CN117305724A - High-elongation high-reaming-performance cold-rolled steel plate with more than 1300MPa and manufacturing method thereof - Google Patents
High-elongation high-reaming-performance cold-rolled steel plate with more than 1300MPa and manufacturing method thereof Download PDFInfo
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 67
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 31
- 238000004321 preservation Methods 0.000 claims abstract description 33
- 238000000137 annealing Methods 0.000 claims abstract description 30
- 238000001816 cooling Methods 0.000 claims abstract description 24
- 239000002244 precipitate Substances 0.000 claims abstract description 16
- 239000012535 impurity Substances 0.000 claims abstract description 15
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 12
- 229910052729 chemical element Inorganic materials 0.000 claims abstract description 9
- 238000005098 hot rolling Methods 0.000 claims abstract description 9
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 9
- 229910052796 boron Inorganic materials 0.000 claims abstract description 8
- 238000005097 cold rolling Methods 0.000 claims abstract description 7
- 238000005266 casting Methods 0.000 claims abstract description 5
- 238000003723 Smelting Methods 0.000 claims abstract description 4
- 229910000831 Steel Inorganic materials 0.000 claims description 74
- 239000010959 steel Substances 0.000 claims description 74
- 229910000734 martensite Inorganic materials 0.000 claims description 27
- 238000000034 method Methods 0.000 claims description 27
- 229910001566 austenite Inorganic materials 0.000 claims description 19
- 229910001563 bainite Inorganic materials 0.000 claims description 14
- 238000002791 soaking Methods 0.000 claims description 11
- 230000000717 retained effect Effects 0.000 claims description 8
- 230000009467 reduction Effects 0.000 claims description 4
- 229910052717 sulfur Inorganic materials 0.000 claims description 4
- 238000005096 rolling process Methods 0.000 claims description 3
- 230000008569 process Effects 0.000 description 18
- 238000013461 design Methods 0.000 description 14
- 229910000797 Ultra-high-strength steel Inorganic materials 0.000 description 6
- 238000012360 testing method Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 5
- 239000000126 substance Substances 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- 230000009286 beneficial effect Effects 0.000 description 4
- 238000010438 heat treatment Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 230000009466 transformation Effects 0.000 description 4
- 239000000203 mixture Substances 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- AJHQUQJABBRDOW-UHFFFAOYSA-N [Nb].[La] Chemical compound [Nb].[La] AJHQUQJABBRDOW-UHFFFAOYSA-N 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000004134 energy conservation Methods 0.000 description 2
- 229910052746 lanthanum Inorganic materials 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- 229910052758 niobium Inorganic materials 0.000 description 2
- 239000010955 niobium Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 238000010998 test method Methods 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910000885 Dual-phase steel Inorganic materials 0.000 description 1
- 238000005299 abrasion Methods 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005279 austempering Methods 0.000 description 1
- 229910052793 cadmium Inorganic materials 0.000 description 1
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000012938 design process Methods 0.000 description 1
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- 238000009826 distribution Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 description 1
- 238000003754 machining Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- GUCVJGMIXFAOAE-UHFFFAOYSA-N niobium atom Chemical compound [Nb] GUCVJGMIXFAOAE-UHFFFAOYSA-N 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000007493 shaping process Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 238000005496 tempering Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
- C21D1/20—Isothermal quenching, e.g. bainitic hardening
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/002—Bainite
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/008—Martensite
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
The invention discloses a high-elongation high-hole-expansion-performance cold-rolled steel plate with the diameter of more than 1300MPa, which contains Fe and unavoidable impurity elements, and also contains the following chemical elements in percentage by mass: c:0.15 to 0.30 percent, si:0.3 to 0.5 percent, mn:1.8 to 2.5 percent of Al:0.01% -0.03%, B:0.001-0.003%; ti:0 to 0.05 percent; and the mass percentages of C and Mn are as follows: C+Mn/6 is more than or equal to 0.52; wherein the microstructure of the cold-rolled steel sheet has nano-precipitates having an average diameter of less than 30 nm. In addition, the invention also discloses a manufacturing method of the cold-rolled steel plate with the grade of more than 1300MPa, which comprises the following steps: (1) smelting and casting; (2) hot rolling; (3) annealing the hot coil heat-preserving cover; (4) cold rolling; (5) annealing; (6) isothermal heat preservation treatment; (7) cooling; (8) flattening.
Description
Technical Field
The present invention relates to a steel material and a method for manufacturing the same, and more particularly, to a cold-rolled steel sheet and a method for manufacturing the same.
