Decoding columnar/equiaxed grain ratio disparity in the weld metal of EH36 steel subjected to CaF ₂ –SiO ₂ fluxes

The columnar/equiaxed grain (C/E) ratio governs the microstructural uniformity and mechanical performance of the weld metal (WM). As the ratio is intrinsically dictated by weld pool solidification kinetics, in situ observation of the solidification process becomes essential for elucidating grain morphology evolution. It has been demonstrated that increasing the SiO 2 content in flux-cored wires reduces the secondary dendrite arm spacing from 42.75 to 31.46 μm, promotes carbon enrichment ahead of the solidification front, enhances constitutional undercooling by 11 °C and suppresses the primary δ phase originating from the initial liquid/solid interface, where columnar grains predominantly form, thereby reducing the C/E ratio from 2.1 to 1.1. These findings may serve as guidance for microstructural design towards high-performance WMs.