Original Article

Evolution and control of MnS inclusions in non-quenched steel during hot processing

¹ North China University of Science and Technology, Tangshan 063000, PR China
² Key Laboratory of lntelligent Equipment Digital Design and Process Simulation, Tangshan University, Tangshan 063000, PR China
³ Shijiazhuang Iron and Steel Co., Ltd., Shijiazhuang 050100, PR China
⁴ Tangshan Iron and Steel Group Co., Ltd. Technology Research and Development Center, Tangshan, 063210, PR China

^* e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 18 January 2026
Accepted: 27 February 2026

Abstract

The abstract has been revised, displayed as: “The effect and mechanism of isothermal homogenization heat treatment on the morphology and distribution of MnS inclusions in 46MnVS5 steel were systematically studied in this paper. By designing isothermal treatment experiments at different temperatures (950–1350 °C) and time (1–10 h), combined with OM, SEM and ASPEX automatic statistical analysis, the evolution law of MnS was revealed. The results show that under 3 h isothermal treatment, MnS undergoes the evolution sequence of “splitting-passivation-spindle-spheroidization” with increasing temperature. The spheroidization effect is optimal at 1250 °C, where the proportion of inclusions with aspect ratio below 3 exceeds 90%. At 1250 °C, the morphology of MnS evolved from elongated to short rod-like, spindle-shaped, and finally spherical with increasing holding time. After 3 h, splitting was largely complete, and the number density transitioned from increasing to decreasing, indicating a shift in dominant mechanism from fragmentation to coalescence and dissolution. Mechanism studies reveal that the evolution process is driven by Ostwald ripening and surface energy minimization, with mass transfer controlled by surface diffusion. Thermodynamic analysis further reveals that the rate-limiting element for Ostwald ripening shifts with temperature, transitioning from Mn at 1050 °C to S at 1250 °C. The optimal homogenization condition (1250 °C, 3 h) resulted in over 90% of MnS inclusions with aspect ratio <3, significantly improving morphological uniformity. The controlling element for Ostwald ripening shifted from Mn at 1050 °C to S at 1250 °C, providing new insight into inclusion engineering. These findings establish a theoretical foundation and practical process route for enhancing the properties of non-quenched and tempered steel.