Many of the outer surface defects of the seamless tube in Ti containing stainless steel were caused by inclusions containing TiN. To prevent these defects, improvements in AOD operations were made. To raise initial carbon contents and initial molten steel temperature, Nitrogen contents has been reduced by about 50 ppm. This has resulted in the change of Inclusion formation from the cohesion of deoxidation products and TiN to the dispersion of them. Precipitation area of TiN was changed from runner brick to the inside of ingot, it decreased cohesion of inclusions and improved cleanliness of steels.
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