Tempering is an important process for T/P92 ferritic heat-resistant steel from the viewpoint of microstructure control,as it facilitates the formation of final tempered martensite under serving conditions.In this study,we have gained deeper insights on the mechanism underlying the microstructural evolution during tempering treatment,including the precipitation of carbides and the coarsening of martensite laths,as systematically analyzed by optical microscopy,transmission electron microscopy,and high-resolution transmission electron microscopy.The chemical composition of the precipitates was analyzed using energy dispersive X-ray spectroscopy.Results indicate the formation of M3C(cementite) precipitates under normalized conditions.However,they tend to dissolve within a short time of tempering,owing to their low thermal stability.This phenomenon was substantiated by X-ray diffraction analysis.Besides,we could observe the precipitation of fine carbonitrides(MX) along the dislocations.The mechanism of carbon diffusion controlled growth of M23C6 can be expressed by the Zener's equation.The movement of Y-junctions was determined to be the fundamental mechanism underlying the martensite lath coarsening process.Vickers hardness was estimated to determine their mechanical properties.Based on the comprehensive analysis of both the microstructural evolution and hardness variation,the process of tempering can be separated into three steps.
Lin-qing XuDan-tian ZhangYong-chang LiuBao-qun NingZhi-xia QiaoZe-sheng YanHui-jun Li
采用Gleeble-1500热力模拟试验机进行热变形实验,研究了轧后不同保温时间(0~600 s)对20Mn Si V钢的组织和显微硬度的影响。结果表明:无论是在奥氏体再结晶区(1050℃)轧制还是在(γ+α)两相区(750℃)轧制,随着轧后保温时间的延长,V元素充分发挥了在钢筋中的析出强化和细晶强化的作用,铁素体和珠光体晶粒都明显细化,改善了钢材的性能。
