Effect of welding process on intergranular corrosion of Incoloy 800H alloy welds

Objective The aim is to examine the validity of different welding processes on welding plugging of the Incoloy 800H heat exchange tubes of the stream generator in high temperature gas cooled-reactor. Methods Self-fusion weldments of Incoloy 800H alloy are made by TIG and laser welding. The resistance to intergranular corrosion performance of both different welded jionts and base meterial is measured with FeSO₄(III)-H₂SO₄ solution. Optical microscopy, scanning electron microscopy and energy dispersive spectrometer are used to study microstructure of welded joints, the morphology and products of corrosion, as well as the corrosion mechanism. Results Results show that the higher power density results in a significantly narrower weld and heat affected zone width for the laser welded joints compared to the TIG welded joints. Submicrosized Cr₂₃C₆ and microsized TiC precipitates are observed along the grain boundaries within the heat affected zones. The intergranular corrosion test shows that the corrosion rate of the laser welded joints is comparable to that of the base material, and it is approximately 39.0% of the TIG joints. The corrosion depth of the heat affected zone inside the same welded joint is the largest, followed by the weld and the base material. Conclusion The Cr depletion at grain boundaries caused by chromium carbide precipitation is the main reason for the difference in intergranular corrosion resistance.