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

2016B0252

AIZAWA Kazuya

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）In situ neutron diffraction study on bainite transformation below

TAKUMI/BL19

the Ms temperature

実施日 Date of Experiment

実験責任者名 Name of principal investigator

2017/2/13~2/16 (3.5 days)

GONG Wu
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.
A steel with the chemical composition of Fe-0.3C-2Mn-2Si(wt%) was used in this study.

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.

In-situ neutron diffraction experiments were conducted on the beam-line 19 ‘TAKUMI’ at J-PARC with athermomechanical processing simulator (Thermecmastor-Z) installed on it. As illustrated in Figure 1, two kindsof heat treatments were performed. In the first one,the specimens were fully austenitized at 900°C for
180s, and then rapidly cooled down to various
temperature (330°C, 280°C, 250°C, 230°C) and heldfor 1.5 hours for isothermal transformation(1-stepisothermal holding process). While the other wascooled down to 250°C, then reheated to 280°C and330°C, and isothermally held (2-step isothermalholdingprocess).

By

analyzingtheneutrondiffraction profiles, kinetics of phase transformations

Figure 1 Heat treatment processes conducted in thein-situ neutron diffraction measurement.

and changes of carbon concentration in each phase were tracked in real time.

12. 実験方法及び結果（つづき） Experimental method and results (continued)
The in situ neutron diffraction experiments during TMCP were successfully performed and the following
results were obtained:(1) The kinetics of phase transformation during
austempering

below

theMs

(300°C)

weremeasured. Figure 2a shows the volume fraction ofthe BCC phase (martensite and bainitic ferrite)
during the austempering at 280°C. The volume
fraction of martensite increased with the decrease oftemperature from the Ms to 280°C. In thesubsequent isothermal holding at 280°C, theincrease of the BCC volume is corresponding to thebainite transformation.
(2)

The

carbonpartition

behavior

duringisothermal transformation was investigated. Figure
2b shows the lattice parameter of austenite
evolution during the isothermal holding at 280°C.
An apparent increase in the lattice parameter ofaustenite indicates that the carbon partition from themartensite and bainitic ferrite to austenite. The
carbon concentration in the retained austenite
decreased with the decrease of austempering
temperature due to the decrease of carbon diffusion

Figure 2 (a) The volume fraction of BCC phase(martensite and bainitic ferrite) (b) the lattice parameterof austenite evolutions during the austempering below
the Ms.

rate.
(3) The specimen austempered at 250°C exhibited the highest volume fraction of austenite. It is the integrated
results of various phenomena including martensite transformation, bainite transformation, carbon partition andcarbide precipitation.

2