongs to these groups is described.

The 1st group composition: Mo, V, Nb

Below the Mo:1.0%

Because Mo has intensity and the flexible effect that improves mother metal, therefore, also can contain as required.But, containing sometimes greater than 1.0% ground, mainly be that the hardness of welding heat affected zone raises, infringement toughness and the C of anti-S C property.Thereby, containing under the situation of Mo, preferably making its amount is below 1.0%.In addition, in order stably to obtain this effect, preferably contain more than 0.05%.

Below the V:0.1%

Because V mainly has the effect that carbonitride when utilizing tempering improves strength of parent, therefore, also can contain as required.But, containing sometimes greater than 0.1% ground, the performance boost effect of mother metal is saturated, causes the toughness deterioration.Thereby, containing under the situation of V, preferably making its amount is below 0.1%.In addition, in order stably to obtain this effect, preferably contain more than 0.005%.

Below the Nb:0.1%

Because Nb has the grain refined utilized and carbide separates out intensity and the flexible effect that improves mother metal, therefore, also can contain as required.But greater than 0.1% o'clock, above-mentioned effect was saturated at its amount, and the obvious damage welding heat affected zone.Thereby, containing under the situation of Nb, preferably making its amount is below 0.1%.In addition, in order stably to obtain this effect, preferably contain more than 0.005%.

The 2nd group: Ni

Below the Ni:1.5%

Since Ni have under solid solution condition the raising steel matrix (matrix: flexible effect matrix), therefore, also can contain as required.But,, also can't improve the characteristic suitable with the rising of alloying constituent even contain greater than 1.5% ground.And erosion resistance is because of Sn and Ni coexistence deterioration sometimes.Thereby, containing under the situation of Ni, preferably making its amount is below 1.5%.In addition, in order stably to obtain this effect, preferably contain more than 0.05%.

The 3rd group: Cr

Below the Cr:1.2%

Because Cr has the effect that improves carbon dioxide corrosion resistant property and improve hardening capacity, therefore, also can contain as required.But, containing sometimes greater than 1.2% ground, even satisfy other member condition, not only be difficult to suppress the sclerosis of welding heat affected zone, and carbon dioxide corrosion resistant property raising effect is also saturated.Thereby, containing under the situation of Cr, preferably making its amount is below 1.2%.In addition, in order stably to obtain this effect, preferably contain more than 0.05%.

The 4th group: Ti

Below the Ti:0.05%

Ti plays the effect of deoxidant element, and forms the oxide compound phase that is made up of Ti, Mn, particularly make the large-line energy welding heat affected zone organize miniaturization, can access the effect that fatigue characteristic promote, therefore, also can contain as required.But, containing sometimes greater than 0.05% ground, the oxide compound of formation is that Ti oxide compound or Ti-Al oxide compound divide bulk density to reduce, and makes the Disability of organizing miniaturization of the heat affected zone of large-line energy welding.Therefore, containing under the situation of Ti, preferably making its amount is below 0.05%.More preferably less than 0.02%.Further be preferably below 0.018%.In addition, in order in steel, stably to form this oxide compound phase, preferably making the Ti total amount in the steel is more than 0.003%.

The 5th group: Ca, Mg

Below the Ca:0.003%

S in Ca and the steel reacts, and in molten steel, forms oxysulfide (oxysulfide).This oxysulfide and MnS etc. are different, can on rolling direction, not extend because of rolling processing, and also be spherical after rolling, therefore, having inhibition is the welding crack of crackle starting point, the effect of hydrogen induced cracking with the top of the inclusion that extends etc.Thereby, also can contain as required.But, greater than 0.003% o'clock, cause the toughness deterioration at its amount.Thereby, containing under the situation of Ca, preferably making its amount is below 0.003%.In addition, in order stably to obtain this effect, preferably contain more than 0.0005%.

