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本文论述了采用高温金相显微镜研究(20、15CrMo、20CrMnMo及18Cr2Ni4-WA)渗碳钢奥氏体晶粒长大动力学及其影响因素。实验结果表明,奥氏体晶粒在850～1200℃范围内有一个晶粒急剧长大的“T_G”温度。奥氏体晶粒异常长大现象,无论在变温或恒温下都可观察到。钢中合金元素Mo、Cr、W可有效地阻碍奥氏体晶粒的长大,增加钢的含碳量将促进奥氏体晶粒的长大。当加热温度低于T_G时,具有板条马氏体原始组织的18Cr2Ni4-WA钢,奥氏体晶粒的长大趋势比具有球化组织者慢,但是,加热温度高于T_G时,前者的奥氏体晶粒长大速率比后者快得多。冷却时,根据抛光试样表面产生的浮凸和室温组织,较详细地研究了板条马氏体(采用未渗碳的18Cr2Ni4WA钢试样)及下贝氏体(采用离子渗碳后的试样)的动态形成过程,观察表明,板条马氏体的最初形核位置通常是在奥氏体晶界或孪晶界处,沿着或平行于奥氏体晶界或与它成一定角度产生第一个板条,板条马氏体束的形成有两种方式:一种是首先形成不相邻的但与母相奥氏体平行的板条,在其间新的板条形核长大成束;另一种是彼此平行依次逐条形核长大。实验结果还表明,下贝氏体的形成速率比板条马氏体的形成速率慢得多,下贝氏体的纵向长大速率大约是其横向长大速率的两倍。
In this paper, the kinetics of austenite grain growth and its influencing factors in (20, 15CrMo, 20CrMnMo and 18Cr2Ni4-WA) carburized steels were investigated by high temperature microscopy. The experimental results show that austenite grains have a sharp “T_G” temperature in the range of 850-1200 ℃. Abnormal growth of austenite grains, both in temperature or temperature can be observed. Steel alloy elements Mo, Cr, W can effectively hinder the growth of austenite grains, increasing the carbon content of steel will promote the growth of austenite grains. When the heating temperature is lower than T_G, the 18Cr2Ni4-WA steel with lath martensite has the tendency of austenite growth slower than that with spheroidization. However, when the heating temperature is higher than T_G, Austenite grain growth rate much faster than the latter. Cooling, according to the surface of the polished specimen produced by the embossment and room temperature organization, a more detailed study of lath martensite (using unburdened 18Cr2Ni4WA steel sample) and the lower bainite (using ion-carburized test Like), the observation shows that the initial nucleation of lath martensite is usually at or at an austenite grain boundary or twin boundary along or parallel to the austenite grain boundaries The first slab is produced and the slab martensitic beam is formed in two ways: one is to first form slabs that are not adjacent but parallel to the parent austenite, with a new slab-like core length Dacheng beam; the other is parallel to each other in turn by the nucleus grew up. The experimental results also show that the formation rate of lower bainite is much slower than that of lath martensite, and the growth rate of lower bainite is about twice that of its horizontal growth rate.