Multiscale modelling of mechanical response in a martensitic steel: A micromechanical and length-scale-dependent framework for precipitate hardening

In this paper, a multiscale finite element (FE) modelling framework is developed with explicit representation of polycrystalline microstructure and sub-micron precipitate structure for a P91 tempered martensitic steel. A dislocation-mechanics-based and length-scale-dependent crystal plasticity model has been formulated to account for slip-based inelastic deformation in the material. The multiscale FE simulations have been validated through the use of uniaxial tensile test data at room temperature. Homogenization analysis is performed to connect the FE models at two length scales. The analysis indicates a strong dependence of dislocation mean free path on the morphology of the sub-micron structure. A linear relationship is found to represent the homogenized constitutive behaviour with respect to precipitate size. Softening effects with respect to precipitate and lath coarsening are identified and quantified at the macroscopic scale through the multiscale modelling framework.