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Austenite memory during reverse transformation of steels at different heating rates

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Title: Austenite memory during reverse transformation of steels at different heating rates
Authors: Saito, Genki Browse this author →KAKEN DB
Nakayama, Tomoya Browse this author
Sakaguchi, Norihito Browse this author →KAKEN DB
Ohno, Munekazu Browse this author →KAKEN DB
Matsuura, Kiyotaka Browse this author →KAKEN DB
Takeuchi, Masayoshi Browse this author
Sano, Taichi Browse this author
Minoguchi, Koki Browse this author
Yamaoka, Takuya Browse this author
Keywords: Transformation
Grain refinement
Orientation relationship
Ferritic steels
Crystallographic orientation
Issue Date: Sep-2019
Publisher: Elsevier
Journal Title: Materialia
Volume: 7
Start Page: UNSP 100409
Publisher DOI: 10.1016/j.mtla.2019.100409
Abstract: The austenite (gamma) structure reversely transformed from martensite in Fe-0.55C mass% C alloy was investigated at high temperatures using in-situ an electron backscatter diffraction (EBSD) method. When the heating rate was varied, a rapidly heating produced fine gamma grains, in contrast, a slow heating induced coarse gamma grains having the same crystal orientations as those of the prior gamma grains; known as "gamma memory". The most likely mechanism for the gamma memory could be variant restrictions owing to cementite (theta). To investigate the effect of theta on the gamma memory, the sample was tempered at 700 degrees C for 24 h and theta was precipitated. The tempered sample exhibited the gamma memory irrespective of the heating rate. To clarify the origin of the gamma memory, we focused on the reversely transformed gamma formed adjacent to the theta and directly observed the orientation relationships (ORs) using the in-situ EBSD. A crystallographic analysis on the between neighboring ferrites (alpha), theta, and gamma revealed the existence of Kurdjumov-Sachs OR between gamma and two alpha (alpha 1 and alpha 2), Isaichev OR between alpha and theta, and Pitsch OR between theta and gamma. In the all possible combinations, the reversely transformed gamma satisfying the K-S OR for two alpha variants was limited to four variants. The theta variant satisfying the Isaichev OR for alpha 1 and alpha 2 was limited to one variant, which was close to one of the four variants by Pitsch OR, which suggests the gamma memory is due to these variant restrictions among alpha-theta-gamma.
Rights: ©2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license
Type: article (author version)
Appears in Collections:工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 齊藤 元貴

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