Hydrogen trapping by carbides in steel

Carbides in steel can act as traps for hydrogen and thereby make the steel less susceptible to hydrogen embrittlement. In order to understand exactly where in the microstructure the hydrogen atoms are trapped, i.e. inside the carbide, at the carbide/matrix interface or in the stress field around the carbide, a combination of atomistic modelling and atom probe tomography (APT) will be used. To understand the phenomenon on a truly atomic scale, ab-initio calculations and Monte Carlo simulations will be carried out to predict preferential trapping sites. Modelling will also be used to predict the optimal composition of MC carbides, and model steels containing carbides with strong and weak hydrogen trapping capability will be produced. Steel samples will be charged with hydrogen, in the form of deuterium. The distribution of deuterium will then be studied using APT, which has the ability to detect the preferred location of the deuterium atoms with nearly atomic resolution. In order to perform such an experiment, equipment and processes for charging and for performing vacuum-cryo transfer into the APT instrument must first be developed. The aim is to understand the effect of carbide crystal structure, composition, size, coherency, etc., on the hydrogen trapping efficiency, which can be used in designing steels with optimal resistance toward hydrogen embrittlement. The majority of the work will be carried out by two post-docs, and the project runs for four years.