The effect of yttrium addition on the chemical composition of the non-metallic phase in liquid steel

Abstract

.The introduction of yttrium as an alloy additive to steel is connected with the formation of non-metallic inclusions resulting in the losses of this element. The presence of yttrium is expected to minimize the precipitation processes caused by sulphur and oxygen in steel. Therefore the order in which the additives are introduced during refining processes decides about yttrium final content in steel in bounded and dissolved form. For defining the amount of the generated non-metallic phase and kinetics of deoxidation and desulphurization processes authors used a non-commercial computer program based on the worked out calculation models. The process was analyzed in view of the order of introducing additives: Al, Y and Ca to preliminarily deoxidized steel. It was revealed that yttrium dosing is connected with the formation of oxide and sulphide phases. The introduction of yttrium prior to aluminium brings about huge losses, mainly as far as oxides formation is concerned. In the case of higher participation of sulphur, this effect is even stronger. When yttrium is introduced after aluminium and calcium, yttrium is used for the formation of its sulphide, and in this way the manganese sulphide formation is reduced. The simulations showed that yttrium should be introduced at the end of the refining process after adding aluminium and calcium. In this case the yttrium losses for the formation of its sulphide and oxide and least.