Effect of Al content on non-metallic inclusions in Fe–23Mn– x Al–0.7C lightweight steels

Abstract

The composition, morphology, number, area, size and average distance of inclusions in Fe–23Mn–xAl–0.7C steels were evaluated through an inclusion automatic analysis system (INCA Feature). According to their composition and morphology, six types of inclusions are classified in the present steels: MnS(Se), AlN, Al₂O₃, AlN–MnS(Se), Al₂O₃–MnS(Se), and other inclusions (i.e. Al₂O₃–AlN and MgO–Al₂O₃). Thermodynamic calculation results show that AlN inclusions are formed in molten steel with Al contents of 3.28 and 6.76 wt-%. Irregularly shaped MnS(Se) inclusions precipitate during the solidification processe. AlN and Al₂O₃ generally serve as sites for the heterogeneous nucleation of MnS(Se). Sometimes, AlN particles can precipitate on the surfaces of Al₂O₃ and MnS(Se) inclusions in the solidification process. As the Al content increases to 6.76 wt-%, a large number of agglomerated AlN and AlN–MnS(Se) inclusions are observed. Agglomerated AlN inclusions normally form in the smelting process due to the combined effects of the cavity bridge force and viscous resistance.