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

Abstract

Herein, the temperature dependence and formation mechanism of surface decarburization behavior are researched for 35CrMo steel in the temperature range of 710–950 °C. In view of the three transformation temperatures A1, A3, and TG (the A3 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 A1–A3, 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 A3–TG, it can be jointly controlled by the decarburized incubation time in single‐phase austenite and the duration holding in the α + γ phase field.

Development of Induction Heating System Ensuring Increased Heating Efficiency of the Charge Material in a Forging

“…The temperature increase initially equals 2 • C/s (at the beginning of the inductor), with an increase to 5 • C/s 15 s after the material is transferred through the incubator. A lowered temperature at the end of the first and beginning of the second section positively affects the leveling of temperatures between the surface and the core and annealing at 800 • C should not cause significant decarburization, which is in agreement with the material's decarburization curve [50]. The heated steel bars (charge) at the moment of exit from the last incubator reach 1176 • C inside and 1198 • C on the examined surface, with an increase of 5 • C/s, similar to the second section.…”

Formation and Deformation Mechanism of Mountain‐Like Surface Crack on the Hot‐Rolled Thick Plate of HSLA Steel

“…In the continuous casting and rolling process, decarburization often occurred on the surface of the slab and the carbon content of the surface was reduced. [23,24] Due to the reduction in carbon content, the proportion of ferrite in the surface microstructure increased. As a result, there was more ferrite in the surface microstructure than the subcutaneous microstructure of the slab.…”

“…The microstructure below the surface is coarse and the pearlite content is high. [23][24][25] Therefore, the color of the unusual microstructure is darker than that of the normal surface.…”

“…This gray area is the microstructure below the surface of the initial side-1, which appears after the large deformation of the initial side-1 in the RD direction. The microstructure below the surface is coarse and the pearlite content is high [23][24][25]. Therefore, the color of the unusual microstructure is darker than that of the normal surface.The formation cause of the mountain-like crack is the surface defect in the continuous casting slab which is caused by Type-I and Type-II inclusions.…”