On the microstructural characteristics influencing the yielding behavior of ultra-fine grained medium-Mn steels

Katharina Steineder, Daniel Krizan, Reinhold Schneider, Coline Beal, Christof Sommitsch

Research output: Contribution to journalArticle

Abstract

This paper systematically investigated the influence of microstructural characteristics such as grain size
and morphology on the yielding behavior of a cold rolled medium-Mn Fe-6.4Mn-0.1C (wt%) steel. By
intercritical annealing of heavily cold-worked and fully martensitic initial state, ultra-fine grained (UFG)
microstructures with different morphologies could be obtained, namely globular in the former case and
predominantly lath-like in the latter case. The influence of these initial microstructures and intercritical
annealing temperature (TIA) on the final microstructure and resulting mechanical properties was presented
in detail. Medium-Mn steels commonly exhibit large yield point elongations (YPE), easily
exceeding 10%. Both low TIA and a globular microstructure remarkably supported the formation of large
YPE. These YPE formed by localized deformation, which was analyzed by infrared (IR) thermography.
Using interrupted tensile testing a vivid linear correlation between decreasing retained austenite (RA)
stability and decreasing YPE could be manifested, while this dependency proved to be valid for several
medium-Mn steel compositions. Besides the effect of the RA stability on YPE, STEM investigations on
deformed tensile samples revealed an entirely different dislocation structure between the UFG globular
and lath-like microstructure, suggesting different active deformation mechanisms depending on the
overall grain size and morphology. Based on this investigation, it was recommended to provide a
martensitic microstructure prior to intercritical annealing in order to limit YPE. Furthermore, special
attention has to be paid to a careful design of the RA stability in order to adjust an appropriate balance
between excellent mechanical properties and reduced YPE.
© 2017 Published by Elsevier Ltd on behalf of Acta Materialia Inc.
Original languageGerman
Article number139 (2017)
Pages (from-to)39 - 50
JournalActa Materialia
Volume139 (2017)
Publication statusPublished - 29 Jul 2017

Fields of Expertise

  • Advanced Materials Science

Cite this