Abstract: In this study, a quenched Cu-Cr-Ni high-strength weathering steel was investigated. The effects of tempering temperature on its microstructure, strength-toughness balance, and precipitates were examined via optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), combined with tensile tests, low-temperature impact tests, and other characterization methods. The results showed that as the tempering temperature increased from 500℃ to 600℃, the microstructure of the experimental steel transformed from lath-shaped tempered sorbite to non-lath morphology. The fraction of rod-like cementite decreased, while that of spheroidized cementite increased, and the size of MC (M=Ti, Nb, V, Mo) precipitates became smaller. Consequently, the yield strength and tensile strength decreased from 935 MPa and 958 MPa to 866 MPa and 888 MPa, respectively, whereas the impact energy at -40℃ and total elongation increased continuously, reaching their maximum values of 280 J and 5.0% at 600℃. When tempered at 550℃, the experimental steel exhibited a yield strength of 895 MPa, a tensile strength of 921 MPa, an elongation of 4.3%, and an impact energy of 271 J at -40℃, demonstrating an comparatively good combination of strength and toughness. This improvement is mainly attributed to the spheroidization of cementite and the uniformly dispersed fine MC precipitates, which alleviate stress concentration. In addition, the tempering-induced softening of the acicular ferrite (α) matrix contributes to the enhanced toughness.

Key words: Cu-Cr-Ni weathering steel, tempering temperature, microstructure, precipitates, mechanical property

摘要： 本工作以淬火态Cu-Cr-Ni高强度耐候钢为研究对象，采用光学显微镜(OM)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段，并结合拉伸和低温冲击等试验研究了回火温度对钢材料显微组织、强韧性及析出相的影响。结果表明，随着回火温度由500℃升高至600℃，实验钢的显微组织由板条状形貌的回火索氏体转变为非板条状，棒状渗碳体占比减少，球状渗碳体占比增加，MC (M为Ti, Nb, V或Mo)析出相尺寸减小，屈服强度和抗拉强度分别由935 MPa和958 MPa降低至866 MPa和888 MPa，-40℃冲击功和总伸长率不断增加，在600℃回火时达到峰值，分别为280 J和5.0%。当回火温度为550℃时，实验钢的屈服强度为895 MPa，抗拉强度为921 MPa，伸长率为4.3%，-40℃下冲击功为271 J，表现出较佳的强韧性匹配。这主要归因于渗碳体的球化和弥散分布的MC相粒子降低了应力集中以及针状α相回火产生的软化作用，从而展现出强韧性。

关键词: Cu-Cr-Ni耐候钢, 回火温度, 显微组织, 析出相, 力学性能