Since 1971, Daido Steel Co., Ltd. has developed the LF process, a ladle refining process which depends primarily on slag refining, aiming an ideal performance of reduction refining instead of electric arc furnace. The main feature of this ladle technology exists in refining under non-oxidizing atmosphere and acceleration of slag-metal reaction through stirring by Ar gas injection, for a desired long time due to the temperature compensation by arc heating. It is possible to obtain clean materials having low oxygen and sulfur levels around 10ppm, or inclusion rating of approximately 1.0 to 0 for every type specified by ASTM-A.
At the early stage of development, several LF units were applied only for the production of high grade steels. In recent years, the application has extended to whole steel industry not only for the quality improvement, but for cost reduction, production increase and especially ladle-CC matching in sequence casting. In 1983, there are 24 LF installations in domestic steel works including 3 integrated steelmakers and the total LF steel will exceed 7 million t.
Many steelplants in Japan are now equipped with FAF(BOF)-LF-RH-CC combined line for high quality steels, in which reduction refining is exclusively entrusted to LF. The portion of special steels produced by this steelmaking process is expected to increase still further.