WO2023246798A1 - 一种高延伸、高扩孔性能的1300MPa以上级冷轧钢板及其制造方法 - Google Patents

一种高延伸、高扩孔性能的1300MPa以上级冷轧钢板及其制造方法 Download PDF

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WO2023246798A1
WO2023246798A1 PCT/CN2023/101458 CN2023101458W WO2023246798A1 WO 2023246798 A1 WO2023246798 A1 WO 2023246798A1 CN 2023101458 W CN2023101458 W CN 2023101458W WO 2023246798 A1 WO2023246798 A1 WO 2023246798A1
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steel plate
rolled steel
cold
temperature
1300mpa
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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 EP23826445.1A priority Critical patent/EP4545666A4/en
Priority to JP2024575238A priority patent/JP7909631B2/ja
Publication of WO2023246798A1 publication Critical patent/WO2023246798A1/zh
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    • 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
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D8/0247—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
    • 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
    • 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
    • C22C38/06—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.
  • ultra-high-strength steel families for automobiles which usually include: dual-phase steel, quenched ductile steel, bainitic steel and complex-phase steel.
  • dual-phase steel and quenched ductile steel have good strength and plasticity, but their hole expansion rate (about 20%-35%) is far lower than that of traditional mild steel for automobiles; while bainitic steel
  • the composite phase steel has a higher hole expansion rate, its elongation is too low. Therefore, in order to meet more diversified market demands, it is necessary to develop an ultra-high-strength cold-rolled steel plate with both high elongation and high hole expansion properties.
  • the present invention hopes to obtain a 1300MPa or above cold-rolled steel plate with high elongation and high hole expansion performance, so as to obtain ultra-high strength while ensuring excellent formability.
  • the publication number is CN104451436A
  • the publication date is March 25, 2015
  • the Chinese patent document titled "Bainitic-Martensite-Austenite Composite Wear-Resistant Steel Plate and Manufacturing Method” discloses a kind of Bainite-martensite-austenite composite wear-resistant steel plate and manufacturing method.
  • Tensite-martensite-austenite composite phase wear-resistant steel plate and manufacturing method its chemical composition in weight percentage is: 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 ⁇ 0.010, P ⁇ 0.015, the balance is Fe and inevitable impurities quality elements.
  • the rolled material can obtain a bainite-martensite-retained austenite complex structure with a retained austenite volume fraction of 5-15%.
  • the yield strength of the material is greater than 1000MPa, the tensile strength is greater than 1300MPa, and the elongation is greater than 15%.
  • the hardness is HB420-500, and the machining performance and welding performance meet the equipment manufacturing requirements; the abrasive wear resistance is more than 1.3 times that of Hardox450, and it is more than 1.5 times that of Hardox450 under weakly acidic environmental conditions.
  • a sufficient amount of retained austenite is obtained through the addition of high Si and Al, and a high elongation is obtained through the TRIP effect of the retained austenite, without considering the hole expansion performance of the steel.
  • 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, an elongation of 6-15%, 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.
  • the ultra-high strength steel disclosed in the above two patent documents CN102776438A and CN102321841A respectively obtains good mechanical properties by adding micro-alloying elements such as niobium, lanthanum, nickel, cadmium, and copper.
  • micro-alloying elements such as niobium, lanthanum, nickel, cadmium, and copper.
  • the performance of the steel plate finally prepared cannot The performance indicators of high elongation and high hole expansion covered by the present invention are achieved.
  • One of the objects of the present invention is to provide a high-grade cold-rolled steel with high elongation and high hole expansion performance of 1300MPa or above.
  • this 1300MPa or above high-grade cold-rolled steel plate adopts reasonable chemical composition design and manufacturing process. It not only has ultra-high strength, but also has high elongation and high hole expansion performance. Its forming performance is excellent and can be effectively used in In the automotive industry, it has very broad application prospects.
  • the present invention provides a high-grade cold-rolled steel plate with high elongation and high hole expansion performance of 1300MPa or above, which contains Fe and inevitable impurity elements, and also contains the following chemical elements in the following mass percentages:
  • the microstructure of the cold-rolled steel plate has nano-precipitates with an average diameter less than 30 nm.
