Effect of Ti, Mo and Cr based precipitates on the hydrogen trapping and embrittlement of Fe–C–X Q&T alloys

• The H-trapping of Ti, Mo and Cr-carbides is studied by TDS and hot/melt extraction.
• The HE-effect on Fe–C–X (X = Ti, Mo or Cr) alloys is evaluated by tensile tests.
• Fe–C–Ti embrittled the most and Fe–C–Mo the least.
• Tempering improved the HE-susceptibility for Fe–C–Cr, but declined it for Fe–C–Ti.
• There is a clear correlation between mobile H and the H-induced ductility loss.

The present work evaluates hydrogen trapping and embrittlement (HE) for different laboratory cast Fe–C–X alloys with Ti, Mo and Cr (=X). Tempering generated X-based precipitates. The materials were examined under two conditions, as quenched and quenched and tempered. The hydrogen trapping capacity of the precipitates and matrix was investigated by thermal desorption spectroscopy (TDS), while hot and melt extraction, performed after cathodic charging, allowed to determine the diffusible and total hydrogen content, respectively. In-situ hydrogen pre-charged tensile specimens were tested to evaluate the hydrogen induced ductility loss. The different carbides exhibited a variable effect on the hydrogen embrittlement. The Fe–C–Ti material embrittled the most and tempering even increased its HE-susceptibility, whereas the opposite was observed for the Fe–C–Cr grade. Finally, the HE-resistance was best for the Fe–C–Mo alloys. Correlation between the mechanical behavior and the TDS and hot/melt extraction results was made as well.