Inclusion Modification by Al Deoxidation and Ca Treatment in Ti Containing 18%Cr Stainless Steel Melts

摘要

Titanium is added to ferritic stainless steels in the range of 0.2-0.3 wt% to improve corrosion resistance and mechanical properties. However, titanium is very reactive with oxygen in liquid steel, and it can cause an unstable Ti yield. Therefore, titanium is generally added after the aluminum deoxidation process in the ladle. However, the inclusions formed by Al-Ti deoxidation can cause nozzle clogging and various defects in final products. Calcium injection can be carried out to resolve these problems. In this study, two different deoxidation patterns of Al->Ti and Al->Ti->Ca additions were carried out in Fe-18%Cr ferritic stainless steel melt at 1873 K. The melt composition and the inclusion morphology changes during the deoxidation process were investigated. With AI->Ti addition, the Al_2O_3 inclusions changed to dual phase AI_2O_3-TiO_x inclusions with time by the reaction with Ti in the melt. The morphology of the inclusions in the melt finally changed to a polygonal type indicating that the inclusions were solid phase. The size and number of inclusions in the melt did not change with time after Ti addition. With of Al->Ti->Ca addition, Ca reacted with AI_2O_3-TiO_x inclusions to form liquid CaO-Al_2O_3 inclusions embedded with solid CaTiO_3 particles. The morphology of the inclusions in the melt were observed to be spherical and polygonal. The size of inclusions in the melt increased and the number of inclusions decreased by the coalescence of liquid inclusions.