Abstract: The behavior of non-metallic inclusions in SPA-H steel produced by BOF→LF→CSP production route of WISCO during LF refining was investigated. Molten steel samples, slag samples were taken from two industrial heats systematically, and the compositions, size distribution and number of inclusions were analyzed using Aspex explorer. The results showed that, the distributions of inclusion compositions in CaO-Al2O3-MgO ternary phase diagram were like straight lines when the interface reactions equilibrium of slag/metal and refractories/metal were attained. Comparing the inclusions transformation of the two industrial heats, by controlling the composition of slag and refining time, a part of the Al2O3 inclusions could be transformed into lowmelting CaO-Al2O3-MgO inclusions，which were eliminated readily during argon gas light bubbling.

Key words: SPA-H steel, argon gas light bubbling, LF, inclusion