The behavior and formation mechanisms of inclusions in Ti-stabilized, 17Cr Austenitic Stainless Steel produced by the ingot casting route were investigated through systematic sampling of liquid steel and rolled products. Analysis methods included total oxygen and nitrogen contents, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy.The results indicate that the composition of inclusions was strongly dependent on the types of added alloying agents. During the AOD refining process, after the addition of ferrosilicon alloy and electrolytic manganese, followed by aluminum, the composition of inclusions changed from manganese silicate-rich inclusions to alumina-rich inclusions. After tapping and titanium wire feeding, pure TiN particles and complex inclusions with Al 2 O 3 -MgO-TiO x cores containing TiN were found to be the dominant inclusions when [pct Ti] was 0.307 mass pct in the molten steel. These findings were confirmed by thermodynamic calculations which indicated that there was a driving force for TiN inclusions to be formed in the liquid phase due to the high contents of [Ti] and [N] in the molten steel. From the start of casting through to the rolled bar, there was no further change in the composition of inclusions compared to the titanium addition stage. Stringer-shaped TiN inclusions were observed in the rolled bar. These inclusions were elongated along the rolling direction with lengths varying from 17 to 84 lm and could have a detrimental impact on the corrosion resistance as well as the mechanical properties of the stainless steel products.
The formation and characteristics of non-metallic inclusions in 316L stainless steel produced by the AOD (argon oxygen decarburization)-ladle furnace-continuous casting process were investigated. The morphology and composition of inclusions changed significantly during the refining and casting processes. After de-oxidation with Si/Mn additions, spherical complex inclusions mainly consisting of calcium silicates were observed. The contents of MgO and Al 2 O 3 in these inclusions continuously increased as the steel moved from the AOD through ladle processing to the tundish. As the temperature decreased from the tundish through to solidification, harmful crystals of MgO/Al 2 O 3 spinel were precipitated within the steel melt as well as within the calcium silicate matrix of existing inclusions. The results obtained from thermodynamic calculations carried out using FactSage™ commercial software agreed well with the information derived from evaluation of the industrial samples enabling recommendations to be made for the avoidance of detrimental spinel inclusions.
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