実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF Experimental Report

提出日 Date of Report

課題番号 Project No.

装置責任者 Name of responsible person

2017A0129

Kazuya Aizawa

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Effect of strain rate on reverse austenite transformation

BL19

behavior in medium Mn steel during thermomechanical

実施日 Date of Experiment

processing

6/22-25

実験責任者名 Name of principal investigator
Akinobu Shibata
所属 Affiliation
Kyoto University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
Fe-5Mn-2Si-0.1C (mass%) alloy

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Nowadays, new class of steels, medium Mn steels containing 3 – 7 mass % Mn, are classified as the3rd generation advanced high strength steel (AHSS), and numerous research groups all over the world
are focusing on the study about medium Mn steels. We utilized thermomechanical processing, i.e.,
precisely controlled heat treatment and deformation at elevated temperature, to control microstructuresand mechanical properties in a medium Mn steel (Fe-5Mn-0.1C-2Si (mass %)).

We found that

thermomechanical processing in some specific conditions could obtain a certain amount of retained
austenite at room temperature (RT). The medium Mn steels containing a certain amount of retained
austenite showed mechanical properties with an excellent strength-ductility balance due todeformation-induced martensitic transformation of the retained austenite, i.e., transformation-induced
plasticity (TRIP). We believe that elucidating the underlying mechanism for the formation of retained
austenite in medium Mn steels not only advances phase transformation theory in metals and alloys, butalso leads to an improvement of thermomechanical processing for achieving excellent mechanicalproperties based on theoretical aspects.
12. 実験方法及び結果（つづき） Experimental method and results (continued)
Recently, we have found throughin-situ neutron diffraction analysis thatthecompressiveaccelerated

thedeformation

austenite

reversetransformation significantly.

In ordertoaustenite

reversebehavior

duringunderstandtransformation
thermomechanicalsystematically,

theinvestigatedeffectaustenite

reverseprocessing
present
strain

study

rate

on

transformation

behavior

duringthermomechanicalprocessinginMnmediumsteel.

In-situ neutron diffraction experimentwasconducted

thermomechanicalusing

theprocessing

simulator installed at BL19 Takumi.
Figure 1 shows the appearance andschematic

illustrationof

theFigure 1 (a) The thermomechanical processing simulator
installed at the BL 19 TAKUMI and schematic illustration of
the testing part of the simulator (b) the geometry of thecompression experiment with respect to the incident anddiffracted neutron beams.

thermomechanical processing simulator.
The cylindrical specimen 11 mm in height and 6.6 mm in diameter with fully martensitic structure washeated up to from 640 ˚C to 720 ˚C (ferrite + austenite two phase region). Then, the specimen was
deformed in compression at a strain rate of 10-2 s-1 or 10 -4 s-1 and kept at the same temperature for10000 s after releasing the load.

The experiment without deformation and with compressivedeformation at a strain rate of 1 s-1 was conducted in our previous beamtime (proposal number:2015E0001).
The volume fraction of reversely transformed austenite at 640 ˚C, 700 ˚C, and 740 ˚C evaluated fromthe neutron diffraction profiles are presented in Figure 2 (black plots: without deformation, blue plots:with compressive deformation at a strain rate of 10-4 s-1, green plots: with compressive deformation at astrain rate of 10-2 s-1, red point: with compressive deformation at a strain rate of 1 s-1). It should be
noted that deformation period changes with strain rate, i.e., about 0.9 s for the strain rate of 1 s-1 andabout 9000 s for the strain rate of 10-4 s-1. The times for start of deformation and finish of deformation
are also indicated in Figure 2. In the case of the deformation at strain rates of 1 s-1 and 10-2 s-1 (redplots and green plots), the volume fraction of reversely transformed austenite was much higher thanthat without deformation. This indicates that the compressive deformation with relatively fast strain
rate accelerated austenite reverse transformation.

On the other hand, we find the interestingtendency that volume fraction of reversely transformed austenite during compressive deformation at astrain rate of 10-4 s-1 (blue plots) was smaller than that without deformation.
22. 実験方法及び結果（つづき） Experimental method and results (continued)
Now we are evaluating changes in lattice constant (i.e., partitioning behavior of alloying elements)
and dislocation density from the obtained neutron diffraction patterns and discussing the effect of strain
rate on austenite reverse transformation behavior.

Figure 2 Volume fractions of reversely transformed austenite at 640 ˚C, 700 ˚C, and 740 ˚C ((blackplots: without deformation, blue plots: with compressive deformation at a strain rate of 10-4 s-1, green
plots: with compressive deformation at a strain rate of 10-2 s-1, red point: with compressivedeformation at a strain rate of 1 s-1).

3