Hydrogen trapping in heat treated and deformed Armco iron

The purpose of this research was to investigate the influence of microstructure of Armco iron on hydrogen trapping by analyzing the trapping ability of grain boundaries and dislocations. Hydrogen traps were introduced into the material by systematically subjecting it to various grades of heat treatment and mechanical deformation. By combining different treatment steps (annealing at different temperatures, cold rolling at various deformation degrees, severe plastic deformation), a wide range of different grain sizes and dislocation densities was created. Microstructural characterization and electrochemical permeation experiments were performed to gain information on the diffusivity of hydrogen in the material and the influence of traps on the diffusivity. An experimental setup according to Devanathan and Stachurski was used. By combining the information on the microstructure obtained from the material characterization with the experimental results, the trapping ability of microstructural features were evaluated. Dislocations have a strong impact on diffusion and hydrogen trapping, while grain boundaries only show this effect in small grain size regions. In specimens with grain sizes in the micrometer range and above, no influence of grain boundaries on diffusion was observed.