Effects of strain rate on mechanical properties and deformation behavior of an austenitic Fe-25Mn-3Al-3Si TWIP-TRIP steel

Journal Article · Wed Nov 08 00:00:00 EST 2017 · Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing

DOI:https://doi.org/10.1016/j.msea.2017.11.017· OSTI ID:1409249

Benzing, Jake T. ^[1]; Poling, Whitney A. ^[2]; Pierce, Dean T.  ^[3]; Bentley, James ^[4]; Findley, Kip O. ^[2]; Raabe, Dierk ^[5]; Wittig, J. E. ^[1]

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1. Vanderbilt Univ., Nashville, TN (United States)
2. Colorado School of Mines, Golden, CO (United States)
3. Colorado School of Mines, Golden, CO (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
4. Microscopy and Microanalytical Sciences, Oak Ridge, TN (United States)
5. Max-Planck-Institut fur Eisenforschung, Dusseldorf (Germany)

The effects of quasi-static and low-dynamic strain rate (ε = 10^–4 /s to ε = 10² /s) on tensile properties and deformation mechanisms were studied in a Fe-25Mn-3Al-3Si (wt%) twinning and transformation-induced plasticity [TWIP-TRIP] steel. The fully austenitic microstructure deforms primarily by dislocation glide but due to the room temperature stacking fault energy [SFE] of 21 ± 3 mJ/m² for this alloy, secondary deformation mechanisms such as mechanical twinning (TWIP) and epsilon martensite formation (TRIP) also play an important role in the deformation behavior. The mechanical twins and epsilon-martensite platelets act as planar obstacles to subsequent dislocation motion on non-coplanar glide planes and reduce the dislocation mean free path. A high-speed thermal camera was used to measure the increase in specimen temperature as a function of strain, which enabled the use of a thermodynamic model to predict the increase in SFE. The influence of strain rate and strain on microstructural parameters such as the thickness and spacing of mechanical twins and epsilon-martensite laths was quantified using dark field transmission electron microscopy, electron channeling contrast imaging, and electron backscattered diffraction. The effect of sheet thickness on mechanical properties was also investigated. Increasing the tensile specimen thickness increased the product of ultimate tensile strength and total elongation, but had no significant effect on uniform elongation or yield strength. The yield strength exhibited a significant increase with increasing strain rate, indicating that dislocation glide becomes more difficult with increasing strain rate due to thermally-activated short-range barriers. Finally, a modest increase in ultimate tensile strength and minimal decrease in uniform elongation were noted at higher strain rates, suggesting adiabatic heating, slight changes in strain-hardening rate and observed strain localizations as root causes, rather than a significant change in the underlying TWIP-TRIP mechanisms at low values of strain.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1409249
• Journal Information: Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing, Vol. 711, Issue C; ISSN 0921-5093
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
High-Mn [Fe-25Mn-3Al-3Si] steel
Strain rate sensitivity
Adiabatic heating
Stacking fault energy (SFE)
Twinning and transformation-induced plasticity (TWIP-TRIP)