Impact of Carbides on Surface Finish and Wear Characteristics of Graphitic Roll Shell Materials for Hot Rolling Applications

Work rolls used in hot rolling of steel suffer severe wear caused by combinations of adhesion, abrasion, rolling contact fatigue, thermal fatigue, and tribo-chemical corrosive attack. Depending on the specific wear mechanisms, the damage of these rolls may comprise material loss, surface and subsurface cracking, as well as degradation of the surface finish. In this contribution, graphite-containing roll shell materials with different fractions and types of carbides were investigated. Wear tests were performed using two customized roll test rigs, which simulate the contact conditions occurring in a hot strip mill between the work roll, the backup roll, and the hot-rolled steel. Wear and damage mechanisms were analyzed using scanning electron microscopy (SEM). A systematic approach was used for correlating the microstructure and wear of the materials. Different types of carbides, mainly MC and M₂C/M₆C, were identified to influence the wear behavior of graphitic shell materials. Increasing the fraction of these carbides decreased the wear rate but increased the surface roughness. Achieving the optimum balance between carbide types, carbide fraction, graphite fraction, and metal matrix hardness has been identified as mandatory for achieving both high wear performance and highest surface quality of roll shells.