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Hydride formation and decomposition in electrolytically charged metastable austenitic stainless steels

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Abstract

An investigation of phase transformations in hydrogen-charged metastable austenitic stainless steels was carried out. Solution-annealed, high-purity, ultralow-carbon Fel8Crl2Ni (305) and laboratory-heat Fel8Cr9Ni (304) stainless steels were examined. The steels were cathodically charged with hydrogen at 1, 10, and 100 mA/cm2, at room temperature for 5 minutes to 32 hours, in an lN H2SO4 solution with 0.25 g/L of NaAsO2 added as a hydrogen recombination poison. Changes in microstructure and hydrogen damage that resulted from charging and subsequent room-temperature aging were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Hydrides from hydrogen charging (hep ε* in 305 SS and fcc γ* and hcp ε* in 304 SS) were observed. The evidence suggests the following mechanisms for hydride formation during charging: (1)γ → ε → ε* hydride and (2) γ → γ* hydride. These hydrides were found to be unstable and decomposed during room-temperature aging in air by the following suggested mechanisms: (1)ε* hydride (hcp) → expanded ε (hcp) phase →α′ (bcc) phase and (2) γ* hydride →γ phase. The transformation from ε* toα′, however, was incomplete, and a substantial fraction of ε was retained. A kinetics model for hydride decomposition and the accompanying phase transformation during aging is proposed.

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Authors and Affiliations

  1. Zettlemoyer Center for Surface Studies, Lehigh University, 18015, Bethlehem, PA

    Shuchun Chen (Post doctoral Fellow) & Ming Gao (Principal Research Scientist)

  2. Department of Mechanical Engineering and Mechanics, Lehigh University, 18015, Bethlehem, PA

    Robert P. Wei (Professor and Chairman)

Authors
  1. Shuchun Chen
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  2. Ming Gao
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  3. Robert P. Wei
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Chen, S., Gao, M. & Wei, R.P. Hydride formation and decomposition in electrolytically charged metastable austenitic stainless steels. Metall Mater Trans A 27, 29–40 (1996). https://doi.org/10.1007/BF02647744

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  • DOI: https://doi.org/10.1007/BF02647744

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