Characteristic and evolution of inclusions in Al-Killed titanium alloyed steel during air contact process

Abstract

Re-oxidation inclusions in steel are extremely detrimental to the quality of final products due to their complex compositions and large sizes. The detailed knowledge of the re-oxidation process and the evolution of re-oxidation inclusions are preconditions for the removing of inclusions and controlling of steel cleanness. This paper simulates the re-oxidation behavior and tracks the evolution of re-oxidation inclusions in Al-killed titanium alloyed steel by controlling the contact between molten steel and air atmosphere. The experimental results show that the elements aluminum (Al), titanium (Ti), and manganese (Mn) are almost oxidized simultaneously after the exposure of molten steel to air. Large spherical Al-Ti-Mn-Fe-O oxides lump Al2 O3 , and spherical Mn-Fe-O inclusions appear successively after re-oxidation happens in Al-killed titanium alloyed molten steel. Inclusions in re-oxidation are greatly different from the ones in start material, which include clustered Al2 O3 , granular Al2 O3 or TiN-type inclusions. The mechanisms of agglomeration and growth of inclusions are inferred from the grooves and voids on the surfaces of inclusions. Rod-like inclusions are formed when inclusions collide with each other end-to-end. The characteristics of re-oxidation inclusions in plant samples differ from those in laboratory samples because a series of reactions between inclusions and the elements Al and Ti in molten steel happen continuously.