By forming sheet metal using a non-proportional biaxial strain path, an improvement to the overall ductility by a factor of 2 is possible against conventional, proportional loading. This anomalous effect has been attributed to the activation of new slip systems, though has only been predicted with crystal plasticity modelling. Two grades of high strength steels will be studied using HRPD, each in a series of pre-strained conditions having followed a range of non-proportional biaxial strain paths. Each deformed condition will be measured in a number of orientations, including measurements parallel to the principal deformation axes. Uniquely, HRPD will enable both ferrite and martensite reflections to be measured, allowing the measurement of dislocation densities from broadened line profiles and strain partitioning to one or more of the phases present.