超高强度钢高温流变行为及热冲压工艺

High temperature rheological behavior and hot stamping process of ultra-high strength steel

为提升某汽车纵梁的力学性能,研究了超高强度钢板的最佳热冲压工艺窗口。首先,通过高温拉伸实验获得了材料的高温流变曲线,并构建了材料的Hansel-Spittel流变本构模型。基于热加工理论,建立了材料的热加工能量耗散图,得到了材料的稳态热加工温度为900℃、应变速率为0.01 s^(-1)。其次,通过淬火实验获得了超高强度钢的强度、硬度、伸长率与加热温度、保温时间之间的关系数据,并建立了力学性能分布数据图。力学性能分布图可以分为3个区域,分别为未奥氏体化区域、不完全奥氏体化区域和完全奥氏体化区域,并通过微观组织分析验证了分区的合理性和有效性。根据能量耗散图和力学性能分布图确定了超高强度钢具有最大能量耗散率,能完全奥氏体化的最佳热冲压工艺窗口为:加热温度900℃、保温时间8 min、应变速率0.01 s^(-1)。最后,使用最佳热冲压参数对某汽车纵梁热冲压工艺进行了数值仿真和生产试制,并获得了具有超高强度的热冲压汽车加强件产品;通过对试制零件进行取样拉伸和微观组织分析,验证了最佳加热温度、保温时间和变形速率的合理性。

To improve the mechanical properties of an automobile longitudinal beam,the optimal hot stamping process window of ultra-high strength steel plate was studied.Firstly,the high temperature rheological curves of the material were obtained through the high temperature tensile experiments,and the Hansel-Spittel rheological constitutive model of the material was constructed.Based on the hot working theory,the hot working energy dissipation diagram of the material was established.It is obtained that the steady-state hot working temperature of the material is 900℃and the strain rate is 0.01 s^(-1).Secondly,through the quenching experiments,the relationship data between strength,hardness,elongation and heating temperature,holding time of ultra-high strength steel were obtained,and the distribution diagram of mechanical properties was established.The mechanical properties distribution diagram can be divided into three areas,namely,non austenitized area,incomplete austenitized area and complete austenitized area,respectively.The rationality and effectiveness of the zoning were verified by microstructure analysis.According to the energy dissipation diagrams and mechanical properties distribution diagrams,the optimum hot stamping process window for ultra-high strength steel with the maximum energy dissipation rate and complete austenitization is determined as follows:heating temperature of 900℃,holding time of 8 min,strain rate of 0.01 s^(-1).Finally,the hot stamping process of an automobile longitudinal beam was simulated and trial produced using the optimal hot stamping parameters,and the hot stamping automobile reinforcement product with ultra-high strength was obtained.The rationality of optimum heating temperature,holding time and deformation rate was verified by sampling,tension and microstructure analysis of the trial parts.