WO2021238917A1 - 一种780MPa级冷轧退火双相钢及其制造方法 - Google Patents

一种780MPa级冷轧退火双相钢及其制造方法 Download PDF

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WO2021238917A1
WO2021238917A1 PCT/CN2021/095808 CN2021095808W WO2021238917A1 WO 2021238917 A1 WO2021238917 A1 WO 2021238917A1 CN 2021095808 W CN2021095808 W CN 2021095808W WO 2021238917 A1 WO2021238917 A1 WO 2021238917A1
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cold
rolled
phase steel
annealed dual
dual
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PCT/CN2021/095808
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French (fr)
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李伟
朱晓东
薛鹏
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宝山钢铁股份有限公司
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Priority to US17/927,875 priority Critical patent/US20230203611A1/en
Priority to JP2022572703A priority patent/JP2023527390A/ja
Priority to CA3180469A priority patent/CA3180469A1/en
Priority to EP21813104.3A priority patent/EP4159885A4/en
Publication of WO2021238917A1 publication Critical patent/WO2021238917A1/zh

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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
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    • 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
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
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    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

Definitions

  • the invention relates to a metal material and a manufacturing method thereof, in particular to a cold-rolled annealing dual-phase steel and a manufacturing method thereof.
  • the high-strength dual-phase steel has good mechanical properties and serviceability, and can be effectively applied to the production of vehicle structural parts.
  • ultra-high-strength steel With the development of ultra-high-strength steel and the current market changes, it is expected that ultra-high-strength steel will have economical and better performance.
  • 780DP steel is still the mainstream application steel, accounting for 60% of the total DP steel. It is widely used in various types of structural parts and safety parts.
  • duplex steel With the continuous development of the trend of weight reduction and energy saving in the automobile industry, and the rapid progress of domestic and foreign steel mills, especially the domestic steel mills, the future development of duplex steel will inevitably focus on low-cost and high-performance integration.
  • the patent number is CA2526488, the publication date is December 2, 2004, and the Canadian patent document titled "Cold-rolled steel sheet with tensile strength of 780MPA or higher local plasticity and suppression of increase in welding hardness" discloses a cold
  • the chemical composition of rolled steel plate is: C: 0.05 ⁇ 0.09%; Si: 0.4 ⁇ 1.3%; Mn: 2.5 ⁇ 3.2%; you can choose to add Mo: 0.05 ⁇ 0.5% or Ni: 0.05 ⁇ 2%; P: 0.001 ⁇ 0.05%; S ⁇ 0.08*Ti-3.43*N+0.004; N ⁇ 0.006%; Al: 0.005 ⁇ 0.10%; Ti: 0.001 ⁇ 0.045%, Nb ⁇ 0.04% or B: 0.0002 ⁇ 0.0015% can also be added.
  • the bainite content is required to be greater than 7%, Pcm ⁇ 0.3, hot rolling at a temperature above Ar3, coiling below 700°C, cold rolling, annealing between 700-900°C, rapid cooling at 550-700°C, and the final minimum strength is 780Mpa high-strength steel.
  • the steel has the characteristics of strong local deformability and low hardness in the welding area.
  • the high Mn content used in the design of the steel will inevitably cause serious band-like structure, which will result in uneven mechanical properties.
  • more Si is added, which is detrimental to the surface quality and welding performance of the steel.
  • the US patent document with publication number US20050167007 and publication date on August 4, 2005 discloses a method for manufacturing a high-strength steel sheet, the chemical composition of which is: 0.05 to 0.13% C, 0.5 to 2.5% Si, 0.5 to 3.5% Mn,0.05 ⁇ 1%Cr,0.05 ⁇ 0.6%Mo, ⁇ 0.1%Al, ⁇ 0.005%S, ⁇ 0.01%N, ⁇ 0.03%P, add 0.005-0.05%Ti or 0.005-0.05%Nb or 0.005-0.2 %V.
  • the steel is hot-rolled above Ar3 temperature, coiled at 450-700°C, cooled and quenched from 700-600°C at a cooling rate of 100°C/s after annealing, and then tempered at 180-450°C to obtain the ultimate tensile strength 780Mpa is a high-strength steel with a hole expansion rate higher than 50%.
  • the main problem of the steel is that the total amount of alloy is too high and the Si content is high, which is not conducive to the weldability and phosphating properties of the steel.
  • the publication number is CN101363099A, the publication date is February 11, 2009, and the Chinese patent document entitled "A tensile strength 1000MPA grade cold-rolled dual-phase steel sheet and its preparation method" discloses an ultra-high-strength dual-phase steel, Including C: 0.14 ⁇ 0.21%, Si: 0.4 ⁇ 0.9%, Mn: 1.5 ⁇ 2.1%, P: ⁇ 0.02%, S ⁇ 0.01%, Nb: 0.001 ⁇ 0.05%, V: 0.001 ⁇ 0.02%, after hot rolling After cold rolling, heat preservation at 760 ⁇ 820°C, cooling rate 40 ⁇ 50°C/s, and overaging at 240 ⁇ 320°C for 180 ⁇ 300s.
  • the steel has a high carbon equivalent design and does not have the characteristics of balanced performance.
  • One of the objectives of the present invention is to provide an economical 780MPa grade cold-rolled and annealed dual-phase steel.
  • the cold-rolled and annealed dual-phase steel is reasonably designed with alloy elements and manufacturing processes, and without the addition of Mo and Cr.