  • the mass percentage content of each chemical element is:
  • the microstructure of the cold-rolled steel plate has nano-precipitates with an average diameter less than 30 nm.
  • microstructure of the 1300MPa or higher grade cold-rolled steel sheet according to the present invention has nano-precipitates with an average diameter of 15 to 28 nm.
  • the addition of C element can not only improve the strength of the steel, but also ensure the occurrence of martensite transformation.
  • the inventor's research found that when the mass percentage of the C element in the steel is less than 0.15%, the strength of the steel plate will be affected, and it is not conducive to the formation and stability of retained austenite; and when the C element in the steel When the mass percentage is higher than 0.30%, the martensite hardness is likely to be too high and the grain size will 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 0.15% and 0.30%.
  • Si element can play a solid solution strengthening effect.
  • the mass percentage of Si element is controlled to Between 0.3% 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 1.8% and 2.5% because: in the present invention, a large amount of carbides will be produced during hot rolling, resulting in insufficient carbon equivalents in the matrix structure.
  • the mass percentage of Mn in the steel is low, When it is 1.8%, insufficient carbon equivalent will lead to insufficient hardenability of the prepared steel, which will not produce sufficient martensite during the annealing process, and the strength of the steel plate will be insufficient; when the mass percentage of Mn element in the steel When it is higher than 2.5%, the carbon equivalent will increase significantly, which will have a negative impact on the welding performance and delayed cracking resistance of the steel. 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 according to the present invention is controlled between 1.8% 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 lead to a decrease in the plasticity of the steel. . The inventor's research found that when the content of B element in steel is less than 0.001%, the role of B element cannot be effectively exerted, and when the content of B element in steel is higher than 0.003%, it will have an adverse effect on the shape 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. At the same time, it is added to the steel.
  • the Ti element also helps refine the grains. 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%. In some embodiments, 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 above 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 mass percentage content of C and Mn elements in steel meets: C+Mn/6 ⁇ 0.52%. In some embodiments, the mass percentages of C and Mn elements in the steel are controlled to satisfy: 0.52% ⁇ C+Mn/6 ⁇ 0.61%. In some embodiments, the mass percentages of C and Mn elements in the steel are controlled to satisfy: 0.55% ⁇ C+Mn/6 ⁇ 0.605%.
  • 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 present invention needs to strictly control the mass percentage of the S element in the steel to satisfy S ⁇ 0.003%.
  • the impurity element N can easily cause cracks or bubbles on the surface of the slab, in the present invention, the mass percentage of the N element is controlled to satisfy N ⁇ 0.006%.
  • the microstructure is retained austenite + fine massive martensite + bainite + the nano-precipitates.
  • the volume phase proportion of martensite is ⁇ 55%, and the volume phase proportion of bainite is greater than 0 and ⁇ 15%.
  • the volume phase ratio of martensite is 55 to 90%, preferably 70 to 86%.
  • the volume phase ratio of bainite is 7 to 14%.
  • the diameter of martensite is not greater than 10 microns.
  • the average diameter of martensite is 5 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 volume phase ratio of martensite is greater than 55%.
  • the C curve of bainite shifts to the left and the C curves of ferrite and pearlite shift to the right, ensuring that a certain volume fraction of bainite is obtained in the final microstructure, and the volume phase ratio of bainite is less than 15%.
  • the elongation is greater than 10% and the hole expansion rate is greater than 40%; when the tensile strength is greater than 1400 and ⁇ 1500MPa, the elongation is greater than 9% and the hole expansion rate is greater than 40%; when the tensile strength When the strength is above 1500MPa, the elongation is greater than 8% and the hole expansion rate is greater than 40%.
  • 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 1300MPa or higher grade cold-rolled steel plate produced by this manufacturing method has ultra-high strength. At the same time, it also has good elongation performance and high hole expansion performance.
