A Kinetic Approach to Hydrogen Diffusion through Steel at 100–350°C

Classical reaction kinetics has been employed to describe the movement of hydrogen in ferritic steels in the range 100–350° C. Predictions based on theory are supported by the results of experiments on three materials. The two processes of lattice diffusion of hydrogen and the release of hydrogen from traps in the metal are combined as consecutive reactions, the former being the rate-controlling step at high temperatures and the latter at low temperatures. In the intermediate region where neither process is predominant, there will be a gradual transition from one mode of reaction to another. Values for both the true lattice and the overall diffusivity coefficients are calculated in the intermediate-temperature region. It is shown that a practical implication of this theory is that it is necessary to select higher temperatures or longer times for post-heat-treatments for wrought steels and weldments in the intermediate-temperature region than had previously been anticipated.