超高强度钢板热冲压同步淬火阶段材料模型的构建与实验分析∗

摘要

实验材料为超高强度钢板 BR1500 HS,利用Gleeble-1500D 热模拟实验机,对该材料在300~600℃温度区间内分别以0．03,0．3,0．6和1 s－1的应变速度进行高温拉伸变形实验,获得了该实验条件下流变应力的变化规律.结果表明,变形温度的降低和应变速率的增大都会使流变应力增大,但流变应力随变形量的增加达到峰值后逐渐趋于稳定.基于应力-应变数据构建 BR1500 HS 同步淬火阶段 Johson-Cook 材料模型,依据此模型对热成形同步淬火阶段进行数值模拟,分析成形件及模具温度场的变化.在实验生产中,模具冷却系统使成形件在保压的同时温度迅速下降,实现其淬火过程,使材料发生马氏体相变,提高成形件的强度.为了实现超高强度钢的热成形同步淬火过程,采用同步冷却热成形系统,通过水流速度及保压时间,使零件马氏体分布均匀化.%High temperature tension tests of ultrahigh-strength steel BR1500 HS were conducted on Gleeble-1500D test machine under the temperature interval of 300-600 ℃ and the strain rates were 0.03,0.3,0.6 and 1 s-1 .Then,the change rule of flow stress was analyzed.The results showed that both the decline of tempera-ture and the increase of strain rate could enlarge the flow stress although the flow stress stabilized after reaching its peak point.After that,the Johson-Cook material modal of BR1500 HS in the synchronous quenching process was established based on the data of stress- strain and the temperature field of die and part was simulated with this modal.The formed part’s temperature decreased sharply during pressure-holding process and achieved its quenching simultaneous.The martensite transformation happened during quenching process,which could im-prove the strength of the formed part.Finally,to realize the synchronous quenching process of ultrahigh-strength steel during hot deformation and to distribute the martensite uniformly,a synchronous cooling system of hot forming was adopted and the parameters as well as the control strategy were optimized.