  • the obtained steel plate reaches 780MPa strength, and obtains a fine and uniform martensite + ferrite dual phase structure to ensure excellent elongation and cold bending performance, and has good formability.
  • the yield strength of the cold-rolled and annealed dual-phase steel is ⁇ 420MPa; its tensile strength is >780MPa; the A 50 gauge length elongation at break ⁇ 18%; the 90-degree cold-bending performance parameter R/t ⁇ 1, where R represents the bending radius, t represents the thickness of the board, and the unit parameter is mm.
  • the present invention provides a 780MPa grade cold-rolled and annealed dual-phase steel, the matrix structure of which is fine and uniform martensite + ferrite, the cold-rolled and annealed dual-phase steel contains mass percentage in addition to Fe
  • the following chemical elements as follows:
  • the cold-rolled and annealed dual-phase steel does not contain Cr and Mo elements.
  • the mass percentage of each chemical element is:
  • the composition design of the cold-rolled and annealed dual-phase steel of the present invention is mainly composed of C and Mn to ensure that the cold-rolled and annealed dual-phase steel can reach the strength of 780MPa.
  • the addition of precious alloying elements such as Mo and Cr can effectively ensure economy.
  • the addition of a small amount of Nb and Ti can achieve the effect of inhibiting the growth of austenite grains and can effectively refine the grains.
  • the special composition design without adding Mo and Cr also makes the strength of the hot-rolled coil not too high, which can ensure the manufacturability of cold-rolled.
  • the design principles of each chemical element are as follows:
  • the addition of C element can increase the strength of the steel and increase the hardness of martensite. If the mass percentage of C in the steel is less than 0.1%, the strength of the steel plate is affected, and is not conducive to the formation and stability of austenite; and when the mass percentage of C in the steel is higher than 0.13%, it will cause Martensite The body hardness is too high and the grain size is coarse, which is not conducive to the formability of the steel plate. At the same time, the carbon equivalent is too high, which is not conducive to welding. Therefore, the mass percentage of C in the cold-rolled and annealed dual-phase steel of the present invention is controlled to be between 0.1% and 0.13%.
  • the mass percentage of C can be controlled between 0.11% and 0.125%.
  • the addition of Si element to the steel can improve the hardenability.
  • the solid-solution Si in the steel can affect the interaction of dislocations, thereby increasing the work hardening rate.
  • the elongation can be appropriately increased, which is beneficial to obtain better formability.
  • the mass percentage of Si in the steel is controlled to be between 0.4% and 0.8%.
  • the mass percentage of Si can be controlled between 0.5% and 0.7%.
  • Mn In the cold-rolled and annealed dual-phase steel of the present invention, the addition of Mn element is beneficial to improve the hardenability of the steel and can effectively increase the strength of the steel plate.
  • the mass percentage of Mn in the steel is less than 1.65%, the strength of the steel plate is insufficient; when the mass percentage of Mn in the steel is higher than 1.9%, the strength of the steel plate is too high, which will reduce its formability . Therefore, the mass percentage of Mn in the cold-rolled and annealed dual-phase steel of the present invention is controlled to be between 1.65% and 1.9%.
  • the mass percentage of Mn can be controlled between 1.7% and 1.8%.
  • Al In the cold-rolled and annealed dual-phase steel of the present invention, the addition of Al element can play the role of deoxidation and grain refinement. In the cold-rolled and annealed dual-phase steel of the present invention, the mass percentage of Al is controlled to be between 0.01% and 0.05%.
  • the mass percentage of Al can be controlled between 0.015% and 0.045%.
  • the Nb element is an important element for grain refinement.
  • the strain-induced precipitates can significantly reduce the recrystallization temperature of deformed austenite through the effects of particle pinning and sub-grain boundaries, provide nucleation particles, and have a significant effect on grain refinement; in the process of continuous deaustenitization Among them, the soaking undissolved carbon and nitride material points will prevent the soaking austenite grains from coarsening through the particle pinning grain boundary mechanism, thereby effectively refining the grains. Therefore, the mass percentage of Nb in the cold-rolled and annealed dual-phase steel of the present invention is controlled to be between 0.01 and 0.03%.
  • the mass percentage of Nb can be controlled between 0.015 and 0.025%.
  • the added strong carbide-forming element Ti also shows a strong effect of inhibiting the growth of austenite grains at high temperatures.
  • the addition of Ti has Helps refine the grains. Therefore, the mass percentage of Ti in the cold-rolled and annealed dual-phase steel of the present invention is controlled to be between 0.01 and 0.03%.
  • the mass percentage of Ti can be controlled between 0.015 and 0.025%.
  • the mass percentage of Nb and Ti in the cold-rolled and annealed dual-phase steel can also conform to the formula: Nb%+Ti% ⁇ 3 ⁇ 0.047%, preferably ⁇ 0.06%.
  • Nb and Ti both represent the mass percentage of the corresponding element, that is, the value before the percentage sign is added in the formula. In some embodiments, 0.047% ⁇ Nb%+Ti% ⁇ 3 ⁇ 0.10%; preferably, 0.06% ⁇ Nb%+Ti% ⁇ 3 ⁇ 0.10%.
  • the mass percentage of each chemical element satisfies at least one of the following items:
  • the inevitable impurities include P, S and N elements, and the content is controlled to at least one of the following items: P ⁇ 0.015%, S ⁇ 0.003%, N ⁇ 0.005%.
