Benefits of thread rolling process to the stress corrosion cracking and fatigue resistance of high strength fasteners

The stress corrosion cracking (SCC) behavior of thread rolled in contrast to cut (machined) Alloy X-750 and Alloy 625 fasteners in a simulated high temperature primary water environment has been evaluated. SCC testing at 360 degrees C and 338 degrees C included 157 small and 40 large 60 degrees. Vee thread studs. Most of the test studs had rolled threads (128 in number) while the remainder (69 in number) had cut threads to provide a baseline for a comparison of SCC initiation resistance. Thread rolled fasteners exhibited improved resistance relative to cut fasteners of the same material condition in terms of both SCC initiation life and applied stress. Tests of fatigue resistance in air at room temperature and both air and primary water at 315 degrees C were conducted on the smaller studs with both cut and rolled threads. Results have shown rolled threads can have significantly improved fatigue lives over those of cut threads in both air and primary water