Background
In recent years, with the increase in global energy crisis and environmental problems, "energy conservation" and "safety" have become the main development directions of the automobile manufacturing industry. The light weight design is adopted to reduce the weight of the automobile, so that the automobile is one of important measures for energy conservation and emission reduction.
In recent years, the ultra-high strength steel is very common in the automobile industry, has good mechanical properties and usability, can be used for manufacturing automobile structural parts, and realizes the light weight of the parts, thereby effectively reducing the weight of the automobile.
In the current automotive industry, the ultra-high strength steel family for automobiles is of a wide variety, which may generally include: dual phase steel, quenched ductile steel, bainitic steel, and complex phase steel. Among them, dual phase steels and quenched ductile steels have good strength and plasticity, but their hole expansion ratio (about 20% -35%) is far lower than that of conventional soft steels for automobiles; while bainitic steels and complex phase steels have a high hole expansion ratio, their elongation is too low. Therefore, in order to meet the more diversified market demands, it is necessary to develop an ultra-high strength cold-rolled steel sheet having both high elongation and high hole expansion properties.
Therefore, aiming at the technical problems of the existing ultra-high strength steel, the invention expects to obtain the cold-rolled steel plate with high extension and high reaming performance and higher than 1300MPa, so as to ensure excellent formability while obtaining ultra-high strength.
In the prior art, although some researchers develop ultra-high strength steel materials, all the technical schemes cannot obtain the corresponding high extension and high reaming performance of the steel plate.
For example: the Chinese patent literature with publication number of CN104451436A and publication date of 2015 of 3 months and 25 days, named as "bainite-martensite-austenite complex phase wear-resistant steel plate and manufacturing method", discloses a bainite-martensite-austenite complex phase wear-resistant steel plate and manufacturing method, wherein the chemical composition of the steel plate comprises the following components in percentage by weight: c:0.20-0.40; mn:0.30-1.50; si:0.80-1.20; cr:0.60-1.00; ni:0.20-0.60; mo:0.20-0.40; cu:0.20-0.50; b:0.0005-0.003; s is less than or equal to 0.010, P is less than or equal to 0.015, and the balance is Fe and unavoidable impurity elements. The rolled material can obtain a bainite-martensite-retained austenite complex phase structure, the volume fraction of the retained austenite is 5-15%, the yield strength of the material is more than 1000MPa, the tensile strength is more than 1300MPa, the elongation is more than 15%, the hardness HB420-500, and the machining performance and the welding performance meet the equipment manufacturing requirement; the abrasion resistance of the abrasive particles reaches more than 1.3 times of Hardox450, and reaches more than 1.5 times of Hardox450 under the working condition of weak acid environment. In this technical solution, by adding high Si and Al, sufficient residual austenite is obtained, the TRIP effect of the retained austenite is used to obtain a high elongation, and the reaming performance of the steel is not considered, which is different from the design thought of the patent.
Also for example: the Chinese patent literature with publication number of CN102776438A and publication date of 2012 of 11 months of 14 days is entitled "a niobium-lanthanum microalloyed Mn-B series ultra-high strength steel plate and heat treatment process thereof", discloses a niobium-lanthanum microalloyed Mn-B series ultra-high strength steel plate and heat treatment process thereof, wherein the steel plate comprises the following chemical components in percentage by weight: 0.14 to 0.35 percent of C, 1.5 to 2.0 percent of Mn, 0.6 to 1.0 percent of Si, less than or equal to 0.015 percent of P, less than or equal to 0.002 percent of S, 0.01 to 0.06 percent of Nb, 0.0005 to 0.0040 percent of B, 0.001 to 0.5 percent of La, and the balance of Fe and unavoidable impurities. In the technical scheme, the adopted heat treatment process system is as follows: austenitizing at 880-940 deg.c for 0.5-5 hr and water quenching; tempering temperature is 190-250 ℃, and heat preservation time is 1-15 hours. In the technical scheme of the patent, the designed steel plate has excellent mechanical properties, the tensile strength reaches 1200-1400MPa, the yield strength is 1000-1300MPa, the elongation is 6-15%, and the steel plate has the characteristics of low production cost and capability of industrially producing steel plates with thickness of 5-25 mm.
