Abstract
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.
Highlights
Maraging steels are high-strength steels with very low carbon contents, which are primarily alloyed with Ni, as well as Co, Mo, Ti, and Al
Various metal powders can be used for Additive manufacturing (AM); the resulting microstructures will differ profoundly from those obtained via the casting, heat treatment, or thermomechanical processing of metals with the same chemical composition
Detailed metallographic examination was performed on the samples using scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD) analysis; the local chemical composition of each sample was characterised
Summary
Maraging steels are high-strength steels with very low carbon contents, which are primarily alloyed with Ni, as well as Co, Mo, Ti, and Al. The laser processing of metals involves high heating and cooling rates (typically around 106 K/s), which result from short interaction times and high thermal gradients [7,8] These rapid changes in temperature often lead to very unusual, non-equilibrium microstructures, including new phases with extended composition ranges [7,8]. AM microstructures differ from those of nonAM materials with an identical composition that received a conventional heat treatment [7,9] Following such rapid cooling, the resultant microstructures may be expected to consist solely of a martensitic matrix that is free from precipitates and retained austenite. The in-situ observation of the failure initiation and propagation, owed to such defects, under tensile loading will be described in this article
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