Nickel Alloy Kovar · temper · default condition
Nickel Alloy Kovar-O
Properties of the O condition, compared with the other Kovar tempers.
Standard stocked condition for stamping, machining, welding and glass/ceramic sealing.
What is Kovar-O?
Kovar-O is Kovar in the O temper — standard stocked condition for stamping, machining, welding and glass/ceramic sealing. Kovar-O has a yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 61% of nickel alloy grades. Elongation at break is 30% and the elastic modulus is 138 GPa (20 Msi). Kovar-O has a density of 8.36 g/cm³ (0.302 lb/in³), heavier than 54% of nickel alloy grades. It melts at 1,450°C (2,642 °F).
Advantages
- Easy to machine — 32/100, better than 95% of nickel alloy grades
- High electrical conductivity — 3.5 % IACS, better than 92% of nickel alloy grades
- Low embodied carbon — 8 kg CO₂/kg, better than 92% of nickel alloy grades
- Conducts heat well — 17 W/m·K (9.82 BTU/hr·ft·°F), better than 83% of nickel alloy grades
- Forms and bends easily — 75/100, better than 81% of nickel alloy grades
Limitations
- Needs corrosion protection — 28/100, worse than 99% of nickel alloy grades
- Low stiffness — 138 GPa (20 Msi), worse than 98% of nickel alloy grades
- Limited service temperature — 450°C (842 °F), worse than 86% of nickel alloy grades
Kovar-O properties
Typical room-temperature values for Kovar-O — 11 properties are specific to this condition; the rest are grade-level values shared by every Kovar temper. Each bar shows where the value sits among the nickel alloy grades in FabDigit's library — further right is higher.
Physical3
Kovar-O has a density of 8.36 g/cm³ (0.302 lb/in³), heavier than 54% of nickel alloy grades. It melts at 1,450°C (2,642 °F).
Mechanical13
Kovar-O has a yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 61% of nickel alloy grades. Elongation at break is 30% and the elastic modulus is 138 GPa (20 Msi).
Thermal5
Kovar-O is rated for continuous service to 450°C (842 °F). It conducts heat at 17 W/m·K (9.82 BTU/hr·ft·°F), better than 83% of nickel alloy grades. Thermal expansion is 5.5 µm/m·K (3.06 µin/in·°F).
Electrical3
Kovar-O conducts electricity at 3.5 % IACS, better than 92% of nickel alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (28/100), worse than 99% of nickel alloy grades.
Sustainability3
Producing a kilogram of Kovar-O takes about 100 MJ of energy and emits 8 kg of CO₂ — less than 93% of nickel alloy grades. Typical recycled content is 25%.
Manufacturability7
Kovar-O's machinability is poor (32/100, better than 95% of nickel alloy grades); weldability very good (80/100); formability very good (75/100).
Common Calculations5
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Other Kovar tempers and conditions
Kovar is also supplied in 5 other conditions. The full side-by-side table is on the Kovar overview.
- ODefaultStandard stocked condition for stamping, machining, welding and glass/ceramic sealing.345 MPa yield · 145 HB
Working with Kovar-O
Is Kovar easy to machine?
Machines like an austenitic Ni-Fe alloy — gummy and work-hardening: use sharp carbide, positive rake, heavy feed, low-to-moderate speed and flood coolant to avoid glazing.
Can Kovar be welded?
Readily GTAW, resistance, electron-beam and laser welded to itself; keep the weld and heat-affected zone clean and low in carbon, and use matching Kovar filler for sealing-critical joints.
Can Kovar be formed, bent or molded?
Annealed strip stamps, spins and deep-draws well; interstage anneals at 800–900 °C in dry hydrogen restore ductility and reset the expansion curve.
What surface finishes work on Kovar?
No anodizing — form a thin controlled Fe/Ni/Co oxide for glass sealing, or electroplate Ni (1–5 µm) with optional gold for solderability, brazing and corrosion protection.
Kovar chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| Ni | 28 – 30 | 29 |
| Co | 16.8 – 17.8 | 17 |
| Clow carbon required for gas-free glass seals | ≤ 0.04 | 0.02 |
| Mn | ≤ 0.5 | 0.3 |
| Si | ≤ 0.2 | 0.1 |
| Al | ≤ 0.1 | — |
| Mg | ≤ 0.1 | — |
| Zr | ≤ 0.1 | — |
| Ti | ≤ 0.1 | — |
| Cr | ≤ 0.2 | — |
| Cu | ≤ 0.2 | — |
| Mo | ≤ 0.2 | — |
| P | ≤ 0.03 | — |
| S | ≤ 0.03 | — |
| Febalance, ≈53–54 % | balance | — |
Kovar-O — frequently asked
What is Kovar-O used for?
Kovar-O is typically used for glass-to-metal seal headers, vacuum tube components, hermetic package bases and lids, microwave and RF device housings, TO-can optoelectronic packages and ceramic-to-metal feedthroughs. In short: glass-sealing low-expansion alloy.
What is the yield strength of Kovar-O?
Kovar-O has a typical yield strength of 345 MPa (50 ksi) and a tensile strength of 520 MPa (75.4 ksi) — weaker than 61% of nickel alloy grades. Strength varies by condition: see the 6 listed tempers.
Is Kovar-O easy to machine?
Not especially — machinability is rated poor (32/100, better than 95% of nickel alloy grades). Machines like an austenitic Ni-Fe alloy — gummy and work-hardening: use sharp carbide, positive rake, heavy feed, low-to-moderate speed and flood coolant to avoid glazing.
Can Kovar-O be welded?
Yes — weldability is rated very good (80/100). Readily GTAW, resistance, electron-beam and laser welded to itself; keep the weld and heat-affected zone clean and low in carbon, and use matching Kovar filler for sealing-critical joints.
What surface finishes work on Kovar-O?
No anodizing — form a thin controlled Fe/Ni/Co oxide for glass sealing, or electroplate Ni (1–5 µm) with optional gold for solderability, brazing and corrosion protection.
Can Kovar-O be formed, bent or molded?
Annealed strip stamps, spins and deep-draws well; interstage anneals at 800–900 °C in dry hydrogen restore ductility and reset the expansion curve.
What is the maximum service temperature of Kovar-O?
Kovar-O is rated for continuous use to about 450°C (842 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
What is the difference between Kovar-O and Kovar-H?
O is the default condition — standard stocked condition for stamping, machining, welding and glass/ceramic sealing. H: highest strength condition, chosen for spring contacts and thin stiff wire; almost no cold-bend reserve and CTE is best re-annealed before sealing. Yield strength is 345 MPa in O versus 760 MPa in H.
Can FabDigit make parts in Kovar-O?
Yes — Kovar-O is available for CNC machining and sheet metal with instant online pricing. Upload a STEP file to get a price and a DFM check.
Sources
- ASTM F15 — Standard Specification for Iron-Nickel-Cobalt Sealing Alloy — ASTM International (2023)
- ASM Handbook Vol. 2 — Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (controlled-expansion alloys) — ASM International (1990)
- Kovar / ASTM F15 alloy technical datasheet — specialty melter (CRS Holdings / Ni-Fe alloy producers) (2021)
Property data is compiled from published supplier and standards handbooks and normalised for comparison. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.