The mechanism of dynamic strain aging for type A serrations in tensile flow curves of Fe-18Mn-0.55C (wt.%) twinning-induced plasticity steel

Seon Keun Oh, Mehmet Emin Kilic, Jae Bok Seol, Jin Sung Hong, Aloysius Soon, Young Kook Lee

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Abstract

To elucidate the mechanism of dynamic strain aging (DSA) causing serrations in the tensile curves of an fcc austenitic Fe-18Mn-0.55C (wt.%) twinning-induced plasticity (TWIP) steel, many tensile tests were performed by varying both tensile temperature (203−323 K) and initial strain rate (ε˙ini = 1 × 10−2 − 1 × 10−4/s). At the ranges of tensile temperature and ε˙ini adopted in this study, only type A serrations appeared, and a critical engineering strain (ec) for serrations decreased with increasing tensile temperature and with decreasing ε˙ini. For the short-range diffusion model based on C-Mn complex, the activation energy value (Qre C) for the reorientation of C in C-Mn complex was calculated by ab-initio simulation. The Qre C value was ~2.4 eV for the fcc austenite matrix, and 0.60 eV and 0.18 eV for the hcp stacking fault depending on diffusion path. There was no intersection between staying time (ts) and reorientation time (tre) calculated using the Qre C values. This indicates that DSA is not caused by the reorientation of C-Mn complexes. In addition, ec revealed no dependency on the concentration of vacancy (Va). Therefore, DSA causing type A serrations is not explained by short-range diffusion models based on C-Mn and C-Va complexes. DSA is elucidated by the dislocation arrest model, which belongs to the long-range diffusion model. The measured activation energy (0.85 eV) corresponding to the activation energy (0.57−1.00 eV) for dislocation pipe diffusion of C and C-segregated dislocations in atom probe tomography (APT) maps support the occurrence of long-range C diffusion.

Original languageEnglish
Pages (from-to)366-375
Number of pages10
JournalActa Materialia
Volume188
DOIs
Publication statusPublished - 2020 Apr 15

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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