CN102639737B - 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 manufacture method thereof

Technical field

The present invention relates to be suitable for steel and manufacture method 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 welding structure thing maximizes is day by day remarkable, expectation high strength and lightweight.But, because design stress when using high-strength steel rises, 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.At structure, with in the Plate Steels such as steel, conventionally implement welding procedure, therefore, likely from weld part, produce fatigue cracking.Thereby, as long as can make the fatigue cracking that produces, expands from weld part be trapped in steel, just contribute to extend the fatigue lifetime of structure.Therefore, the various steel with fatigue cracking expansion inhibition have been proposed.

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

Such technology has also been proposed in patent documentation 2: make the tissue of the welding heat affected zone (HAZ) of the high-tensile steel of tensile strength 490MPa～780MPa take bainite as main body, 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, in order to strengthen the whole tissue that contains bainite and martensite, the restriction of carbon equivalent (Ceq) is set.

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

Conventionally, when weather resistant steel is exposed in atomospheric corrosion environment, on its surface, be formed with the rusty scale with protectiveness, the Corrosion Of Steel after suppressing.Therefore, weather resistant steel can safeguard that steel are used for the structures such as bridge by the minimum of open ground use as not application.

But; not only regional by the sea; even and in the more area of the salt amount of wafting as the area that is also scattered with snow melt salt, frostproofer in inland portion, be difficult to be formed with the rusty scale with protectiveness on the surface of weather resistant steel, be difficult to the effect that performance suppresses corrosion.Therefore, in these areas, cannot use exposed weather resistant steel, it is normal conditions that the application of the ordinary steel that ordinary steel enforcement application is used is used.But, in the situation that this ordinary steel is used in application, by corrosion, being caused filming deteriorated, needs carry out application for approximately every 10 years again, and therefore, the expense that maintains administrative institute's need is very large.

In recent years, in the salt amount of wafting, as NaCl, there is 0.05mg/dm ²/ day(0.05mdd) above area, for example, in riviera, utilize the standardized climate-resistant steel of Japanese Industrial Standards (JIS) (JIS G 3114: welding structure weathering resistance hot-strip) because producing squamous rust, stratiform rust etc. and the amount of being corroded is larger, therefore, cannot without application in the situation that, use (with reference to building province building institute, (company) steel social hall, (company) Japanese bridge is built association: be applied to the design and construction main points that the joint research report (XX) that bridge is relevant-nothing be coated with weathering resistance bridge (change edition-1993.3) to climate-resistant steel).

Like this, wait under the more environment of salt in area by the sea, conventionally common iron is carried out to application and process.But present situation is: build near riviera river mouth, sprinkled with the bridge corrosion in the road of the intermountain portion of snow melt salt etc. significantly, no longer application.For these again application to spend great workload, therefore, strong request can without application the steel that use.

Recently, having developed the Ni that the Ni of a kind of interpolation 1%～3% left and right forms is high weather resistance steel.But, can clearly in the salt amount of wafting, be greater than in the area of 0.3mdd～0.4mdd, in the situation that only adding this Ni, be difficult to be applied to can without application the steel that use.

Because the corrosion of steel becomes along with the salt amount of wafting increases acutely, therefore, from the viewpoint of erosion resistance and economy, the weather resistant steel that need to form based on the salt amount of wafting.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 crossbeam outer exposed in rainfall, dew with in sunshine.On the other hand, though be exposed in dew in crossbeam inside, can not be caught in the rain.Conventionally, in the more environment of the salt amount of wafting, can say that the corrosion of crossbeam inside is outside more violent than crossbeam.

In addition, in the environment sprinkled with snow melt salt, frostproofer on road, the car during this salt is traveling is rolled, and is attached on the bridge of supporting road, therefore, becomes harsh corrosive environment.And away from inferior being also exposed in harsh salt damage environment Xia， this area of eaves of seashore, becoming the salt amount of wafting is harsh corrosive environment more than 1mdd slightly.

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

For example, the weather resistant steel that a kind of increase chromium (Cr) amount forms has been proposed in patent documentation 3, and, the weather resistant steel that a kind of increase nickel (Ni) amount forms has 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 the steel with fatigue cracking expansion inhibition of above-mentioned proposition and the steel with erosion resistance have problem points as described as follows.

The technology that patent documentation 1 proposes is for ferritic phase is existed in wider temperature range, using the Al that adds high density as prerequisite.But though Al contributes to ferritic phase to generate, Al makes the significantly reduced element of toughness with one of desired fundamental characteristics of steel as structure.Therefore, adopt this technology, although suppress the unrelieved stress of weld part, can expect to improve fatigue strength, the toughness itself of resisting static load is just not enough.Not only from the viewpoint of fatigue strength, from the viewpoint of the anti-brittle rupture of opposing static load, also must carry out the shape of building material, the design of size, in the technology of patent documentation 1 proposition, cannot improve evenly intensity viability.

