Transformation-induced plasticity in an ultrafine-grained steel: An in situ neutron diffraction study

An ultrafine-grained steel with an average grain size of about 350nm was developed. The tensile testing at ambient temperature shows a threefold increase in the yield strength compared to its coarse-grained counterpart. Moreover, the increase in the strength was achieved without the sacrifice of the ductility due to strain-induced martensitic transformation. The evolution of lattice strains and phase fractions of the austenite and martensite phases during the deformation was investigated using in situ neutron diffraction to provide a micromechanical understanding of the transformation-induced plasticity responsible for the combination of high strength and ductility.