Elevated temperature fatigue behaviour of structural materials for advanced ultra supercritical application

Nickel-based alloy 617 with controlled composition (designated as alloy 617M) and ferritic/martensitic 10% Cr steel are candidate materials for the steam rotor forgings in the high and low pressure regions respectively, in the Indian advanced ultra supercritical (AUSC) programme. Present investigation deals with the high cycle fatigue (HCF) behaviour of alloy 617M, 10% Cr steel and the dissimilar metal weld (DMW) joints of alloy 617M and 10% Cr steel over a wide temperature range (300–973 K). Constant life Haigh diagrams corresponding to different cyclic lives were constructed through tests performed using different R-ratios at 973 K.Influence of mean stress was established through Goodman diagrams at 853 K, using different R-ratios. Weld-strength reduction factor was determined based on HCF tests conducted on the DMW joints.