Below the Mg:0.003%

Mg generates and contains the Mg oxide compound, becomes the generation nuclear of TiN, has the fine dispersive effect of the TiN of making, and therefore, also can contain as required.But greater than 0.003% o'clock, oxide compound too much caused ductility to reduce at its amount.Thereby, containing under the situation of Mg, preferably making its amount is below 0.003%.In addition, in order stably to obtain this effect, preferably contain more than 0.0005%.

And steel of the present invention need be below 0.003 by the Bq value that following (1) formula is tried to achieve, and need be 0.15～0.35 by the Ceq value that following (2) formula is tried to achieve.

$\mathrm{Bq}=B-\frac{10.8}{14.1}\&times;(N-\frac{\mathrm{Ti}}{3.4})---\left(1\right)$

$\mathrm{Ceq}=C+\frac{1}{24}\mathrm{Si}+\frac{1}{6}\mathrm{Mn}+\frac{1}{40}\mathrm{Ni}+\frac{1}{5}\mathrm{Cr}+\frac{1}{4}\mathrm{Mo}+10B---\left(2\right)$

Wherein, each symbol of element in the above-mentioned formula is meant the amount (quality %) of each element.In addition, be substitution 0 (zero) under the situation of impurity levels at the amount of each element.

Below the Bq:0.003

For the hardening capacity of bringing into play B promotes effect, need to eliminate the influence of the N in the steel.Its reason is that B is easy to combine with N, when in steel, having freely N, is easy to combine with N and generates BN.Therefore,, fix, B is present in the steel as TiN through adding Ti accordingly with the N amount.The B amount is big more, and the hardening capacity of B is high more.But, greater than 0.003 o'clock, form thick iron carbon boride in the Bq value of trying to achieve by (1) formula, cause the fatigue characteristic deterioration.Thereby the Bq value need be for below 0.003.

In addition, for the hardening capacity that stably obtains B improves effect, preferably making the Bq value of above-mentioned (1) defined is more than 0.0001.More preferably more than 0.0005, further be preferably more than 0.001.

Ceq：0.15～0.35

The Ceq that is tried to achieve by above-mentioned (2) formula is so-called carbon equivalent, is the hardening capacity of estimating steel, the index of weldableness, is widely used usually.

The inventor etc. are to the fatigue characteristic that improve welding joint and be used to satisfy common tensile strength (TS) Charpy bar above for 500MPa and 0 ℃ as structure with steel and absorb merit value vE ₀For the prerequisite of requirement such more than the 27J is sought.As a result, less than 0.15% o'clock, intensity reduced in the Ceq value, on the other hand, can be clearly at Ceq greater than 0.35% o'clock, the hardening capacity of steel raises, the Hardness Distribution of joint is inhomogeneous, butt junction fatigue strength produces detrimentally affect.In addition, greater than 0.35 o'clock, also have following shortcoming at Ceq: cause the deterioration of weldableness, the welding procedure difficulty, the purposes of steel obviously is restricted.Thereby making the Ceq value is 0.15～0.35%.In addition, the preferred lower limit of Ceq is 0.20%.In addition, the preferred upper limit of Ceq is 0.30%.

In addition, steel of the present invention need 2mm be 5 * 10 with the per 1 square of mm of the oxide compound number of inner compartment apart from the top layer ⁴Below individual.Its reason is, exists greater than 5 * 10 ⁴During individual oxide compound, the generation source of fatigue cracking increases, and fatigue characteristic reduce.

At this, the oxide compound number utilizes the sequential determination shown in following (i)～(iii).

(i) will cut out small pieces as sightingpiston with the vertical cross section of rolling direction of the steel of making, utilize nital corrosion sightingpiston, make test film.

(ii) above-mentioned test film is placed on the scanning electron microscope (SEM) that has energy dispersion type fluorescent x-ray analyzer (EDX); The zone that 0.05mm is square is as 1 visual field; Utilize 2000 times of multiplying powers to 2mm observes with 5 visual fields in interior zone apart from the top layer, measure the oxide compound number in each visual field.At this moment, the differentiation of oxide compound and other inclusiones is carried out through the compositional analysis of EDX.In addition, for fear of the deviation of visual field, zone, change the mensuration that the degree of depth is carried out the oxide compound number from the top layer to degree of depth 2mm.

