In situ neutron diffraction investigation of the collaborative deformation-transformation mechanism in TRIP-assisted steels at room and elevated temperatures

The deformation behaviour of two transformation induced plasticity (TRIP)-assisted steels with slightly different microstructures due to different thermo-mechanically controlled processing (TMCP) was investigated by the in situ neutron diffraction technique during tensile straining at room temperature and two elevated (50 and 100 degrees C) temperatures. The essential feature of the TRIP deformation mechanism was found to be significant stress redistribution at the yield point. The applied tensile load is redistributed within the complex TRIP-steel microstructure in such a way that the retained austenite bears a significantly larger load than the ferrite-bainite alpha-matrix. The macroscopic yielding of the steel then takes place through the simultaneous cooperative activity of the austenite-to-martensite trans-formation in the austenite phase and plastic deformation in the alpha-matrix. It is concluded that, although its volume fraction is small, the martensitically transforming retained austenite phase dispersed within the alpha-matrix governs the plastic deformation of TRIP-assisted steels. Crown Copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.