INFLUENCE OF PRIOR DEFORMATION ON THE SENSITIZATION OF AISI TYPE 316LN STAINLESS-STEEL

The sensitization behaviour of a nuclear grade AISI 316LN stainless st eel (SS) was studied for various cold-work levels ranging from 0% (mil l-annealed) to 25% reduction in thickness. ASTM standard A262 Practice s A and E were adopted to detect the susceptibility to intergranular c orrosion. The results obtained in these tests were used to construct t ime-temperature-sensitization (TTS) diagrams. Using these data, the cr itical linear cooling rate was calculated, above which there is no ris k of sensitization. In order to predict the sensitization behaviour du ring practical cooling conditions, Continuous-cooling-sensitization (C CS) diagrams were established utilising the TTS diagrams by a mathemat ical method. The influences of prior deformation and nitrogen in the a lloy on the sensitization kinetics are discussed. It was found that ni trogen addition retards the sensitization kinetics and that t(min) (mi nimum time required for sensitization at nose temperature) increases b y two orders of magnitude in Type 316LN SS compared to that of Type 31 6 SS at the different prior deformation levels. Cold-working up to 15% accelerates the onset of carbide precipitation and on further cold wo rking there is not much difference in the kinetics. Desensitization is faster in highly cold-worked material, especially at high temperature s.