Heat-to-Heat Variability in the Corrosion Resistance and Microstructure of Low Carbon AISI 316 Nuclear Grade Stainless Steel

This paper considers the heat-to-heat variability in corrosion resistance and microstructure that might be encountered in low carbon AISI 316 nuclear grade stainless steels (SSs). The results will show that although these low carbon steels are rather resistant to sensitization by chromium depletion, they vary significantly in their grain size, Inclusion content, and micro-structural homogeneity. Aging for as long as 1000 h at 550 C did not produce grain boundary precipitation in any of these alloys; aging for 100 h at 650 C produced Laves phase along the grain boundaries of two alloys and chromium-rich M₂₃C₆ carbides in the other. Impurity segregation was low in all three alloys. The two alloys that contained Laves phase along their grain boundaries exhibited very little corrosion in the modified Strauss test. The other heat showed only slightly more corrosion because of very limited carbide precipitation. All of the alloys underwent corrosion in the more oxidizing Huey test. The amount of corrosion in this test increased with increasing aging temperature and time, and the alloy that contained chromium carbides corroded to the greatest extent. In both corrosion tests, compositional banding clearly affected the results.