Microstructural characterisation and in-situ straining of additive-manufactured X3NiCoMoTi 18-9-5 maraging steel

Additive manufacturing (AM) is an advanced technology used for the manufacture of products that have intricate shapes and complex inner geometries. Various metal powders can be used for AM; however, the resulting microstructures will differ profoundly from those obtained via the casting, heat treatment, or thermomechanical processing of metals with the same chemical composition. This is because of the rapid heating and cooling rates used during three-dimensional (3D) printing. Further complications arise from the repeated heating and cooling of some regions, which is owed to the step-by-step formation of the solidified layers. A powder consisting of 1.2709 (X3NiCoMoTi 18-9-5) low-carbon maraging steel was used in an AM experiment. Given the high residual stresses that exist within printed metals, a post-processing heat treatment is desirable to limit the risk of cracking. In this study, solution annealing and hardening treatments were applied to the printed samples to induce changes in their microstructures and mechanical properties. The mechanical properties and microstructures of the builds were characterised and compared to those of a bar of conventional steel with the same chemical composition. During tensile loading, the fracture that was initiated at the sites of metallurgical defects was observed in situ.