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The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels
Bibliography: pages 107-108.
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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Centre for Materials Engineering
2016
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| _version_ | 1867613181666394112 |
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| access_status_str | Open Access |
| author | Leitch, John Edward |
| author2 | Ball, Anthony |
| author_browse | Ball, Anthony Leitch, John Edward |
| author_facet | Ball, Anthony Leitch, John Edward |
| author_sort | Leitch, John Edward |
| collection | Thesis |
| description | Bibliography: pages 107-108. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/22176 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:03.909Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| publisher | Centre for Materials Engineering |
| publisherStr | Centre for Materials Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/22176 The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels Leitch, John Edward Ball, Anthony Steel - Metallurgy. Chrome steel. Ferritic steel Materials Engineering Bibliography: pages 107-108. The effects of exposure to temperatures in the range 475 - 800°C on the hardness and associated microstructure of high chromium ferritic steels has been investigated. Low-carbon 26Cr-1Mo steels containing 0,02 - 0,04% nitrogen were found to constitute an age hardening system when quenched from a temperature of nitrogen solubility and exposed at temperatures in the range 600 - 700°C. TEM observations on thin foils revealed that hardening was associated with the formation of a high density of Cr-N zones. These grew on over-ageing into disc-shaped Cr-N precipitates situated on {100} lattice planes, and ultimately became large incoherent precipitates. Ageing at 475°C and 550°C produced hardening due to the formation of chromium-rich ferrite phases α' as a result of the miscibility gap in the Fe-Cr phase diagram. However the presence of interstitial nitrogen in solution in the steel considerably reduced the rate of hardening, especially at 475°C. TEM examination confirmed that this effect was due to the formation of Cr-N zones in preference to α'. This type of decomposition occurs by a mechanism of nucleation and growth, forming zones similar to those formed during an ageing at 600°C. When depleted of interstitial nitrogen, through precipitation at 800°C or through zone formation at 475°C, the specimens aged at 475°C underwent spinodal decomposition. Thus nitrogen in solid solution was found to have a significant effect on the 475°C hardening reaction. Precision X-ray diffraction measurements revealed the presence of secondary diffraction peaks associated with the Bragg peaks, which comfirmed the formation of Cr-rich phases during ageing at 475°C. The calculated associated lattice parameter measurements allowed estimates of the compositions of the decomposition phases to be made. These were calculated to be about 6-18% Cr in the Fe-rich and 60-80% Cr in the Cr-rich phases of the 26Cr-1Mo steel. 2016-10-19T03:50:33Z 2016-10-19T03:50:33Z 1987 Master Thesis Masters MSc (Eng) http://hdl.handle.net/11427/22176 eng application/pdf Centre for Materials Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Steel - Metallurgy. Chrome steel. Ferritic steel Materials Engineering Leitch, John Edward The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels |
| thesis_degree_str | Master's |
| title | The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels |
| title_full | The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels |
| title_fullStr | The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels |
| title_full_unstemmed | The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels |
| title_short | The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels |
| title_sort | role of interstitial nitrogen in the precipitation hardening reactions in high chromium ferritic steels |
| topic | Steel - Metallurgy. Chrome steel. Ferritic steel Materials Engineering |
| url | http://hdl.handle.net/11427/22176 |
| work_keys_str_mv | AT leitchjohnedward theroleofinterstitialnitrogenintheprecipitationhardeningreactionsinhighchromiumferriticsteels AT leitchjohnedward roleofinterstitialnitrogenintheprecipitationhardeningreactionsinhighchromiumferriticsteels |