CN102953001B - Cold-rolled steel sheet with tensile strength larger than 900 MPa and manufacturing method thereof - Google Patents
Cold-rolled steel sheet with tensile strength larger than 900 MPa and manufacturing method thereof Download PDFInfo
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Abstract
The invention discloses a cold-rolled steel sheet with tensile strength larger than 900 MPa and a manufacturing method of the cold-rolled steel sheet. The cold-rolled steel sheet is composed of the following ingredients in percentage by weight: 0.06-0.095wt% of C, 0.1-0.4wt% of Si, 1.2-1.6wt% of Mn, 0.001-0.004% of B, not larger than 0.015wt% of P, not larger than 0.004wt% of S, 0.003-0.007wt% of N, 0.01-0.03wt% of Nb, 0.03-0.06% of Ti, 0.015-0.045wt% of Al, 0.002-0.007wt% of Ca and the rest balance of Fe and inevitable impurities. Cold-rolled high strength steel with tensile strength larger than 900 MPa and excellent cold bending property and delayed cracking resistance is obtained by reasonable ingredient design and technique design in the invention, and the steel has the characteristics of small and uniform tissues and excellent cold bending property. Meanwhile, the delayed cracking resistance of the steel is excellent, so that the steel meets the manufacturing demands of safety elements and structural members of automobiles.
Description
Technical field
The present invention relates to cold-rolled steel sheet and manufacture method, particularly the above cold-rolled steel sheet of a kind of tensile strength 900MPa and manufacture method, this steel has cold-bending property excellence, the feature of anti-delayed fracture excellent property.
Background technology
Automotive industry, for the needs of loss of weight, requires the steel plate using more high strength.Wherein, tensile strength more and more becomes the first-selection of automobile industry at 900MPa and above ultrahigh-strength steel thereof, because the steel of this intensity rank, can effectively alleviate body of a motor car weight, improves security.High Strength Steel Plate is in automobile manufacturing process, and its deformability mainly occurs by crackle and expansion controls, therefore, very high for partial plastic forming Capability Requirement, also namely requires higher to hole expansibility and bending property.Traditional high-strength steel, often there is lower yield tensile ratio and higher unit elongation, possessed good draw forming ability, but due to partial plastic forming not enough in manufacturing based on the high-strength steel parts of the forming modes such as bending, alternating bending and reaming, easily there is the defect such as avulsion, necking down.Generally in high-strength steel easily there is component segregation containing comparatively high alloy element in castingprocesses, cause uneven due to composition and tissue of follow-up material, cause local deformaton ability to decline, namely hole expansibility and clod wash poor etc.In addition, all unavoidably there is inclusion in steel, plastic occluded foreignsubstance can extend in the operation of rolling of steel, becomes micro-crack source, reduces the partial plastic forming ability of steel further.
Also there is the possibility of delayed fracture in high-strength steel, generally there is internal stress after forming in steel plate, if be now subject to the invasion and attack of hydrogen, hydrogen is gathered in the expansion that crack tip can cause crackle, presents " the delayed fracture phenomenon " of progressively crack propagation and final cracking under the effect of internal stress.The application of delayed fracture corresponding high-strength steel is an important problem, because delayed fracture is not easy to find, progressively occurs, may cause a series of problem concerning safety in part use procedure.
Japanese Patent Laid-Open 11-350038 discloses the steel of a kind of ductility and the good 980MPa of plasticity, its Composition Design is, C:0.1-0.15%, Si:0.8-1.5%, Mn:1.5-2.0%, P:0.01-0.05%, S≤0.005%, Sol Al:0.01-0.07%, N :≤0.01%, one or more in Nb:0.001-0.02%, V:0.001-0.02%, Ti:0.001-0.02%.Carbon equivalent=(C+Mn/6+Si/24)=0.4-0.52, in more than Ar3 hot rolling, 500-650 DEG C is batched, is incubated between Ac1-AC3, be cooled to 580-720 DEG C, after being as cold as room temperature soon, 230-300 DEG C of overaging.
The clear 63-38526 of Japanese Patent introduces the excellent high tensile steel plate of a kind of bending property and manufacture method thereof, C:0.1-0.2%, Si≤0.7%, Mn:1.5-2.5%, S≤0.008%, Al :≤0.1%, Ti:0.05-0.15%, or adds Ca:0.005%.By 850-950 DEG C of finish to gauge, 500-650 DEG C is batched, less than 930 DEG C annealing more than recrystallization temperature, 3-200 DEG C/s cools, then 2-10 minute is incubated, holding temperature controls, between 1100 DEG C ~ annealing temperature and 1200 DEG C ~ annealing temperature, finally to obtain the high-strength steel of 100kg, and bending radius can reach 0.5 ~ 1mm.Typical case's speed of cooling 70 DEG C/s.
