Effects of δ-ferrite and welding structure on high-cycle fatigue properties of austenitic stainless steels weld metals

We studied the effects of delta-ferrite and welding structure on high-cycle fatigue properties for austenitic stainless steel weld metals at cryogenic temperatures. SUS304L and SUS316L weld metals contained 0% delta-ferrite (0% material) and 10% delta-ferrite (10% material) were prepared. High-cycle fatigue tests were carried out at 293, 77 and 4 K. The S-N curves of those weld metals shifted towards higher stress levels, i.e., the longer life side, with decreasing test temperature. The ratios of 10(6)-cycles fatigue strength (FS) to tensile strength (TS) of 0% material decreased from 0.8 to 0.45 and those of 10% material decreased between 0.35 to 0.65 with decreasing test temperature. Fatigue crack initiation sites of SUS304L 10% material were almost at blowholes, and those of SUS316L 10% material were at weld pass interface boundaries. On the other hand, those of 0% materials were considered to be due to the interface of the solidification structure. Although 6 ferrite reduces toughness at cryogenic temperatures in austenitic stainless steel weld metals, the effects of delta-ferrite on high-cycle fatigue properties are not significant.