Studies on metallurgical and impact toughness behavior of variably sensitized weld metal and heat affected zone of AISI 304L welds

Abstract

Influence of sensitization on the metallurgical and impact toughness behavior of different gas tungsten arc AISI 304L welds has been investigated. Each weld has been characterized individually to understand the role of welding conditions on the carbide precipitation behavior which influences its impact toughness performance. Weld metal subjected to sensitization conditions leads to carbide formation that occurs inter-dendritically along the δ–γ interface. Low heat input weld metal possessing lathy ferrite morphology shows relatively a low degree of sensitization (DOS) as compared to the high heat input weld metal possessing vermicular ferrite morphology. Grain coarsening in the heat affected zone (HAZ) of these welds is found to influence the DOS significantly. As welding heat input increases, HAZ grain coarsening also increases, which results into higher DOS. An increase in the post-weld thermal aging time results into higher DOS, which significantly degrades the impact toughness of the weld metal as well as the HAZ of these joints. Charpy V-notch (CVN) testing results under cryogenic testing conditions of (−196°C) show that carbide formation causes a severe degradation of the impact toughness of these welds as examined through their scanning electron fractographs, which show the formation of deep and wide intergranular cracks.