Time and temperature dependence of surface segregation in commercial steel, studied by Auger electron spectroscopy

Abstract

In situ Auger electron spectroscopy measurements of the time and temperature dependence of phosphorus and tin segregation in a 5Ni-Cr-Mo-V (wt-%) rotor steel are presented and analysed in terms of the theory presented earlier by Lea and Seah. The complete C curve, constant segregation contours on the time–temperature diagram are analysed in terms of the diffusion, segregation, and evaporation parameters involved. It is shown that an inversion of the measured C curve occurs if the magnitude of the activation energy for evaporation is lower than that for diffusion. Phosphorus in iron is an example of this case, whereas for tin the reverse is true. Additionally, it is shown that the kinetics for surface segregation may be much faster than for grain boundary segregation if the latter provides a source of material to feed the former.