Hydride formation and decomposition in electrolytically charged metastable austenitic stainless steels
- Lehigh Univ., Bethlehem, PA (United States)
An investigation of phase transformations in hydrogen-charged metastable austenitic stainless steels was carried out. Solution-annealed, high-purity, ultralow-carbon Fe18Cr12Ni (305) and laboratory-heat Fe18Cr9Ni (304) stainless steels were examined. The steels were cathodically charged with hydrogen at 1, 10, and 100 mA/cm{sup 2}, at room temperature for 5 minutes to 32 hours, in an 1N H{sub 2}SO{sub 4} solution with 0.25 g/L of NaAsO{sub 2} 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 (hcp {var_epsilon}* in 305 SS and fcc {gamma}* and hcp {var_epsilon}* in 304 SS) were observed. The evidence suggests the following mechanisms for hydride formation during charging: (1) {gamma} {yields} {var_epsilon} {yields} {var_epsilon}* hydride and (2) {gamma} {yields} {gamma}* hydride. These hydrides were found to be unstable and decomposed during room-temperature aging in air by the following suggested mechanisms: (1) {var_epsilon}* hydride (hcp) {yields} expanded {var_epsilon} (hcp) phase {yields} {alpha}{prime} (bcc) phase and (2) {gamma}* hydride {yields} {gamma} phase. The transformation from {var_epsilon}* to {alpha}{prime}, however, was incomplete, and a substantial fraction of {var_epsilon} was retained. A kinetics model for hydride decomposition and the accompanying phase transformation during aging is proposed.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG02-88ER45354
- OSTI ID:
- 203516
- Journal Information:
- Metallurgical Transactions, A, Journal Name: Metallurgical Transactions, A Journal Issue: 1 Vol. 27; ISSN 0360-2133; ISSN MTTABN
- Country of Publication:
- United States
- Language:
- English
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