In the technology proposing at patent documentation 2, by adding the B that can improve hardening capacity in crystal boundary, suppress efficiently grain boundary ferrite, suppress grain boundary ferrite and generate.But, because B is the element that reduces the toughness of welding heat affected zone, therefore to note the use of B.In welded-joint, the fatigue characteristic of being not only opposing repeated load are important, and due to the brittle rupture that will prevent that static load from causing, therefore guarantee that toughness is also important.Particularly, the major part of scantling is decided by the latter's toughness, and for necessary part, in the Fatigue Design system of present situation of fatigue survey of confirming anti-fatigure failure, toughness and fatigue characteristic are equally also important.In this looks like, also consider the situation of welding conditions, the change of for example weld heat input, 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 although the region of the waft salt amount of the weather resistant steel that forms of amount below to a certain degree in can improve weathering resistance, but surpassing under the harsh salt environment of this degree, make on the contrary weathering resistance deteriorated.

In the situation that the weather resistant 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, very expensive as the material for purposes such as bridges.For fear of this point, when reducing Ni amount, how weathering resistance is not improved, in the situation that the salt amount of wafting is more, be created in steel surface generate stratiform peel off rust, corrode remarkable, be unable to undergo the such problem of life-time service.

And in the weldable steel structure using under the more environment of the salt amount of wafting, the separability of resistance to application becomes very large problem.; 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 if implement application; also exist application to peel off very soon and corrode such problem, needing every several years～more than ten years to implement the brushing again of application.In addition, when the brushing again of implementing application, as its front operation, need on bridge once, assemble scaffolding and again implement sandblasting having corroded, therefore will spend great cost.And even be also difficult to completely except derust in the situation that again implementing sandblasting, even cannot be completely except application again on the steel that derust, the application life-span also significantly shortens.In the most situation of the separability of resistance to application, depend on that the corrosion resistance of steel comprising as substrate is in interior characteristic.

Thereby strong expectation extends 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 product-life-management of considering bridge, it is also very important extending the application life-span.

Summary of the invention

the problem that invention will solve

The present invention makes in order to address this problem, and its object is to provide steel and the manufacture method thereof of the element, fatigue cracking extended attribute and the excellent corrosion resistance that do not contain in a large number the infringement toughness such as Al, B.

At this, the meaning of above-mentioned erosion resistance refers to erosion resistance in perchloride environment (comprise application do not peel off and suppress the corrosion of painting defect portion and maintain erosion resistance (separability of resistance to application) and the weathering resistance during without application).

for the scheme of dealing with problems

The inventor etc. in order to achieve the above object, the fatigue characteristic of first having carried out being conceived to welding joint and the research of correlationship that is present in the degree of cleaning of the inclusion in steel, learn between the degree of cleaning in the whole cross section of steel and joint fatigue characteristic without any correlationship.

Therefore, be conceived to the more steel surface of addendum modification, after carrying out more detailed investigation, clear and definite joint fatigue characteristic largely depend on the characteristic of steel surface, can lifting sub fatigue characteristic by improving the degree of cleaning of steel surface.More particularly, by inclusion analysis be limited to from surface of steel plate along thickness of slab direction to the region of the 2mm degree of depth, for each steel plate, obtain degree of cleaning, after investigation and the correlationship of joint fatigue characteristic, conclude and have extremely strong correlationship.As the reason of concluding this correlationship, the addendum modification of being commonly considered as steel surface is large 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 under heavily stressed yet.On the other hand, because the addendum modification of steel surface is larger, therefore, it is generally acknowledged and in the interface of inclusion and substrate microstructure, produce be full of cracks, fatigue characteristic are deteriorated.Thereby it is the thickness of slab central part at steel conventionally 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 found that: under such environment, and FeCl ₃the dry wet of solution is the essential condition of corrosion repeatedly, utilizing Fe ³⁺hydrolysis make under state that pH reduces, and pass through Fe ³⁺play the effect of oxygenant and corrosion is accelerated.

Corrosion reaction is now as follows.

As cathodic reaction, reaction below main generation.

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

And, except this reaction, also there is following cathodic reaction simultaneously.

2H ₂O＋O ₂＋2e ^－→4OH ^－，

2H ^＋＋2e ^－→H ₂

On the other hand, with respect to above-mentioned Fe ³⁺reduction reaction, there is following anodic reaction.

