高强度钢板BR1500HS热成形微观结构和力学性能研究

Research on microstructure and mechanical properties of high strength steels BR1500HS during hot stamping

以BR1500HS高强度钢为研究对象,采用金相显微镜、显微硬度仪和万能拉伸实验机对比分析了其热成形前后的微观组织和力学性能,同时得到了试样在不同冷却速度时的时间-温度曲线图,即马氏体转变曲线.分析结果表明,高强钢BR1500HS室温条件下其微观组织为90F＋10B,其屈服强度、抗拉强度分别为462,627MPa;而经热成形后的微观组织最好为98M ＋1B＋1F,最大硬度、抗拉强度值分别为501.2HRV、1633.69MPa,与此同时,得硬度、抗拉强度值排序情况与组织中马氏体含量排序情况基本吻合.马氏体转变曲线表明,BR1500HS的马氏体转变温度范围为375-325℃,其转变发生在保压冷却时间为15-25s区间,且当冷却速率值超过40 ℃/s时,马氏体转变进行得较为充分.

In this paper,comparative analysis for microstructure and mechanical properties of high strength steel BR1500 HS between before hot stamping and after hot stamping were investigated through optical microscopy,micro hardness tester and universal tensile tester.Meanwhile,relationship between time and temperature at different cooling rates was obtained,as well as martensitic transformation curve.The analysis results showed:the original microstructure of high strength steel BR1500 HS at room temperature was 90F+10B,yield strength and tensile strength were 462 and 627 MPa respectively;while the best microstructure of forming part was98M+1B+1F,and the maximum hardness and maximum tensile strength were 501.2HRV and 1 633.69 MPa respectively,both hardness and tensile strength were basically matched with the martensite content obtained by experimental observations.Martensitic transformation curve shows:temperature range for martensitic transition of BR1500 HS was 375-325℃,and time range for martensitic transition was 15-25s;when cooling rate was greater than 40 ℃/s,martensitic transformation more fully.