Prediction of Ductility-Dip Cracking in Narrow Groove Welds Using Computer Simulation of Strain Accumulation

Ductility-dip cracking (DDC) in high chromium nickel-base weld metals has been an issue during fabrication and repair of nuclear power plant components for many years. DDC is a solid-state cracking phenomenon, and several theories [1‐10] have been proposed for the mechanism. Research conducted to develop these theories has primarily been performed using test methods involving small-scale specimens that may not replicate actual welding conditions (e.g., strain-to-fracture, hot-ductility, and varestraint). Due to the complexities of welding, there are potentially significant differences in the strain, strain-rates, stresses, and thermal cycles that can occur between these small-scale test methods and actual welding conditions. To eliminate this uncertainty, a high-restraint, narrow groove weld mockup was developed to assess DDC in this work. Filler metals 52 and 52M (AWS specifications ERNiCrFe-7 and ERNiCrFe-7A, respectively), compositions considered susceptible to DDC, are deposited with cold wire GTAW in a narrow groove with precise heat input and bead placement controls to isolate the occurrence of DDC to a known region of the weld deposit. Computer modeling using SysWeld^™ with validated weld parameter inputs was also performed to simulate the narrow groove weld. Comparison of test specimens to computer simulations shows that the highest occurrence of DDC is in weld regions with multiple reheat cycles and high strain accumulation. This and future work is intended to develop a method to predict DDC susceptibility in multi-pass welds and to develop procedures and techniques that minimize the occurrence of DDC.