The Effect of Timing for Adjusting Titanium and Slag Oxidation on the Cleanliness of DC04-N Steel during the Ruhrstah Hereaeus Process

In this work, the effect of the timing of titanium adjustment and slag oxidation on the cleanliness of DC04-N steel during the Ruhrstah Hereaeus (RH) refining process is investigated. The results demonstrate that as the process progresses, the total oxygen content, nitrogen content, and the number of inclusions in the steel gradually decline. Meanwhile, the inclusions are mainly Al₂O₃-bearing inclusions during the RH refining process, including single Al₂O₃, Al₂O₃–TiO_x and MgO–Al₂O₃–TiO_x. Statistical analyses reveal that the interval time for adding Al and Ti has been reduced from 6 to 3 min, the quantity of Al₂O₃–TiO_x and MgO–Al₂O₃–TiO_x inclusions has increased. Moreover, it is found that the oxidation state of the refining slag exerts a significant impact on the number of inclusions in DC04-N steels. As the deoxygenation products, that is, Al₂O₃-bearing inclusions, are continuously adsorbed by the slag, the FeO and MnO contents in the refining slag gradually decrease, while the Al₂O₃ content and the C/A ratio gradually increase. Therefore, it is recommended to appropriately extend the time interval for adding Al and Ti and weaken the oxidation of the top slag through modification during the RH refining process, which is beneficial for achieving high-cleanliness Al-killed low-carbon steel.