Laser Processing of Fe-Cr-B Alloys: Microstructure Evolution, Non-Equilibrium Solidification and Wear–Corrosion Performance

Fe-Cr-B alloys are recognized as candidate wear- and corrosion-resistant materials strengthened by high-hardness boride phases. Conventional casting produces coarse continuous network borides and severe elemental segregation under near-equilibrium slow solidification (10−1–102 K/s), resulting in high brittleness and limited service reliability. Laser processing includes laser cladding (103–106 K/s), LPBF/DED (106–108 K/s) and laser remelting, which feature extreme non-equilibrium rapid solidification but differ significantly in thermal gradient G, solidification rate R, and phase evolution behavior. To avoid over-extrapolation, this review strictly classifies evidence into direct LPBF evidence, direct DED evidence, laser cladding evidence, casting evidence, and indirect inference. Quantitative comparisons reveal that laser cladding refines borides from 150 to 300 μm to 10.8–20 μm, while DED further achieves 1–5 μm equiaxed grains and relative density > 98%. Meanwhile, laser-cladding Fe-Cr-B coatings achieve a maximum hardness of ~1052 HV0.5, and ~18% higher wear resistance and ~70% lower cavitation mass loss compared with cast counterparts. Non-equilibrium mechanisms including solute trapping, interface absolute stability, constitutional undercooling, and columnar-to-equiaxed transition (CET) controlled by the Gn/R ratio are systematically analyzed. Thermal–solutal coupling, grain nucleation, and boride precipitation kinetics under rapid cooling are emphasized. Current limitations include incomplete non-equilibrium thermodynamic databases, insufficient standardization, limited post-processing (heat treatment, HIP) studies, and missing unified performance datasets. Future directions are proposed toward quantitative phase-field modeling, standardized tribocorrosion characterization, high-throughput experiments, and machine learning-assisted optimization. This review provides a rigorous analytical framework for the composition–process–microstructure–performance design of laser-processed Fe-Cr-B alloys.