CFRP precision molding dies for mass production~ Newly developed low thermal expansion cast alloys ~Kotaro ONA1, Haruyasu OHNO1, Naoki SAKAGUCHI1, Shin UTSUNOMIYA2
1 Shinhokoku Steel Corporation, Saitama, JAPAN
2 National Astronomical Observatory of Japan, Tokyo, JAPANResults and discussion

Equivalent CTE(a) As-cast

010mm
Average grain size: 101 mm

Macrostructure images obtained from (a) the as-cast and (b) the cryogenic treated and annealed
specimens in Fe-32%Ni-5%Co alloys.

400

Conventional cast alloy

34.3%NiOptimumcomposition

35.1%Ni

Casting process using researchmelting furnace

Temperature

Foged alloy

300

160
0.2% Yield strength

Young’s modulus(473 K)200(673 K)

100

140

120

100

02. Sample preparation

80Invar

Kovar

Invar

Kovar

Types of alloys
Recrystaillzation

600mm
Reversetransformation

Cryogenic treatment by liquid
nitrogen immersion
Time77 K
Dislocation strengthening

Martensite phase

600mm

Mechanical properties of the developed invar and kovar alloys. For comparison,
those of the conventional alloys and forged alloys are also shown.

600mm

Optical microscope images of Fe-x%Ni invar alloys after cryogenic treatment at 77 K.
29.5%Ni

30.0%Ni

Optimumcomposition

 Conclusions

30.5%Ni

77 K

1.

Novel LTE cast alloys with equivalent CTE of CFRP
were developed by precise control of Ni content,
which would enable high precision molding.

2.

The mechanical properties could be drastically
improved by the cryogenic treatment and annealing,
while maintaining the low thermalexpansion.

Refinement strengthening

3. Microstructural characterization

Microstructural observation by
optical microscopy

Optical microscopy
X-ray diffractometry

Thermal expansion measurement
Tensile test of round specimens

300mm300mm

300mm

Optical microscope images of Fe-x%Ni-15%Co kovar alloys after cryogenic treatment at 77 K.

4. Evaluation of properties
Developed cast alloy

131130130

0.2% Yield strength, sYS / MPa

33.2%Ni800

Drastic improvementB) Optimization of Ni and Co contents

Fe-x%Ni cast alloy
Fe-x%Ni-15%Co cast alloy

600
Temperature, T / K

Thermal expansion curves of the developed invar and kovar alloys. For
comparison, those of the conventional alloys are also shown.

XRD profiles for the as-cast and the cryogenic treated andannealed specimens in Fe-32%Ni-5%Co alloys.

1. Materials

Conventional alloy
Developed alloy

0Young’s modulus, E / GPa

7090
110
Diffraction angle, 2q / degree

Kovar cast alloy

53(200)50

ExperimentalRandomization(222)

To clarify the effect of cryogenic treatment and annealing on the microstructuralcharacteristics and mechanical properties in invar and kovar cast alloys in order to develop
novel LTE cast alloys for CFRP precision molding dies for mass production.

Cryogenic treated and annealed

Coarse columnar grains
were formed in the as-cast
Fe-32%Ni-5%Co specimen,
whereas the equiaxed finegrains with random texture
could be obtained by thecryogenic treatment andannealing.

(311)

 Objective(220)

Invar and Kovar cast alloys with high yield strength

Sharp texture(200)

Refinement strengthening(111)

Fine grained fcc

Intensity [arb. unit]

bcc + fcc

As-cast0110

fcc

Invar cast alloy225

fcc(b) Cryogenic treated and annealed

60080

High dislocation
density

Thermal expansion [1div.=0.1%]

Average grain size: 1660 mm

Developed heat treatment
 Cryogenic treatment + annealing Equiaxed fine grains

Temperature, T / degree C
200
40010mm120

Dislocation strengthening

Coarse columnar grains formed
during solidification process cause
strength deterioration in cast alloys.

C) Improvement of mechanical properties

145
140

Invar and Kovar cast alloys(Fe-36%Ni, Fe-29%Ni-17%Co)
 Low thermal expansion(extremely close to CFRP) Low elasticity and yield strengthA) Grain refinement and randomization

123

As CFRP designs have become increasingly large and complex especially in aerospace industry,
low thermal expansion (LTE) cast alloys are currently attracted attention as mold die for CFRP.

107
110

Objective and need

Evaluation of mechanical properties
using universal testing machine

Optimum compositions were determined by precise control of Ni
contents to obtain LTE alloys with equivalent coefficient of thermal
expansion (CTE) of CFRP.

Contact••

新報国製鉄株式会社
September 23-26 2019 Anaheim, CA

SHINHOKOKU STEEL CORPORATION•

Kotaro ONA

ona@shst.co.jp (R&D dept.)

en.eigyo@shst.co.jp (Sales dept.)•www.shst.co.jp