Strain localization and deformation behavior in ferrite-pearlite steel unraveled by high-resolution in-situ testing integrated with crystal plasticity simulations

Abstract

This paper attempts to study the microstructural stress-strain evolution and strain localization in the ferrite-pearlite steel by high-resolution experimental-numerical integrated testing. Ferrite crystal orientations measured by electron backscatter diffraction (EBSD) were mapped onto precise scanning electron microscopy (SEM) micrographs of ferrite and cementite lamellar morphologies. Furthermore, in-situ SEM tensile testing was employed to map strains during the deformation using digital image correlation (DIC) at high spatial resolutions. Finally, spectral solver-based crystal plasticity (CP) simulations loaded by the local SEM-DIC boundary conditions were performed and compared to the experimental data. Crucially, all microstructure data was carefully aligned, and strains were filtered to the same spatial resolution, measured to be as small as ~75 nm. This integrated methodology yields new insights in the high degree of plastic strain partitioning between ferrite grains and pearlite colonies, and ferrite and cementite lamellae inside pearlite. One-to-one experimental-numerical comparison augmented with the numerical variation of the ferrite constitutive model, pearlite interlamellar spacing, and lamellar orientation reveals how the ferrite-cementite strain partitioning and the onset of strain localization depend on the morphology and distribution of ferrite grains and pearlite colonies. Importantly, this comparison showcases the limitations of state-of-the-art simulations in their capability to predict specific mechanisms and correct degrees of strain heterogeneity.