WO2023246737A1 - 一种1300MPa以上级冷轧钢板及其制造方法 - Google Patents

一种1300MPa以上级冷轧钢板及其制造方法 Download PDF

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WO2023246737A1
WO2023246737A1 PCT/CN2023/101256 CN2023101256W WO2023246737A1 WO 2023246737 A1 WO2023246737 A1 WO 2023246737A1 CN 2023101256 W CN2023101256 W CN 2023101256W WO 2023246737 A1 WO2023246737 A1 WO 2023246737A1
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cold
rolled steel
steel plate
tensile strength
manufacturing
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French (fr)
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薛鹏
朱晓东
李伟
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Baoshan Iron and Steel Co Ltd
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Baoshan Iron and Steel Co Ltd
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Priority to EP23826384.2A priority Critical patent/EP4545665A4/en
Priority to JP2024575242A priority patent/JP2025521343A/ja
Publication of WO2023246737A1 publication Critical patent/WO2023246737A1/zh
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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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys 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
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0242—Flattening; Dressing; Flexing
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C21D2211/001—Austenite
    • 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

Definitions

  • the present invention relates to a steel material and a manufacturing method thereof, in particular to a cold-rolled steel plate and a manufacturing method thereof.
  • ultra-high-strength steel has good mechanical properties and usability. It can be used to manufacture automotive structural parts and achieve lightweight parts, thereby effectively reducing vehicle weight. In the current automobile industry, when actually preparing vehicles, the need for weight reduction and safety requires the use of higher strength steel plates. Among them, ultra-high-strength steel with a tensile strength of 1000 MPa and above has great potential for weight reduction and safety performance. It can be used in the manufacture of safety parts, reinforcement parts and structural parts, and has good promotion prospects.
  • high-strength steel with a tensile strength of more than 1000MPa naturally has the characteristics of stress corrosion cracking (delayed cracking).
  • This high-strength steel plate is prone to a slow cracking process under the action of stress and corrosive media.
  • the resulting Delayed cracking has caused considerable problems in the application of high-strength steel and greatly limited the application of ultra-high-strength steel.
  • delayed cracking refers to the problem that cracking does not occur when the part is made, but as time goes by, under the dual action of stress and corrosive media, stress corrosion cracking occurs, eventually leading to the failure of the part and the loss of safety protection.
  • the medium hydrogen plays a role in promoting the initiation and propagation of cracks.
  • Delayed cracking is the biggest risk in the application of advanced high-strength steels.
  • the public number is CN102822375A
  • the public date is December 12, 2012
  • the name is The Chinese patent document "Ultra-high-strength cold-rolled steel plate and its manufacturing method” discloses an ultra-high-strength cold-rolled steel plate and its manufacturing method, with C: 0.05-0.4%, Si ⁇ 2.0%, and Mn: 1.0-3.0 %, P ⁇ 0.05%, S ⁇ 0.02%, Al: 0.01-0.05%, N ⁇ 0.05%.
  • the cold-rolled steel plate needs to be cooled from Ac3 to the range of Ms point - Ms point + 200°C at a cooling rate of 20°C/s or more (gas cooling).
  • the above cooling rate water cooling is used to cool to below 100°C to obtain high-strength steel with a tensile strength of 1320MPa or above, and the flatness of the steel plate is below 10mm.
  • the publication number is CN102776438A
  • the publication date is November 14, 2012
  • the Chinese patent document titled "A niobium-lanthanum microalloyed Mn-B series ultra-high-strength steel plate and its heat treatment process” discloses a Niobium-lanthanum microalloyed Mn-B series ultra-high strength steel plate and its heat treatment process.
  • the chemical composition and content (weight percentage) of the steel plate are: C 0.14%-0.35%, Mn 1.5%-2.0%, Si 0.6%-1.0 %, P ⁇ 0.015%, S ⁇ 0.002%, Nb 0.01%-0.06%, B 0.0005%-0.0040%, La 0.001%-0.5%, the balance is Fe and inevitable impurities.
  • the heat treatment process system adopted is: austenitizing temperature is 880-940°C, holding time is 0.5-5 hours and then water quenched; tempering temperature is 190-250°C, holding time is 1-15 hours .
  • the designed steel plate has excellent mechanical properties, with a tensile strength of 1200-1400MPa, a yield strength of 1000-1300MPa, and an elongation of 6-15%. It has low production cost and can be industrially produced 5- Characteristics of 25mm thickness steel plate.
  • the publication number is CN102321841A
  • the publication date is January 18, 2012
  • the Chinese patent document titled "Steel for track shoes with tensile strength reaching 1300MPa and manufacturing method thereof" discloses a kind of steel with tensile strength reaching 1300MPa
  • the steel for track shoes and its manufacturing method, its chemical composition in weight percentage is C: 0.20 ⁇ 0.30%, Mn: 0.80 ⁇ 1.40%, Si: 0.15 ⁇ 0.35%, P: 0 ⁇ 0.015%, S: 0 ⁇ 0.016%, Cr: 0 ⁇ 0.30%, Ni: 0 ⁇ 0.25%, Cu: 0 ⁇ 0.30%, Ti: 0.01 ⁇ 0.02%, Al: 0.02 ⁇ 0.06%, B: 0.0005 ⁇ 0.0035%, the rest is Fe and insoluble Impurity elements to avoid.
  • the tensile strength of the steel designed in this technical solution reaches more than 1340MPa, the elongation after fracture is less than 12%, its "U"-shaped notch impact absorption energy is greater than 72J, high strength, few quenching cracks and internal cracks, and long service life. long.
  • One of the purposes of the present invention is to provide a new 1300MPa or higher grade cold-rolled steel plate.
  • the 1300MPa or higher grade cold-rolled steel plate adopts reasonable chemical composition design and manufacturing process. It has ultra-high strength and excellent performance. Delayed cracking resistance and bending properties. When the preset stress is greater than or equal to 1.05 times the tensile strength, the cold-rolled steel plate can be soaked in hydrochloric acid with a concentration of 1 mol/L for more than 300 hours without delayed cracking. It is especially suitable for the manufacture of automobile safety structural parts. Good prospects for promotion and application.
  • the present invention provides a high-grade cold-rolled steel plate of 1300MPa or above, which contains Fe and inevitable impurity elements, and also contains the following chemical elements in the following mass percentages:
  • the mass percentage content of each chemical element is:
  • the addition of C element can not only improve the strength of the steel, but also increase the hardness of martensite to ensure that martensite transformation occurs.
  • the inventor's research found that when the mass percentage of the C element in the steel is less than 0.1%, the strength of the steel plate will be affected and is not conducive to the formation and stability of austenite; and when the mass percentage of the C element in the steel is When the content is higher than 0.30%, it is easy to cause the martensite hardness to be too high and the grain size to be coarse, which is not conducive to the formability of the steel plate. Therefore, considering the influence of C element content on steel properties, in the cold-rolled steel plate above 1300 MPa according to the present invention, the mass percentage content of C element is controlled between 0.10% and 0.30%.
  • Si In the 1300MPa or above grade cold-rolled steel plate according to the present invention, adding Si element can improve the hardenability of the steel.
  • solid solution Si in steel can affect the interaction of dislocations, increase the work hardening rate, and appropriately increase the elongation, which is beneficial to the steel's better formability.
  • Si The mass percentage of elements is controlled between 0.1% and 0.5%.
  • Mn In the cold-rolled steel plate above 1300MPa according to the present invention, adding Mn element can not only improve the hardenability of the steel, but also effectively improve the strength of the steel plate.
  • the mass percentage of Mn in the steel is selected to be between 0.8% and 2.5% because: when the mass percentage of Mn in the steel is less than 0.8%, the prepared steel will have insufficient hardenability and will not survive annealing. A sufficient amount of martensite cannot be produced during the process, and the strength of the steel plate is insufficient; when the mass percentage of the Mn element in the steel is higher than 2.5%, the carbon equivalent will significantly increase, which affects the welding performance and delayed cracking resistance of the steel. All have negative effects. Therefore, considering the influence of Mn element content on steel properties, the mass percentage content of Mn element in the 1300MPa or above grade cold-rolled steel plate of the present invention is controlled between 0.8% and 2.5%.
  • Al In the cold-rolled steel plate above 1300MPa described in the present invention, adding an appropriate amount of Al element to the steel can play a deoxidizing effect and refine the grains. Therefore, in order to exert the beneficial effects of Al element, in the present invention, the mass percentage content of Al element is controlled between 0.01% and 0.03%.