The composition characteristic of above patent be carbon content more than 0.1%, and manganese content is higher.When carbon content higher than 0.1% time, the situation that column crystal grows fast is easily there is in process of setting, and the space between column crystal is larger, the molten steel of soluterich easily flow into column crystal gap, cause the aggravation of segregation, in addition Mn content is higher, segregation degree high and be difficult to eliminate, therefore all unfavorable for tissue, the homogeneity of performance and cold-bending property, microcosmic easily causes performance inconsistency and uneven, longitudinal bending performance is undesirable, and anisotropy is large, and the performance of anti-delayed fracture is undesirable.
Summary of the invention
The object of the present invention is to provide the above cold-rolled steel sheet of a kind of tensile strength 900MPa and manufacture method, designed by reasonable component design and processes, obtain the cold-bending property of more than tensile strength 900MPa and the cold rolling high strength steel of anti-delayed fracture excellent property, the feature of this steel is that fine microstructures is even, and cold-bending property is excellent; Meanwhile, the anti-delayed fracture excellent property of steel, makes it meet the requirement of car safety part and structural part manufacture.
For achieving the above object, technical scheme of the present invention is:
Draw point of the present invention requires higher problem to high-strength steel to local plasticity, by suitable Composition Design and technological design, under normal process conditions, just can obtain excellent combination mechanical property.Concrete measure is, by the appropriate design of carbon, silicon, manganese, boron, titanium, nitrogen, Ca, obtains desirable tissue and distribution of carbides, reduces segregation tendency, obtains desirable homogeneity of structure.Select lower carbon content scope, thus control the process of setting of steel, reduce the overgrowth of column crystal in casting cycle, reduce C, Mn, S, P segregation in steel, thus alleviate banded structure; Select lower Si content, be conducive to reducing the defects such as surface of steel plate red rust, adopt lower Fe content, reducing the machining stress of hot rolling, cold rolling process on the one hand, being conducive to the macrosegregation avoiding being difficult to eliminate, in order to make up the low deficiency of Mn content simultaneously, add certain B element to ensure hardening capacity, B is interstitial element, has good diffustivity, and its segregation is easier to eliminate or improve.Whole Composition Control is to reduce segregation, and reduction banded structure is main thought.The contents level controlling nitrogen, in higher scope, is added beyond the Ti of stoichiometric ratio simultaneously, ensures to generate enough TiN, as the trap of hydrogen invasion, avoids hydrogen to be gathered in tiny crack tip, alleviates hydrogen-induced delayed cracking.Low S design, adds Ca and improves inclusion shape, improve the detrimentally affect of inclusion to cold-bending property.The Ti simultaneously exceeding stoichiometric ratio separates out with the form of TiC, is conducive to thinning microstructure, improves homogeneity of structure.Hot rolling technology have employed higher finishing temperature and coiling temperature normally on the low side, can ensure homogeneous microstructure, again can crystal grain thinning; Can not be higher during annealing annealing holding temperature, and sufficient bag temperature time, to realize uniform composition as far as possible, avoid banded formation, be cooled to simultaneously more than 700 DEG C just just with high speed but to less than 200 DEG C, to avoid diffustivity segregation, obtain the tissue of even refinement simultaneously.The finished product carbon equivalent is low, surface quality is high, the cold-bending property simultaneously had and anti-delayed fracture performance.
Particularly, the above cold-rolled steel sheet of tensile strength 900MPa of the present invention, its composition by weight percent is:
C：0.06～0.095wt％，
Si：0.1～0.4wt％，
Mn：1.2～1.6wt％，
B：0.001～0.004％，
P：≤0.015wt％，
S：≤0.004wt％，
N：0.003～0.007wt％，
Nb：0.01～0.03wt％，
Ti：0.03～0.06％，
Al：0.015～0.045wt％，
Ca：0.002～0.007wt％，
Surplus is Fe and inevitable impurity.
Preferably, its composition by weight percent is: C:0.07 ~ 0.09wt%, Si:0.15 ~ 0.35wt%, Mn:1.2 ~ 1.6wt%, B:0.002 ~ 0.004%, P :≤0.01wt%, S :≤0.002wt%, N:0.0035 ~ 0.0055wt%, Nb:0.01 ~ 0.03wt%, Ti:0.035 ~ 0.05%, Al:0.02 ~ 0.04wt%, Ca:0.003 ~ 0.006wt%.
