Evaluations of creep rupture properties of dissimilar weld joints of 2.25Cr-1Mo, 9Cr-1Mo, and 9Cr-1MoVNb steels with Alloy 800 at 823 K were carried out. The joints were fabricated by a fusion welding process employing an INCONEL 182 weld electrode. All the joints displayed lower creep rupture strength than their respective ferritic steel base metals, and the strength reduction was greater in the 2.25Cr-1Mo steel joint and less in the 9Cr-1Mo steel joint. Failure location in the joints was found to shift from the ferritic steel base metal to the intercritical region of the heat-affected zone (HAZ) of the ferritic steel (type IV cracking) with the decrease in stress. At still lower stresses, the failure in the joints occurred at the ferritic/austenitic weld interface. The stress-life variation of the joints showed two-slope behavior and the slope change coincided with the occurrence of ferritic/austenitic weld interface cracking. Preferential creep cavitation in the soft intercritical HAZ induced type IV failure, whereas creep cavitation at the interfacial particles induced ferritic/austenitic weld interface cracking. Micromechanisms of the type IV failure and the ferritic/austenitic interface cracking in the dissimilar weld joint of the ferritic steels and relative cracking susceptibility of the joints are discussed based on microstructural investigation, mechanical testing, and finite element analysis (FEA) of the stress state across the joint.
Low cycle fatigue (LCF) tests were performed on Inconel ® Alloy 783 at a strain rate of 3×10 -3 s -1 and a strain amplitude of ±0.6%. The tests were conducted in the temperature range, 573 to 923 K besides room temperature. Further, influence of strain amplitude on LCF behaviour was studied at a constant temperature of 923 K using strain amplitudes in the range, ±0.3 to ±0.8%. Creep-fatigue interaction tests were conducted at a strain amplitude of ±0.4%, at 923 K. The material generally showed a stable stress response followed by a region of continuous softening upto failure. Also, the alloy was seen to exhibit dynamic strain ageing (DSA) in the temperature range, 573 to 723 K as evidenced by the observed peaks in the half-life stress in the above temperature range. Dynamic strain ageing was seen to offset the softening exhibited by the alloy outside the above temperature range. Fractography/EDS analysis of the failed samples showed numerous brittle Nb-rich precipitates that were seen to influence crack propagation. A continuous reduction in the LCF life was noticed with increase in the test temperature. The observed material behaviour has been correlated with the damage mechanisms through microstructural observations.
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