A research team at the National University of Singapore has developed a pathway to customize the mechanical properties of AISI 4340 low-alloy steel by tuning the laser powder bed fusion (L-PBF) process parameters to control its microstructure. By systematically varying laser power and volumetric energy density, the team utilized process-induced thermal cycling to stabilize varying amounts of retained austenite within a tempered martensite matrix. Combining experiments and finite element simulations, they showed that these metastable retained austenite phases undergo transformation-induced plasticity (TRIP) during deformation, significantly enhancing strain hardening capability. This enabled researchers to tailor the yield-to-tensile strength ratio of the material between 0.65 and 0.82. The best-performing sample achieved a tensile strength exceeding 1747 MPa in the as-built condition while maintaining elongation above 10%, surpassing most reported L-PBF steel properties. The study confirms that selection of L-PBF process parameters can significantly influence thermal history, microstructure, and mechanical response, offering new insights into integrated microstructure-property design for high-strength steel.