(iii) that the oxide compound number in each visual field is average, with MV as apart from top layer 2mm with oxide compound number in the interior zone.

B. the method for manufacture of steel of the present invention

When making the steel of fatigue cracking extended attribute of the present invention and excellent corrosion resistance, preferably begin to adjust from refining stage.That is, in refining stage, be blown into processing or vacuum refinement processing, can reduce the oxide compound of skin section through the design non-active gas.Specifically, be blown into when handling carrying out non-active gas, the way that under the condition that satisfies following (3) formula, in molten steel, is blown into non-active gas is effective.

$\frac{G_1\&times;H_1\&times;t_1}{S_1\&times;D_1}\&GreaterEqual;2.0---\left(3\right)$

Wherein, the definition of the symbol in above-mentioned (3) formula is described below.

G ₁: be blown into the non-active gas flow (NL/min) in the molten steel

H ₁: be blown into the distance (m) of the top of nozzle from non-active gas to liquid steel level

t ₁: non-active gas is blown into the time (min)

S ₁: casting ladle molten steel amount (ton)

D ₁: casting ladle internal diameter (m)

As long as under the condition that satisfies above-mentioned (3) formula, carry out non-active gas and be blown into processing, just can molten steel fully be stirred and blows.That is, initial in blowing, the silicon oxidation in the iron liquid and become silicon-dioxide, silicon-dioxide reacts with the calcined lime, the red stone that add in the stove, begins to form CaO-SiO ₂-FeO class slag.Simultaneously, temperature rises in the stove, and waste material (scrap) also begins to dissolve.At the blowing initial stage, the carbon concentration in the iron liquid is higher, and therefore, the purity oxygen and the carbon that are blown into react efficiently, becomes carbon monoxide and carries out decarburization.In this stage, the feed speed of purity oxygen is controlled the speed of decarburization.When carrying out decarburization, the temperature of molten steel further rises.Along with decarburization is carried out, carbon concentration reduces, and in decarburizing reaction, the carbon in the molten steel moves to be controlled the speed of decarburization.When the stirring by molten steel caused carbon mobile insufficient, the purity oxygen that is blown into reacted except being used in carbon, also is used to make the iron oxidation, and red stone increases in slag, and the yield rate of iron reduces.In order to prevent this point, be blown into gas from furnace bottom actively.

On the other hand, when carrying out the vacuum refinement processing, preferably under the condition that satisfies following (4) formula, in molten steel, be blown into non-active gas.

$\frac{{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="HDA00001656895900011.png"\; state="\{\{state\}\}">G</figure-callout>}}_2\&times;{{\mathrm{<figure-callout\; id="2"\; label="D"\; filenames="HDA00001656895900011.png"\; state="\{\{state\}\}">D</figure-callout>}}_2}^2\&times;t_2}{{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="HDA00001656895900011.png"\; state="\{\{state\}\}">S</figure-callout>}}_2}\&GreaterEqual;5.5---\left(4\right)$

Wherein, the definition of the symbol in above-mentioned (4) formula is described below.

G ₂: the molten steel employed non-active gas flow (NL/min) that refluxes

D ₂: soaking tub internal diameter (m)

t ₂: vacuum processing time (min)

S ₂: casting ladle molten steel amount (ton)

Under the situation of carrying out the vacuum refinement processing, the condition of above-mentioned as satisfying (4) formula preferably adds molten steel in the container of decompression, reduce equilibrium partial pressure, removes the gaseous constituent in the molten steel.

And,, when refining, preferably avoid making Al carry out most of deoxidation at the refining initial stage in order to improve the degree of cleaning of steel.Preferably with together adjustment of the composition except that Al such as Mn and Si, and then utilize Ti etc. to carry out deoxidation, before being about to tapping, Al is put in the micro-molten steel then, the molten steel that obtains is cast.