For another example: the Chinese patent document with publication number of CN102321841A and publication date of 2012 of 1 month and 18 days, named as "steel for track shoes with tensile strength reaching 1300MPa and manufacturing method thereof", discloses steel for track shoes with tensile strength reaching 1300MPa and manufacturing method thereof, wherein the steel comprises the following chemical components in percentage by weight: 0.20 to 0.30 percent of Mn:0.80 to 1.40 percent of Si:0.15 to 0.35 percent, P:0 to 0.015 percent, S:0 to 0.016 percent, cr:0 to 0.30 percent of Ni:0 to 0.25 percent, cu:0 to 0.30 percent of Ti:0.01 to 0.02 percent of Al:0.02 to 0.06 percent, B:0.0005 to 0.0035 percent, and the balance of Fe and unavoidable impurity elements. The steel designed by the technical scheme has the tensile strength of more than 1340MPa, the elongation after breaking of less than 12 percent, the U-shaped notch impact absorption power of more than 72J, high strength, few quenching cracks and internal cracks and long service life.
The ultra-high strength steels disclosed in the above patent documents CN102776438A and CN102321841a respectively obtain good mechanical properties by adding micro-alloy elements such as niobium, lanthanum, nickel, cadmium, copper, etc., and the properties of the finally prepared steel sheet cannot reach the high-elongation and high-reaming performance indexes covered by the present invention.
Disclosure of Invention
The invention aims to provide a 1300MPa or higher cold-rolled steel plate with high extension and high reaming performance, which adopts reasonable chemical composition design and manufacturing process, has ultrahigh strength and high extension and high reaming performance, has excellent forming performance, can be effectively applied to the automobile industry, and has very wide application prospect.
In order to achieve the above object, the present invention provides a cold rolled steel sheet with high elongation and high hole expansion performance, which comprises Fe and unavoidable impurity elements, and further comprises the following chemical elements in percentage by mass:
C：0.15％～0.30％，Si：0.3％～0.5％，Mn：1.8％～2.5％，Al：0.01％～0.03％，B：0.001-0.003％；Ti：0～0.05％；
and the mass percentages of C and Mn are as follows: C+Mn/6 is more than or equal to 0.52%;
wherein the microstructure of the cold-rolled steel sheet has nano-precipitates having an average diameter of less than 30 nm.
Further, in the cold-rolled steel sheet with the grade of more than 1300MPa, the mass percentage of each chemical element is as follows:
c:0.15 to 0.30 percent, si:0.3 to 0.5 percent, mn:1.8 to 2.5 percent of Al:0.01% -0.03%, B:0.001-0.003%; ti:0 to 0.05 percent, and the balance of Fe and other unavoidable impurities;
and the mass percentages of C and Mn are as follows: C+Mn/6 is more than or equal to 0.52%;
wherein the microstructure of the cold-rolled steel sheet has nano-precipitates having an average diameter of less than 30 nm.
In the cold-rolled steel sheet with the grade of more than 1300MPa, the design principle of each chemical element is specifically as follows:
c: in the cold-rolled steel sheet with the grade of more than 1300MPa, the addition of the element C not only can improve the strength of the steel, but also can ensure the occurrence of martensitic transformation. The inventor researches find that when the mass percent of the C element in the steel is lower than 0.15%, the strength of the steel plate is affected, and the formation amount and stability of the residual austenite are not facilitated; when the content of C element in steel is more than 0.30% by mass, the martensite hardness is easily excessively high, and the grain size is coarse, which is disadvantageous to the formability of the steel sheet. Therefore, in the cold-rolled steel sheet with the pressure of more than 1300MPa, the mass percent of the C element is controlled to be between 0.15 and 0.30 percent in consideration of the influence of the C element content on the steel performance.
Si: in the cold-rolled steel sheet with the grade above 1300MPa, si element can play a solid solution strengthening role, and in the cold-rolled steel sheet with the grade above 1300MPa, the mass percentage of the Si element is controlled to be between 0.3 and 0.5 percent.
Mn: in the cold-rolled steel sheet with the grade of more than 1300MPa, mn element is added, so that the hardenability of the steel can be improved, and the strength of the steel sheet can be effectively improved. The mass percentage of Mn in the selected steel is between 1.8 and 2.5 percent because: according to the invention, a large amount of carbide is generated during hot rolling to cause insufficient carbon equivalent of a matrix structure, when the mass percentage of Mn in steel is lower than 1.8%, the insufficient carbon equivalent can cause insufficient hardenability of the prepared steel, enough martensite cannot be generated during annealing, and the strength of the steel plate is insufficient; when the mass percentage of Mn element in the steel is higher than 2.5%, the carbon equivalent is remarkably improved, which has negative effects on the welding performance and delayed cracking resistance of the steel. Therefore, considering the influence of the Mn element content on the steel performance, in the 1300MPa or above grade cold-rolled steel sheet, the mass percent of the Mn element is controlled to be between 1.8 and 2.5 percent.
