Effect of Ti-Zr oxide particles on MnS precipitation in low S steels

Abstract

The effect of Zr addition in the steel deoxidized with Ti was investigated to obtain uniform distribution of oxides and MnS. The dependence of the oxide distribution on cooling rate in Ti deoxidized steel became smaller and the number of oxide particles in the center of an ingot increased by the addition of Zr. It can be considered that Zr oxides may work as crystallization sites of Ti oxides during solidification of steel, in addition to the effects of Zr described in previous report; that is, refinement of the oxide particles and increase in their specific gravity to suppress their decrease in molten steel by flotation. Large number of fine MnS precipitated on Mn-Si-Ti-Zr complex oxide particles in the steel deoxidized with Mn, Si, Ti and Zr under the condition based on the result of a model calculation. Fine acicular ferrite formed in the steel sample after heat cycle test, and small Mn-Si-Ti-Zr oxides were observed in the center of the acicular ferrite.