  • the phase ratio (volume ratio) of the martensite is> 55%.
  • the grain diameter of the martensite is not greater than 5 microns, and the grain diameter of the ferrite is not greater than 5 microns.
  • its performance satisfies at least one of the following items: yield strength ⁇ 420MPa, preferably ⁇ 430MPa; its tensile strength>780MPa, preferably ⁇ 800MPa; A 50 gauge length breaking elongation ⁇ 18%; 90 degree cold bending performance characterization parameter R/t ⁇ 1, where R represents the bending radius, t represents the plate thickness, and the unit parameter is mm.
  • its performance satisfies the following: yield strength ⁇ 420MPa, preferably ⁇ 430MPa; its tensile strength>780MPa, preferably ⁇ 800MPa; A 50 gauge length fracture Elongation ⁇ 18%; 90-degree cold bending performance characterization parameter R/t ⁇ 1, where R represents the bending radius, t represents the plate thickness, and the unit parameter is mm.
  • the yield ratio of the cold-rolled and annealed dual-phase steel of the present invention is 0.53-0.57.
  • another object of the present invention is to provide a method for manufacturing cold-rolled and annealed dual-phase steel.
  • the cold-rolled and annealed dual-phase steel produced by the method has the characteristics of high strength, excellent elongation, and cold bending performance. Its yield strength ⁇ 420MPa, tensile strength >780MPa, A 50 gauge length elongation at break ⁇ 18%, 90 degree cold bending performance parameter R/t ⁇ 1, where R represents the bending radius, t represents the plate thickness, and the unit parameter is mm.
  • the present invention proposes the above-mentioned manufacturing method of cold-rolled and annealed dual-phase steel, which includes the following steps:
  • Annealing soaking temperature is 770-820°C
  • annealing time is 40 ⁇ 200s
  • the annealing soaking temperature is controlled to be 770-820°C, because: when the annealing soaking temperature is lower than 770°C , It is impossible to obtain 780MPa tensile strength steel; and if the annealing soaking temperature is higher than 820°C, the grain size will be coarse and the forming performance will be greatly reduced. Therefore, controlling the annealing soaking temperature to 770-820°C can ensure that the tensile strength of 780MPa is obtained, and the obtained grain size can be fine, so that the cold-rolled annealed dual-phase steel can obtain better forming properties.
  • the annealing soaking temperature can be controlled at 790-810°C. between.
  • step (2) the slab is first heated to 1160-1220°C, preferably 1165-1215°C, kept at the temperature for more than 0.6 hours, preferably 0.6-1.5 hours, and then used Hot rolling at a temperature of 850-900°C, and rapid cooling at a speed of 30-80°C/s after rolling; controlling the coiling temperature to 500-600°C, preferably 520-600°C, and air cooling after coiling.
  • step (3) the cold rolling reduction rate is controlled to be 50-70%.
  • the tempering temperature is controlled to be 200-270°C, and the tempering time is 100-400s, preferably 150-400s.
  • step (6) the leveling reduction rate is controlled to be ⁇ 0.3%.
  • the annealing soaking temperature is 790-810°C.
  • the cold-rolled and annealed dual-phase steel and the manufacturing method thereof according to the present invention have the following advantages and beneficial effects:
  • the cold-rolled and annealed dual-phase steel of the present invention adopts a reasonable alloy chemical composition design. Under the premise of not adding Mo and Cr, a steel sheet with a martensite + ferrite dual-phase structure with a tensile strength greater than 780 MPa is obtained. Yield strength ⁇ 420MPa, tensile strength >780MPa, its A 50 gauge length elongation at break ⁇ 18%, and the 90-degree cold bending performance parameter R/t ⁇ 1. It achieves the characteristics of high strength, excellent elongation and cold bending performance while having good economy.
  • the manufacturing method of the present invention through reasonable design and control of specific process parameters, makes the cold-rolled and annealed dual-phase steel obtained by the manufacturing method of the present invention not only has good economy, but also has high strength and excellent The characteristics of elongation and cold bending performance.
  • Figure 1 shows the structure of the cold rolled and annealed dual phase steel of Example 1.
  • Table 1 lists the mass percentages of various chemical elements in the steel grades corresponding to the cold-rolled and annealed dual-phase steels of Examples 1-7 and the steels of Comparative Examples 1-14.
  • Hot rolling heat the slab to 1160-1220°C, hold for more than 0.6 hours, then hot-roll it at a temperature of 850-900°C, and cool it quickly at a speed of 30-80°C/s after rolling; control the coiling
  • the temperature is 500-600°C, air cooling after coiling
  • the annealing soaking temperature is controlled to 770-820°C, or it can be preferably controlled between 790-810°C
  • the annealing time is controlled to 40-200s, and then cooled to a fast speed at a rate of 3-5°C/s Cooling start temperature, and then rapid cooling at a rate of 30-80°C/s, where the rapid cooling start temperature is 650-730°C, and the rapid cooling end temperature is 200-270°C;
  • Tempering Control the tempering temperature to 200-270°C, and the tempering time to 100-400s.
  • Table 2-1 and Table 2-2 list the specific process parameters of the cold-rolled and annealed dual-phase steel of Example 1-7 and the steel of Comparative Example 1-14.
  • the cold-rolled and annealed dual-phase steels of Examples 1-7 and Comparative Examples 1-14 were subjected to various performance tests, and the obtained test results are listed in Table 3.