In the Composition Design of steel of the present invention:
C: affect martensitic hardness and content is very large to intensity effect.Carbon content high unfavorable to weldability while casting cycle in column crystal easily grow up, cause intercrystalline segregation.The present invention selects carbon content between 0.06-0.095wt%, effectively can avoid the hypertrophy of column crystal, if carbon content is lower than 0.06%, and insufficient strength; If higher than 0.095%, column crystal is flourishing, not easily the shaft-like ferrite crystal grain such as formation.
Si: play the effect improving unit elongation in steel.Si is also very large to the tissue effect of steel.Si easily forms oxide film at surface enrichment.The span of control of Si is 0.1-0.4%, if higher than 0.4%, easily affects surface quality.
Mn: the hardening capacity that can improve steel, effectively improve the intensity of steel, Mn is segregation in steel, is easily rolled into the Mn enrichment region of the distribution that becomes band in the hot rolling, forms banded structure, be unfavorable for cold-bending property.The content choosing Mn is 1.2-1.6%, coordinates low-carbon (LC) design, greatly improves the generation of banded structure.
B: the hardening capacity that can improve steel, effectively improves the intensity of steel; When not adding Mo, add B 0.002-0.004%, lower than the B of 0.002%, insufficient strength, higher higher than the B intensity of 0.004%.
P: be impurity element in steel, requirement≤0.015wt%.
S: be impurity element in steel, forms MnS and has a strong impact on hole expansibility, require≤0.004%.
Al: the effect serving desoxydatoin and crystal grain thinning in steel, requires Al:0.015-0.045wt%.
N: generate TiN, TiN in steel as hydrogen trap, can being formed a certain amount of rear beneficial to improving hydrogen-induced delayed cracking, requiring 0.003-0.007wt% with Ti reaction.It is not obvious, too high unfavorable to clod wash that too low TiN separates out the effect improving delayed fracture less.
Ti:0.02-0.045%, plays the effect of fixed nitrogen element and crystal grain thinning.
Nb: be precipitation strength element, play the effect of adjusting strength, requires to be distributed between 0.01-0.03wt%.
Ca: to MnS modification, makes it to form dispersion and short inclusion, is conducive to improving cold-bending property.The addition of Ca should ensure Ca/S >=1.5.
The compound action that present component is designed to multiple element produces useful effect jointly.In raising cold-bending property, designed by low-carbon (LC), be aided with manganese, the compound of boron adds, and Ca process and microalloy crystal grain thinning.Adopt lower carbon, and adopt rational continuous casting process for cooling, the growth of column crystal in casting cycle can be reduced, finally obtain the cast structure of the carbide of granular ferrite+Dispersed precipitate.Because carbide becomes the small-particle of Dispersed precipitate to be distributed on ferrite matrix, therefore effectively alleviate C, Mn segregation in steel, thus alleviate banded structure; The banded martensitic stucture of continuous distribution can be avoided the formation of.In hardenability element, adopt lower Fe content, be aided with the good B of diffustivity, be conducive to alleviating segregation and eliminating the macrosegregation being difficult to eliminate.Adopt low S to design, add Ca and improve inclusion shape.Alleviate the detrimentally affect of inclusion to cold-bending property.
In the improvement of delayed fracture performance, adopt low-carbon (LC) design on the one hand, can reduce the martensitic hardness of formation, improve the intensity of steel by improving martensite volume, the supression effect of softer martensite On Crack Propagation is better.Meanwhile, because the segregation of steel is comparatively slight, in steel, the component segregation district of rich carbon and rich Mn is less, can not form the martensitic phase of high rigidity, therefore, further increases the anti-delayed fracture performance of steel.Be added beyond the Ti of stoichiometric ratio simultaneously, ensure to generate enough TiN, as the trap of hydrogen invasion, avoid hydrogen to be gathered in tiny crack tip, alleviate hydrogen-induced delayed cracking.The Ti simultaneously exceeding stoichiometric ratio separates out with the form of TiC, is conducive to thinning microstructure, improves homogeneity of structure.
The manufacture method of the above cold-rolled steel sheet of tensile strength 900MPa of the present invention, it comprises the steps:
1) smelt, smelt by mentioned component, deeply de-S, converter adds refining, is controlled by S below 0.004%, reduces MnS and is mingled with;
2) continuous casting, the pulling speed of continuous casting of 0.9 ~ 1.4 m/min, contributes to inclusion floating and reduces segregation;
3) hot rolling, hot rolling after being heated to 1200 ~ 1280 DEG C, finishing temperature 840 ~ 940 DEG C, rolls rear quick cooling, speed of cooling 15 ~ 40 DEG C/s, is cooled to batch between 500 ~ 620 DEG C;
4) cold rolling, 40 ~ 65% drafts;
5) anneal, 830 ~ 860 DEG C of insulations, insulation 60 ~ 200s; 5 ~ 10 DEG C/s is cooled to, between 700 ~ 750 DEG C, be cooled to less than 300 DEG C in the mode of water-cooled, then after 200 ~ 300 DEG C of tempering 100 ~ 400s, more smooth through 0.1 ~ 0.3%.
