Formation of break-out induced by longitudinal crack of billet

Abstract

Due to the characteristics of large shrinkage, peritectic steel is sensitive to longitudinal crack defects. Through the analysis of the breakout shell of a domestic factory, the mechanism of longitudinal crack breakout of peritectic steel is revealed. The following conclusions are obtained: the carbon content of the steel is 0.077%, which is in the peritectic range, but Mn / S = 128, and the ratio of manganese and sulfur is relatively high. Although P + S = 0.0263%, the longitudinal crack defect still occurs when the harmful elements are very low. When breakout occurs, the superheat is 35 °C, the drawing speed is 2.5m/min, which is one of the main causes of longitudinal crack. The longitudinal crack occurs about 200-600mm away from the mold bottom and on the center of the side. After the original shell is formed, intermittent unevenness occurs. This unevenness can sometimes be repaired, but sometimes can’t. Therefore, the longitudinal crack and break-out are easy to occur after the thinner blank shell leaves the mold.