Low temperature paraequilibrium nitriding is an effective method to enhance surface hardness and corrosion resistance in austenitic stainless steels, provided that equilibrium nitride formation is suppressed. Following the standard double HCl “activation” procedure developed by Swagelok Company to remove the passivating Cr2O3-rich native oxide, nitriding was done in a gas mixture of NH3/H2/N2. Three processing parameters (nitriding temperature, nitriding activity and duration) were controlled independently to understand both thermodynamic and kinetic aspects of the process.
Supersaturated nitrogen interstitials (7 ~ 25 at.%) were introduced into 316L stainless steel samples, which yielded a lattice expansion ranging from 1% to 10%. Room temperature ferromagnetism in expanded austenite in stainless steels was then induced due to the great increase in Fe-Fe interatomic distance. A combined of XRD, MFM and EBSD study revealed that the minimum lattice expansion required for ferromagnetism is ~ 5%. A nitrogen content of ~ 14 at.% was estimated (by AES) as the threshold required for the paramagnetic-to-ferromagnetic transition. The correlation of lattice parameter expansion and nitrogen content indicates that transition from paramagnetic austenite to ferromagnetic austenite played a role in the highly distorted lattice parameters of nitrogen-enriched expanded austenite.
Orientation-dependent nitrogen surface concentration and case depth were investigated using EBSD orientation mapping and AES cross-sectional line scans. In particular, <100>-oriented grains demonstrated a higher surface nitrogen concentration and a deeper case depth as compared to <111>-oriented grains.
Three different scenarios of low-temperature gas-phase nitrocarburizing processes were designed and compared. Dual-layered expanded austenites were obtained. The concentration depth profiles of nitrogen and carbon atoms can all be described as an outer layer of nitrogen-enriched region, with carbon atoms accumulated at the diffusion front of nitrogen. The total case depth obtained is mainly determined by the diffusion time of carbon. Grazing angle XRD and TEM were employed to study the precipitates formed after nitrocarburizing.
","abstract_html":"<p>Low temperature paraequilibrium nitriding is an effective method to enhance surface hardness and corrosion resistance in austenitic stainless steels, provided that equilibrium nitride formation is suppressed. Following the standard double HCl “activation” procedure developed by Swagelok Company to remove the passivating Cr2O3-rich native oxide, nitriding was done in a gas mixture of NH3/H2/N2. Three processing parameters (nitriding temperature, nitriding activity and duration) were controlled independently to understand both thermodynamic and kinetic aspects of the process.</p><p>Supersaturated nitrogen interstitials (7 ~ 25 at.%) were introduced into 316L stainless steel samples, which yielded a lattice expansion ranging from 1% to 10%. Room temperature ferromagnetism in expanded austenite in stainless steels was then induced due to the great increase in Fe-Fe interatomic distance. A combined of XRD, MFM and EBSD study revealed that the minimum lattice expansion required for ferromagnetism is ~ 5%. A nitrogen content of ~ 14 at.% was estimated (by AES) as the threshold required for the paramagnetic-to-ferromagnetic transition. The correlation of lattice parameter expansion and nitrogen content indicates that transition from paramagnetic austenite to ferromagnetic austenite played a role in the highly distorted lattice parameters of nitrogen-enriched expanded austenite.</p><p>Orientation-dependent nitrogen surface concentration and case depth were investigated using EBSD orientation mapping and AES cross-sectional line scans. In particular, <100>-oriented grains demonstrated a higher surface nitrogen concentration and a deeper case depth as compared to <111>-oriented grains. </p><p>Three different scenarios of low-temperature gas-phase nitrocarburizing processes were designed and compared. Dual-layered expanded austenites were obtained. The concentration depth profiles of nitrogen and carbon atoms can all be described as an outer layer of nitrogen-enriched region, with carbon atoms accumulated at the diffusion front of nitrogen. The total case depth obtained is mainly determined by the diffusion time of carbon. Grazing angle XRD and TEM were employed to study the precipitates formed after nitrocarburizing.</p>","abstract_has_math":false,"creators":["Wu, Dandan"],"institution":"Case Western Reserve University School of Graduate Studies","degree_name":"Doctor of Philosophy","degree_level":"doctoral","degree_discipline":"Materials Science and Engineering","degree_department":null,"school":null,"contributors":["Heuer, Arthur"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2013,"date_issued":"2013-03-12","date_published":"2013-03-12","updated_at":"2026-07-24T03:35:52Z","subjects":["Materials Science"],"languages":["English"],"rights":["unrestricted","This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws."],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://rave.ohiolink.edu/etdc/view?acc_num=case1346900583","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Heuer, Arthur"]},{"key":"dc:creator","label":"Author","values":["Wu, Dandan"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2013-03-12"]},{"key":"dc:publisher","label":"Institution","values":["Case Western Reserve University School of Graduate Studies / OhioLINK"]},{"key":"dc:type","label":"Dc Type","values":["Electronic Thesis or Dissertation"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Materials Science and Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["doctoral"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Doctor of Philosophy"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["Case Western Reserve University School of Graduate Studies"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Materials Science"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["English"]},{"key":"dc:rights","label":"Dc Rights","values":["unrestricted","This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws."]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://rave.ohiolink.edu/etdc/view?acc_num=case1346900583"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Low temperature paraequilibrium nitriding is an effective method to enhance surface hardness and corrosion resistance in austenitic stainless steels, provided that equilibrium nitride formation is suppressed. Following the standard double HCl “activation” procedure developed by Swagelok Company to remove the passivating Cr2O3-rich native oxide, nitriding was done in a gas mixture of NH3/H2/N2. Three processing parameters (nitriding temperature, nitriding activity and duration) were controlled independently to understand both thermodynamic and kinetic aspects of the process.