  • the present invention proposes the above-mentioned manufacturing method of high-grade cold-rolled steel plate above 1300MPa, which includes the steps:
  • Annealing of the thermal insulation cover of the hot coil anneal the thermal insulation cover quickly after coiling, the annealing time is 0.5-6 hours, and the temperature drop per hour is less than or equal to 6°C;
  • Annealing Control the annealing soaking temperature to 830-860°C, the holding time to 40-80s, and then cool to 730-780°C at a cooling rate of 5-15°C/s; then cool to 50-700°C /s speed cooling to the isothermal holding temperature;
  • insulation temperature is 400-550°C, insulation time is 100-300s;
  • Cooling cool to room temperature at a rate of 30°C/s-100°C/s;
  • the inventor optimized the manufacturing process and improved the process flow.
  • the rapid use of thermal insulation cover annealing after hot coil coiling is one of the inventor's unique innovations.
  • the steel material remains at a lower temperature for a longer period of time.
  • Time holding annealing will generate fine and dispersed nano-precipitates ⁇ carbide.
  • fine dispersed ⁇ carbides can be further inherited into the final continuously annealed finished steel plate.
  • This dispersed and precipitated carbide can not only improve the overall strength, reduce the strength difference between phases, and reduce the strength difference between grain boundaries and within grains, it can also strengthen grain boundaries during the deformation process, thus improving the strength of steel and expanding holes.
  • the dual role of rate is one of the inventor's unique innovations.
  • the annealing soaking temperature It is limited to 830-860°C because what it wants to achieve is complete austenitizing temperature soaking annealing.
  • the annealing soaking temperature is lower than 830°C, complete austenitization cannot be achieved to obtain sufficient tensile strength; and when the annealing soaking temperature is higher than 860°C, the hole expansion rate of the steel will be significant. dramatically drop.
  • the annealing soaking temperature can be preferably controlled between 830-850°C, so as to ensure complete austenitization and ensure that the obtained grain size is not coarsened, thus Fine dispersed nanoprecipitates with an average size less than 30 nm are retained in the final microstructure.
  • the austenite isothermal heat preservation treatment process in step (6) designed by the present invention is another unique innovation of this patent. After annealing, it is controlled to be isothermal above the bainite transformation end temperature. This process determines Determining the shape and size of the final martensite, this patented process mainly includes: full austenitization temperature soaking (i.e., continuous annealing soaking temperature 830-860°C) - rapid cooling (i.e. speed of 50-700°C/s Cool to the isothermal insulation temperature) - Insulation in the bainitic transformation zone (i.e. isothermal insulation treatment, the insulation temperature is 400-550°C) - Control the cooling rate.
  • full austenitization temperature soaking i.e., continuous annealing soaking temperature 830-860°C
  • rapid cooling i.e. speed of 50-700°C/s Cool to the isothermal insulation temperature
  • Insulation in the bainitic transformation zone i.e. isothermal insulation treatment, the insulation temperature is
  • the martensite in the final microstructure is small massive martensite with a diameter of no more than 10 microns, and the bainite in the steel can be reduced through reasonable process design. Control it below 15% to avoid having a great impact on the strength of the steel. Correspondingly, through reasonable control of the cooling rate process design, it is necessary to ensure that a martensite structure with a volume phase ratio of ⁇ 55% is generated, and that there is still some untransformed austenite remaining after the martensite transformation. The austenitic form remains.
  • the fine martensite structure is beneficial to strength and elongation, while the retained austenite greatly increases the elongation through the TRIP effect.
  • the isothermal holding temperature and isothermal holding time of each specific component need to be specifically set according to the dynamic CCT curve.
  • step (6) designed by the present invention in the isothermal heat preservation treatment, the heat preservation temperature is controlled to be 400-550°C, and the heat preservation time is 100-300 s.
  • the holding temperature is lower than 400°C or the holding time is lower than 100 s, it is not conducive to the formation of bainite, nor is it conducive to enriching the untransformed austenite with carbon to generate retained austenite.
  • the holding temperature is higher than 550°C or the holding time is higher than 300s, there is no guarantee that the nano-precipitates produced by hot rolling will not coarsen.
  • step (2) first heat to 1100-1250°C, keep the temperature for more than 0.5 hours (such as 0.5-2h), and then hot-roll at a temperature above Ar3. After rolling, Rapid cooling at a speed of 30-80°C/s, and the coiling temperature is controlled at 150-250°C.
