Effect of high magnetic field on the microstructure evolution and mechanical properties of M50 bearing steel during tempering

The effect of high magnetic field (12 T) on the microstructure evolution and mechanical properties during tempering of M50 bearing steel have been investigated for evaluating the application prospect of magnetic field in steels. Microstructural observation shows that the high magnetic field can obviously accelerate the decomposition of retained austenite (RA) during the moderate tempering (at 300 or 380 degrees C), which could be ascribed to the increased dislocation in RA by the magnetic field-Induced deformation of martensite. Meanwhile, the cementite precipitation is also increased by the applied high magnetic field because of the higher nucleation rate. Moreover, at higher tempering temperature of 530 degrees C, the Fe content in the precipitated carbides increases after applying high magnetic field, which is related to the different magnetization of carbides caused by various element content. Characterization of mechanical properties indicates that the tempered martensite embrittlement is significantly intensified during tempering at 380 degrees C, which is resulted from the accelerated RA decomposition and improved cementite precipitation under high magnetic field. When tempered at 530 degrees C in high magnetic field, the dislocation recovery is retarded and then the Vickers hardness and ultimate tensile strength (UTS) are thus improved by dislocation strengthening. This finding suggests the potential of high magnetic field (12 T) in optimizing the properties of M50 bearing steel during tempering (530 degrees C).