Phase analysis of complex non-metallic inclusions in Al-deoxidized 42CrMo4 steel after contact with MgO–C refractories

Abstract

This study extensively investigated characteristic non-metallic inclusions in oxidized and deoxidized 42CrMo4 steel after contact to MgO–C refractories, proposing possible formation and modification mechanisms of non-metallic inclusions. The structures and compositions of different inclusion species were analyzed, revealing various types: crystalline, amorphous, and complex inclusions containing both crystalline and amorphous phases. The latter always consisted of an amorphous Mn–Si–Al–O matrix containing various crystalline phases such as Al2O3, MnAl2O4 and/or MnTiO3. The formation of amorphous Mn–Si–Al–O inclusions was attributed to steel melt oxidation, while pure crystalline corundum inclusions resulted from both the steel melt oxidation and deoxidation. Alumina inclusions exhibited different shapes, likely because of variations in aluminum and oxygen supersaturation in the steel melt during their formation. Complex inclusions were suggested to form through precipitation on existing inclusions and mutual collision of pre-existing inclusions, facilitated by the non-wetting behavior of solid alumina inclusions in the steel melt.