Hydrogen embrittlement of super duplex stainless steel – Towards understanding the effects of microstructure and strain. (5th July 2018)

• Record Type: Journal Article
• Authors: Örnek, Cem; Reccagni, Pierfranco; Kivisäkk, Ulf; Bettini, Eleonora; Engelberg, Dirk L.; Pan, Jinshan
• Is Part Of: International journal of hydrogen energy. Volume 43:Number 27(2018)
• Page Start: 12543
• Page End: 12555
• Publication Date: 2018-07-05
• Subjects: Super duplex stainless steel -- Hydrogen embrittlement -- Load partitioning -- Volta potential -- Austenite spacing; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2018.05.028
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: The effects of austenite spacing, hydrogen charging, and applied tensile strain on the local Volta potential evolution and micro-deformation behaviour of grade 2507 (UNS S32750) super duplex stainless steel were studied. A novel in-situ methodological approach using Digital Image Correlation (DIC) and Scanning Kelvin Probe Force Microscopy (SKPFM) was employed. The microstructure with small austenite spacing showed load partitioning of tensile micro-strains to the austenite during elastic loading, with the ferrite then taking up most tensile strain at large plastic deformation. The opposite trend was seen when the microstructure was pre-charged with hydrogen, with more intense strain localisation formed due to local hydrogen hardening. The hydrogen-charged microstructure with large austenite spacing showed a contrasting micro-mechanical response, resulting in heterogeneous strain localisation with high strain intensities in both phases in the elastic regime. The austenite was hydrogen-hardened, whereas the ferrite became more strain-hardened. SKPFM measured Volta potentials revealed the development of local cathodic sites in the ferrite associated with hydrogen damage (blister), with anodic sites related to trapped hydrogen and/or micro voids in the microstructure with small austenite spacing. Discrete cathodic sites with large Volta potential variations across the ferrite were seen in the coarse-grained microstructure, indicating enhanced susceptibility to micro-galvanic activity. Microstructures with large austenite spacing were more susceptible to hydrogen embrittlement, related to the development of tensile strains in the ferrite. Highlights: Load partitioning between ferrite and austenite was influenced by austenite spacing. Tensile strains developed in large ferrite grains with austenite being compressive. Compressive strains developed in small ferrite grains with austenite being tensile. Hydrogen charging caused local loss of electrochemical nobility. Reason for hydrogen embrittlement is the tensile nature of the ferrite.