Hydrogen Trapping in Cold Worked High-Purity Iron

Abstract

Hydrogen trapping in deformed iron has been studied by time lag measurements based upon a double-step electrochemical permeation technique. Two types of trapping sites, TI and TII, have been confirmed to exist in iron deformed 35% by rolling. TI sites have a binding energy of 63.1 kJ/mol and a density of 1×1023/m3. Most of them annihilate by annealing below 673 K. TII sites have a binding energy of 46.4 kJ/mol and a density of 7×1023/m3. TII sites are also significantly reduced by annealing at temperatures below 573 K, while a further reduction occurs by recrystallization around 730 K. TI and TII sites are believed to be vacancies trapped by interstitial impurity atoms and core sites of dislocations, respectively. The significant reduction of TII by annealing at low temperatures suggests that the segregation of interstitial impurity atoms to dislocation-core sites precludes their occupancy by hydrogen. An another type of traps having a binding energy of about 30 kJ/mol has also been presumed to exist.