Numerical Analysis of Microstructure and Hardness Distribution in Fe-10Ni Welds

Fe-10Ni is a high-strength, high-impact-toughness steel developed for naval structural applications. Gas metal arc welding in spray transfer mode (GMAW-s) with a Fe-10Ni filler metal produces welds with complex, deep, finger-like penetration profiles. The GMAW-s process is preferred for its higher productivity, but multipass groove welds exhibit lower impact toughness than those made with gas tungsten arc welding (GTAW). This study developed a numerical simulation framework to analyze microstructure and hardness distribution in multipass Fe-10Ni groove welds produced by GMAW-s. The framework utilized finite element analysis (FEA) models of GMAW-s processes for groove and bead-on-plate welds, a heat-source model reproducing the fusion-zone profile in GMAW-s welds, and experimentally derived thermal history–hardness and thermal history–microstructure relationships. The accuracy of the framework was confirmed by comparing FEA predictions with experimental results on heat-affected zone thermal histories and the spatial distributions of hardness and microstructure in multipass weld metal. Fe-10Ni weld metal exhibited a weak response to tempering by short-term subcritical reheats from multipass welding, resulting in a low weld metal hardness range, within 40 HV0.2. However, the GMAW-s weld metal showed pronounced variation in the spatial distribution of as-solidified, reaustenitized, and tempered microstructures. As-solidified martensite, known to reduce impact toughness in Fe-10Ni welds, was found to occupy up to 0.43 fraction of the weld metal cross section. By linking thermal history to microstructure and properties, the proposed framework provides a pathway for computationally guided welding process optimization, aiming to reduce the regions of as-solidified martensitic microstructure and improve impact toughness in GMAW-s multipass Fe-10Ni welds.