Under the situation of casting steel ingot, must be extra through utilizing the rolling operation of making steel billet (slab) of piecemeal before hot rolling, yield rate also reduces.Therefore, casting is preferred utilizes continuous casting to carry out.Under the situation of continuous casting, the segregation of steel billet also produces detrimentally affect to the toughness of welding heat affected zone, therefore, preferably carries out in segregation portion that C is below 0.29%, P is below 0.30%, Mn is management such below 3.5%.

In addition; Except that above-mentioned condition; Ejection traffic management during as casting also can apply electromagnetic braking with 1000 Gausses～5000 Gausses, does not perhaps carry out the induction stirring processing with 250 Gausses～1000 Gausses to solidifying molten steel; Depress the portion of finally solidifying with the gradient about 1mm/m, from the squeeze out molten steel of dense thick segregation of the final portion of solidifying.Through above-mentioned management project is suitably made up, can access the steel billet that degree of cleaning are good and center segregation is less.

Then, the steel billet of making like this is heated to 900 ℃～1180 ℃ TR and to carry out hot rolling preferable.At this moment, both can the steel billet reheat that temporarily is cooled to room temperature also can be utilized so-called direct sending rolling technology, and after continuous casting, not be cooled to room temperature and just maintain said temperature or heating through soaking pit with keeping intact.At this, Heating temperature less than 900 ℃ situation under, constantly insufficient in slab heating to austenitic reverse transformation, deterioration in characteristics afterwards.On the other hand, in Heating temperature during greater than 1180 ℃, thickization of austenite crystal when the heating steel billet, the toughness of being not only thickness of slab central part and whole mother metal all reduces.

The hot rolled condition is described below: make hot rolled precision work temperature be 650 ℃～1000 ℃ preferable.During less than 650 ℃, the resistance to deformation of steel is risen, and therefore, is difficult to the steel shape after the hot rolling is finish-machined to target shape in the precision work temperature.When the precision work temperature was higher, the not controlled rolling crystal grain micronized effect that produces can't be guaranteed the toughness of mother metal.Thereby, with the ceiling restriction of precision work temperature at 1000 ℃.

Then, the average cooling rate in 620 ℃～500 ℃ TR is under 5 ℃/second～50 ℃/second the condition, and the hot-finished material that obtains is quickened cooling from 620 ℃～950 ℃ TR, and it is preferable in the TR below 500 ℃, to finish cooling.And the backheat temperature amplitude after cooling finishes is preferable below 70 ℃.

Through under such condition, cooling off, can improve fatigue characteristic.

That is, the average cooling rate in 620 ℃～500 ℃ TR is easy to therefore, particularly can't guarantee the sufficient ys of steel central part along with thick carbide generates bainite structure etc. during less than 5 ℃/second.On the other hand, the speed of cooling in this TR near the skin section of steel, be easy to overquenching, so the toughness on top layer might reduce during greater than 50 ℃/second.Therefore, in the present invention, making the average cooling rate in 620 ℃～500 ℃ the TR is 5 ℃/second～50 ℃/second.

When the cooling in this cooling stops temperature greater than 500 ℃, be not only the central part of steel and in skin section, the generation of the bainite of martensite or bottom etc. is also insufficient, therefore, can't guarantee intensity.Thereby it is below 500 ℃ that cooling stops temperature.Utilize this thermal treatment, be easy to obtain martensite or bainite structure.Under the situation of steel, mainly become bainite structure with chemical constitution of the present invention.

Under the condition shown in the table 3; The casting sheet is hot-rolled down to suitable thickness of slab; Cool off; Obtained test use steel plate, this casting sheet be with through utilize converter to come steel, the non-active gas shown in the enforcement table 2 of the chemical constitution shown in the melting table 1 to be blown into to handle or vacuum refinement handle after enforcement cast continuously and obtain.

Table 1

Table 2

The melting condition of table 2 steel

* be meant the meaning of the scope that breaks away from the present invention's regulation.

