Following purification technology for line pipes or cold sheets has been developed and put to practical use in some works of Nippon Steel Corporation.
(1) Synthetic refining system of hot metal pretreatment, top and bottom blowing converter and multi-functional secondary refining, namely ladle injection under reduced pressure (V-KIP), flux injection during RH treatment (RH-Injection, RH-PB) are successfully in operation. Consequently final product of [P] ≤ 50 ppm, [S] ≤ 10 ppm and [H] ≤ 1.5 ppm can be stably produced.
(2)Ar injection into RH vacuum vessel or DH snorkel and vacuum vessel drastically improved decarburization rate of ultra low carbon level.
Technology of nitrogen removal during top and bottom blowing in converter and protection of molten steel from nitrogen adsorption between the end point of converter and casting have been operated. Consequently final product of [C] _??_ 10 ppm, [N] _??_ 10 ppm can be produced.
