Influence of δ ferrite on impact toughness of M50NiL bearing steel

Abstract

M50NiL bearing steel is widely used in the aerospace field because of its excellent properties. δ ferrite would affect the impact toughness of steel, but there is little research on it in M50NiL bearing steel. In this study, the effect of the δ-ferrite content on the impact toughness of M50NiL bearing steel and the corresponding mechanism were investigated through microstructure characterization and mechanical property testing. The results indicated that the impact toughness of the steel at room temperature, as well as the energy needed for crack initiation and crack propagation, improved with δ-ferrite content reduction. This suggests that the presence of δ ferrite in M50NiL steel is detrimental to its impact toughness and that reducing the δ-ferrite content can suppress crack initiation and crack propagation, significantly improving the impact toughness. The adverse effect of δ ferrite on impact toughness is mainly attributed to the fact that δ ferrite is prone to crack initiation and cannot effectively prevent crack propagation due to its low strength and shear resistance. Additionally, the difference in microstructure and strength between the δ ferrite and martensite matrix may weaken the interface, which is conducive to crack initiation and rapid propagation.