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Research Papers

Metallurgical Investigations on Hyperplasticity in Dual Phase Steel Sheets

[+] Author and Article Information
Javad Samei

Department of Mechanical, Automotive,
and Materials Engineering,
University of Windsor,
401 Sunset Avenue,
Windsor, ON N9B3P4, Canada
e-mail: sameij@uwindsor.ca

Daniel E. Green

Department of Mechanical, Automotive,
and Materials Engineering,
University of Windsor,
401 Sunset Avenue,
Windsor, ON N9B3P4, Canada
e-mail: dgreen@uwindsor.ca

Sergey Golovashchenko

Ford Research and Advanced Engineering,
Dearborn, MI 48124
e-mail: sgolovas@ford.com

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MANUFACTURING SCIENCE AND ENGINEERING. Manuscript received August 26, 2013; final manuscript received April 13, 2014; published online May 21, 2014. Assoc. Editor: Brad L. Kinsey.

J. Manuf. Sci. Eng 136(4), 041010 (May 21, 2014) (6 pages) Paper No: MANU-13-1330; doi: 10.1115/1.4027492 History: Received August 26, 2013; Revised April 13, 2014

Several researchers have reported that dual phase steel sheets exhibit hyperplasticity, that is, a significant formability improvement under certain high strain rate forming conditions. Hyperplastic behavior of dual phase steels formed using an electrohydraulic forming (EHF) process was previously investigated by the authors at both macro- (Golovashchenko et al., 2013, “Formability of Dual Phase Steels in Electrohydraulic Forming,” J. Mater. Process. Technol., 213, pp. 1191–1212) and microscales (Samei et al., 2013, “Quantitative Microstructural Analysis of Formability Enhancement in Dual Phase Steels Subject to Electrohydraulic Forming,” J. Mater. Eng. Perform., 22(7), pp. 2080–2088). A relative deformation improvement of approximately 20% in ferrite grains and 100% in martensite islands was reported in the EHF specimens compared to specimens formed under quasi-static conditions. In this paper, the remarkable deformation improvements of the constituents are discussed in terms of metallurgical mechanisms of deformation. The nucleation and multiplication of dislocations in ferrite and deformation twinning in martensite were found to be the principal mechanisms responsible for the significant improvements of deformation in EHF. In addition, these mechanisms enhance the plastic compatibility between the two phases which reduces the risk of decohesion and delays the onset of fracture in EHF specimens.

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References

Figures

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Fig. 4

Hardness of the ferrite grains in the Nakazima and EHF specimens at von Mises strains of 0.1 and 0.2

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Fig. 2

DP980 specimens: (a) dome-shaped Nakazima specimen and (b) EHF conical specimen

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Fig. 1

Schematic presentation of (a) the Nakazima test and (b) EHF process

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Fig. 5

Deformation twinning in martensite deformed by EHF in (a) DP780 and (b) DP980; the SAD is shown by the small square box

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Fig. 6

Plastic deformation in specimens at approximately 0.30 von Mises strain: (a) DP980-EHF, (b) DP980-Nakazima, (c) DP500-EHF, and (d) DP780-EHF. The dark gray matrix is ferrite and the light gray phase is martensite.

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Fig. 3

DP780 Nakazima specimen: (a) accumulation of dislocations shown by “X” at the ferrite/martensite interface and (b) dislocation cells in the vicinity of the ferrite/martensite interface

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Fig. 7

Interfacial microcracks in (a) DP780 and (b) DP980 specimen identified by arrows

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Fig. 8

Martensite to ferrite (a) minor and (b) major microstrain ratio as a function of the macrostrains in Nakazima specimens formed under quasi-static and high strain rate forming (EHF) conditions

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