Dynamic Strain Aging and Serration Behavior of Three High-Manganese Austenitic Steels
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INCE the development of Fe-Mn-C Hadfield steel, various kinds of high-manganese austenitic steels have been widely used for cryogenic, damping, non-magnetic, wear-resistant, anti-corrosion, and automotive applications.[1–3] Over the last decade, high-manganese twinning-induced plasticity (TWIP) steels for automotive applications have received considerable attention owing to their excellent combination of strength and ductility.[4–9] According to previous studies, the best combination of strength and ductility in TWIP steels can be achieved by deformation twinning in a specific range of stacking fault energy (SFE), i.e., 18 to 45 mJ/m2, which is mainly dependent on chemical composition, temperature, and grain size.[10,11] For commercialization, however, high-manganese steel still has to overcome several problems, such as the temperature drop of molten steel, nozzle blocking, and surface oxidation during steel manufacturing processes, as well as post-forming cracking and weldability to itself or other materials during the application process.[12–14]
SEUNG-YONG LEE and BYOUNGCHUL HWANG are with the Department of Materials Science and Engineering, Seoul National University of Science and Technology, Seoul, 01811, Korea. Contact e-mail: [email protected] Manuscript submitted July 17, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
On the other hand, the dynamic strain aging (DSA) phenomenon has been regarded as one of the most important issues in high-manganese austenitic steels because it can induce the Portevin–Le Chatelier effect, leading to inhomogeneous deformation and discontinuous yielding.[15–17] It is well established that DSA is typically caused by the interaction between mobile dislocation and solute atoms.[18,19] In the case of high-manganese steels, the DSA mechanism has been explained by the interaction between the rearrangement of C in a Mn-C pair and perfect dislocation[15] or the interaction between the single hopping of carbon atoms in Mn-C clusters and partial dislocation in stacking fault region,[16] which result in the incremental flow stress and negative strain-rate sensitivity, mainly under quasi-static strain rates. The strain-rate dependence of flow stress in Hadfield steel[15] and TWIP steels, e.g., Fe-18Mn-0.6C[20] and Fe-22Mn-0.6C,[21] respectively, has been studied in terms of DSA and deformation twinning. Nevertheless, there have been few attempts to investigate DSA and tensile behavior of high-manganese austenitic steels with different compositions and SFEs. In the present study, three high-manganese austenitic steels with different Mn, C, and Al contents were fabricated, and then tensile and strain-rate jump tests under quasi-static strain rates were carried out to understand the strain-rate dependence of flow stress in terms of DSA and tensile behavior.
Table I.
Chemical Composition, Initial Grain Size, and Stacking Fault Energy (SFE) of Three High-Manganese Austenitic Steels Investigated in this Study Chemical Composition (Wt Pct)
Steel
Fe.
Mn
C
Al
Grain size (lm)
SFEa (mJ/m2)
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