Cracking Failure of Hardfacing Layer of Repaired Backup-Roller in Rolling Mill

A worn backup-roller in rolling mill was repaired by hardfacing technology. The routine flaw detection after machining revealed that randomly distributed circumferential short cracks occurred on the surface of repaired roller. Sectional observation throughout hardfacing region showed that intensively distributed transverse short cracks were also present inside the outer layer of hardfacing region. Detailed metallographic analysis and fractographic investigation indicate that the transverse short cracks are crystallization cracks, caused by hot-cracking. General excessive element of P in the outer layer and the segregation of impurity elements P, S within the interdendritic space and at the grain boundary are metallurgical factors responsible for hot-cracking. Occurrence of the bending load on the roller, resulting from the great self-weight of roller, is mechanical factor leading to forming transverse crystallization cracks.