高强韧U20Mn2SiCrNiMo贝氏体钢轨热处理工艺的优化

研究正火-回火和等温热处理工艺对U20Mn2SiCrNiMo贝氏体钢轨显微组织和力学性能的影响。结果表明:试验钢经900℃正火+300℃回火后的力学性能为抗拉强度为1396MPa,伸长率为16.0%,冲击吸收功K_U2为57J,HB硬度值402;试验钢经870～930℃加热空冷至300℃等温处理后,抗拉强度基本保持在1300 MPa左右,伸长率为17.0%,冲击吸收功K_U2≥80 J,HB硬度值375～395;和传统的正火+回火工艺相比,优化的等温热处理工艺可以大幅提高U20Mn2SiCrNiMo贝氏体钢轨的冲击韧性,室温冲击吸收功由57J提高到80J以上,提高40%～56%,而断后伸长率基本保持不变,抗拉强度和踏面硬度略有降低。最佳优化工艺为:870℃正火后空冷至300℃保温4h后空冷。

Optimization of Heat Treatment Process of High Strength-Toughness U20Mn2SiCrNiMo Bainite Steel Rail

The effect of normalizing + tempering and isothermal heat treatment processes on the microstructure and mechanical properties of U20Mn2SiCrNiMo bainite steel rail has been studied. The results show that as the test steel is normalized at 900 °C + tempered at 300 °C ,the mechanical properties are tensile strength 1396 MPa,elongation 16.0% impact absorption work K_U2 57 J,and HB hardness value 402；as the test steel is heated at 870 ~ 930 °C after air-cooied to 300 °C isothermal treatment,the mechanical properties are tensile strength 300 MPa,elongation 17.0% ,impact absorption work K_U2 ≥80 J,HB hardness value 375 ~ 395 ；By comparison with the traditional normalizing + tempering process, the optimized isothermal heat treatment process can greatly improve the impact toughness of U20Mn2SiCrNiMo bainite steel rails i. e. the room temperature impact absorption work has been increased from 57 J to more than 80 J ,by 40% ~ 56% , while the elongation after breaking remains basically unchanged, tensile strength and tread hardness slightly lower. The best optimized process is normalizing at 870 °C. , air-cooling to 300°C for 4 hours air-cooling.