对不同温度（760，800，840℃）淬火+350℃回火处理的45钢进行了疲劳裂纹扩展速率试验，得到了疲劳裂纹扩展速率曲线，研究了淬火温度对其疲劳裂纹扩展行为的影响。结果表明：与840℃淬火（常规淬火）后的相比，760，800℃亚温淬火后试验钢组织中存在未溶铁素体，且800℃亚温淬火后的马氏体组织细小，韧性较好；试验钢的疲劳裂纹扩展速率曲线在裂纹稳定扩展阶段符合Paris公式，随着淬火温度的升高，裂纹扩展速率减小；疲劳断口分为裂纹低速扩展区、裂纹稳定扩展区和瞬断区3个区域，800℃亚温淬火后的低速扩展区相对平坦，稳定扩展区则比较粗糙，存在准解理形貌，瞬断区有明显的撕裂棱、剪切唇和韧窝形貌，高度差达到283.9 μm左右，韧性断裂所占比例较大。

The fatigue crack propagation rate test was conducted on 45 steel after quenching at different temperatures (760,800,840℃) and tempering at 350℃, and then the fatigue crack propagation rate curves were obtained. The effects of quenching temperature on the fatigue crack propagation behavior were also studied. The results show that compared to that quenched at 840℃ (conversional quenching), the undissolved ferrite existed in the microstructure of tested steel after subcritical quenching at 760 and 800℃. After subcritical quenching at 800℃, the martensite structure was fine and the ductility was good. The fatigue crack propagation rate curves of tested steel were in accordance with Paris law and the crack propagation rate decreased with the increase of quenching temperature. The fatigue fracture was composed of crack low propagation region, crack stable propagation region and final fracture region. After subcritcal quenching at 800℃, the low propagation region was relatively flat; the stable propagation region was relatively rough and showed quasi-cleavage morphology; the final fracture region showed obvious tearing edge, shear lip and dimple morphology, with the height difference of about 283.9 μm, indicating a large proportion of dutile fracture.