Evolution behavior of oxide inclusions in Si-Mn deoxidized steel during billet heating process

In order to minimize the impact of oxide inclusions on the quality of Si-Mn deoxidized steel, the effects of heat treatment temperature and holding time on the inclusion composition and morphology were studied. LX82A billets were heated isothermally at 1000, 1100, and 1200?C for 8, 10, and 12 hours, respectively. The experimental results show that as the heat treatment temperature increases, calcium treatment and the reduction of the w(Al2O3 + MgO) / w(SiO2 + MnO) ratio enhance the deformability of the oxide inclusions. This causes a gradual transition in inclusion shape from oval to round. At 1200?C, the oxide inclusions are predominantly regular and round. With increasing heat treatment temperature and holding time, the oxide inclusions in Si-Mn deoxidized steel shift from the CaO-SiO2-Al2O3 system to the MnO-SiO2-Al2O3 system. At a constant temperature, the highest inclusion transformation rate and the most uniform composition occur at a 10-hour holding time. At 1200?C, an alternative calcium treatment and the steel matrix-inclusion interface reaction increase the MnO content at the interface, reducing the manganese content in the steel and forming a Mn-depleted zone. This decreases austenite stability, enhances ferrite nucleation, and improves the steel quality and performance. Therefore, controlling the heat treatment temperature around 1200?C is crucial.