含Cu低碳钢CCT曲线及马氏体相变原位观察

Continuous cooling transformation curve of Cu bearing low carbon steel and in-situ observation of its martensitic transformation

利用Linseie L78 RITA淬火/相变热膨胀仪,测定了一种含Cu低碳钢的相变点,绘制了连续冷却转变曲线,结合光学显微镜和显微硬度法分析了冷却速率对相变组织演变规律的影响,利用高温激光共聚焦显微镜对马氏体相变过程进行了原位观察。结果表明:冷却速率为0.5~8℃/s时,随冷却速率的增加,铁素体含量减少,粒状贝氏体(GB)逐渐演变为板条贝氏体(LB),硬度逐渐升高;冷却速率大于15℃/s时,组织全部为板条马氏体。原位观察表明马氏体优先在晶界或晶内位错塞积处形核,新生马氏体在先形核马氏体板条间以一定取向形核长大。

Continuous cooling transformation curves of a Cu bearing low carbon steel were determined by Linseie L78 RITA dilatometer.Effect of cooling rate on microstructure evolution was investigated by means of optical microscope and microhardness measurement.Martensitic transformation was in-situ observed by using high temperature laser confocal microscope. The results show that when the cooling rates are between 0. 5-8 ℃/s,with the increase of the cooling rate,the ferrite content decrease,the granular bainite is gradually evolved into the lath bainite,and the microhardness gradually rised. Full lath martensite structure appears when the cooling rate is greater than or equal to15 ℃/s. In-situ observation results show that martensite priorly nucleates at the grain boundary or dislocation pile-up area,the fresh martensite nucleates and grows in a certain orientation relationship.