In this research, the small punch (SP) test was applied to examine the local creep characteristics of a narrow gap weldment. To find the local creep property, an Ni-based 617 alloy and its narrow gap weldment. which is one of candidates for advanced fossil power plants, were employed. Thin square specimens were machined at three different locations: weld metal, base metal, and HAZ near the base metal from the Inconel 617 alloy narrow gap weldment. The results of the SPC test were evaluated. The microstructure of narrow gap weldment was observed by scanning electron microscopy and optical microscopy to investigate the effect of the microstructure on the creep properties of the weld zone. The creep rupture part of the weldment was observed by scanning electron microscopy. Finally, four different creep characteristics of the narrow gap weldment were obtained by the SPC test with good validity.

This study aims to investigate the fatigue life of T-Type fillet welded joints for excavators subjected to bending loads, and also to verify the predicted fatigue life of the welded part using the effective notch stress method. Moreover, this study aims to determine an optimal toe angle of the T-Type fillet welded structure. In this context, the fatigue lives of T-Type fillet welded specimens (SM490A) were measured and the effective notch stress method for predicting the fatigue life of the T-Type fillet welded structure was verified by comparing with the FAT-225 curve of IIW (International Institute of Welding) as was suggested for the current types of welded structures. Considering simultaneously the scattering factor of the welded structure, the stress condition at the toe part higher than the root part, and the stress minimization condition of the toe part, the optimum toe angle at the T-Type fillet welding was identified at 30°. Likewise, the maximum stress (310.5 MPa) when the toe angle was 30° was about 14% less than the maximum stress (354.0 MPa) at 45°, and the fatigue life was improved by about 30%.