中锰钢中原奥氏体晶粒尺寸对马氏体相变的影响

对中锰钢中原奥氏体晶粒尺寸对马氏体相变动力学的影响进行了分析。利用SEM、XRD、热膨胀相变仪和EBSD等检测手段,研究了不同原奥氏体晶粒尺寸下马氏体相变速率和马氏体板条组织的变化。通过不同温度的奥氏体化处理,分别得到了尺寸为(190±15)、(36±2)、(11±2)和(4.8±2) μm的原奥氏体晶粒。结果表明:随着原奥氏体晶粒尺寸的降低,马氏体相变开始温度由289 ℃降低到250 ℃,而马氏体的相变速率先升高后降低。分析表明,马氏体的相变速率与马氏体的形核点数量直接相关,而马氏体的形核点数量受原奥氏体晶粒尺寸大小和马氏体板条的宽长比影响。当原奥氏体晶粒尺寸小于5 μm时,马氏体板条的宽长比明显增加,马氏体形核点数目随过冷度增加而增加的速率明显降低,从而造成马氏体相变速率降低。

Effect of prior austenite grain size on martensitic transformation in medium manganese steel

Effect of prior austenite grain size in medium manganese steel on kinetics of martensitic transformation was studied. The kinetics of martensitic transformation and microstructure evolution were analyzed by combining with SEM, XRD, thermal dilatometer and EBSD results. Different prior austenite grain sizes with (190±15), (36±2), (11±2) and (4.8±2) μm were achieved, respectively, by heating at different austenitizing temperatures. The results show that with the decreasing of prior austenite grain size, the martensite start temperature decrease from 289 ℃ to 250 ℃, while the kinetic of martensitic transformation increase at first then decrease. The kinetics of martensitic transformation is closely related to the number of martensite nucleation cites per unit volume, while the number of martensite nucleation cites are closed to the prior austenite grain size and the martensite lath aspect ratio. When the size of prior austenite grain decreases to 5 μm, the aspect ratio of martensite lath increases, while the increase rate of martensite nucleation cites with undercooling significantly reduces, which results in the decrease of the rate of martensite transformation.