Ferrite in the HAZ of Dissimilar Temperature Probe Welds

Abstract Protector tubes for temperature sensors were welded onto experimental gas turbine compressor blades. While the blades were made of a high alloy hard-martensitic stainless chromium steel, a high alloy metastable austenitic stainless steel was used for the tiny protector tubes. The dissimilar weld joint was applied using manual GTAW. A large amount of blocky delta ferrite formed in the HAZ immediately adjacent to the fusion line, on the side of the martensitic steel. Delta ferrite in such dissimilar welds might detrimentally affect the mechanical properties of the weld joint. It was therefore recommended not to use the affected experimental blades in test engine service. Even though no failure occurred in this case, one was prevented by declaring the subject instrumented parts unfit for test engine service.