Kovar 4J29 · UNS K94610 · W. Nr. 1.3981 · GB 4J29
Kovar 4J29 (K94610): composition, properties, fittings and flanges
Kovar 4J29 (K94610, W. Nr. 1.3981, GB 4J29) is Iron-nickel-cobalt controlled-expansion sealing alloy. Kovar 4J29 is specified at Nickel 28.5 - 29.5, Cobalt 16.8 - 17.8. Kovar is the glass and ceramic sealing alloy: its expansion curve is matched to borosilicate glass and alumina, so a seal can be fired and cooled without…
- UNS
- K94610
- W. Nr.
- 1.3981
- Density
- 8.36 g/cm³ (0.302 lb/in³)
- Key strength
- 517 MPa / 75 ksi
Identification and standards
| Short form | Kovar 4J29 · UNS K94610 · W. Nr. 1.3981 · GB 4J29 |
|---|---|
| Classification | Iron-nickel-cobalt controlled-expansion sealing alloy |
| UNS | K94610 |
| Werkstoff number | 1.3981 |
| Material family | Precision Alloys |
Chemical composition
| Element | Composition (wt %) | Why it is there |
|---|---|---|
| Iron (Fe) | Balance | Matrix |
| Nickel (Ni) | 28.5 - 29.5 | Sets the expansion curve |
| Cobalt (Co) | 16.8 - 17.8 | Matches borosilicate glass expansion |
| Manganese (Mn) | 0.50 max | Deoxidation |
| Silicon (Si) | 0.30 max | Deoxidation |
| Carbon (C) | 0.03 max | - |
| Phosphorus (P) | 0.020 max | - |
| Sulphur (S) | 0.020 max | - |
Note Single figures are maximum limits unless shown as a range. Always confirm against the heat-specific EN 10204 3.1 certificate supplied with your order.
Mechanical properties
| Tensile strength, min (annealed) | 517 MPa / 75 ksi |
|---|---|
| 0.2 % yield strength, min | 345 MPa / 50 ksi |
| Elongation in 2 in, min | 30 % |
| Typical hardness, annealed | 150 - 190 HB |
| Mean coefficient of thermal expansion, 20-400 °C | 4.6 - 5.5 x 10⁻⁶ /°C |
Warning Values depend on product form, section thickness and heat treatment. Larger sections generally achieve lower strength than thin product; always design against the applicable code allowable stress rather than these figures.
Physical properties
| Density | 8.36 g/cm³ (0.302 lb/in³) |
|---|---|
| Melting range | 1450 °C (2640 °F) |
| Modulus of elasticity | 138 GPa (20.0 x 10⁶ psi) |
| Thermal conductivity at 20 °C | 17.3 W/m·K |
| Curie temperature | About 435 °C |
| Specific heat capacity | 439 J/kg·K |
Specifications by product form
| Forgings & flanges | ASTM F15 / GB/T 15018 (UNS K94610) |
|---|---|
| Butt weld fittings | Not normally supplied - bar, strip and wire forms |
| Seamless pipe & tube | To order against ASTM F15 chemistry |
| Plate / sheet / strip | ASTM F15 / GB/T 15018 |
| Bar / rod | ASTM F15 / GB/T 15018 |
| Welding consumables | Matching Kovar filler or electron beam welding |
| UNS / EN / China | UNS K94610 · W. Nr. 1.3981 · GB 4J29 |
Product forms available
Hangbo supplies this grade in the following forms. Sizes outside the listed range can often be produced to order.
- Forged flanges blanks and finished flanges to ASME B16.5, B16.47 Series A/B and B16.36
- Butt weld elbows, tees, reducers, caps and stub ends to ASME B16.9 and MSS SP-43
- Seamless pipe and tube to the applicable ASTM / ASME pipe specification
- Forged rings, discs and hubs machined to your drawing
Typical applications
- Glass-to-metal and ceramic-to-metal hermetic seals
- Semiconductor and microelectronic packages
- Vacuum tube, relay and sensor enclosures
- Aerospace and defence electronic housings
Welding, forming and machining
- Welding
- Weld with matching Kovar filler in a controlled atmosphere, or use electron beam and laser welding. The expansion match is destroyed if the weld metal composition drifts.
- Heat treatment
- Anneal at 830 - 880 °C in hydrogen or vacuum, then a stabilising treatment at 600 °C to lock dimensional stability.
- Hot and cold forming
- Hot work in the range stated by the mill for this grade, then re-solution or re-age before final machining so that the delivered condition matches the certificate.
- Machining
- Machine with sharp carbide or high-speed steel tooling, positive rake, constant feed and ample coolant. Never dwell - the surface work-hardens quickly.
Buy Kovar 4J29 from Hangbo
Material is supplied with full heat-number traceability, solution annealing or ageing performed under calibrated furnace control, and an EN 10204 3.1 certificate covering chemical analysis, mechanical properties, heat treatment records and the agreed NDT scope. Positive material identification and third party inspection and test reports from SGS are available for critical service.