Size effect on evaluation of detrapping rate constants for hydrogen in thermal desorption analysis of ferritic steels

Ebihara, Kenichi   ; Kaburaki, Hideo; Takai, Kenichi*

In order to understand the mechanism of hydrogen(H) embrittlement it is necessary to grasp properly the H state in steels. In the thermal desorption analysis, the H state is deduced from thermal desorption spectra which are obtained by measuring hydrogen desorbed from a steel specimen heated at a constant rate. However, because the desorption spectra include the influence of experimental conditions and of initial H distribution as well as information of the H state, the spectra must be interpreted using the numerical simulation. In the presentation, we examined the influence of the initial H distribution, which varies according to experimental conditions, on the specimen size dependence of the method to evaluate the detrapping rate constant from experimental spectra. As a result, though the influence of the initial distribution becomes remarkable when the size is large, its influence was very small in the range less than 2mm for iron and less than 8mm for tempered martensitic steels.