Strain ageing embrittlement behaviour of X80 self-shielded flux-cored girth weld metal

Strain ageing embrittlement behaviour of X80 self-shielded flux-cored arc welding (FCAW) girth weld metal at different strain ageing conditions (1% prestrain, and aged at 150 degrees C/100 degrees C for 1 -6 h, and 80 degrees C for 1-30 days) was studied. Microstructure of FCAW girth weld generally consisted of coarse granular bainite and lath bainite. After strain ageing, toughness notably decreased, and higher ageing temperature or longer ageing induced lower toughness, until ageing is fully yielded. At initial stage of strain ageing, more dimples were found accompanying with cleavage facet. With the progress of strain ageing, the embrittlement was more obvious, while larger cleavage facet and less dimples were found. Meanwhile, the critical size for cleavage fracture initiation site became smaller. Martensite-austenite constituent (1-2 mu m) was found to initiate cleavage fracture when partially strain aged, while submicron inclusions could initiate cleavage facet when fully strain aged.