Enhancing the strength and toughness of martensite–bainite multiphase microstructure in 2 GPa-grade ultra-high-strength steel via low-temperature tempering.
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| Title: | Enhancing the strength and toughness of martensite–bainite multiphase microstructure in 2 GPa-grade ultra-high-strength steel via low-temperature tempering. |
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| Authors: | Gu, Yanfeng1,2 (AUTHOR), Song, Yanli1,2 (AUTHOR) ylsong@whut.edu.cn, Huang, Zongbin3 (AUTHOR) zongbin.huang@sgmw.com.cn, Lu, Jue1,2 (AUTHOR), Li, Ye1,2 (AUTHOR), Lu, Dongzhen1,2 (AUTHOR) |
| Source: | Journal of Materials Science. Jul2026, Vol. 61 Issue 28, p20292-20316. 25p. |
| Subjects: | Tempering, Carbides, Bainite, Mechanical behavior of materials, Martensite, High strength steel, Microstructure, Tensile strength |
| Abstract: | To address the challenge of imbalanced microstructural strength and toughness in ultra-high strength steel (UHSS) following hot stamping, this work investigates the effect of low-temperature tempering on the martensite–bainite (M–B) multiphase microstructure of 34MnB5 steel obtained via isothermal quenching. By systematically varying tempering temperatures (170 °C/270 °C/370 °C) and durations (10 min/20 min/30 min), combined with uniaxial tensile testing, Vickers hardness measurements, and multi-scale microstructural characterization, the influence of low-temperature tempering on microstructural evolution and strength-toughness matching in 2 GPa-grade steel was comprehensively investigated. Results indicate that 10-min tempering at 170 °C yields optimal comprehensive mechanical properties. Compared to isothermal quenching, this treatment significantly enhances strength-ductility matching, with the product of strength and elongation increased from 18340.7 to 20284.9 MPa% (a 10.6% increase), yield strength rose from 1445 to 1514 MPa (a 4.8% increase), and total elongation improved from 9.4 to 10.9% (a 16.0% increase). Microstructural analysis indicates that ε-carbides (average diameter ~9.58 nm) and granular carbides (average diameter ~99.6 nm) precipitated under the optimal tempering process (170 °C for 10 min) effectively pin dislocations, while martensitic lath interfaces inhibit long-range migration of dislocations. Their synergistic action homogenizes dislocation distribution, significantly alleviating localized stress concentrations. With extended tempering duration or elevated temperatures, coarsening of ε-carbides and granular carbides occurs, alongside broadening of martensitic lamellae, leading to diminished material strength and total elongation. Geometric phase analysis (GPA) reveals that the strain level at the lower bainite–martensite interface in the as-quenched specimen is significantly higher than that at the martensite–martensite interface. After low-temperature tempering, the strain level decreases, and the strain disparity between the two types of interfaces is reduced, resulting in a more uniform strain distribution within the microstructure. This study confirms that an appropriate low-temperature tempering process refines carbides, stabilizes lath interfaces, and alleviates stress concentration, thereby achieving an optimal balance between strength and toughness in the isothermally quenched microstructure of ultra-high strength steel. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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