| Abstract Scope |
This presentation summarizes studies on metallurgical phenomena related to weldability and service performance of welds in advanced alloys, performed in the last 20 years at the Welding Engineering Laboratory of The Ohio State University.
Susceptibilities to solidification and ductility-dip cracking (DDC) in high-chromium nickel-base filler metals, stress relief cracking (SRC) in creep resistant alloys, and hydrogen assisted cracking (HAC) in dissimilar metal welds (DMWs) have been evaluated using originally developed cast pin tear test, fixed displacement thermal cycling test, SRC test, and delayed hydrogen cracking test.
The effects of dilution and partitioning of alloying elements on solidification cracking susceptibility in dissimilar metal overlays was elucidated developing pseudo-binary solidification diagrams. Such diagrams were applied to understand the mechanism of shrinkage porosity formation in low alloy steel filler metal / Ni-base substrate DMWs.
The phenomenon of carbon migration in the fusion boundary region of DMWs, leading to brittle failures at high temperature service and during exposure to hydrogen charging environments, was investigated using thermodynamic and kinetic simulations, allowing to better understand the effects of materials composition, welding and post weld heat treatment (PWHT) procedures. Thermodynamic and kinetic simulations helped explaining the beneficial effect of multiple short-term reheats imposed by temperbead welding, as compared to conventional PWHT, on the resistance to SRC and impact toughness in low alloy creep resistant steels.
Digital image correlation instrumented cross-weld tensile testing allowed to explain the improved resistance to HAC in overmatching weld metal DMWs. Fast weld metal string hardening and its constraining effect prevents strain concentration in the HAC susceptible dissimilar fusion boundary region.
A hypothesis for the effect of imposed mechanical energy (IME) on DDC susceptibility in welds of high-chromium Ni-base filler metals was successfully validated using FEA modeling of highly restrained welds and is being applied in welding process optimization for mitigation of DDC. |