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Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels
High temperature deformation
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| Format: | Thesis |
| Language: | English |
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2014
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| _version_ | 1867613446632112128 |
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| access_status_str | Open Access |
| author2 | Stumpf, Waldo E. |
| author_browse | Stumpf, Waldo E. |
| author_facet | Stumpf, Waldo E. |
| collection | Thesis |
| dc_rights_str_mv | Richard Nkhoma: rnkhoma@gmail.com, University of Pretoria; Copyright original printed version: Public domain |
| description | High temperature deformation |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/41456 |
| institution | University of Pretoria (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:36:17.013Z |
| 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 |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/41456 Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels Stumpf, Waldo E. Siyasiya, Charles Witness rnkhoma@gmail.com Chimkonda Nkhoma, R.K. (Richard Kasanalowe) dynamic recrystallisation (DRX), dynamic recovery (DRV), AISI 321, constitutive equation, mean flow stress (MFS), dynamic recrystallisation to dynamic recovery transition temperature (DRTT), hot working, modelling. High temperature deformation Although the austenitic stainless steels 304 and 321 are often treated nominally as equivalents in their hot rolling characteristics, the question remains whether any subtle differences between the two allow further optimisation of their respective hot rolling schedules. The hot workability of these two types of austenitic stainless steels was compared through single-hit Gleeble simulated thermomechanical processing between 800℃ and 1200℃ while the strain rate was varied between 0.001s and 5s . It was found that the constants for the hyperbolic sinh equation for hot working of AISI 321 steel are Q = 465 kJ/mol, = 9.76 × 10 MPa , = 0.009 MPa and ! = 6.1 while for 304 steel the constants are Q = 446 kJ/mol, = 2.14 × 10 MPa , = 0.008 MPa and ! = 6.1. It is shown that the occurrence of dynamic recrystallisation starts when the Zener-Hollomon parameter Z ≈ 6.4 × 10 s for both steels but that the differences in the values of Q and A3 (the structure factor) between the two steels does lead to consistently lower steady state stresses for the steel 321 than is found in the steel 304 at the same Z values. This may, therefore, offer some scope for further optimisation of the hot rolling schedules and in particular in the mill loads of these two respective steels. A modelled constitutive equation derived from hot working tests to predict hot rolling mill loads is proposed and validated against industrial hot rolling data for AISI 321 stainless steel. Good correlation is found between the predicted Mean Flow Stress, the Zener-Hollomon Z parameter and actual industrial mill load values from mill logs if allowances are made for differences in Von Mises plane strain conversion, friction and front or back end tension. The multipass hot working behaviour of this steel was simulated through Gleeble thermomechanical compression testing with the deformation temperature varying between 1200℃ down to 800℃ and the strain rate between 0.001s -1 and 5s -1 . At strain rates greater than 0.05s -1 , dynamic recovery as a softening mechanism was dominant, increasing the dynamic recrystallisation to dynamic recovery transition temperature DRTT to higher temperatures. This implies that through extrapolation to typical industrial strain rates of about 60s -1 ,most likely no dynamic recrystallisation in plant hot rolling occurs in this steel but only dynamic recovery. Grain refinement by DRX is, therefore, unlikely in this steel under plant hot rolling conditions. Finally, mill load modelling using the hot working constitutive constants of the near-equivalent 304 instead of those specifically determined for 321, introduces measurable differences in the predicted mill loads. The use of alloy-specific hot working constants even for near-equivalent steels is, therefore, recommended. Key words: dynamic recrystallisation (DRX), dynamic recovery (DRV), AISI 321, constitutive equation, mean flow stress (MFS), dynamic recrystallisation to dynamic recovery transition temperature (DRTT), hot working, modelling. www.sciencedirect.com/science/article/pii/S0925838814002035 http://www.hanser-elibrary.com/doi/abs/10.3139/146.111093 2014-08-20T09:13:10Z 2014-08-20T09:13:10Z 2014-04-04 2014-08-20 Thesis http://hdl.handle.net/2263/41456 en Richard Nkhoma: rnkhoma@gmail.com, University of Pretoria; Copyright original printed version: Public domain application/pdf |
| spellingShingle | dynamic recrystallisation (DRX), dynamic recovery (DRV), AISI 321, constitutive equation, mean flow stress (MFS), dynamic recrystallisation to dynamic recovery transition temperature (DRTT), hot working, modelling. Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels |
| title | Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels |
| title_full | Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels |
| title_fullStr | Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels |
| title_full_unstemmed | Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels |
| title_short | Hot Working Characteristics of AISI 321 in Comparison to AISI 304 Austenitic Stainless Steels |
| title_sort | hot working characteristics of aisi 321 in comparison to aisi 304 austenitic stainless steels |
| topic | dynamic recrystallisation (DRX), dynamic recovery (DRV), AISI 321, constitutive equation, mean flow stress (MFS), dynamic recrystallisation to dynamic recovery transition temperature (DRTT), hot working, modelling. |
| url | http://hdl.handle.net/2263/41456 |