Novel tooling materials with extremely highdimensional stability for press forming of CFRTP

Hiromichi T. Fujii*, Naoki Sakaguchi, Haruyasu Ohno, Kotaro Ona* fujii@shst.co.jp
Principal researcher
SHINHOKOKU STEEL CORP.
(SHINHOKOKU MATERIAL CORP., 10/1/2021 ~)October 19-21, 2021 / www.theCAMX.org

Personal introduction• Speaker Name:

Hiromichi T. Fujii• Company:

Shinhokoku Steel Corp.
(Shinhokoku Material Corp., 10/1/2021 ~)• Job Title:

Principal researcher• Brief bio information;– Visiting Scholar, University of Cambridge, 2008– Ph.D. (Engineering), Graduate School of Engineering, Tohoku University, 2009
– Assistant Professor, Tohoku University, 2009-2018– Visiting Scholar, The Ohio State University, 2010-2011– Principal Researcher, Shinhokoku Steel Corp., 2019-THE
FUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

Page 3October 19-21, 2021 / www.theCAMX.org

Invar alloy used as a tooling material of CFRP moldingInvar alloy✓✓✓

Moldingtemp.

Fe-36mass%Ni alloy
Low thermal expansion (R.T. ~ 200ºC)
Tooling material for CFRP components inaerospace industryRequirements for tooling material✓✓✓

Close dimensional change to CFRP
between room and molding temps.
(Match the CTE* values of productionand tooling materials)
High durability
Thermal stability* Coefficient of thermal expansion

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

Large difference
Small difference

Comparison of relative thermal expansion curves to a dimension atroom temperature between tooling materials.

fujii@shst.co.jp

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October 19-21, 2021 / www.theCAMX.org

Background and research motivation
CFRTP components✓✓✓Weight reduction
Mass production
High dimensional accuracy

Potential of tooling technology✓ Precise molding✓ Intricate structure with small curvature✓ Stable production of high qualitycomponents✓ Cost reduction
Summary of lifetime cost in each tooling material for small
CFRP component with an intricate structure.

THE
FUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

Page 5October 19-21, 2021 / www.theCAMX.org

Press forming with advanced invar alloy molds
Tooling materials for press forming✓ Near-net shape(As-cast structure)✓ High durability(Decrease in aged deterioration)✓ Thermal stability(Precise molding of intricate structure)✓ Maintenance free(Automation of factory, mass production)

Press forming with the advanced invar alloy molds that allow mass
production of the small CFRP components with intricate structure.

Cast invar alloys with supreme durability can be a powerful tool for CFRTP press forming

THE
FUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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October 19-21, 2021 / www.theCAMX.org

Objective

To reveal the relationship between chemical composition and thermalexpansion characteristics in the low thermal expansion alloys, and theeffects of microstructural control on mechanical properties.

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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October 19-21, 2021 / www.theCAMX.org

Sample preparation
Chemical composition✓

Fe64-x-yNi31+xCo5+y alloys(Base composition: Fe65Ni35, Fe64Ni31Co5 and Fe55Ni28Co17)

Thermal treatment

Cryogenic treatment

Cryogenic treatment

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

Page 8October 19-21, 2021 / www.theCAMX.org

Thermal treatment developed for strength improvement
 Developed cast invar alloy
Casting

Near-net shape

Developed
thermaltreatment

Fine grains

Finishprocessing

High rigidity
Low CTE

10mm

 Conventional cast invar alloy
Casting

Near-net shape

Thermaltreatment

Coarse grains

Finishprocessing

Low CTE

10mm

 Forged invar alloy
Casting

Ingot

ForgingHigh rigidity

THE
FUTURE

Fine grains
Precisionmachining

Thermaltreatment

Finishprocessing

Low CTE

H.T. Fujii

SHINHOKOKU STEEL CORP.

10mm

fujii@shst.co.jp

Page 9October 19-21, 2021 / www.theCAMX.org

Results and discussion

October 19-21, 2021 / www.theCAMX.org
September 21-24, 2020 / www.theCAMX.org

Conventional low thermal expansion alloys
Low thermal expansion characteristics✓✓Magnetic contraction and natural thermalexpansion are canceled by each otherbelow Curie temperature
Temperature range can be expanded byincreasing Curie temperature

Naturalthermal
expansion

Curie temperature of iron based alloys✓Strongly depend on their chemicalcompositions

Low thermal expansion

Thermal expansion curves obtained from super invar (Fe64Ni31Co5)
and kovar (Fe55Ni28Co17) alloys. For comparison, a curve of pureiron is also shown by dotted line.

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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Formulation of Curie temperature in low thermal expansion alloys
Dependence of Curie temperature on
chemical composition✓✓

Linear relationship between Fe content andCurie temperature
Curie temperature could be raised by over
100ºC compared to conventional alloys

Empirical equation of Curie temperature✓Scott’s equation*
𝜃 = 19.5 𝐶𝑁𝑖 + 𝐶𝐶𝑜 − 22𝐶𝑀𝑛 − 465
𝜃 = 19.5 100 − 𝐶𝐹𝑒 − 465
𝜃 = −19.5𝐶𝐹𝑒 + 1485
* “Physics and applications of invar alloys”,
Maruzen Company, (1978), 528-531.

