Impact of precipitates on the hydrogen embrittlement behavior of a V-alloyed medium-manganese austenitic stainless steel

Abstract

This paper discusses the avoidance of hydrogen embrittlement (HE) in a medium manganese stainless steel X20CrNiMnVN18-5-10. We adopted a HE-mitigation strategy that relies on improving its intrinsic resistance to hydrogen by adjusting an ultrafine microstructure (∼1.3 µm) containing a significant amount of nano-sized V- and Cr-based precipitates in the size range of 20 - ≥200 nm. The precipitation state was characterized using a high-resolution scanning transmission electron microscope. Slow strain rate tests at a strain rate of 10−6 s−1 were conducted on specimens with/without hydrogen pre-charging to evaluate the HE susceptibility. Thermal desorption analysis was applied to explore the hydrogen trapping behavior in cold-rolled, annealed and hydrogen pre-charged states. Hydrogen uptake and hydrogen desorption behaviors show a dependence on the size of precipitates. It is remarked that the large precipitates trap a larger amount of hydrogen and show a higher temperature desorption peak than the small precipitates do. The high-temperature hydrogen desorption peaks (>400 °C) indicate that the observed nano-sized precipitates provide irreversible trapping sites, where hydrogen uptake occurs. The investigated steel X20CrNiMnVN18-5-10 demonstrates an enhanced intrinsic resistance to HE in comparison to medium and high manganese as well as stainless steels. The findings suggest that microstructure engineering with sufficient number of hydrogen traps in an ultrafine-grained microstructure is an appropriate HE mitigation strategy that allows designing hydrogen-resistant advanced high strength steels.