对直径为8 mm的密封螺塞用锻造正火态45钢棒进行（750~880）℃×15 min淬火和550℃×30 min高温回火处理，研究了不同淬火温度下试样的显微组织、断口形貌和硬度，分析淬火温度对开裂的影响，并对热处理工艺进行优化。结果表明：当淬火温度为750，780℃时，淬火后试样均未发生开裂，而当淬火温度为800～880℃时均发生了开裂；随着淬火温度的升高，组织中铁素体减少，晶粒尺寸增大，硬度先升高后降低；在800~830℃淬火时，淬火开裂的原因为过冷奥氏体在马氏体转变相区冷却速率过大，组织应力在试样外层集中，裂纹以沿晶和穿晶混合方式扩展；在850~880℃淬火时，淬火温度较高，晶界弱化，在组织应力与热应力的共同作用下裂纹沿晶界扩展。在830℃淬火前增加3~5 s室温缓冷工序再回火后45钢既可获得最佳的回火索氏体组织与较高的硬度，又可避免淬火开裂。

45 steel rods in forged and normalized state with a diameter of 8 mm for sealing plug were quenched at 750-880℃ for 15 min and high temperature tempered at 550℃ for 30 min. The microstructure, fracture morphology and hardness of the specimens at different quenching temperatures were studied. The effect of quenching temperature on quenching cracking was analyzed and the heat treatment process was optimized. The results show that the specimens did not crack after quenching at 750℃ and 780℃, and cracked after quenching at 800-880℃. With increasing quenching temperature, the ferrite content in microstructure decreased, the grain size increased, and the hardness first increased and then decreased. When the quenching temperature ranged from 800℃ to 830℃, the cause of quenching cracking was that the cooling rate of undercooled austenite in the martensite transformation phase region was too large, and the structural stress was concentrated in the outer layer of the specimen, which led to the propagation of crack in a mixed mode of intergranular and transgranular. When the quenching temperature ranged from 850℃ to 880℃, the grain boundary was weakened due to the higher quenching temperature, and cracks propagated along grain boundaries under the combined action of the structural stress and the thermal stress. The best tempered sorbite structure and relatively high hardness of 45 steel could be obtained and the quenching cracking could be avoided by setting a slow cooling process of 3-5 s at room temperature before quenching at 830℃ and then tempering.