Metallurgical effects on the corrosion resistance of a low temperature sensitized welded aisi type 304 stainless steel

The low temperature sensitization (LTS) of a welded AISI Type 304 stainless steel was studied. Both the microstructural changes and the degree of sensitization (DOS) were examined in samples aged for times up to 1500 days at 350-500°C. The DOS was observed to increase at temperatures below the normal sensitization range and the increase could be attributed to the growth of chromium-rich grain boundary carbides. The (T, r) dependence for LTS was determined on the basis of intergranular corrosion (I.G.C.) tests. These results indicated a departure from a linear Arrhenius temperature dependence, suggesting a change in the growth mechanism of M₂₃C₆ grain boundary carbides at low temperatures. The possible reasons for this change are discussed in terms of the observed microstructures.