Abstract: In the ladle slag conditioning treatment after BOF tapping in production of automobile sheet steel, measures must be taken to prevent the reaction between the high [O] content liquid steel and the top slag in addition to add enough amount of conditioning agent. Otherwise, the mass fraction of Fe_tO in the slag will rise back to 8 %-14 %, or even higher, though it can be lowered to low content level temporally in conditioning treatment. The technology developed by Hanbao Steelmaking Plant of Hansteel Co., Ltd. to restrain the slag-steel reaction in ladle slag conditioning treatment is introduced in this article, which are 1) using aluminum-slag pellets as the slag conditioning agent which can slowly release Al in and after the conditioning treatment, 2) adding lime after BOF tapping instead of during tapping, 3) increasing ratio of w(CaO)/w(Al₂O₃) of the ladle slag to lower its fluidity,and 4) using week bottom stirring. With the developed technology, TFe mass fraction of the ladle slags before and after RH refining is lowered to less than 3 % and 5 %, respectively. Re-oxidation of the molten steel due to the ladle slag has been controlled. Contents of the total oxygen and non-metallic inclusions of the liquid steel in CC tundish are reduced and nozzle clogging in continuous casting has been effectively controlled.

Key words: automobile sheet steel, BOF, ladle slag, Fe_tO content, conditioning treatment, cleanliness