  • step (2) the hot rolling temperature is not higher than 920°C.
  • the coiling temperature is preferably 150-230°C.
  • step (3) the starting temperature of the annealing of the heat insulation cover is the same as the coiling temperature, and the cooling rate is 2-6°C per hour.
  • step (4) the cold rolling reduction rate is controlled to 50-70%.
  • the annealing soaking temperature is controlled to be 830-850°C.
  • step (8) the flatness rate is controlled to be 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 has developed 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 both high elongation and high hole expansion performance can be obtained.
  • This 1300MPa or higher grade cold-rolled steel plate has very excellent mechanical properties. Its microstructure of retained austenite + fine massive martensite + bainite + nano-precipitates can ensure that the steel plate has excellent elongation, Hole expansion performance and good formability.
  • the performance of the cold-rolled steel plate designed by the present invention satisfies: when the tensile strength is 1300-1400MPa, the elongation is greater than 10%, and the hole expansion rate is greater than 40%; when the tensile strength is greater than 1400 and ⁇ 1500MPa, the elongation The rate is greater than 9% and the hole expansion rate is greater than 40%; when the tensile strength is above 1500MPa, the elongation is greater than 8% and the hole expansion rate is greater than 40%. It can be effectively used in the automotive industry and has good promotion prospects and applications. 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 0.5 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 150-250°C.
  • Annealing of hot coil thermal insulation cover anneal the thermal insulation cover quickly after coiling, and control the annealing time to 0.5-6 hours.
  • the thermal insulation cover utilizes the internal heat of the steel coil, and the temperature drop per hour is less than 6°C.
  • Annealing Control the annealing soaking temperature to 830-860°C, preferably 830-850°C, and control the holding time to 40-80s, and then cool to a temperature between 730-780°C at a cooling rate of 5-15°C/s. time; and then cool to the isothermal holding temperature at a speed of 50-700°C/s.
  • Isothermal insulation treatment The annealed steel plate is subjected to isothermal insulation treatment, and the insulation temperature is controlled to 400-550°C, and the insulation time is controlled to 100-300s.
  • Cooling Cool the steel plate after isothermal insulation treatment to room temperature at a rate of 30°C/s-100°C/s.
  • 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)-(8) 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 of Examples 1-18 all had: retained austenite + fine massive martensite + bainite + nanometer precipitates.
  • 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 diameters of martensite and nano-precipitates. , the relevant analysis and detection results are listed in Table 3 below.
  • the microstructure was observed using a ZEISS Axio Imager M2m optical microscope.
  • 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.
  • Table 3 lists the analysis and detection results of the microstructure of the 1300MPa or higher grade cold-rolled steel plates of Examples 1-18.
  • the volume phase ratio of martensite in the 1300MPa or above grade cold-rolled steel plates of Examples 1-18 is between 70-86%, and the volume phase ratio of bainite is between Between 7-14%, the diameter of its martensite is between 5.1-8.9 microns, and the average diameter of its nano-precipitates is between 15-28nm.
  • 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 hole expansion rate were obtained, and the obtained mechanical property testing 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.
  • Hole expansion rate test According to the hole expansion test method of GB/T 24524-2021 metal material thin plates and thin strips, a detection test was performed to detect the hole expansion rate of the 1300MPa or above cold-rolled steel plates obtained in Examples 1-18.
  • 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 designed by the present invention not only have ultra-high strength, but also have good elongation performance and hole expansion performance.
  • the yield strength of the cold-rolled steel plates above 1300MPa prepared in Examples 1-18 is between 1067-1292MPa, the tensile strength is between 1328-1552MPa, and the elongation is between 8.5-12.3 %, and the hole expansion rate is between 43-54%.
