Effect of the batch annealing atmosphere on the oxide scale of hot-rolled AISI 430 stainless steel

Abstract The main purpose of this experiment is to study the effect of batch annealing atmospheres on oxide scales by annealing in air, hydrogen and nitrogen at 1123 K for 72, 90 and 108 ks. Grazing incidence x-ray diffraction (GIXRD) and energy dispersive X-ray (EDX) were used to characterize oxide scales after batch annealing process. The morphology and oxide scale of the studied specimens were investigated by scanning electron microscopy (SEM) and optical microscope. Result obtained by GIXRD showed Fe3O4 and spinel FeCr2O4 oxide scales on the as-received hot-rolled specimens. After batch annealing in air, Fe2O3 and (Fe,Cr)2O3 oxide scales were found. Whereas after batch annealing in hydrogen, Fe3O4 and spinel FeCr2O4 oxide scales were found. In addition, after batch annealing in nitrogen, Fe3O4, (Fe,Cr)2O3 and spinel FeCr2O4 oxide scales were seen. Oxide scales after batch annealing in air are thicker than the scales after batch annealing in hydrogen, however thinner than those scales after batch annealing in nitrogen. The oxide scales thickness after batch annealing in hydrogen is quite equivalent to that found in the as-received hot-rolled oxide scales. Cracks were observed perpendicular to the rolling direction. Weight change after batch annealing in air is higher than that after batch annealing in nitrogen and hydrogen, respectively.