Study of the Hydrogen diffusion and trapping mechanisms into quenched and tempered HSLA steels using electrochemical permeation technique

摘要

Hydrogen embrittlement may be responsible for premature failure of steels when exposed to hydrogen environment (H-2S, cathodic protection .. .)• Different mechanisms have been described in literature. Despite this fact, hydrogen diffusion and trapping phenomenon remain misunderstood. The purpose of this article is to contribute to the understanding of the processes of hydrogen diffusion and trapping in high strength steels, expecting to discriminate critical parameters for the susceptibility to hydrogen embrittlement. Investigations were carried out on quenched and tempered martensitic Fe-C-Mo and Fe-C-Cr steels, differing by their chemical composition and microstructure. Hydrogen diffusion was studied within an acid media (H-2SO-4) by using an electrochemical permeation setup under a cathodic charging. The influence of charging conditions at ambient temperature shows a relation between the apparent diffusion coefficient D-app and the apparent subsurface concentration of hydrogen C-oapp, associated with hydrogen diffusion and/or with hydrogen trapping into the material. Dislocations were determined to be the major trapping site into the material with an activation energy about 0.60eV and the amount of trapping sites about 1.1 l×l0~25m"3 for the Fe-C-Mo steel and 0.59×l0~25m~(-3)for the Fe-C-Cr steel. At the macroscopic scale, precipitates don't seem to have a significant impact on the trapping process based on the electrochemical permeation technique.