Effect of Tellurium Modification on MnS Inclusions in Nonquenched and Tempered Steel

To improve the machinability and service reliability of nonquenched and tempered steel, this study combines experiments with theoretical simulations to elucidate the synergistic effects of tellurium (Te) on the morphological evolution, hot deformation behavior, interfacial matching, and mechanical performance of MnS. The results show that in steel, the main inclusions are large, elongated MnS particles, which are prone to plastic deformation during hot working. When the Te content in the steel reaches 0.016%, the original inclusions are transformed into MnTe–MnS composite inclusions with smaller sizes and morphologies approaching spherical or ellipsoidal shapes. These composite inclusions exhibit excellent morphological stability during high‐temperature deformation. First‐principles calculation results indicate that MnTe has a relatively high bulk modulus but lower shear modulus, Young's modulus, and hardness, exhibiting characteristics of ductility. 2D lattice disregistry analysis further indicates that MnTe matches MnS better than either phase matches the Fe matrix, and MnTe also shows superior lattice compatibility with Fe. Consequently, MnTe is more likely to nucleate on MnS surfaces, forming stable MnTe–MnS that alleviate stress concentration at the inclusion–matrix interface and enhance interfacial bonding stability. These findings provide a theoretical basis for regulating sulfide inclusion morphology in steel and for optimizing its microstructure and mechanical properties.