The solidification and in-service transformation behaviour of type 316 and 347 welds fabricated with type 321 plate

Characterization of the microstructure of AISI type 316 (containing molybdenum) and 347 (containing niobium) stainless welds fabricated with type 321 plate (containing titanium) material has been performed, to assess the effects of using a non-matching filler metal to weld this type of austenitic plate. Such an assessment is essential if the long-term properties of these types of weldment are to be predicted confidently. The solidification mode was generally in close agreement with previously published data, although dilution of the filler material with plate resulted in one exception to the anticipated result. Precipitation was characterized in the as-received (type 347 weld only), post-weld heat-treated and service-aged material, and compared with the predictions of thermodynamic data where these are available. Agreement with such predictions was generally good, although kinetic constraints and the formation of a previously unreported Laves-type (Ti, Cr)₂Nb phase meant that the precipitation sequence was complex.