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© GNU Su-Jin Kim© GNU Su-Jin Kim

Deformation & StrengtheningDeformation & StrengtheningMaterial ScienceMaterial Science

Deformation & Strengthening

변형 경화


Deformation & StrengtheningDeformation & StrengtheningMaterial ScienceMaterial Science 2

Dislocation Motion ( 전위 )• Metals - plastic deformation occurs by dislocation movement• If dislocations can't move, plastic deformation doesn't occur!

• Single Crystal Slip ( 단결정미끄럼 )


Deformation & StrengtheningDeformation & StrengtheningMaterial ScienceMaterial Science

Slip Motion in Polycrystals ( 다결정미끄럼 )Polycrystals stronger than single crystals grain boundaries

are barriers to dislocation motion.



Anisotropy can be induced by rolling a polycrystalline metal.

- before rolling

235 m

- after rolling

- anisotropic( 이방성 ) since rolling affects grain orientation and shape.

rolling direction

Anisotropy in y

- isotropic( 등방성 ) since grains are equiaxed & randomly oriented.



Strengthening( 강화 ): 1: Reduce Grain Size( 결정립 미세화 )

Smaller grain size increase grain boundaries, barriers to make slip difficult.



Strengthening by 2. Solid Solution Alloying ( 합금 )• Reduce mobility of dislocations and increase strength



Ex: Solid SolutionStrengthening in Copper

• Tensile strength & yield strength increase with wt% Ni.

• Alloying increases y and TS.

Adapted from Fig. 7.16(a) and (b), Callister & Rethwisch 8e.

Ten

sile

str

engt

h (M

Pa)

wt.% Ni, (Concentration C)

200

300

400

0 10 20 30 40 50 Yie

ld s

tren

gth

(MP

a)wt.%Ni, (Concentration C)

60

120

180

0 10 20 30 40 50



Strengthening: 3: Cold Work (Strain Hardening, 변형경화 )

• Deformation at room temperature (for most metals). • Cod work increase strength and decrease ductility.

-Forging

Ao Ad

force

dieblank

force

-Rolling

roll

AoAd

roll



Impact of Cold Work ( 냉간가공 효과 )

• Yield strength (y) & Tensile strength (TS) increases.

• Ductility (%EL or %AR) decreases.

As cold work is increased

low carbon steel



• 1 hour treatment at Tanneal... ( 풀림 ) decreases TS and increases %EL.• Effects of cold work are nullified!

Annealing( 풀림 ) After Cold Working te

nsi

le s

tre

ngth

(M

Pa)

duc

tility

(%

EL

)tensile strength

ductility

Recovery

Recrystallization

Grain Growth

600

300

400

500

60

50

40

30

20

annealing temperature (ºC)200100 300 400 500 600 700 • Three Annealing stages:

1. Recovery 2. Recrystallization 3. Grain Growth



33% coldworkedbrass

New crystalsnucleate after3 sec. at 580C.

0.6 mm 0.6 mm

Three Stages During Heat Treatment:2. Recrystallization( 재결정 )• New grains are formed

TR = recrystallization temperature =

0.3Tm < TR < 0.6Tm

After 4seconds

After 8seconds

0.6 mm0.6 mm

• All cold-worked grains are eventually consumed/replaced.



Three Stages During Heat Treatment:3. Grain Growth( 결정립성정 )• At longer times, average grain size increases.

After 8 s,580ºC

After 15 min,580ºC

0.6 mm 0.6 mm

- Small grains shrink and large grains continue to grow



TR

TR = recrystallization temperature

º

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