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High strength and ductility combination in nano-/ultrafine-grained medium-Mn steel by tuning the stability of reverted austenite involving intercritical annealing

  • Jun HuEmail author
  • Jia-Mei Zhang
  • Guo-Sheng Sun
  • Lin-Xiu Du
  • Yue Liu
  • Ying Dong
  • R. D. K. Misra
Metals

Abstract

The structure–property relationship in 0.06C–5.5Mn steel subjected to different annealing temperatures and time was studied. Mn played a stronger effect on stabilizing austenite in comparison with Ni, and low-C medium-Mn steel possessed excellent hardenability. The reverse transformation of martensite to austenite occurred during intercritical annealing, and the volume fraction was first increased and then decreased on increasing annealing temperature or prolonging annealing time, indicative of change in thermal stability by element partitioning and coarsening of grain size. Correspondingly, the elongation was first increased and then decreased, consistent with the variation in the stability of reverted austenite. The yield strength was gradually decreased because of several factors, including recrystallization of α′ martensite, decreased stability of reverted austenite, and coarse grain size. The maximum product of strength and ductility was obtained on annealing at 650 °C for 10 min, which was attributed to the optimal stability of reverted austenite rather than the highest volume fraction, and tensile strength and elongation were 1120 MPa and 23.3%. The strain partitioning behavior of two phases was elucidated by analyzing Lüders straining and continuous work hardening after yield point elongation, and the deformation mechanism was strongly related to the stability of reverted austenite.

Notes

Acknowledgements

The authors gratefully acknowledge financial support by the National Natural Science Foundation of China (Grant No. 51604072) and the Fundamental Research Funds for the Central Universities (Grant No. N170704016). R.D.K. Misra also acknowledges continued collaboration with Northeastern University as Honorary Professor in providing guidance in research.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

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© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  1. 1.The State Key Laboratory of Rolling and AutomationNortheastern UniversityShenyangChina
  2. 2.Laboratory for Excellence in Advanced Steel Research, Department of Metallurgical, Materials and Biomedical EngineeringUniversity of Texas at El PasoEl PasoUSA

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