HyFerrA: Hydrogen trapping in steels with F/A interfaces

Multiphase steels are being considered as the vital material of the modern industrialized economy, where a big role is given to renewable energy sources with reduced or zero greenhouse gas emissions. High hopes are related to hydrogen (H) as a sustainable energy carrier for environmentally friendly power supply, in accordance with the European Green Deal and the Sustainable Development Goals of the United Nations. Application of high strength steels for safe generation, transportation and storage of H poses high risks related to one of the major material issues related to H-material interaction also known as H embrittlement (HE). The high strength multiphase steels with martensite and austenite phases have a higher resistivity to HE than conventional martensitic steels, though they have been found to suffer from HE as well. High H solubility in the plastic austenite phase and its transformation into the very susceptible to HE, high strength martensite phase make investigations of this phenomenon an especially complex and resource- intensive task. During this phase transformation, H and other alloying elements are non-uniformly distributed within the microstructure and in particular at the interface between the two phases. There is an experimental evidence that such interfaces play a key role in HE and serve as most likely sites for crack initiation and growth. One of our most recent investigations has revealed a very unusual behaviour showing that a multiphase steel exhibited a remarkable H accumulation when subjected to a high degree of mechanical pre- straining during continuous electrochemical charging with H. This effect has occurred only after the material has been strained during in situ H charging, and it has been absent when H charging has been done without mechanical load. This material behaviour could be directly related to the presence of the retained austenite () phase and, most likely, properties of its interfaces with the alloy matrix, which will be a subject of the present research work. The goal of this project is to determine the role of applied mechanical load and H charging in anomalous hydrogen diffusion and uptake in multiphase steels with austenite under continuous charging conditions. Successful implementation of the project is going to provide fundamental understanding of the basic mechanisms behind the observed anomalous H uptake by the austenite under applied load conditions during in situ charging. The insights obtained within the project are expected to contribute to future design of experimental and computational set-ups for studying HE in steels with retained austenite and application-specific design of new HE-resistant multiphase steels for H storage and transport applications.