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

Thereby the combined reaction of corrosion is 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⁺again play the effect of oxygenant, accelerated corrosion.Now, Fe ²⁺the speed of response of atmospheric oxidation conventionally slower under low pH environment, but accelerated in dense thick chloride soln, be easy to generate Fe ³⁺.Owing to being the reaction of such circulation, therefore, can be clearly under the very many environment of the salt amount of wafting, sustainable supply Fe all the time ³⁺, the corrosion of steel is accelerated, and erosion resistance is significantly deteriorated.

The mechanism of the corrosion based on in this salt environment such as the inventor, studies for the impact of weathering resistance various alloying elements, and result has drawn the opinion shown in following (a)～(c).

(a) Sn is as Sn ²⁺dissolve, utilize 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 improves the basic element of effect in the more environment of the salt amount of wafting as erosion resistance, manifests erosion resistance and improve effect in long environment of moistening time.But, under the environment can be clearly larger at chloride concentration, the local decline of pH is such, thus for example adhering to by salt humidity change dry wet repeatedly and generate under the so more dry environment of β-FeOOH, Cu on the contrary promotes corrosion.

(c) steel that like this, contain energetically Sn and suppressed Cu amount can be expected higher erosion resistance.And, because erosion resistance is higher, therefore, even steel are carried out to application, the application being 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,, the in the situation that of application, can expect the effect of higher erosion resistance.Thereby, except erosion resistance, also have can extend the life-span of application, by the effect of studying for a second time courses one has flunked overlay painting interval and drawing longlyer.Particularly in the improvement of the separability of resistance to application in ship domain, bridge field, bring into play effect.

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

(1) steel of a kind of fatigue cracking extended attribute and excellent corrosion resistance, it is characterized in that, there is such chemical constitution, , by mass%, contain C:0.01%～0.14%, Si:0.04%～0.6%, Mn:0.5%～2.0%, below P:0.01%, below S:0.003%, Cu: be less than 0.2%, B: be greater than below 0.0007% and 0.005%, Al: be less than 0.05%, below N:0.007%, following and Sn:0.03%～0.50% of O:0.003%, remainder consists of Fe and impurity, and Cu/Sn ratio is below 1, and, the Bq value of being obtained by following (1) formula is below 0.003, the Ceq value of being obtained by following (2) formula is 0.15～0.35, and, the every 1 square of mm of oxide compound number of take in interior region apart from top layer 2mm is 5 * 10 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 above-mentioned formula refers to the amount (quality %) of each element.In addition, in the situation that the amount of each element is impurity levels substitution 0(zero).

(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 mass%, these steel also contain below Mo:1.0%, below V:0.1% and Nb:0.1% with the more than a kind element of lower selection.

(3) 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, by mass%, these steel also contain below Ni:1.5%.

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

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

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

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

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

Process B: the molten steel obtaining is cast continuously, obtain having the operation of the steel billet of the chemical constitution of any one in above-mentioned (1)～(6);

Operation C: by after the heating steel billet to 900 obtaining ℃～1180 ℃, be to implement the operation that hot rolling obtains hot-finished material under the condition of 650 ℃～1000 ℃ in precision work temperature;

Step D: the average cooling rate in the temperature range of 620 ℃～500 ℃ is under the condition of 5 ℃/sec～50 ℃/sec, the hot-finished material obtaining is accelerated cooling from the temperature range of 620 ℃～950 ℃, in the temperature range below 500 ℃, finish cooling operation

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

Wherein, described in the symbol in above-mentioned (3) formula is defined as follows.

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

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

T ₁: non-active gas blowing time (min)

S ₁: casting ladle molten steel amount (ton)

D ₁: casting ladle internal diameter (m).

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

Operation A1: meeting the operation of under the condition of following (4) formula, molten steel being carried out to vacuum refinement processing;

Process B: the molten steel obtaining is cast continuously, obtain having the operation of the steel billet of the chemical constitution of any one in above-mentioned (1)～(6);

Operation C: by after the heating steel billet to 900 obtaining ℃～1180 ℃, be to implement the operation that hot rolling obtains hot-finished material under the condition of 650 ℃～1000 ℃ in precision work temperature;

Step D: the average cooling rate in the temperature range of 620 ℃～500 ℃ is under the condition of 5 ℃/sec～50 ℃/sec, the hot-finished material obtaining is accelerated cooling from the temperature range of 620 ℃～950 ℃, in the temperature range below 500 ℃, finish cooling operation

$\frac{G_2\×{D_2}^2\×t_2}{S_2}\≥5.5---\left(4\right)$

Wherein, the symbol in above-mentioned (4) formula is defined as follows.

