Transformation induced plasticity (TRIP) steels, known for their high strain hardening and postponed necking, are indispensable materials in industrial sectors such as transportation, power generation, automotive and aerospace. To optimize shaping operations and component performance, simulation tools capable of predicting the impact of different stress states and strain paths on TRIP micromechanics and TRIP component behaviour are increasingly vital. The multi-level material laws employed involve features on multiple length-scales to model polycrystal aggregate behaviour based on elementary deformation mechanisms in individual grains. Calibration and validation of these models, whether phenomenological or physics-based, need detailed reference data, ideally from in-situ experiments probing multiple scales at the same time.

In-situ synchrotron X-ray diffraction (SXRD) is a powerful tool for this purpose, as it provides access to phase fractions, transformation kinetics, crystallographic texture, lattice strains, load partitioning among phases, defect densities and other microstructural features, simultaneously. Using in-situ SXRD we recorded such comprehensive dataset for a metastable austenitic stainless steel, which exhibits TRIP due to the strain-induced formation of α’ and ε martensites. The focus of the present contribution lies on the part of the dataset related to quantifying the influence of temperature and uniaxial load direction on strain partitioning and load sharing between differently orientated families of austenite and martensite grains. Particular attention is paid to two aspects: (i) the impacts of volume change and mechanical driving force linked to the martensitic transformations; (ii) the evolution of the dislocation density in austenite. Both aspects correlate well with observed tension-compression asymmetries, and they naturally explain the load direction dependent strain hardening of austenite. Next to providing fundamental insights into the multi-scale micromechanics of TRIP steel, those findings help develop new crystal plasticity laws, which are sensitive to load direction and temperature.