Abstract
In order to better understand the high temperature low cycle fatigue behavior of Alloy 617 weldments, this work focuses on the comparative study of the low cycle fatigue behavior of Alloy 617 base metal and weldments, made from automated gas tungsten arc welding with Alloy 617 filler wire. Low cycle fatigue tests were carried out by a series of fully reversed strain-controls (strain ratio, Rε = −1), i.e., 0.6%, 0.9%, 1.2% and 1.5% at a high temperature of 900 °C and a constant strain rate of 10−3/s. At all the testing conditions, the weldment specimens showed lower fatigue lives compared with the base metal due to their microstructural heterogeneities. The effect of very high temperature deformation behavior regarding cyclic stress response varied as a complex function of material property and total strain range. The Alloy 617 base weldments showed some cyclic hardening as a function of total strain range. However, the Alloy 617 base metal showed some cyclic softening induced by solute drag creep during low cycle fatigue. An analysis of the low cycle fatigue data based on a Coffin-Manson relationship was carried out. Fracture surface characterizations were performed on selected fractured specimens using standard metallographic techniques.
Highlights
The Generation Nuclear Plant (NGNP) being developed in the Republic of Korea is theVery High Temperature gas-cooled Reactor (VHTR)
The behavior of Alloy 617 weldments is not yet fully understood, and there remains a need for further experiments; a lot of data needs to be supplemented at very high temperatures due to the variability in the fatigue response of the element parts of the weldments to confirm the suitability of a baseline draft Code Case [6]
The low cycle fatigue (LCF) tests of Alloy 617 base metal and weldments were conducted at a high temperature of LCF tests base metal and weldments were a high temperature of
Summary
The Generation Nuclear Plant (NGNP) being developed in the Republic of Korea is the. The low cycle fatigue (LCF) loadings represent a predominant failure mode from the temperature gradient induced thermal strain during operation as well as in the startups and shutdowns and in power transients or with temperature change of the flowing coolant having a low loading rate [5,6,7,8] Because of these shortcomings, significant consideration of LCF behavior is needed in the design and life assessment of such components working in high temperature conditions. The behavior of Alloy 617 weldments is not yet fully understood, and there remains a need for further experiments; a lot of data needs to be supplemented at very high temperatures due to the variability in the fatigue response of the element parts of the weldments (i.e., weld, HAZ, and base metal) to confirm the suitability of a baseline draft Code Case [6]. The LCF fracture surface microstructures were characterized on selected fractured specimens, and the microstructural changes under various conditions are reported quantitatively using standard metallographic techniques
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