Al: in the cold-rolled steel sheet with the grade of more than 1300MPa, proper amount of Al element is added into the steel to play a role in deoxidizing and refining grains. Therefore, in order to exert the beneficial effects of the Al element, the mass percentage of the Al element is controlled to be between 0.01 and 0.03 percent in the invention.
B: in the 1300MPa or above grade cold-rolled steel sheet, B is an element capable of remarkably improving the hardenability of steel, and the addition of B element can promote the formation of martensite and ensure the strength of martensitic steel. However, it should be noted that the B element content in the steel is not too high, and if more B is added after the grain boundary defect is filled, the plasticity of the steel is lowered due to the precipitation of the "boron phase" at the grain boundary. The inventors have found that when the content of the B element in the steel is less than 0.001%, the effect of the B element cannot be effectively exerted, and when the content of the B element in the steel is more than 0.003%, the shaping of the steel is adversely affected. Therefore, in the 1300MPa or higher grade cold-rolled steel sheet according to the present invention, the mass percentage of B element is controlled to be 0.001-0.003% in consideration of the influence of B element content on the steel properties.
Ti: in the 1300MPa or above grade cold-rolled steel sheet, the added strong carbide forming element Ti can show a strong effect of inhibiting the growth of austenite grains at high temperature, and meanwhile, the addition of the Ti element into the steel is also beneficial to grain refinement. Therefore, in order to exert the beneficial effects of the Ti element, the mass percentage of the Ti element is controlled to be between 0 and 0.05 percent in the invention.
In addition, it should be noted that, in order to ensure that the strength of the steel is greater than 1300MPa, in the cold-rolled steel sheet with the grade above 1300MPa designed by the invention, the inventor controls the mass percentage content of a single chemical element, and simultaneously further controls the mass percentage content of C, mn element in the steel to satisfy the following conditions: C+Mn/6 is more than or equal to 0.52 percent.
Further, in the cold-rolled steel sheet with the grade of more than 1300MPa, among unavoidable impurities, P is less than or equal to 0.015%, S is less than or equal to 0.003%, and N is less than or equal to 0.006%.
In the 1300MPa or above grade cold-rolled steel plate, the P element, the S element and the N element are all impurity elements in steel, and the content of the impurity elements in the steel is reduced as far as possible under the condition of technical conditions, so as to obtain the steel with better performance and better quality. Therefore, except special requirements, the content of the P element in the steel is reduced as much as possible, and the mass percent of the P element is controlled to be less than or equal to 0.015 percent.
In addition, the MnS formed by the combination of the impurity element S can seriously affect the forming performance of the steel, so that the mass percent of the S element in the steel is required to be strictly controlled to be less than or equal to 0.003 percent. In addition, since the impurity element N easily causes cracks or bubbles to occur on the surface of the slab, in the present invention, the mass percentage of the N element is controlled to satisfy N.ltoreq.0.006%.
Further, in the 1300MPa or higher cold-rolled steel sheet, the microstructure is retained austenite, fine massive martensite and bainite, and the nano precipitates.
Further, in the cold-rolled steel sheet of 1300MPa or above, the volume phase proportion of martensite is more than or equal to 55%, and the volume phase proportion of bainite is more than 0 and less than 15%.
Further, in the 1300MPa or higher cold-rolled steel sheet according to the present invention, the diameter of the martensite is not more than 10. Mu.m.
In the invention, the components of the steel design are a component system taking C+Mn+B as a main component, and the volume phase proportion of martensite can be ensured to be more than 55% through the matching design of elements C, mn and B. Meanwhile, the bainitic curve is ensured to move left, the ferrite and pearlite C curve is ensured to move right, a certain volume fraction of the bainitic is ensured to be obtained in the final microstructure, and the volume phase proportion of the bainitic is less than 15%.
It should be noted that, in the present invention, through reasonable design of the alloy elements and the manufacturing process, the present invention can specifically obtain: the microstructure of retained austenite + fine bulk martensite (the diameter of bulk martensite is not more than 10 microns) +bainite + nano precipitates, and the average diameter of the nano precipitates is less than 30nm, and the microstructure determines that the cold-rolled steel plate has good elongation and hole expansion rate.
Further, in the cold-rolled steel sheet of 1300MPa or more according to the present invention, the properties thereof satisfy:
when the tensile strength is 1300-1400MPa, the elongation is more than 10%, and the hole expansion rate is more than 40%; when the tensile strength is more than 1400 and less than or equal to 1500MPa, the elongation is more than 9 percent, and the reaming ratio is more than 40 percent; when the tensile strength is above 1500MPa, the elongation is more than 8%, and the hole expansion rate is more than 40%.
