Hydrogen trapping energy levels and hydrogen diffusion at high and low strain rates (~10⁵ s⁻¹ and 10⁻⁷ s⁻¹) in lean duplex stainless steel

Duplex stainless steels (DSS) alloys are high strength steels combined with ductility and excellent resistance to stress corrosion cracking, which makes them attractive for the pressure vessels or underwater pipelines industries. Hydrogen embrittlement (HE) is caused by the action of hydrogen in combination with residual or applied stress and can lead to the mechanical degradation of a material. Dynamic and quasi-static experiments were conducted at room temperature and strain rates of 10⁵ s⁻¹ and 10⁻⁷ s⁻¹ on gas-phase hydrogen charged DSS. Hydrogen trapping in the various defects and its effect on the mechanical properties are discussed in details. A linear model of Lee and Lee was applied to calculate the trap activation energies. It was found that lower strain rates (~10⁻⁷ s⁻¹) will create less deep hydrogen trapping energies values; ~40% lower than in non-loaded sample. In addition, higher dynamic pressure will create higher trapping energy sites for hydrogen. Based on our experimental studies we developed an analytical model for hydrogen trapping. We have found that the strain rate has a direct influence on both hydrogen diffusion and hydrogen potential trapping sites. During deformation processes created at low strain rates (~10⁻⁷ s⁻¹) hydrogen has enough time to migrate with dislocations from deeper potential trapping sites to lower potential trapping sites.