State of hydrogen in cold rolled pure iron that is hydrogen charged at room temperature to 120

Combining the peak separation of TDA (Thermal Desorption Analysis) curve with Fermi-Dirac statistics, the published TDA curves on a cold-rolled pure iron, which were hydrogen-charged by exposure to gaseous hydrogen or cathodic polarization, have been analyzed. When hydrogen is charged at 60 and 90℃ for 4 hours by cathodic polar-ization, dis-location trap density is decreased by segregation of carbon atoms along dislocation. With the prolonged exposure to gaseous hydrogen up to 90 hours, the decreased trap site density is restored and the trapping ability is recovered. This recovery is certainly due to the removal of carbon atoms fa-cilitated by methane forming reaction with hydrogen. Accordingly, the state of hydrogen is transitioned, whether by cathodic polarization or gaseous hydrogen exposure. In both cases, hydrogen is reallocated in ac-cordance with the equilibrium Fermi-Dirac relation at room temperature, showing that the details of cooling practice do not impinge. Other than dislocation trap, grain boundary or vacancy trap is also affected by tem-perature and duration of hydrogen charging; both temperature and duration rendered grain boundary and vacancy traps increased, except-ing the decrease of grain boundary trap site density by prolonged exposure to gaseous hydrogen. Present analyzing method can further predict the state of hydrogen at the high temper-ature of hydrogen charging. The predicted equilibrium hy-drogen concentration in lattice site is in accordance with the result obtained by da Silva upon thermodynamic consideration.