针对42CrMo合金钢棒材轧后硬度过大的问题，采用Gleeble热模拟试验机研究了42CrMo合金钢冷却时的组织转变规律，并对比了常规轧制和低温轧制后42CrMo合金钢的硬度与显微组织。结果表明：冷却速率达到0.3 ℃·s^-1以上时，42CrMo合金钢中开始出现贝氏体相变；当冷却速率为1.0~10.0 ℃·s^-1时，只发生贝氏体和马氏体转变。采用常规轧制工艺，42CrMo合金钢的硬度在300~320 HBW之间，显微组织主要为铁素体+珠光体+贝氏体；采用低温轧制工艺，将终轧温度控制在800 ℃， 42CrMo合金钢的硬度可降到240 HBW，显微组织主要为铁素体+珠光体。

Aiming at the problem of excessive hardness of 42CrMo alloy steel bar after rolling, the microstructure transformation of 42CrMo alloy steel during cooling was studied by Gleeble thermal simulation test machine, and the hardness and microstructure of 42CrMo alloy steel after conventional rolling and low temperature rolling were compared. The results show that bainite transformation begin to appear in 42CrMo alloy steel when the cooling rate was above 0.3 ℃·s^-1. When the cooling rate was 1.0~10.0 ℃·s^-1, only bainite and martensite transformation occurred. By conventional rolling process, the hardness of the 42CrMo alloy steel was between 300~320 HBW, and the microstructure was mainly ferrite+pearlite+bainite. By low temperature rolling process, the hardness of the 42CrMo alloy steel can be reduced to 240 HBW and the microstructure was mainly ferrite + pearlite when the finishing rolling temperature was controlled at 800 ℃.