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Research Papers

Micromechanical Finite Element Analysis of the Effects of Martensite Particle Size and Ferrite Grain Boundaries on the Overall Mechanical Behavior of Dual Phase Steel

[+] Author and Article Information
Najmul H. Abid

Department of Mechanical Engineering,
McGill University,
Montreal, QC H3A 0C3, Canada

Rashid K. Abu Al-Rub

Institute Center for Energy,
Mechanical and Materials
Engineering Department,
Masdar Institute of Science and Technology,
Abu Dhabi 54224, UAE;
Mechanical Engineering Department,
Khalifa University of Science and Technology,
Abu Dhabi 54224, UAE
e-mails: rabualrub@masdar.ac.ae;
rashedkamel@yahoo.com

Anthony N. Palazotto

Department of Aeronautics and Astronautics,
Air Force Institute of Technology,
WPAFB, OH 45433-7765

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received October 17, 2015; final manuscript received March 23, 2017; published online May 25, 2017. Assoc. Editor: Mohammed Zikry.

J. Eng. Mater. Technol 139(4), 041006 (May 25, 2017) (8 pages) Paper No: MATS-15-1262; doi: 10.1115/1.4036687 History: Received October 17, 2015; Revised March 23, 2017

This paper focuses on micromechanical finite element (FE) modeling of the effects of size and morphology (particularly elongation or aspect ratio (AR) along the loading direction) of martensite particles and the ferrite grains on the overall mechanical behavior of dual-phase (DP) steels. To capture the size-effect of the martensite particles and ferrite grains, the core and mantle approach is adapted in which a thin interphase of geometrically necessary dislocations (GNDs) is embedded at the martensite–ferrite boundaries. It is shown that as the martensite particles size decreases or their aspect ratio increases, both the strength and ductility of DP steel increase simultaneously. On the other hand, as the ferrite grain size decreases or its aspect ratio increases, the overall strength increases on the expense of the ductility. The conclusions from this study can be used in guiding the microstructural design of DP steels.

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Figures

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Fig. 1

(a) Virtual RVE with Vf,M = 40% and (b) corresponding finite element mesh

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Fig. 2

Stress–strain responses of DP980 used for (a) modeling martensite particle size-effect (microcompression pillar testing data from Ghassemi-Armaki et al. [36]) and (b) modeling ferrite grain size-effect (X-ray diffraction data from Jia et al. [56])

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Fig. 3

RVEs generated with a constant ferrite–martensite interphase thickness of 1 μm with varying martensite morphology of (a)–(c) equiaxed and (d)–(f) elongated. The dimension of the elongated and equiaxed RVEs are 50 × 50 μm and 100 × 100 μm, respectively.

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Fig. 4

Macroscopic responses of RVEs with varying martensite particle size (a) with and (b) without a constant 1 μm interphase (Vf,M = 40%)

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Fig. 5

Contours of equivalent plastic strain for elongated RVEs with varying martensite phase sizes of 7 μm, 5 μm, and 3 μm without interphase

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Fig. 6

Contours of equivalent plastic strain for elongated RVEs with varying martensite phase size of 7 μm, 5 μm, and 3 μm with interphase

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Fig. 7

Virtual RVEs of constant 40% Vf,M with varying grain sizes of (a) and (d) 7 μm, (b) and (e) 5 μm, and (c) and (f) 2 μm with a constant morphology of martensite islands. (a)–(c) show elongated martensite and (d)–(f) show equiaxed martensite.

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Fig. 8

Comparing the macroscopic stress–strain responses ofRVEs with varying ferrite grain sizes and martensite morphology while martensite volume fraction is set constant (Vf,M = 40%). The results are compared for the case where ferrite grains are not considered.

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Fig. 9

(a) UTS, yield strength and (b) strain at UTS, and strain at 95% UTS as a function of grain size for both equiaxed and elongated martensite particles

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Fig. 10

Virtual RVEs with constant grain sizes of 5 μm but extended with a factor of (a) 1, (b) 5, and (c) 10 with a constant volume fraction and arrangement of martensite islands (Vf,M = 40%). (a)–(c) show elongated martensite and (d)–(f) show equiaxed martensite.

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Fig. 11

Comparing the macroscopic responses of RVEs, constant 40% Vf,M with ferrite grains elongated with a factor of one, five, and ten for (a) equiaxed martensite phase and (b) elongated martensite phase for direction of loading

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