Effect of Mn on tempering stability of retained austenite in bainite steel
ZHANG Shao-long1, ZHOU Wen1,2, HU Feng1,2, WU Kai-ming1,2,3, PAN Xian-ming4
1. Collaborative Innovation Center for Advanced Steels, Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 2. Hubei Province Key Laboratory of Systems Science in Metallurgical Process,Wuhan University of Science and Technology, Wuhan 430081, Hubei, China; 3. Metals Valley and Band Foshan Metallic Composite Co., Ltd., Foshan 528000, Guangdong, China; 4. Hubei Province Key Laboratory of High Performance Special Steel, Daye Special Steel Co., Ltd., Huangshi 435001, Hubei, China
Abstract：In order to study the effect of Mn mass percent (0.1% and 1.5%) on the tempering stability of retained austenite (RA) in carbide-free bainite steel,scanning electron microscopy (SEM),electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to study the stability and mechanical properties of retained austenite. The results show that the hot-rolled microstructure of 0.1Mn steel is mainly composed of granular bainite (GB)+lath bainite (LB),while the hot-rolled microstructure of 1.5Mn steel is mainly lath bainite,and the content of retained austenite in 1.5Mn steel is higher,and the yield strength and tensile strength are better than 0.1Mn steel. After tempering at 300-500 ℃,the volume fraction of RA gradually decreases to complete decomposition,and the yield strength and tensile strength increase first and then decrease,but the elongation increases gradually. The best tempering performance is obtained at 300 ℃. The main reason is that during the tempering of retained austenite at 300 ℃,the block retained austenite decomposes into supersaturated martensite/bainite,and the carbon diffuses from the supersaturated martensite/bainite to the adjacent retained austenite to increase its content,so that the thermal stability is improved,and TRIP effect is produced in the process of stretching,so that the strength and plasticity of the test steel is improved. The mechanical properties of 1.5Mn steel is obviously better than that of the 0.1Mn steel,mainly because Mn and C can have synergistic effect to promote the stability of austenite and improve the elongation. In addition,the increase of Mn content increases the carbon equivalent,so that the strength of the test steel is enhanced. Based on the modified C-J model,the work hardening behavior of two test steels during tensile process is characterized. It was found that the strain hardening index of the 1.5Mn steel is always greater than that of the 0.1Mn steel,and the test steels showed three-stage strain hardening characteristics.
张绍龙, 周雯, 胡锋, 吴开明, 潘先明. 锰对贝氏体钢中残余奥氏体回火稳定性的影响[J]. 钢铁, 2023, 58(2): 113-125.
ZHANG Shao-long, ZHOU Wen, HU Feng, WU Kai-ming, PAN Xian-ming. Effect of Mn on tempering stability of retained austenite in bainite steel[J]. Iron and Steel, 2023, 58(2): 113-125.
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2023, Vol. 58 
