New insight into the role of austenite grain size in the bainitic transformation of low carbon steel
Bainitic transformation plays a crucial role in determining the mechanical properties of low carbon steel, especially for applications in the automotive industry. Regarding the effect of prior austenite grain size (PAGS), extensive studies have focused on the acceleration or deceleration of bainitic...
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Elsevier
2025-09-01
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| Series: | Journal of Materials Research and Technology |
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| author | Feilong Liu Shaojie Song Lei Wang Kexing Song Feng Liu |
| author_facet | Feilong Liu Shaojie Song Lei Wang Kexing Song Feng Liu |
| author_sort | Feilong Liu |
| collection | DOAJ |
| description | Bainitic transformation plays a crucial role in determining the mechanical properties of low carbon steel, especially for applications in the automotive industry. Regarding the effect of prior austenite grain size (PAGS), extensive studies have focused on the acceleration or deceleration of bainitic transformation kinetics but have relatively neglected the formation of hierarchical microstructures. Through a conjoint analysis of transformation kinetics and variant grouping, a new insight into the role of PAGS in the bainitic transformation behavior of carbide-free low carbon steel is proposed. A systematic study involving three distribution states of PAGS obtained in different austenitizing temperatures reveals significant differences in bainitic transformation kinetics and heterogeneous microstructures, but little influence on final mechanical properties. Different from the traditional consideration of thermodynamic and kinetic constraints on bainitic transformation, the strain accommodation arising from crystallographic variant grouping, as another degree of freedom, can greatly alter the effect of PAGS. Through the separate fitting of the kinetic model for different PAGSs, larger grains exhibit lower activation energy for autocatalytic nucleation, QA, facilitating the activation of multiple variant grouping to accommodate strain accumulations, as compared to smaller grains. Although the kinetic model assumes constant strain energy, according to the thermo-kinetic correlation, the role of variant accommodation is mainly reflected in the change of QA, whose decrease corresponds to the strain energy release and multiple variant formation. Finally, the similar evolution of driving forces and generalized stability reveals a negligible difference in the mechanical properties. |
| format | Article |
| id | doaj-art-23d8400276d44c6e92d492b245fea830 |
| institution | DOAJ |
| issn | 2238-7854 |
| language | English |
| publishDate | 2025-09-01 |
| publisher | Elsevier |
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| series | Journal of Materials Research and Technology |
| spelling | doaj-art-23d8400276d44c6e92d492b245fea8302025-08-20T02:49:55ZengElsevierJournal of Materials Research and Technology2238-78542025-09-0138997101310.1016/j.jmrt.2025.07.271New insight into the role of austenite grain size in the bainitic transformation of low carbon steelFeilong Liu0Shaojie Song1Lei Wang2Kexing Song3Feng Liu4State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, 710072, ChinaState Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, 710072, China; Corresponding author. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, 710072, China.State Key Laboratory of Performance and Structure Safety of Petroleum Tubular Goods and Equipment Materials, CNPC Tubular Goods Research Institute, Xi'an, 710077, ChinaHenan Academy of Sciences, Zhengzhou, 450046, ChinaState Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, 710072, China; Analytical & Testing Center, Northwestern Polytechnical University, Xi'an, 710072, China; Corresponding author. State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an, 710072, China.Bainitic transformation plays a crucial role in determining the mechanical properties of low carbon steel, especially for applications in the automotive industry. Regarding the effect of prior austenite grain size (PAGS), extensive studies have focused on the acceleration or deceleration of bainitic transformation kinetics but have relatively neglected the formation of hierarchical microstructures. Through a conjoint analysis of transformation kinetics and variant grouping, a new insight into the role of PAGS in the bainitic transformation behavior of carbide-free low carbon steel is proposed. A systematic study involving three distribution states of PAGS obtained in different austenitizing temperatures reveals significant differences in bainitic transformation kinetics and heterogeneous microstructures, but little influence on final mechanical properties. Different from the traditional consideration of thermodynamic and kinetic constraints on bainitic transformation, the strain accommodation arising from crystallographic variant grouping, as another degree of freedom, can greatly alter the effect of PAGS. Through the separate fitting of the kinetic model for different PAGSs, larger grains exhibit lower activation energy for autocatalytic nucleation, QA, facilitating the activation of multiple variant grouping to accommodate strain accumulations, as compared to smaller grains. Although the kinetic model assumes constant strain energy, according to the thermo-kinetic correlation, the role of variant accommodation is mainly reflected in the change of QA, whose decrease corresponds to the strain energy release and multiple variant formation. Finally, the similar evolution of driving forces and generalized stability reveals a negligible difference in the mechanical properties.http://www.sciencedirect.com/science/article/pii/S2238785425019283Bainitic transformationLow-carbon steelAustenite grain sizeVariant selectionMechanical properties |
| spellingShingle | Feilong Liu Shaojie Song Lei Wang Kexing Song Feng Liu New insight into the role of austenite grain size in the bainitic transformation of low carbon steel Journal of Materials Research and Technology Bainitic transformation Low-carbon steel Austenite grain size Variant selection Mechanical properties |
| title | New insight into the role of austenite grain size in the bainitic transformation of low carbon steel |
| title_full | New insight into the role of austenite grain size in the bainitic transformation of low carbon steel |
| title_fullStr | New insight into the role of austenite grain size in the bainitic transformation of low carbon steel |
| title_full_unstemmed | New insight into the role of austenite grain size in the bainitic transformation of low carbon steel |
| title_short | New insight into the role of austenite grain size in the bainitic transformation of low carbon steel |
| title_sort | new insight into the role of austenite grain size in the bainitic transformation of low carbon steel |
| topic | Bainitic transformation Low-carbon steel Austenite grain size Variant selection Mechanical properties |
| url | http://www.sciencedirect.com/science/article/pii/S2238785425019283 |
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