The Role of High Magnetic Fields in the Evolution of Microstructure and Mechanical Properties in Medium Manganese Steel

The influence of the external magnetic field on the microstructures and mechanical properties of medium manganese steel during tempering is investigated. Microstructural analysis reveals that a high magnetic field accelerates martensite recovery, and the width of martensitic laths increased by 150% and 130% after tempering at 200 or 500 °C, respectively. This phenomenon is likely attributed to the magnetic field influence on elevating the diffusion activation energy. Dislocation motion is accelerated due to the magnetic field, leading to dislocation accumulation. The dislocation provides more nucleation sites for the carbide precipitation compared to without the magnetic field. Furthermore, a magnetic field triggers carbide precipitation, with rod-shaped transforming into spherical ones. The mechanical properties of specimens after tempering with a magnetic field are slightly higher than those of the specimens tempered without a magnetic field, which is due to the synergistic effect of the precipitation and dislocation motion. Special attention has been paid to emphasizing the medium-temperature tempering brittleness that arises from the precipitation and micro-voids along martensite lath and prior austenite grain boundaries. The mechanism of a magnetic field-induced transformation is further explored in this study, which has important theoretical and practical implications for the creation of advanced steel materials.