Kovar Alloy Rods
Iron-Nickel-Cobalt Controlled-Expansion Sealing Alloy | For Glass-to-Metal/Ceramic-to-Metal Sealing | 4J29
Kovar is a classic iron-nickel-cobalt solid-solution-strengthened alloy characterized by a controlled coefficient of thermal expansion suitable for glass-to-metal sealing.
Within the temperature range of 20°C to 450°C, the alloy exhibits a coefficient of linear expansion that closely matches that of borosilicate hard glass and alumina ceramics. It forms a highly dense surface oxide layer that is readily wetted by molten glass and is chemically inert to mercury, making it a core material for vacuum electronic devices, microelectronic packaging, and semiconductor device housings.
The reference price range for Kovar alloy rods is $35.00–$60.00/kg; actual pricing depends on the outer diameter tolerance grade, delivery hardness condition, and fluctuations in international spot market prices for cobalt and nickel. The minimum order quantity (MOQ) for standard-specification ground and cold-drawn round rods is 20–50 kg, with shipment arranged within 10–20 working days. All rods are supplied with a standard-compliant original Mill Test Certificate (MTC), which includes data such as spectral analysis of chemical composition and measured thermal expansion curves.
Implementation Standards and Supply Condition
US Standard: ASTM F15 (Standard Specification for Iron-Nickel-Cobalt Sealing Alloy),UNS K94610
European Standard: DIN 17745 (1.3981 / Vacon 12)
Chinese Standard: YB/T 5231 (Technical Specifications for Iron-Nickel-Cobalt Glass-Sealing Alloy 4J29)
Round bars: hot-rolled, forged, cold-drawn
Other forms of bars: Customizable based on drawings or cross-sections.
Smelting method: The alloy may be melted using a vacuum induction furnace, a non-vacuum induction furnace, an electric arc furnace, or by other melting methods that meet customer requirements.
Non-destructive Testing: The alloy rods are inspected using ultrasonic testing methods; other non-destructive testing methods may also be employed.
chemical component
| element | Fe | Ni | Co | C | Mn | Si | Cu | Cr | Mo | P | S |
| Content (%) | Balance | 28.50 – 29.50% | 16.80 – 17.80% | max 0.03% | max 0.50% | max 0.30% | max 0.20% | max 0.20% | max 0.20% | max 0.02% | max 0.02% |
Data based on YB/T 5231-2014.
Thermal Expansion
| temperature interval | Coefficient of linear expansion(× 10-6/k) | Matching medium |
| 20 °C – 400 °C | 4.6 – 5.2 × 10-6 | Hard silicon boron glass |
| 20 °C – 450 °C | 5.1 – 5.5 × 10-6 | Aluminum oxide ceramics |
mechanical property
| Supply Condition | Tensile Strength | Yield Strength Rp0.2 | Elongation |
| Annealed | 450 – 550 MPa | min290 MPa | min25% |
| Cold-Drawn | 650 – 850 MPa | min550 MPa | min10% |
Mechanical property data for the annealed state are established in accordance with YB/T 5231 and ASTM F15 standards; data for the cold-drawn state represent typical values for rod products. Please refer to the Material Test Certificate (MTC) accompanying the shipment for actual measured values.
Operating environment
Temperature Conditions: Suitable for an operating temperature range of -60°C to +450°C; within this range, the linear expansion coefficient remains stable and matches that of hard glass. The Curie point is approximately 430°C; while ferromagnetic properties are lost above this temperature, the expansion coefficient remains relatively stable.
Atmosphere and Medium Conditions: Suitable for sealing and operation in hydrogen, inert atmospheres, and vacuum environments. The dense oxide film (e.g., Fe₂O₃, NiO) formed on the alloy surface reacts with SiO₂ and B₂O₃ in the glass to create chemical bonds, ensuring a hermetic seal. The alloy does not react with mercury, making it suitable for instruments involving mercury-based discharges.
Stress Conditions: Suitable for glass-to-metal or ceramic-to-metal sealing interfaces subject to thermal matching stresses; the matching of expansion coefficients minimizes interfacial stress.
Functional Scope: 4J29 is a controlled-expansion sealing alloy designed to match the thermal expansion coefficient of sealing materials; it is not intended for applications requiring high-temperature strength or corrosion resistance. The alloy experiences significant strength degradation during long-term service above 450°C and lacks high-temperature load-bearing capacity. Its corrosion resistance in corrosive media is limited, making it unsuitable for chemically corrosive environments. It should not be selected for use as a high-temperature structural material or a corrosion-resistant material.
Operating Conditions to Avoid: Heating in sulfur-containing atmospheres must be avoided, as sulfur causes hot shortness. The oxide layer must be thoroughly removed via pickling or sandblasting prior to sealing; failure to do so will result in porosity or cracking. Oxy-acetylene welding should be avoided, as it causes severe oxidation in the high-temperature zone.
Production challenges
The primary manufacturing challenge for 4J29 lies not merely in achieving the specified Ni and Co contents, but in maintaining stable consistency across composition, processing, heat treatment, and final thermal expansion properties.
Variations in the Ni-to-Co ratio affect the material's thermal expansion curve; therefore, strict compositional control is required during the smelting stage. For precision rods, dimensional changes, work hardening, and microstructural uniformity must also be controlled during hot and cold processing.
Kovar exhibits good ductility and machinability, allowing for operations such as drawing, stamping, and machining; however, significant cold deformation leads to work hardening, so intermediate annealing may be necessary during continuous cold processing.
For products ultimately intended for glass-to-metal or ceramic-to-metal sealing, thermal expansion characteristics following heat treatment are a critical quality indicator. Even if the chemical composition meets specifications, improper heat treatment or microstructural control can result in deviations between actual sealing performance and design values.
Lork Group
Marketing Operations Department
Email: claire@lorkgroup.com
WhatsApp: +86 19937075488
Hot Tags: Kovar, 4J29, Alloy K, UNS K94610, W.Nr. 1.3981, ASTM F15, YB/T 5231, Fe-Ni-Co alloy, controlled expansion alloy, glass-to-metal sealing alloy, hard glass sealing rod, electronic vacuum component material
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