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Research Papers

Prediction of Stress–Strain Curves of Metastable Austenitic Stainless Steel Considering Deformation-Induced Martensitic Transformation

[+] Author and Article Information
T. Kumnorkaew

Department of Mechanical Engineering,
Faculty of Engineering,
Rajamangala University of Technology
Krungthep,
2 Nanglinji Road,
Tungmahamek, Sathorn,
Bangkok 10120, Thailand

V. Uthaisangsuk

Department of Mechanical Engineering,
Faculty of Engineering,
King Mongkut's University of
Technology Thonburi,
126 Pracha Uthit Road,
Bang Mod, Thung Khru,
Bangkok 10140, Thailand
e-mail: vitoon.uth@kmutt.ac.th

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received April 26, 2016; final manuscript received November 22, 2016; published online March 23, 2017. Assoc. Editor: Antonios Kontsos.

J. Eng. Mater. Technol 139(3), 031002 (Mar 23, 2017) (9 pages) Paper No: MATS-16-1125; doi: 10.1115/1.4035623 History: Received April 26, 2016; Revised November 22, 2016

Transformation-induced plasticity (TRIP) effect is the outstanding mechanism of austenitic stainless steel. It plays an important role in increasing formability of the steel due to higher local strain hardening during deformation. In order to better understand forming behavior of this steel grade, the strain-induced martensitic transformation of the 304 stainless steel was investigated. Uniaxial tensile tests were performed at different temperatures for the steel up to varying strain levels. Stress–strain curves and work hardening rates with typical TRIP effect characteristics were obtained. Metallographic observations in combination with X-ray diffraction method were employed for determining microstructure evolution. Higher volume fraction of martensite was found by increasing deformation level and decreasing forming temperature. Subsequently, micromechanics models based on the Mecking–Kocks approach and Gladman-type mixture law were applied to predict amount of transformed martensite and overall flow stress curves. Hereby, individual constituents of the steel and their developments were taken into account. Additionally, finite element (FE) simulations of two representative volume element (RVE) models were conducted, in which effective stress–strain responses and local stress and strain distributions in the microstructures were described under consideration of the TRIP effect. It was found that flow stress curves calculated by the mixture law and RVE simulations fairly agreed with the experimental results. The RVE models with different morphologies of martensite provided similar effective stress–strain behavior, but unlike local stress and strain distributions, which could in turn affect the strain-induced martensitic transformation.

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References

Figures

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Fig. 1

Modified geometries of used tensile test specimen according to DIN50114

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Fig. 2

Schematic approach for determining flow stress curve of the M/A constituent

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Fig. 3

Two-dimensional RVE models for M/A microstructure with two different shapes of martensitic islands of the investigated stainless steel 304 at a given strain and temperature

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Fig. 4

Experimental flow stress curves of the investigated steel by uniaxial tensile tests at the temperatures of −50, 25, and 50 °C

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Fig. 5

Experimentally determined strain hardening rates of the investigated steel at the temperatures of −50, 25, and 50 °C

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Fig. 6

Determined volume fractions of the strain-induced transformed martensite as a function of plastic true strain at different temperatures for the examined steel (symbols: experiments and dashed lines: calculations)

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Fig. 7

Calculated rates of strain-induced martensitic transformation as a function of plastic true strain at various temperatures for the examined steel grade 304

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Fig. 8

Microstructures of the examined steel at (a) initial state and (b) plastic strain of 0.4

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Fig. 9

Comparison between analytically predicted (σRM) and experimentally determined (σexp) stress–strain curves of the investigated steel at the temperature of −50 °C along with modeled individual stress–strain curves of the austenitic (σγ) and martensitic (σα′) phase

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Fig. 10

Comparisons between calculated and experimental plastic stress–strain curves of the investigated steel at all the tested temperatures

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Fig. 11

Calculated dislocation densities of the investigated steel at various forming temperatures as a function of plastic strain

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Fig. 12

Flow stress curves of the examined steel grade 304 steel at the temperature of 50 °C obtained by tensile tests, two-phase mixture law, and RVE simulations

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Fig. 13

Flow stress curves of the examined steel grade 304 steel at the temperature of 25 °C obtained by tensile tests, two-phase mixture law, and RVE simulations

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Fig. 14

Flow stress curves of the examined steel grade 304 steel at the temperature of −50 °C obtained by tensile tests, two-phase mixture law, and RVE simulations

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Fig. 15

Calculated local equivalent stress distributions in microstructure with circular shape of martensite for the investigated steel grade 304 under a uniaxial tensile strain of (a) 10% and (b) 50% at room temperature

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Fig. 16

Calculated local equivalent stress distributions in microstructure with ellipsoid shape of martensite for the investigated steel grade 304 under a uniaxial tensile strain of (a) 10% and (b) 50% at room temperature

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Fig. 17

Calculated local equivalent strain distributions in microstructure with circular shape of martensite for the investigated steel grade 304 under a uniaxial tensile strain of (a) 10% and (b) 50% at room temperature

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Fig. 18

Calculated local equivalent strain distributions in microstructure with ellipsoid shape of martensite for the investigated steel grade 304 under a uniaxial tensile strain of (a) 10% and (b) 50% at room temperature

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