Table 3

Table 3 heating rolling condition

* be meant the meaning of the scope that breaks away from the present invention's regulation.

*

* the average cooling rate in 1:620 ℃～500 ℃ TRs.

Use above-mentioned test to use steel plate, utilize following method to measure tensile strength and toughness, oxide compound number, the thickness of slab reduction of repeated stress failure life-span, welding heat affected zone and peel off area occupation ratio.

Fatigue test

Use above-mentioned test to use steel plate, under the welding conditions shown in the table 4, make the cross welding joint of the non-transmission type of load, be used for fatigue test.In addition, Fig. 1 representes the shape and size of connector test body.The connector by using fillet weld is welded and is made.In Fig. 1, Reference numeral 1 and 2 is mother metal steel plates, and Reference numeral 5 is weld parts.Each connector test body is applied repetition axle power load, measured the fatigue cracking at welding reinforcement terminal the generation life-span, be the repeated stress failure life-span.Table 5 expression fatigue test condition.

Table 4

Table 4 welding conditions

CO 2Welding
	Welding material DW-1001.2mm φ
250A
	26V
26cm/min
	15kJ/cm
Target location 1～2mm
	Welding torch angle 30 degree

Table 5 fatigue test condition

± 50tonf electricity fluid pressure type closed loop protracted test machine
	Load Control
Maximum nominal stress 420MPa
	Minimum nominal stress 350MPa
Nominal stress scope 70MPa
	Load ratio (=minimum load/ultimate load)=0.83
In the atmosphere at room temperature
	Recurrence rate 10Hz
When the displacement when be defined as ultimate load fatigue lifetime increases 1mm

The tensile strength of welding heat affected zone

Above-mentioned test with steel plate in, parallel with rolling surface and with the vertical direction of rolling direction on the acquisition test sheet, implement tension test according to the method for Japanese JIS Z 2241 (1998) defineds, obtain tensile strength (TS).

The toughness of welding heat affected zone

By above-mentioned test with steel plate (thickness of slab (t)) in thick of surface of steel plate (1/4) t along parallel with rolling surface and with the vertical direction acquisition test of rolling direction sheet; Method according to Japanese JIS Z 2242 (1998) defineds is implemented shock test, obtains 0 ℃ absorption merit (vE0).

The oxide compound number

Utilize the order shown in following (i)～(iii) to obtain apart from top layer 2mm with the oxide compound number in the interior zone.

(i) will cut out small pieces as sightingpiston with the vertical cross section of rolling direction of the steel of making, utilize nital corrosion sightingpiston, make test film.

(ii) above-mentioned test film is placed on the SEM that has EDX; The zone that 0.05mm is square is as 1 visual field; Utilize 2000 times of multiplying powers to 2mm observes with 5 visual fields (roughly equally spaced 5 visual fields) in interior zone apart from the top layer, measure the oxide compound number in each visual field.At this moment, the differentiation of oxide compound and other inclusiones is carried out through the compositional analysis of EDX.In addition, for fear of the deviation of visual field, zone, change the mensuration that the degree of depth is carried out the oxide compound number from the top layer to degree of depth 2mm.

(iii) that the oxide compound number in each visual field is average, with MV as apart from top layer 2mm with oxide compound number in the interior zone.

Thickness of slab reduction and peel off area occupation ratio

About erosion resistance, utilize SAE (Society of Automotive Engineers) J2334 test that the test film that the steel that obtain certainly obtain is estimated.SAE J2334 test is with moistening: 50 ℃, 100%RH, 6 hours, salt adhere to: 0.5%NaCl, 0.1%CaCl ₂, 0.075%NaHCO ₃, aqueous solution dipping, 0.25 hour, drying: 60 ℃, 50%RH, 17.75 hours are as 1 circulation accelerated test of (adding up to 24 hours), etch state and weather exposure test similar (Nagano win positive people under husband, the mountain, interior Tian Renzhu: environmentally conscious materials, be total to and stand publication (2004), p.74).In addition, this test is to simulate the test of salt amount greater than the harsh like this corrosive environment of 1mdd of wafting.

