Control of formation of spinel inclusion in type 304 stainless steel by slag composition

The inclusion Of the SpinCl, MgO-Al2O3 in type 304 stainless steel slabcauses defect ofsurface, deterioration ofmcchanical property and so on. Thus, it is required to redUCC the spine] inclusion. In this study, inclusions in molten type 304 stainless steel at each Successive reactor, which were AOD, LF and tUndish, were investigated in order to control the formation ofthe spinel in type 304 stainless steel slab. The formation of the spinel inclusions in the slab was discussed from the viewpoint of the effect of slag conaposition. The A1203 content in inclusion increased in the Course of production process from AOD to slab. Moreover, the A1203 Content in inclusion in the slab increased with the increase of Al2O3 content in slag and %CaO/%SiO, ratio of'slag. The following formation mechanism ofinCIL1sion is proposed based on these results. The origin Of inclusion is forined by incorporation between the suspended AOD slag in molten steel and the cleoxiclation products that are SiO2 and Al2O3, When the temperature of molten steel falls, the original inclusion works as a FILICleation site, namely, Al2O3,03 as a secondary dcoxidation product precipitates at the original inclusion. Accordingly, the Al2O3 content in the inclusion increases. Based on the formation mechanism ofinclusion, the semi-crnpirical model was constructed. This model revealed that reduction of AI,03 content in slag and %CaO/%SiO, ratio ofslag was effective for eliminating the formation ofliarmful spinel inclusion.