Tribological characterization of a high speed steel roll material at elevated temperature
High speed steel rolls have prevailed in hot rolling mills due to their excellent wear resistance, high hardness and oxidation resistance. The thermal cycling ol the rolls causes the surface oxidation, which significantly changes the contact and tribological behaviour between work roll and hot rolled material. In the paper, the formation and growth ol oxide scale ol a high speed steel roll material were in- situ investigated by a High Temperature Microscope. In- situ observations indicate that the oxide scales of the high speed steel first nucleate at the carbides/matrix interfaces, and then rapidly spread to cover the carbides and followed by continuous growth over the whole surface. The selective oxidation of high speed steel has a significant impact on the roll surface morphology. Water vapour in oxidizing atmosphere increases the oxidation rates of carbides and the matrix. The two-high mini mill coupled with the Gleeble 3500 thermo- mechanical simulator was used to measure the tribological contact behaviour between high speed steel work roll and mild steel strip sample under the stalled hot rolling conditions. The experimental results show that fresh ground and pre- oxidized roll surfaces exhibit quite different ways of tribological behaviours. The rolling force of pre-oxidized rolls is always higher than that of fresh ground rolls whatever in different reductions, or temperatures. The surface conditions of work roll have a decisive effect on the strip roughness.