  • Examples 1-18 designed by the present invention when the tensile strength of the prepared steel plate is 1300-1400MPa (ie, Example 4-6, Example 10-12), its elongation is specifically in Between 11.1-12.3%, the hole expansion rate is specifically between 53-46%; and when the tensile strength is greater than 1400 and ⁇ 1500MPa (i.e. Examples 1-3, 16-18), the elongation rate is specifically Between 9.1-9.7%, the hole expansion rate is specifically between 46-55%; when the tensile strength is above 1500MPa (ie, Examples 7-9, 13-15), the elongation is specifically between 8.5 -9.7%, and its hole expansion rate is specifically between 47-50%.

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Abstract

本发明公开了一种高延伸高扩孔性能的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：0.15％～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％；并且C和Mn的质量百分含量满足：C+Mn/6≥0.52；其中所述冷轧钢板的微观组织具有平均直径小于30nm的纳米析出物。所述冷轧钢板具有超高强度的同时，还兼具有高延伸、高扩孔性能，其成型性能优异。

Description

一种高延伸、高扩孔性能的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，汽车用超高强钢家族品种较多，其通常可以包括：双相钢、淬火延性钢、贝氏体钢和复相钢。其中，双相钢和淬火延性钢具有良好的强度与塑性，但它们的扩孔率(约为20％-35％)远远低于传统汽车用软钢的扩孔率；而贝氏体钢和复相钢的虽然具有较高的扩孔率，但其延伸率却过低。因此，为了面对更加多样化的市场需求，有必要开发出一种兼具高延伸、高扩孔性能的超高强度的冷轧钢板。
为此，针对现有超高强钢所存在的技术问题，本发明期望获得一种高延伸高扩孔性能的1300MPa以上级冷轧钢板，以在获得超高强度的同时，保证具有优异的成型性能。
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，但这些技术方案均无法获得本发明钢板对对应的高延伸、高扩孔性能。
例如：公开号为CN104451436A，公开日为2015年3月25日，名称为“贝氏体-马氏体-奥氏体复相耐磨钢板及制造方法”的中国专利文献，公开了一种贝氏体-马氏体-奥氏体复相耐磨钢板及制造方法，其化学组成按重量百分含量为：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≤0.010，P≤0.015，余量为Fe和不可避免的杂 质元素。轧材可得到贝氏体-马氏体-残余奥氏体复相组织，残余奥氏体体积分数5-15％，材料的屈服强度大于1000MPa，抗拉强度大于1300MPa，延伸率大于15％，硬度HB420-500，机加工性能及焊接性能满足设备制造要求；磨粒磨损耐磨性达到Hardox450的1.3倍以上，弱酸性环境工况下达到Hardox450的1.5倍以上。在该技术方案中，其通过高Si、Al的添加，以获得足量残余奥氏体，通过残余奥氏体的TRIP效应获得高延伸率，其并未考虑钢材的扩孔性能。
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％，并具有生产成本低，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。
上述CN102776438A和CN102321841A的这两个专利文献中公开的超高强度钢分别通过添加铌、镧、镍、镉、铜等微合金元素，来获得良好的机械性能，其最终所制备的钢板的性能无法达到本发明所覆盖高延伸、高扩孔性能指标。
发明内容
本发明的目的之一在于提供一种高延伸高扩孔性能的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，还兼具有高延伸、高扩孔性能，其成型性能优异，可以有效应用于汽车行业中，并具有十分广阔的应用前景。
为了实现上述目的，本发明提供了一种高延伸高扩孔性能的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：0.15％～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％；
并且C和Mn的质量百分含量满足：C+Mn/6≥0.52％；
其中所述冷轧钢板的微观组织具有平均直径小于30nm的纳米析出物。
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：0.15％～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％，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≥0.52％；
