Abstract: The horizontal roll of a roughing mill with material of spheroidal graphite cast steel cracked in radial direction after a short time in service. The causes of cracking of the horizontal roll were analyzed by macroscopic inspection, chemical composition analysis, hardness test and metallographic examination. The results show that the poor microstructure was the main reason for cracking of the horizontal roll. High temperature diffusion annealing was not carried out in the production process of the horizontal roll, which resulted in serious segregation and dendritic microstructure of the horizontal roll. The carbides in the dendrite gap were coarse and large in number, and the carbides in dendrite arm were distributed in intermittent reticular form. At the same time, the process control of the molten steel graphitization was poor during the casting process, which resulted in less graphites and poor spheroidization effect.