Role of vacuum on cleanliness improvement of steel during electroslag remelting

To clarify the effect of vacuum on cleanliness of steel during electroslag remelting, the interaction between slag and steel under air, Ar and vacuum condition were investigated by laboratory experiments. The results show that the number, size and area fraction of inclusions decreases in the remelted steel. Compared with the steels remelted under air and Ar atmospheres, the inclusion number, size and area fraction of steel remelted under vacuum condition are lower because the steel surface oxidation is inhibited and the reaction of C and O to form CO gas in liquid steel is promoted under vacuum conditions. The removal of inclusions in the remelted steel contributes to the elimination of large carbides. Under vacuum condition, the highest desulphurization rate is acquired because the oxygen content is the lowest and the floating of the CO gas formed by C deoxidization speeds up mass transfer. Reduction of the white speckles resulted by S segregation is attributed to the sharp decrease of the S content. Compared with the steels remelted under air and Ar atmospheres, the steel remelted under vacuum shows the higher cleanliness.