TRITIUM DISTRIBUTION AT THE CRACK-TIP OF HIGH-STRENGTH STEELS SUBMITTED TO STRESS-CORROSION CRACKING

The experimental results presented in this article are the first direct evidence of hydrogen diffusion in 4120 and 4130 high-strength steels undergoing a stress corrosion cracking (SCC) test with an enhancement of the hydrogen concentration at the crack tip. The hydrogen entry is evidenced by electrochemical permeation experiments performed either at the corrosion potential or under cathodic polarization in selected microstructures. The autoradiography of tritium associated with microdensitometric measurements allows measurement of the hydrogen distribution and local concentration at the crack tip of specimens undergoing SCC in a tritiated aqueous medium. The small enhancement in the tritium concentration measured at the crack tip of the 4120 steel may be a consequence of a strong contribution of trapping sites throughout the microstructure, prevailing on the effect of the stress state on the local concentration of tritium.