热镀锌TRIP钢的微观组织结构及演变规律

Microstructure and its evolution of hot-dip galvanized trip steel

利用光学显微镜、透射电镜、X射线衍射和相变仪对热镀锌TRIP钢的微观组织进行了定性观察和定量计算,在此基础上对热镀锌TRIP钢残留奥氏体的演变规律和马氏体的精细结构进行了研究。定性观察表明热镀锌TRIP钢的微观组织由铁素体,贝氏体,残留奥氏体和马氏体构成,在贝氏体相变结束后的冷却过程中还存在马氏体相变;通过对微观组织计算发现,受贝氏体等温相变时间影响,热镀锌TRIP钢中的马氏体碳含量在0.80%~1.0%之间,贝氏体等温时间越长,最终组织中马氏体碳含量越高,Ms点越低;在贝氏体相变结束后,部分碳含量不高的奥氏体在随后的冷却过程中发生马氏体相变,以马-奥岛的形式存在,马氏体的精细结构以孪晶马氏体为主,存在少量位错马氏体。

Microstructure of hot-dip galvanized TRIP steel was studied by means of optical microscope,transmission electron microscopy( TEM),X-ray diffraction( XRD) and dilatometry. Based on the experimental data,it can be found that martensite transformation occurs after the stage of isothermal bainite transformation because of the shorter bainite transformation. The microstructure of the steel consists of ferrite,bainite,retained austenite and martensite. The amount of ferrite,bainite,retained austenite and martensite is quantitatively calculated,the carbon content in martensite is 0. 80%-1. 0% and increases with the increasing of isothermal bainitic transformation period,meanwhile the temperature of Msis reduced with the prolonging of isothermal bainitic transformation time. By quantitative calculation,after the stage of isothermal bainitic transformation,the on transformed austenite with lower carbon content would transform to martensite,forming M-A island. Fine structure of the martensite in M-A island mainly consists of twin sub-structure with a little dislocation martensite.