Effects of Different Austenitising Conditions on the Strength–Ductility Balance in a High-Strength Low-Alloy Steel
Abstract
:1. Introduction
2. Materials and Experimental Procedure
3. Result and Discussion
3.1. Microstructural Characteristics
3.2. Mechanical Properties
3.3. Effect of Austenitising Conditions on Microstructural Properties
3.4. Nano-Sized Precipitate Structure
3.5. Strengthening Mechanism
4. Conclusions
- (1)
- When the hot-rolled sample was reheated to 15 °C above the austenitic transition temperature for 20 min and then cooled to 25 °C below the austenitic transition temperature for 25 min, more low-angle boundaries were formed, and the smallest effective grain size was achieved.
- (2)
- Compared with the hot-rolled sample, the tensile and yield strengths of the 810-20 sample (the sample was first heated to 15 °C above the austenite transition temperature for 20 min, then cooled to 25 °C below the austenite transition point for 25 min, and finally air-cooled to room temperature) increased by 10.2% and 3.1%, respectively, while the elongation increased by 162.5%, exhibiting a good strength–ductility balance.
- (3)
- By adopting an appropriate austenitisation process, precipitates can refine crystalline grains during austenitisation, thus enhancing the comprehensive mechanical properties of the steel.
- (4)
- Excessively high austenitisation temperatures coarsen the steel microstructure, decreasing the microstructural refinement efficiency via precipitation and consequently weakening the comprehensive mechanical properties of the steel.
- (5)
- After heat treatment, a large number of fine particles with sizes of approximately 5–12 nm are dispersed in the matrix, and a few precipitates have nearly spherical shapes with sizes of approximately 102–130 nm. The precipitate exhibits a core–shell structure, in which the Fe–C compound forms the shell, and the Ti–C compound forms the core.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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C | Si | Mn | P | Ti | Cr | S | Mo | Nb | Fe |
---|---|---|---|---|---|---|---|---|---|
0.3 | 0.25 | 1.39 | 0.007 | 0.15 | 0.3 | 0.003 | 0.19 | 0.04 | Bal. |
Sample | Rot-rolled | 809-10 | 809-20 | 824-10 | 824-20 | 839-10 | 839-20 |
---|---|---|---|---|---|---|---|
Yield strength/MPa | 564 | 443 | 583 | 551 | 445 | 416 | 463 |
Tensile strength/MPa | 751 | 693 | 843 | 798 | 775 | 705 | 767 |
Elongation/% | 8 | 25 | 21 | 16.5 | 20 | 18.5 | 19.5 |
Sample | Average Effective Grain Size/μm | Dislocation Density/nm−2 | Average Large Precipitate Size/nm | Average Small Precipitate Size/nm |
---|---|---|---|---|
Rot-rolled | 6.26 | 1.26 × 10−2 | 109.58 | 8.56 |
809-10 | 4.35 | 0.491 × 10−2 | 113.43 | 8.83 |
809-20 | 3.68 | 0.906 × 10−2 | 115.68 | 9.28 |
824-20 | 5.35 | 0.641 × 10−2 | 121.32 | 12.21 |
839-20 | 7.26 | 0.437 × 10−2 | 126.74 | 13.52 |
Sample | Austenite Transformation Fraction/% | |
---|---|---|
By Model in Reference [19] | By JMatPro | |
809-10 | 41.5 | 49.1 |
809-20 | 87.6 | 93 |
824-20 | 100 | 100 |
839-20 | 100 | 100 |
Sample | Precipitation Hardening/MPa | Grain Refining Hardening/MPa | Dislocation Hardening/MPa | σy |
---|---|---|---|---|
Rot-rolled | 50.32 | 279.7 | 224.6 | 595.36 |
809-10 | 64.99 | 335.6 | 126.18 | 566.23 |
809-20 | 65.91 | 364.8 | 171.36 | 643.36 |
824-20 | 66.19 | 302.6 | 144.10 | 556.75 |
839-20 | 66.43 | 259.8 | 119.02 | 496.65 |
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Luo, L.; Dong, D.; Jiang, Z.; Chen, T.; Li, Y. Effects of Different Austenitising Conditions on the Strength–Ductility Balance in a High-Strength Low-Alloy Steel. Metals 2024, 14, 850. https://doi.org/10.3390/met14080850
Luo L, Dong D, Jiang Z, Chen T, Li Y. Effects of Different Austenitising Conditions on the Strength–Ductility Balance in a High-Strength Low-Alloy Steel. Metals. 2024; 14(8):850. https://doi.org/10.3390/met14080850
Chicago/Turabian StyleLuo, Liang, Duyu Dong, Zheng Jiang, Tao Chen, and Yimin Li. 2024. "Effects of Different Austenitising Conditions on the Strength–Ductility Balance in a High-Strength Low-Alloy Steel" Metals 14, no. 8: 850. https://doi.org/10.3390/met14080850