Effect of Cr atom doping on the carbide stability and mechanical properties of high carbon chromium bearing steels

Carbides (MC, M3C and M7C3 at different Cr doping concentrations), as important influencing factors for the properties of high-carbon chromium bearing steel, their molecular transformation processes, structural stability, mechanical properties and electronic properties were calculated by first-principles. The results showed that the doping of Cr contributed to the movement of metal atoms change from translation to rotation during the transformation of carbide molecules, increased the reaction barrier of MC→M3C→M7C3 transformation, and inhibited the intermolecular transformation of carbides. Meanwhile, the doping of Cr affected the structural stability and mechanical stability of the three kinds of carbide. It was also found that the orientation of Fe–C covalent bond was reduced to weaken the strength of covalent bond in carbides by doping Cr atoms, that contributed to improving the plasticity of carbides, and the Cr–Fe metal bond was formed to enhance the strength of the covalent bond in the carbide by doping Cr atoms, that helped improve the hardness of the carbide. Therefore, in MC-type carbide, the carbide plasticity was best at the Cr doping concentration of 0.25 (vs. 0.75 for M3C-type and 0 for M7C3-type) and the hardness reached a maximum of 17.7 GPa at the Cr doping concentration of 1.0 (vs. 0.5 with 51.9 GPa for M3C-type and 0.75 with 11.0 GPa for M7C3-type). This study provided a new research idea for analyzing the carbide properties of bearing steel.