Use of quantitative metallography in the evaluation of hydrogen action during martensitic transformations

Experiments based on image analysis method and electrochemical potentiostat ic tests were performed with particular attention to the influence of hydro gen on the stabilisation of austenite of Fe-32 wt.%Ni alloy. This alloy exh ibits great hydrogen absorption capacity (25 wt. ppm) and this presence mod ifies the martensitic transformation essentially at temperatures near M-S ( -40 degrees C). In the whole range of the quenching temperatures, the diffe rence between the volume fraction of martensite, measured on specimens with hydrogen or without hydrogen, is constant. It was found that the value of the interfacial area of the martensite plate groups S-V is the best paramet er describing the interfacial area between martensite and austenite. It was also found that there is a general relationship, expressed by a linear fun ction, between this morphological parameter and an anodic current I. (C) 19 99 Elsevier Science S.A. All rights reserved.