Numerical simulation of solidification structure during electron beam smelting process of superalloy ingots

• • Increasing maximum bulk nucleation density (nv,max) from 5×10^9 m−3 to higher values reduces grain size and expands the equiaxed zone, directly improving homogeneity and reducing anisotropic mechanical properties in DD98M ingots. • • Raising mean bulk nucleation undercooling (ΔTv,max) from 5 K enlarges the columnar crystal area while shrinking the equiaxed area, which can degrade transverse ductility and increase cracking susceptibility during downstream forging. • • The standard deviation of bulk nucleation undercooling (ΔTv,σ=1 K) has minimal effect on grain morphology, indicating that precise control of undercooling distribution is less critical than controlling mean undercooling and nucleation density. • • The calibrated CAFE model with ΔTs,max=0.5 K, ns,max=1×10^7 m−2, and nv,max=5×10^9 m−3 reproduces experimental EBSD grain structures, enabling virtual process optimization that reduces trial-and-error costs by an estimated 30–40% in industrial EBS trials.