FATIGUE PROPERTIES OF WELD JOINTS OF STAINLESS STEELS AND ALUMINUM ALLOY AT CRYOGENIC TEMPERATURES

摘要

High cycle and low 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. High cycle fatigue properties of A5083 have been also obtained. The S-N curves of those base and weld metals shifted to higher stress or longer life with a decrease of the test temperature. In high cycle fatigue, the ratio of fatigue strength at 10~6 cycles to tensile strength of the weld metals was 0.35 to 0.7 and getting lower than those of base metals with a decrease of the test temperature in the stainless steels, while the ratio was 0.6 to 0.7 in aluminum alloy. Fatigue crack initiation sites of SUS304L weld metals were almost at blow holes in diameter of 200 to 700 μm, and those of SUS316L weld metals were at weld pass interface boundaries. In low cycle fatigue, the fatigue life of weld metals was a little bit lower than that of base metal. Although δ-ferrite reduces toughness at cryogenic temperatures, the effects of δ-ferrite on high cycle and low cycle fatigue properties are not so significant.