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Failure in steel weldments operating at high temperatures often occurs in the heat affected zone (HAZ) adjacent to the weld. Such failures can be a result of material inhomogeneity within the HAZ and in the case of tempered martensite steels has been linked with regions of untransformed (ferrite) phase or over-tempered martensite within the intercritical region of the HAZ (IC-HAZ). In this work, two-dimensional Voronoi tessellation is used to construct polygonal Voronoi cells to represent the microstructure of the HAZ of a weld in a tempered martensite steel. The Voronoi construction is treated as a representative volume element (RVE) of the material and is discretized by 8-node linear brick elements, with periodic boundary conditions. The lattice orientation at each material point is specified by three Euler angles, which are assumed to be randomly distributed, to represent the initial lack of texture in the IC-HAZ. The constitutive response is represented by a nonlinear, rate-dependent, finite-strain crystal plasticity model. The results indicate that small amounts of ferrite can induce significant enhancements in stress and inelastic deformation at the interface of the ferrite and martensite grains. This localisation of stress and strain may be critical for microcrack and/or void formation and may be a contributory factor to Type IV cracking.

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