Influence of ferrite grain orientation on the formation of selective oxidation particles

In the continuous annealing process, steel sheets are annealed at 800°C in an atmosphere of nitrogen and hydrogen (5 vol.%) containing low partial water pressure (20-50 Pa). Under these conditions, the most oxidizable alloying elements in the steel segregate towards the surface where they form oxide particles. The growth of these selective oxide particles was observed to depend on the orientation of the ferrite grains: the oxides’ surface density is larger on the Fe(100) surface than on the Fe(110) surface and the mean equivalent diameter of the oxides is larger on the Fe(110) surface than on the Fe(100) surface. Based on density-functional calculations, elementary processes at the atomic scale were also proposed to explain these differences.