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Kobe Steel, LTD. Proprietary Information1
Technologies for reliable titanium alloy forgings focusing on ultrasonic inspection
in aerospace industry
Yoshinori Ito, Hiroyuki Takamatsu and Keiji KinoshitaKobe Steel, Ltd.
Kobe Steel, LTD. Proprietary Information
Outline of aerospace sector in Kobe Steel
2
VAR MeltingFurnace
Open Die Forging Press
Closed Die Forging Press
Ring RollingMill
Heat treatment Inspection Shipment
• Kobe Steel has integrated production line for titanium alloy products which allows us consistent quality design and quality control.
Kobe Steel, LTD. Proprietary Information
Long Supply History for Aerospace – 55 years
3
• No. 1 titanium supplier on the aerospace market in Japan.• First delivery for aerospace application was in 1959.
Supply Record for V2500 Jet Engine
(Courtesy IHI)
Fan Cases :More than 10,000 pcs Deliverywith Internal Ingots since 1985
Compressor Disks and Shafts :More than 6,000 pcs Deliverywith Internal Ingots since 1986
Kobe Steel, LTD. Proprietary Information
New production facilities
4
Japan Aeroforge: 50,000 metric ton forging press Started-up in 2013
• Recently, we have installed new production facilities which allowed us provide large titanium forgings meeting specifications in aircraft industry.
• 50,000 metric ton forging press, Heat Treatment Plant, Inspection Plant, et al.
Kobe Steel, LTD. Proprietary Information5
Technology platform for process design
• Mechanical tests• Inspections
• Forging simulation using FEM• Initial condition
Cycles to Failure
Stre
ss
• Process design is key technology to provide high quality titanium forgings. • Establishment of forging simulation technique and processing window is essential.
• Tensile properties• Fatigue properties• Toughness• Ultrasonic inspection• Metallograph
et al.
• Forging method• Forging condition• Dies shape• Preform shape
et al.
• Temperature, StrainStrain rate
• Shape, Load et al.
Process design
• Processing window
• Based on microstructure, properties et al.
Kobe Steel, LTD. Proprietary Information6
Forging simulation using FEM analysis
Equivalent strain distribution Temperature distribution
Isothermal flow stress curves (Input data in FEM)
Stress-strain curves (Compression test)
Removed the adiabatic heating effect
Optimized boundary condition
0
50
100
150
200
250
300
350
400
450
500
0.0 0.5 1.0 1.5 2.0 2.5
Stre
ss /M
Pa
Strain
850℃
900℃
950℃
1000℃
1050℃
1100℃
0
50
100
150
200
250
300
350
0 0.2 0.4 0.6 0.8
Stre
ss /M
Pa
Strain
850℃
900℃
950℃
1000℃
1050℃
1100℃
Kobe Steel, LTD. Proprietary Information7
Experimental facilities for process design
Thermo-mechanical simulator (Small test piece)
Lab-scale forging press
Microstructural analysis,characterization
Process Microstructure Properties
Kobe Steel, LTD. Proprietary Information8
Technologies of improving ultrasonic detectability
Our goal• Design our forging process (Shapes of dies and preforms, and process
conditions et al.) to optimize mechanical properties and ultrasonic detectability.
• Ultrasonic simulation • UT operation
-1.E-01
-8.E-02
-6.E-02
-4.E-02
-2.E-02
0.E+00
2.E-02
4.E-02
6.E-02
8.E-02
1.E-01
0.E+00 2.E-06 4.E-06 6.E-06 8.E-06 1.E-05
時間(s)
z変
位(a
.u.)
Time /s
Ampl
itude
(a.u
.)
• Forging simulation using FEM• Initial condition
• Processing window
Kobe Steel, LTD. Proprietary Information9
Necessity of ultrasonic inspection
• Each defects in titanium alloys have the potential to cause catastrophic aircraft engine failures.
Ultrasonic inspection
Defects in forgings • Inclusions (Hard alpha et al.)• Cracks• Voids(Rarely occurred, but it is crucial.)
Titanium alloy forgings
Sign
al
Defects?Microstructure
(Noise)?
Time
Surface echo Bottom echo
Kobe Steel, LTD. Proprietary Information10
Influence on ultrasonic detectability
• Clarification of the effect of microstructure on ultrasonic noise.• Establishment of a prediction technique of ultrasonic noise.