  • the performance test method refers to the GB/T 13239-2006 low-temperature tensile test method for metallic materials, prepares standard specimens, performs static stretching on a tensile testing machine, and obtains the corresponding stress-strain curve. After data processing, the yield strength and resistance are finally obtained. Tensile strength and elongation at break parameters.
  • Table 3 lists the performance test results of the cold-rolled and annealed dual-phase steels of Examples 1-7 and the steels of Comparative Examples 1-14.
  • Example 1 To (MPa) (MPa) (%) (mm) (mm) (mm) To Example 1 454 800 22.3 1.0 1.1 0.91
  • Example 3 474 856 19.5 1.0 1.1 0.91
  • Example 4 449 832 20.5 1.0 1.2 0.83
  • Example 5 458 827 20.8 1.0 1.2 0.83
  • Example 6 476 872 19.7 1.0 1.2 0.83
  • Example 7 489 884 18.4 1.0 1.1 0.91 Comparative example 1 386 768 25.2 1.0 1.2 0.83 Comparative example 2 525 934 14.6 1.5 1.0 1.50 Comparative example 3 393 777 24.3 1.0 1.0 1.00 Comparative example 4 518 941 15.1 1.5 1.1 1.36 Comparative example 5 404 835 19.6 1.0 1.0 1.00 Comparative example 6 408 828 20.1 1.0 1.1 0.91 Comparative example 7 383 765 24.7 1.0 1.1 0.91 Comparative example 8 525 936 16.6 1.5 1.3
  • the yield strength are ⁇ 420MPa; average tensile strength> 780MPa, A 50 gauge breaking extension rate ⁇ 18% , 90-degree cold bending performance parameter R/t ⁇ 1 (R represents the bending radius, t represents the plate thickness, and the unit parameter is mm).
  • R/t ⁇ 1 90-degree cold bending performance parameter
  • the properties of the cold-rolled and annealed dual-phase steels of each embodiment are very excellent. Without the addition of precious alloying elements such as Mo and Cr, a tensile strength greater than 780 MPa is obtained, with good elongation and excellent cold resistance. Bending performance.

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Abstract

本发明公开了一种抗拉强度＞780MPa级的冷轧退火双相钢，其基体组织为细小均匀的马氏体+铁素体，冷轧退火双相钢含有质量百分比如下的下述化学元素：C：0.1％～0.13％，Si：0.4％～0.8％，Mn：1.65％～1.9％，Al：0.01％～0.05％，Nb：0.01～0.03％，Ti：0.01～0.03％；并且冷轧退火双相钢不含有Cr和Mo元素。此外本发明还公开了一种冷轧退火双相钢的制造方法，其包括冶炼和连铸、热轧、冷轧、退火、回火和平整。本发明冷轧退火双相钢不仅有经济性，还具有高强度和优良延伸率以及冷弯性能的特性。

Description

一种780MPa级冷轧退火双相钢及其制造方法 技术领域
本发明涉及一种金属材料及其制造方法，尤其涉及一种冷轧退火双相钢及其制造方法。
背景技术
随着全球能源危机和环境问题的加剧，节能和安全成为了汽车制造业的主要发展方向。其中，降低车重是节能和减少排放措施之一。而高强度双相钢具有良好的机械性能和使用性能，可以有效适用于车辆结构件的生产制造。