  • B In the cold-rolled steel plate above 1300MPa according to the present invention, B is an element that can significantly improve the hardenability of the steel. Adding 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 steel should not be too high. After the grain boundary defects are filled, if more B is added, the "boron phase" at the grain boundary will precipitate, which will increase the grain boundary energy potential. , at the same time, the "boron phase” will also serve as the core of the new phase, which will increase the nucleation speed and lead to a decrease in the hardenability of the steel. Therefore, considering the influence of B element content on steel properties, in the 1300MPa or above grade cold-rolled steel plate of the present invention, the mass percentage content of B element is controlled between 0.001-0.003%.
  • the added strong carbide-forming element Ti will show a strong effect of inhibiting the growth of austenite grains at high temperatures.
  • Ti is added to the steel. Elements also help refine the grain. Therefore, in order to exert the beneficial effects of Ti element, in the present invention, the mass percentage content of Ti element is controlled between 0 and 0.05%. Preferably, the mass percentage of Ti element is controlled between 0.01% and 0.05%.
  • the inventor In order to ensure that the strength of the steel is greater than 1300MPa, in the 1300MPa or higher grade cold-rolled steel plate designed by the present invention, the inventor not only controls the mass percentage content of a single chemical element, but also further controls the content of C and Mn elements in the steel.
  • the mass percentage content meets: C+Mn/6 ⁇ 0.35%.
  • P element, S element and N element are all impurity elements in the steel.
  • it should be Reduce the content of impurity elements in steel as much as possible. Therefore, except for special requirements, the content of P element in steel should be reduced as much as possible, and the mass percentage content of P element should be controlled to P ⁇ 0.015%.
  • the mass percentage of the S element in the steel is strictly controlled to satisfy S ⁇ 0.003%.
  • the mass percentage of the N element is controlled to satisfy N ⁇ 0.006%.
  • the microstructure is retained austenite + fine massive tempered martensite + bainite.
  • the volume phase ratio of tempered martensite is ⁇ 55%, and the volume phase ratio of bainite is greater than 0 and ⁇ 15%.
  • the volume phase ratio of tempered martensite is 55 to 90% or 65 to 90%.
  • the volume phase ratio of bainite is 5 to 15%.
  • the diameter of the tempered martensite is not greater than 10 microns; preferably, the diameter of the tempered martensite is 4 to 9 microns.
  • the composition of the steel designed is a composition system mainly composed of C+Mn+B.
  • C, Mn, and B elements Through the coordinated design of C, Mn, and B elements, it can ensure that the martensite volume fraction content is greater than 55%.
  • the present invention can ensure that the cold-rolled steel plate obtains retained austenite + fine massive tempered martensite (blocks) through the reasonable design of alloy elements and manufacturing processes.
  • the diameter of martensite is no more than 10 microns) + the microstructure of bainite.
  • fine dispersed precipitates that can serve as hydrogen traps can be produced internally.
  • the above are all factors that are beneficial to the improvement of delayed cracking performance; and the acquisition of retained austenite is not only beneficial to Delaying cracking is also beneficial to improving the formability of cold-rolled steel plates.
  • the 90-degree cold bending performance characterization parameter R/t has a limit value ⁇ 2.5.
  • the 90-degree cold bending performance characterization parameter R/t has a limit value ⁇ 3
  • the 90-degree cold bending performance characterization parameters R/t limit value ⁇ 3.5 when the tensile strength is above 1650MPa, the 90-degree cold bending performance parameter R/t limit value ⁇ 4, where R represents the bending radius and t represents the plate thickness;
  • the 90-degree cold bending performance characterization parameter R/t has a limit value of 2.0-2.5.
  • the 90-degree cold bending performance characterization parameter R/t The t limit value is 2.5-3.
  • the 90-degree cold bending performance characterizing parameter R/t has a limit value of 3.0-3.5.
  • the 90-degree cold bending performance The limit value of the characterization parameter R/t is 3.5-4.
  • delayed cracking will not occur when soaked in hydrochloric acid with a concentration of 1 mol/L for more than 300 hours.
  • the preset stress is greater than or equal to 1.15 times the tensile strength
  • delayed cracking will not occur when soaked in hydrochloric acid with a concentration of 1 mol/L for more than 300 hours.
  • the preset stress is greater than or equal to 1.2 times the tensile strength
  • delayed cracking will not occur when soaked in hydrochloric acid with a concentration of 1 mol/L for more than 300 hours.
  • the acquisition of retained austenite + fine massive tempered martensite + bainite jointly determines the characteristics of the 1300MPa or above cold-rolled steel plate designed by the present invention. Good molding performance.
  • the 90-degree cold bending performance characterization parameter R/t has a limit value ⁇ 2.5, and when the tensile strength is 1401-1500MPa , the limit value of the 90-degree cold bending performance characterization parameter R/t ⁇ 3, when the tensile strength is 1501-1650MPa, the 90-degree cold bending performance characterization parameter R/t limit value ⁇ 3.5, when the tensile strength is above 1650MPa,
  • the limit value of the 90-degree cold bending performance parameter R/t is ⁇ 4.
  • another object of the present invention is to provide a manufacturing method for the above-mentioned 1300MPa or higher grade cold-rolled steel plate, which optimizes the design of the manufacturing process.
  • the cold-rolled steel plate produced by this manufacturing method not only has ultra-high strength, but also has high strength. Has excellent delayed cracking resistance and bending properties.
  • the present invention proposes the above-mentioned manufacturing method of high-grade cold-rolled steel plate above 1300MPa, which includes the steps:
  • the tempering temperature is 400-550°C, the tempering time is 10-300s, and then cooled to room temperature at a speed of more than 30°C/s;
  • Discontinuous tempering The tempering temperature is 180-260°C, and the tempering time is 0.5-6h.
  • the acquisition of bainite is one of the characteristics of the present invention.
  • the steel can first obtain part of the bainite to ensure subsequent generation.
  • the martensite surrounds the fine dispersion nucleation of bainite and does not grow violently, thus eventually forming fine massive martensite, which can eventually obtain fine massive tempered martensite with a diameter of no more than 10 microns.
  • another feature of the present invention is the optimized design of two tempers in the manufacturing method. After the first continuous tempering process is completed, and after the flattening is completed, a discontinuous secondary tempering is further used.
  • the purpose of this design is to temper the martensite structure and enrich the untransformed austenite with carbon, so that the final retained austenite + fine massive tempered martensite + bainite can be obtained after cooling organize.
  • the tempering temperature is specifically controlled to be 400-550°C, and the tempering time is controlled to be 10-300 s, because this process determines the final morphology of martensite. and size.
  • the present invention can finally obtain fine massive tempered martensite with a diameter of no more than 10 microns.
  • the tempering temperature and tempering time of each specific component need to be based on the dynamic CCT curve.
  • the specific setting is to ensure that a proportion of bainite of less than 15% is obtained, which will not have a great impact on the strength of the steel.
  • the tempering temperature is specifically controlled to be 180-260°C and the tempering time is 0.5-6h.
  • This process is technologically independent from the aforementioned steps (4) and (5), so it is called a discontinuous tempering process. Its essence is a discontinuous low-temperature over-aging tempering process, which can be implemented in a bell-type furnace.
  • the martensite structure can be tempered and the untransformed austenite can be enriched with carbon, so that the final retained austenite + fine tempered martensite + bainite can be obtained after cooling. organize.
  • the discontinuous tempering process in step (7) also needs to be reasonably designed according to the specific ingredients.
  • the tempering temperature in the discontinuous tempering process is specifically controlled to be 180-260°C, and the tempering time is 0.5-6h.
  • step (2) first heat to 1100-1250°C, keep the temperature for more than 0.3 hours (such as 0.3-2h), and then use Ar3 (austenite transformation temperature) or more Temperature hot rolling, after rolling, it is quickly cooled at a speed of 30-80°C/s, and the coiling temperature is controlled at 530-600°C.
  • Ar3 austenite transformation temperature
  • step (2) the hot rolling temperature does not exceed 920°C.
