Abstract

An effective procedure and parameter window was developed for underwater friction stir welding (UWFSW) 304L stainless steel with a PCBN tool. UWFSW produced statistically significant: increases in yield strengths, decreases in percent elongation. The ultimate tensile strength was found to be significantly higher at certain parameters. Although sigma was identified in the UWFSWs, a significant reduction of sigma was found in UWFSWs compared to ambient FSWs. The degree of sensitization in UWFSWs was evaluated using double loop EPR testing and oxalic acid electro-etched metallography. Results were compared to base metal, ambient FSW, and arc welds. Upper and lower sensitization localization bands were identified in the UWFSWs. Although higher sensitization levels were present in UWFSWs compared to the arc weld, ambient FSW, and heat treated base metals, the UWFSWs were found less susceptible to corrosion than arc welds due to the subsurface location of the sensitization bands. A SCC analysis of UWFSWs relative to base metal and arc weldments was performed. U-bends were exposed to two 3.5% NaCl cyclic immersion experiments at 21 °C and 63 °C for 1000 hours each. A tertiary test was conducted in a 25% NaCl boiling solution. The UWFSW u-bends were no more susceptible to SCC than base metal in the cyclic immersion tests. In the boiling NaCl test, the SCC of the UWFSWs showed significant improvement over the SCC of arc welds. Arc u-bends cracked entirely within the weld bead and HAZ, while SCC in the UWFSWs showed no cracking localization.

Degree

MS

College and Department

Ira A. Fulton College of Engineering and Technology; Mechanical Engineering

Rights

http://lib.byu.edu/about/copyright/

Date Submitted

2005-06-30

Document Type

Thesis

Handle

http://hdl.lib.byu.edu/1877/etd872

Keywords

friction stir weld, FSW, underwater friction stir weld, UWFSW, stainless steel, stir zone, 304L, austenite, austenitic, procedure, process window, welding parameters, corrosion, intergranular stress corrosion cracking, SCC, u-bend, sensitization, PCBN, double loop, EPR, current ratio, potentiostat, electrochemical reactivation, sampling area, quantification, tensile strength, ductility, elongation, statistical significance, microstructure, optical microscopy, oxidation, surface finish, base metal, sigma, Murakami, oxalic acid electro-etch, arc weld comparison, cyclic immersion test, boiling NaCl test, subsurface location, residual stress, improvement, superiority, ASTM standard, HAZ, heat affected zone

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