THE ELECTROCHEMICAL PERMEATION OF HYDROGEN IN STEELS WITHOUT PALLADIUM COATING .2. STUDY OF THE INFLUENCE OF MICROSTRUCTURE ON HYDROGEN DIFFUSION

The presence of graded microstructures such as those encountered in he at affected zones (HAZ) may modify the material susceptibility to hydr ogen induced cracking. In an attempt to clarify the role played by the different microstructures present in HAZ, large simulated HAZ were pr oduced using a Gleeble machine and studied by the hydrogen electrochem ical permeation technique. The method was applied without palladium co atings but the surface electrochemical conditions were strictly contro lled. The permeation and outgassing rates are clearly related to the v olume fraction of martensite. In ferrite-pearlite structures, the infl uence of small AIN- and NbC-type precipitates on permeation rate was a lso shown.