随着超高强钢的发展以及目前市场的变化，期望超高强钢具有经济型以及更优的性能。目前780DP钢仍是主流应用钢，占整个DP钢总量的60％比例，其广泛地应用于各种类型的结构件、安全件。随着汽车行业减重节能的趋势不断发展，国内外特别是国内钢厂水平的迅速进步，未来双相钢的发展，必然会是以低成本和高性能综合为主。
专利号为CA2526488，公开日为2004年12月2日，名称为“具有780MPA的拉伸强度或更高的局部塑性和抑制焊接硬度增加的冷轧钢板”的加拿大专利文献，公开了一种冷轧钢板，其化学成分为：C：0.05～0.09％；Si：0.4～1.3％；Mn：2.5～3.2％；可以选择添加Mo：0.05～0.5％或者Ni：0.05～2％；P：0.001～0.05％；S≤0.08*Ti-3.43*N+0.004；N≤0.006％；Al：0.005～0.10％；Ti：0.001～0.045％，还可以添加Nb≤0.04％或者B：0.0002～0.0015％，可以添加Ca进行处理；其它为Fe和不可避免杂质。要求贝氏体含量大于7％，Pcm≤0.3，通过Ar3以上温度热轧，700℃以下卷取，冷轧、700～900℃之间退火，550～700℃开始快速冷却，最终获得强度最小为780Mpa的高强度钢。该钢具有局部变形能力强，焊接区域硬度低的特点。但是，该钢在设计中采用了较高的Mn含量，必然会造成严重的带状组织，从而造成力学性能的不均匀性。另外，在加入了高Mn的情况下，又加入了比较多的Si，对钢的表面质量和焊接性能均不利。
公开号为US20050167007，公开日为2005年8月4日的美国专利文献公开了一 种高强度钢板的制造方法，其化学成分为：0.05～0.13％C,0.5～2.5％Si,0.5～3.5％Mn,0.05～1％Cr，0.05～0.6％Mo，≤0.1％Al，≤0.005％S，≤0.01％N，≤0.03％P，添加0.005～0.05％Ti或者0.005～0.05％Nb或者0.005～0.2％V。该钢经Ar3温度以上热轧，450～700℃卷取，退火后以100℃/s的冷速从700～600℃冷却淬火，然后在180～450℃之间回火，最终得到抗拉强度780Mpa的扩孔率高于50％的高强钢。该钢的主要问题是合金总量过高，Si含量高，不利于钢的焊接性和磷化性能。
公开号为CN101363099A，公开日为2009年2月11日，名称为“一种抗拉强度1000MPA级冷轧双相钢板及制备方法”的中国专利文献，公开了一种超高强度双相钢，包括C：0.14～0.21％，Si：0.4～0.9％，Mn：1.5～2.1％，P：≤0.02％，S≤0.01％，Nb：0.001～0.05％，V：0.001～0.02％，经热轧冷轧后，在760～820℃间保温，冷速40～50℃/s，在240～320℃过时效180～300s。该钢的碳当量设计较高，并且不具备性能均衡的特点。
由此可见，现有设计780Mpa双相钢的专利技术，有的虽然涉及较好的成型性能，但或采用了高C含量和高Si含量，或含有较多的Cr、Ni、Mo等合金含量，不利于钢的焊接性、表面质量和磷化性能，同时成本较高。此外，有些高Si含量的钢虽扩孔率很高且弯曲性能较好，但屈强比高，冲压性能下降。
发明内容
本发明的目的之一在于提供一种经济型780MPa级的冷轧退火双相钢，该冷轧退火双相钢通过合金元素和制造工艺的合理设计，在不添加Mo、Cr的前提下，使得到的钢板达到780MPa级强度，获得细小均匀的马氏体+铁素体双相组织以保证延伸率和冷弯性能上表现优良，具有较好成型性。该冷轧退火双相钢的屈服强度≥420MPa；其抗拉强度＞780MPa；A 50标距断裂延伸率≥18％；90度冷弯性能表征参量R/t≤1，其中R表示弯曲半径，t表示板厚，单位参量为mm。
为了实现上述目的，本发明提供了一种780MPa级冷轧退火双相钢，其基体组织为细小均匀的马氏体+铁素体，所述冷轧退火双相钢除了Fe以外还含有质量百分比如下的下述化学元素：
C：0.1％～0.13％，Si：0.4％～0.8％，Mn：1.65％～1.9％，Al：0.01％～0.05％，Nb：0.01～0.03％，Ti：0.01～0.03％；
并且所述冷轧退火双相钢不含有Cr和Mo元素。
进一步地，在本发明所述的冷轧退火双相钢中，其各化学元素质量百分比为：
C：0.1％～0.13％，Si：0.4％～0.8％，Mn：1.65％～1.9％，Al：0.01％～0.05％，Nb：0.01～0.03％，Ti：0.01～0.03％，余量为Fe和其他不可避免的杂质。
在本发明所述的冷轧退火双相钢中，本发明冷轧退火双相钢成分设计以C、Mn为主的成分体系，保证冷轧退火双相钢可以达到780MPa级强度，该钢不添加Mo、Cr等贵重合金元素可以有效保证经济型。Nb、Ti的微量添加，达到抑制奥氏体晶粒长大的效果，可以有效的细化晶粒。不添加Mo、Cr的特殊成分设计，也使得热轧卷的强度不太高，可以保证冷轧的可制造性。各化学元素的设计原理如下所述：
C：在本发明所述的冷轧退火双相钢中，C元素的添加可以提高钢的强度，提高马氏体的硬度。若钢中C的质量百分比低于0.1％，则钢板的强度受到影响，并且不利于奥氏体的形成量和稳定性；而当钢中C的质量百分比高于0.13％，则会造成马氏体硬度过高，晶粒尺寸粗大，不利于钢板的成型性能，同时碳当量过高，不利于焊接使用。因此在本发明所述的冷轧退火双相钢中控制C的质量百分比在0.1％～0.13％之间。
在一些优选的实施方式中，C的质量百分比可以控制在0.11％～0.125％之间。
Si：在本发明所述的冷轧退火双相钢中，钢中添加Si元素可以提高淬透性。并且钢中固溶的Si可以影响位错的交互作用，从而增加加工硬化率，在双相钢中可以适当提高延伸率，有益于获得较好的成型性。但需要注意的是，若钢中Si的质量百分比过高，则会不利于表面质量的控制。因此，在本发明所述的冷轧退火双相钢中控制Si的质量百分比在0.4％～0.8％之间。
