微合金钢回温变形时的组织转变和铁素体动态再结晶行为

Microstructure Transformation and Ferrite Dynamic Recrystallization Behavior of Microalloyed Steel During Temperature-reversion Deforming

采用GLEEBLE 3800热模拟机进行回温变形热压缩实验,研究回温温度对微合金钢组织转变和铁素体动态再结晶行为的影响。利用金相显微镜、扫描电镜、透射电镜和背散射电子衍射观察实验钢的微观组织和晶粒取向,并对形变时的应力-应变曲线进行分析。结果表明:实验钢回温变形可获得超细晶组织,晶粒平均等效直径约2μm;在回温过程中变形发生动态回复形成亚晶组织,峰值温度变形发生铁素体动态再结晶形成超细晶粒;动态再结晶机制包括晶界迁移和亚晶的转动生长,回温到700℃和750℃时以前者为主,再结晶不充分,保留了条带状变形铁素体,800℃变形时,两者共同作用,形成均匀的等轴状超细晶组织;通过线性回归计算得到实验钢峰值温度变形时铁素体动态再结晶激活能Qd=250.18kJ/mol。

Temperature-reversion deformation of microalloyed steel was simulated by thermal simula- tor GLEEBLE 3800. The effect of reverting temperature on microstructure transformation and ferrite dynamic recrystallization behavior was studied. OM,SEM and TEM were used to investigate the mor- phology of experimental steels, and the orientation relationship of microstructure was analyzed by EBSD. And true stress-true strain curves of experimental steel during deformation were analyzed. The results show that ultrafine grains with equivalent diameter of 2μm are obtained by temperature- reverting deformation. Dynamic recovery induced by deformation during temperature-reversion pro- duces subgrain structure. Ultrafine grains are formed by ferrite dynamic recrystallization during de- formation at peak temperature. There are two mechanisms of dynamic recrystallization, i.e. grain boundary migration and subgrain rotation growing. The former dominants when the steels are de- formed at 700℃ or 750℃, where recrystallization is inadequate and lots of band like ferrite retains. And the two mechanisms work simultaneously at 800℃, which lead to homogeneous equiaxed ultra- fine grain structure. The ferrite dynamic recrystallization activation energy Qd is 250.18kJ/mol calcu- lated by linear regression.