Influence du soufre sur la diffusion intergranulaire dans la solution solide austenitique Fe-Cr-Ni (18% Cr, 10% Ni)

Abstract

By studying the grain boundaries diffusivities of Fe59, Ni63 and Cr51 firstly into the austenitic solid solution with 18wt%Cr and 10wt%Ni of very high purity (impurity level less than 5·10 −4wt% and secondly into the same material doped with 70·10 −4wt% of sulphur, have shown that: if there is a sulphur segregation at high temperature (θ > 850°C) it is very moderate, and the more likely mechanism is the substitution of iron and nickel atoms by sulphur atoms, chromium level being approximatively unchanged in comparison with the bulk one. Results obtained show that sulphur increases the true diffusion kinetics of iron and nickel while it lowers the chromium one; at low temperature (θ < 850°C) it seems that the segregation leads to the precipitation of 3D compounds formed with chromium and sulphur, into the grain boundaries. True diffusion kinetics of iron and chromium are faster at precipitate-matrix interface boundaries than along the boundary diluted with sulphur, the nickel one being unaffected by precipitates.