Exploring unified peak separation of TDA curves by gaussian distribution function and quantitative analysis of the state of hydrogen

Abstract

Thermal Desorption Analysis (TDA) was conducted at multiple research institutions on common specimens, after hydrogen charging with various methods. The specimens were SCM435 steel with/without pre-straining and Vanadium alloyed steel (V steel). Hydrogen charging methods were cathodic charging, soaking in FIP solution and exposure to cyclic corrosion test. All the TDA spectra (TDA curves) were separated systematically by Gaussian distribution function with unified parameters that are independent to method of hydrogen charging or research institute. They were basically composed of hydrogen trapped by cementite other than dislocation and grain boundary. The pre-strained SCM435 steel contains additional hydrogen trap sites of vacancy and vacancy cluster together with micro-void. The V steel contains further two types of trap sites, regarding two types of V carbide. The amount of trapped hydrogen was able to be analyzed quantitatively by Fermi-Dirac statistics considering entropy change as pre-exponential factor. It was shown to be controlled mostly by de-trapping process and should be changed according to the binding energy of trap site. This qualitative analysis was favorable for restoring the released hydrogen before TDA measurement.