Variation of total oxygen in RH refining and operation improvement

In order to control the total oxygen at an appropriate level, investigations on deoxidation and purification were carried out in ultra-low carbon and low carbon steels by means of the RH vacuum degasser in the General Steelmaking Mill, Wuhan Iron & Steel Co. Ltd. The results show that influential factors of total oxygen removal in the order from main to subordinate are the free oxygen level in the tapping molten steel, interaction between the free oxygen and slag, slag in the ladle, and the vacuum treatment time, respectively. The clean molten steel with a total oxygen content of 10×10^-6 and nonmetallic inclusions less than 10 μm in size was produced by the optimizing process. A new equation involving the change of total oxygen concentration via the ladle with time is approved, which considers the influences of apparent oxygen equilibrium content, circulation, and diffusion mass transfer on the removal rate of oxide inclusions.