Tolouei, Ehsan, Saadati, Mohammad, Morin, Jean -Benoit, Garcia-Mateo, Carlos et Jahazi, Mohammad.
2025.
« Influence of bainitic transformation temperature on microstructure evolution during isothermal holding and subsequent cooling ».
Materials Chemistry and Physics, vol. 345.
Prévisualisation |
PDF
Jahazi-M-2025-31235.pdf - Version publiée Licence d'utilisation : Creative Commons CC BY-NC-ND. Télécharger (12MB) | Prévisualisation |
Résumé
Modified mold steels have recently gained attention as a novel approach in steel grades due to their high-performance applications. In this study, high-resolution dilatometry was used to study the isothermal bainitic transformation of a medium-carbon low-alloy steel after full austenitization at 900 °C, followed by austempering for 3 h at temperatures ranging from 380 to 450 °C. The results showed that no bainitic phase transformation occurred at 450 °C, while an incomplete transformation was observed at all lower tested temperatures, and martensitic transformation occurred upon cooling at the final stage. Increasing the austempering temperature from 380 °C to 425 °C resulted in a lower volume fraction of bainite and a higher amount of martensite, whereas at 450 °C, a full lath martensite microstructure formed during final cooling. Electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) analyses revealed that increasing the isothermal holding temperature led to increased thickness of the bainitic blocks and a higher volume fraction of martensite. Vickers hardness increased from 412 to 500 HV between 380 and 450 °C holding temperatures. This increase was attributed to the phase volume fraction, the carbon content of martensite, and the thickness of bainitic ferrite blocks. Nanoindentation tests were conducted on different martensitic and bainitic regions to compare the influence of isothermal holding temperature on the characteristics of the phases. The results indicated that as the isothermal temperature increased, the carbon content of martensite decreased, leading to a reduction in the nanohardness of the martensitic regions from 8.3 GPa at 400 °C to 7.8 GPa at 425 °C and 6.9 GPa at 450 °C. Furthermore, the average block thickness of bainitic ferrite increased from 0.71 μm to 1.98 μm as the isothermal temperature was raised from 380 °C to 425 °C, resulting in a decrease in nanohardness from 6.3 to 5.4 GPa. These findings are interpreted in terms of the evolution of bainitic block thickness and the carbon content of martensite at different austempering temperatures, as well as their impact on the hardness of the phases.
| Type de document: | Article publié dans une revue, révisé par les pairs |
|---|---|
| Professeur: | Professeur Jahazi, Mohammad |
| Affiliation: | Génie mécanique |
| Date de dépôt: | 30 juill. 2025 13:24 |
| Dernière modification: | 13 août 2025 21:55 |
| URI: | https://espace2.etsmtl.ca/id/eprint/31235 |
Actions (Authentification requise)
 |
Dernière vérification avant le dépôt |