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

Publikation: Beitrag in einer FachzeitschriftArtikelForschungBegutachtung

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.
Originalsprachedeutsch
Aufsatznummer139 (2017)
Seiten (von - bis)39 - 50
FachzeitschriftActa materialia
Jahrgang139 (2017)
PublikationsstatusVeröffentlicht - 29 Jul 2017

Fields of Expertise

  • Advanced Materials Science

Dies zitieren

On the microstructural characteristics influencing the yielding behavior of ultra-fine grained medium-Mn steels. / Steineder, Katharina; Krizan, Daniel; Schneider, Reinhold; Beal, Coline; Sommitsch, Christof.

in: Acta materialia, Jahrgang 139 (2017), 139 (2017), 29.07.2017, S. 39 - 50.

Publikation: Beitrag in einer FachzeitschriftArtikelForschungBegutachtung

Steineder, Katharina ; Krizan, Daniel ; Schneider, Reinhold ; Beal, Coline ; Sommitsch, Christof. / On the microstructural characteristics influencing the yielding behavior of ultra-fine grained medium-Mn steels. in: Acta materialia. 2017 ; Jahrgang 139 (2017). S. 39 - 50.
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abstract = "This paper systematically investigated the influence of microstructural characteristics such as grain sizeand morphology on the yielding behavior of a cold rolled medium-Mn Fe-6.4Mn-0.1C (wt{\%}) steel. Byintercritical 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 andpredominantly lath-like in the latter case. The influence of these initial microstructures and intercriticalannealing temperature (TIA) on the final microstructure and resulting mechanical properties was presentedin detail. Medium-Mn steels commonly exhibit large yield point elongations (YPE), easilyexceeding 10{\%}. Both low TIA and a globular microstructure remarkably supported the formation of largeYPE. 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 severalmedium-Mn steel compositions. Besides the effect of the RA stability on YPE, STEM investigations ondeformed tensile samples revealed an entirely different dislocation structure between the UFG globularand lath-like microstructure, suggesting different active deformation mechanisms depending on theoverall grain size and morphology. Based on this investigation, it was recommended to provide amartensitic microstructure prior to intercritical annealing in order to limit YPE. Furthermore, specialattention has to be paid to a careful design of the RA stability in order to adjust an appropriate balancebetween excellent mechanical properties and reduced YPE.{\circledC} 2017 Published by Elsevier Ltd on behalf of Acta Materialia Inc.",
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AU - Schneider, Reinhold

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AU - Sommitsch, Christof

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N2 - This paper systematically investigated the influence of microstructural characteristics such as grain sizeand morphology on the yielding behavior of a cold rolled medium-Mn Fe-6.4Mn-0.1C (wt%) steel. Byintercritical 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 andpredominantly lath-like in the latter case. The influence of these initial microstructures and intercriticalannealing temperature (TIA) on the final microstructure and resulting mechanical properties was presentedin detail. Medium-Mn steels commonly exhibit large yield point elongations (YPE), easilyexceeding 10%. Both low TIA and a globular microstructure remarkably supported the formation of largeYPE. 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 severalmedium-Mn steel compositions. Besides the effect of the RA stability on YPE, STEM investigations ondeformed tensile samples revealed an entirely different dislocation structure between the UFG globularand lath-like microstructure, suggesting different active deformation mechanisms depending on theoverall grain size and morphology. Based on this investigation, it was recommended to provide amartensitic microstructure prior to intercritical annealing in order to limit YPE. Furthermore, specialattention has to be paid to a careful design of the RA stability in order to adjust an appropriate balancebetween excellent mechanical properties and reduced YPE.© 2017 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

AB - This paper systematically investigated the influence of microstructural characteristics such as grain sizeand morphology on the yielding behavior of a cold rolled medium-Mn Fe-6.4Mn-0.1C (wt%) steel. Byintercritical 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 andpredominantly lath-like in the latter case. The influence of these initial microstructures and intercriticalannealing temperature (TIA) on the final microstructure and resulting mechanical properties was presentedin detail. Medium-Mn steels commonly exhibit large yield point elongations (YPE), easilyexceeding 10%. Both low TIA and a globular microstructure remarkably supported the formation of largeYPE. 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 severalmedium-Mn steel compositions. Besides the effect of the RA stability on YPE, STEM investigations ondeformed tensile samples revealed an entirely different dislocation structure between the UFG globularand lath-like microstructure, suggesting different active deformation mechanisms depending on theoverall grain size and morphology. Based on this investigation, it was recommended to provide amartensitic microstructure prior to intercritical annealing in order to limit YPE. Furthermore, specialattention has to be paid to a careful design of the RA stability in order to adjust an appropriate balancebetween excellent mechanical properties and reduced YPE.© 2017 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

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