KOVAR
| Nominal Chemical Composition |
29% nickel
53% Iron
17% Cobalt |
|
|
| Coefficient of Thermal Expansion |
| 30°-200° |
5.5 |
30°-600° |
7.9 |
| 30°-300° |
5.1 |
30°-700° |
9.3 |
| 30°-400° |
4.9 |
30°-800° |
10.4 |
| 30°-450° |
5.3 |
30°-900° |
11.5 |
| 30°-500° |
6.2 |
|
| |
|
|
| Glass Matches |
| Corning |
7052 or 7050,7055,7056,& others |
| Kimble |
EN-1 (Owens-Corning) |
|
K650 |
|
K704 | |
|
|
| Physical Properties |
| Density |
.302 lb/in |
| Specific Gravity |
8.36 |
| Curie Temp |
815°F/435° |
| Melting Point |
2640°F/1450°C |
| Specific Heat |
.105 Cal/gm/degree °C @ 0°C
.155 @ 430°C |
| Heat of Fusion |
64 Cal/gram |
| Thermal Conductivity |
120 BTU-in/fl/hour°F @77°F
17.3 w/meter xk |
| Electrical Resistivity |
294 ohm/cir ml ft
490 microohm/mm | |
|
|
| Mechanical Properties |
| Shear Modulus |
7.5 x 10° |
| Modulus of Elasticity |
20 x 10° |
| Ultimate Strength |
75000 psi |
| Yield Strength |
50000 psi |
| Kink Point |
806°F/430°C |
| Poisson's Ratio |
317 |
| Elongation |
30% |
| Velocity of Sound |
16300 ft/sec | | |
Heat Treatment - Because of its effect on the actual structure of the Kovar Alloys, there is a distinction made between heat treating the material to facilitate fabrication and heat treating the material to insure optimum conditions for glass sealing, plating or brazing
Stress Relief Annealing - To relieve stress and work hardening of parts at intermediate stages of fabrication. It is intended particularly for drawing, forming and spinning operations.
- Wash and degrease parts
- Anneal in atmosphere controlled furnace. Atmosphere may be wet or dry hydrogen, dissociated ammonia, cracked gas or similar neutral atmosphere
- Annealing temperature is not critical; however, high temperatures (greater than 900°C) or extended time periods (longer than 60 minutes) should be avoided because such treatments promote grain growth. Typical cycle 850°C for 30 minutes
-
Parts should be held at temperature for the indicated time and then furnace cooled to less than 175°C to avoid oxidation and/or thermal shock (which may cause distortion)
Heat Treatment for Oxidation
-
Make sure that proper methods are used to clean, degrease and bright dip parts
-
Oxidation - Heat treat in an electric air furnace to 850°C to 900°C until parts are cherry red (dull red heat). the length of heat cycle is approximately 3 minutes. but due to differences in humidity and furnaces, the proper cycle has to be varied. Then reduce heat approximately 10°C per minute. When parts are cooled, oxide will be formed. The oxide may appear from light gray to black in color. Black is normally considered to be over-oxidation and is not necessarily desirable for a good glass to metal seal
Invar and Kovar are registered trademarks of CRS Holding,
a subsidiary of Carpenter Technologies. | |
Technical Data