  • step (3) the cold rolling reduction rate is controlled to 45-65%.
  • step (4) the annealing soaking temperature is controlled to be 830-870°C, the holding time is 30-150s, and then the cooling rate is 5-15°C/s. to between 730-780°C; and then cooled to the continuous tempering temperature at a speed of 50-700°C/s.
  • the annealing soaking temperature is limited to 830-870°C, and the holding time is 30-150s, because what it wants to achieve is complete austenite. Soaking annealing temperature.
  • the annealing soaking temperature used in step (4) is lower than 830°C and less than 30s, sufficient tensile strength cannot be obtained; and when the annealing soaking temperature used is higher than 870°C and longer than 150s , it will lead to a significant decrease in the formability of the steel.
  • the annealing soaking temperature can be preferably controlled between 850-860°C, so as to ensure complete austenitization and ensure that the obtained grain size is not coarsened, thus Get better molding performance.
  • step (4) the annealing soaking temperature is controlled to be 850-860°C.
  • the tempering temperature is 430-550°C.
  • the tempering time is 50-300s.
  • the cooling rate is 30 to 50°C/s.
  • step (6) the flatness rate is controlled to 0-0.3%.
  • the 1300MPa or higher grade cold-rolled steel plate and its manufacturing method according to the present invention have the following advantages and beneficial effects:
  • the present invention develops a new 1300MPa or higher grade cold-rolled steel plate and its manufacturing method. Through reasonable component matching and process design, a 1300MPa or higher grade cold-rolled steel plate with low delayed cracking sensitivity and high bending performance can be obtained.
  • This 1300MPa or higher grade cold-rolled steel plate has very excellent delayed cracking resistance.
  • the preset stress is greater than or equal to 1.05 times the tensile strength, it can be immersed in hydrochloric acid with a concentration of 1mol/L for more than 300 hours without delayed cracking.
  • the microstructure of retained austenite + fine massive tempered martensite + bainite possessed by this cold-rolled steel plate directly determines that the cold-rolled steel plate designed in the present invention has good formability.
  • the 90-degree cold bending performance characterization parameter R/t has a limit value of ⁇ 2.5.
  • the 90-degree cold bending performance characterization parameter R/t The t limit value is ⁇ 3.
  • the 90-degree cold bending performance characterization parameter R/t limit value is ⁇ 3.5.
  • the 90-degree cold bending performance characterization parameter R/ t limit value ⁇ 4, where R represents the bending radius and t represents the plate thickness.
  • the cold-rolled steel plate designed in the present invention not only has ultra-high strength, but also has excellent delayed cracking resistance and bending forming performance. It can effectively prepare automotive parts and be used in In the automobile industry, it has good promotion prospects and application value.
  • Table 1 lists the mass percentage proportions of each chemical element designed for the 1300MPa or higher grade cold-rolled steel plates of Examples 1-18.
  • the 1300MPa or above high-grade cold-rolled steel plates of Examples 1-18 of the present invention are all produced using the following steps:
  • Hot rolling The obtained slab is first heated to 1100-1250°C and kept warm for more than 0.3 hours, and then hot-rolled at a temperature above Ar3. After rolling, it is rapidly cooled at a speed of 30-80°C/s and cooled to Coiling is carried out after the coiling temperature is reached, and the coiling temperature is controlled to be 530-600°C.
  • Annealing Control the annealing soaking temperature to 830-870°C, preferably 850-860°C, the holding time is 30-150s, and then cool to between 730-780°C at a cooling rate of 5-15°C/s; Then it is cooled to the continuous tempering temperature at a speed of 50-700°C/s.
  • Continuous tempering temperature control the tempering temperature to 400-550°C, control the tempering time to 10-300s, and then cool to room temperature at a speed of more than 30°C/s.
  • Discontinuous tempering Perform discontinuous tempering on the flattened steel plate, and control the tempering temperature to 180-260°C and the tempering time to 0.5-6h.
  • Table 2-1 and Table 2-2 list the specific process parameters of the above-mentioned process steps for the 1300MPa or higher grade cold-rolled steel plates of Examples 1-18.
  • the 1300MPa or above cold-rolled steel plates of finished product examples 1-18 obtained through the above process steps (1)-(7) were sampled respectively, and the microstructure of the steel plates in each example was observed and analyzed. It was found that the microstructure of the cold-rolled steel plates in each example was retained austenite + fine massive tempered martensite + bainite. In this article, the microstructure was observed using a ZEISS Axio Imager M2m optical microscope. In addition, the details of the nanoprecipitates and microstructure were further observed and analyzed through a spherical aberration corrected field emission transmission electron microscope (TEM; model JEOL ARM-200F). The TEM working acceleration voltage was 200kV.
  • TEM spherical aberration corrected field emission transmission electron microscope
  • the inventor further analyzed the volume phase ratio of each component in the microstructure of the 1300MPa or above cold-rolled steel plates of finished Examples 1-18, and detected the diameter of the tempered martensite. Related The analysis and test results are listed in Table 3 below.
  • the volume phase ratio of tempered martensite in the 1300MPa and above grade cold-rolled steel plates of Examples 1-18 is between 68-91%, and the volume phase ratio of bainite is between 68-91%. Between 5-14%, and the diameter of its tempered martensite is between 4.3-8.7 microns.
  • the 1300MPa or above cold-rolled steel plates of the finished product examples 1-18 can be further sampled respectively, and the relevant mechanical properties of the cold-rolled steel plate samples of each embodiment can be tested to determine Its mechanical strength, elongation and bending properties were obtained, and the obtained mechanical property test results are listed in Table 4.
  • Tensile test test According to GB/T 228 (Tensile Test of Metal Materials) Part 1: Room Temperature Test Method, a detection test is performed to detect the yield strength and tensile strength of the 1300MPa or above cold-rolled steel plates obtained in Examples 1-18. Strength and elongation.
  • the bending performance of the cold-rolled steel plates in each embodiment is characterized by the limit value of the 90-degree cold bending performance parameter R/t, in which the plate thickness t is fixed and the bending radius R that ensures no cracking during bending changes.
  • the R/t limit value can be obtained.
  • Table 4 lists the mechanical property test results of the cold-rolled steel above 1300MPa in Examples 1-18.
  • the 1300MPa or higher grade cold-rolled steel plates of Examples 1-18 of the present invention not only have ultra-high strength, but also have good cold bending deformation ability, and their yield strength is between 1128-1503MPa. Its tensile strength is between 1321-1738MPa, and its elongation is between 6.1-10.1%.
  • the 90-degree cold bending performance characterization parameter R/t has a limit value ⁇ 2.5.
  • the 90-degree cold bending performance characterization parameter R/t The limit value of the cold bending performance characterization parameter R/t ⁇ 3.
  • the 90-degree cold bending performance characterization parameter R/t has the limit value ⁇ 3.5.
  • the 90-degree cold bending performance The limit value of bending performance parameter R/t is ⁇ 4. It can be seen that the cold-rolled steel plates of these Examples 1-18 not only have ultra-high strength, but also have very excellent bending deformation properties.
  • the cold-rolled steel plates of Examples 1-18 prepared by the present invention not only have the above-mentioned excellent mechanical properties, but also have excellent delayed cracking resistance.
  • the inventors sampled the steel plates of each example again, and controlled the cold-rolled steel plates of each example to undergo an acid soak test, that is, soaked in hydrochloric acid solution The test was evaluated.
  • the wire-cut samples were loaded to 1.05, 1.1, 1.15, and 1.2 times the tensile strength by bending, and soaked in 0.1 mol/L HCl solution for 300 hours. The solution was not changed. Before each change of solution, The brush removes surface corrosion products, and the test time is controlled to 300h.
  • the sample plate is observed.
  • the sample plate has no cracks, it means that the ability to resist delayed cracking under this stress condition is better, and is marked as "OK"; if the sample plate cracks, it means that the sample plate has cracks. Has poor resistance to delayed cracking under stress conditions and is marked "NG”.
  • Table 5 lists the test results of the cold-rolled steel plates of Examples 1-18 after the acid bubble test.
  • the prepared cold-rolled steel plates of Examples 1-18 have very excellent delayed cracking resistance. Under the condition of a preset stress of 1.05 times the tensile strength, all the example steel plates have excellent resistance to delayed cracking at 1 mol/L. No delayed cracking occurred after being soaked in concentrated hydrochloric acid for more than 300 hours.

