Behavior and Hot Cracking Susceptibility of Filler Metal 52 M (ERNiCrFe-7A) Overlays on Cast Austenitic Stainless Steel Base Materials

Operating experience in the nuclear power industry has shown that dissimilar metal welds joined with Inconel 82/182 (ERNiCr-3/ENiCrFe-3) filler metal in the primary loop of pressurized water reactor (PWR) plants are susceptible to primary water stress corrosion cracking (PWSCC). Repair of these dissimilar metal weld joints by weld overlay (WOL) using the PWSCC resistant 52 M (ERNiCrFe-7A) filler metal has been successfully applied in numerous PWRs. The typical dissimilar metal joint consists of a low alloy steel vessel nozzle welded to an austenitic stainless steel safe end. The WOL extends from the low alloy steel nozzle over the safe end and most often onto the adjoining wrought or cast stainless steel pipe. Recent experience shows that 52 M is susceptible to hot cracking when welded over specific heats of centrifugally cast stainless steel pipe. The cracking was attributed to unexpectedly high dilution caused by a synergistic influence of Silicon (Si) and Sulfur (S) on weld pool behavior and bead shape. This paper presents the cause and mechanism of 52 M hot cracking when welding over cast stainless steel, and discusses the synergistic influence of Si, S and other trace elements on the weld bead shape and dilution. In addition, the influence of gas tungsten arc (GTA) welding parameters is discussed in relation to the successful application of 52 M WOL on cast austenitic stainless steel base metals.