AM对低碳贝氏体钢等温相变和显微组织的影响

Effect of AM on isothermal transformation and microstructure of low carbon bainite steel

设计了马氏体起始相变温度(M_(s))以上和以下5个不同温度等温淬火实验,研究了M_(s)以上和以下温度等温淬火对低碳贝氏体钢组织和相变动力学的影响。结果表明,试样在M_(s)以下等温淬火时,保温前生成的先马氏体(AM)显著缩短了等温贝氏体相变孕育期,加速贝氏体形核,细化贝氏体组织。然而,M_(s)以下等温淬火时,总的等温贝氏体相变动力学与先马氏体的体积分数(f_(AM))有很大关系,当f_(AM)较低时,AM的形成缩短了贝氏体相变孕育期,加速了贝氏体相变,当f_(AM)过高时,又阻碍贝氏体相变,延长贝氏体总的相变时间。最后,采用Austin-Rickett(AR)和Johnson-Mehl-Avrami-Kolgomorov(JMAK)动力学模型对等温贝氏体相变动力学进行分析,结果表明,与AR模型相比,JMAK模型更适用于本研究的实验结果。

The austempering experiments with different temperatures above or below martensite starting temperature(M_(s))were designed to investigate the effects of austempering temperature on microstructure and bainite transformation kinetics of a low carbon bainitic steel.The results show that when isothermal treatment is austempered below M_(s),the athermal martensite(AM)formed before austempering significantly shortens the incubation period of isothermal bainite transformation,accelerates bainite nucleation and refines the microstructure of bainite.However,in the case of austempering below M_(s),the total isothermal bainite transformation kinetics has a great relationship with the volume fraction of athermal martensite(f_(AM)).When the f_(AM)is low,the formation of AM shortens the incubation period of bainite transformation and accelerates the bainite transformation;when the f_(AM)is too high,it hinders the bainite transformation and prolongs the total transformation time of bainite.Furthermore,the isothermal bainite transformation kinetics were analyzed by Austin-Rickett(AR)and Johnson-Mehl-Avrami-Kolgomorov(JMAK)kinetics models,respectively.The result shows that the JMAK kinetics model is more suitable than AR kinetics model for the experimental results of this study.