Host: The Iron and Steel Institute of Japan
Pages 197-200
V microalloying has been reported to reduce hydrogen embrittlement (HE) susceptibility by trapping hydrogen at V carbides to remove mobile hydrogen that would otherwise accumulate and lead to embrittlement. However, it is unclear whether alloy carbides can offer any benefit to HE resistance once traps saturate under high hydrogen concentrations. In this study, the HE susceptibilities of quenched and tempered 0.4C-1.0Mn-1.0Cr alloys of 1100 MPa tensile strength with and without a 0.15 wt pct V addition were compared for notched specimens hydrogen charged in situ or pre-charged. Cathodic charging was conducted in a 0.5 M H2SO4 + 100 ppm As2O3 solution with a 0.125 mA∙cm-2 applied current density. The bulk hydrogen concentration was estimated using melt extraction measurements. HE susceptibility was reduced with the addition of V for 0.5-24 h pre-charging times, demonstrating that, despite increasing hydrogen absorption, V carbide traps effectively mitigated hydrogen accumulation at the notch. In situ cathodic charging also showed that V carbides deterred embrittlement despite higher hydrogen concentration measured in the notched region of the V-added alloy following the test. These results show that, although V carbide precipitation promotes hydrogen absorption, alloy carbides effectively deter hydrogen accumulation and HE, even at the high hydrogen concentrations employed in this study. However, hydrogen can detrap from V carbides and thus reduce mechanical performance when charged specimens are held in ambient conditions for 96 h before testing.
