The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels

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dc.contributor.advisorBall, Anthonyen_ZA
dc.contributor.authorLeitch, John Edwarden_ZA
dc.date.accessioned2016-10-19T03:50:33Z
dc.date.available2016-10-19T03:50:33Z
dc.date.issued1987en_ZA
dc.descriptionBibliography: pages 107-108.en_ZA
dc.description.abstractThe 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.en_ZA
dc.identifier.apacitationLeitch, J. E. (1987). <i>The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels</i>. (Thesis). University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering. Retrieved from http://hdl.handle.net/11427/22176en_ZA
dc.identifier.chicagocitationLeitch, John Edward. <i>"The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels."</i> Thesis., University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 1987. http://hdl.handle.net/11427/22176en_ZA
dc.identifier.citationLeitch, J. 1987. The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Leitch, John Edward AB - 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. DA - 1987 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1987 T1 - The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels TI - The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels UR - http://hdl.handle.net/11427/22176 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/22176
dc.identifier.vancouvercitationLeitch JE. The role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steels. [Thesis]. University of Cape Town ,Faculty of Engineering & the Built Environment ,Centre for Materials Engineering, 1987 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/22176en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentCentre for Materials Engineeringen_ZA
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherSteel - Metallurgy.en_ZA
dc.subject.otherChrome steel.en_ZA
dc.subject.otherFerritic steelen_ZA
dc.subject.otherMaterials Engineeringen_ZA
dc.titleThe role of interstitial nitrogen in the precipitation hardening reactions in high-chromium ferritic steelsen_ZA
dc.typeMaster Thesis
dc.type.qualificationlevelMasters
dc.type.qualificationnameMSc (Eng)en_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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