Strain partitioning and strain localization in medium manganese steels measured by in situ microscopic digital image correlation

In situ microscopic-digital image correlation (mu-DIC) is used to investigate the strain partitioning and strain localization behavior in a medium manganese steel. Continuous yielding results from strain partitioning with higher strain in the reverted austenite (gamma(R)) islands and less strain in the tempered martensite (alpha(temp)') matrix, both in hot and cold rolled material. mu-DIC experiments are performed to further understand the effects of texture and grain morphology on strain partitioning which cannot be locally resolved through high resolution x-ray or neutron diffraction experiments. Apart from strain partitioning, strain localization is observed in hot rolled samples within colonies of lamellar gamma(R) islands. This localization does not only depend on the crystallographic orientation, but also on the spatial alignment of an austenite island relative to the loading direction. The effects of texture, spatial and colony alignment are interpreted within the concept of a relative grain size effect resulting in different yield stresses in the hot and cold rolled samples showing continuous yielding. Strain partitioning and strain localization based on texture and spatial alignment can be extended to numerous dual phase morphologies with similar texture, colony and spatial alignment effects.