After 120 circulations of SAE J2334 off-test, remove the rusty scale on each test film surface, measured the thickness of slab reduction.At this, " thickness of slab reduction " is the average thickness of slab reduction of test film, is to use weight before and after the test to reduce and the surface-area of test film calculates.

In addition; In order to investigate the separability of anti-the application; Utilizing air-jet method is the mode application modified epoxy coating (BANNOH200: Chinese coating system) of 150 μ m with dry film thickness on the test film of 150 * 70mm size; Draw after the lattice with the degree of depth that arrives steel substrate, likewise utilize SAE J2334 to test and estimate.

Chemical constitution and the method for manufacture and the various test-results of table 6 expression steel.

Table 6

As shown in table 6, can know: all satisfying in the present invention's example 1～10 of condition of the present invention in chemical constitution and method of manufacture, is 5 * 10 apart from top layer 2mm with the oxide compound number in the interior zone ⁴Individual/mm ²Below, in any example, the repeated stress failure life-span, (repeat number) was greater than 5 * 10 ⁶Inferior and da/dn is 5 * 10 ^-5Below, therefore, have sufficient fatigue cracking extended attribute.In addition, have higher erosion resistance, the lattice portion of drawing under the situation of application do not find in any steel plate of corrosive yet, peels off all lessly, therefore, can elongate studying for a second time courses one has flunked at interval of application.

On the other hand; Though satisfy scope given to this invention but method of manufacture breaks away from comparative example 1 and comparative example 2 and the chemical constitution of condition of the present invention breaks away from the comparative example 3～comparative example 6 of scope given to this invention in chemical constitution, equal extreme difference of repeated stress failure life-span is 10 ⁴The order of magnitude.

Particularly more at the Cu amount, Cu/Sn is greater than in 1 the comparative example 3, produced small crackle when rolling in the end.In the less comparative example 4 of Sn, the erosion resistance under the more environment of the salt amount of wafting reduces, and peeling off area occupation ratio also is 80%.

Utilizability on the industry

Therefore the fatigue cracking extended attribute and the excellent corrosion resistance of steel of the present invention, are suitable for hull, civil construction thing, construction implement, hydraulic pressure iron pipe, oceanic tectonic thing, line pipe etc. and require welding structure thing of fatigue cracking extended attribute etc.

Description of reference numerals

1, mother metal steel plate; 2, mother metal steel plate; 5, weld part.

Claims (8)

1. the steel of fatigue cracking extended attribute and excellent corrosion resistance is characterized in that having such chemical constitution; Promptly; By quality %, contain below C:0.01%～0.14%, Si:0.04%～0.6%, Mn:0.5%～2.0%, P:0.01%, below the S:0.003%, Cu: less than 0.2%, B: greater than 0.0007% and be 0.005% below, Al: less than 0.05%, reach Sn:0.03%～0.50% below the N:0.007%, below the O:0.003%, remainder is made up of Fe and impurity; And the Cu/Sn ratio is below 1; And the Bq value of being obtained by following (1) formula is below 0.003, and the Ceq value of being obtained by following (2) formula is 0.15～0.35; And, be 5 * 10 apart from top layer 2mm with the per 1 square of mm of the oxide compound number in the interior zone ⁴Below individual,

$\mathrm{Bq}=B-\frac{10.8}{14.1}\&times;(N-\frac{\mathrm{Ti}}{3.4})---\left(1\right)$

$\mathrm{Ceq}=C+\frac{1}{24}\mathrm{Si}+\frac{1}{6}\mathrm{Mn}+\frac{1}{40}\mathrm{Ni}+\frac{1}{5}\mathrm{Cr}+\frac{1}{4}\mathrm{Mo}+10B---\left(2\right)$

Wherein, each symbol of element in the above-mentioned formula is meant the amount (in quality %) of each element.In addition, be substitution 0 (zero) under the situation of impurity levels at the amount of each element.

