Crystal plasticity modeling and experimental characterization of strain localization and forming limits in ferrite-pearlite steels

The main objective of this study is to predict the deformation behavior, strain localization, and forming limits of ferrite-pearlite steels by incorporating the contributions of the microstructural characteristics and mechanical properties of the underlying microstructure. A realistic microstructure-based micromechanical approach in the framework of the crystal plasticity (CP) model was carried out using the periodic representative volume element (RVE) generated from the scanning electron microscopy (SEM) image. The homogenized stress–strain curve of the realistic RVE was validated with the experimental data with an error of less than 6.71% at large strains. Afterward, the initial microstructural inhomogeneity criterion was applied to the realistic RVE under various loading paths to predict the forming limit diagram (FLD), which compared with the experimental results of the Nakazima-stretch forming test. Consequently, the contributions of the pearlite volume fraction and the microstructural morphology were studied by extending this approach to the synthetic microstructures with various pearlite volume fractions. In conclusion, the microstructure-level inhomogeneity at the microscopic level results in intense stress/strain partitioning and strain localization, emerging in the form of micro-localized deformation bands. Moreover, it has been found that the local deformation pattern at the micron-scale significantly depends on the microstructural morphology and loading direction.