Influence of material inhomogeneity on the mechanical response of a tempered martensite steel

Failure in steel weldments operating at high temperatures often occurs in the heat-affected zone adjacent to the weld. Such failures can be a result of material inhomogeneity within the heat-affected zone and in the case of tempered martensite steels have been linked with regions of untransformed alpha (ferrite) phase or over-tempered martensite within the intercritical region of the heat-affected zone. In this work, two-dimensional Voronoi tessellation is used to construct polygonal Voronoi cells to represent the microstructure of the heat-affected zone of a weld in a tempered martensite steel. The Voronoi construction is treated as a representative volume element of the material and is discretised 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 intercritical region of the heat-affected zone. 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.This publication has emanated in part from research conducted with the financial support of Science Foundation Ireland under Grant No. 14/IA/2604. The modelling work was supported by the Irish Centre for High-End Computing (ICHEC). Helpful discussions with Mr Brian Golden, Dr Yina Guo of the Bernal Institute at University of Limerick, Ireland, and Prof. Fengshi Yin of Shan Dong University of Technology, China. Mr Stephen Scully and Ms Adelina Adams of ESB Energy International (Ireland) are gratefully acknowledged.peer-reviewe