闪速加热对2000 MPa级热成形钢显微组织和力学性能的影响

doi:10.11900/0412.1961.2023.00036

金属学报 DOI: 10.11900/0412.1961.2023.00036

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闪速加热对2000 MPa级热成形钢显微组织和力学性能的影响

谢泽东,丁灿灿,温鹏宇,罗海文

北京科技大学冶金与生态工程学院北京 100083

Effect of Flash Heating on Microstructure and Mechanical Properties of 2000 MPa Hot Stamping Steel

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摘要: 研究了一种新型2000 MPa级热成形钢以150℃/s闪速加热至850~950℃后再回火的显微组织和拉伸力学性能。结果表明，与常规加热工艺相比，在相同温度下闪速加热可同时改善材料的强度和塑性。2000 MPa级热成形钢经闪速加热至950℃可获得最佳力学性能，抗拉强度为2180 MPa、延伸率为13%，较相同温度下常规加热样品分别提高了约200 MPa和4%，这是由于闪速加热导致淬火后形成的马氏体组织显著细化、位错密度更高且残余奥氏体更多。残余奥氏体的增多主要与初始组织中富C/Mn渗碳体在闪速加热时固溶形成的C/Mn富集区未及时扩散均匀化相关。随着闪速加热温度升高，更多渗碳体可以固溶，因此残余奥氏体体积分数逐渐增大，奥氏体逆转变动力学模拟计算结果也证实了这一点。

关键词 ：热成形钢, 闪速加热, 力学性能, 渗碳体, 残余奥氏体

Abstract：Hot stamping steels (HSSs) have been widely used in automobiles, to reduce weight and improve safety due to their ultrahigh strength and ease of synthesis at high temperatures. At present, steel sheets with high strength and good ductility are needed to further reduce the weight of manufactured products. The most popular HSS grade in use at present is 22MnB5, which has an ultimate tensile strength (UTS) of 1500 MPa, but it has a ductility of less than 7%, which is quite poor. Driven by the demand for weight reduction in the automotive industries, we have developed a 2000 MPa HSS by employing a new alloying design and an ultrafast heating process. The latter has received much less attention than the former, although it demonstrates huge potential for improving mechanical properties and production efficiency of HSSs. In this study, we experimented with heating processes, including conventional and flash heating, at a ramp of 150℃/s in the temperature range of 850°C–950℃ before tempering at 150℃; furthermore, we examined their effects on the microstructures and mechanical properties of a new type of 2000 MPa HSS. Compared with the conventional heating at a relatively low ramp rate, the flash heating improved the strength and ductility of 2000 MPa HSS, simultaneously. Moreover, their best tensile properties were achieved after flash heating to 950℃: UTS was 2180 MPa and total elongation was 13%, which were approximately 200 MPa and 4% higher than those obtained using conventional heating, respectively. This is because flash heating results in the formation of a more refined hierarchical martensite structure after quenching, with a higher dislocation density and a larger fraction of retained austenite (RA). RA was formed by dissolving cementite particles containing high C/Mn concentrations, which were then inherited in the formed austenite after quenching due to insufficient time for the homogenization of solute C/Mn by diffusion during the flash heating. The volume fraction of RA increased gradually with an increase in the flash heating temperature as, then, more cementite particles were dissolved. This was also confirmed by kinetic simulations that reversed the austenitization on the dissolving cementite. Finally, we propose that flash heating technology is a promising technology for the production of ultra-strong and ductile HSS sheets.

Key words： hot stamping steel flash heating mechanical properties cementite retained austenite

收稿日期: 2023-02-03

基金资助:国家自然科学基金项目;国家自然科学基金项目;中央高校基本科研业务费

通讯作者: 罗海文

Corresponding author: hai wenluo

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引用本文:

谢泽东丁灿灿温鹏宇罗海文. 闪速加热对2000 MPa级热成形钢显微组织和力学性能的影响[J]. 金属学报, 10.11900/0412.1961.2023.00036.

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https://www.ams.org.cn/CN/Y0/V/I/0

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