Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel
Dissertation (MEng)--University of Pretoria, 2013.
Saved in:
| Other Authors: | |
|---|---|
| Format: | Thesis |
| Language: | English |
| Published: |
University of Pretoria
2014
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613658962460672 |
|---|---|
| access_status_str | Open Access |
| author2 | Siyasiya, Charles Witness |
| author_browse | Siyasiya, Charles Witness |
| author_facet | Siyasiya, Charles Witness |
| collection | Thesis |
| dc_rights_str_mv | © 2013 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 | Dissertation (MEng)--University of Pretoria, 2013. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/40839 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:39:39.216Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2014 |
| publishDateRange | 2014 |
| publishDateSort | 2014 |
| 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:2263/40839 Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel Siyasiya, Charles Witness givenm@mintek.co.za Stumpf, Waldo E. Maruma, Mpho Given Formability XRD (NbTi)(C,N) Texture Cold rolling Annealing Ridging UCTD Dissertation (MEng)--University of Pretoria, 2013. Global warming and air pollution are the major problems facing the world today. Therefore strict environmental legislation on the emission of harmful gases from motor vehicles has forced the automobile industry to search for alternative materials or new materials for exhaust systems. In order to produce cleaner exhaust gases, the exhaust temperature needs to be increased to approximately 900oC. Therefore, exhaust manifolds are exposed repeatedly to hot gases as they are nearest to the engine requiring good oxidation resistance, thermal fatigue properties, cold workability and weldability. One such material to meet the above characteristics is AISI 441 ferritic stainless steel, a dual stabilised Ti and Nb ferritic stainless steel. Ti and Nb are added to stainless steel to stabilise C and N due to their high tendency to form carbonitrides (Ti,Nb)(C,N) and laves phase (Fe2Nb) and Fe3Nb3C. With 18% Cr content, this steel has a good corrosion resistance at elevated temperatures. Included in many applications of this steel are those requiring deep drawing and related forming operations. However, the drawability and stretchability of ferritic stainless steels is inferior to that of the more expensive austenitic stainless steels. For instance, Columbus Stainless has experienced ridging/roping problems at times during the manufacturing process of type AISI 441 ferritic stainless steel. It is believed that this problem is related to crystallographic texture of materials which have effect on formability. The R-value in FSS can be improved through optimisation of chemical composition, which includes reducing the carbon content, and processing conditions such as reducing the slab reheating temperature, increasing annealing temperature and refining the hot band grain size. Therefore the aim of this research project was firstly to investigate effect of amount of cold reduction and annealing temperature on texture evolution and its influence on formability. The as received 4.5 mm hot band steel was cold rolled by 62, 78 and 82% reductions respectively followed by isothermal annealing of each at 900oC, 950oC and 1025oC for 3 minutes. Orientation distribution function (ODF) through X-ray diffractometer (XRD) measurement was used to characterise the crystallographic texture formed in the steel using PANanalytical X’Pert PRO diffractrometer with X’celerator detector and variable divergence. Microstructures were characterised using optical microscopy and scanning electron microscope (SEM). The results show that steels that received 78% cold reduction and annealed at 1025oC recorded the highest Rm-value and lowest ΔR-value which enhances its deep drawing capability. In addition, this steel showed the highest intensity of shifted γ-fibre, notably {554}<225> and {334}<483>. It can therefore be concluded that the γ-fibre which favours deep drawing, is optimal after 78% cold reduction and annealing at 1025oC. The second objective was to investigate the effect of (Nb+Ti) content on the crystallographic texture and the subsequent formability and ridging severity. AISI 441 ferritic stainless steel with different amount of (Nb+Ti) content was used i.e. Steel A (0.26Nb+0.2Ti), Steel B (0.44Nb+0.15Ti) and steel C (0.7Nb+0.32Ti). After a strain of 10%, steels A exhibited the least resistance against surface ridging with average roughness Ra of 1.5 μm followed by steels B with an average roughness Ra of 1.1μm. Steel C showed the highest resistance to ridging with an average roughness Ra of 0.64 μm. This was attributed to the increase in carbonitrites (NbTi)(C,N) due to increased (Nb+Ti) content which acted as nucleation sites for γ-fibre. gm2014 Materials Science and Metallurgical Engineering unrestricted 2014-07-17T12:15:22Z 2014-07-17T12:15:22Z 2014-04-08 2013 Dissertation Maruma, MG 2013, Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/40839> E14/4/290/gm http://hdl.handle.net/2263/40839 en © 2013 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 | Formability XRD (NbTi)(C,N) Texture Cold rolling Annealing Ridging UCTD Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel |
| title | Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel |
| title_full | Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel |
| title_fullStr | Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel |
| title_full_unstemmed | Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel |
| title_short | Effect of composition and thermomechanical processing on the texture evolution, formability and ridging behavior of type AISI 441 ferritic stainless steel |
| title_sort | effect of composition and thermomechanical processing on the texture evolution formability and ridging behavior of type aisi 441 ferritic stainless steel |
| topic | Formability XRD (NbTi)(C,N) Texture Cold rolling Annealing Ridging UCTD |
| url | http://hdl.handle.net/2263/40839 |