1998 Volume 84 Issue 12 Pages 888-895
High cycle fatigue properties of base and weld metals of SUS304L and SUS316L and the effects of welding structure and δ 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 tanks 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 106 cycles to tensile strength of the weld metals were 0.35 to 0.7 and getting lower than those of base metals with decreasing tem-perature. Fatigue crack initiation site of SUS304L weld metals initiated almost at blow holes of approximately 200700μm 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 AI/Mn oxides, which were formed at weld pass interface boundary during welding. The decrease in fatigue strength at 106cycles at cryogenic temperatures was due to very small welding defects and a virtual crack. Although δ ferrite reduces toughness at cryogenic temperatures, the effects of δ ferrite on high cycle fatigue properties are not clear or significant.
