The interaction of hydrogen with lattice defects in iron and steel were studied by thermal analysis and permeation experiments using gas chromatograph.
The evolution rate peak of dislocation was observed at 220℃ in thermal analysis experiments of cold worked pure iron specimens which heat treated in various conditions when heating rate is 3℃/min. The amount of hydrogen trapped at dislocation obtained from peak height measured in as cold worked specimen was smaller than that in slightly annealed specimen where the dislocation arrangement was loosened by thermal effect rather than tangled in highly cold worked state. These results show that hydrogen is trapped at the stress field of dislocation rather than dislocation core. The recovery of cold worked specimen was proceeded more rapidly when it was heat treated in hydrogen atmosphere than in vacuum, and it is verified that the dislocation mobility is increased by hydrogen. The peak temperature was not varied with the change of dislocation arrangement so it is thought that the trap activation energy of dislocation is constant.
Permeabilities and diffusivities of hydrogen in carbon steels were decreased with the increase of carbon content and the trap binding energy of ferrite-carbide interface was calculated from the difference of diffusivities. It is also obtained from the relation between hydrogen charging temperature and the amount of hydrogen trapped measured by thermal analysis. These two values were well agreed and the trap binding energy was averaged as 9.6 KJ/mol.
The evolution rate peak of iron oxide inclusion was observed at 422℃ when heating rate was 3℃/min. The trap activation energy and trap binding energy were measured as 47.2 KJ/mol and 15.7 KJ/mol, respectively.
The hydrogen energy levels around ferrite-carbide interface and iron oxide inclusion were estimated using trap activation energy and trap binding energy measured.
