Hydrogen embrittlement (HE) is a complex phenomenon that affects a lot of metals characterized by a degradation of the mechanical properties. UNS S31603 with a minimum yield strength (YS) of 25 ksi (170 MPa), is frequently used for hydrogen applications due to its low susceptibility to HE, which is promoted by a high austenite stability. However, its use is limited when higher strength is required. Here, nitrogen-strengthened (UNS S20910), CrMnN and high interstitial (HIS) austenitic stainless steels in solution-annealed condition displaying YS higher than 55 ksi (380 MPa) could be part of a solution. The strength of these steels can be further increased by strain-hardening to YS higher than 758 MPa (110 ksi).
This paper discusses the susceptibility of high strength UNS S20910, CrMnN and HIS to hydrogen embrittlement. Characterization of microstructure, mechanical properties, and HE was performed for the materials in solution-annealed and strain-hardened condition. Slow strain rate tests (SSRT) were carried out in hydrogen atmosphere at 10 MPa (100 bar) and room temperature. UNS S20910 and CrMnN with a YS higher than 850 MPa (123 ksi) are resistant against hydrogen embrittlement showing a ductile fracture mode. On the other hand, HIS-steels are susceptible to HE with a loss in ductility.
Hydrogen is considered an alternative energy source for fossil fuels, and consequently the requirements for materials used in hydrogen applications have been increased. These materials need to have high resistance against hydrogen embrittlement (HE).1 HE, that affects several metallic materials, is a complex phenomenon characterized by a degradation of the mechanical properties, in particular ductility. Austenitic stainless steels (ASS), especially UNS S31603, are frequently used for hydrogen applications due to their lower HE compared with other stainless steels. Hydrogen embrittlement susceptibility depends on different factors, like Ni content, Ni equivalent (Nieq), Md30, austenite stability and stacking fault energy (SFE).2-6 Austenitic stainless steels with Ni content below 12.5 wt%. are commonly considered being susceptible to HE.3,4 Austenite stability against strain induced α′-martensite can be determined by Md30 temperature and Nieq. Md30 is the lowest temperature where 50 % strain induced α’-martensite is formed at a true strain of 0.3.7 It can be calculated by Equation (1) according to Nohara.8 Austenitic stainless steels with Md30 > –80 °C have low stability of austenite phase and are more prone to HE.3,4 Nieq shows the relative effect of alloying elements on the austenite stability and the tendency of forming the austenite phase. It can be determined by Equation (2).9 Ni equivalent should be higher than 27 % to avoid hydrogen embrittlement. 2,4 Even though, Nieq and Md30, that are calculated with the nominal chemical composition, give an assessment of austenite stability and HE susceptibility, they cannot predict HE for some stable austenitic grades. Finally, stacking fault energy and deformation mechanisms have as well an influence on the HE resistance.4,6,10 Austenitic stainless steels with SFE lower than 40 mJ/m2 will expected to exhibit a degradation on the HE resistance.11 However, the initial deformation mode can have an important parameter to determine the HE susceptibility.4
