Creep properties measurements of heat-affected zones of high Cr ferritic steel by SP creep test

The small punch (SP) creep test using a TEM disk-type specimen (phi 3 x t0.25 mm) was applied to the fusion zone (FZ), the coarsened grain heat-affected zone (CGHAZ), the fine grain HAZ (FGHAZ), the tempered HAZ (THAZ) and the base metal (BM), respectively, which were removed from the joint of 8Cr-2W-VTa steel welded by an electron beam welding, in order to investigate the creep properties of such local regimes. Experimental results revealed that the SP creep rupture of the FGHAZ was accompanied by creep void formation even if the rupture time was relatively short and its creep rupture strength was inferior to those of the other regimes. This reduction in rupture strength seemed to be attributable to the microstructural changes during the welding thermal cycles, which were represented by the annihilation of clear lath martensitic structure and the change in precipitate distribution.