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Acta Metall Sin  2020, Vol. 56 Issue (4): 429-443    DOI: 10.11900/0412.1961.2020.00003
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Strength, Ductility and Fracture Strain ofPress-Hardening Steels
YI Hongliang1,2(),CHANG Zhiyuan1,CAI Helong1,DU Pengju1,YANG Dapeng1
1.State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China
2.Easyforming Materials Technology Co. , Ltd. , Suzhou 215123, China
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Abstract  

Press-hardening steels (PHS) are increasingly used for vehicle body structure components because of their lightening potential owning to superiorly high strength, adequate ductility and fracture resistance. New PHS grades with higher strength and enhanced fracture resistance are being widely studied now for achieving further vehicle weight reduction, and the recent development in this field is reviewed in this article. Combining quenching and partitioning (Q&P) with the hot stamping process has been explored by some researchers, as well as tempering after the hot stamping using the medium-Mn steels. A certain amount of austenite could remain by the above processes and the resulted tensile strength can exceed 1500 MPa while tensile ductility of 10%~16% can be achieved utilizing the transformation-induced plasticity (TRIP) effect. A V micro-alloyed steel (34MnB5V) for hot stamping has been designed, utilizing both grain refinement and precipitation strengthening of VC. The tensile strength of the newly developed 34MnB5V exceeds 2000 MPa which is much higher than that of the most commonly used PHS 22MnB5 (1500 MPa). Meanwhile, the ductility and bending properties of the above two steels are comparable. Al-Si coated PHS is usually adopted to avoid oxidation during heating and improve its corrosion resistance after stamping. However, its bendability after forming is lower than that of the bare grade when surface decarburization is absent. The thickness of the brittle Fe2Al5 phase was reduced and the carbon enrichment at the interface of α-Fe and martensite matrix was weakened after hot stamping by thinning of the Al-Si coating. Thus, the bending property was improved. The applicability of the new designed processes for the existing production lines should be considered in future studies. The bending test should be adopted for the deformability evaluation rather than the uniaxial tensile test simply. The welding property and the mechanism of hydrogen embrittlement should also be studied for industrial application of the new developed steels.

Key words:  light weighting      hot stamping steel      Al-Si coating      ductility      bendability      fracture resistance     
Received:  03 January 2020     
ZTFLH:  TG142.41  
Fund: National Natural Science Foundation of China(51722402);National Natural Science Foundation of China(U1560204);Fundamental Research Funds for the Central Universities(N170705001);111 Project(B16009)
Corresponding Authors:  Hongliang YI     E-mail:  hlyi@ral.neu.edu.cn

Cite this article: 

YI Hongliang,CHANG Zhiyuan,CAI Helong,DU Pengju,YANG Dapeng. Strength, Ductility and Fracture Strain ofPress-Hardening Steels. Acta Metall Sin, 2020, 56(4): 429-443.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2020.00003     OR     https://www.ams.org.cn/EN/Y2020/V56/I4/429

Fig.1  Bending crush energy absorption test of automobile parts(a) device (b) crack extension of the hot stamped part by crush
Fig.2  Schematics of VDA 238-100 bending process (a) and strain state during bending (b) (α, t,ε represent bending angle, sheet thickness and principal strain in the circumferential direction, respectively)
SteelCSiMnTiBVFe
22MnB50.220.221.330.0290.0031-Bal.
34MnB5V0.340.321.390.0300.00250.11~0.30Bal.
