Wang Xian-Wen, Hu Qing-Feng, Zhang Chao-Lei, Chen Lie, Zhu Chang-Yong, Tao Bo, Jiang Bo, Liu Ya-Zheng
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China.
Jianlong Beiman Special Steel Co., Ltd., Qiqihar 161041, China.
Materials (Basel). 2022 May 24;15(11):3763. doi: 10.3390/ma15113763.
Optimizing the heat treatment procedure with 13 mm diameter 38Si7 spring steel is critical for developing high-performance, low-cost, large spring steel for railway clips. The effects of quenching temperature, holding time, tempering temperature, and tempering time on the microstructure and mechanical properties were investigated using an orthogonal experiment, designed with four factors and three levels. The best heat treatment settings were explored, as well as the variation laws of mechanical properties, decarburization behavior, and fracture morphology. The results demonstrated that quenching temperature and tempering temperature had the most impact on plasticity and tempering temperature, while time had the most effect on strength. The optimized heat treatment schemes made the elongation increase by up to 106% and the reduction in area increase by up to 67%, compared with the standard BS EN 10089-2002, and there were mixed fractures caused by ductility and brittleness. The fracture tests showed a good performance of 20.2 GPa·%, and the heat treatment processes' minimum decarburization depth of 93.4 μm was determined. The optimized process would obtain stronger plastic deposition and better decarburization performance. The microstructure was simply lightly tempered martensite, and the matrix still retained the acicular martensite. The optimal heat treatment process is quenching at 900 °C for 30 min (water cooling), followed by tempering at 430 °C for 60 min (air cooling). The research led to a solution for increasing the overall mechanical characteristics and decreasing the surface decarburization of 38Si7 spring steel with a diameter of 13 mm, and it set the foundation for increasing the mass production of railway clips of this size.
优化直径为13毫米的38Si7弹簧钢的热处理工艺对于开发用于铁路夹的高性能、低成本大型弹簧钢至关重要。采用四因素三水平的正交试验，研究了淬火温度、保温时间、回火温度和回火时间对组织和力学性能的影响。探索了最佳热处理工艺参数，以及力学性能、脱碳行为和断口形貌的变化规律。结果表明，淬火温度和回火温度对塑性影响最大，回火温度影响最为显著，而时间对强度影响最大。与标准BS EN 10089-2002相比，优化后的热处理工艺使伸长率提高了106%，断面收缩率提高了67%，出现了韧性和脆性混合断裂。断裂试验显示性能良好，为20.2 GPa·%，并确定了热处理工艺的最小脱碳深度为93.4μm。优化后的工艺将获得更强的塑性沉积和更好的脱碳性能。微观组织为简单的轻度回火马氏体，基体仍保留针状马氏体。最佳热处理工艺为900℃淬火30分钟（水冷），然后430℃回火60分钟（空冷）。该研究为提高直径13毫米的38Si7弹簧钢的综合力学性能和减少表面脱碳提供了解决方案，并为增加这种尺寸铁路夹的大规模生产奠定了基础。
