Assessing neighbourhood effects on martensitic transformations in complex-phase steels

Transformation-Induced Plasticity and complex-phase steels exploit deformation-induced austenite-to-martensite transformations to achieve both exceptional strength and ductility. Prior grain-averaged measurements during beamtime MA4750 have demonstrated the sensitivity of austenite stability, a key predictor of mechanical properties, to austenite grain orientation, size and neighbourhood configuration. However, deviations from these Type-II relationships were observed, - for example, the orientation of martensite grains was correctly predicted from the parent austenite grain orientation and the Type-I stress state of the material, but these predictions failed 25% of the time, which was attributed to the presence of Type-III sub-grain strain fields that modify the local martensite orientation selection criteria. Scanning 3D X-Ray Diffraction and DCT will therefore be used in-situ to measure these features over a range of complex-phase steel alloy compositions and deformation levels.