Table 1  Chemical compositions of 22MnB5 and 34MnB5V[14]
Fig.3  Prior austenite grain boundaries of 22MnB5 (a) and 34MnB5V (b) austenitized for 4 min at 900 ℃, and TEM images of quenched lath martensite (c) and VC precipitation particles (d) in 34MnB5V
Fig.4  Tensile curves (a) and three points bending load-angle curves (b) of 22MnB5 and 34MnB5V
Fig.5  Door beam using 34MnB5V press-hardening steels (a) and vehicle crash test (b)
Fig.6  Schematics of the quenching and partitioning (Q&P) process (a) and the press-hardening process (b) (α' and γ represent martensite and austenite, respectively)
Fig.7  Mechanical properties of 22MnB5 and the press-hardening steels treated by Q&P process[17,18,19,20] and designed by quenching and flash-partitioning (Q&FP) concept[21] (adjusted to JIS5 standard specimen geometry[36])
Fig.8  Bright-field (a, c) and dark-field (b, d) TEM images of the press-hardening steels QFP1500[21] (a, b) and QFP1800 (c, d) designed by Q&FP concept (γ presents retained austenite and the insets in Figs.8b and d show the SAED patterns of γ)
Fig.9  Engineering stress-strain curves of 22MnB5 and the press-hardening steels designed by Q&FP concept
Fig.10  Schematic of medium-Mn steels with warm stamping processes (a) and the engineering stress-strain curves of medium-Mn[23] steels with warm stamping and 22MnB5 (b)
Fig.11  Schematic of medium-Mn PHS with quenching-tempering & partitioning (Q-T&P) and quenching-baking & partitioning (Q-B&P) processes (a), and the engineering stress-strain curves of medium-Mn PHS with Q-T&P and Q-B&P[44] processes and 22MnB5 (b)
Fig.12  SEM images of Al-Si coated press-hardening steels with pre-coating thickness of about 25 μm(a) after hot dipping (b) after hot stamping
Fig.13  High carbon embrittlement model between Al-Si coating and boron steel after hot stamping for the Al-Si coating plate with the coating thicknesses of 25 μm (a) and 10 μm (b), respectivelyColor online
Fig.14  SEM images of Al-Si coated press-hardening steels with pre-coating thickness of about 10 μm after hot dipping (a) and after hot stamping (b)
Fig.15  The C concentration profiles of α′ matrix and α-Fe after hot stamping for the Al-Si coating plate with the coating thicknesses of 25 μm (a) and 10 μm (b), respectively
Fig.16  Bending load-displacement curves (a, b) and crack propagation after crushing (c~e) of Al-Si coated press hardening parts for the pre-coating thicknesses of 25 μm and 10 μm(a) hot stamped (b) hot stamped and baked (Crack extension of the hot stamped and baked parts by crush)(c) 14 d after crushing (10 μm) (d) 14 d after crushing (25 μm) (e) brittle fracture morphology (25 μm)
[1] Li J, Lu H Z, Yi H L, et al. Lightweight of passenger car and niobium-microalloying steel [M]. Beijing: Beijing Institute of Technology Press, 2015: 3
[1] 李 军, 路洪洲, 易红亮等. 乘用车轻量化及微合金化钢板的应用 [M]. 北京: 北京理工大学出版社, 2015: 3
[2] Ma M T, Yi H L. Application of high strength steel to manufacturing auto [J]. Heat Treat., 2011, 26(6): 9
[2] 马鸣图, 易红亮. 高强度钢在汽车制造中的应用 [J]. 热处理, 2011, 26(6): 9
[3] Yi H L, Sun L, Xiong X C. Challenges in the formability of the next generation of automotive steel sheets [J]. Mater. Sci. Technol., 2018, 34: 1112
[4] Lee Y K, Han J. Current opinion in medium manganese steel [J]. Mater. Sci. Technol., 2015, 31: 843
[5] Chang Y, Li X D, Zhao K M, et al. Influence of stress on martensitic transformation and mechanical properties of hot stamped AHSS parts [J]. Mater. Sci. Eng., 2015, A629: 1
[6] Taylor T, Clough A. Critical review of automotive hot-stamped sheet steel from an industrial perspective [J]. Mater. Sci. Technol., 2018, 34: 809
[7] Akisue O, Usuda M. New types of steel sheets for automobile weight reduction [J]. Nippon Steel Tech. Rep., 1993, 57: 11
[8] Lu Q, Wang J, Liu Y, et al. Impact toughness of a medium-Mn steel after hot stamping [A]. Proceeding of the 6th International Conference on Hot Sheet Metal Forming of High-Performance Steel [C]. Warrendale: Association for Iron & Steel Technology, 2017: 737
[9] Larour P, Pauli T, Kurz T, et al. Influence of post uniform tensile and bending properties on the crash behaviour of AHSS and press-hardening steel grades [A]. International Deep Drawing Research Group Conference in Tools and Technologies for the Processing of Ultra High Strength Steels [C]. Graz: TU Graz, 2010: 27