其中所述冷轧钢板的微观组织具有平均直径小于30nm的纳米析出物。
进一步地，在本发明所述的1300MPa以上级冷轧钢板的微观组织具有平均直径15～28nm的纳米析出物。
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0.15％时，则钢板的强度会受到影响，并且不利于残余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，并导致晶粒尺寸粗大，进而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0.15％～0.30％之间。
Si：在本发明所述的1300MPa以上级冷轧钢板中，Si元素能够起到固溶强化作用，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0.3％～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1.8％～2.5％之间，是因为：本发明在热轧时会产生大量碳化物造成基体组织碳当量不足，当钢中Mn的质量百分含量低于1.8％时，则碳当量不足会导致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，则碳当量会显著提高，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1.8％～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元素能够促进马氏体生成，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，反而会致使钢材的塑性下降。发明人研究发现，当钢中B元素的含量低于0.001％时，则无法有效发挥B元素的作用，而当钢中B元素含量高于0.003％时，则会对钢材的塑形产生不利影响。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，同时向钢中添加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。在一些实施方案中，将Ti元素的质量百分含量控制在0.01～0.05％之间。
此外，需要注意的是，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≥0.52％。在一些实施方案中，控制钢中C、Mn元素的质量百分含量满足：0.52％≤C+Mn/6≤0.61％。在一些实施方案中，控制钢中C、Mn元素的质量百分含量满足：0.55％≤C+Mn/6≤ 0.605％。
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，因而本发明需严格控制钢中S元素的质量百分含量满足S≤0.003％。此外，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+细小的块状马氏体+贝氏体+所述纳米析出物。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其中马氏体的体积相比例≥55％，贝氏体的体积相比例大于0且＜15％。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其中马氏体的体积相比例为55～90％，优选70～86％。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其中贝氏体的体积相比例为7～14％。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其中马氏体的直径不大于10微米。
进一步地，在本发明所述的1300MPa以上级冷轧钢板中，其中马氏体的平均直径为5～9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，可以保证马氏体的体积相比例大于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，保证最终微观组织组织中获得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，本发明通过合金元素和制造工艺的合理设计，可以具体获得：残余奥氏体+细小的块状马氏体(块状马氏体的直径不大于10微米)+贝氏体+纳米析出物的微观组织，且其纳米析出物的平均直径小于30nm，该组织决 定了本发明所述的冷轧钢板具有良好的延伸率和扩孔率。
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，延伸率大于10％，扩孔率大于40％；当抗拉强度大于1400且≤1500MPa时，延伸率大于9％，扩孔率大于40％；当抗拉强度在1500MPa以上时，延伸率大于8％，扩孔率大于40％。
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1300MPa以上级冷轧钢板在具有超高强度的同时，还具有良好的延伸性能和高扩孔性能。
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)热卷保温罩退火：在卷取后迅速采用保温罩退火，退火时间为0.5-6小时，每小时温降小于等于6℃；
(4)冷轧；
(5)退火：控制退火均热温度为830-860℃，保温时间为40-80s，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的速度冷却到等温保温温度；
(6)等温保温处理：保温温度为400-550℃，保温时间为100-300s；
(7)冷却；以30℃/s-100℃/s的速度冷却到室温；
(8)平整。