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

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

Fatigue cracking extended attribute and the excellent corrosion resistance of steel of the present invention, therefore, be 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.

Accompanying drawing explanation

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

Embodiment

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

First, chemical constitution of steel of the present invention etc. is described.In the following description, " % " relevant to amount refers to " quality % ".

C：0.01％～0.14％

C is in order to ensure the required element of intensity.When its amount is less than 0.01%, cannot guarantee required intensity.But when its amount is greater than 0.14%, the in the situation that of welding, welding heat affected zone (HAZ), mother metal are all difficult to guarantee toughness.Thereby the amount of C is 0.01%～0.14%.Under C amount preferred, be limited to 0.03%, be limited to 0.10% on preferred.

Si：0.04％～0.6％

Si has desoxydatoin, and, also contribute to promote the intensity of steel.In order to obtain these effects, need to contain more than 0.04% Si.But, when its amount is greater than 0.6%, can cause toughness drop.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.When its amount is less than 0.5%, hardening capacity is not enough, cannot obtain intensity and the toughness of expectation.But, at Mn, being greater than 2.0% ground containing sometimes, segregation increases, and hardening capacity is too high, welding heat affected zone, the equal toughness drop of mother metal when welding.Thereby the amount of Mn is 0.5%～2.0%.

below P:0.01%

P is inevitably present in steel as impurity.When its amount is greater than 0.01%, not only can segregates in crystal boundary and make toughness drop, and when welding, cause heat cracking.Thereby the amount of P need to be limited in below 0.01%.P is fewer unreasonablely to be thought.

below S:0003%

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

cu: be less than 0.2%

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

b: be greater than below 0.0007% and 0.005%

B has the element that promotes hardening capacity and put forward high-intensity effect.In order to obtain this effect, need to be greater than 0.0007% ground and contain.But when its amount is greater than 0.005%, fatigue characteristic are deteriorated.Thereby the amount of B is greater than below 0.0007% and 0.005%.

al: be less than 0.05%

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

below N:0.007%

N is inevitably present in the element in steel as impurity.The in the situation that of its a large amount of existence, 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 O:0.003%

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

Sn：0.03％～0.50％

Sn becomes Sn ²⁺and dissolve, there is the effect that the inhibitor utilizing in acidic chloride solution is used for suppressing corrosion.In addition, Sn has the Fe of making ³⁺reduce rapidly, reduce the Fe as oxygenant ³⁺the effect of concentration, thus Fe suppressed ³⁺corrosion promoter action, therefore, promote high weathering resistance of wafting in salt time-sharing environment.In addition, there is the anode dissolution reaction that suppresses steel and the effect that promotes erosion resistance in Sn.And, by containing Sn, can bring into play in the more environment of the salinity of wafting and also can promote the effect of the weathering resistance of Cr.These effects obtain by the Sn containing more than 0.03%, and these amounts that act on Sn are saturated while being greater than 0.50%.Thereby the amount of Sn is 0.03%～0.50%.The preferred scope of Sn amount is 0.03%～0.20%.

cu/Sn ratio: below 1

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

Steel of the present invention have above-mentioned chemical constitution, and remainder consists of Fe and impurity.At this, the meaning of impurity refers to the composition of mainly sneaking into from such raw materials such as ore, waste materials due to a variety of causes of manufacturing process when industrial manufacture steel, is can not produce to the present invention the composition of allowing in dysgenic scope.

In steel of the present invention, can contain as required the more than a kind of composition of at least 1 group selection from below the 1st group～the 5th group.Below, to belonging to the composition of these groups, describe.

the composition of the 1st group: Mo, V, Nb

below Mo:1.0%

Because Mo has the intensity of mother metal of raising and the effect of toughness, therefore, also can contain as required.But, be greater than 1.0% ground containing sometimes, be mainly that the hardness of welding heat affected zone raises, infringement toughness and the C of resistance to S C.Thereby in the situation that containing 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 V:0.1%

Because V mainly has the effect that carbonitride while utilizing tempering improves strength of parent, therefore, also can contain as required.But, being greater than 0.1% ground containing sometimes, the performance boost effect of mother metal is saturated, causes toughness deteriorated.Thereby in the situation that containing 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 Nb:0.1%

Because Nb has the grain refined utilized and Carbide Precipitation improves the intensity of mother metal and the effect of toughness, therefore, also can contain as required.But when its amount is greater than 0.1%, above-mentioned effect is saturated, and obvious damage welding heat affected zone.Thereby in the situation that containing 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 Ni:1.5%

