Recent developments and perspectives of advanced high-strength medium Mn steel: from material design to failure mechanisms

doi: 10.1088/2752-5724/ac7fae

Chengpeng Huang^{1, 2},
Chen Hu^{1, 2},
Yuxuan Liu^{1, 2},
Zhiyuan Liang^3
,,
Mingxin Huang^{1, 2
,}

1.
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong, People’s Republic of China
2.
Shenzhen Institute of Research and Innovation, The University of Hong Kong, Shenzhen, People’s Republic of China
3.
Songshan Lake Materials Laboratory, Dongguan 523808, People’s Republic of China

More Information

Corresponding author: E-mail: liangzhiyuan@sslab.org.cn; E-mail: mxhuang@hku.hk

摘要

Abstract: Advanced high-strength steels are key structural materials for the development of next-generation energy-efficient and environmentally friendly vehicles. Medium Mn steel, as one of the latest generation advanced high-strength steels, has attracted tremendous attentions over the past decade due to its excellent mechanical properties. Here, the state-of-the-art developments of medium Mn steel are systematically reviewed with focus on the following crucial aspects: (a) the alloy design strategies; (b) the thermomechanical processing routes for the optimizations of microstructure and mechanical properties; (c) the fracture mechanisms and toughening strategies; (d) the hydrogen embrittlement mechanisms and improvement strategies.
- medium Mn steel /
- alloy design /
- mechanical property /
- fracture mechanism /
- hydrogen embrittlement
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Figure 1. Total elongation versus ultimate tensile strength of various AHSS grades.

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Figure 2. (a) Equilibrium austenite fraction in 0.1C-1.5Mn and 0.1C-6Mn steels overlapped with recrystallization fraction of cold-rolled microstructure; and (b) influence of Al and Si on austenite fraction. Reprinted from [30]. Copyright (2017), with permission from Elsevier (c) Composition-dependent stacking fault energy (SFE) maps of Fe-C-Mn system and (d) Fe-C-Mn-1.5Al system. Reproduced from [31]. CC BY 4.0.

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Figure 3. Thermomechanical processing routes of high-performance MMS. (a) Intercritical annealing; (b) quenching and partitioning; (c) chemical patterning; (d) warm rolling and warm stamping; (e) deforming and partitioning.

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Figure 4. Microstructures and mechanical properties of MMS produced by different IA processes. Microstructure of (a) HR-IA, (b) CR-IA, (c) CR-FA, characterized by scanning electron microscope (SEM) (a1), (b1), (c1), electron backscatter diffraction (EBSD) phase mapping (a2), (b2), (c2), transmission electron microscope (TEM) (a3), (b3), (c3), and energy dispersive x-ray spectroscopy (EDXS) line profiling (a4), (b4), (c4). Note here the HR-IA MMS has a composition of 0.2C-7Mn-3Al (wt.%), and the CR-IA and CR-FA MMS have a composition of 0.23C-5.38Mn-1.7Al (wt.%). (d) Engineering strain-stress curves of HR-IA and CR-FA MMS with composition of 0.2C-7Mn-3Al (wt.%). (e) Engineering strain-stress curves and (f) HDI stress with increasing true strain of CR-IA and CR-FA MMS with composition of 0.23C-5.38Mn-1.7Al (wt.%). Reprinted from [40, 41]. Copyright (2021), with permission from Elsevier.

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Figure 5. Microstructure and mechanical property of MMS produced by Q&P process. (a) EBSD phase map and (b) EBSD inverse pole figure (IPF) map (c) SEM image of a typical RT-Q&P MMS with a composition of 0.2C-10Mn-2Al-0.1V (wt.%). Reproduced from [44]. CC BY 4.0. (d) Engineering stress-strain curves of the present RT-Q&P MMS, commercial dual phase steel and press hardening steel. Reproduced from [42], with permission from Springer Nature.

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Figure 6. Microstructures and mechanical properties of MMS produced by chemical patterning process. (a) TEM image of the initial pearlite. (b) TEM image of the chemical patterned MMS. (c) EDXS line profile of Mn distribution of the initial pearlite. (d) EDXS line profile of Mn distribution of the chemical patterned MMS. (e) Engineering stress-strain curves and (f) corresponding true strain hardening rate curves of the initial pearlite steel and chemical patterned MMS with different processing parameters. Note that this MMS has a composition of 0.51C-4.35Mn (wt.%). Reprinted from [45]. Copyright (2018), with permission from Elsevier.

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Figure 7. Microstructures and mechanical properties of MMS produced by WR and WS processes. Microstructure of (a) WR 0% (b) WR 89% (c) WS MMS characterized by TEM (a1), (b1), SEM (c1) and EBSD phase mapping (a2), (b2), (c2). Note that the WR MMS has a composition of 0.22C-4.88Mn-3.11Al-0.62Si (wt.%), and the WS MMS have a composition of 0.25C-6.94Mn-0.23Al-0.38Si-3.29Cr-0.12Nb (wt.%). (d) Engineering strain-stress curves of WR 0% and WR 89% MMS. (e) Engineering strain-stress curves of the baked and non-baked WS MMS and commercial 22MnB5 hot stamping steel. (a), (b), (d) Reprinted from [48]. Copyright (2019), with permission from Elsevier. (c), (e) Reprinted from [60]. Copyright (2021), with permission from Elsevier.