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Abstract

本发明公开了一种1300MPa以上级冷轧钢板及其制造方法，所述冷轧钢板含有Fe及不可避免的杂质元素，其还含有质量百分含量如下的下述各化学元素：C：0.10％～0.30％，Si：0.1％～0.5％，Mn：0.8％～2.5％，Al：0.01％～0.03％，B：0.001-0.003％；Ti：0～0.05％，并且C和Mn的质量百分含量满足：C+Mn/6≥0.35％。该1300MPa以上级冷轧钢板采用了合理的化学成分设计以及制造工艺，在具有超高强度的同时还具有优异的抗延迟开裂性能和弯曲性能。

Description

一种1300MPa以上级冷轧钢板及其制造方法 技术领域
本发明涉及一种钢材及其制造方法，尤其涉及一种冷轧钢板及其制造方法。
背景技术
近年来，随着全球能源危机和环境问题的加剧，“节能”和“安全”已经成为了汽车制造业的主要发展方向。其中，在制备汽车时，采取轻量化的设计以降低车重，便是节能减排的重要措施之一。
近年来，超高强钢在汽车行业中的使用十分常见，超高强钢具有良好的机械性能和使用性能，其能够用于制造汽车结构件，并实现零部件的轻量化，从而有效降低车重。在当前汽车工业中，在实际制备车辆时，出于减重和安全性的需要，要求使用更高强度的钢板。其中，抗拉强度在1000Mpa及其以上的超高强度钢在减重和安全性能方面颇具减重潜力，其可以用于安全件、加强件和结构件的制造，并具有良好的推广前景。
然而，抗拉强度在1000MPa以上的高强钢天然的具有应力腐蚀开裂(延迟开裂)的特性，这种高强度钢板很容易在应力和腐蚀性介质的作用下发生缓慢开裂的过程，其所出现的延迟开裂对于高强钢的应用造成了相当的困扰，极大限制的了超高强钢的应用。
所谓延迟开裂，就是指零件制成时不发生开裂，但随着时间的推移，在应力和腐蚀介质的双重作用下，发生应力腐蚀开裂，最终导致零件失效，安全保护作用失去的问题，这个过程中氢起到了促进裂纹萌生和扩展的作用。通常来说，在当前现有的高强钢中，钢材的强度越高，则延迟开裂倾向也就越趋于严重，延迟开裂是先进高强钢应用的最大的风险。
在当前现有技术中，虽然已有部分研究人员开发出来超高强度的钢材，但这些技术方案均没有很好的解决超高强钢所存在的延迟开裂的问题。
例如：公开号为CN102822375A，公开日为2012年12月12日，名称为 “超高强度冷轧钢板及其制造方法”的中国专利文献，公开了一种超高强度冷轧钢板及其制造方法，其C：0.05-0.4％，Si≤2.0％，Mn：1.0-3.0％，P≤0.05％，S≤0.02％，Al：0.01-0.05％，N≤0.05％。该冷轧钢板在连续退火中，需要从Ac3以20℃/s以上(气体冷却)的冷速，冷却到Ms点-Ms点+200℃范围，保持0.1-60s后，并以100℃/s以上的冷速(水冷)，冷却到100℃以下，以得到抗拉强度1320MPa以上的高强钢，且钢板的平坦度在10mm以下。
又例如：公开号为CN102776438A，公开日为2012年11月14日，名称为“一种铌镧微合金化Mn-B系超高强度钢板及其热处理工艺”的中国专利文献，公开了一种铌镧微合金化Mn-B系超高强度钢板及其热处理工艺，其钢板的化学成分及含量(重量百分比)为：C 0.14％-0.35％，Mn 1.5％-2.0％，Si 0.6％-1.0％，P≤0.015％，S≤0.002％，Nb 0.01％-0.06％，B 0.0005％-0.0040％，La 0.001％-0.5％，余量为Fe和不可避免的杂质。在该技术方案中，其所采用的热处理工艺制度为：奥氏体化温度为880-940℃，保温时间0.5-5小时后水淬；回火温度190-250℃，保温时间1-15小时。在这种专利技术方案中，所设计的钢板具有优良的力学性能，其抗拉强度达到1200-1400MPa，屈服强度1000-1300MPa，延伸率6-15％，具有生产成本低，可工业化生产5-25mm厚度规格钢板的特点。
再例如：公开号为CN102321841A，公开日为2012年1月18日，名称为“抗拉强度达到1300MPa的履带板用钢及其制造方法”的中国专利文献，公开了一种抗拉强度达到1300MPa的履带板用钢及其制造方法，其化学组分按重量百分比为C：0.20～0.30％、Mn：0.80～1.40％、Si：0.15～0.35％、P：0～0.015％、S：0～0.016％、Cr：0～0.30％、Ni：0～0.25％、Cu：0～0.30％、Ti：0.01～0.02％、Al：0.02～0.06％，B：0.0005～0.0035％、其余为Fe和不可避免的杂质元素。该技术方案所设计的这种钢材的抗拉强度达到1340MPa以上、断后伸长率低于12％，其“U”型缺口冲击吸收功大于72J，强度高，淬火裂纹和内部裂纹少，使用寿命长。
在上述这三种专利文献中，虽然获得的钢材均具有超高的强度以及良好的机械性能。但这三种技术方案均不涉及对超高强钢材的抗延迟开裂性能的改善。
发明内容
本发明的目的之一在于提供一种新的1300MPa以上级冷轧钢板，该1300MPa以上级冷轧钢板采用了合理的化学成分设计以及制造工艺，其在具有超高强度的同时，还具有优异的抗延迟开裂性能和弯曲性能。该冷轧钢板在预置应力大于等于1.05倍抗拉强度的情况下，可以在1mol/L浓度的盐酸内浸泡300小时以上而不发生延迟开裂，其特别适于汽车安全结构件的制造，具有良好的推广应用前景。
为了实现上述目的，本发明提供了一种1300MPa以上级冷轧钢板，其含有Fe及不可避免的杂质元素，其还含有质量百分含量如下的下述各化学元素：
C：0.10％～0.30％，Si：0.1％～0.5％，Mn：0.8％～2.5％，Al：0.01％～0.03％，B：0.001-0.003％；Ti：0～0.05％；
并且C和Mn的质量百分含量满足：C+Mn/6≥0.35％。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其各化学元素质量百分含量为：
C：0.10％～0.30％，Si：0.1％～0.5％，Mn：0.8％～2.5％，Al：0.01％～0.03％，B：0.001-0.003％；Ti：0～0.05％，余量为Fe和其他不可避免的杂质；
并且C和Mn的质量百分含量满足：C+Mn/6≥0.35％。
在本发明所述的1300MPa以上级冷轧钢板中，各化学元素的设计原理具体如下所述：
C：在本发明所述的1300MPa以上级冷轧钢板中，C元素的添加不仅可以提高钢材的强度，还可以提高马氏体的硬度，以保证马氏体相变发生。发明人研究发现，当钢中C元素的质量百分含量低于0.1％时，钢板的强度会受到影响，并且不利于奥氏体的形成量和稳定性；而当钢中C元素的质量百分含量高于0.30％时，则容易造成马氏体硬度过高，晶粒尺寸粗大，其不利于钢板的成型性能。因此，考虑到C元素含量对钢材性能的影响，在本发明所述的1300MPa以上冷轧钢板中，将C元素的质量百分含量控制在0.10％～0.30％之间。
Si：在本发明所述的1300MPa以上级冷轧钢板中，添加Si元素可以提高钢材的淬透性。并且，钢中固溶的Si可以影响位错的交互作用，增加加工硬化率，并可以适当提高延伸率，有益于钢材获得较好的成型性。基于此，为了发挥Si元素的有益效果，在本发明所述的1300MPa以上级冷轧钢板中，将Si 元素的质量百分含量控制在0.1％～0.5％之间。
Mn：在本发明所述的1300MPa以上级冷轧钢板中，添加Mn元素不仅能够提高钢材的淬透性，还可以有效提高钢板的强度。而选取钢中Mn的质量百分含量在0.8％～2.5％之间，是因为：当钢中Mn的质量百分含量低于0.8％时，则所制备的钢材淬透性不足，其在退火过程中无法产生足量的马氏体，钢板的强度不足；而当钢中Mn元素的质量百分含量高于2.5％时，碳当量会显著提高，其对于钢材的焊接性能和抗延迟开裂性能均有负面影响。因此，考虑到Mn元素含量对钢材性能的影响，在本发明所述的1300MPa以上级冷轧钢板中，将Mn元素的质量百分含量控制在0.8％～2.5％之间。
Al：在本发明所述的1300MPa以上级冷轧钢板中，钢中添加适量的Al元素可以起到脱氧作用和细化晶粒的作用。因此，为发挥Al元素的有益效果，在本发明中，将Al元素的质量百分含量控制在0.01％～0.03％之间。
B：在本发明所述的1300MPa以上级冷轧钢板中，B是能够显著提高钢材淬透性的元素，添加B元素能促进马氏体生成，并保证马氏体钢的强度。但需要注意的是，钢中B元素含量也不宜过高，在晶界缺陷被填完以后，若加入更多的B，则由于晶界的“硼相″沉淀，反而增加了晶界能位，同时“硼相”也将做为新相的核心，促使成核速度增加，致使钢材的淬透性下降。因此，考虑到B元素含量对钢材性能的影响，在本发明所述的1300MPa以上级冷轧钢板中，将B元素的质量百分含量控制在0.001-0.003％之间。
Ti：在本发明所述的1300MPa以上级冷轧钢板中，添加的强碳化物形成元素Ti在高温下会显示出一种强烈的抑制奥氏体晶粒长大的效果，同时钢中添加Ti元素也有助于细化晶粒。因此，为发挥Ti元素的有益效果，在本发明中，将Ti元素的质量百分含量控制在0～0.05％之间。优选地，将Ti元素的质量百分含量控制在0.01～0.05％之间。
为保证钢的强度大于1300MPa，在本发明所设计的这种1300MPa以上级冷轧钢板中，发明人在控制单一化学元素质量百分含量的同时，还进一步地控制了钢中C、Mn元素的质量百分含量满足：C+Mn/6≥0.35％。优选地，0.35％≤C+Mn/6≤0.60％；更优选地，0.37％≤C+Mn/6≤0.56％
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，在不可避免的杂质中，P≤0.015％，S≤0.003％，N≤0.006％。
在本发明所述的1300MPa以上级冷轧钢板中，P元素、S元素和N元素均为钢中的杂质元素，在技术条件允许情况下，为了获得性能更好且质量更优的钢材，应尽可能降低钢中杂质元素的含量。因此，除特殊要求外应尽可能降低钢中P元素含量，并具体将P元素的质量百分含量控制为P≤0.015％。
