Resistance to sensitization and intergranular corrosion through extreme randomization of grain boundaries

Two grades of austenitic stainless steel, type 304 and 316L, were cold rolled to different reductions by unidirectional and by cross rolling. Subsequent solutionizing of the cold rolled samples produced noticeable textural differences in type 304, but insignificant differences in type 316L. Both the solutionized materials had however the same trend in grain boundary character distribution (GBCD): an increasing fraction of random boundaries with an increasing presolutionizing reduction percentage. The degree of sensitization (DOS) was measured by the double loop electrochemical potentiokinetic reactivation (DL-EPR) test in both the alloys. The susceptibility to intergranular corrosion was assessed by the standard weight loss technique (practice B, A262 ASTM) in type 304 alloy. These increased with increase in random boundary concentration, but then dropped significantly beyond a 'critical' concentration-a pattern observed in both the grades. Such a pattern may be explained from a balance between nucleation rate of Cr-carbides and grain boundary Cr-flux, though postulating an exact model is premature at this stage. The present study, however, demonstrates a clear possibility of remarkable improvement in DOS and IGC through extreme grain boundary randomization. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.