| Abstract Scope |
U.S. Navy researchers developed a solid wire consumable based on the Fe-10Ni alloy system. The weld metal demonstrated acceptable mechanical properties for gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW). However, GTA weld metal exhibited significantly higher impact toughness than GMA weld metal. This work aims to reduce impact toughness variability in Fe-10Ni groove welds produced with GMAW.
To achieve this, the effect of different regions within GMAW multi-pass welds on impact toughness was investigated using Charpy V-Notch (CVN) testing. CVN samples were machined from a Fe-10Ni weld build-up and subjected to thermal simulations using the Gleeble thermo-mechanical simulator. Thermal histories were extracted from calibrated multi-pass groove FEA models for single reheat weld metal heat-affected zone (HAZ) regions, including coarse-grain HAZ (CGHAZ) and fine-grain HAZ (FGHAZ). To assess multiple reheats, thermal histories were also extracted for regions that experienced additional intercritical reheats (IC-CGHAZ, IC-FGHAZ) or subcritical tempering reheats (T-CGHAZ, T-FGHAZ).
Additional Charpy samples were machined from a single V-groove weld to evaluate as-deposited impact toughness. The influence of intercritical or tempering reheats on as-deposited impact toughness was also examined. All samples were tested according to ASTM E23 at 0°F and -60°F. Charpy energies were obtained, and fractography was conducted using a scanning electron microscope (SEM) to analyze fracture modes and correlation with impact energy.
Microstructural characterization was performed using electron backscattered diffraction (EBSD) and energy dispersive spectrometry (EDS) to assess grain morphology, dislocation structures, and phase composition. Transmission Electron Microscopy (TEM) thin foils were prepared for tested conditions to examine dislocation density changes, rearrangement into cell structures, and secondary particles such as carbides due to reheating.
This study contributes to understanding how multi-pass welding thermal cycles influence impact toughness variability in Fe-10Ni welds. The findings will support future process parameter optimization to enhance impact toughness. |