此外，杂质元素S所配合形成的MnS会严重影响钢材的成形性能，因而在本发明中，严格控制钢中S元素的质量百分含量满足S≤0.003％。另外，由于杂质元素N容易导致板坯表面产生裂纹或气泡，因而，在本发明中，控制N元素的质量百分含量满足N≤0.006％。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其微观组织为残余奥氏体+细小的块状回火马氏体+贝氏体。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其中回火马氏体的体积相比例≥55％，贝氏体的体积相比例大于0且＜15％。优选地，回火马氏体的体积相比例为55～90％或65～90％。优选地，贝氏体的体积相比例为5～15％。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其中回火马氏体的直径不大于10微米；优选地，回火马氏体的直径为4～9微米。
在本发明中，本发明钢设计的成分是以C+Mn+B为主的成分体系，其通过C、Mn、B元素的配合设计，可以保证马氏体体积分数含量大于55％。同时保证贝氏体C曲线左移，铁素体和珠光体C曲线右移，以确保最终获得的微观组织中具有一定体积分数的贝氏体，且贝氏体的体积相比例小于15％。
需要说明的是，在本发明中，根据前期经验及研究结果，本发明通过合金元素和制造工艺的合理设计，能够确保冷轧钢板获得残余奥氏体+细小块状回火马氏体(块状马氏体的直径不大于10微米)+贝氏体的微观组织。其中，马氏体回火后应力降低、硬度下降，同时内部能够产生可作为氢陷阱的细小弥散析出物，以上均是有利于延迟开裂性能改善的因素；而残余奥氏体的获得不仅有利于延迟开裂，还有利于提升冷轧钢板的成型性能。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其性能满足：
当抗拉强度为1300-1400MPa时，90度冷弯性能表征参量R/t极限值≤2.5，当抗拉强度大于1400MPa且≤1500MPa时，90度冷弯性能表征参量R/t极限值≤3，当抗拉强度大于1500MPa且≤1650MPa时，90度冷弯性能表征参量 R/t极限值≤3.5，当抗拉强度在1650MPa以上时，90度冷弯性能表征参量R/t极限值≤4，其中R表示弯曲半径，t表示板厚；
在预置应力大于等于1.05倍抗拉强度的情况下，在1mol/L浓度的盐酸内浸泡300小时以上不发生延迟开裂。
优选地，当抗拉强度为1300-1400MPa时，90度冷弯性能表征参量R/t极限值为2.0-2.5，当抗拉强度大于1400MPa且≤1500MPa时，90度冷弯性能表征参量R/t极限值为2.5-3，当抗拉强度大于1500MPa且≤1650MPa时，90度冷弯性能表征参量R/t极限值为3.0-3.5，当抗拉强度在1650MPa以上时，90度冷弯性能表征参量R/t极限值为3.5-4。
优选地，在预置应力大于等于1.1倍抗拉强度的情况下，在1mol/L浓度的盐酸内浸泡300小时以上不发生延迟开裂。优选地，在预置应力大于等于1.15倍抗拉强度的情况下，在1mol/L浓度的盐酸内浸泡300小时以上不发生延迟开裂。优选地，在预置应力大于等于1.2倍抗拉强度的情况下，在1mol/L浓度的盐酸内浸泡300小时以上不发生延迟开裂。
需要说明的是，在本发明中，残余奥氏体+细小的块状回火马氏体+贝氏体的获得共同决定了本发明所设计的这种1300MPa以上级冷轧钢板中钢板所具备的良好的成型性能。在本发明所设计的这种1300MPa以上级冷轧钢板中，当抗拉强度为1300-1400MPa时，90度冷弯性能表征参量R/t极限值≤2.5，当抗拉强度为1401-1500MPa时，90度冷弯性能表征参量R/t极限值≤3，当抗拉强度为1501-1650MPa时，90度冷弯性能表征参量R/t极限值≤3.5，当抗拉强度为1650MPa以上时，90度冷弯性能表征参量R/t极限值≤4。
相应地，本发明的另一目的在于提供上述1300MPa以上级冷轧钢板的制造方法，其对制造工艺进行了优化设计，采用该制造方法制得的冷轧钢板在具有超高强度的同时，还具有优异的抗延迟开裂性能和弯曲性能。
为了实现上述目的，本发明提出了上述的1300MPa以上级冷轧钢板的制造方法，其包括步骤：
(1)冶炼和铸造；
(2)热轧；
(3)冷轧；
(4)退火；
(5)连续式回火温度：回火温度为400-550℃，回火时间为10-300s，然后再以30℃/s以上的速度冷却到室温；
(6)平整；
(7)非连续式回火：回火温度为180-260℃，回火时间为0.5-6h。
在本发明所设计的这种技术方案中，贝氏体的获得是本发明的特点之一，在步骤(4)连续退火的冷却过程中，钢材能够先获得部分贝氏体，以保证后续生成的马氏体围绕贝氏体细小弥散形核并不剧烈长大，从而最终形成细小块状马氏体，其最终可以获得直径不大于10微米的细小块状回火马氏体。
此外，本发明的另一特点辨识在制造方法中优化设计了两次回火，其在第一次连续式回火工艺完成后，在平整完成后，还进一步地采用了非连续式二次回火。这一设计的目的是为了使马氏体组织回火，同时使未转变的奥氏体富碳，以便冷却后获得最终的残余奥氏体+细小的块状回火马氏体+贝氏体组织。
在本发明中，在步骤(5)的连续式回火工艺中，具体控制回火温度为400-550℃，控制回火时间为10-300s，是因为此工艺决定了最终马氏体的形态及尺寸。在本发明所设计的这种制造方法中，本发明最终可以获得直径不大于10微米的细小块状回火马氏体，其每种具体成分的回火温度和回火时间需要根据动态CCT曲线具体设定，以确保获得15％以下比例的贝氏体，其不会对钢材的强度造成很大影响。
另外，在步骤(7)的非连续式回火工艺中，其具体控制回火温度为180-260℃，回火时间为0.5-6h。此工艺在工艺上独立于前述的步骤(4)和(5)，因此称为非连续式的回火工艺，其实质是非连续式低温过时效回火工艺，可用罩式炉实现。利用该非连续式回火工艺，可以使马氏体组织回火，同时使未转变的奥氏体富碳，以便冷却后获得最终的残余奥氏体+细小回火马氏体+贝氏体组织。马氏体回火后应力降低、硬度下降，同时内部产生可作为氢陷阱的细小弥散析出物，以上均是有利于延迟开裂性能改善的因素。而残余奥氏体的获得不仅有利于延迟开裂，还有利于提升钢材的成型性能。
需要注意的是，步骤(7)的这种非连续回火工艺也需要根据具体成分合理地设计工艺，当回火温度太高和/或回火时间太长时，均有可能造成钢材强度降低，或者使材料出现严重的屈服平台，影响冲压性能；而当回火温度太低和/或回火时间太短时，则无法明显使马氏体回火，不能获得足量的残余奥氏 体，无法改善成型性能。因此，为了确保钢材的性能，在本发明中，具体控制非连续回火工艺中的回火温度为180-260℃，回火时间为0.5-6h。
进一步地，在本发明所述的制造方法中，在步骤(2)中，先加热至1100-1250℃，保温0.3小时以上(如0.3～2h)，然后采用Ar3(奥氏体转变温度)以上温度热轧，轧后以30-80℃/s的速度快速冷却，控制卷取温度为530-600℃。
进一步地，在本发明所述的制造方法中，在步骤(2)中，热轧温度不超过920℃。
进一步地，在本发明所述的制造方法中，在步骤(3)中，控制冷轧压下率为45-65％。
进一步地，在本发明所述的制造方法中，在步骤(4)中，控制退火均热温度为830-870℃，保温时间为30-150s，然后以5-15℃/s的冷却速度冷却到730-780℃之间；然后再以50-700℃/s的速度冷却到连续式回火温度。
在本发明上述技术方案中，在步骤(4)的退火步骤中，将退火均热温度限定在830-870℃之间，保温时间为30-150s，是因为其所要实现的是完全奥氏体化温度均热退火。当在步骤(4)中所采用的退火均热温度低于830℃，且小于30s时，则无法获得足够的抗拉强度；而当所采用的退火均热温度高于870℃，且大于150s时，则会导致钢材的成型性能大幅下降。
相应地，在一些优选的实施方式中，可以优选地控制退火均热温度在850-860℃之间，这样即能保证完全奥氏体化，又能保证获得的晶粒尺寸不粗化，从而得到较好的成型性能。
进一步地，在本发明所述的制造方法中，在步骤(4)中，控制退火均热温度为850-860℃。
进一步地，在本发明所述的制造方法中，在步骤(5)中，回火温度为430-550℃。
进一步地，在本发明所述的制造方法中，在步骤(5)中，回火时间为50-300s。
进一步地，在本发明所述的制造方法中，在步骤(5)中，优选地，冷却速度为30～50℃/s。
进一步地，在本发明所述的制造方法中，在步骤(6)中，控制平整率为 0-0.3％。
相较于现有技术，本发明所述的1300MPa以上级冷轧钢板及其制造方法具有如下所述的优点以及有益效果：
本发明开发了一种新的1300MPa以上级冷轧钢板及其制造方法，其通过合理的成分匹配及工艺设计，可以获得低延迟开裂敏感性、高弯曲性能的1300MPa以上级冷轧钢板。
该1300MPa以上级冷轧钢板具有十分优异的抗延迟开裂性能，其在预置应力大于等于1.05倍抗拉强度的情况下，可以在1mol/L浓度的盐酸内浸泡300小时以上不发生延迟开裂。同时，这种冷轧钢板所具备的残余奥氏体+细小的块状回火马氏体+贝氏体的微观组织直接决定了本发明设计的冷轧钢板具有良好的成型性能，所设计的这种冷轧钢板当抗拉强度为1300-1400MPa时，90度冷弯性能表征参量R/t极限值≤2.5，当抗拉强度大于1400MPa且≤1500MPa时，90度冷弯性能表征参量R/t极限值≤3，当抗拉强度大于1500MPa且≤1650MPa时，90度冷弯性能表征参量R/t极限值≤3.5，当抗拉强度在1650MPa以上时，90度冷弯性能表征参量R/t极限值≤4，其中R表示弯曲半径，t表示板厚。
综上所述可以看出，本发明所设计的这种冷轧钢板在具备超高强度的同时，还具有优异的抗延迟开裂性能和弯曲成型性能，其可以有效制备汽车零部件，并应用于汽车工业中，具有良好的推广前景和应用价值。
具体实施方式
下面将结合具体的实施例对本发明所述的1300MPa以上级冷轧钢板及其制造方法做进一步的解释和说明，然而该解释和说明并不对本发明的技术方案构成不当限定。
实施例1-18
表1列出了实施例1-18的1300MPa以上级冷轧钢板所设计的各个化学元素的质量百分配比。
表1.(wt％，余量为Fe和除P、S、N以外其他不可避免的杂质)

