LAUSR

The oxidation characteristics of a roll-grade high-speed steel with different tempering heat treatments were studied under thermal cycling conditions at 650 °C in laboratory dry air. The oxidation kinetics of the steel could be described by the parabolic rate law and were a function the tempering temperature. Characterization of the oxide scales was conducted by X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. It was found that the chemical composition of the oxide scales depended on the tempering temperature and favoured the formation of Fe3O4, Fe2O3, (Fe,Cr)3O4 and (Fe,Cr)2O3. Thermal cycling of the steel promoted the fracture and spallation of the oxide scales formed, causing increments in the oxidation rates. The steel also experienced a progressive reduction in its hardness with the number of thermal cycles applied, which could be also related to the thermal process. The results of this investigation are explained in terms of the microstructural evolution of the alloy due to variations in the tempering temperature.