Description
Madhumanti Bhattacharyya1, Arnab Kundu1, Indrajit Charit1, Krishnan S Raja1, Jens Darsell2, Saumyadeep Jana2; 1University of Idaho, 2Pacific Northwest National Laboratory
Recently, applicability of friction stir welding (FSW) as a potential crack repair technique in stainless steel dry storage canisters has garnered much interest. The present work aims to explore the microstructure-mechanical property correlations in FSWed 304L stainless steel joints. FSW was carried out at two temperatures (725 and 825 °C) in order to repair simulated cracks created by electrical discharge machining in hot rolled-annealed stainless steel plates. A robust algorithm was used to maintain constant temperature during welding through tool RPM variation. Optical microscopy revealed the overall microstructural gradient across the weld. Microstructural examination using transmission electron microscopy revealed ultrafine grains (UFG) formed at the stir zone due to dynamic recrystallization during FSW. The UFG microstructure results in a significant increase in hardness within the stir zone compared to the base metal, as evaluated from Vickers microhardness testing. Further, residual stress distribution across the welds was evaluated using X-ray diffraction.