Abstract
The transformation of non-metallic inclusions in the first continuous casting bloom of a bearing steel was studied through industrial trials and theoretical calculations. The spatial composition distribution of inclusions in the continuous casting bloom was predicted using a comprehensive model coupling heat transfer, thermodynamics, kinetics and industrial parameters. The effect of cooling rate on the transformation of composition of inclusions was investigated. The total oxygen in the first bloom gradually decreased from 12 ppm at the cast start to 7 ppm at 10 m cast length, and this variety in the total oxygen resulted in the decrease of the Al2O3 content in inclusions from 70% at the casting start to 50% at 10 m cast length. The transformation of inclusions during the continuous casting occurred preferentially at the quarter thickness of the bloom and the reaction zone gradually moved from the subsurface to the center of the bloom. Isothermal transformation diagrams and continuous cooling transformation diagrams of inclusions were established to characterize the transformation kinetics of inclusions. Inclusions at the subsurface of the CC bloom transformed at the mold cooling zone in the actual cooling of the continuous casting bloom, while inclusions at the center transformed at the air-cooling zone. The transformation ratio of inclusions in the CC bloom was determined by the cooling rate and the transformation rate was dominated by the temperature.
