EFFECT OF GRAIN SIZE AND SECOND PHASE PARTICLES ON THE HYDROGEN OCCLUSIVITY OF IRON AND STEELS.

The trapping of hydrogen by various interfaces in iron and steels has been studied. The hydrogen content of pure iron specimens was found to depend on both the extent and the nature of grain boundaries; high angle boundaries held more hydrogen than those of low angle, and thus specimens with low angle grain boundaries were less susceptible to hydrogen damage. Inclusions and thermo-mechanical treatments were also significant in determining the hydrogen pick-up in iron. A critical volume fraction of inclusions was detected, below which no hydrogen-induced cracking occurred. Ferrite/pearlite and pearlite/pearlite colony interfaces in steel were found to trap hydrogen, whereas the ferrite/cementite interface within the pearlitic colonies had little effect on the hydrogen occlusivity.