本发明所述的实施例1-18的1300MPa以上级冷轧钢板均采用以下步骤制得：
(1)按照表1所示的化学成分进行冶炼和铸造，以获得铸坯。
(2)热轧：针对获得的铸坯，先加热至1100-1250℃，并保温0.3小时以上，然后采用Ar3以上温度热轧，轧后以30-80℃/s的速度快速冷却，冷却至卷取温度后进行卷取，控制卷取温度为530-600℃。
(3)冷轧：控制冷轧压下率为45-65％。
(4)退火：控制退火均热温度为830-870℃，优选为850-860℃，保温时间为30-150s，然后以5-15℃/s的冷却速度冷却到730-780℃之间；然后再以50-700℃/s的速度冷却到连续式回火温度。
(5)连续式回火温度：控制回火温度为400-550℃，控制回火时间为10-300s，然后再以30℃/s以上的速度冷却到室温。
(6)平整：控制平整率为0-0.3％。
(7)非连续式回火：对平整后的钢板进行非连续式回火，并控制回火温度为180-260℃，回火时间为0.5-6h。
本发明所述的实施例1-18的1300MPa以上级冷轧钢板的化学元素成分和相关工艺设计均满足符合本发明设计规范要求。
表2-1和表2-2列出了实施例1-18的1300MPa以上级冷轧钢板在上述工艺步骤中的具体工艺参数。
表2-1.
注：在上述表2-1中，实施例1-18所采用的热轧温度均＞Ar3，各实施例在本发明要求工艺范围内的Ar3在730-850℃之间。
表2-2.

