The cryogenic low-cycle fatigue performance of 9%Ni steel joint made by flux cored arc welding

Abstract

Low-cycle fatigue (LCF) test was performed at 296 K and 80 K to investigate the effects of cryogenic environment on the LCF performance of 9%Ni steel joints welded by flux cored arc welding (FCAW). The test results indicated that the LCF performance in cryogenic environment was higher than that at room temperature. The gap of fatigue lifetime decreased with the increment of strain amplitude. The LCF performance at room temperature and in cryogenic environment was very close when total strain amplitude was 0.8%. The LCF specimens underwent cyclic hardening and cyclic softening before fracture at room temperature. No obvious cyclic softening was observed during LCF test at cryogenic temperature. The fracture location was at PMZ at room temperature, but at weld center in cryogenic environment. The transformation of brass texture mainly occurred in PMZ at cryogenic temperature after LCF test. The strengthening effects of brass texture in PMZ increased the stress concentration in weld center. The microvoids appeared near precipitates at grain boundaries led to the intergranular propagation of fatigue cracks in weld center. Research results contributed to safe service and fatigue lifetime estimation of LNG containers made by 9% Ni steel in cryogenic environment.