在一些优选的实施方式中，Si的质量百分比可以控制在0.5％～0.7％之间。
Mn：在本发明所述的冷轧退火双相钢中，添加Mn元素有利于提高钢的淬透性，可以有效提高钢板的强度。但需要注意的是，当钢中Mn的质量百分比低于1.65％时，钢板的强度不足；当钢中Mn的质量百分比高于1.9％时，则钢板的强度过高，会使得其成型性能下降。因此，在本发明所述的冷轧退火双相钢中控制Mn的质量百分比在1.65％～1.9％之间。
在一些优选的实施方式中，Mn的质量百分比可以控制在1.7％～1.8％之间。
Al：在本发明所述的冷轧退火双相钢中，Al元素的添加，可以起到脱氧作用和细化晶粒的作用。在本发明所述的冷轧退火双相钢中控制Al的质量百分比在0.01％～0.05％之间。
在一些优选的实施方式中，Al的质量百分比可以控制在0.015％～0.045％之间。
Nb：在本发明所述的冷轧退火双相钢中，Nb元素是细化晶粒的重要元素，在微合金钢中加入少量的强碳化物形成元素Nb后，在控制轧制过程中，可以应变诱导析出相通过质点钉扎和亚晶界的作用而相当显著的降低变形奥氏体的再结晶温度，提供形核质点，对细化晶粒作用明显；在连退奥氏体化过程中，均热未溶的碳、氮化物质点将通过质点钉扎晶界机制而阻止均热奥氏体晶粒的粗化，从而有效细化晶粒。因此，在本发明所述的冷轧退火双相钢中控制Nb的质量百分比在0.01～0.03％之间。
在一些优选的实施方式中，Nb的质量百分比可以控制在0.015～0.025％之间。
Ti：在本发明所述的冷轧退火双相钢中，添加的强碳化物形成元素Ti在高温下也显示出一种强烈的抑制奥氏体晶粒长大的效果，同时Ti的添加有助于细化晶粒。因此，在本发明所述的冷轧退火双相钢中控制Ti的质量百分比在0.01～0.03％之间。
在一些优选的实施方式中，Ti的质量百分比可以控制在0.015～0.025％之间。
在上述成分设计中，冷轧退火双相钢中不添加Mo、Cr等贵重合金元素以确保经济型，同时为了保证在40-100℃/s正常连续退火气体冷却速度下获得780MPa级抗拉强度，成分中需要保证C、Mn的合金添加含量以提供足够的淬透性。但C、Mn合金元素的含量需要有上限控制，以保证优良的焊接性能及成型性能，避免强度超出上限。
由于钢生产过程中Al的氮化物与Nb、Ti的碳氮化物的竞争析出关系，综合本发明成分体系中Al、N的含量，Nb、Ti的添加需要保证一定的量才能起到细化晶粒的作用。所以冷轧退火双相钢中的Nb、Ti质量百分含量还可以符合公式：Nb％+Ti％×3≥0.047％，优选≥0.06％。式中Nb和Ti均表示相应元素的质量百分含量，即公式中带入百分号前面的数值。在一些实施方案中，0.047％≤Nb％+Ti％×3≤0.10％；优选地，0.06％≤Nb％+Ti％×3≤0.10％。
进一步地，在本发明所述的冷轧退火双相钢中，其各化学元素的质量百分含量满足下述各项的至少其中一项：
C：0.11％～0.125％，
Si：0.5％～0.7％，
Mn：1.7％～1.8％，
Al：0.015％～0.045％，
Nb：0.015～0.025％，
Ti：0.015～0.025％。
进一步地，在本发明所述的冷轧退火双相钢中，其中不可避免的杂质包括P、S和N元素，其含量控制为下述各项的至少其中之一：P≤0.015％，S≤0.003％，N≤0.005％。
上述技术方案中，在本发明所述的冷轧退火双相钢中，P、N和S均是钢中不可避免的杂质元素，在钢中P、N和S元素含量越低，实施效果越好。S形成的MnS严重影响成形性能，N容易导致板坯表面产生裂纹或气泡。因此，在本发明所述的冷轧退火双相钢中，控制P的质量百分比为P≤0.015％，控制S的质量百分比为S≤0.003％，控制N的质量百分比为N≤0.005％。
进一步地，在本发明所述的冷轧退火双相钢中，所述马氏体的相比例(体积比)＞55％。
进一步地，在本发明所述的冷轧退火双相钢中，所述马氏体的晶粒直径不大于5微米，所述铁素体的晶粒直径不大于5微米。
进一步地，在本发明所述的冷轧退火双相钢中，其性能满足下述各项的至少其中之一：屈服强度≥420MPa、优选≥430MPa；其抗拉强度＞780MPa、优选≥800MPa；A 50标距断裂延伸率≥18％；90度冷弯性能表征参量R/t≤1，其中R表示弯曲半径，t表示板厚，单位参量为mm。
进一步地，在本发明所述的冷轧退火双相钢中，其性能满足下述各项：屈服强度≥420MPa、优选≥430MPa；其抗拉强度＞780MPa、优选≥800MPa；A 50标距断裂延伸率≥18％；90度冷弯性能表征参量R/t≤1，其中R表示弯曲半径，t表示板厚，单位参量为mm。
进一步地，本发明所述的冷轧退火双相钢的屈强比为0.53-0.57。
相应地，本发明的另一目的在于提供一种冷轧退火双相钢的制造方法，采用该制造方法制得的冷轧退火双相钢具有高强度和优良延伸率以及冷弯性能的特性，其屈服强度≥420MPa，抗拉强度＞780MPa，A 50标距断裂延伸率≥18％，90度冷弯性能表征参量R/t≤1，其中R表示弯曲半径，t表示板厚，单位参量为mm。
为了实现上述目的，本发明提出了上述的冷轧退火双相钢的制造方法，包括步骤：
(1)冶炼和连铸；
(2)热轧；
(3)冷轧；
(4)退火：退火均热温度为770-820℃，退火时间为40～200s，然后以3-5℃/s的速度冷却到快冷开始温度，然后以30～80℃/s的速度快速冷却，其中快冷开始温度为650～730℃，快冷结束温度为200-270℃；
(5)回火；
(6)平整。
