Fracture Mechanical Assessment of the Corrosion Fatigue Characteristics at the Low Fatigue Limit of a Multi-pass Welded Ni-Based Alloy 617

摘要

The most effective methodology for developing green power-plant systems is to increase the generating efficiency of steam power plants. Ni-based alloys prove applicable for performance improvements. This study assessed the electrochemical-corrosion characteristics of multi-pass welded Ni-based Alloy 617 in as-welded and post-weld heat-treated (PWHT) conditions and tested for corrosion fatigue in a 3.5 wt.% NaCl solution at 70°C to determine the corrosion-fatigue characteristics at the low fatigue limit. The results showed a linear increase in the corrosion rate with an increase in solution temperature. Degrading the weld at 700 °C for 24 h increased the corrosion rates above those of the as-welded samples, regardless of whether they were subjected to PWHT. Corrosion-fatigue cracks grew at the low fatigue limit, which was about 48.4 % (327MPa) of the static tensile strength (675.1MPa) of the weld, and 43.1% of the base metal (759.4MPa). The corrosion-fatigue crack-growth rates are greater after PWHT than before. However, the difference between samples due to PWHT is insignificant.