Characterization of the GTAW fusion line phases for superferritic stainless steel weldments

During the study of GTA welding of several superferritic stainless steel alloys, using multi-pass welds of austenitic fillers, poor tensile properties were observed. Tensile specimens were observed to fail at the fusion line with the shape of the fracture exactly matching that of the weld/base metal interface. The weld corrosion test results were also not as satisfactory as the base metal tests. Localized corrosion was observed at the weld fusion line. This was attributed to the presence of an excess brittle phase at the weld fusion line. In this study, samples from 29Cr–4Mo–2Ni alloy welds were made using Inconel 625 filler material and the gas tungsten arc welding procedure. The samples were metallographically examined after brittle phases were found at the fusion line. A composition that the Fe–Cr–Ni phase diagram at 650°C predicts a mix of austenite and sigma phase has been found on the broken face of a tensile specimen, using SEM/XEDS quantitative analysis. X-ray diffraction independently confirmed the presence of a mixture of austenite and sigma phase on the broken tensile sample.