Characterization of the cyclic softening and remaining creep behaviour of P92 steel weldment

Different micro-regions of weldment are expected to present various cyclic softening behaviours during creep-fatigue interaction (CFI), which has a significant influence on the remaining mechanical properties. The present work aims to investigate the cyclic softening and remaining creep behaviour of different micro-regions of P92 steel weldment using electron backscattered diffraction (EBSD) and nanoindentation technology. CFI tests were performed and interrupted at various pre-set fatigue cycles at elevated temperature of 650 degrees C and hold time of 180 s, and thereafter EBSD analyses, nanoindentation tests and high-temperature creep tests were conducted on these interrupted specimens. Experimental results reveal that the microstructure of the parent metal and fine austenite grain heat-affected zone, which is adjacent to the intercritical heat affected zone, are sensitive to CFI loading. Notably, the microstructural evolution in intercritical heat affected zone almost reaches saturated after fatigue cycles of 20%Nf. Nanoindentation results uncover that the intercritical heat affected zone exhibits the lowest elastic modulus and micro hardness, and with increasing the number of fatigue cycles, the weakest region changes. Accordingly, creep fracture location transits and creep life was degraded. Finally, a fatigue damage parameter based on the microhardness was developed to capture the effects of CFI on remaining creep life. (c) 2021 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

This study investigated the cyclic softening and remaining creep behavior of different micro-regions of P92 steel weldment using EBSD and nanoindentation. The experimental results showed that the intercritical heat-affected zone was most sensitive to CFI loading, with changes in microstructure and decreased remaining creep life as the number of fatigue cycles increased.