Effect of interface between cementite and ferrite on diffusion of hydrogen in carbon steels

Abstract

Diffusion coefficient of hydrogen in 0 approx. 0.6 mass% carbon steels with spheroidized cementite-ferrite and pearlite-ferrite structures have been measured by the electrochemical permeation method at 278 approx. 318 K. The temperature and carbon concentration dependence of the diffusion coefficients has been discussed by using a simple trapping model. The diffusivity of hydrogen is lowered with increasing carbon concentration and depends on the micro-structure. This is caused by the trapping effects of cementite-ferrite interfaces and dislocations. The binding energy between cementite-ferrite interface and a hydrogen atom is estimated to be slightly less for the planar cementite than that for the spherical cementite.