Material characteristicsDensity, Wave speed,Attenuation,Grain size, Grain shape,Texture, et al.
Inspection characteristicsFrequency (Wavelength), Diameter of transducer,Focal length, Focussed or flat, et al.
200μm
Microstructure of beta forged Ti-6246 alloy
Beta forged Ti-6246 alloy• It have good strength and toughness balance so it is used for critical parts
(disks et al.) in aircraft engine. But it is well known that beta forged titanium alloys generate high backscattering noise due to microstructure.
Kobe Steel, LTD. Proprietary Information11
F..D
.
(Non-deformation)0% reduction 67% reduction
0
0.005
0.01
0.015
0.02
0.025
230 235 240 245 250R
MS
sig
nal l
evel
/ V
Time/μs
67%
Surface echo Bottom echo
0%
Lab-scale experimental results
β grain boundary
Elongated β grain
200μm200μm
Ultrasonic signals (Measured)Microstructures
F..D. : Forging direction
• Frequency: 5MHz
Kobe Steel, LTD. Proprietary Information12
Lab-scale experimental results
0
0.005
0.01
0.015
0.02
0.025
230 235 240 245 250R
MS
sig
nal l
evel
/ V
Time/μs
: Parallel to the F.D. : Perpendicular to the F.D.
Incident ultrasonic wave
Elongated β grain
Parallel
Perpendicular
F.D
.
F..D. : Forging direction
Kobe Steel, LTD. Proprietary Information13
Computer simulation regarding ultrasonic scattering
Computer simulation based on FEM
Multilayered model(Titanium alloy)
Transducer
Homogeneous body
Air
d m
Planar grain boundaries
Grain (Velocity 1)
-0.10-0.08-0.06-0.04-0.020.000.020.040.060.080.10
0.0 2.0 4.0 6.0 8.0 10.0In
tens
ity o
f sig
nal (
a.u.
) Time/μs
Transmitter pulse Bottom echo
Backscattering
Ultrasonic signals (Simulated)
Kobe Steel, LTD. Proprietary Information14
Computer simulation regarding ultrasonic scattering
Transducer
Pro
paga
tion
dire
ctio
n
Transducer
10mm
10m
m
Case 1 Case 2 Ultrasonic signals (Simulated)
• These simulation models provide similar profiles to experimental results.
Time/s
Am
plitu
de (a
.u.)
Kobe Steel, LTD. Proprietary Information15
Concept of process design for ultrasonic detectability
• Ultrasonic simulationusing FEM
-1.E-01
-8.E-02
-6.E-02
-4.E-02
-2.E-02
0.E+00
2.E-02
4.E-02
6.E-02
8.E-02
1.E-01
0.E+00 2.E-06 4.E-06 6.E-06 8.E-06 1.E-05
時間(s)
z変
位(a
.u.)
Time /s
Ampl
itude
(a.u
.)
• Forging simulation using FEM• Initial condition
Kobe Steel, LTD. Proprietary Information16
Practical application to production-scale parts
Heating
Machining
Hot die forgingFan AC followed by STA
Disc 1: Not applied Disc 2: Applied
• Material : Ti-6246 alloy
General Appearance of disks • Diameter: approx. 700mm• Thickness: approx. 50mm
Kobe Steel, LTD. Proprietary Information17
Practical application to production-scale parts
: Not applied: Applied
C-Scan images
A-Scan images
Disc 1: Not applied Disc 2: Applied
• It allows us to provide forging parts with lower backscattering noise (Higher reliability).
Lower noise (Good)Higher noise (Bad)
Kobe Steel, LTD. Proprietary Information18
Conclusions
• Kobe steel is an integrated manufacturer of titanium forgings, from melting process to final products, and we have essential technologies to provide high quality titanium forgings, such as forging simulation, dies design, process design, et al.
• Besides mechanical properties, ultrasonic detectability is required for critical parts (like disks) in aircraft engine. It is well known that ultrasonic testing for titanium alloy forgings is difficult because ultrasonic backscattering noise due to microstructural features can mask reflection from defects.
• This talk introduced the outline of our technologies to improve the ultrasonic detectability of titanium forgings.
Kobe Steel, LTD. Proprietary Information19
Thank you for your attention.