37th John Player Memorial Lecture

Design of strong, tough & affordable engineering alloys

Fe

Ru

Os

Hs

Fe

Ru

Os

Hs

6d 2s

ferrite

austenite

DISPLACIVE

RECONSTRUCTIVE

c

r

s

1

Surface 1 Surface 2

Srinivasan & Wayman, 1968

50 µm

50 µm

UPPER BAINITE(High Temperature)

LOWER BAINITE(Low Temperature)

Carbon supersaturated plate

Carbon diffusion into austenite

Carbon diffusion into austenite and carbide

precipitation in ferrite

Carbide precipitation from austenite

5004003000

1

2

Temperature / °C

D

eca

rburi

stio

n t

ime /

s

Fe-0.4C wt%

TAe3Ae1

o

Carbon Concentration

T1

T1

Ae3'

T'o

x

Carbon in austenite

Tem

pera

ture

0.20.10.0250

300

350

400

450

500

Carbon in austenite / mole fraction

Temperature / °C

Ae3'TT'o o

UPPER BAINITE(High Temperature)

LOWER BAINITE(Low Temperature)

Carbon supersaturated plate

Carbon diffusion into austenite

Carbon diffusion into austenite and carbide precipitation in ferrite

Carbide precipitation from austenite

0.2 µm

30020010000

10

20

30

40

50

60

70

Test temperature / °C

Charpy impact / Jwith

carbides

1 µm

Carbide-free alloys

Fe 0.4C 2Si 3MnFe 0.2C 2Si 3MnFe 0.4C 2Si 4Ni

wt %

2001000-100-2000

10

20

30

40

50

60

700.4C-3Mn-2Si

Test temperature / °C

Charpy impact / J

Very poor toughness!

50 µm

Carbon

x x T_0

54321300

400

500

600

Carbon / at.%

Fe-CFe-Ni-Si-C

Fe-Mn-Si-C

T-zero curves

50 µm

0.4C-3Mn-2Si0.4C-4Ni -2Si0.2C-3Mn-2Si

Impact Energy

2001000-100-2000

10

20

30

40

50

60

70

Test temperature / °C

120010008006004002000

Pearlite

Martensite

Bainite

kilocycles to Crack Initiation

Yates, Jerath

Yates, Jerath

100806040200

Pearlite

Martensite

Bainite

RailWheel

Rolling Contact Wear Rate (mg/m of slip)

Advances in carbide-free bainitic steels

250020001500100020

40

60

80

100

120

140

160

180

Ultimate tensile strength / MPa

Fract

ure

tou

ghness

/ M

Pa √

m

18 wt% Ni maraging steel

QT

an apple weighs 1 Newton

1 m

= 1 Pa

1201008060402000

2000

4000

6000

8000

10000

Fibre or Whisker Diameter / µm

Tensile Strength / MPa

"Scifer"

Whisker

1201008060402000

2000

4000

6000

8000

10000

Fibre or Whisker Diameter / µm

Tensile Strength / MPa

"Scifer"

Whisker

Scifer, 5.5 GPa with ductility!

Kobe Steel

Atom probe image of Scifer,

5.5 GPa steel wire

Bhadeshia and Harada, 1993

1 Denier: weight in grams, of 9 km of fibre

10 Denier

Scifer is 9 Denier

200 °C for 20 days 200 °C for 20 days

2.5 GPa2.5 GPa

Caballero, Mateo & Bhadeshia

Advances in carbide-free bainitic steels

250020001500100020

40

60

80

100

120

140

160

180

Ultimate tensile strength / MPa

Fract

ure

tou

ghness

/ M

Pa √

m

18 wt% Ni maraging steel

QT

www.msm.cam.ac.uk

0 50 100 150 200

Pressure / kbar

800

400

0

ε

1200

1600

0 50 100 150 200

Pressure / kbar

800

400

0

ε

1200

1600 Bundy (1965)