Effect of Carbon Content on the Hydrogen Diffusion in Cold Worked Iron

Abstract

The effect of cold work on the hydrogen permeation in iron specimens with two levels of carbon content (30 and 110 ppm) has been studied in the temperature range between 273 and 333 K by means of the electrochemical permeation technique. The effective hydrogen diffusivity (D_eff) in the fully annealed specimens are independent of carbon content, and expressed as D=7.69×10⁻⁸exp(−5800J/mol·RT) m²s⁻¹. The decrease of hydrogen diffusivity by cold deformation, however, is much larger in the specimen with higher carbon content. The trap density estimated from the permeation tests exhibits a linear relationship with the inverse square of the average cell size. This indicated that the reduction of hydrogen diffusivity in cold worked iron specimens depends on the dislocation density and that the difference in carbon content affects the diffusivity indirectly through the dislocation multiplication. The binding energies for the traps obtained are 23–27 kJ·mol⁻¹, and are in good agreement with that for the elastic fieled of a dislocation.