Hydrogen trapping phenomena in iron and steel was investigated by thermal analysis and permeation experiments. To see the hydrogen trapping effect in one type of trapping site, one type of trapping site was isolated.
Evolution rate peaks of thermal analysis were observed at 112℃, 215℃, 305℃ in pure iron and 116℃, 205℃, 387℃ in carbon steel respectively, when the hydrogen charged specimen with various defects were heated at constant heating rate of 2.6℃/min. Analysis suggests that in pure iron the evolution rate peak at 112℃ corresponds to hydrogen release from grain boundary, 215℃, dislocation, 305℃ microvoid and in carbon steel 116℃, ferrite-cementite interface, 205℃, dislocation. The activation energies for evolution of the trapped hydrogen from grain biundary, dislocation, microvoid, and ferrite-cementite were found to be 4.1 kcal/mole, 6.4 kcal/mole, 8.4 kcal/mole and 4.4 kcal/mole respectively. They were determined experimentally from the changes of measured peak temperatures at different heating rate.
Trapping site - hydrogen binding energies determined by permeation experiment are 6.3 kcal/mole and 6.9 kcal/mole for dislocation and microvoid respectively.
Hydrogen energy level around trapping site is suggested from trap activation energy and trapping site - hydrogen binding energy calculated.
It was also observed that most of hydrogen trapped in dislocation if the relative density of specimen is greater than 98.95% and in microvoids if less than 98.95%. From experimental results, it is suggested hydrogen exists in microvoid as molecule.
Below 300℃, total hydrogen solubility of pure iron is greater than lattice hydrogen equilibrium solubility extrapolated from high temperature and lattice hydrogen equilibrium solubility in pure iron follows Sievert's law.
Apparent hydrogen diffusivity determined by permeation experiment increases as applied hydrogen pressure increases and this phenomena can be explained by the model considered trapping rate and detrapping rate from trapping site.
