Sensitivity of Crystal Stress Distributions to the Definition of Virtual Two-Phase Samples

An extensive set of finite element simulations of crystal stress distributions in the duplex stainless steel, LDX-2101, have been performed to investigate the sensitivity of the simulation output to the definition of the virtual samples. The rolled LDX-2101  material investigated has a microstructure comprising approximately equal volume fractions of ferrite and austenite, with the two phases exhibiting a columnar structure but different grain sizes and morphologies. Two major aspects are thoroughly covered in the sensitivity study—the single-crystal elastic and plastic properties of the two constituent phases, and their spatial arrangement. The simulations are evaluated against experimental data for the macroscopic stress–strain behavior (including strain-rate jump tests) as well as lattice strain data measured by neutron diffraction under in situ  loading. Published values for the austenite and ferrite single-crystal elastic constants performed well, allowing the distribution of stress within the elastic domain and the lattice strain transients in the elastic–plastic transition to be captured with good fidelity. For the plastic parameters, it was found that using identical values for initial slip system strength, hardening rate, and saturation strength for the two phases did as well overall as combinations using different values for the two phases. However, consistent with previous work by others, it was necessary to use significantly different values of strain-rate sensitivity to capture the results of the strain-rate jump tests. Four microstructure types were investigated, ranging from one that incorporates all the principal attributes of the duplex microstructure to one that includes none of them. With the material properties for LDX-2101  that best matched the experimental data, the microstructure had little influence on the results of the simulations—only large differences in phase strengths resulted in significant effects of the microstructure. Based on these results, a simplified microstructure consisting of equiaxed austenite and ferrite grains but retaining major features of the phase structure is justified for this material.