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Item

Unit

Ball bearing steel

Stainless steel

Si3N4

ZrO2

SiC

Al2O3

Capability of physics mechanics

Density D

g/cm3

7.85

7.90

3.20～3.30

6.00

3.10

3.95

Coefficient of thermal expansion

α

10-6/K

10.0

11.0

3.2

10.5

4.5

8.5

Modulus of elasticity

E

GPa

208

200

300～320

210

≥350

380

Poisson Ratio

　Mu

0.30

0.30

0.26

0.30

0.20

0.22

Hardness

Hv
H RC

　HV
HRC

700
62

≤300
58-62

1300～1600
75～80

1000～1200
70

≥2500
85～90

1600～1800
80

Bending Strength

σ RT

MPa

2400

600～1000

950～1200

≥450

300～500

Fracture Toughness

KI C

MPam1/2

25

5.0～7.0

8.0～10.0

3.0～4.0

3.0～4.0

Heat Conductivity      λ

W/mk

30～40

15

35

2～3

150

30

Specific Resistance

Ωmm2/m

0.1～1

0.75

1018

1015

101-3

10

Usage mechanics

Maximum Operation Temperature

℃

120

300

800

800

1400

Degree of resistant to acid base

weak

weak

strong

strong

strong

strong

Stress circulation times(50% Breakage probability)

times

107

107～10 9

105

Friction Quotiety

big

big

small

small

small

Magnetism

yes

yes

no

no

no

no

Operation centrifugal force

big

big

small

bigger

small

medium

Temperature rise of the movement

high

high

low

low

-

Dimensional stability

Varies with temperature

great

Varies with temperature

great

Varies with temperature

Insulativity

no

no

yes

yes

no

yes

Expiration Form

Flake off

Flake off

cracking

cracking

cracking