Residual stress field determination in steel crash-box using synchrotron energy dispersive diffraction

3rd generation AHSS (advanced high-strength steel) family encompasses different innovating microstructure concepts, among which Medium Manganese Austenite Reverse Transformation steels. The ground-breaking properties of these steels are achieved thanks to their particular duplex microstructures, which contain a fine “ferritic” matrix and a large amount of retained austenite. The refined matrix explains the superior strength and toughness of these steels while retained austenite explains their good formability thanks to an efficient TRIP effect. The mechanical stability of retained austenite and the related strain-induced transformation kinetics depends on many factors: local chemical composition of austenite, size, morphology, internal stresses, crystallographic orientation, dislocation density and microstructure neighborhood of austenite as well as the macroscopic loading (deformation temperature, strain rate and stress tri-axiality).

The present study aims at evaluating the stress gradients and metallurgical behaviors of the phases in highly deformed area in the crash boxes (folded area). Due to the geometry of the investigated areas and specimens size, we have used the energy dispersive setup from P61A synchrotron beamline (PETRA III, DESY, Hamburg) to scan the highly deformed area to follow the stress gradients. We will present the first results of investigations on different steel microstructures and compare them to finite element model.