Accordingly, another object of the present invention is to provide a method for manufacturing the above 1300MPa or higher cold-rolled steel sheet, which optimizes the manufacturing process, and the 1300MPa or higher cold-rolled steel sheet manufactured by the manufacturing method has excellent elongation and high hole expansion properties while having ultra-high strength.
In order to achieve the above object, the present invention provides a method for manufacturing a 1300MPa or higher cold-rolled steel sheet, comprising the steps of:
(1) Smelting and casting;
(2) Hot rolling;
(3) Annealing the hot coil heat preservation cover: rapidly annealing by adopting a heat preservation cover after coiling, wherein the annealing time is 0.5-6 hours, and the temperature drop per hour is less than 6 ℃;
(4) Cold rolling;
(5) Annealing: controlling the annealing soaking temperature to be 830-860 ℃ and the heat preservation time to be 40-80s, and then cooling to 730-780 ℃ at the cooling speed of 5-15 ℃/s; then cooling to isothermal heat preservation temperature at the speed of 50-700 ℃/s;
(6) Isothermal heat preservation treatment: the heat preservation temperature is 400-550 ℃, and the heat preservation time is 100-300s;
(7) Cooling; cooling to room temperature at a rate of 30 ℃/s to 100 ℃/s;
(8) Leveling.
In the technical scheme designed by the invention, the inventor performs optimal design on the manufacturing process, and improves the process flow.
In the invention, the rapid adoption of heat preservation cover annealing after hot coil coiling is one of the unique innovation points of the inventor, and based on reasonable components and process design, in the process of the step (3), steel is subjected to heat preservation annealing at a lower temperature for a long time, so that nano precipitates epsilon carbide with fine dispersion distribution can be generated. Then, fine dispersed epsilon carbides can be further inherited into the final continuously annealed finished steel sheet through reasonable process design. The carbide which is dispersed and precipitated not only can improve the overall strength, reduce the strength difference between each phase and the strength difference between the grain boundary and the crystal, but also can strengthen the grain boundary in the deformation process, thereby playing the double roles of improving the strength and the hole expansion rate of the steel.
In addition, in the above-described aspect of the present invention, in the annealing step of step (5), the annealing soaking temperature is defined to be between 830 and 860 ℃ because it is to be achieved that the soaking annealing is performed at the complete austenitizing temperature. When the annealing soaking temperature is lower than 830 ℃, sufficient tensile strength cannot be obtained by complete austenitization; when the annealing soaking temperature is higher than 860 ℃, the hole expansion rate of the steel is obviously and greatly reduced. Accordingly, in some preferred embodiments, it may be preferable to control the annealing soak temperature between 830-850 ℃, which ensures both complete austenitization and no coarsening of the grain size obtained, thereby retaining finely dispersed nano-precipitates with average sizes less than 30nm in the final microstructure.
In addition, the austenite isothermal heat preservation treatment process in the step (6) designed in the invention is another unique innovation point of the patent, the isothermal heat preservation treatment process is controlled above the bainite transformation ending temperature after annealing, the process determines the form and the size of the final martensite, and the process mainly comprises the following steps: soaking at full austenitizing temperature (i.e. soaking temperature of 830-860 ℃ for continuous annealing), rapid cooling (i.e. cooling to isothermal holding temperature at a speed of 50-700 ℃/s), holding the bainite transformation region (i.e. isothermal holding treatment, holding temperature of 400-550 ℃) and cooling at a controlled cooling speed. Part of bainite is obtained first in the austempering process, so that martensite which is generated later can be ensured to surround fine dispersed nucleation of bainite and not grow up severely, and fine massive martensite is finally formed.
In the cold-rolled steel plate designed by the invention, martensite in the final microstructure is tiny block-shaped martensite with the diameter not more than 10 microns, and the bainite in the steel can be controlled below 15% through reasonable process design, so that great influence on the strength of the steel is avoided. Accordingly, the subsequent process design by reasonably controlling the cooling speed ensures that not only the martensite structure with the volume phase proportion of more than or equal to 55 percent is generated, but also the austenite which is still partially not converted after the martensite phase transformation is kept in the form of residual austenite. The fine martensitic structure contributes to strength and elongation, while the retained austenite greatly increases elongation by TRIP effect.
In the manufacturing method of the present invention, the isothermal holding temperature and isothermal holding time of each specific component need to be specifically set according to the dynamic CCT curve.