THEFUTURE

H.T. Fujii

Relationship between Curie temperature and Fe content in the Fe64-x-yNi31+xCo5+y.
Curie temperatures were estimated from inflection points of thermal expansion
curves.

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

Page 12October 19-21, 2021 / www.theCAMX.org

Development of novel low thermal expansion alloys
Control of low thermal expansion
characteristics

✓
✓R.T.

Thermal expansion curves obtained from newly developed alloys
by controlling Curie temperature. For comparison, the curves of
conventional super invar and kovar alloys are also shown by
dotted lines.

THEFUTURE

H.T. Fujii

Lower thermal expansion than conventionalalloysExpanded temperature range by increasing
Curie temperature
Average CTE between room and specifictemperatures [10-6 / ºC]

Material

Curie
temperature[ºC]

R.T. ~ 200ºC

R.T. ~ 300ºC

R.T. ~ 400ºC

Developed alloy A
Developed alloy BSuper invar
Kovar

314
363
250
378

1.3
2.3
1.7
5.2

1.92.34.1
4.9

4.4
3.7
6.9
5.4

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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Control of coefficient of thermal expansion
Average coefficient of thermal expansion✓Optimum Fe content for minimum CTE
could be easily determined from theconcave relationship✓Controllable by adjusting only Fe content
with 0.1% accuracy in desired
temperature range

Relationship between average coefficients of thermal expansion
and Fe content. The average coefficients of thermal expansion
were measured between room temperature and 100ºC.

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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Mechanical properties improved by heat treatment
Effect of thermal treatment onmechanical properties✓✓✓

Reverse austenite transformation frommartensitic phase formed by cryogenic
treatment
Grain refinement and increase indislocation density
Drastic improvement of yield strength

0.2% yield strength and Young’s modulus of the as-cast and the thermallytreated invar, super invar and kovar alloys. For comparison, those of the forgedalloys were also shown.

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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October 19-21, 2021 / www.theCAMX.org

Formation of martensitic grains by cryogenic treatment

AustenitematrixTHE
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Lenticularmartensite

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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Microstructural control to improve mechanical properties
Control of martensitic transformation✓✓

Linear relationship between area fraction ofmartensitic phase and Ni content
Drastic decrease with the slightest increasein Ni content

Cryogenic and heat treatments✓✓

Fine and equiaxed grains microstructure
Mechanical properties could be improved byadjustment of only Ni content

Relationship between area fraction of martensite phases formed during
cryogenic treatment and Ni contents in the Fe-Ni based low thermal
expansion alloys.

THE
FUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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October 19-21, 2021 / www.theCAMX.org

Effect of martensitic phase on mechanical properties
Mechanical properties determined by areafraction of martensitic phase✓✓Yield strength and tensile strength increased
with increasing the area fraction before
plateauing at 60%.
There was no significant dependence ofYoung’s modulus on the area fraction

Relationship between 0.2% yield strength after austenitetransformation and the area fraction of martensite phases formed
during cryogenic treatment by liquid nitrogen in the Fe64-x-yNi31+xCo5+yalloys.

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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Summary✓ The Curie temperatures of the developed materials were linearly decreased withincreasing Fe content. They could be raised above 350ºC without loss of their low
thermal expansion characteristics by the adjustment of only Fe content.

✓ The average CTE in the arbitrary temperature range could be controlled by theadjustment of Fe content. Improvement of mechanical properties of the developedmaterials through reverse martensitic transformation was dependent with the area
fraction of martensite phases formed during cryogenic treatment.

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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Hiromichi T. Fujii, Ph.D.
新報国製鉄株式会社
SHINHOKOKU STEEL CORPORATION

fujii@shst.co.jp
Principal researcher
SHINHOKOKU STEEL CORP.

CAMX 2021 発表論文
題 目： “Novel tooling materials with extremely high dimensional stability for press forming of CFRTP”
著 者： Hiromichi T. Fujii, Naoki Sakaguchi, Haruyasu Ohno, and Kotaro Ona
年： 2021頁： TP21-0295 (14 pages)
概 要；
Press forming of carbon fiber reinforced thermoplastic (CFRTP) pre-preg has been attracted attention as a promising technique to drasticallyreduce its production cycle time. Consideration of thermal expansion differences between tooling material and CFRTP part is essential toachieve the desired dimensional tolerances in the press forming. An invar alloy is known as one of low thermal expansion materials and has
been used as a tooling material for the autoclave molding. However, its low thermal expansion characteristics is lost above approximately
200ºC and normal thermal expansion occurs above the Curie temperature of 240ºC. In the press forming of CFRTP generally conductedabove 250ºC, therefore, the invar alloy cannot be used as a tooling material to achieve precise forming. In this study, novel tooling materials
with high dimensional stability between room and press forming temperatures were developed with the aim of precise press forming of
CFRTP components.
URL: https://www.nasampe.org/store/viewproduct.aspx?id=19557540

THEFUTURE

H.T. Fujii

SHINHOKOKU STEEL CORP.

fujii@shst.co.jp

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October 19-21, 2021 / www.theCAMX.org