Heat treatment and properties of SCM435 steel for 12.9 grade bolts used in high-speed trains

doi:10.13251/j.issn.0254-6051.2025.04.027

Abstract

Abstract: For 12.9 grade high strength bolts used in high-speed trains, the heat treatment process of SCM435 steel for the bolts and its mechanical properties, delayed-fracture resistance, and high-cycle fatigue property were studied. The results show that the optimal quenching and tempering process for the SCM435 steel is quenching at 880 ℃ for 30 min followed by tempering at 500 ℃ for 60 min. The properties of the specimens treated by the process meet the strength and plasticity requirements of 12.9 grade bolts. Under the optimal heat treatment process, the delayed-fracture strength ratio (DFSR) of the bolt steel specimens is 0.69. Through the tension-tension fatigue test, the stress level is grade 3, and the tension-tension fatigue strength is (756 ± 441) MPa.

Key words: SCM435 steel, 12.9 grade bolts, heat treatment, mechanical properties, delayed-fracture resistance, high-cycle fatigue property

CLC Number:

TG142.4

Qi Cheng, Wang Xiaoyu, Ma Jinsuo, Xie Jiacheng, Wang Jiajie, Yang Yichun, Wu Meng, Mao Xiangyang. Heat treatment and properties of SCM435 steel for 12.9 grade bolts used in high-speed trains[J]. Heat Treatment of Metals, 2025, 50(4): 187-192.

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