Abstract: SEN cloggings of Al-killed resulfurized gearing steel after calcium treatment were analyzed.And the castability of molten steel was improved by optimizing the processe.The results showed that SEN clogging was mainly caused by the CaS and Ca-Al-Mg-O inclusions with high melting-point.The inclusion composition in the Al-killed resulfurized gearing steel wass mainly depended on the ratio of [O] content to [S] content in the steel after Ca-treatment and sulphur addition. By raising the [O] content, CaO contnets in inclusions increased and the castablity of the molten steel was improved. Under the condition of weaker deoxidization process,CaO content increases and CaS content decreases in inclusions. As a result,castability of molten steel improved greatly, with the continuous casting heats increased from 4 to 7 or more.

Key words: Al-killed resulfurized steel, oxygen content, inclusion composition, SEN clogging