Investigation and minimization of slag spot surface defects in continuous casting of high carbon steel billets through statistical evaluation

Abstract

Slag spot surface defects often appear during continuous casting of high carbon steel billets due to the solidification characteristics of molten steel in the mold. To target the problem of surface slag spot defects that occur frequently during the continuous casting of high-carbon steel strands, we analyzed the influence of molten steel superheat, accumulated service time and the water inlet temperature of the mold, the size of the submerged entry nozzle and the physical and chemical properties of the mold powder on the slag spot defects. The production practice shows that by adjusting the superheat of molten steel to 30–35 °C, the water inlet temperature of the mold is stable at 33–35 °C. To adjust the internal and external diameter of the immersion nozzle to 30–70 mm, the viscosity and melting temperature of the mold powder were adjusted from 0.45–0.55 Pa·s, 1100–1140 °C to 0.15–0.25 Pa·s, 1020–1060 °C. The final billet surface quality was improved significantly, the billet surface was smooth, the oscillation marks were relatively smooth and regular and the slag trench ratio was reduced from the original maximum of 40–50% to less than 1%.