A new generation of nanostructured high-carbon, silicon-rich bainitic steels offer notable strength (2000 MPa), toughness (30 MPa m1/2) and ductility (30%) in both quasi-static and dynamic loading conditions. The excellent mechanical properties arise from the combination of very fine bainitic ferrite laths with average thickness of ~50 nm and retained austenite, which undergoes TRansformation Induced Plasticity (TRIP). Hence, the strengthening mechanism of these steels is governed by the microstructural characteristic of individual constituent phases and particularly the stability of retained austenite. The in-situ neutron diffraction technique will be combined with detail microstructure (EBSD) examination to obtain comprehensive information on transformation kinetics of retained austenite over a temperature range.