TDA曲線の解析による高強度マルテンサイト鋼での水素侵入挙動評価

Results of thermal desorption analysis (TDA) measurement, which had been obtained on high strength martensitic steels by a research group of ISIJ, were subjected to peak separation by Gaussian distribution function to determine the amounts of trapped hydrogen; dislocation, grain boundary, vacancy and vacancy cluster. Then they were followed by the quantitative analysis with Fermi-Dirac statistics that contained pre-exponential factor representing entropy change. They are helpful in analyzing the hydrogen penetration behavior; effect of applied stress on hydrogen penetration and hydrogen pick-up during cyclic corrosion test (CCT).The effect of applied tensile stress appeared uneven over trap sites. Considering from Fermi-Dirac statistics, it is reasonable to conclude that the amounts of trapped hydrogen are not affected by the stress. At dislocation and grain boundary sites, their trap densities increased with applied stress and result in the apparent in-creases of trapped hydrogen.Hydrogen penetration behavior of trap sites was fairly reproduced using error function on the pre-strained material. Further, by applying Fermi-Dirac statistics, the state of hydrogen was determined, which was comparable to the saturation in CCT exposure of unstrained material, namely hydrogen pick-up of 0.2 ppm. It corresponds to that of 3.5 weeks exposure and almost agrees with the saturation, in the reproduced penetration behavior.