Effect of heat treatment on inclusions and microstructure of U76CrRE rare earth heavy rail steel
Li Xiangchuan, Yang Jichun, Bai Guojun, Fan Zhiming
2022, 47(8):
200-210.
doi:10.13251/j.issn.0254-6051.2022.08.034
Abstract
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U76CrRE billets were heat treated at 1100 ℃, 1200 ℃ and 1300 ℃ for 1 h, 2 h and 3 h, respectively. The inclusions were observed by FEI-QUANTA400 scanning electron microscope, the microstructure and hardness were observed and tested by means of Axiovert Zeiss optical microscope and Qness-Q10A+automatic microhardness tester. The results show that the heat treatment has obvious effect on the inclusions in the U76CrRE rare earth heavy rail steel, and the shape and size of inclusions are significantly improved. With the increase of heating temperature, the morphology and size of MnS and compound inclusions can be further optimized. When heated at 1100 ℃, the size of MnS and compound inclusions decreases with the increase of holding time, and the shape is obviously improved. When heated at 1200 ℃, the size of MnS decreases and the size of compound inclusions increases with the increase of holding time. The grain size of the U76CrRE rare earth heavy rail steel increases obviously with the increase of heating temperature, and the hardness shows a trend of first decreasing and then increasing, while decreases gradually with the extension of holding time. When heated at 1100 ℃, the microstructure of the tested steel is martensite, bainite and retained austenite, and the grain boundary is not obvious. After holding at 1200 ℃ and 1300 ℃ for more than 1 h, the network cementite in the tested steel is obvious. When heat treated at 1300 ℃ for 1 h, the carbon deposition at the grain boundary is serious and the carbides are not effectively dissolved. When held at 1200 ℃ for 1 h, the grains of the tested steel are uniform, the grain boundaries are obvious, the microstructure is mainly retained austenite and pearlite, and the microstructure is uniform.
