Effect of Mg on the elemental segregation behavior of H13 hot-work die steel

To Address the severe interdendritic segregation in as-cast H13 steel, this study investigates the mechanism by which trace magnesium modification regulates elemental segregation. The results show that the addition of 16 ppm magnesium effectively inhibits elemental segregation in as-cast H13 hot-work die steel. Compared with magnesium-free H13 steel, magnesium refines the dendritic structure and substantially reduces concentration gradients of carbon, chromium, molybdenum, and vanadium between intragranular and interdendritic regions. After magnesium modification, the effective solute partition coefficients of these alloying elements approach unity, directly confirming the mitigation of microsegregation. First-principles calculations reveal that magnesium atoms preferentially adsorb on low-index γ-Fe surfaces, reducing their surface energies by 18–20% and promoting equiaxed grain formation. Concurrently, magnesium increases the segregation energies of molybdenum, chromium, and vanadium at the solid–liquid interface, hindering their enrichment. Trace magnesium addition is an economically feasible process approach to homogenize as-cast microstructures and inhibit primary carbide precipitation, providing mechanistic support for magnesium microalloying in hot-work die steels.