在本发明中，将经过上述工艺步骤(1)-(7)得到的成品实施例1-18的1300MPa以上级冷轧钢板分别取样，并对各实施例钢板的微观组织进行观察和分析，观察发现，各实施例的冷轧钢板的微观组织均为残余奥氏体+细小的块状回火马氏体+贝氏体。本文中，微观组织用ZEISS Axio Imager M2m型光学显微镜来观察。另外，纳米析出物和微观组织的细节进一步通过球差矫正场发射透射电镜(TEM；型号JEOL ARM-200F)来观测分析，TEM工作加速电压为200kV。
此外，发明人还进一步地对成品实施例1-18的1300MPa以上级冷轧钢板的微观组织中各组分的体积相比例进行了分析，并对回火马氏体的直径进行了检测，相关分析和检测结果列于下述表3之中。
表3.

通过分析和检测可以看出，在本发明中，实施例1-18的1300MPa以上级冷轧钢板的回火马氏体的体积相比例在68-91％之间，贝氏体的体积相比例在5-14％之间，且其回火马氏体的直径在4.3-8.7微米之间。
相应地，在完成上述观察以及分析之后，可以进一步地制得的成品实施例1-18的1300MPa以上级冷轧钢板分别取样，并对各实施例的冷轧钢板样品进行相关力学性能测试，以获得其力学强度、延伸率和弯曲性能，并将所得的力学性能检测结果列于表4中。
相关力学性能测试方法如下所述：
拉伸试验测试：根据GB/T 228(金属材料拉伸试验》第1部分：室温试验方法，进行检测试验，以检测获得实施例1-18的1300MPa以上级冷轧钢板的屈服强度、抗拉强度和延伸率。
另外，各实施例冷轧钢板的弯曲性能由90度冷弯性能表征参量R/t极限值进行表征，其中板厚t是固定的，保证弯曲不开裂的弯曲半径R是变化的。保证弯曲不开裂的弯角半径R最小时，能够获得R/t极限值。所获得的90度冷弯性能表征参量R/t极限值越大，则意味着弯曲能力越差；所获得的90度冷弯性能表征参量R/t越小，则意味着弯曲能力越好。
表4列出了实施例1-18的1300MPa以上级冷轧钢的力学性能测试结果。
表4.

