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Abstract
Segregation of trace and alloying elements to the free surface of a 3Cr-0.5Mo rotor steel at high temperature shows three kinetically distinct regions of surface composition. The first involves the rapid cosegregation of Cr and N. The slower emergence of P to the surface destroys the Cr-N surface interaction, causing evaporation of P and N from the surface and desegregation of Cr. This effect, which forms the second stage, arises from a strong surface interaction between P and N forming volatile phosphorus nitride. In the third stage, which occurs after much longer times, S, Sb, and Sn reach appreciable surface coverages.