Microstructural study and residual stress measurement of a hot rolling work roll material during isothermal oxidation
Compact oxide scale at a high speed steel (HSS) work roll surface during hot rolling process can act as an effective solid lubricant and a protective layer for better product surface quality. In this study, considering practical hot rolling process time, microstructure and surface roughness of three oxide scales on a HSS work roll have been systematically characterized with a help of scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). It has been found that growth of the oxide scale follows a parabolic rate law and the dominant oxide phase is hematite. In addition, surface roughness increases dramatically when the oxidation time is less than 30 min and then changes slightly, when the HSS specimens were isothermally oxidized at 600 °C in a dry air. Residual stress evolutions with oxidation time have also been examined in details using X-ray diffraction (XRD) method. Measurement of microhardness at the HSS specimen surface revealed that development of defects and decrease of compressive residual stress in the oxide layer lead to a slight decrease in the microhardness.