An Experimental and Thermodynamic Study of Non-Metallic Inclusions in High Si Stainless Steels Regarding Clogging During Casting

Abstract

Clogging of high Si-containing stainless steel grades was studied by metallographic examinations of steel samples from clogged and non-clogged heats as well as by thermodynamic modeling using Thermo-Calc and FactSage. Morphology, composition, number and size of inclusions and clusters in the steel samples were determined on a polished surface of the steel samples by using a scanning electron microscope equipped with energy-dispersive X-ray spectrometer. The results showed that the content of Al in ferroalloys added during ladle treatment should be controlled to avoid a formation of spinel MgOAl2O3 inclusions in liquid steel and a resulting clogging during casting. The thermodynamic calculations showed that the Al content in a melt during ladle treatment and casting should not be larger than 0.003% to obtain <1% of MgOAl2O3 inclusions in the liquid steel for a 1.9% silicon content. Moreover, calculations also showed that if the Si content increased from 1.9% (non-clogging heats) to 2.65% (clogging heats), the number of MgOAl2O3 inclusions decreased slightly. Moreover, it was found that an increased amount of FeSi additions for correction of Si content in the melt increase the Al content. As a result, the number of spinels and clusters increases, which is the primary cause for clogging during casting of these steel grades.