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RESEARCH PRODUCT

Localized hydrogen cracking in the austenitic phase of a duplex stainless steel

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The aim of this study is to investigate the role of hydrogen on the mechanical behavior of an austenitic phase, in the particular situation of duplex stainless steels. In these duplex alloys, in presence of hydrogen, the ferritic phase is embrittled by hydrogen and the resistance to cracking is mainly related to the behavior of the austenitic phase. Thus, a discussion of the role of hydrogen at the crack tip of a duplex alloy (as function of the microstructure) has been proposed by T. Perng and C.J. Altester after experiments conducted in gaseous environment. A similar experimental approach has been followed in this study; slow strain rate tests (SSRT) have been performed on duplex stainless steels in gaseous environments for low hydrogen charging conditions. The main question is then related to the conditions for hydrogen entry and embrittlement of the austenitic phase ({gamma}). Because hydrogen is spread everywhere in the ferritic matrix ({alpha}), it was asked if the behavior of the austenitic phase of the duplex was comparable to that of a purely austenitic sample during hydrogen charging. Critical experiments have been conducted to answer this question. SSRT (strain rate = 10{sup {minus}6}s{sup {minus}1}) were performed on duplex stainless steelsmore » in a pressure vessel under 30 bar of hydrogen or deuterium at room temperature. Complementary chemical analysis by Secondary Ionic Mass Spectroscopy (SIMS) allowed to image the spatial distribution of deuterium as function of the microstructure. The role of hydrogen will be then mainly illustrated on the basis of microscopic examinations of the crack path transition from the ferritic to the austenitic grains, and discussed through the corrosion enhanced plasticity model proposed by T. Magnin for SCC in ductile materials.« less