Measurement of the diffusion coefficient in Fe-18.5Cr-10Ni alloy through diffusion couple experiments in a hydrogen environment

To elucidate the mechanism underlying the reduction in creep strength of Type 304 austenitic stainless steel in hydrogen environments, diffusion couple experiments were conducted to measure the diffusion coefficient of an Fe-18.5Cr-10Ni (mass%) alloy with a chemical composition similar to that of Type 304. The experiments were performed in atmospheric pressure argon and hydrogen at temperatures ranging from 1073 K to 1273 K. The presence of hydrogen was found to lower the activation energy for lattice diffusion, thereby increasing the diffusion coefficient at temperatures below 1223 K. Extrapolation to 873 K suggests that the diffusion coefficient in pure hydrogen was 8.3 times greater than in argon. Notably, this ratio aligns well with the previously reported increase in minimum creep rate by a factor of 8.1 at the same temperature. These findings provide strong evidence that hydrogen-enhanced diffusion promotes dislocation climb, thereby accelerating creep rate and reducing creep strength.