実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report
June 19, 2017

課題番号 Project No.2016B0087

装置責任者 Name of responsible person

実験課題名 Title of experiment

S. Harjo

In situ Neutron Diffraction during Low-Cycle Fatigue Testing on

装置名 Name of Instrument/（BL No.）

Fe-Mn-Si-Based Alloys.

TAKUMI (BL19)

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Takahiro SAWAGUCHI

Feb. 24-28, 2017 (5 days)

所属 Affiliation: National Institute for Materials ScienceMar. 2, 2017 (1 day)

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-15Mn-10Cr-8Ni-4Si (mass%) alloy, Solid Fe-15Mn-10Cr-8Ni-3Si (mass%) alloy, Solid Fe-30Mn-4Si-2Al (mass %) alloy, Solid Fe-30Mn-3Si-3Al (mass %) alloy, Solid Fe-28Mn-6Si-5Cr (mass %) alloy, Solid

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.

Three kinds of measurements were performed at BL19 of MLF J-PARC. The obtained results are still underanalyses and discussion in order to make presentation and then submission as full papers.
(1) An evidence for reversible martensitic transformation under cyclic loading
We have proposed that low-cycle fatigue lives of Fe-high Mn alloys can be drastically improved when areversible two-way martensitic transformations between γ-austenite and ε-martensite occurs. Up to now,
however, the microstructural evidence for the latter phenomenon is limited. In the present experiment, wetried to prove the reversible martensitic transformation under cyclic loading in a Fe-30Mn-4Si-2Al steel thatexhibits an extraordinarily long LCF life. A dog-bone typespecimens was subjected to cyclic tension-compression
loadings at room temperature, at the total strain range of0.04, and at the strain rate range of 0.0004 - 0.004 s-1.
During the cyclic deformation, neutron diffraction profiles
were obtained by the two detector banks set at 90 degrees
with respect to the incident beam. Fig. 1 exhibits theapplied load history and the corresponding diffraction
intensities of 10-11 ε in the two directions, which clearlyshows the reversible martensitic transformation.
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Fig. 1 Applied load history (a) anddiffraction intensities of 10-11 epsilon
in the two directions (b) for 4Si-2Al

2. 実験方法及び結果（つづき） Experimental method and results (continued)(2) Effect of phase stability on the reversible martensitic transformation
The effect of phase stability between the γ- and ε-phases on the reversible martensitic transformation
was examined by the LCF in-situ neutron diffraction at room temperature in different Fe-30Mn-(6-x)Si-xAlalloys, and by the LCF in-situ neutron diffraction at different temperatures in a Fe-28Mn-6Si-5Cr shapememory alloy.
In the both cases, the reversible martensitic transformation is obvious at a certain thermodynamiccondition, i.e. at room temperature in the Fe-30Mn-4Si-2Al alloy and at 423 K in a Fe-28Mn-6Si-5Cr shapememory alloy. As compared to these, decrease in Al content in the Fe-Mn-Si-Al system or decrease indeformation temperature in the shape memory alloy resulted in rapid increase in the ε fraction under cyclicloading. For example, Fig. 2 exhibits the changes in diffraction profiles and load with time for
Fe-30Mn-5Si-1Al alloy in the transverse direction. The diffraction intensities rather monotonically increase
undercyclicloading,andthereversible

transformation is less obvious. On the other hand,increase in Al content in the Fe-Mn-Si-Al system
or increase in deformation temperature in theshape memory alloy diminished the ε-martensite.
The results clearly indicate that the phasestability between the γ- and ε-phases is one of themost important controlling factors affecting thereversiblemartensitictransformation.

Anoptimum condition is considered to be ΔGγ→ε ≈ 0,
where both of the forward and reverse martensitic
transformations

canoccurwithanFig. 2 Changes in diffraction profiles and load withtime for 5Si-1Al in the transverse direction (ledequalpossibility.

(3) Comparison between tensile and cyclic deformations in Fe-15Mn-10Cr-8Ni-4Si alloy
Using a Fe-15Mn-10Cr-8Ni-4Si alloy, which is used as fatigue-resistant seismic dampers in a realconstruction, a comparative study was made on dynamic change in tensile and cyclically deformed
microstructure by means of neutron diffraction. A special attention was paid to the evolution of martensite
fractions of two types of martensites, namely ε-martensite and α’-martensite.
It is well known that the α’-martensite is formed at the intersections of the crossing ε-martensite variant
plates on different {111} habit planes. In the studied alloy, this was more obviously observed in the tensile
deformed microstructure, whereas the cyclic deformation exhibited less α’-martensite. The increase in theε-martensite versus accumulated plastic strain under cyclic deformation is also much slower than theincrease in the ε-martensite versus monotonic increase in the tensile plastic strain.
The result suggests suppressed growth of both types of martensite under the cyclic deformation. Further
analysis on this topic is still underway. Additional microstructural observations by ex-situ methods, such as
EBSD and TEM is also ongoing.

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