在本发明所述的冷轧退火双相钢的制造方法中，在所述步骤(4)中，控制退火均热温度为770-820℃，是因为：当退火均热温度低于770℃时，无法获得780MPa抗拉强度的钢；而若退火均热温度高于820℃，则晶粒尺寸粗大，会使成型性能大幅下降。因此，控制退火均热温度为770-820℃即能够保证获得780MPa的抗拉强度，又能保证获得的晶粒尺寸细小，从而使冷轧退火双相钢得到较好的成型性能。
在一些优选的实施方式中，为了获得更优的实施效果，使获得的晶粒尺寸更加细小，获得的钢的机械性适中，成型性能更优，退火均热温度可以控制在790-810℃之间。
进一步地，在本发明所述的制造方法中，在步骤(2)中，将板坯先加热至1160-1220℃、优选1165-1215℃，保温0.6小时以上、优选0.6-1.5小时，然后采用850-900℃的温度热轧，轧后以30-80℃/s的速度快速冷却；控制卷取温度为500-600℃、优选520-600℃，卷取后空冷。
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，控制回火温度为200-270℃，回火时间为100-400s、优选150-400s。
进一步地，在本发明所述的制造方法中，在步骤(6)中，控制平整压下率≤0.3％。
进一步地，在本发明所述的制造方法中，在步骤(4)中，所述退火均热温度为790-810℃。
本发明所述的冷轧退火双相钢及其制造方法相较于现有技术具有如下所述的优点以及有益效果：
本发明所述的冷轧退火双相钢采用合理的合金化学成分设计，在不添加Mo、Cr的前提下，获得抗拉强度大于780MPa的马氏体+铁素体双相组织的钢板，其屈服强 度≥420MPa，抗拉强度＞780MPa，其A 50标距断裂延伸率≥18％，90度冷弯性能表征参量R/t≤1。实现了在具有良好经济性的同时，还具有高强度以及优良的延伸率和冷弯性能的特性。
相应地，本发明所述的制造方法通过对具体工艺参数合理设计和控制，使得采用本发明所述的制造方法所获得的冷轧退火双相钢不仅具有良好经济性，还具有高强度以及优良的延伸率和冷弯性能的特性。
附图说明
图1显示实施例1的冷轧退火双相钢的组织。
具体实施方式
下面将结合具体的实施例对本发明所述的经济型780MPa级的冷轧退火双相钢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1-7和对比例1-14
表1列出了实施例1-7的冷轧退火双相钢和对比例1-14钢对应的钢种中各化学元素质量百分比。
表1.(wt％，余量为Fe和其他除了P、S以及N以外的不可避免的杂质)
Figure PCTCN2021095808-appb-000001
Figure PCTCN2021095808-appb-000002
本发明所述实施例1-7的冷轧退火双相钢和对比例1-14的钢均采用以下步骤制得：
(1)冶炼和连铸：获得要求的合金成分，尽量降低S、P的含量；
(2)热轧：将板坯先加热至1160-1220℃，保温0.6小时以上，然后采用850-900℃的温度热轧，轧后以30-80℃/s的速度快速冷却；控制卷取温度为500-600℃，卷取后空冷；
(3)冷轧：控制冷轧压下率为50-70％；
(4)退火：退火均热温度控制为770-820℃，也可以优选地控制在790-810℃之间，控制退火时间为40～200s，然后以3-5℃/s的速度冷却到快冷开始温度，然后以30～80℃/s的速度快速冷却，其中快冷开始温度为650～730℃，快冷结束温度为200-270℃；
(5)回火：控制回火温度为200-270℃，回火时间为100-400s。
(6)平整：控制平整压下率≤0.3％。
需要说明的是，实施例1-7的冷轧退火双相钢的化学成分和相关工艺参数均满足本发明设计规范控制要求。对比例1-6的钢化学成分均存在未能满足本发明设计的要求的参数；对比例7-14对应的N钢种的化学成分虽然满足本发明设计要求，但是相关工艺参数均存在未能满足本发明设计规范的参数。
表2-1和表2-2列出了实施例1-7的冷轧退火双相钢和对比例1-14钢的具体工艺参数。
表2-1
Figure PCTCN2021095808-appb-000003
Figure PCTCN2021095808-appb-000004
表2-2
Figure PCTCN2021095808-appb-000005
Figure PCTCN2021095808-appb-000006
需要说明的是，如表2-2所示，各实施例和对比例的快冷结束温度与回火温度相同，这是因为，在实际工艺操作过程中，快冷操作结束后即进行回火操作。
将实施例1-7的冷轧退火双相钢和对比例1-14钢进行各项性能测试，所得的测试结果列于表3中。性能测试方法参照GB/T 13239-2006金属材料低温拉伸试验方法，制备标准试样，在拉伸试验机上进行静态拉伸，得到相应应力-应变曲线，经过数据处理，最终得到屈服强度、抗拉强度和断裂延伸率参数。
表3列出了实施例1-7的冷轧退火双相钢和对比例1-14钢的性能测试结果。
表3
序号 屈服强度 抗拉强度 A 50断裂延伸率 90°弯曲半径R 板厚t R/t
  (MPa) (MPa) (％) (mm) (mm)  
实施例1 454 800 22.3 1.0 1.1 0.91
实施例2 435 812 21.5 1.0 1.1 0.91
实施例3 474 856 19.5 1.0 1.1 0.91
实施例4 449 832 20.5 1.0 1.2 0.83
实施例5 458 827 20.8 1.0 1.2 0.83
实施例6 476 872 19.7 1.0 1.2 0.83
实施例7 489 884 18.4 1.0 1.1 0.91
对比例1 386 768 25.2 1.0 1.2 0.83
