Characterisation and understanding of TRIP steels

The aim of this article is to understand the static and dynamic tensile behaviour of a high strength low alloy TRIP steel based on the evolution of the retained austenite ratio. Quantification of retained austenite has been done using a x-ray quantitative method treating diffraction patterns like a powder pattern. The determination of the phase volume fraction by Mössbauer spectroscopy has been used to complete XRD determination taking advantage of being insensitive to texture. In the case of TRIP steels as well as for the bainite transformation, the Mössbauer spectroscopy gives rise to the interstitial content of the retained austenite which to a large extent, controls the TRIP effect. Most of the time, the relationship between the transformation of retained austenite to martensite (gradual strain-dependent phase transformation process) and mechanical properties are obtained for static tensile conditions. In the present paper, the time dependence of the transformation of retained austenite to martensite during high speed tensile impact testing has been analysed in parallel with the results obtained for static conditions. The gradual transformation with increasing strain rate has been considered taking into account the effect of transformed martensite on strain hardening and stress