[10] Larour P, Naito J, Pichler A, et al. Side impact crash behavior of press-hardened steels-correlation with mechanical properties [A]. Proceeding of the 5th International Conference on Hot Sheet Metal Forming of High-Performance Steel [C]. Auerbach: Verlag Wissenschaftliche Scripten, 2015: 281
[11] Kurz T, Larour P, Lackner J, et al. Press-hardening of zinc coated steel—Characterization of a new materials for a new process [J]. IOP Conf. Ser. Mater. Sci. Eng., 2016, 159: 012075
[12] Cheong K, Omer K, Butcher C, et al. Evaluation of the VDA 238-100 tight radius bending test using digital image correlation strain measurement [J]. J. Phys. Conf. Ser., 2017, 896: 012075
[13] VDA 238-100: Plate bending test for metallic materials [S]. 2010
[14] Yi H L, Liu H L, Chang Z Y, et al. Steel for hot stamping forming, hot stamping forming process and hot-stamping formed component [P]. Chin Pat, 10535069.3, 2016
[14] (易红亮, 刘宏亮, 常智渊等. 热冲压成形用钢材、热冲压成形工艺及热冲压成形构件 [P]. 中国专利, 10535069.3, 2016)
[15] Chang Z Y, Liu Z Y, Liu H L, et al. Microstructures and mechanical properties of an ultra-fine grained 2GPa press-hardening steel [A]. 6th International Conference on Advanced Steels [C]. Jeju: Korean Federation of Science & Technology Societies, 2018: 93
[16] Liu H P, Jin X J, Dong H, et al. Martensitic microstructural transformations from the hot stamping, quenching and partitioning process [J]. Mater. Charact., 2011, 62: 223
[17] Liu H P, Lu X W, Jin X J, et al. Enhanced mechanical properties of a hot stamped advanced high-strength steel treated by quenching and partitioning process [J]. Scr. Mater., 2011, 64: 749
[18] Seo E J, Cho L, De Cooman B C. Application of quenching and partitioning (Q&P) processing to press hardening steel [J]. Metall. Mater. Trans., 2014, 45A: 4022
[19] Linke B M, Gerber T, Hatscher A, et al. Impact of Si on microstructure and mechanical properties of 22MnB5 hot stamping steel treated by quenching & partitioning (Q&P) [J]. Metall. Mater. Trans., 2018, 49A: 54
[20] Zhu B, Liu Z, Wang Y N, et al. Application of a model for quenching and partitioning in hot stamping of high-strength steel [J]. Metall. Mater. Trans., 2018, 49A: 1304
[21] Cai H L, Chen P, Oh J K, et al. Quenching and flash-partitioning enables austenite stabilization during press-hardening processing [J]. Scr. Mater., 2020, 178: 77
[22] Chang Y, Wang C Y, Zhao K M, et al. An introduction to medium-Mn steel: Metallurgy, mechanical properties and warm stamping process [J]. Mater. Des., 2016, 94: 424
[23] Li X D, Chang Y, Wang C Y, et al. Comparison of the hot-stamped boron-alloyed steel and the warm-stamped medium-Mn steel on microstructure and mechanical properties [J]. Mater. Sci. Eng., 2017, A679: 240
[24] Yi H L, Du P J, Wang B G. A new invention of press-hardened steel achieving 1880 MPa tensile strength combined with 16% elongation in hot-stamped parts [A]. Proceeding of the 5th International Conference on Hot Sheet Metal Forming of High-Performance Steel [C]. Auerbach: Verlag Wissenschaftliche Scripten, 2015: 725
[25] Yi H L, Chang Z Y, Liu Z Y, et al. Hot stamped component, precoated steel sheet used for hot stamping and hot stamping process [P]. Chin Pat, 10401259.5, 2018
[25] 易红亮,常智渊,刘钊源等. 热冲压成形构件、热冲压成形用预涂镀钢板及热冲压成形工艺 [P]. 中国专利, 10401259.5, 2018)
[26] Karbasian H, Tekkaya A E. A review on hot stamping [J]. J. Mater. Process. Technol., 2010, 210: 2103
[27] Naderi M. Hot stamping of ultra high strength steels [D]. Aachen: University of Aachen, 2007
[28] Rana R, Singh S B. Automotive Steels: Design, Metallurgy, Processing and Applications [M]. Cambridge: Woodhead Publishing, 2017: 387
[29] Yang G W, Sun X J, Li Z D, et al. Effects of vanadium on the microstructure and mechanical properties of a high strength low alloy martensite steel [J]. Mater. Des., 2013, 50: 102
[30] Bhadeshia H, Honeycombe R. Steels: Microstructure and Properties [M]. Oxford: Butterworth-Heinemann, 2017: 111
[31] Kelly P M, Nutting J. The martensite transformation in carbon steels [J]. Proc. Roy. Soc. London, 1960, 259A: 45
[32] Ohmori A, Torizuka S, Nagai K. Strain-hardening due to dispersed cementite for low carbon ultrafine-grained steels [J].ISIJ Int., 2004, 44: 1063
