High Temperature Oxidation of a Work Roll Grade High Speed Steel

High speed steels are used for the manufacture of the work rolls used in hot rolling steel mills. An understanding of the degradation phenomena of work rolls is essential, particularly in fields related to the oxidation of the surface, given the importance of the surface quality of the rolled product at the end of the process and its close relation with the changes experienced by the surface of the rolls. The high temperature oxidation behaviour of a work roll grade high speed steel was studied using gravimetric means under isothermal conditions at 550 and 615 degrees C in dry air and in a mixture of dry air and water vapour. At both temperatures, the mass gain of the samples exposed to the mixture of dry air and water vapour was considerably higher than that of the samples exposed to dry air. For all the experimental conditions, oxide growth was better described by the parabolic rate law. The composition of the oxide layer was influenced by the oxidant atmosphere, as the layer in the water vapour containing environment included an iron-chromium spinel (M3O4), magnetite and hematite, whereas the layer in the dry air condition consisted of iron-chromium spinel, hematite and vanadium oxide. The effect of composition of the oxidant atmosphere on the rate of oxidation of the steel and the components of the oxide scale is discussed.