Recent change in refining process in Nippon Steel Corporation and metallurgical phenomena in the new process

Since the 1980s, Nippon Steel has been developing multistage refining processes, mainly in the area of hot metal pretreatment, due to increasing demand for high-purity steels. In recent years, in order to cope with the new problems that have arisen with the changing business environment, e.g. raw material conditions and environmental regulations and establishing a more efficient process with respect to productivity, resources and energy, several rearrangements have been carried out with emphasis on primary refining. The major change in the new process comprises (1) high-efficiency hot metal desulfurization and (2) desiliconization and dephosphorization using basic oxygen furnaces. Consequently, high-speed treatment, fluoride-free refining, decrease in CaO consumption and waste slag and improvement of heat balance have been accomplished. Some of the metallurgical phenomena concerning the new process are discussed and future works are suggested.