In additive manufacturing (AM) metallic materials, heat treatment (HT) is a common process for modifying the unstable and anisotropic microstructure. Selective laser melting (SLM) Corrax maraging stainless steel is a novel material that has been applied in mold materials with conformal cooling channels in industry. However, the influences of HTs on the various mechanical properties of SLM Corrax steels are still not fully clarified. The aim of this research was thus to clarify the effects of solution treatment (S) and integrated solution-aging treatment (SA) on the hardness and impact toughness of SLM Corrax maraging stainless steel. Furthermore, to identify the roles of building direction (BD) on the hardness and impact toughness, parallelly built (P) and vertically built (V) SLM Corrax steels were fabricated and compared. The microstructures were examined by X-ray diffraction, electron backscatter diffraction, and electron probe micro-analysis, and to observe the fracture surface, scanning electron microscopy was used. The results showed that both the impact energies and apparent hardnesses were dominated by the HT. S treatment simultaneously decreased the impact energies and apparent hardnesses. SA treatment increased the apparent hardnesses but decreased the impact energies. BD did not apparently affect either the hardness or the toughness. Furthermore, the percentage of austenite did not affect the impact energies of the various material conditions. In the SA condition, the apparent hardnesses of P and V specimens were 49.9 HRC and 49.3 HRC, respectively. The impact energies of SA-P and SA-V specimens were 20 J and 17 J, respectively. The low anisotropy of SA specimens in hardness and toughness can be attributed to the weak texture and is advantageous to the material’s stability during service.

Selective laser melting (SLM) enables the production of complexly shaped metals with programmable mechanical responses, yet most lattice studies still rely on a single unit cell and a simple columnar build, severely restricting performance improvements. Here, we examine how combining distinct unit cells and rearranging them within the build volume affects the compressive behavior of SLM Corrax maraging stainless steel lattice structures. Three designs are additively manufactured as follows: a columnar cubic-FCCZ lattice, an alternating cubic and FCCZ lattice, and a hybrid lattice (cubic+FCCZ unit cell). In situ 2D digital image correlation (DIC) and finite element analysis (FEA) are used to resolve full-field strain evolution and failure modes under quasi-static compression. The hybrid lattice achieves the highest first maximum compressive strength (418 ± 5.78 MPa) and energy absorption (128.5 ± 6.83 MJ/m³), with its specific energy absorption (44.2 ± 1.48 kJ/kg) outperforming that of the columnar cubic-FCCZ lattice and alternating cubic and FCCZ lattice by 21.76% and 8.07%, respectively. The enhanced performance is attributed to the more uniform stress distribution and delayed shear band localization afforded by the hybrid lattice. These findings show that simultaneously optimizing unit cell geometry and arrangement can significantly expand the design space of metal lattices and provide a practical approach to improving the compressive strength and energy absorption capacity of load-bearing SLM components.