Grade and chemical composition

Grade

Mass fraction (%)

C

P

S

Mn

Si

Cu

Cr

Mo

Ni

Co

Fe

≤

Kovar

0.03

0.020

0.020

0.5

0.30

0.20

0.20

0.20

28.5~29.5

16.8~17.8

Balance

tensile strength for strips 

Status

tensile strength /MPa

soft

<570

hard

>700

hardness of strip in deep punching status

status

thickness/mm

Hardness Hv

deep punching

>2.5

≤170

≤2.5

≤165

coefficient of linear expansion

Grade

heat treating regime

a/(10-6/K)

20~300°C

20~400°C

20~450°C

Kovar

Heat the sample to 900±20°C in hydrogen atmosphere, keep the temperature for one hour, heat again to 1100±20°C and keep the temperature for 15min, then cool to below 200°C at the speed ≤5°C/min and discharge.

4.6~5.2

5.1~5.5

4.3~5.1

4.6~5.2

coefficient of expansion

Grade

Average coefficient of expansion a/(10-6/K)

20~200°C

20~300°C

20~400°C

20~450°C

20~500°C

20,600°C

20~700°C

20.800°C

Kovar

5.9

5.3

5.1

5.3

6.2

7.8

9.2

10.2