Effect of Intermetallic Compounds Precipitated at Grain-Boundaries on Intergranular Corrosion of Type 316L Stainless Steel in Nitric Acid Solution

Abstract

As observed, Type 316 stainless steel with a low carbon content (Type 316L SS) sensitized at a temperature between 550°C and 700°C and submitted to the 65% nitric acid test, suffers from very severe intergranular corrosion (IGC). However the IGC mechanism of this alloy has not been well explained by the well known chromium depleted zone theory. In this study, the IGC mechanism of Type 316L SS in the 65% nitric acid test is discussed based on the analysis of grain boundary precipitates and the observation of the dissolution behavior of these precipitates. The obtained results are as follows; 1) IGC of sensitized Type 316L SS is not caused by the grain boundary precipitation of the σ phase (FeCr) but by the Laves [(Fe, Cr)₂Mo] and the χ phases (Fe₁₈Cr₆Mo₅). 2) IGC is caused by the dissolution of Laves and χ phases.