In the step (6) designed by the invention, the isothermal heat preservation temperature is controlled to be 400-550 ℃ and the heat preservation time is 100-300s. When the holding temperature is lower than 400 ℃ or the holding time is lower than 100 seconds, the generation of bainite is not facilitated, and the carbon enrichment of unconverted austenite to residual austenite is also not facilitated. And when the heat preservation temperature is higher than 550 ℃ or the heat preservation time is higher than 300s, the nano-precipitates generated by hot rolling cannot be ensured not to coarsen.
Further, in the manufacturing method of the invention, in the step (2), the temperature is firstly heated to 1100-1250 ℃, the heat is preserved for more than 0.5 hours, then the hot rolling is carried out at the temperature of more than Ar3, the rapid cooling is carried out at the speed of 30-80 ℃/s after the rolling, and the coiling temperature is controlled to be 150-250 ℃.
Further, in the manufacturing method according to the present invention, in the step (4), the cold rolling reduction is controlled to be 50 to 70%.
Further, in the manufacturing method of the present invention, in the step (5), the annealing soaking temperature is controlled to be 830-850 ℃.
Further, in the manufacturing method according to the present invention, in the step (8), the flatness ratio is controlled to be 0 to 0.3%.
Compared with the prior art, the cold-rolled steel sheet with the grade of more than 1300MPa and the manufacturing method thereof have the following advantages and beneficial effects:
the invention develops a novel cold-rolled steel plate with the thickness of more than 1300MPa and a manufacturing method thereof, and the cold-rolled steel plate with the thickness of more than 1300MPa with high extension and high reaming performance can be obtained through reasonable component matching and process design.
The cold-rolled steel plate with the pressure of above 1300MPa has excellent mechanical properties, and the microstructure of retained austenite, fine massive martensite, bainite and nano precipitates can ensure that the steel plate has excellent elongation, reaming performance and better formability. The performance of the cold-rolled steel plate designed by the invention meets the following conditions: when the tensile strength is 1300-1400MPa, the elongation is more than 10%, and the hole expansion rate is more than 40%; when the tensile strength is more than 1400 and less than or equal to 1500MPa, the elongation is more than 9 percent, and the reaming ratio is more than 40 percent; when the tensile strength is above 1500MPa, the elongation is more than 8%, the hole expansion rate is more than 40%, and the high-strength steel can be effectively applied to the automobile industry, and has good popularization prospect and application value.
Detailed Description
The cold rolled steel sheet with high elongation and high hole expansion properties of 1300MPa or more and the manufacturing method thereof, which are designed according to the present invention, will be further explained and illustrated with reference to specific examples, but the explanation and illustration do not constitute undue limitations on the technical solution of the present invention.
Examples 1 to 18
Table 1 shows the mass percentages of the respective chemical elements designed for the cold rolled steel sheets of 1300MPa or more of examples 1 to 18.
Table 1 (wt.%), the balance Fe and unavoidable impurities other than P, S, N
The cold-rolled steel plates with the pressure of above 1300MPa of the examples 1-18 are prepared by the following steps:
(1) Smelting and casting were performed according to the chemical compositions shown in table 1 to obtain a cast slab.
(2) And (3) hot rolling: for the obtained casting blank, heating to 1100-1250 ℃, preserving heat for more than 0.5 hours, hot rolling at the temperature of Ar3, rapidly cooling at the speed of 30-80 ℃/s after rolling, coiling after cooling to the coiling temperature, and controlling the coiling temperature to be 150-250 ℃.
(3) Annealing the hot coil heat preservation cover: and (3) rapidly annealing by adopting a heat preservation cover after coiling, and controlling the annealing time to be 0.5-6 hours, wherein the heat preservation cover utilizes the internal heat of a steel coil, and the temperature drop per hour is less than 6 ℃.
(4) Cold rolling: the cold rolling reduction rate is controlled to be 50-70%.
(5) Annealing: controlling the annealing soaking temperature to be 830-860 ℃, preferably 830-850 ℃, controlling the heat preservation time to be 40-80s, and then cooling to be 730-780 ℃ at a cooling speed of 5-15 ℃/s; then cooling to isothermal holding temperature at the speed of 50-700 ℃/s.
(6) Isothermal heat preservation treatment: and carrying out isothermal heat preservation treatment on the annealed steel plate, controlling the heat preservation temperature to be 400-550 ℃ and controlling the heat preservation time to be 100-300s.
(7) Cooling; and cooling the steel plate subjected to isothermal heat preservation to room temperature at a speed of 30 ℃/s-100 ℃/s.
(8) Leveling: the flatness is controlled to be 0-0.3%.
