The kinetics of hydrogen attack of steels

Abstract

The hydrogen attack of steel involves the formation of methane bubbles along the grain boundaries and their subsequent link-up to form fissures. This paper presents a detailed model for the kinetics of growth of such methane bubbles. The model considers two parallel processes which can control the growth-one involving the bubble growth by direct power-law creep and the other involving combinations of surface diffusion, grain boundary diffusion and matrix accommodation processes. The proposed model is more general and complete than the earlier ones and considers for the first time the possibility of bubble growth being controlled by surface diffusion and accommodation processes. The predictions of the model are shown to compare well with the experimental results obtained in our lab and with the literature data. The model also indicates the relative importance of lower carbon activity and increased creep stength of steel to its hydrogen attack resistance.