Temperature Dependence and Formation Mechanism of Surface Decarburization Behavior in 35CrMo Steel

Herein, the temperature dependence and formation mechanism of surface decarburization behavior are researched for 35CrMo steel in the temperature range of 710-950 degrees C. In view of the three transformation temperatures A(1), A(3), and T-G (the A(3) temperature for pure iron), the decarburized microstructural characteristics can be divided into four types: nondecarburization, complete decarburization, complete and partial decarburizations, and partial decarburization. The absolute thickness of the total decarburization layer is the sum of the thicknesses of oxide layer, complete decarburization layer, and partial decarburization layer, and it follows an exponential relationship with the temperature. The absolute thickness of complete decarburization layer, including the thicknesses of the oxide layer and the visible complete decarburization layer, decreases with increasing temperature. In the temperature range of A(1)-A(3), the complete decarburization rate is primarily controlled by the austenitization degree and the diffusivity of carbon in ferrite and austenite, whereas in the temperature range of A(3)-T-G, it can be jointly controlled by the decarburized incubation time in single-phase austenite and the duration holding in the alpha + gamma phase field.