Supersaturated nitrogen interstitials (7 ~ 25 at.%) were introduced into 316L stainless steel samples, which yielded a lattice expansion ranging from 1% to 10%. Room temperature ferromagnetism in expanded austenite in stainless steels was then induced due to the great increase in Fe-Fe interatomic distance. A combined of XRD, MFM and EBSD study revealed that the minimum lattice expansion required for ferromagnetism is ~ 5%. A nitrogen content of ~ 14 at.% was estimated (by AES) as the threshold required for the paramagnetic-to-ferromagnetic transition. The correlation of lattice parameter expansion and nitrogen content indicates that transition from paramagnetic austenite to ferromagnetic austenite played a role in the highly distorted lattice parameters of nitrogen-enriched expanded austenite.
Orientation-dependent nitrogen surface concentration and case depth were investigated using EBSD orientation mapping and AES cross-sectional line scans. In particular, <100>-oriented grains demonstrated a higher surface nitrogen concentration and a deeper case depth as compared to <111>-oriented grains.
Three different scenarios of low-temperature gas-phase nitrocarburizing processes were designed and compared. Dual-layered expanded austenites were obtained. The concentration depth profiles of nitrogen and carbon atoms can all be described as an outer layer of nitrogen-enriched region, with carbon atoms accumulated at the diffusion front of nitrogen. The total case depth obtained is mainly determined by the diffusion time of carbon. Grazing angle XRD and TEM were employed to study the precipitates formed after nitrocarburizing.
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Supersaturated nitrogen interstitials (7 ~ 25 at.%) were introduced into 316L stainless steel samples, which yielded a lattice expansion ranging from 1% to 10%. Room temperature ferromagnetism in expanded austenite in stainless steels was then induced due to the great increase in Fe-Fe interatomic distance. A combined of XRD, MFM and EBSD study revealed that the minimum lattice expansion required for ferromagnetism is ~ 5%. A nitrogen content of ~ 14 at.% was estimated (by AES) as the threshold required for the paramagnetic-to-ferromagnetic transition. The correlation of lattice parameter expansion and nitrogen content indicates that transition from paramagnetic austenite to ferromagnetic austenite played a role in the highly distorted lattice parameters of nitrogen-enriched expanded austenite.
Orientation-dependent nitrogen surface concentration and case depth were investigated using EBSD orientation mapping and AES cross-sectional line scans. In particular, <100>-oriented grains demonstrated a higher surface nitrogen concentration and a deeper case depth as compared to <111>-oriented grains.
Three different scenarios of low-temperature gas-phase nitrocarburizing processes were designed and compared. Dual-layered expanded austenites were obtained. The concentration depth profiles of nitrogen and carbon atoms can all be described as an outer layer of nitrogen-enriched region, with carbon atoms accumulated at the diffusion front of nitrogen. The total case depth obtained is mainly determined by the diffusion time of carbon. Grazing angle XRD and TEM were employed to study the precipitates formed after nitrocarburizing.
"],"dc:format":["application/pdf","8.65 MB"],"dc:identifier":["http://rave.ohiolink.edu/etdc/view?acc_num=case1346900583"],"dc:language":["English"],"dc:publisher":["Case Western Reserve University School of Graduate Studies / OhioLINK"],"dc:rights":["unrestricted","This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws."],"dc:subject":["Materials Science"],"dc:title":["Low-Temperature Gas-Phase Nitriding and Nitrocarburizing of 316L Austenitic Stainless Steel"],"dc:type":["Electronic Thesis or Dissertation"],"thesis:degree_discipline":["Materials Science and Engineering"],"thesis:degree_level":["doctoral"],"thesis:degree_name":["Doctor of Philosophy"],"thesis:institution_name":["Case Western Reserve University School of Graduate Studies"]},"updated_at":"2026-07-24T03:35:52Z"}