Characterization of surface decarburization and oxidation behavior of Cr–Mo cold heading steel

Abstract Herein, the surface decarburization and oxidation characteristics of Cr–Mo cold heading steel are investigated via optical microscopy, scanning electron microscopy, and electron backscatter diffraction under different temperatures. Furthermore, the competitive mechanisms of decarburization and oxidation are analyzed. The results indicate that the heating temperature considerably affects the decarburization and oxidation characteristics of the steel sample. With an increase in the temperature, the depth of the total decarburization layer increases. The fully decarburized layer is prominent between 750 and 850°C and culminates at 800°C. The oxide thickness parabolically increases, and Cr 2 O 3 is present, which inhibits oxidation. Between 700 and 950°C, the oxidation weight gain is slow. The main structure of the oxide scale is the dense Fe 3 O 4 layer, inhibiting decarburization. The oxidation rate increases at 950°C, and the proportion of loose FeO layer in the oxide scale exceeds 66%, promoting decarburization. At >1,000°C, the surface decarburization and oxidation rate simultaneously increase.