High cycle fatigue properties of austenitic stainless steel welds at cryogenic temperatures

High cycle fatigue properties of base and weld metals of SUS304L and SUS316L and the effects of welding structure and delta ferrite on the fatigue properties have been investigated at cryogenic temperatures in order to evaluate the long-life reliability of the structural materials used in liquid hydrogen huge tankers or storage ranks and to develop a welding process for those applications. The S-N curves of base and weld metals shifted to higher stress or longer life side with a decrease in test temperature. The ratio of fatigue strength at 10(6) cycles to tensile strength of the weld metals were 0.35 to 0.7 and getting lower than those of base metals with decreasing temperature. Fatigue crack initiation site of SUS304L weld metals initiated almost at blow holes of approximately 200 similar to 700 mu m diameter, and that of SUS316L weld metals initiated at a virtual crack. A virtual crack of SUS316L weld metal was caused by carbides of M23C6, and Al/Mn oxides, which were formed at weld pass interface boundary during welding. The decrease in fatigue strength at 10(6) cycles at cryogenic temperatures was due to very small welding defects and a virtual crack. Although delta ferrite reduces toughness at cryogenic temperatures, the effects of delta ferrite on high cycle fatigue properties are not clear or significant.