Evolution Mechanism of Inclusions in Al-killed, Ti-bearing 11Cr Stainless Steel with Ca Treatment

The evolution mechanism of non-metallic inclusions in Al-killed, Ti-bearing 11Cr stainless steel with Ca treatment was investigated by industrial trials and thermodynamic calculation. The morphology, composition, and size distribution of inclusions in steel specimens were analyzed by scanning electron microscopy and energy dispersive spectroscopy. The alloy addition and calcium contents in steel significantly influenced the characteristics of inclusions according to the present study. After the addition of AI, there were mainly alumina-rich inclusions in steel. With the titanium addition after calcium treatment, three types of inclusions were formed: irregular MgO-Al2O3-TiOx inclusion, spherical CaO-MgO-Al2O3-TiOx inclusion, and irregular dual phase Ti-containing inclusion. At the end of LF refining process, solid calcium titanates inclusions were formed due to the high calcium content in steel. The evolution of these inclusions was consistent with thermodynamic calculation, which indicated that the compositions of inclusions in steel specimens after the addition of titanium were mostly located in Al2O3-TiOx stable phase. Based on the characteristics of inclusions in steel and thermodynamic calculation, calcium could reduce the stability of spinel and strongly modify solid alumina and Al2O3-TiOx inclusions to form liquid oxides or solid calcium titanates. At the same time, the effects of calcium content in Al-killed, Ti-bearing 11Cr molten steel on the formation of inclusions were discussed through the coupling of thermodynamics calculation and experimental results.