Bright Shiny Kovar Foil Wear Resistant Astm F15 / Uns K94610 With
Weldability
4J29, is a nickel-cobalt ferrous alloy compositionally identical to Fernico 1, designed to have substantially the same thermal expansion characteristics as borosilicate glass (~5 × 10−6 /K between 30 and 200 °C, to ~10 × 10−6 /K at 800 °C) in order to allow a tight mechanical joint between
the two materials over a range of temperatures. Corresponding to GB 4J29, ASTM F15, UNS K94610); KOVAR is a hard
glass iron-based seal bond containing 29% nickel and 17% cobalt. It finds application in glass-to-metal seals in scientific
apparatus, and conductors entering glass envelopes of electronic
parts such as vacuum tubes (valves), X-ray and microwave tubes and some lightbulbs.
Kovar was invented to meet the need for a reliable glass-to-metal
seal, which is required in electronic devices such as light bulbs, vaccum
tubes, cathode ray tubes, and in vacuum systems in chemistry and
other scientific research. The alloy has a coefficient of linear expansion similar to that of
hard glass in the range of 20-450 ° C, which can be effectively
sealed with the corresponding hard glass, and has a high Curie
point and good low temperature structure stability, oxidation of
the alloy. The film is dense, easy to weld and weld, has good
plasticity, and can be cut and processed. It is widely used in the
manufacture of electric vacuum components, launch tubes, picture
tubes, switch tubes, transistors, sealed plugs and relay housings.
Kovar alloy is more wear-resistant because of its cobalt content. Most metals cannot seal to glass because their coefficient of
thermal expansion is not the same as glass, so as the joint cools
after fabrication the stresses due to the differential expansion
rates of the glass and metal cause the joint to crack.
Chemical composition
| C | Mn | Si | P | S | Cu | Cr | Mo | NI | Co | Fe |
| ≤ |
| 0.03 | 0.5 | 0.30 | 0.02 | 0.02 | 0.2 | 0.2 | 0.2 | 28.5~29.5 | 16.8~7..8 | Margin |
Heat Treatment
Because of its effect on the actual structure of the material,
there is a distinction made between heat treating the material to facilitate fabrication and
heat treating the material to ensure 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.
1. Wash and degrease parts.
2. Anneal in atmosphere controlled furnace. Atmosphere may be wet or dry hydrogen, dissociated ammonia, cracked gas or similar neutral atmosphere.
3. Annealing temperature is not critical; however, high
temperatures (greater than 900 oC) or extended time periods (longer than 60
minutes) should be avoided because such treatments promote grain growth.
Typical cycle: 850 oC for 30 minutes.
4. Parts should be held at temperature for the indicated time and
then furnace cooled to less than 175 oC to avoid oxidation and/or thermal shock
(which may cause distortion).
