抄録
In high Cr ferritic steels, premature failure at the welded joint has recently been a worldwide issue. This failure occurs at fine-grained heat-affected zone (FGHAZ) and it is known as “Type-IV creep damage”. In this study, the modified small punch (SP) creep test with a rectangular-type specimen (10×6×0.5 mm) was applied to the interrupted uniaxial creep specimens of welded joint of KA-SUS410J3 for investigating the change in local creep property due to the uniaxial creep. The rectangular-type specimens consisting of weld metal, heat affected zone and base metal were removed at the different distances from the outer surface, and all the specimens were subjected to the SP creep test at 690 °C and 200 N. Experimental results revealed that the rupture times measured on the interrupted uniaxial specimens were shorter than that on the as-received, although the fracture occurred along the FGHAZ on all the specimens. This decrease in rupture strength was dependent on the distance from the outer surface, and it was much more pronounced just below the outer surface for the uniaxial specimen interrupted at 93% of the rupture life. Additionally, the distribution of the decrease in SP creep rupture strength was qualitatively in good agreement with the degree of damage and/or degradation such as creep cavity and softening. Consequently, the modified SP creep test was expected to be a strong tool for detecting and evaluating the creep damage accumulated in the welded joint.
