Investigation of the effect of carbon on the reversible hydrogen trapping behavior in lab-cast martensitic Fe C steels

Abstract

The present study evaluates the active hydrogen trapping sites of three martensitic Fe C alloys with a carbon content of 0.2 wt%, 0.4 wt% and 1.1 wt% by thermal desorption spectroscopy (TDS). The absence of additional alloying elements reduces the microstructural complexity and allows focussing on the carbon effects only. The TDS spectra are extrapolated towards cryogenic temperatures, enabling to deconvolute the desorption spectrum in Gaussian curves corresponding with H detrapping from lattice positions, dislocations, high angle grain boundaries and cementite. The activation energy for hydrogen desorption and the amount of H trapped at each site is further profoundly evaluated. It is found that the carbon content controls the amount of hydrogen trapped at dislocations and its activation energy for detrapping decreases with increasing carbon content. The trap density of the high angle grain boundaries is controlled only by the prior austenitic grain size and the corresponding activation energy for H desorption is independent of the carbon content. Hydrogen trapping at cementite was only detected in the samples with the highest carbon content (Fe-1.1C). • Interaction between hydrogen and martensitic Fe C steels is investigated by TDS. • The main hydrogen trapping sites are dislocations and high angle grain boundaries. • C content strongly influences the H trapping characteristics at dislocations. • Amount of H trapped at HAGBs merely depends on the prior austenitic grain size. • H trapping at cementite is only relevant for hypereutectoid compositions.