High cycle fatigue tests at cryogenic temperatures were performed for titanium alloys and austenitic steels. The S-N curves shifted to higher stress or longer life side with a decrease in test temperature with some exceptions in forged Ti-6Al-4V alloys. There was little change in fatigue strength between 77K and 4K for the forged Ti-6Al-4V alloys. Fatigue strength at 106 cycles increased in proportion to a gain in strength by temperature decrease. However, a ratio of the farigue strength to tensile or yield strength depended on material and its processing. From the viewpoint of combination of yield strength and fatigue strength, austenitic steels had a higher fatigue strength than titanium alloys at a given yield strength. Among the titanium alloys, the rolled ones exceeded the forged ones.
