GRAIN-BOUNDARY STRUCTURE AND CHROMIUM SEGREGATION IN A 316 STAINLESS-STEEL

Analytical electron microscopy (AEM) has been used to examine the relationship between grain boundary structure and the segregation of chromium in a sensitised AISI 316 stainless steel. Fifty grain boundaries have been analysed. Among the boundaries there was a threefold difference in full width half maximum (FWHM) of the chromium concentration profiles. This variation is interpreted in terms of the different long-range stress fields created by different combinations of structural units in each boundary. From the narrowness of their profiles, it is deduced that the SIGMA = 3, 11, 13a, 13b and 29a boundaries are favoured while the SIGMA = 9 boundary is non-favoured. There was no correlation between FWHM and grain boundary chromium concentration. Additionally, we observe that it is not pre-requisite for the boundary plane to be close to {111} for a chromium carbide to nucleae. There is also no correlation between the boundary normal and either the FWHM of the chromium concentration profile or the grain boundary chromium concentration.