From heat-treatment maps to repairable tooling of LPBF-produced M789 maraging stainless steel

Laser powder bed fusion (LPBF) can produce corrosion-resistant, ultra-high-strength maraging stainless steels for tooling, but post-processing routes balancing strength, toughness, thermal stability, and repairability remain unclear. We establish an internally consistent heat-treatment map for cobalt-free M789 across direct aging, solution annealing, and combined routes. As-built material exhibited 1.0 GPa ultimate tensile strength, 320 HV10, and Charpy impact energy up to 135 J. Direct aging at 500°C–520°C for 3 h reached 1.87 GPa and 562–572 HV10, matching the conventional 1000°C/1 h + 500°C/3 h route but reducing toughness to 11 J. Exposure at 350°C for up to 2880 h resulted in modest strengthening, ductility loss, and a chemically stratified oxide scale. LPBF redeposition onto printed M789 produced a metallurgically sound repair, supporting additive repair of thermally and mechanically demanding tooling.