Effect of Grain Size on Oxidation Behavior of P91 Steel in Water Vapor

Isothermal oxidation test was carried out for two P91 steels with different grain sizes in water vapor by using a self-designed tubular device.The oxidation film was studied by means of SEM,XRD and EDS.The results show that oxidation kinetic curves obeyed the parabolic law.P91 steel with coarse grain exhibited more weight gain than that of with fine grain at 650℃ in water vapor for 300 h.A Cr-rich oxide layer formed sooner on fine grain P91 steel at the initial stage (<30 h),the outward diffusion of iron ion was retarded by this layer and so the oxidation rate was decreased.