中文摘要：

采用激光扫描共聚焦显微镜原位观察了SA508—3钢连续冷却时夹杂物的析出及贝氏体的形成过程，研究了冷却速度和冷却方式对夹杂物析出及贝氏体形成的影响。结果发现利用激光扫描共聚焦显微镜实验可以在试样表面制备出一定数量的氮碳复合夹杂物Fe（N，C）。随着冷速的提高，视频中出现夹杂物的温度降低，夹杂物的析出量和尺寸增加。采用两阶段冷却方式冷却，快冷时析出大量粗大弥散分布的夹杂物，慢冷时析出大量细小弥散分布的夹杂物。夹杂物能否诱导贝氏体形核与夹杂物的尺寸和分布密度有关。尺寸为1～5μm、分布密度为50～100个／mm2的Fe（N，c）有利于诱导贝氏体形成。

英文摘要：

In situ observation of the precipitation of inclusions and formation of bainite during continuous cooling of SA508-3 steel was carried out by Laser scanning confoeal microscope （LSCM）. The influences of cooling rate and cooling manner on the precipitation of inclusions and formation of bainite were studied. The results showed that the LSCM experiment could be used to prepare a certain number of complex inclusions Fe （ N, C） on the surface of sample. With the increasing of cooling rate, the temperature for inclusions appeared on the video decreased, and the quantity and size of precipitated inclusions increased. When the samples were cooled at the manner of two stages, a large number of coarse inclusions and small inclusions precipitated during quick cooling and subsequently slow cooling, respectively. The nucleation of bainite induced by inclusions was related to the size and distribution density of inclusions. Fe （ N, C） with the diameter of 1 - 5μm and distribution density of 50-- 100/mm2 were favorable to the induction nucleation of bainite.