Due to Ni have under solid solution condition, improve steel matrix (matrix: the effect of toughness matrix), therefore, also can contain as required.But, even if be greater than 1.5% ground, contain, also cannot improve the characteristic suitable with the rising of alloying constituent.And erosion resistance coexists deteriorated because of Sn and Ni sometimes.Thereby in the situation that containing 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 Cr:1.2%

Because Cr has the effect that improves carbon dioxide corrosion resistant and improve hardening capacity, therefore, also can contain as required.But, being greater than 1.2% ground containing sometimes, even if meet other member condition, be not only difficult to suppress the sclerosis of welding heat affected zone, and carbon dioxide corrosion resistant raising effect is also saturated.Thereby in the situation that containing 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 Ti:0.05%

Ti plays the effect of deoxidant element, and forms the oxidation phase consist of Ti, Mn, particularly make Large Heat Input Welding heat affected zone organize miniaturization, can access the effect that fatigue characteristic promote, therefore, also can contain as required.But, being greater than 0.05% ground containing sometimes, 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 Heat Input Welding.Therefore,, in the situation that containing Ti, preferably making its amount is below 0.05%.More preferably be less than 0.02%.More preferably below 0.018%.In addition, in order stably to form this oxidation phase in steel, it is more than 0.003% preferably making the Ti total amount in steel.

the 5th group: Ca, Mg

below Ca:0.003%

Ca reacts with the S in steel, forms oxysulfide (oxysulfide) in molten steel.This oxysulfide and MnS etc. are different, can in rolling direction, not extend because of rolling processing, and rolling after, be also spherical, therefore, the top etc. with the inclusion that suppresses to take extension is the welding crack of crackle starting point, the effect of hydrogen induced cracking.Thereby, also can contain as required.But, when its amount is greater than 0.003%, cause toughness deteriorated.Thereby in the situation that containing 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 Mg:0.003%

Mg generates containing Mg oxide compound, becomes the generation core of TiN, has the effect that makes the fine dispersion of TiN, therefore, also can contain as required.But when its amount is greater than 0.003%, oxide compound too much causes ductility to reduce.Thereby in the situation that containing 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 the Bq value that steel of the present invention need to be tried to achieve by following (1) formula is below 0.003, the Ceq value that need to be tried to achieve by following (2) formula is 0.15～0.35.

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

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

Wherein, each symbol of element in above-mentioned formula refers to the amount (quality %) of each element.In addition, in the situation that the amount of each element is impurity levels substitution 0(zero).

below Bq:0.003

In order to bring into play the hardening capacity of B, promote effect, need to eliminate the impact of the N in steel.Its reason is, B is easy to be combined with N, while there is freely N in steel, is easy to be combined with N and generates BN.Therefore, by adding accordingly Ti with N amount, as TiN, fix, B is present in steel.B amount is larger, and the hardening capacity of B is higher.But, in the Bq value of being tried to achieve by (1) formula, be greater than at 0.003 o'clock, form thick iron carbon boride, cause fatigue characteristic deteriorated.Thereby Bq value need to be for below 0.003.

In addition, in order stably to obtain the hardening capacity of B, improve effect, it is more than 0.0001 preferably making the Bq value of above-mentioned (1) defined.More preferably more than 0.0005, more preferably more than 0.001.

Ceq：0.15～0.35

The Ceq being tried to achieve by above-mentioned (2) formula is so-called carbon equivalent, is to evaluate the hardening capacity of steel, the index of weldability is widely used conventionally.

The inventor etc. absorb merit value vE to improving the fatigue characteristic of welding joint and being used for meeting common tensile strength (TS) Charpy bar above for 500MPa and 0 ℃ as structure with steel ₀for the prerequisite of the above such requirement of 27J is sought.As a result, in Ceq value, be less than at 0.15 o'clock, strength decreased, on the other hand, can clearly be greater than at 0.35 o'clock at Ceq, and the hardening capacity of steel raises, and the Hardness Distribution of joint is inhomogeneous, and butt junction fatigue strength produces detrimentally affect.In addition, at Ceq, be greater than at 0.35 o'clock, also there is following shortcoming: cause the deteriorated of weldability, welding procedure difficulty, the purposes of steel is obviously restricted.Thereby making 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, need to take the every 1 square of mm of oxide compound number of inner compartment apart from top layer 2mm be 5 * 10 to steel of the present invention ⁴below individual.Its reason is, exists and is greater than 5 * 10 ⁴during individual oxide compound, the generation source of fatigue cracking increases, and fatigue characteristic reduce.

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

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

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

Oxide compound number in each visual field is average (iii), using mean value as apart from top layer 2mm with oxide compound number in interior region.

b. the manufacture method of steel of the present invention

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

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

Wherein, described in the symbol in above-mentioned (3) formula is defined as follows.

