Effect of Dislocation Networks on Precipitate Morphology in Maraging Steels

We introduce high dislocation densities in a maraging steel using High Pressure Torsion (HPT) processing, followed by ageing them. This gives rise to tensile behaviour substantially different from that of conventional maraging steels. Our Atom Probe Tomography (APT) studies on the steel, show that the morphologies of the Fe-Mo precipitates in such samples with a high density of networks of dislocations is disc-like. Finite element simulations of stress distributions and strain partitioning in such microstructures help explain the reduced macroscopic ductility in them. Using phase field modelling, we show that such morphologies are a result of faster diffusion paths provided by the dislocations. Thus, in addition to providing nucleation sites for precipitation, the faster diffusion paths influence the precipitate morphology and hence the macroscopic mechanical behaviour.