Large sized creep rupture and interruption tests were performed for specimens made from KASTPA29 steel equivalent material thick plate weld joint. SEM observations revealed that microvoids were nucleated at grain boundary of FGHAZ. Growth and cross-linking of micro-voids, heavily damaged and almost separated grain boundaries, grain-sized voids and larger voids whose size were 2 to 3 times of fine grains were also observed. These microstructural features were considered to show Type IV damage evolution. It was estimated that nucleation and accumulation of Type IV damage were strongly affected by microstructure before weld heat.

View full abstract