Abstract
In the present work, low-cycle fatigue (LCF) test and crack tip opening displacement (CTOD) test were performed for 9% Ni steel flux cored arc welding (FCAW) joint at room temperature (296 K) and cryogenic temperature (80 K). At cryogenic temperature, the strain amplitude had a far greater impact on fatigue life of 9%Ni steel welded joint and it decreased dramatically lead to a significant increase in fatigue life. It was found that most fracture initiation of joints located in fusion area at room temperature, while it occurred in weld seam at low temperature. The fracture toughness of weld seam was higher than that of fusion zone no matter the testing temperature. The effect of precipitated phase was the true reason. The fatigue cracks propagated in transgranular mode at room temperature, ultimately, and intergranular mode at low temperature in both LCF specimens and CTOD specimens.
Highlights
IntroductionPerformance of cryogenic material has gained more attention than before
In recent years, performance of cryogenic material has gained more attention than before
It was inferred that the weakest position in the joint was the fusion area while weld metal at cryogenic temperature
Summary
Performance of cryogenic material has gained more attention than before. Studies in Ni-based alloys, while plentiful, are predominantly focused on fatigue and fracture property at room and high temperature [3,4,5,6,7]. Some researches were carried out on the effects of precipitates in the weld metal of nickel based alloy. [8] studied the deposited metal of Ni–Cr–Mo–Nb alloy in TIG cold wire welding They identified that the precipitated phases were Laves phase and complex carbide particles. [11] found that the carbide located at grain boundary, increased noticeably the incidence of cracks From this point of view, influences of precipitated phases deserve more attention on the study of fatigue property. The fatigue property and fracture toughness of welded joints of 9%Ni steel by FCAW under cryogenic environment were studied. The effect of cryogenic environment on the LCF and fracture toughness were invested in the paper
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