Deep cryogenic treatment (DCT) and secondary tempering for 40CrNiMoA steel were carried out to obtain the desirable microstructures corresponding to excellent mechanical properties suiting for the preparation of flex spline of harmonic drive reducer. The effects of DCT and secondary tempering on microstructural characteristics and mechanical properties were investigated by x-ray diffraction, scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy, in association with property measurements. The results show that the DCT promotes the transformation of retained austenite to martensite, the precipitation and homogeneous distribution of carbides as well as the refinement of martensitic substructures. The structural and morphological changes significantly improve the hardness, yield and tensile strength of steels, but slightly lower the elongation of them. Further secondary tempering at special temperatures can successively increase the elongation and fracture toughness of the DCT-treated 40CrNiMoA steels at the cost of slight decrease in hardness and strength due to the reduction in dislocation density. Therefore, the DCT in combination with secondary tempering can improve the comprehensive mechanical properties of 40CrNiMoA steels to produce the flex spline with a higher lifetime.

对40CrNiMoA钢进行了深低温处理（DCT）和二次回火，以获得与优良机械性能相对应的理想显微组织，适合制备谐波传动减速器的挠性花键。通过X射线衍射，扫描电子显微镜，电子背散射衍射和透射电子显微镜以及性能测量，研究了DCT和二次回火对显微组织特性和力学性能的影响。结果表明，DCT促进了残余奥氏体向马氏体的转变，碳化物的析出和均匀分布以及马氏体亚结构的细化。结构和形态的变化显着提高了硬度，钢的屈服强度和抗拉强度，但伸长率略有降低。在特殊温度下进行进一步的二次回火可以依次增加DCT处理的40CrNiMoA钢的延伸率和断裂韧性，但由于位错密度的降低而使硬度和强度略有下降。因此，DCT与二次回火相结合可以改善40CrNiMoA钢的综合机械性能，从而生产出使用寿命更长的挠性花键。