Controlling the Morphology of MnS Inclusions in Steel by Electropulsing

Controlling the morphology of MnS inclusions is crucial for mitigating anisotropy and enhancing the performance of steels. This study introduces electropulsing treatment as a method to regulate the morphology and size of MnS inclusions. Systematic experiments conducted on non‐quenched and tempered steel reveal that electropulsing treatment facilitates the formation of spherical MnS during solidification. Under the experimental conditions of 200 Hz and 200 A, the proportion of MnS inclusions with an aspect ratio exceeding 3 significantly decreased from 26% to 9%, accompanied by a corresponding reduction in the average aspect ratio. This spheroidization phenomenon arises from the dual influence of pulsed current on both the thermodynamic and kinetic aspects of MnS precipitation. From a thermodynamic perspective, the pulsed current effectively lowers the nucleation barrier for MnS, promoting its earlier precipitation with an increased number density across a wider range of solidification fractions. Kinetically, the forced convection induced by the pulsed current not only substantially alleviates solute micro‐segregation within the interdendritic regions but also accelerates the diffusional mass transfer of Mn and S elements. This synergistic effect promotes the dispersed nucleation of MnS while effectively inhibiting its subsequent coarsening, providing novel insights into the physical microstructure control of steels.