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

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

T ₁: non-active gas blowing time (min)

S ₁: casting ladle molten steel amount (ton)

D ₁: casting ladle internal diameter (m)

As long as carrying out non-active gas under the condition that meets above-mentioned (3) formula is blown into processing, just molten steel fully can be stirred and blows.That is, initial in blowing, the silicon oxidation in iron liquid and become silicon-dioxide, silicon-dioxide reacts with calcined lime, ferric oxide in adding stove to, starts to form CaO-SiO ₂-FeO class slag.Meanwhile, in stove, temperature rises, and waste material (scrap) also starts to dissolve.At the blowing initial stage, the carbon concentration in iron liquid is higher, and therefore, the purity oxygen being blown into reacts efficiently with carbon, 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 molten steel moves to be controlled the speed of decarburization.When the stirring by molten steel causes that the movement of carbon is insufficient, the purity oxygen being blown into reacts except being used in carbon, and also, for making iron oxidation, in slag, ferric oxide increases, and the yield rate of iron reduces.In order to prevent this point, from furnace bottom, be blown into gas actively.

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

$\frac{G_2\×{D_2}^2\×t_2}{S_2}\≥5.5---\left(4\right)$

Wherein, described in the symbol in above-mentioned (4) formula is defined as follows.

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

D ₂: soaking tub internal diameter (m)

T ₂: vacuum processing time (min)

S ₂: casting ladle molten steel amount (ton)

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

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

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

In addition, except above-mentioned condition, ejection traffic management during as casting, also can apply electromagnetic braking with 1000 Gauss～5000 Gausses, or to solidifying molten steel, do not carry out induction stirring processing with 250 Gauss～1000 Gausses, gradient with about 1mm/m is depressed the portion of finally solidifying, from the squeeze out molten steel of dense thick segregation of the final portion of solidifying.By above-mentioned management project is suitably combined, can access the steel billet that degree of cleaning are good and center segregation is less.

Then, the temperature range of the heating steel billet to 900 of manufacturing like this ℃～1180 ℃ is carried out to hot rolling better.Now, both the steel billet that is temporarily cooled to room temperature can be reheated, also can utilize so-called direct sending rolling technology, and after continuous casting, not be cooled to room temperature and just through soaking pit, maintain said temperature or heating with keeping intact.At this, in the situation that Heating temperature is less than 900 ℃, constantly insufficient to austenitic reverse transformation at heating of plate blank, deterioration in characteristics afterwards.On the other hand, when Heating temperature is greater than 1180 ℃, austenite crystal coarsening when heating steel billet, the toughness of being not only thickness of slab central part and whole mother metal all reduces.

The condition of hot rolling is as described below: the precision work temperature that makes hot rolling be 650 ℃～1000 ℃ better.When precision work temperature is less than 650 ℃, the resistance to deformation of steel is risen, and therefore, is difficult to the steel shape after hot rolling to be finish-machined to target shape.When precision work temperature is higher, the crystal grain micronized effect that not controlled rolling produces, cannot guarantee the toughness of mother metal.Thereby, by the ceiling restriction of precision work temperature at 1000 ℃.

Then, average cooling rate in the temperature range of 620 ℃～500 ℃ is under the condition of 5 ℃/sec～50 ℃/sec, the hot-finished material obtaining is cooling from the temperature range acceleration of 620 ℃～950 ℃, in the temperature range below 500 ℃, finish cooling better.And, the backheat temperature amplitude after cooling end be 70 ℃ better below.

By cooling under such condition, can improve fatigue characteristic.

That is,, when the average cooling rate in the temperature range of 620 ℃～500 ℃ is less than 5 ℃/sec, be easy to, along with thick carbide generates bainite structure etc., therefore, particularly cannot guarantee the sufficient yield strength of steel central part.On the other hand, when the speed of cooling in this temperature range is greater than 50 ℃/sec, near the skin section of steel, be easy to overquenching, so the toughness on top layer likely reduces.Therefore, in the present invention, making the average cooling rate in the temperature range of 620 ℃～500 ℃ is 5 ℃/sec～50 ℃/sec.

When cooling in this is cooling stops temperature and be 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, cannot guarantee intensity.Thereby the cooling temperature that stops is below 500 ℃.Utilize this thermal treatment, be easy to obtain martensite or bainite structure.In the situation that there are the steel of chemical constitution of the present invention, mainly become bainite structure.

