1990 Volume 76 Issue 11 Pages 1932-1939
In steelmaking process, the refining technology are progressed greatly by the introduction of combined blowing converter and the spread of the process of hot metal pretreatment. At Mizushima Works, the top-and-bottom blowing converter (K-BOP) were introduced in April 1980 and the hot metal pretreatment facilities had the capacity of pretreating all hot metal in November 1988. For the purpose of the development of best K-BOP only for decarburization practice, we made the experiments of reducing the bottom oxygen flow rate. As a result, it was able to reduce to 0.25 Nm3/min·t from 0.8 Nm3/min·t (conventional way) with same metallurgical characteristics, when the inert gas is used at final stage of blowing at the rate of 0.35 Nm3/min·t or above using pretreated hot metal. Based on this principle, we changed the K-BOP's tuyeres and obtained the prolongation of converter life and the reduction of process gas cost. Furthermore, by using the pretreated hot metal and controlling the converter slag basicity to more than 5 and the (%MgO) to around 10% and deoxidizing the ladle slag, the quality and cleanliness of ultra low carbon steel for cold-rolled sheet is able to be improved drastically.
