Hydrogen Trapping Characteristics and Mechanical Degradation in a Duplex Stainless Steel

Abstract

We investigated the hydrogen behaviors and corresponding mechanical degradation in the duplex stainless steel under the ex-situ and in-situ cathodic charging condition. In the ex-situ condition, where the hydrogen charging was conducted prior to the slow strain tensile test, the hydrogen uptake linearly increased with the charging time. The absorbed hydrogen was thought to be trapped at dislocation and grain boundary in ferrite at early stage of cathodic charging, but the ferrite-austenite interface gradually involved in the hydrogen trapping at the prolonged charging time, leading to the increase of trap activation energy as the charging time elapsed. When the cathodic charging was conducted during the slow strain tensile test, i.e. in-situ condition, the hydrogen uptake was remarkably accelerated and the hydrogen penetrated more deeply into the steel interior. It is believed to be attributed to the transport of hydrogen atoms from the surface by gliding dislocations. The elongation loss in the duplex stainless steel became less sensitive to the hydrogen content as the charging time increased and more than 60% of ductility was preserved even with diffusible hydrogen content around 50 ppm, which represented a remarkable resistance to the hydrogen embrittlement compared to those in the conventional high strength steels.