对比例2 525 934 14.6 1.5 1.0 1.50
对比例3 393 777 24.3 1.0 1.0 1.00
对比例4 518 941 15.1 1.5 1.1 1.36
对比例5 404 835 19.6 1.0 1.0 1.00
对比例6 408 828 20.1 1.0 1.1 0.91
对比例7 383 765 24.7 1.0 1.1 0.91
对比例8 525 936 16.6 1.5 1.3 1.15
对比例9 543 952 15.8 1.5 1.0 1.50
对比例10 394 774 24.5 1.0 1.0 1.00
对比例11 390 772 24.5 1.0 1.0 1.00
对比例12 537 947 15.5 1.5 1.2 1.25
对比例13 534 942 15.3 1.5 1.1 1.36
对比例14 385 774 24.5 1.0 1.0 1.00
由表3可看出，满足本发明设计规范控制要求的实施例1-7的性能优异，其屈服强度均≥420MPa；其抗拉强度均＞780MPa，A 50标距断裂延伸率均≥18％，90度冷弯性能表征参量R/t≤1(R表示弯曲半径，t表示板厚，单位参量为mm)。各实施例的冷轧退火双相钢的各项性能十分优异，在未添加Mo、Cr等贵重合金元素的前提下，获得了大于780MPa的抗拉强度，具有较好的延伸率和优良的冷弯性能。
需要说明的是，本发明的保护范围中现有技术部分并不局限于本申请文件所给出的实施例，所有不与本发明的方案相矛盾的现有技术，包括但不局限于在先专利文献、在先公开出版物，在先公开使用等等，都可纳入本发明的保护范围。此外， 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. 一种抗拉强度＞780MPa的冷轧退火双相钢，其特征在于，其基体组织为细小均匀的马氏体+铁素体，所述冷轧退火双相钢除了Fe以外还含有质量百分比如下的下述化学元素：
    C：0.1％～0.13％，Si：0.4％～0.8％，Mn：1.65％～1.9％，Al：0.01％～0.05％，Nb：0.01～0.03％，Ti：0.01～0.03％；
    并且所述冷轧退火双相钢不含有Cr和Mo元素。
  2. 如权利要求1所述的冷轧退火双相钢，其特征在于，其各化学元素质量百分比为：
    C：0.1％～0.13％，Si：0.4％～0.8％，Mn：1.65％～1.9％，Al：0.01％～0.05％，Nb：0.01～0.03％，Ti：0.01～0.03％，余量为Fe和其他不可避免的杂质。
  3. 如权利要求1或2所述的冷轧退火双相钢，其特征在于，其各化学元素的质量百分含量满足下述各项的至少其中一项：
    C：0.11％～0.125％，
    Si：0.5％～0.7％，
    Mn：1.7％～1.8％，
    Al：0.015％～0.045％，
    Nb：0.015～0.025％，
    Ti：0.015～0.025％。
  4. 如权利要求2所述的冷轧退火双相钢，其特征在于，其中不可避免的杂质包括P、S和N元素，其含量控制为下述各项的至少其中之一：P≤0.015％，S≤0.003％，N≤0.005％。
  5. 如权利要求1-3中任一项所述的冷轧退火双相钢，其特征在于，Nb和Ti的质量百分比含量还满足：Nb％+Ti％×3≥0.047％。
  6. 如权利要求1-3中任一项所述的冷轧退火双相钢，其特征在于，所述马氏体的相比例＞55％。
  7. 如权利要求1-3中任一项所述的冷轧退火双相钢，其特征在于，所述马氏体的晶粒直径不大于5微米，所述铁素体的晶粒直径不大于5微米。
  8. 如权利要求1-3中任一项所述的冷轧退火双相钢，其特征在于，其性能满足下述各项的至少其中之一：屈服强度≥420MPa；其抗拉强度＞780MPa；A 50标距断裂延伸率≥18％；90度冷弯性能表征参量R/t≤1，其中R表示弯曲半径，t表示板厚，单位参量为mm。
  9. 如权利要求5所述的冷轧退火双相钢，其特征在于，Nb和Ti的质量百分比含量还满足：0.047％≤Nb％+Ti％×3≤0.10％。
  10. 一种如权利要求1-9中任意一项所述的冷轧退火双相钢的制造方法，其特征在于，包括步骤：
    (1)冶炼和连铸；
    (2)热轧；
    (3)冷轧；
    (4)退火：退火均热温度为770-820℃，退火时间为40～200s，然后以3-5℃/s的速度冷却到快冷开始温度，然后以30～80℃/s的速度快速冷却，其中快冷开始温度为650～730℃，快冷结束温度为200-270℃；
    (5)回火；
    (6)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，将板坯先加热至1160-1220℃，保温0.6小时以上，然后采用850-900℃的温度热轧，轧后以30-80℃/s的速度快速冷却；控制卷取温度为500-600℃，卷取后空冷。
  12. 如权利要求10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50-70％。
  13. 如权利要求10所述的制造方法，其特征在于，在步骤(5)中，控制回火温度为200-270℃，回火时间为100-400s。
  14. 如权利要求10所述的制造方法，其特征在于，在步骤(6)中，控制平整压下率≤0.3％。
  15. 如权利要求10-14中任意一项所述的制造方法，其特征在于，在步骤(4)中，所述退火均热温度为790-810℃。
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