Effect of calcium treatment on non-metallic inclusions in an Al-killed Ti-bearing ferrite stainless steel

The modification of inclusions with different calcium content in Al-killed Ti-bearing steels has been studied by laboratory experiments. The initial inclusion was MgO-Al 2 O 3 -TiO x with a MgO · Al 2 O 3 spinel core. For the steel with a low calcium content, only the MgO-Al 2 O 3 -TiO x out layer was modified to a CaO-Al 2 O 3 -TiO x out layer. The spinel core was gradually modified to a CaO-Al 2 O 3 -MgO or CaO-Al 2 O 3 with the more calcium addition. The population density function (PDF) of inclusions showed a lognormal type after the calcium addition, and then shifted to a power-law type with time. It was indicated that the higher calcium content, the faster modification of inclusions reaching the equilibrium. Thermodynamic calculations showed that the composition inclusions were significantly related to the Al, Ti, and Ca contents. In this study, the calcium content in steel at 30 ppm was more conducive to the formation of liquid inclusions.