[33] Song R, Ponge D, Raabe D, et al. Overview of processing, microstructure and mechanical properties of ultrafine grained bcc steels [J]. Mater. Sci. Eng., 2006, A441: 1
[34] Jia N, Shen Y F, Liang J W, et al. Nanoscale spheroidized cementite induced ultrahigh strength-ductility combination in innovatively processed ultrafine-grained low alloy medium-carbon steel [J]. Sci. Rep., 2017, 7: 2679
[35] Speer J G, Matlock D K, De Cooman B C, et al. Carbon partitioning into austenite after martensite transformation [J]. Acta Mater., 2003, 51: 2611
[36] Hanlon D N, van Bohemen S M C, Celotto S. Critical assessment 10: tensile elongation of strong automotive steels as function of test piece geometry [J]. Mater. Sci. Technol., 2015, 31: 385
[37] Krauss G. Martensite in steel: Strength and structure [J]. Mater. Sci. Eng., 1999, A273-275: 40
[38] Hutchinson B, Hagstr?m J, Karlsson O, et al. Microstructures and hardness of as-quenched martensites (0.1-0.5%C) [J]. Acta Mater., 2011, 59: 5845
[39] Matsuda H, Mizuno R, Funakawa Y, et al. Effects of auto-tempering behaviour of martensite on mechanical properties of ultra high strength steel sheets [J]. J. Alloys Compd., 2013, 577: S661
[40] Hsu T Y, Xu Z Y. Design of structure, composition and heat treatment process for high strength steel [J]. Mater. Sci. Forum, 2007, 561-565: 2283
[41] Rong Y H, Chen N L, Jin X J, et al. Advanced high strength steels and their process development [M]. Beijing: High Education Press, 2019
[41] 戎咏华, 陈乃录, 金学军等. 先进高强度钢及其工艺发展 [M]. 北京: 高等教育出版社, 2019
[42] Luo H W, Shi J, Wang C, et al. Experimental and numerical analysis on formation of stable austenite during the intercritical annealing of 5Mn steel [J]. Acta. Mater., 2011, 59: 4002
[43] Yang F, Luo H W, Dong H, et al. Effects of intercritical annealing temperature on the tensile behavior of cold rolled 7Mn steel and the constitutive modeling [J]. Acta. Metall. Sin., 2018, 54: 859
[43] 阳 锋, 罗海文, 董 瀚等. 退火温度对冷轧7Mn钢拉伸行为的影响及模拟研究 [J]. 金属学报, 2018, 54: 859
[44] Hou Z R, Opitz T, Xiong X C, et al. Bake-partitioning in a press-hardening steel [J]. Scr. Mater., 2019, 162: 492
[45] Pang J C, Lu Q, Wang J F, et al. A new low density press hardening steel with superior performance [A]. Proceeding of the 7th International Conference on Hot Sheet Metal Forming of High-Performance Steel [C]. Auerbach: Verlag Wissenschaftliche Scripten, 2019: 123
[46] Wang K. Research on microstructure evolution and deformation-induced cracking of Al-Si and galvannealed coatings on hot stamping steel [D]. Wuhan: Huazhong University of Science & Technology, 2017
[46] 王 凯. 热成形钢铝硅及锌基镀层组织转变与形变开裂研究 [D]. 武汉: 华中科技大学, 2017
[47] Drillet P, Spehner D, Kefferstein R. Coated steel strips, methods of making the same, methods of using the same, stamping blanks prepared from the same, stamped products prepared from the same, and articles of manufacture which contain such a stamped product [P]. Chin Pat, 80056246.4, 2006
[47] Drillet P, Spehner D, Kefferstein R. 涂覆的钢带材、其制备方法、其使用方法、由其制备的冲压坯料、由其制备的冲压产品和含有这样的冲压产品的制品 [P]. 中国专利, 80056246.4, 2006)
[48] Windmann M, R?ttger A, Theisen W. Phase formation at the interface between a boron alloyed steel substrate and an Al-rich coating [J]. Surf. Coat. Technol., 2013, 226: 130
[49] Fan D W, Kim H S, Oh J K, et al. Coating degradation in hot press forming [J]. ISIJ Int., 2010, 50: 561
[50] Fan D W, De Cooman B C. Formation of an aluminide coating on hot stamped steel [J]. ISIJ Int., 2010, 50: 1713
[51] Grigorieva R, Drillet P, Mataigne J M, et al. Phase transformations in the Al-Si coating during the austenitization step [J]. Solid State Phenom., 2011, 172-174: 784
[52] WS 01007: Materials for components made of hot-formed steels without coating [S]. 2012
[53] GMW14400: Pre-coated or uncoated heat-treatable sheet steel [S]. 2019
[54] Choi W S, De Cooman B C. Characterization of the bendability of press-hardened 22MnB5 steel [J]. Steel Res. Int., 2014, 85: 824
[55] Cho L, Sulistiyo D H, Seo E J, et al. Hydrogen absorption and embrittlement of ultra-high strength aluminized press hardening steel [J]. Mater. Sci. Eng., 2018, A734: 416
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