Abstract This study investigated the effect of subcritical reheats on the grain refinement mechanism, martensitic substructure, hardness, and impact toughness in a multipass gas metal arc weld (GMAW) of Fe-10Ni steel weld metal. Prior-austenite grain (PAG) size, effective grain size, high-angle grain boundary (HAGB) density, hardness, and Charpy V-notch (CVN) energy were quantified. Reaustenitization of the coarse-grained dendritic as-solidified microstructure produced substantially refined equiaxed grains, reducing PAG and effective grain sizes respectively by up to two orders of magnitude and fourfold, while significantly increasing HAGB density. The extent of refinement was governed by peak reaustenitization temperature and time above A C3 , controlled by cooling rate. Subsequent supercritical and intercritical reheats of simulated CGHAZ refined the grain size to levels comparable to single supercritical reheats. Grain growth during austenitization was governed by boundary migration in the absence of carbide pinning, related to low weld metal carbon content and the carbide formers, V and Mo, being tied in weld metal oxide particles. A critical HAGB density of ~0.57 µm⁻ 1 , corresponding to PAG ~31 µm and effective grain size ~3 µm, marked the transition to coarse martensite formation. Weld metal hardness was relatively insensitive to reaustenitization reheats. In contrast, reaustenitized conditions showed improved CVN energy relative to the as-welded condition, with superior toughness in 1000 °C reheats attributed to refined grains, higher HAGB density, and absence of coarse martensite. These results demonstrate that reaustenitization effectively refines the Fe-10Ni weld metal microstructure, increases HAGB density, suppresses coarse martensite, and governs impact toughness variability in multipass welds.
Matan et al. (Tue,) studied this question.
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