Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces
The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, <i>T<sub>min</sub></i>...
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| Format: | Article |
| Language: | English |
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MDPI AG
2022-12-01
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| Series: | Metals |
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| Online Access: | https://www.mdpi.com/2075-4701/12/12/2155 |
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| author | Dannis Rorisang Nkarapa Maubane Roelf Johannes Mostert Kevin Mark Banks |
| author_facet | Dannis Rorisang Nkarapa Maubane Roelf Johannes Mostert Kevin Mark Banks |
| author_sort | Dannis Rorisang Nkarapa Maubane |
| collection | DOAJ |
| description | The influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, <i>T<sub>min</sub></i>, rebounding to various maximum temperatures, <i>T<sub>max</sub></i>, followed by secondary cooling. The negative effect of a low <i>T<sub>min</sub></i> on hot ductility could not be readily reversed, even at relatively high temperatures. Quantitative metallography was employed to study the evolution of the microstructure during rebounding and secondary cooling. Following primary cooling to temperatures just above the <i>Ar<sub>3</sub></i>, thin films of allotriomorphic ferrite formed on the austenite grain boundaries. These films did not completely transform to austenite during the rebound at 3 °C/s up to temperatures as high as 1130 °C and persisted during slow secondary cooling up to the simulated straightening operation. Whilst dilatometry did not indicate the presence of ferrite after high rebound temperatures, metallography provided clear evidence of its existence, albeit in very small quantities. Coincident with the ferrite at these high temperatures was the predicted (TC-PRISMA) grain boundary precipitation of AlN in bcc iron during the rebound from a <i>T<sub>min</sub></i> of 730 °C. Importantly no thin ferrite films were observed, and AlN precipitation was not predicted to occur when <i>T<sub>min</sub></i> was restricted to 830 °C. Cooling below this temperature promotes austenite grain boundary ferrite films and AlN precipitation, which both increase the risk of corner cracking in C–Mn steels. |
| first_indexed | 2024-03-09T16:06:40Z |
| format | Article |
| id | doaj.art-f09d1cd6184145ba9165d0a6e1a34e81 |
| institution | Directory Open Access Journal |
| issn | 2075-4701 |
| language | English |
| last_indexed | 2024-03-09T16:06:40Z |
| publishDate | 2022-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Metals |
| spelling | doaj.art-f09d1cd6184145ba9165d0a6e1a34e812023-11-24T16:41:50ZengMDPI AGMetals2075-47012022-12-011212215510.3390/met12122155Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner SurfacesDannis Rorisang Nkarapa Maubane0Roelf Johannes Mostert1Kevin Mark Banks2Department of Materials Science and Metallurgical Engineering, University of Pretoria, Pretoria 0002, South AfricaDepartment of Materials Science and Metallurgical Engineering, University of Pretoria, Pretoria 0002, South AfricaDepartment of Materials Science and Metallurgical Engineering, University of Pretoria, Pretoria 0002, South AfricaThe influence of primary cooling and rebound temperature at C–Mn slab corner surfaces during continuous casting on ferrite film transformation and AlN precipitation was investigated. Laboratory simulations included primary cooling to minimum temperature, <i>T<sub>min</sub></i>, rebounding to various maximum temperatures, <i>T<sub>max</sub></i>, followed by secondary cooling. The negative effect of a low <i>T<sub>min</sub></i> on hot ductility could not be readily reversed, even at relatively high temperatures. Quantitative metallography was employed to study the evolution of the microstructure during rebounding and secondary cooling. Following primary cooling to temperatures just above the <i>Ar<sub>3</sub></i>, thin films of allotriomorphic ferrite formed on the austenite grain boundaries. These films did not completely transform to austenite during the rebound at 3 °C/s up to temperatures as high as 1130 °C and persisted during slow secondary cooling up to the simulated straightening operation. Whilst dilatometry did not indicate the presence of ferrite after high rebound temperatures, metallography provided clear evidence of its existence, albeit in very small quantities. Coincident with the ferrite at these high temperatures was the predicted (TC-PRISMA) grain boundary precipitation of AlN in bcc iron during the rebound from a <i>T<sub>min</sub></i> of 730 °C. Importantly no thin ferrite films were observed, and AlN precipitation was not predicted to occur when <i>T<sub>min</sub></i> was restricted to 830 °C. Cooling below this temperature promotes austenite grain boundary ferrite films and AlN precipitation, which both increase the risk of corner cracking in C–Mn steels.https://www.mdpi.com/2075-4701/12/12/2155continuous castingprimary coolingrebound temperatureferrite filmsAlN |
| spellingShingle | Dannis Rorisang Nkarapa Maubane Roelf Johannes Mostert Kevin Mark Banks Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces Metals continuous casting primary cooling rebound temperature ferrite films AlN |
| title | Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces |
| title_full | Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces |
| title_fullStr | Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces |
| title_full_unstemmed | Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces |
| title_short | Re-Austenitisation of Thin Ferrite Films in C–Mn Steels during Thermal Rebound at Continuously Cast Slab Corner Surfaces |
| title_sort | re austenitisation of thin ferrite films in c mn steels during thermal rebound at continuously cast slab corner surfaces |
| topic | continuous casting primary cooling rebound temperature ferrite films AlN |
| url | https://www.mdpi.com/2075-4701/12/12/2155 |
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