large chunks of extremely strong steel · 2014. 8. 11. · co 2d 5d 79 690 co+ al 16h 3d 78 690...
TRANSCRIPT
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Large Chunks ofExtremely Strong Steel
52nd Hatfield Memorial Lecture
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an apple weighs
1 Newton
1 m
= 1 Pa
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Brenner, 1956
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Scifer, 5.5 GPa and ductile
Kobe Steel
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1 Denier: weight in grams, of 9 km offibre
50-10 Denier
Scifer is 9 Denier
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Morinobu Endo, 2004
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Claimed strength of carbonnanotube is 130 GPaEdwards, Acta Astronautica, 2000
Claimed modulus is 1.2 TPaTerrones et al., Phil. Trans. Roy. Soc., 2004
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36000 km
tethered space elevatorArthur C. Clark (1979)
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geosynchronousorbit
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strength 130 GPa
modulus 1.2 TPa
215005420Nanotube
60004650Dynamite
m s-1J g-1
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data from Pan et al. 1999, Yu et al.2000
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An equilibrium number of defects.
Strength of a nanotube rope 2 mmlong is less than 2000 MPa
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•Strength produced by deformationlimits shape: wires, sheets...
•Strength in small particles relies onperfection. Doomed as size increases.
Summary
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Smallest size that can be achieved ina polycrystalline substance?
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Yokota & Bhadeshia, 2004
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Thermomechanical processinglimited by recalescence
Summary
Need to store the heat
Reduce rate
Transform at low temperature
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DISPLACIVE
RECONSTRUCTIVE
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Swallow and Bhadeshia,1996
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0
200
400
600
800
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Carbon / wt%
Tem
pera
ture
/ K
Fe-2Si-3Mn-C wt%
BS
MS
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1.E+00
1.E+04
1.E+08
0 0.5 1 1.5
Carbon / wt%
Tim
e /
sFe-2Si-3Mn-C wt%
1 month1 year
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C Si Mn Mo Cr V P
0.98 1.46 1.89 0.26 1.26 0.09 < 0.002
wt%
Low transformation temperature
Bainitic hardenability
Reasonable transformation time
Elimination of cementite
Austenite grain size control
Avoidance of temper embrittlement
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Tempe
ratu
re
Time
1200 oC2 days
1000 oC15 min
Isothermal transformation
125 oC-325 oChours-monthsslow
cooling
Air cooling
Quench
AustenitisationHomogenisation
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300
400
500
600
700
1.E+04 1.E+05 1.E+06 1.E+07
Time/ s
Vic
kers
Har
dne
ss
T = 200°C
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0
100
200
300
400
500
600
700
1.E+00 1.E+02 1.E+04 1.E+06 1.E+08
Time / s
Tem
pera
ture
/ o C
BS ~ 350oC
MS = 120oC
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Cookingtemperature?
180 to 220 °C
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X-ray diffraction results
0
20
40
60
80
100
200 250 300 325
Temperature/ oC
Perc
ent
age
of
phase
bainitic ferrite
retained austenite
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50 nm
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20 nm
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Conclusions
Low temperature transformation: 0.25 T/Tm
Fine microstructure: 20-40 nm thick plates
Carbide-free
Designed using theory alone
Typical mechanical properties:
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Cobalt (1.5 wt%) and aluminium (1 wt%)increase the stability of ferrite relativeto austenite
Refine austenite grain size
Faster Transformation
C Si Mn Mo Cr V P
0.98 1.46 1.89 0.26 1.26 0.09 < 0.002
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Original 5h 3/4d 63 550
Co 4h 11h 77 640
Co + Al 1h 8h 76 640
200oC
250oC
300oC
Steel Beginning End % Bainite HV
Original 4d 9d 69 618
Co 2d 5d 79 690
Co+ Al 16h 3d 78 690
Original 2.5h 1/2d 55 420
Co 1h 5h 66 490
Co + Al 0.5h 4h 66 490
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400
450
500
550
600
650
700
300 350 400 450 500 550 600 650
Temperature / oC
H V
30 min60 min24 h
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Fe-0.34C-5.08Cr-1.43Mo-0.92V-0.4Mn-1.07Si wt%
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excess carbon in solid solution in ferrite !
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Peet, Babu, Miller, Bhadeshia, 2004
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Peet, Bhadeshia, 2004
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Hammond and Cross, 2004
Velocity km s-1
Str
ess
/ G
Pa
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GRP
mild steel
“superbainite”
vehicle steel
GRP
Peter Brown (DSTL)
Dave Crowther (QinetiQ)
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“more serious battlefield threats”
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650 HV
590 HV
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ballistic mass efficiency
consider unit area of armour
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R. A. Jaramillo, S. S. Babu, G. M. Ludtka, R. A. Kisner, J. B.Wilgen, G. Makiewicz-Ludtka, D. M. Nicholson, S. M. Kelly,M. Murugananth and H. K. D. H. Bhadeshia
Scripta Materialia, (2004) in press.
30 Tesla field, 485 HV
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Francisca Garcia Caballero
Carlos Garcia Mateo
Mathew Peet
Kazu Hase
Pippa Swanell
Tomoyuki Yokota
Mohamed Sherif
Howard Stone
www.msm.cam.ac.uk/phase-trans
Suresh Babu
Daniel Crespo
Marimuthu Murugananth