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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。
The phase transition point of a mild steel containing Cu was measured by Linseie L78 RITA quenching / phase change dilatometer, and the continuous cooling transformation curve was drawn. The evolution of cooling rate on the phase transformation microstructure was analyzed by optical microscopy and microhardness method The effect of laser scanning confocal microscopy on the martensitic transformation was observed in situ. The results show that with the cooling rate increasing from 0.5 to 8 ℃ / s, the ferrite content decreases and the granular bainite (GB) gradually evolves into lath bainite (LB) with the cooling rate increasing. The hardness increases gradually. Cooling rate greater than 15 ℃ / s, all the lath martensite. In-situ observation showed that martensite preferentially nucleated at the grain boundaries or intragranular dislocations, and newly formed martensite nucleated and grew in a certain orientation between the earlier nucleated martensite laths.