Effect of austenite grain size on the deformation induced γ→ε martensitic transformation and mechanical properties in an Fe-27 mass%Mn alloy

Hideshi Nakatsu, Takeshi Miyata, Setsuo Takaki

Research output: Contribution to journalArticle

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Abstract

In an Fe-27 mass%Mn alloy, which has a fully austenitic structure at room temperature and undergoes deformation-induced transformation from austenite (γ) to epsilon martensite (ε), the effects of γ grain size on the deformation-induced ε transformation and mechanical properties have been investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffraction analysis. The mean γ grain size was controlled to be between 10 and 100 μm by a recrystallization method. With grain refining, the formation of ε is suppressed and mechanical properties are improved. When the size of γ grains is as large as 100 μm, very thin ε plates form in the early stage of tensile deformation. But when refined to around 10 μm, they do not form during the deformation up to the true strain of 0.1 but only the dislocation density increases. For the formation of deformation induced ε, a lot of partial dislocations have to move on {111}γ planes closely. In the alloy with fine γ grains, however, the number of dislocations which can be piled up on each {111}γ plane is decreased by grain-refining, so that a secondary slip system acts prior to the formation of ε plates. This is the reason why the deformation induced ε transformation is suppressed by grain-refining. Moreover, in the alloy with large γ grains, a significant stress concentration takes place at grain boundaries on which deformation induced ε plates impinge, and this results in the onset of a quasi-cleavage fracture attributed in grain boundary exfoliation. Austenite grain refining gives the favorable effect as follows: 1) reducing the stress concentration at grain boundaries, 2) uniform dispersion of deformation strain, thus this quasi-cleavage fracture is completely suppressed by the grain-refining to 10 μm.

Original languageEnglish
Pages (from-to)936-943
Number of pages8
JournalNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
Volume60
Issue number10
DOIs
Publication statusPublished - Jan 1 1996

Fingerprint

Martensitic transformations
martensitic transformation
austenite
Austenite
grain size
mechanical properties
refining
Mechanical properties
Refining
Grain boundaries
grain boundaries
stress concentration
Stress concentration
cleavage
tensile deformation
thin plates
martensite
Martensite
X ray diffraction analysis
Optical microscopy

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys
  • Materials Chemistry

Cite this

Effect of austenite grain size on the deformation induced γ→ε martensitic transformation and mechanical properties in an Fe-27 mass%Mn alloy. / Nakatsu, Hideshi; Miyata, Takeshi; Takaki, Setsuo.

In: Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, Vol. 60, No. 10, 01.01.1996, p. 936-943.

Research output: Contribution to journalArticle

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