Abstract: By Formastor-F quenching dilatometer thermal simulation and VL2000DX-SVF17SP high temperature laser scanning confocal microscope ( LSCM) observation, the dilatation curve and microstructure of a low carbon bainite rail steel of U25CrNi (/% ：0.25C, 1.73Si, 1.69Mn ,0.012P,0.002S, 1.40Cr,0.57Ni,0.49Mo,0. 06V) during continuous cooling process from 950 °C at different cooling rates are studied. The results show that at low cooling rate (0. 2 °C/s) , the microstructure of test steel is mainly bainite ； as the cooling rate increases to 1 °C/s, the microstructure gradually transforms to bainite and martensite, and the size of the bainite plate gradually decreases with the increase of the cooling rate； when the cooling rate reaches 2 °C/s, basically only the martensite transformation occurs during the cooling process, and the hardness of the test steel gradually increases with the increase of the cooling rate.

摘要： 利用Formastor-F淬火膨胀仪热模拟和VL2000DX-SVF17SP高温激光共聚焦显微镜观察,研究了U25CrNi低碳贝氏体钢轨(/%:0.25C,1.73Si,1.69Mn,0.012P,0.002S,1.40Cr,0.57]Ni,0.49Mo,0.06V)从950℃以不同冷却速度连续冷却后的膨胀曲线和金相组织。结果表明,低冷速下(0.2℃/s),实验钢组织主要为贝氏体;随冷却速度增大至1℃/s,实验钢组织逐渐过渡为贝氏体和马氏体,且贝氏体板条尺寸随冷速增大而逐渐减小;当冷速达到2℃/s时,冷却过程中基本只发生马氏体相变,实验钢硬度随冷速增大而逐渐增大。

关键词: 原位观察, 热膨胀法, 相变温度, 组织