中文摘要：

利用超高温激光共聚焦显微镜对45钢在不同冷却速度下的凝固过程中枝晶的形成进行原位观察,研究45钢在不同的冷却速度下,凝固过程中的枝晶生长状况。凝固结束后,对枝晶的形貌进行观察、测量和分析枝晶间距,研究冷速度对枝晶及最终凝固组织的影响。结果表明：在凝固过程中随着温度的降低,枝晶不断生长,新核也不断形成,随着冷却速度的加快,枝晶组织明显细化。冷却速率由50℃/min到400℃/min的过程中,一次枝晶间距由0.54mm减小至0.34mm。

英文摘要：

In situ observations of dendrite formation in the process of solidification of 45 steel under different cooling rate was explored by use of high temperature laser confocal microscope.The dendritic growth in 45 steel during different cooling rate was studied.After the solidification,the morphology of dendritic crystal was observed;the primary dendrite arm spacing was measured and analyzed.The effect of cooling rate on the dendritic and final solidification structure was studied.The results showed that the dendrite growth continually and the new nuclear also constantly form with the decrease of temperature in the process of solidification;the structure of dendritic structure obviously refined with the increase of cooling rate.The primary dendrite spacing decreased from 0.54 mm to 0.34 mm in the process of cooling rate from 50 ℃ /min to 400 ℃ /min.