关键词: 冷镦钢, 脱碳, 加热, 氧化, 冷却速率

Abstract: Decarburization and oxidation mass gain of ML40Cr steel under different heating temperatures (700-1150 ℃) and heating time (10-60 min) were studied through resistance furnace heating tests, and the decarburization behavior during the post-rolling cooling process was simulated. The results show that with the increase of heating temperature and time, the oxidation mass gain of the ML40Cr steel tends to increase, and the oxidation rate is the fastest between 900-1050 ℃. When the heating temperature is lower than 725 ℃, there is no obvious decarburization in the ML40Cr steel. When heated between 750-1150 ℃, the total decarburized layer of the steel generally increases with the increase of time and temperature. The depth of the decarburized layer increases sharply above 1000 ℃, and decarburization is most severe at 1150 ℃. The thickness of the burn-off layer and oxide scale are calculated using the oxidation mass gain, and the total decarburisation depth is theoretically calculated by models of the Li, Choi and theoretical decarburization-burning loss. Comparative analysis reveal that oxidation primarily affects total decarburisation by consuming the decarburisation depth through oxidation burn-off, whereas the influence of the oxide scale on decarburisation is minimal. The full decarburized depth only appears when heated between 750-800 ℃, with no significant ferrite decarburizing observed above 825 ℃. Surface carbon content influences the formation of ferrite decarburizing. The surface carbon content affects the occurrence of full decarburization. A high surface carbon content reduces or even prevents the occurrence of full decarburization. Simulation of post-rolling cooling demonstrates that as the cooling rate decreases, both full and total decarburisation of the steel increase. When the cooling rate is below 3 ℃/s, the depth of the decarburized layer increases significantly during the cooling process.

Key words: cold heading steel, decarburisation, heating, oxidation, cooling rate