On the Refining Condition of Extremely Low Carbon and Nitrogen Stainless Steel in VOD Process

VOD process has been improved for the production of super ferritic stainless steel which is characteristic in ultra low carbon and nitrogen contents. (1) According to the data of 60t VOD, the obtained carbon content is influenced not only by well known factors, Cr% and temperature of molten steel, but also by the bubbling condition and oxygen blowing pattern. (2) It is observed in an experiment in 10kg VIF that decarburization in low carbon range proceeds mainly by a reaction between oxide which is formed by oxygen blowing and carbon in molten steel. If agglomeration of oxide is prevented by an appropriate bubbling and oxygen blowing pattern, the course of decarburization is expressed as a first-order reaction until ultra low carbon range. (3) The obtained nitrogen content is affected by air leakage into the vacuum vessel and the rate of decarburization. When air leakage is much, nitrogen content increases in low carbon range. (4) For the production of ultra low carbon and nitrogen stainless steel, it is necessary to pay attention to the pattern of molten steel temperature, bubbling condition, and prevention of air leakage.