The chemical element components and the related process design of the cold-rolled steel sheet with the grade of more than 1300MPa of the embodiments 1-18 all meet the requirements of the design specification of the invention.
Specific process parameters of the 1300MPa or higher cold-rolled steel sheets of examples 1 to 18 in the above process steps are shown in tables 2 to 1 and 2 to 2.
Table 2-1.
Note that: in the above Table 2-1, examples 1-18 all employed hot rolling temperatures > Ar3, and Ar3 in each example was between 740-860℃within the scope of the claimed process.
Table 2-2.
In the present invention, the cold rolled steel sheets of 1300MPa or more of the final product examples 1 to 18 obtained through the above process steps (1) to (8) were sampled, and the microstructure of each example steel sheet was observed and analyzed, and it was observed that the microstructure of each cold rolled steel sheet of examples 1 to 18 had: retained austenite + fine bulk martensite + bainite + nano precipitates.
Furthermore, the inventors further analyzed the volume phase ratio of each component in the microstructure of 1300MPa or more grade cold rolled steel sheets of final examples 1-18, and examined the diameters of martensite and nano-precipitates, and the results of the relevant analysis and examination are shown in Table 3 below.
Table 3 shows the results of analysis and detection of the microstructure of 1300MPa or more cold-rolled steel sheets for examples 1 to 18.
Table 3.
It can be seen from analysis and examination that in the present invention, the volume phase ratio of martensite of the cold rolled steel sheet of 1300MPa or more of examples 1 to 18 is between 70 and 86%, the volume phase ratio of bainite is between 7 and 14%, the diameter of martensite is between 5.1 and 8.9 μm, and the average diameter of nano precipitates is between 15 and 28 nm.
Accordingly, after the above observation and analysis were completed, further prepared cold rolled steel sheets of 1300MPa or more of the final examples 1 to 18 were sampled, respectively, and the cold rolled steel sheet samples of each example were subjected to the relevant mechanical properties test to obtain the mechanical strength, elongation and hole expansion ratio thereof, and the obtained mechanical properties test results were listed in table 4.
The related mechanical property testing method is as follows:
tensile test: according to GB/T228 (tensile test of metallic materials, section 1: room temperature test method), a test was conducted to examine the yield strength, tensile strength and elongation of the 1300MPa or higher cold-rolled steel sheets of examples 1 to 18.
Hole expansion rate test: according to GB/T24524-2021 metal sheet and strip hole expansion test method, a detection test was conducted to detect the hole expansion rate of the 1300MPa or higher cold-rolled steel sheet of examples 1-18.
Table 4 shows the mechanical properties of the cold rolled steels of 1300MPa or more of examples 1-18.
Table 4.
As shown in Table 4, the cold rolled steel sheets of 1300MPa or more of examples 1 to 18 according to the present invention have excellent elongation and hole expansion properties while having ultra-high strength.
Referring to Table 4, it is apparent that the yield strength of the cold rolled steel sheet of 1300MPa or more prepared in examples 1 to 18 is 1067 to 1292MPa, the tensile strength is 1328 to 1552MPa, the elongation is 8.5 to 12.3%, and the hole expansion ratio is 43 to 54%.
And, in such examples 1 to 18 according to the present invention, when the tensile strength of the produced steel sheet is 1300 to 1400MPa (i.e., examples 4 to 6, examples 10 to 12), the elongation thereof is specifically 11.1 to 12.3%, and the hole expansion thereof is specifically 53 to 46%; when the tensile strength is more than 1400 and less than or equal to 1500MPa (namely, examples 1-3 and examples 16-18), the elongation is particularly between 9.1 and 9.7 percent, and the hole expansion rate is particularly between 46 and 55 percent; when the tensile strength is 1500MPa or more (i.e., examples 7 to 9, examples 13 to 15), the elongation thereof is specifically 8.5 to 9.7%, and the hole expansion thereof is specifically 47 to 50%.
It should be noted that the combination of the technical features in the present invention is not limited to the combination described in the claims or the combination described in the specific embodiments, and all the technical features described in the present invention may be freely combined or combined in any manner unless contradiction occurs between them.
It should also be noted that the above-recited embodiments are merely specific examples of the present invention. It is apparent that the present invention is not limited to the above embodiments, and similar changes or modifications will be apparent to those skilled in the art from the present disclosure, and it is intended to be within the scope of the present invention.
