Influence of chemical composition, prior deformation and prolonged thermal aging on the sensitization characteristics of austenitic stainless steels

Sensitization behaviour of austenitic stainless steels are greatly influenced by several metallurgical factors such as chemical composition, degree of prior deformation, grain size, aging temperature–time. The need for generation of data on sensitization kinetics for specific composition of stainless steels to take care of the heat to heat variation for the fabrication of critical components is often questioned. An attempt was made in this investigation to understand this aspect by establishing time–temperature–sensitization diagrams, continuous-cooling–sensitization diagrams and critical cooling rate for three sets of AISI 316 stainless steel in which as the wt% of carbon decreases, that of nitrogen increases so as to encompass the normal span of concentration range usually encountered in different heats. A systematic trend is observed in these experimentally determined sensitization data of these typical stainless steels. This would eliminate the need for the independent generation of sensitization data for stainless steel of specified composition which is within the range investigated here. The database reported for these alloys will also help to recommend the limits of critical cooling rate to avoid sensitization during fabrication.