esomat.shape.deformation

8/4/2019 ESOMAT.shape.deformation

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Developments in Martensitic

and Bainitic Steels:Role of Shape Deformationwww.msm.cam.ac.uk/phase-trans

ds

1


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Diffusion of all atoms during

nucleation and growth.

Sluggish below about 850 K.

Invariant-plane strain shape

deformation with large shear

component.

No iron or substitutionalsolute diffusion.

Thin plate shape.

Cooperative growth of

ferrite & cementite.

No change in bulkcomposition.

Diffusionless

nucleation & growth.

Carbon diffusion duringparaequilibrium nuc leation. No

diffusion during growth.

Carbon diffusion during

paraequilibrium nuc leation &

growth.

ALLOTRIOMORPHIC

FERRITE

IDIOMORPHIC

FERRITE

MASSIVE FERRITE

PEARLITE

WIDMANSTATTEN

FERRITE

..

BAINITE & ACICULAR

FERRITE

MARTENSITE

RECONSTRUCTIVE DISPLACIVE


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Watson and McDougall


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Swallow & Bhadeshia,1996


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Chang et al., 1996

Lower bainite, transformedwith and without stress


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14001200100080060040020000-100

0

100

200

300

400

500

bainite

austenite

Temperature / C

ResidualStress/MP

a


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14001200100080060040020000-100

0

100

200

300

400

500

martensite

bainite

austenite

Temperature / C

ResidualStress/M

Pa

Jones & Alberry, 1977


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Ohta et al., 2000-2003


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Ohta et al., 2000-2003


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Chang et al., 1996

Lower bainite, transformedwith and without stress


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Ohta et al., 2000-2003


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Ohta et al., 2000-2003


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c

r

ds

1


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Singh & Bhadeshia, 1998


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What is the minimum temperature atwhich bainite can be obtained?


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The nucleation of bainite

must involve the partitioningof carbon.

The mechanism of nucleation is

otherwise identical to that ofmartensite.


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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 precipitationfrom austenite


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Bainite-start temperature


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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%

Temperature/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%

Time

/s

Fe-2Si-3Mn-C wt%

1 month 1 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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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

Temper

ature/oC

BS~ 350oC

MS= 120oC


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X-ray diffraction results

0

20

40

60

80

100

200 250 300 325

Temperature/o

C

Percentage

of

phase

bainitic ferrite

retained austenite


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50 nm

a

gg

g a


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20 nm

g ga

a

a


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Cobalt (1.5 wt%) and aluminium (1 wt%)increase the stability of ferrite relative

to 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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Scifer, 5.5 GPa with

ductility!

Kobe Steel


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1201008060402000

2000

4000

6000

8000

10000

Fibre or Whisker Diameter / m

TensileStren

gth/MPa

"Scifer"

Whisker

1 D i i ht i f 9 k f


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1 Denier: weight in grams, of 9 km offibre

50-10 Denier

Scifer is 9 Denier


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Uejiet al.,

2002
http://../Slides/Slides/hard.bainite.ppt


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Uejiet al.,

2002

C l t l li i t t il
http://../Slides/Slides/hard.bainite.ppt


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ds

1

Can completely eliminate tensileresidual stresses in welded joints.

Extremely fine, strong and toughsteel in bulk form.


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Tempered

400C 30 min

Tempered400C 30 min

500 MPa stress

Stewart et al., 1994


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Martensite, low and high stress


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et al.,

esomat.shape.deformation

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