Failure Analysis of Fracture Roller in φ700 mm for a Rolling Mill

The reasons for fracture failure of a rolling mill roller made of H11 steel were analyzed through chemical composition analysis, mechanical property test, microstructure and fracture observation according to its working conditions. Results show that the failure mode of the roller was fatigue fracture resulting from co-effect of bending and twisting. There were several fatigue sources on the fracture close to the surface and the subsurface of the roller. The surface hardness of the roller was lower than standard value because of some elements′ contents beyond standard range. There were many inclusions of oxides and sulfides like Al2O3 and MnS, distributing in the roller material dispersively. These were internal cause of generation of fatigue crack. Under the co-effect of bending and twisting, fatigue cracks initiated from the stress concentration zones of the roller, such as the transition round angle zone under the neck, then propagated along the direction of 45° angle with the roller axis, resulting in the roller fracture failure at last.