Further, described pulling speed of continuous casting is 1 ~ 1.2 m/min.
Again, in described hot-rolled step, be heated to 1220 ~ 1260 DEG C, finishing temperature 860 ~ 920 DEG C, roll rear evenly cooling fast, speed of cooling 20 ~ 40 DEG C/s, is cooled to batch between 520 ~ 600 DEG C.
In addition, in described annealing process, holding temperature 840 ~ 860 DEG C, insulation 80 ~ 100s; 5 ~ 10 DEG C/s is cooled to, between 720 ~ 750 DEG C, be cooled to less than 200 DEG C in the mode of water-cooled, then after 200 ~ 300 DEG C of tempering 100 ~ 400s, more smooth through 0.1 ~ 0.3%.
Beneficial effect of the present invention:
The raising of feature mainly for cold-bending property of steel of the present invention and improvement two aspects of anti-delayed fracture performance.Designed by low-carbon (LC), be aided with manganese, the compound of boron adds, and Ca process and microalloy crystal grain thinning, and effectively alleviate C, Mn segregation in steel, alleviate banded structure, while inclusion shape improve, thus improve the cold-bending property of steel.
In addition, by adopting low-carbon (LC) design, can reduce the martensitic hardness of formation, the supression effect of softer martensite On Crack Propagation is better.Meanwhile, because the segregation of steel is comparatively slight, the martensitic phase of extreme hardness can not be formed, therefore, favourable to the anti-delayed fracture performance of raising.Be added beyond the Ti of stoichiometric ratio simultaneously, ensure to generate enough TiN, as the trap of hydrogen invasion, avoid hydrogen to be gathered in tiny crack tip, alleviate hydrogen-induced delayed cracking.
In addition, hot rolling technology of the present invention have employed higher finishing temperature and lower coiling temperature, can ensure homogeneous microstructure, again can crystal grain thinning; By higher annealing holding temperature during annealing, and sufficient soaking time, to realize uniform composition as far as possible, avoid banded formation.In the tissue of steel of the present invention, martensite is evenly distributed, and banded structure is slight, and the amount of inclusions is few and be evenly distributed; Can produce the high-strength steel of more than intensity 900MPa according to the present invention, cold-bending property is good, anti-delayed fracture excellent property, and meanwhile, carbon equivalent is low, and be conducive to welding, surface quality is good.High-strength steel balancing performance of the present invention is stablized, and can adapt to the needs that automobile component manufacture well.
Embodiment
Below in conjunction with embodiment, the present invention will be further described.
The chemical composition that table 1 is steel embodiment of the present invention.The technique that table 2 is steel of the present invention.Table 3 for steel of the present invention through smeltings, hot rolling, cold rolling, anneal and smooth after the Performance Strength that obtains.As can be seen from Table 3, can produce the high strength dual phase steel of more than intensity 900MPa according to the present invention, its cold-bending property is good.Adopt its delayed fracture characteristic of the curved test of U, specimen size is the rectangular specimen U bend diameter of 150mm × 20mm is 80mm, is curved by sample U-shaped, and fixes with bolt.The HCl solution of preparation 5%, at room temperature immerses solution by sample, record sample crackle crack initiation time and rupture time.
Compared steel 1 takes from commercially available conventional 1000MPa high-strength steel, compared steel 2 for intensity be the steel not having delayed fracture to be inclined to of 600MPa.Compared steel 1 can meet service requirements substantially, may there is the tendency of delayed fracture; And compared steel 2 intensity is low, do not have delayed fracture to be inclined to, choose as contrast delayed fracture characteristic of the present invention.Can see that steel of the present invention is obviously better than compared steel 1 in the performance of delayed fracture simulation test, reach the level equal with compared steel 2, show the high-strength steel of the present invention relative to same intensity rank, its delayed fracture characteristic has larger improvement, close to the low strength rank steel grade not having delayed fracture to be inclined to.
Table 1 unit: wt%
Table 2
Table 3
Claims (6)
1. the above cold-rolled steel sheet of tensile strength 900MPa, its composition by weight percent is:
C：0.06～0.095wt％，
Si：0.1～0.4wt％，
Mn：1.2～1.6wt％，
B：0.001～0.004％，
P：≤0.015wt％，
S：≤0.004wt％，
N：0.003～0.007wt％，
Nb：0.01～0.03wt％，
Ti：0.03～0.06％，
Al：0.015～0.045wt％，
Ca：0.002～0.007wt％，
Surplus is Fe and inevitable impurity.
