PSI - Issue 77

Karel Trojan et al. / Procedia Structural Integrity 77 (2026) 537–542 Karel Trojan / Structural Integrity Procedia 00 (2026) 000–000

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1. Introduction Additive Manufacturing (AM), particularly Selective Laser Melting (SLM), is a highly promising technique for consolidating metal powders and producing complex 3D components. This process involves layer-by-layer melting of a thin powder bed using a scanning energy source. The localized heating and cooling during SLM, determined by the scanning strategy, result in a complex distribution of residual stresses (RS), as demonstrated by Bartlett et al. (2019). These RS can reach magnitudes close to the yield strength of the material, significantly influencing both the manufacturing process and the mechanical performance of the final part. The size and orientation of RS are strongly dependent on key printing parameters such as laser power, scanning speed, and scanning strategy. Tensile (RS) in steels arise from the combined effects of thermal gradients and phase transformations during processing. These stresses are particularly detrimental in fatigue-sensitive applications and, when combined with defects, can promote brittle fracture, as described by Köhler et al. (2012). Generally, tensile RS result from material shrinkage, while compressive RS are induced by phase transformations such as the conversion of austenite to martensite, bainite, or ferrite. The dominant mechanism depends on factors like material type, geometry, and thermal conditions, as discussed by Bhadeshia (2002). In this study, MS1 maraging steel samples were subjected to high cycle fatigue testing to evaluate the impact of RS on fatigue behaviour. Fatigue crack initiation and propagation are crucial to fatigue performance and are closely linked to surface roughness, microstructural features (including dislocation density, crystallite size, and microcracks), and residual stresses, as noted by Schne ller et al. (2019). Furthermore, Čapek et al. (2023) investigated the correlation between RS and surface fatigue crack behaviour in laser-welded materials using X-ray diffraction, revealing that both RS and microstructural distribution significantly affect fatigue life. Overall, the distribution of internal residual stresses in AM components is highly sensitive to the printing strategy and plays a critical role in sample deformation and fatigue crack formation. Therefore, this research aims to minimize residual stresses in 3D-printed maraging steel to enhance its fatigue resistance and mechanical reliability.

Nomenclature AM

additive manufacturing selective laser melting

SLM

RS residual stress FWHM full width at half maximum diffraction angle angle between the sample surface and the diffracting lattice planes load amplitude ′ fatigue strength coefficient fatigue exponent endurance limit 2. Materials and Methods

Standardized fatigue test specimens with a circular cross-section of 5 mm diameter were produced using an EOS M290 selective laser melting machine from C300 maraging steel (commercially known as MS1), see Fig. 1. The samples were printed vertically, with their axial axis perpendicular to the build platform, using the process parameters listed in Table 1. The chemical composition, see Table 2, corresponds to 18% Ni Maraging 300 (US classification), 1.2709 (European), and X3NiCoMoTi 18-9-5 (German designation). MS1 steel is a very high-strength material known for its excellent machinability and the ability to be hardened up to 54 HRC. It also offers good thermal conductivity, making it suitable for demanding industrial applications. MS1 is commonly used in series injection moulding, high volume production, and tooling applications such as aluminium die casting. Its mechanical properties also make it ideal for manufacturing high-performance parts that require both durability and precision.