Observation of hydrogen distribution in high-strength steel

“The diffusible hydrogen” in Cr-Mo steels are observed with autoradiography technique. Specimens with “the diffusible hydrogen” are prepared by an electrochemical cathodic charging method and those without “the diffusible hydrogen” by annealing at 373 K after charging hydrogen. TEM autoradiographs suggests, by the developed silver grains, that the hydrogen trapping sites are the grain boundary and internal interface of ferrite-cementite and ferrite-lath structure. After keeping the sample at 373 K, the silver grains disappeared. Most of hydrogen trapping sites release almost all the hydrogen at 373 K. It is clear that these sites of high-strength steels supplies “the diffusible hydrogen”. Hydrogen absorption characteristics of quench hardening tempering Cr-Mo steels have been evaluated by thermal desorption spectrometry (TDS). From tritium electron microscopic autoradiography and TDS analysis, the lower temperature (360 K–370 K) peaks show “the diffusing hydrogen” which is released a few days. “The diffusible hydrogen” from trapping sites such as the internal interface of ferrite-cementite or ferrite-lath structure are distinguished to “the diffusing hydrogen.”