Effect of Slag Composition on Inclusion Control in LF-VD Process for Ultra-low Oxygen Alloyed Structural Steel

Inclusion control in LF-VD process for ultra-low oxygen alloyed structural steel is investigated. It is found that after Al-deoxidation during tapping process, with slag of high basicity, high Al2O3 content and low oxidizing property, Al2O3 inclusions, which are the product of Al-deoxidation could transform to MgO-Al2O3 spinel, and later on to CaOMgO-Al2O3 inclusions of lower melting point, which are inclined to be eliminated by floatation, thus total oxygen content would be lowered. On the other hand, residual inclusions in steel are mostly ultra-fine in size, and could be deformed slightly in hot-working process of steel, enhancing fatigue life of steel.