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Figure 8. Microstructure and mechanical property of MMS produced by D&P process. (a) EBSD phase map. (b) EBSD IPF map. (c) TEM image showing the dislocation cell structure in a large martensite grain. The inset is the selected-area diffraction pattern (SADP). (d) TEM image showing the ultrafine nanolamellar martensite lath and austenite lath. (e) The SADP of the area of (d). (f) Engineering stress-strain curves of the D&P steel with a composition of 0.47C-10Mn-2Al-0.7V (wt.%). (g) Ashby map in terms of uniform elongation versus yield strength of the D&P steel. From [62, 63]. Reprinted with permission from AAAS.

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Figure 9. SEM observations near the fracture surface of the tensile samples, showing the void formation at different sites (marked by red elliptical frames) in an MMS with a chemical composition of 0.2C-10.4Mn-2.9Al (wt.%) produced by CR-IA processing route. IA temperature: (a)-(c) 700 C, (d), (e) 750 C. Reprinted from [74]. Copyright (2019), with permission from Elsevier.

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Figure 10. EBSD IPF maps of the fractured samples showing the long cleavage cracks in coarse-grained -ferrite (indicated by white arrows) in an MMS with a chemical composition of 0.3C-6Mn-3Al-1.5Si (wt.%) produced by HR-IA processing route. IA temperature: (a) 760 C, (b) 800 C, (c) 840 C, (d) 880 C. Reprinted from [78]. Copyright (2017), with permission from Elsevier.

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Figure 11. SEM fractographs of (a) AsQ and (b) RQ MMS samples fractured at 77 K. Cross-sectional EBSD fractographs observed in the normal direction (ND) of (c) AsQ and (d) RQ MMS samples fractured at 77 K. White arrows indicate the <100> orientations of each packet. The MMS has a chemical composition of 0.1C-5Mn (wt.%). Reprinted from [79]. Copyright (2021), with permission from Elsevier.

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Figure 12. SEM fractographs of an MMS after Charpy impact tests at (a) room temperature and (b) -90 C. Note that the MMS has a chemical composition of 0.2C-9.4Mn-2.1Al (wt.%) produced by CR-IA processing route.

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Figure 13. (a) Ashby map in terms of yield strength versus fracture toughness of various metals. From [63]. Reprinted with permission from AAAS. (b) Ashby map in terms of yield strength versus Charpy impact energy of various low-alloy BBC steels. From [83]. Reprinted with permission from AAAS.

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Figure 14. SEM micrographs taken close to the crack tip of TRIP steel; (a) crack propagation path; (b) decohesion between two martensite grains; (c) decohesion between ferrite and martensite grains; and (d) cleavage of a martensite grain. Reprinted from [89]. Copyright (2008), with permission from Elsevier.

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Figure 15. Delamination toughening mechanism of MMS steel with a composition of 0.44C-9.95Mn-1.87Al-0.67V (wt.%) produced by D&P processing route. (a) Schematic diagram of fractured C(T) sample with extensive long and short delamination cracks. (b) and (c) Images of the fracture surface of C(T) sample showing numerous thin-layer delamination cracks. (d) and (e) SEM image and schematic diagram of the cross-section of the fracture sample showing the development of delamination cracks along the elongated PAGBs. The blue arrows indicate short delamination cracks, the black arrows indicate the long delamination cracks, the pink arrows indicate the secondary delamination cracks that usually observed in the vicinity of long delamination cracks. From [63]. Reprinted with permission from AAAS.

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Figure 16. Hydrogen desorption rate curves of MMS with (a), (c), (e) low and (b), (d), (f) high Al content at different conditions. Reprinted from [116]. Copyright (2012), with permission from Elsevier.

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Figure 17. Schematic diagrams of H diffusion and distribution in the MMS with a composition of 0.2C-10.2Mn-2.8Al-1Si (wt.%) fabricated by IA at (a) 700 C and (b) 800 C. Reprinted from [117]. Copyright (2020), with permission from Elsevier.

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Figure 18. (a) Elongation loss of the base and different micro-alloyed MMS. (b) Hydrogen desorption rate curves and (c), (d) Ag decoration of the base and high Nb-alloyed MMS, respectively. Reprinted from [123]. Copyright (2020), with permission from Elsevier.

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Figure 19. The microstructures of (a) 770 C and (b), (c) 850 C intercritically annealed MMS after 5% tensile strain. Note that the MMS has a composition of 0.2C-4.88Mn-3.11Al-0.62Si (wt.%). White and yellow arrows indicate micro-cracks at / and / boundaries, respectively. Reprinted from [125]. Copyright (2019), with permission from Elsevier.

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Figure 20. Slow strain rate tensile (SSRT) curves of the MMS intercritically annealed at 750 C for (a) 10 min (b) 60 min and (c) 360 min. (d) Variations of index of relative susceptibility to HE (HEI) with intercritical annealing time. Note that the MMS has a composition of the 0.2C-5Mn-3Al-0.6Si (wt.%). Reprinted from [126]. Copyright (2018), with permission from Elsevier.

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Figure 21. (a) SSRT curves, (b) hydrogen desorption rate curves, (c) evolution of austenite volume fraction with increasing strain, and (d) stress level in different region of the MMS with 25% and 75% cold rolling reduction prior to IA. Note that this MMS has a composition of 0.14C-7.65Mn-1.49Al (wt.%). Reprinted from [127]. Copyright (2021), with permission from Elsevier.

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Figure 22. (a) Schematic diagram of blunting of crack by chemical heterogeneity. (b) A representative blunted and arrested H-induced crack. (c) APT result of the tip marked in (b). Reproduced from [128]. CC BY 4.0.

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Figure 23. (a) SSRT curves, (b) nanoindentation curves and (c) nano-hardness of Cu-Free and Cu-Added MMS, respectively. Reprinted from [130]. Copyright (2020), with permission from Elsevier.

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