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 heat affected zones (HAZ) may modify the material susceptibility to hydrogen induced cracking. In an attempt to clarify the role played by the different microstructures present in HAZ, large simulated HAZ were produced using a Gleeble machine and studied by the hydrogen electrochemical permeation technique. The method was applied without palladium coatings but the surface electrochemical conditions were strictly controlled. The permeation and outgassing rates are clearly related to the volume fraction of martensite. In ferrite-pearlite structures, the influence of small AIN- and NbC-type precipitates on permeation rate was also shown.