PNNL

Abstract

Friction stir welding and processing (FSW&P) is considered as a new fabrication method for canisters and repair of existing dry cask storage system canisters (generally made of austenitic stainless steel). Low heat input compared to fusion joining processes and grain refinement associated with low-temperature FSW&P result in material with improved mechanical properties and equivalent generalized corrosion performance relative to base metal. But FSW&P of austenitic stainless steel requires significant tool forge axial force to produce a weld (or run). Exploratory runs show that forge axial force can be dramatically reduced ~50% relative to forces reported in literature. The correlation between axial force and resultant plunge depth was also investigated. Other than that, detailed microstructural characterization was conducted to display the microstructural variation within the nugget zone.