Abstract
The amount of trapped hydrogen was determined with the aid of Gaussian distribution function, to study the state of hydrogen. In CCT (cyclic corrosion test), hydrogen absorption is cyclically interrupted, and this causes the delay of hydrogen saturation. The V alloyed steel, which contains strong hydrogen trap sites, desorbs hydrogen limitedly: It attains the equilibrium state to the environment in rather short-term exposure to CCT environment. Com-bining the amount of the strongly trapped hydrogen with Fermi-Dirac statis-tics, the hydrogen occupation at lattice site (the occupancy, in short) was successfully determined as 4×10-7. This value is not affected by the kind of steel or the amount of pre-straining; it only depends to the environment. In the case of immersion in ammonium thiocyanate aqueous solution, the occu-pancy has a power law relationship with the concentration of the solution and this allows to determine the concentration of ammonium thiocyanate, which is equivalent to CCT exposure, as 0.5%. The experimental methods with this hydrogen charging solution were additionally explored for evaluat-ing the hydrogen embrittlement. (170 words)