2. the above cold-rolled steel sheet of tensile strength 900MPa as claimed in claim 1, it is characterized in that, its composition by weight percent is preferably C:0.07 ~ 0.09wt%, Si:0.15 ~ 0.35wt%, Mn:1.2 ~ 1.6wt%, B:0.002 ~ 0.004%, P :≤0.01wt%, S :≤0.002wt%, N:0.0035 ~ 0.0055wt%, Nb:0.01 ~ 0.03wt%, Ti:0.035 ~ 0.05%, Al:0.02 ~ 0.04wt%, Ca:0.003 ~ 0.006wt%.
3. the manufacture method of the above cold-rolled steel sheet of tensile strength 900MPa as claimed in claim 1 or 2, it comprises the steps:
1) smelt, smelt by mentioned component, deeply de-S, converter adds refining, is controlled by S below 0.004%, reduces MnS and is mingled with;
2) continuous casting, the pulling speed of continuous casting of 0.9 ~ 1.4 m/min, contributes to inclusion floating and reduces segregation;
3) hot rolling, hot rolling after being heated to 1200 ~ 1280 DEG C, finishing temperature 840 ~ 940 DEG C, rolls rear quick cooling, speed of cooling 15 ~ 40 DEG C/s, is cooled to batch between 500 ~ 620 DEG C;
4) cold rolling, 40 ~ 65% drafts;
5) anneal, 830 ~ 860 DEG C of insulations, insulation 60 ~ 200s; 5 ~ 10 DEG C/s is cooled to, between 700 ~ 750 DEG C, be cooled to less than 300 DEG C in the mode of water-cooled, then after 200 ~ 300 DEG C of tempering 100 ~ 400s, more smooth through 0.1 ~ 0.3%.
4. the manufacture method of the above cold-rolled steel sheet of tensile strength 900MPa as claimed in claim 3, it is characterized in that, described pulling speed of continuous casting is 1 ~ 1.2 m/min.
5. the manufacture method of the above cold-rolled steel sheet of tensile strength 900MPa as claimed in claim 3, it is characterized in that, in described hot-rolled step, be heated to 1220 ~ 1260 DEG C, finishing temperature 860 ~ 920 DEG C, roll rear evenly cooling fast, speed of cooling 20 ~ 40 DEG C/s, is cooled to batch between 520 ~ 600 DEG C.
6. the manufacture method of the above cold-rolled steel sheet of tensile strength 900MPa as claimed in claim 3, is characterized in that, in described annealing process, and holding temperature 840 ~ 860 DEG C, insulation 80 ~ 100s; 5 ~ 10 DEG C/s is cooled to, between 720 ~ 750 DEG C, be cooled to less than 200 DEG C in the mode of water-cooled, then after 200 ~ 300 DEG C of tempering 100 ~ 400s, more smooth through 0.1 ~ 0.3%.
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| CN102747280B (en) * | 2012-07-31 | 2014-10-01 | 宝山钢铁股份有限公司 | Wear resistant steel plate with high intensity and high toughness and production method thereof |
| CN107699791B (en) * | 2017-09-28 | 2019-05-03 | 邯郸钢铁集团有限责任公司 | 900MPa grades high cold-bending property low alloy high strength steel plate and preparation method thereof |
| CN111218620B (en) * | 2018-11-23 | 2021-10-22 | 宝山钢铁股份有限公司 | High-yield-ratio cold-rolled dual-phase steel and manufacturing method thereof |
| CN117660829A (en) * | 2022-08-23 | 2024-03-08 | 宝山钢铁股份有限公司 | 60 kg-level cold-rolled low-alloy annealed dual-phase steel and manufacturing method thereof |
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| CN1788099A (en) * | 2003-06-19 | 2006-06-14 | 新日本制铁株式会社 | High strength steel plate excellent in formability and method for production thereof |
| CN101851732A (en) * | 2009-03-31 | 2010-10-06 | 株式会社神户制钢所 | The high strength cold rolled steel plate of excellent in bending workability |
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| CN1788099A (en) * | 2003-06-19 | 2006-06-14 | 新日本制铁株式会社 | High strength steel plate excellent in formability and method for production thereof |
| CN101851732A (en) * | 2009-03-31 | 2010-10-06 | 株式会社神户制钢所 | The high strength cold rolled steel plate of excellent in bending workability |
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