Under the conditions shown in Table 3, slab is hot-rolled down to suitable thickness of slab, carry out cooling, obtained test steels plate, this slab is by by utilizing converter to come steel, the non-active gas shown in enforcement table 2 of the chemical constitution shown in melting table 1 to be blown into process or vacuum refinement is implemented continuous casting after processing and obtained.

table 1

table 2

The melting condition of table 2 steel

* refer to the meaning of the scope that departs from the present invention's regulation.

table 3

Table 3 heating rolling condition

* refer to the meaning of the scope that departs from the present invention's regulation.

*

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

Use above-mentioned test steels 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 peeled off area occupation ratio.

fatigue test

Use above-mentioned test steels plate, under the welding conditions shown in table 4, make the cross welding joint of the non-transmission type of load, for fatigue test.In addition, Fig. 1 represents the shape and size of connector test body.Connector by using fillet weld seam 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 to repetition axle power load, measured the fatigue cracking of welding reinforcement terminal the generation life-span, be the repeated stress failure life-span.Table 5 represents 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 is controlled
Maximum nominal stress 420MPa
	Minimum nominal stress 350MPa
Nominal stress scope 70MPa
	Load ratio (=minimum load/ultimate load)=0.83
In atmosphere at room temperature
	Recurrence rate 10Hz
When displacement when be defined as ultimate load fatigue lifetime increases 1mm

the tensile strength of welding heat affected zone

In above-mentioned test steels plate, acquisition test sheet in parallel with rolling surface and vertical with rolling direction direction, according to Japanese JIS Z 2241(1998) method of defined implements tension test, obtains tensile strength (TS).

the toughness of welding heat affected zone

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

oxide compound number

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

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

(ii) above-mentioned test film is placed on the SEM with EDX, using the square region of 0.05mm as 1 visual field, utilize 2000 times of multiplying powers to observing with 5 visual fields (roughly equally spaced 5 visual fields) in interior region apart from top layer 2mm, measure the oxide compound number in each visual field.Now, the differentiation of oxide compound and other inclusiones is undertaken by the compositional analysis of EDX.In addition, for fear of the deviation of visual field, the region from top layer to degree of depth 2mm, change the mensuration that the degree of depth is carried out oxide compound number.

Oxide compound number in each visual field is average (iii), using mean value as apart from top layer 2mm with oxide compound number in interior region.

thickness of slab reduction and peel off area occupation ratio

About erosion resistance, utilizing SAE(Society of Automotive Engineers) J2334 test test film that the steel that certainly obtain are obtained evaluates.SAE J2334 test is by 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, dry: 60 ℃, 50%RH, 17.75 hours accelerated tests as 1 circulation (adding up to 24 hours), etch state and weather exposure test similar (Nagano win positive people, interior Tian Renzhu under husband, mountain: Viewpoint of Eco materials, be total to and stand publication (2004), p.74).In addition, this test is to simulate the test that the salt amount of wafting is greater than the harsh like this corrosive environment of 1mdd.

After 120 circulations of SAE J2334 off-test, remove the rusty scale on each test film surface, measured thickness of slab reduction.At this, " thickness of slab reduction " is the average thickness of slab reduction of test film, is that the weight minimizing of use-testing front and back and the surface-area of test film calculate.

In addition, in order to investigate the separability of resistance to application, utilize air-jet method to take the mode application modified epoxy coating (BANNOH200: Chinese coating system) that dry film thickness is 150 μ m on the test film of 150 * 70mm size, after drawing lattice with the degree of depth of arrival steel substrate, similarly utilize SAE J2334 test to evaluate.

Table 6 represents chemical constitution and manufacture method and the various test-results of steel.

table 6

As shown in table 6, known: in chemical constitution and manufacture method, all meet in the inventive example 1～10 of condition of the present invention, the oxide compound number of take in interior region apart from top layer 2mm is 5 * 10 ⁴individual/mm ²below, in any example, the repeated stress failure life-span (repeat number) is greater than 5 * 10 ⁶inferior and da/dn is 5 * 10 ^-5below, therefore, there is sufficient fatigue cracking extended attribute.In addition, have higher erosion resistance, the lattice portion of the drawing in the situation that of application do not find in any steel plate of corrosion yet, peels off all lessly, therefore, can elongate the interval of studying for a second time courses one has flunked of application.

