Prevention of the Formation of Longitudinal Facial Cracks on Continuously Cast Slabs by Improving Mold Powder and Mold Oscillation

Abstract

Improving mold powders and optimizing mold oscillation have been made to decrease longitudinal facial cracks occurring on continuously cast slabs, aiming at direct reheating of slabs without surface conditioning.
Controlling the melting characteristics of mold powders to avoid fluctuation in the thickness of molten slag of appropriate viscosity on the meniscus of steel melt has proved to be much effective. Optimized melting characteristics have been determined for casting speeds of up to 1.8 m/min. Also, oscillation of mold has been so adjusted as to give suitable flow of slag film in mold and solidified steel shell boundary by making negative stripping time t_N to fall in the range between 0.2 and 0.3 s.
These countermeasures followed by decreased water cooling intensity just below the mold have enabled us to increase the fraction of direct reheatable slabs free from surface defects up to 200000 ton/mo., about 40%. of crude steel production.