Multiscale Mechanical Characterisation of Additively Manufactured Maraging Steel Aided by Crystal Plasticity Analysis

Tensile test results obtained from millimetre- and micrometre-scale specimens were correlated using crystal plasticity analysis to examine the microstructural factors dominating the mechanical properties of the as-built maraging steel produced by the laser powder bed fusion (LPBF) method for repairing die-casting tools. Micrometre-scale tensile tests revealed that the mechanical properties of single prior austenite grain (PAG) structures are dominated by the deformation of the coarse block according to Schmid's law rather than by habit-plane-orientation-dependent slip deformation. This is owing to the low aspect ratio of the lath structure in the maraging steel produced by the LPBF method. In the millimetre-scale tensile specimens consisting of multiple PAGs in the gauge section, anisotropy of the ultimate tensile strength and elongation-to-failure was not observed, which was attributed to the high energy density in LPBF process. It was revealed that the specimen with the loading direction (LD) parallel to the build direction exhibited earlier work softening than the specimen with the LD perpendicular to the build direction, regardless of the energy density. This anisotropy was examined using crystal plasticity analysis with material parameters obtained through the fitting analysis of micrometre-scale specimens. The analysis results indicated that the anisotropic work-hardening behaviour related to the build direction was due to differences in the overall Schmid factor and the degree of lattice rotation, both of which stemmed from the texture. As the anisotropic mechanical properties observed in this study were insignificant, the application of the high-energy-density LPBF method to maraging steel is useful for repairing mechanical components.