2. the steel of fatigue cracking extended attribute according to claim 1 and excellent corrosion resistance is characterized in that,

By quality %, these steel also contain below Mo:1.0%, below the V:0.1% and below the Nb:0.1% the element more than a kind of selection.

3. the steel of fatigue cracking extended attribute according to claim 1 and 2 and excellent corrosion resistance is characterized in that,

By quality %, these steel also contain below the Ni:1.5%.

4. according to the steel of each described fatigue cracking extended attribute and excellent corrosion resistance in the claim 1～3, it is characterized in that,

By quality %, these steel also contain below the Cr:1.2%.

5. according to the steel of each described fatigue cracking extended attribute and excellent corrosion resistance in the claim 1～4, it is characterized in that,

By quality %, these steel also contain below the Ti:0.05%.

6. according to the steel of each described fatigue cracking extended attribute and excellent corrosion resistance in the claim 1～5, it is characterized in that,

By quality %, these steel also contain below the Ca:0.003% and below the Mg:0.003% in a kind of or two kinds.

7. the method for manufacture of the steel of fatigue cracking extended attribute and excellent corrosion resistance is characterized in that,

Comprise following operation A～D, and the backheat temperature amplitude after the cooling of step D is finished is below 70 ℃,

Operation A: the operation that under the condition that satisfies following (3) formula, in molten steel, is blown into non-active gas;

Process B: the molten steel to obtaining casts continuously, obtains having the operation of the steel billet of each described chemical constitution in the claim 1～6;

Operation C: the steel billet that obtains being heated to after 900 ℃～1180 ℃, is to implement the operation that hot rolling obtains hot-finished material under 650 ℃～1000 ℃ the condition in the precision work temperature;

Step D: the average cooling rate in 620 ℃～500 ℃ TR is under 5 ℃/second～50 ℃/second the condition; The hot-finished material that obtains is quickened cooling from 620 ℃～950 ℃ TR; In the TR below 500 ℃, finish the refrigerative operation

$\frac{G_1\&times;H_1\&times;t_1}{S_1\&times;D_1}\&GreaterEqual;2.0---\left(3\right)$

Wherein, the definition of the symbol in above-mentioned (3) formula is described below:

G ₁: be blown into the non-active gas flow (NL/min) in the molten steel

H ₁: be blown into the distance (m) of the top of nozzle from non-active gas to liquid steel level

t ₁: non-active gas is blown into the time (min)

S ₁: casting ladle molten steel amount (ton)

D ₁: casting ladle internal diameter (m).

8. the method for manufacture of the steel of fatigue cracking extended attribute and excellent corrosion resistance is characterized in that,

Comprise following operation A1～D, and the backheat temperature amplitude after the cooling of step D is finished is below 70 ℃,

Operation A1: under the condition that satisfies following (4) formula, molten steel is carried out the vacuum refinement treatment procedures;

Process B: the molten steel to obtaining casts continuously, obtains having the operation of the steel billet of each described chemical constitution in the claim 1～6;

Operation C: the steel billet that obtains being heated to after 900 ℃～1180 ℃, is to implement the operation that hot rolling obtains hot-finished material under 650 ℃～1000 ℃ the condition in the precision work temperature;

Step D: the average cooling rate in 620 ℃～500 ℃ TR is under 5 ℃/second～50 ℃/second the condition; The hot-finished material that obtains is quickened cooling from 620 ℃～950 ℃ TR; In the TR below 500 ℃, finish the refrigerative operation

$\frac{G_2\&times;{D_2}^2\&times;t_2}{S_2}\&GreaterEqual;5.5---\left(4\right)$

Wherein, the definition of the symbol in above-mentioned (4) formula is described below:

G ₂: the molten steel employed non-active gas flow (NL/min) that refluxes

D ₂: soaking tub internal diameter (m)

t ₂: vacuum processing time (min)

S ₂: casting ladle molten steel amount (ton).

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