压缩变形对XH1650D钢连续冷却相变的影响

Study on Continuous Cooling Phase Transformation of Compress Deformed XH1650D Steel

通过MMS-200热模拟试验机测定了XH1650D钢未变形和两道次压缩变形后不同冷速(0.1~10℃/s)下的连续冷却相变行为,利用膨胀法获得连续冷却转变曲线,并采用LEICA DMi8金相显微镜观察了不同冷速下的金相组织和珠光体晶粒尺寸。结果表明:压缩变形后XH1650D钢的奥氏体晶粒得到细化,淬透性降低,同时促进了铁素体+珠光体的转变,抑制了贝氏体的转变,使得连续冷却转变曲线左移;变形提高了XH1650D钢的铁素体+珠光体的相变温度,增加了获得贝氏体的临界冷却速度;铁素体+珠光体的相变开始温度/结束温度由0.1℃/s的704℃/683℃提高到0.1℃/s的736℃/683℃,获得贝氏体的临界冷却速度由0.5℃/s增至1.5℃/s。在实际轧制中,为获得对后续生产有利的铁素体+珠光体组织,XH1650D钢的冷速应控制在低于1.5℃/s为宜。XH1650D钢的临界点温度为A_(c1)=812℃,A_(c3)=843℃。

The phase transformation temperature range of undeformed and double pass compressed XH1650D steel at different cooling rates(0.1~10℃/s)is measured by MMS-200 thermo simulation tester.The continuous cooling transition(CCT)curve is obtained by using the expansion method.The microstructure at different cooling rates and the pearlite grain size are observed by LEICA DMi8 metallographic microscope.The results show that:after compressed deformation,the austenite grain of XH1650D steel is refined and the quenching property is reduced,which promotes the ferrite+pearlite transformation and restrains the bainite transformation and lets the CCT curve move left.The deformation increases the ferrite+pearlite phase transition temperature and increases the critical cooling speed of obtaining bainite.The ferrite+pearlite phase transition start/end temperature is increased from 704℃/683℃to 736℃/683℃at 0.1℃/s cooling speed,and the critical cooling speed of obtaining bainite is increased from 0.5℃/s to 1.5℃/s.In the process,to obtain the ferrite+pearlite,it is appropriate that the cold speed of XH1650D steel should be controlled at less than 1.5℃/s.The critical point temperature of XH1650D steel is A_(c1)=812℃and A_(c3)=843℃.