Two strain-hardening mechanisms in nanocrystalline austenitic steel: An in situ synchrotron X-ray diffraction study

The mechanical behaviour of nanocrystalline austenitic steels with and without yttria particles was investigated using in situ synchrotron diffraction during tensile deformation. Two different strain-hardening regimes were found. The first regime can be assigned predominantly to a martensitic phase transformation, the second to deformation twinning in the fragmented retained austenite. The kinetics of martensitic phase transformation is remarkably enhanced in the nanocrystalline structure.