Abstract: The formation mechanism of longitudinal crack of round billet was expounded. The main causes of longitudinal crack of round billet were found out by field investigation and data analysis through anatomical analysis of longitudinal crack shell of round billet at Masteel. The main causes were as follows: harmful element sulfur content in molten steel, poor performance of mold fluxes, off-center and improper inserting depth of submerged entry nozzle, inappropriate temperature and speed of casting, inappropriate radian o and cooling intensity of the mould . According to the actual production situation on the spot,some measures were taken to reduce the longitudinal crack rate of round billet from 0.63 % to 0, the longitudinal crack of round billet was controlled, and the zero longitudinal crack breakout rate was realized.

Key words: continuous casting round billet, longitudinal crack breakout, mold flux, submerged entry nozzle, crystallizer