Influence of hydrogen on the low cycle fatigue performance of P91 steel

The present work aims to assess the influence of hydrogen on strain controlled low cycle fatigue (LCF) properties of P91 steel. Specimens were electrochemically charged using H2SO4 solution, subsequently uniaxial tensile and LCF tests were performed at ambient temperature. An increase in strength and reduction in elongation are noticed for hydrogen charged samples relative to as received or uncharged specimens. Hydrogenated specimens depict drastic reduction in fatigue life as compared to the uncharged specimens. Irrespective of imposed strain amplitude, P91 steel show cyclic softening nature throughout its life. The peak stress amplitude and rate of cyclic softening for hydrogenated specimens are found to be more than the as received specimens at all strain amplitudes. The magnitude of proportional limit from master curve depicts that as received specimen exhibit near Masing behavior whereas hydrogenated specimens reveal non-Masing behavior. Local misorientation analyses carried out by electron back scattered diffraction technique are correlated with the evolution of local plastic strain and substructural development. The fracture morphology of tensile test transformed from dimple failure for uncharged specimen to quasi cleavage fracture for hydrogenated specimens. Finite element simulation considering Chaboche kinematic hardening rule is utilized to simulate the cyclic stress strain behavior of as received and hydrogenated specimens. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.