Claims (12)
1. A cold-rolled steel plate with high elongation and high hole expansion performance and more than 1300MPa contains Fe and unavoidable impurity elements, and is characterized by further comprising the following chemical elements in percentage by mass:
C：0.15％～0.30％，Si：0.3％～0.5％，Mn：1.8％～2.5％，Al：0.01％～0.03％，B：0.001-0.003％；Ti：0～0.05％；
and the mass percentages of C and Mn are as follows: C+Mn/6 is more than or equal to 0.52%;
wherein the microstructure of the cold-rolled steel sheet has nano-precipitates having an average diameter of less than 30 nm.
2. The cold-rolled steel sheet of 1300MPa or more according to claim 1, wherein the mass percentages of the chemical elements are:
c:0.15 to 0.30 percent, si:0.3 to 0.5 percent, mn:1.8 to 2.5 percent of Al:0.01% -0.03%, B:0.001-0.003%; ti:0 to 0.05 percent, and the balance of Fe and other unavoidable impurities;
and the mass percentages of C and Mn are as follows: C+Mn/6 is more than or equal to 0.52%;
wherein the microstructure of the cold-rolled steel sheet has nano-precipitates having an average diameter of less than 30 nm.
3. The cold-rolled steel sheet of 1300MPa or more as claimed in claim 1 or 2, wherein among the unavoidable impurities, P is 0.015% or less, S is 0.003% or less, and N is 0.006% or less.
4. The 1300MPa or higher cold-rolled steel sheet according to claim 1 or 2, wherein the microstructure is retained austenite+fine bulk martensite+bainite+the nano-precipitates.
5. The cold-rolled steel sheet of 1300MPa or more according to claim 4, wherein the volume phase ratio of martensite is not less than 55%, and the volume phase ratio of bainite is not less than 0% but less than 15%.
6. The 1300MPa or higher cold-rolled steel sheet according to claim 4, wherein the martensite has a diameter of not more than 10 μm.
7. The 1300MPa or higher cold-rolled steel sheet according to claim 1 or 2, characterized in that its properties satisfy:
when the tensile strength is 1300-1400MPa, the elongation is more than 10%, and the hole expansion rate is more than 40%;
when the tensile strength is more than 1400 and less than or equal to 1500MPa, the elongation is more than 9 percent, and the reaming ratio is more than 40 percent;
when the tensile strength is more than 1500MPa, the elongation is more than 8 percent, and the reaming ratio is more than 40 percent.
8. The method for manufacturing a 1300MPa or higher cold-rolled steel sheet according to any one of claims 1 to 7, comprising the steps of:
(1) Smelting and casting;
(2) Hot rolling;
(3) Annealing the hot coil heat preservation cover: rapidly annealing by adopting a heat preservation cover after coiling, wherein the annealing time is 0.5-6 hours, and the temperature drop per hour is less than 6 ℃;
(4) Cold rolling;
(5) Annealing: controlling the annealing soaking temperature to be 830-860 ℃ and the heat preservation time to be 40-80s, and then cooling to 730-780 ℃ at the cooling speed of 5-15 ℃/s; then cooling to isothermal heat preservation temperature at the speed of 50-700 ℃/s;
(6) Isothermal heat preservation treatment: the heat preservation temperature is 400-550 ℃, and the heat preservation time is 100-300s;
(7) Cooling; cooling to room temperature at a rate of 30 ℃/s to 100 ℃/s;
(8) Leveling.
9. The method according to claim 8, wherein in the step (2), the steel is heated to 1100 to 1250 ℃ and kept at the temperature for 0.5 hours or more, then hot rolled at a temperature of Ar3 or more, and after the rolling, the steel is rapidly cooled at a speed of 30 to 80 ℃/s, and the coiling temperature is controlled to 150 to 250 ℃.
10. The manufacturing method according to claim 8, wherein in the step (4), the cold rolling reduction is controlled to be 50 to 70%.
11. The method of manufacturing according to claim 8, wherein in step (5), the annealing soaking temperature is controlled to be 830 to 850 ℃.
12. The method according to claim 8, wherein in the step (8), the flatness is controlled to be 0 to 0.3%.
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| CN202210711333.XA CN117305724A (en) | 2022-06-22 | 2022-06-22 | High-elongation high-reaming-performance cold-rolled steel plate with more than 1300MPa and manufacturing method thereof |
| PCT/CN2023/101458 WO2023246798A1 (en) | 2022-06-22 | 2023-06-20 | 1,300-mpa-grade or more cold-rolled steel plate having high extension and high hole-expansion performance and manufacturing method therefor |
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| CN109628846B (en) * | 2018-12-20 | 2020-08-04 | 唐山钢铁集团有限责任公司 | 1300 MPa-grade ultrahigh-strength cold-rolled steel plate for automobiles and production method thereof |
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