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Delta ferrite in modified 9Cr–1Mo steel weld metal
Thesis (PhD (Metallurgy))--University of Pretoria, 2024.
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University of Pretoria
2024
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| _version_ | 1867613613487816704 |
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| access_status_str | Open Access |
| author2 | Pistorius, Pieter Georg Hendrik |
| author_browse | Pistorius, Pieter Georg Hendrik |
| author_facet | Pistorius, Pieter Georg Hendrik |
| collection | Thesis |
| dc_rights_str_mv | © 2023 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD (Metallurgy))--University of Pretoria, 2024. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/99641 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:38:55.836Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2024 |
| publishDateRange | 2024 |
| publishDateSort | 2024 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/99641 Delta ferrite in modified 9Cr–1Mo steel weld metal Pistorius, Pieter Georg Hendrik sibusiso.mahlalela@up.ac.za Mahlalela, Sibusiso Samuel UCTD Sustainable Development Goals (SDGs) Modified 9Cr–1Mo (P91) steel Delta ferrite Gas–metal arc welding Direct laser deposition Thermo-Calc simulation Thesis (PhD (Metallurgy))--University of Pretoria, 2024. The role of chemical composition on the presence of δ-ferrite in P91 weld metal in the as-welded condition was studied by systematically varying five alloying elements (Cr, Ni, Mn, Si, and Mo) in 28 gas–metal arc welds. The effect of thermal treatment on the δ-ferrite content was also investigated. Metallography analysis of the as-welded beads showed that 18 of the 28 welds contained 0.3% to 6.2% δ-ferrite in martensite. Twenty of the 28 welds fully complied with chemical composition specifications, including the limit of the sum of (Mn + Ni). Of the twenty welds that complied with the AWS A5.28/A5.28M:2020 (ER90S-B9) chemical composition specification, thirteen contained δ-ferrite. Based on these results, lower specification limits for Mo and Si are proposed to ensure a fully martensitic microstructure. Empirical formulae were applied to evaluate their accuracy in predicting the P91 as-welded microstructure: ten of the 28 welds (36%) were incorrectly predicted. Based on these results, the recommended Schaeffler Creq and Kaltenhauser ferrite factor maximum limits should be lowered to 11.5 and 6, respectively, to limit the presence of δ-ferrite in P91 as-welded microstructure. Phase-transformation temperatures were evaluated against the amount of δ-ferrite in beads in the as-welded condition. It was observed that a wider (Ae4 − Ae3) temperature range was beneficial in suppressing δ-ferrite in the final as-welded microstructure. Higher peak temperatures and slower cooling rate during welding also reduced the amount of δ-ferrite in P91 weld metal. Southern African Institute for Welding Materials Science and Metallurgical Engineering PhD (Metallurgy) Unrestricted Faculty of Engineering, Built Environment and Information Technology SDG-07: Affordable and clean energy SDG-09: Industry, innovation and infrastructure SDG-12: Responsible consumption and production SDG-13: Climate action 2024-11-27T13:59:29Z 2024-11-27T13:59:29Z 2025-04 2024-10-01 Thesis * A2025 http://hdl.handle.net/2263/99641 10.25403/UPresearchdata.27448827 en © 2023 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Sustainable Development Goals (SDGs) Modified 9Cr–1Mo (P91) steel Delta ferrite Gas–metal arc welding Direct laser deposition Thermo-Calc simulation Delta ferrite in modified 9Cr–1Mo steel weld metal |
| title | Delta ferrite in modified 9Cr–1Mo steel weld metal |
| title_full | Delta ferrite in modified 9Cr–1Mo steel weld metal |
| title_fullStr | Delta ferrite in modified 9Cr–1Mo steel weld metal |
| title_full_unstemmed | Delta ferrite in modified 9Cr–1Mo steel weld metal |
| title_short | Delta ferrite in modified 9Cr–1Mo steel weld metal |
| title_sort | delta ferrite in modified 9cr 1mo steel weld metal |
| topic | UCTD Sustainable Development Goals (SDGs) Modified 9Cr–1Mo (P91) steel Delta ferrite Gas–metal arc welding Direct laser deposition Thermo-Calc simulation |
| url | http://hdl.handle.net/2263/99641 |