| To investigate the behavior of hydrogen in dual phase steels, stress relaxation test and hydrogen permeation test have been performed. The dual phase steels were heat-treated in two different ways, an intermediate air cooling and an intermediate quenching, to change martensite volume fraction and morphology. The electrochemical permeation results showed that ferrite-martensite interfaces and martensite lattices were major hydrogen trap sites. The results of stress relaxation tests were as follows: at the low initial strain, hardening was observed as the results of hydrogen-precipitate(martensite)-dislocation interactions but at the high initial strain, softening was occurred because of the growth of microvoid. Hydrogen embrittlement was completely reversible ; after removal of the hydrogen by anodic desorption at +200㎷ for 20 hours, the total elongation was the same before the hydrogen charging. |
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