在本发明所设计的这种技术方案中，发明人对制造工艺进行了优化设计，其对工艺流程进行了改进。
在本发明中，在热卷卷取后迅速采用保温罩退火是本发明人的独特创新点之一，基于合理的成分和工艺设计，在步骤(3)的工艺中，钢材在较低温度长时间保温退火，会生成细小弥散分布的纳米析出物ε碳化物。然后，通过合理的工艺设计可以进一步使细小弥散的ε碳化物遗传到最终连续退火的成品钢板中。这种弥散析出的碳化物不仅能够提高整体强度、降低各相间的强度差、降低晶界和晶内的强度差，其还可以在变形过程中强化晶界，从而起到提高钢材强度和扩孔率的双重作用。
此外，在本发明上述技术方案中，在步骤(5)的退火步骤中，将退火均热温度 限定在830-860℃之间，是因为其所要实现的是完全奥氏体化温度均热退火。当所采用的退火均热温度低于830℃时，则无法完全奥氏体化获得足够的抗拉强度；而当所采用的退火均热温度高于860℃时，则会导致钢材的扩孔率明显大幅下降。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830-850℃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，从而在最终微观组织中保留平均尺寸小于30nm的细小弥散纳米析出物。
另外，在本发明所设计的步骤(6)的奥氏体等温保温处理工艺是本专利的另一独特创新点，其在退火后控制在贝氏体相变结束温度以上进行等温，此工艺决定了最终马氏体的形态及尺寸，本专利工艺主要包括：全奥氏体化温度均热(即连续退火的均热温度830-860℃)-快速冷却(即50-700℃/s的速度冷却到等温保温温度)-贝氏体相变区保温(即等温保温处理，保温温度为400-550℃)-控制冷速冷却。在奥氏体等温淬火的过程中先获得部分贝氏体，可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。
在本发明所设计的这种冷轧钢板中，其最终微观组织中的马氏体为直径不大于10微米的细小块状马氏体，其通过合理的工艺设计可以将钢中的贝氏体控制在15％以下，从而避免对钢材的强度造成很大影响。相应地，后续通过合理的控制冷却速度工艺设计，既要保证生成体积相比例≥55％的马氏体组织，又要保证马氏体相变后仍然有部分未转变完成的奥氏体以残余奥氏体的形式保留下来。细小的马氏体组织有利于强度和延伸率，而残余奥氏体通过TRIP效应大幅提高延伸率。
在本发明所述的这种制造方法中，每种具体成分的等温保温温度和等温保温时间需要根据动态CCT曲线具体设定。
在本发明所设计的步骤(6)中，在等温保温处理中，其控制保温温度为400-550℃，保温时间为100-300s。当保温温度低于400℃或者保温时间低于100s时，即不利于贝氏体的生成，也不利于使未转变的奥氏体富碳生成残余奥氏体。而当保温温度高于550℃或者保温时间高于300s，则不能保证热轧产生的纳米析出物不粗化。
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0.5小时以上(如0.5～2h)，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150-250℃。
进一步地，在本发明所述的制造方法中，在步骤(2)中，热轧温度不高于920℃。
进一步地，在本发明所述的制造方法中，在步骤(2)中，卷取温度优选为150-230℃。
进一步地，在本发明所述的制造方法中，在步骤(3)中，保温罩退火的开始温度与卷取温度相同，降温速率为每小时2-6℃。
进一步地，在本发明所述的制造方法中，在步骤(4)中，控制冷轧压下率为50-70％。
进一步地，在本发明所述的制造方法中，在步骤(5)中，控制退火均热温度为830-850℃。
进一步地，在本发明所述的制造方法中，在步骤(8)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，可以获得一张兼具高延伸、高扩孔性能的1300MPa以上级冷轧钢板。
该1300MPa以上级冷轧钢板具有十分优异的力学性能，其所具备的残余奥氏体+细小的块状马氏体+贝氏体+纳米析出物的微观组织可以确保钢板获得优良的延伸率、扩孔性能以及较好的成型性。本发明所设计的这种的冷轧钢板的性能满足：当抗拉强度为1300-1400MPa时，延伸率大于10％，扩孔率大于40％；当抗拉强度大于1400且≤1500MPa时，延伸率大于9％，扩孔率大于40％；当抗拉强度在1500MPa以上时，延伸率大于8％，扩孔率大于40％，其可以有效应用于汽车工业中，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设计的这种高延伸高扩孔性能的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0.5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150-250℃。
(3)热卷保温罩退火：在卷取后迅速采用保温罩退火，并控制退火时间为0.5-6小时，保温罩利用钢卷内热，每小时温降小于6℃。
(4)冷轧：控制冷轧压下率为50-70％。
(5)退火：控制退火均热温度为830-860℃，优选为830-850℃，并控制保温时间为40-80s，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的速度冷却到等温保温温度。
(6)等温保温处理：将退火后的钢板进行等温保温处理，并控制保温温度为400-550℃，控制保温时间为100-300s。
(7)冷却；将等温保温处理后的钢板以30℃/s-100℃/s的速度冷却到室温。
(8)平整：控制平整率为0-0.3％。
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740-860℃之间。
表2-2.

