(1. Special Steel Department, Central Iron and Steel Research Institute, Beijing 100081, China 2. Faculty of Materials and Metallurgical Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China 3. School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, Hubei, China)
Abstract:In order to obtain a fully spheroidizing microstructure, the spheroidizing annealing process for ultra-high carbon steel with 2% aluminum addition (UHCS-2Al) was studied based on the mechanism of divorced eutectoid transformation. It is found that the forging microstructure of the ultra-high carbon steel with aluminum addition is composed of the pearlite with different interlamellar spacing and the continuous carbide networks due to the inhomogeneity of the composition. It is difficult to make it completely spheroidization only by using divorced eutectoid transformation process. The thickness of carbide networks is below 1 μm, normalizing below[Acm]temperature can obtain uniform and fine pearlites and eliminate carbide networks. It can also reduce the number of strip shape carbides in normalizing microstructure by increasing the normalizing temperature, which is beneficial to get better spheroidizing microstructure. The complete spheroidizing microstructure for UHCS-2Al consisted of ultrafine ferrite and fine spherical cementite was obtained after normalizing at 900-925 ℃, austenitizing at 830 ℃ and then isothermal treatment for 4 h at 760 ℃.
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