Hydrogen trapping and hydrogen induced mechanical degradation in lab cast Fe-C-Cr alloys

This study evaluates the hydrogen trapping ability of Cr23C6 precipitates and hence its effect on the hydrogen induced mechanical degradation in laboratory cast Fe-C-Cr materials. Two main conditions are compared: an as-quenched and a quenched and tempered condition containing carbides. Three materials were cast with a variable carbon content to study the role of the carbides in alloys with variable strength level. Mechanical tests are performed on both in-situ hydrogen charged and uncharged tensile samples. The presence of carbides decreases the susceptibility to hydrogen embrittlement. Thermal desorption spectroscopy and hot/melt extraction are performed to determine which trapping sites are active. A clear correlation between the degree of hydrogen induced embrittlement and the hydrogen mobility is confirmed by determining the hydrogen diffusivity and linking it to the available trapping sites. A slightly modified temper treatment is applied to vary the carbide size and evaluate its effect on the hydrogen embrittlement resistance and the trapping ability of the present carbides.