Multiscale numerical study of tempered martensitic grade 91 (P) steel at high shear strain

Tempered martensitic steel Grade 91 with 9% wt. Cr and 1% wt. Mo (P91) has been developed to have high strength, good corrosion, and creep resistance at high temperatures, as well as good weldability. This alloy is mainly used for power plant components which face harsh operating conditions of stress and temperature.

Early failures have been reported in some P91 components. A multi-length scale study and model of P91 at a high deformation level will help understand the reasons behind these failures as well as create a computational lifetime prediction tool, based on creep damage calculations. A shear specimen has been designed, based on ASTM (B831–05), to achieve uniform shear strains (> 30%) while minimising out-of-plane deformation to allow for microstructure analysis using ex-situ electron backscattering diffraction (EBSD). This study is aimed at developing a multi-length scale finite element model, as shown in Figure 0.1, which can capture the deformation of P91. Here, the macro-scale deformation is modelled using an isotropic hardening J2 (von Mises) plasticity model while a crystal plasticity model is used for modelling the micro-scale deformation.

The FE model is validated at a range of strain levels, up to 30%, through EBSD, digital image correlation (DIC) and force-displacement measurements, carried out as a separate part of the project¹