Modelling the effects of dissolved hydrogen and global stress on stress corrosion cracking of Fe-Ni, Cr-Ni and Fe-Cr model alloys in high temperature water

摘要

Based on a recently presented SCC model for pure nickel in high temperature nuclear environments the described numerical procedure is extended to Fe-Ni, Cr-Ni and Fe-Cr model alloys. With the local anodic path corrosion as the crack initiation phase, the corresponding oxides precipitate while the crack tip solution may acidify and establish local hydrogen reduction. Depending on the applied global stress, local plastic straining will then provide an active crack tip surface that transfers atomic hydrogen to the plastic zone ahead of the crack tip. The respective hydrogen assisted crack propagation phase is then controlled by the calculated local hydrogen reduction charge and the plastic strain distribution ahead of the crack tip. The specific results for each model alloy show that at constant dissolved oxygen increasing dissolved hydrogen contents are exhibiting peak crack growth rates at hydrogen levels decreasing both with increasing temperatures and global stress. The maximum crack growth rates decrease with increasing temperature an decreasing stress. The results are in accordance with experimental investigations regarding the effects of dissolved hydrogen on corrosion rates in high temperature water. They are explained by the interaction between the electrochemical parameters of the reactions.