如表4所示，本发明所述的实施例1-18的1300MPa以上级冷轧钢板在具有超高强度的同时，还具有良好的冷弯曲变形能力，其屈服强度在1128-1503MPa之间，其抗拉强度在1321-1738MPa之间，其延伸率在6.1-10.1％之间。同时，在这些实施例1-18可以看出，当抗拉强度为1300-1400MPa时，90度冷弯性能表征参量R/t极限值≤2.5，当抗拉强度为1401-1500MPa时，90度冷弯性能表征参量R/t极限值≤3，当抗拉强度为1501-1650MPa时，90度冷弯性能表征参量R/t极限值≤3.5，当抗拉强度为1650MPa以上时，90度冷弯性能表征参量R/t极限值≤4。由此可见，这些实施例1-18的冷轧钢板在具有超高强度的同时，还具有十分优异的弯曲变型性能。
相应地，本发明所制备的这种实施例1-18的冷轧钢板，不仅具有上述优异的力学性能，其同时还具备有优异的抗延迟开裂性能。
为了验证所制备实施例1-18的冷轧钢板的抗延迟开裂性能，发明人对各实施例钢板再次进行了取样，并控制各实施例的冷轧钢板进行泡酸试验，即采用盐酸溶液浸泡试验进行评价，线切割加工的试样通过弯曲分别加载至1.05、1.1、1.15、1.2倍抗拉强度，并在0.1mol/L的HCl溶液中浸泡300h，不更换溶液，每次更换溶液前用毛刷去除表面腐蚀产物，控制试验时间为300h。
在本发明中，在完成上述泡酸实验后，对样板进行观察，当样板无开裂，则代表该应力条件下抗延迟开裂能力较优，标记为“OK”；若样板出现开裂，则表示该应力条件下抗延迟开裂性能不佳，并标记为“NG”。
表5列出了实施例1-18的冷轧钢板在进行泡酸试验后的试验结果。
表5.
如上述表5所示，所制备的实施例1-18的冷轧钢板具有十分优异的抗延迟开裂性能，所有的实施例钢板在预置应力1.05倍抗拉强度的情况下，在1mol/L浓度的盐酸内浸泡300小时以上，均不发生延迟开裂。
需要说明的是，本案中各技术特征的组合方式并不限本案权利要求中所记载的组合方式或是具体实施例所记载的组合方式，本案记载的所有技术特征可以以任何方式进行自由组合或结合，除非相互之间产生矛盾。
还需要注意的是，以上所列举的实施例仅为本发明的具体实施例。显然本发明不局限于以上实施例，随之做出的类似变化或变形是本领域技术人员能从本发明公开的内容直接得出或者很容易便联想到的，均应属于本发明的保护范围。

Claims (15)

  1. 一种1300MPa以上级冷轧钢板，其含有Fe及不可避免的杂质元素，其特征在于，其还含有质量百分含量如下的下述各化学元素：
    C：0.10％～0.30％，Si：0.1％～0.5％，Mn：0.8％～2.5％，Al：0.01％～0.03％，B：0.001-0.003％；Ti：0～0.05％；
    并且C和Mn的质量百分含量满足：C+Mn/6≥0.35％。
  2. 如权利要求1所述的1300MPa以上级冷轧钢板，其特征在于，其各化学元素质量百分含量为：
    C：0.10％～0.30％，Si：0.1％～0.5％，Mn：0.8％～2.5％，Al：0.01％～0.03％，B：0.001-0.003％；Ti：0～0.05％，余量为Fe和其他不可避免的杂质；
    并且C和Mn的质量百分含量满足：C+Mn/6≥0.35％；
    优选地，Ti：0.01～0.05％。
  3. 如权利要求1或2所述的1300MPa以上级冷轧钢板，其特征在于，在不可避免的杂质中，P≤0.015％，S≤0.003％，N≤0.006％。
  4. 如权利要求1或2所述的1300MPa以上级冷轧钢板，其特征在于，其微观组织为残余奥氏体+细小的块状回火马氏体+贝氏体。
  5. 如权利要求4所述的1300MPa以上级冷轧钢板，其特征在于，其中回火马氏体的体积相比例≥55％，贝氏体的体积相比例大于0且＜15％；优选地，回火马氏体的体积相比例为55～90％，优选65～90％，贝氏体的体积相比例为5～15％。
  6. 如权利要求4所述的1300MPa以上级冷轧钢板，其特征在于，其中回火马氏体的直径不大于10微米；优选地，回火马氏体的直径为4～9微米。
  7. 如权利要求1或2所述的1300MPa以上级冷轧钢板，其特征在于，其性能满足：
    当抗拉强度为1300-1400MPa时，90度冷弯性能表征参量R/t极限值≤2.5，当抗拉强度大于1400MPa且≤1500MPa时，90度冷弯性能表征参量R/t极限值≤3，当抗拉强度大于1500MPa且≤1650MPa时，90度冷弯性能表征参量R/t极限值≤3.5，当抗拉强度在1650MPa以上时，90度 冷弯性能表征参量R/t极限值≤4，其中R表示弯曲半径，t表示板厚；
    在预置应力1.05倍抗拉强度的情况下，在1mol/L浓度的盐酸内浸泡300小时以上不发生延迟开裂；
    优选地，当抗拉强度为1300-1400MPa时，90度冷弯性能表征参量R/t极限值为2.0-2.5，当抗拉强度大于1400MPa且≤1500MPa时，90度冷弯性能表征参量R/t极限值为2.5-3，当抗拉强度大于1500MPa且≤1650MPa时，90度冷弯性能表征参量R/t极限值为3.0-3.5，当抗拉强度在1650MPa以上时，90度冷弯性能表征参量R/t极限值为3.5-4。
  8. 如权利要求1-7中任意一项所述的1300MPa以上级冷轧钢板的制造方法，其特征在于，其包括步骤：
    (1)冶炼和铸造；
    (2)热轧；
    (3)冷轧；
    (4)退火；
    (5)连续式回火温度：回火温度为400-550℃，回火时间为10-300s，然后再以30℃/s以上的速度冷却到室温；
    (6)平整；
    (7)非连续式回火：回火温度为180-260℃，回火时间为0.5-6h。
  9. 如权利要求8所述的制造方法，其特征在于，在步骤(2)中，先加热至1100-1250℃，保温0.3小时以上，然后采用Ar3以上温度热轧，轧后以30-80℃/s的速度快速冷却，控制卷取温度为530-600℃。
  10. 如权利要求9所述的制造方法，其特征在于，优选地，热轧温度不超过920℃。
  11. 如权利要求8所述的制造方法，其特征在于，在步骤(3)中，控制冷轧压下率为45-65％。
  12. 如权利要求8所述的制造方法，其特征在于，在步骤(4)中，控制退火均热温度为830-870℃，保温时间30-150s，然后以5-15℃/s的冷却速度冷却到730-780℃之间；然后再以50-700℃/s的速度冷却到连续式回火温度。
  13. 如权利要求11所述的制造方法，其特征在于，在步骤(4)中，控制退火 均热温度为850-860℃。
  14. 如权利要求11所述的制造方法，其特征在于，在步骤(5)中，优选地，冷却速度为30～50℃/s。
  15. 如权利要求8所述的制造方法，其特征在于，在步骤(6)中，控制平整率为0-0.3％。
PCT/CN2023/101256 2022-06-22 2023-06-20 一种1300MPa以上级冷轧钢板及其制造方法 Ceased WO2023246737A1 (zh)

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