Refining effect of IF steel produced by RH forced and natural decarburization process

Owing to insufficient converter heat, IF steel is produced via the BOF—LF—RH—CC process in the Xichang Steel & Vanadium Co.LTD of Pangang Group, Xichang, China. To explore the refining effect of IF steel produced via the RH forced and natural decarburization process, this work employed standard analysis methods such as production data statistics, total oxygen and nitrogen analysis, automatic scanning electron microscopy, scanning electron microscopy, and energy spectroscopy. The effects of different decarburization processes on the ladle slag oxidability and cleanliness of steel were investigated in detail. Compared with the natural decarburization process heats, results show that the forced decarburization process heats exhibit (1) lower average O content in molten steel after BOF and before RH, (2) a similar level of the O content in molten steel after decarburization with that of the natural decarburization process, and (3) 1.3% lower average T.Fe mass fraction in the ladle slag after RH treatment. To ensure the RH decarburization effect, the final carbon content increased and molten steel oxygen content reduced in the converter to the maximum extent. The forced oxygen blowing decarburization process was then used to compensate for the molten steel oxygen content during RH refining by increasing oxygen blowing properly, which can significantly decrease the ladle slag oxidability of IF steel. Both the natural decarburization and forced decarburization processes are ideal for controlling the T.O content of a hot–rolled sheet. Compared with the natural decarburization process, the forced decarburization process can effectively reduce the N content of IF steel, which is related to a more violent carbon–oxygen reaction in a vacuum chamber, resulting in a high volume of CO bubbles and a large gas–liquid reaction area. The decarburization process has no obvious influence on the type, size, and number of inclusions in the hot–rolled sheet of IF steel that mainly consist of Al₂O₃, Al₂O₃–TiO_x, and other inclusions. The average sizes of the above three 4.5, 4.4, and 6.5 μm, respectively, according to the equivalent circle diameter of inclusions. In addition, more than 75% of inclusions are within 8 μm. During the RH refining process, reducing the O content in molten steel after RH decarburization to the maximum extent is beneficial to improve the cleanliness of molten steel.