On the other hand, though meet scope given to this invention but manufacture method departs from the comparative example 1 of condition of the present invention and comparative example 2 and chemical constitution departs 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, Cu/Sn more at Cu amount is greater than in 1 comparative example 3, produced small crackle during rolling in 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 is also 80%.

utilizability in industry

Fatigue cracking extended attribute and the excellent corrosion resistance of steel of the present invention, therefore, be 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 (19)

1. the steel of a fatigue cracking extended attribute and excellent corrosion resistance, it is characterized in that, there is such chemical constitution, , by mass%, contain C:0.01%～0.14%, Si:0.04%～0.6%, Mn:0.5%～2.0%, below P:0.01%, below S:0.003%, Cu: be less than 0.2%, B: be greater than 0.0007% and be below 0.005%, Al: be less than 0.05%, below N:0.007%, following and Sn:0.03%～0.50% of O:0.003%, remainder consists of Fe and impurity, and Cu/Sn ratio is below 1, and, the Bq value of being obtained by following (1) formula is below 0.003, the Ceq value of being obtained by following (2) formula is 0.15～0.35, and, the every 1 square of mm of oxide compound number of take in interior region apart from top layer 2mm is 5 * 10 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 above-mentioned formula refers to the amount in quality % of each element, in addition, in the situation that the amount of each element is impurity levels substitution 0.

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

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

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

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

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

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

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

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

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

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

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

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

8. the steel of fatigue cracking extended attribute according to claim 4 and excellent corrosion resistance, is characterized in that,

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

9. the steel of fatigue cracking extended attribute according to claim 5 and excellent corrosion resistance, is characterized in that,

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

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

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The steel of 11. fatigue cracking extended attributes according to claim 3 and excellent corrosion resistance, is characterized in that,

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The steel of 12. fatigue cracking extended attributes according to claim 4 and excellent corrosion resistance, is characterized in that,

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The steel of 13. fatigue cracking extended attributes according to claim 5 and excellent corrosion resistance, is characterized in that,

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The steel of 14. fatigue cracking extended attributes according to claim 6 and excellent corrosion resistance, is characterized in that,

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The steel of 15. fatigue cracking extended attributes according to claim 7 and excellent corrosion resistance, is characterized in that,

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The steel of 16. fatigue cracking extended attributes according to claim 8 and excellent corrosion resistance, is characterized in that,

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The steel of 17. fatigue cracking extended attributes according to claim 9 and excellent corrosion resistance, is characterized in that,

By mass%, these steel also contain the following and Mg:0.003% of Ca:0.003% with lower a kind of or two kinds.

The manufacture method of the steel of 18. 1 kinds of fatigue cracking extended attributes and excellent corrosion resistance, is characterized in that,

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

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

Process B: the molten steel obtaining is cast continuously, obtain having the operation of the steel billet of the chemical constitution described in claim 1～17 any one;

Operation C: by after the heating steel billet to 900 obtaining ℃～1180 ℃, be to implement the operation that hot rolling obtains hot-finished material under the condition of 650 ℃～1000 ℃ in precision work temperature;

Step D: the average cooling rate in the temperature range of 620 ℃～500 ℃ is under the condition of 5 ℃/sec～50 ℃/sec, the hot-finished material obtaining is accelerated cooling from the temperature range of 620 ℃～950 ℃, in the temperature range below 500 ℃, finish cooling operation

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

Wherein, described in the symbol in above-mentioned (3) formula is defined as follows:

G ₁: the non-active gas flow ，Qi unit being blown in molten steel is NL/min

H ₁: the top that is blown into nozzle from non-active gas is m to the distance ，Qi unit of liquid steel level

T ₁: non-active gas blowing time ，Qi unit is min

S ₁: casting ladle molten steel Liang，Qi unit is ton

D ₁: casting ladle internal diameter ，Qi unit is m.

The manufacture method of the steel of 19. 1 kinds of fatigue cracking extended attributes and excellent corrosion resistance, is characterized in that,

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

Operation A1: meeting the operation of under the condition of following (4) formula, molten steel being carried out to vacuum refinement processing;

Process B: the molten steel obtaining is cast continuously, obtain having the operation of the steel billet of the chemical constitution described in claim 1～17 any one;

Operation C: by after the heating steel billet to 900 obtaining ℃～1180 ℃, be to implement the operation that hot rolling obtains hot-finished material under the condition of 650 ℃～1000 ℃ in precision work temperature;

Step D: the average cooling rate in the temperature range of 620 ℃～500 ℃ is under the condition of 5 ℃/sec～50 ℃/sec, the hot-finished material obtaining is accelerated cooling from the temperature range of 620 ℃～950 ℃, in the temperature range below 500 ℃, finish cooling operation

$\frac{G_2\×{D_2}^2\×t_2}{S_2}\≥5.5---\left(4\right)$

Wherein, described in the symbol in above-mentioned (4) formula is defined as follows:

G ₂: the non-active gas flow ，Qi unit that molten steel backflow is used is NL/min

D ₂: soaking tub internal diameter ，Qi unit is m

T ₂: vacuum processing time ，Qi unit is min

S ₂: casting ladle molten steel Liang，Qi unit is ton.