Prediction of multiaxial deformation of 316H stainless steel at high temperature using a multiscale crystal plasticity approach

Steel components in advanced gas-cooled reactors (AGRs) are subject to multiaxial deformation at high temperatures. Neutron diffraction has been used to study the {111}, {200}, {220} and {311} grain family, also known as lattice plane, response during in-situ loading and relaxation of notched bars of 316H stainless steel at 550 °C. These experimental conditions have been modelled using a multiscale approach that employs finite element models at the continuum, component, scale as boundary conditions for a crystal plasticity finite element model. For the bar with the highest triaxiality factor at the diffracting region, the CPFE model was in good agreement with the experiment results. The most notable difference was the reduced accumulation of intergranular strain in the {200} grain family and significant stiffness difference in the {220} grain family in the transverse direction. For the bar with the lowest triaxiality factor at the diffraction region, the agreement between the CPFE model and experiment was acceptable but poorer than the bar with the higher triaxiality factor. This is due to the CPFE sensitivity to the macroscopic boundary conditions applied. Reasonable agreement was achieved for the relaxation dwells. The modelling has shown that multiaxial conditions, enforced by the multiscale approach, cause an increase in stiffness in the CPFE response, resulting in the reduction in the intergranular strain accumulated.