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dc.contributor.advisorFindley, Kip Owen
dc.contributor.advisorCho, Lawrence
dc.contributor.authorKathayat, Pawan
dc.date.accessioned2023-10-25T18:12:46Z
dc.date.available2023-10-25T18:12:46Z
dc.date.issued2023
dc.identifierKathayat_mines_0052N_12573.pdf
dc.identifierT 9504
dc.identifier.urihttps://hdl.handle.net/11124/178478
dc.descriptionIncludes bibliographical references.
dc.description2023 Spring.
dc.description.abstractHydrogen is a potential fuel source for automotive and heavy equipment applications, with the only byproduct being water; it has also been used as an alternative to coal for the carbon-free, sustainable manufacturing of “green” iron and steel. One challenging task for implementing hydrogen technology is the infrastructure cost. The alloys widely used for hydrogen fueling infrastructure are austenitic stainless steels because of their high resistance against hydrogen embrittlement. These alloys have a high nickel (Ni) content, the cost of which is relatively high. It is, therefore, essential to develop lower-cost options without significantly lowering the hydrogen embrittlement resistance and mechanical properties. In this study, high manganese (Mn) austenitic alloys were designed as an alternative to high Ni austenitic stainless steel alloys because the cost of Mn is substantially lower than Ni. In addition, Mn, similar to Ni, is a powerful austenite stabilizer. Two heats of high Mn alloys with different stacking fault energies (SFE) of ⁓29 mJ·m-2 and 49 mJ·m-2 were acquired, and on the basis of their hydrogen performance, a new vanadium (V)-microalloyed high Mn alloy was designed. The V-microalloyed high Mn alloy composition was designed to achieve a stacking fault energy above 39 mJ·m-2 to avoid planar slip deformation mechanisms, including deformation-induced twinning and ε-martensite formation. V was added to the designed alloy for thermomechanical processing and potential precipitate strengthening. Post-processing parameters such as cold working and cold working in conjunction with aging were performed with the V-microalloyed high Mn steel. Hydrogen embrittlement characteristics of the designed high Mn steels having different SFE values were compared against 316L stainless steel, which was received in a cold-rolled condition. Hydrogen embrittlement sensitivity was investigated using circular notch tensile specimens cathodically charged with hydrogen in a 0.05M NaOH electrolytic solution. The 316L stainless steel exhibited no notch strength loss, and the fracture surfaces showed ductile fracture features regardless of the testing environment, which validated its high hydrogen embrittlement resistance. The high Mn alloys with SFE of ⁓29 mJ·m-2 and 49 mJ·m-2 had notch strength losses of 11 pct and 6 pct, respectively. When tested in hydrogen, the high Mn steel with low SFE exhibited transgranular (brittle) fracture, whereas the high Mn steel with high SFE exhibited only ductile fracture, similar to the 316L stainless steel. The ε-martensite phase was detected in the high Mn steel with SFE of ⁓29 mJ·m-2 condition after tensile deformation, which is consistent with its lower SFE. The V-microalloyed high Mn steel in the as-hot-rolled condition had a notch strength loss of 17 pct, and demonstrated intergranular (brittle) fracture with some ductile fracture features, i.e. dimples, observed near the notch root of the fractured specimen. The V-microalloyed high Mn steel in the cold worked condition had notch strength loss of 5 pct, and showed brittle fracture. The V-microalloyed high Mn steel in the cold worked and aged condition indicated no notch strength loss in hydrogen, and the fracture surface showed ductile features at the root notch, indicating comparable performance to 316L stainless steel.
dc.format.mediumborn digital
dc.format.mediummasters theses
dc.languageEnglish
dc.language.isoeng
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2023 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.titleMicrostructural engineering of Mn alloyed austenitic steel for hydrogen storage and delivery
dc.typeText
dc.date.updated2023-10-18T07:07:33Z
dc.contributor.committeememberSpeer, J. G.
dc.contributor.committeememberDe Moor, Emmanuel
thesis.degree.nameMaster of Science (M.S.)
thesis.degree.levelMasters
thesis.degree.disciplineMetallurgical and Materials Engineering
thesis.degree.grantorColorado School of Mines


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