The grain-boundary segregation of phosphorus and carbon in an Fe-P-C alloyduring cooling

Grain-boundary segregation in the Fe-P-C system has been examined using Aug er Electron Spectroscopy on specimens which were cooled slowly to various i ntermediate temperatures after equilibration at 600 degrees C, and then que nched prior to examination. The aim was to monitor the segregation of phosp horus and carbon through temperature ranges which offered the extremes of b oth solutes having long-range lattice mobility to that where only carbon wa s mobile. This approach revealed new complexities in the segregation proces s. It was found that phosphorus continued to segregate during the early sta ges of both furnace and air cooling, i.e. when long-range lattice diffusion remained possible. At intermediate temperatures, when the mobility of phos phorus was limited, an apparently competitive process occurred between the solutes, i.e. phosphorus de-segregated whilst the grain-boundary concentrat ion of carbon increased. At temperatures less than approximately 200 degree s C, carbon segregation continued under furnace cooling but not under air c ooling but in neither case did phosphorus continue to de-segregate. A theor etical framework is developed which can account qualitatively for these seg regation characteristics. (C) 1998 Acta Metallurgica Inc. Published by Else vier Science Ltd. All rights reserved.