在本发明中，将经过上述工艺步骤(1)-(8)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，实施例1-18的冷轧钢板的微观组织均具有：残余奥氏体+细小的块状马氏体+贝氏体+纳米析出物。
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，并对马氏体和纳米析出物的直径进行了检测，相关分析和检测结果列于下述表3之中。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。
表3列出了针对实施例1-18的1300MPa以上级冷轧钢板的微观组织的分析和检测结果。
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以上级冷轧钢板的马氏体的体积相比例在70-86％之间，其贝氏体的体积相比例在7-14％之间，且其马氏体的直径在5.1-8.9微米之间，其纳米析出物的平均直径在15-28nm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、延伸率和扩孔率，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。
扩孔率试验：根据GB/T 24524-2021金属材料薄板和薄带扩孔试验方法，进行检测试验，以检测获得实施例1-18的1300MPa以上级冷轧钢板的扩孔率。
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.
如上述表4所示，本发明所设计的这种实施例1-18的1300MPa以上级冷轧钢板在具有超高强度的同时，还具有良好的延伸性能和扩孔性能。
参阅表4不难看出，实施例1-18所对应制备的1300MPa以上级冷轧钢板的屈服强度在1067-1292MPa之间，其抗拉强度在1328-1552MPa之间，其延伸率在8.5-12.3％之间，扩孔率在43-54％之间。
并且，在本发明所设计的这种实施例1-18中，当所制备的钢板的抗拉强度为1300-1400MPa时(即实施例4-6、实施例10-12)，其延伸率具体在11.1-12.3％之间，其扩孔率具体在53-46％之间；而当抗拉强度大于1400且≤1500MPa时(即实施例1-3、实施例16-18)，其延伸率具体在9.1-9.7％之间，其扩孔率具体在46-55％之间；当抗拉强度为1500MPa以上时(即实施例7-9、实施例13-15)，其延伸率具体在8.5-9.7％之间，其扩孔率具体在47-50％之间。
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. 一种高延伸高扩孔性能的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：0.15％～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％；
    并且C和Mn的质量百分含量满足：C+Mn/6≥0.52％；
    其中所述冷轧钢板的微观组织具有平均直径小于30nm的纳米析出物。
  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：0.15％～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％，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≥0.52％；
    其中所述冷轧钢板的微观组织具有平均直径小于30nm的纳米析出物。
  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+细小的块状马氏体+贝氏体+所述纳米析出物。
  5. 如权利要求4所述的1300MPa以上级冷轧钢板，其特征在于，其中马氏体的体积相比例≥55％，贝氏体的体积相比例大于0且＜15％。
  6. 如权利要求5所述的1300MPa以上级冷轧钢板，其特征在于，其中马氏体的体积相比例为70～86％，贝氏体的体积相比例为7～14％。
  7. 如权利要求4所述的1300MPa以上级冷轧钢板，其特征在于，其中马氏体的直径不大于10微米。
  8. 如权利要求7所述的1300MPa以上级冷轧钢板，其特征在于，其中马氏体的平均直径为5～9微米。
  9. 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，延伸率大于10％，扩孔率大于40％；
    当抗拉强度大于1400且≤1500MPa时，延伸率大于9％，扩孔率大于40％；
    当抗拉强度为1500MPa以上时，延伸率大于8％，扩孔率大于40％。
  10. 如权利要求1-9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)热卷保温罩退火：在卷取后迅速采用保温罩退火，退火时间为0.5-6小时，每小时温降小于等于6℃；
    (4)冷轧；
    (5)退火：控制退火均热温度为830-860℃，保温时间为40-80s，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的速度冷却到等温保温温度；
    (6)等温保温处理：保温温度为400-550℃，保温时间为100-300s；
    (7)冷却；以30℃/s-100℃/s的速度冷却到室温；
    (8)平整。
  11. 如权利要求10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0.5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150-250℃。
  12. 如权利要求11所述的制造方法，其特征在于，在步骤(2)中，热轧温度不高于920℃，卷取温度为150-230℃；优选地，在步骤(3)中，保温罩退火的开始温度与卷取温度相同，降温速率为每小时2-6℃。
  13. 如权利要求10所述的制造方法，其特征在于，在步骤(4)中，控制冷轧压下率为50-70％。
  14. 如权利要求10所述的制造方法，其特征在于，在步骤(5)中，控制退火均热温度为830-850℃。
  15. 如权利要求10所述的制造方法，其特征在于，在步骤(8)中，控制平整率为0-0.3％。
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