采用膨胀法结合金相检验和硬度测试，在相变膨胀仪上测定了30CrNiMo8钢的临界点温度，绘制了过冷奥氏体连续冷却转变曲线，研究了不同冷却速率对30CrNiMo8钢显微组织和硬度的影响。结果表明：当冷却速率为0.02~7℃·s^-1时，随着冷却速率的增加，30CrNiMo8钢的显微组织由粒状贝氏体为主逐渐转变为马氏体为主，硬度也逐渐升高；马氏体转变的临界冷却速率为1.0~1.5℃·s^-1，30CrNiMo8钢的淬透性较好。

The critical temperatures of 30CrNiMo8 steel were determined by dilatometer method combined with metallographic test and hardness test on a thermal dilatometer. Also, the continuous cooling transformation curves of super-cooled austenite were obtained. The influence of different cooling rates on microstructure and hardness of 30CrNiMo8 steel was studied. The results show that:with the increase of cooling rate between 0.02-7℃ ·s^-1, the microstructure of 30CrNiMo8 steel transformed from granular bainite mainly to martensite mainly, and the hardness also increased gradually; the critical cooling rate of martensite transformation was 1.0-1.5℃ ·s^-1, which showed 30CrNiMo8 steel had better hardenability.