Nickel Alloy Kovar-H (Hardened)
Heat-treated state
UNS K94610 · ASTM F15 · EN 1.3981
Highest strength condition, chosen for spring contacts and thin stiff wire; almost no cold-bend reserve and CTE is best re-annealed before sealing.
Values for the H condition
Other Kovar tempers and conditions
Kovar is listed in 6 conditions; see the grade overview at Kovar.
Compare all 6 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Wet-hydrogen (decarburizing) annealed sealing grade | Pick when parts must be glass-sealed or vacuum-fired: hydrogen anneal removes carbon and residual gas for bubble-free seals. | 310 | 490 | 33 | 135 HB | 3.5 % IACS |
ODefault Annealed | Standard stocked condition for stamping, machining, welding and glass/ceramic sealing. | 345 | 520 | 30 | 145 HB | — |
Quarter hard | Use when stamped parts need extra stiffness but still some bend ductility. | 480 | 620 | 15 | 10 HRC | 3.4 % IACS |
Cold drawn | Standard as-supplied bar/wire condition for machined pins, headers and feedthrough leads. | 540 | 660 | 14 | 16 HRC | 3.4 % IACS |
Half hard | For flat springs, contacts and lids where moderate strength and flatness matter more than deep forming. | 620 | 720 | 8 | 22 HRC | 3.4 % IACS |
HThis page Hardened | Highest strength condition, chosen for spring contacts and thin stiff wire; almost no cold-bend reserve and CTE is best re-annealed before sealing. | 760 | 860 | 3 | 30 HRC | 3.4 % IACS |
What is Kovar-H?
Kovar-H is Kovar heat treated to 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. Kovar-H has a yield strength of 760 MPa (110 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 83% of nickel alloy grades. Elongation at break is 3% and the elastic modulus is 140 GPa (20.3 Msi). Kovar-H 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). O is the default condition FabDigit quotes; H is available on request or by drawing note.
Advantages
- Easy to machine — 40/100, better than 98% of nickel alloy grades
- Low embodied carbon — 8 kg CO₂/kg, better than 93% of nickel alloy grades
- High electrical conductivity — 3.4 % IACS, better than 90% of nickel alloy grades
- Conducts heat well — 17 W/m·K (9.82 BTU/hr·ft·°F), better than 84% of nickel alloy grades
- High strength — 760 MPa (110 ksi), better than 83% of nickel alloy grades
Limitations
- Limited service temperature — 200°C (392 °F), worse than 100% of nickel alloy grades
- Needs corrosion protection — 27/100, worse than 99% of nickel alloy grades
- Low stiffness — 140 GPa (20.3 Msi), worse than 97% of nickel alloy grades
- Limited ductility — 3%, worse than 93% of nickel alloy grades
- Limited formability — 20/100, worse than 75% of nickel alloy grades
Kovar-H properties
Typical room-temperature values for Kovar-H; 21 are specific to this condition. Other listed values are Kovar reference data and may not represent this condition. Bars are the position among nickel alloy grades.
Physical3
Kovar-H 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-H has a yield strength of 760 MPa (110 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 83% of nickel alloy grades. Elongation at break is 3% and the elastic modulus is 140 GPa (20.3 Msi).
Thermal5
Kovar-H is rated for continuous service to 200°C (392 °F). It conducts heat at 17 W/m·K (9.82 BTU/hr·ft·°F), better than 84% of nickel alloy grades. Thermal expansion is 5.5 µm/m·K (3.06 µin/in·°F).
Electrical3
Kovar-H conducts electricity at 3.4 % IACS, better than 90% of nickel alloy grades.
Chemical & Environmental3
Corrosion resistance is poor (27/100), worse than 99% of nickel alloy grades.
Sustainability3
Producing a kilogram of Kovar-H takes about 100 MJ of energy and emits 8 kg of CO₂ — less than 95% of nickel alloy grades. Typical recycled content is 25%.
Manufacturability7
Kovar-H's machinability is fair (40/100, better than 98% of nickel alloy grades); weldability very good (70/100); formability poor (20/100).
Values are nominal handbook figures for design screening. Confirm any required mill or lot documentation when quoting.
Working with Kovar-H
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-H — frequently asked
What is Kovar-H used for?
Kovar-H 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-H?
Kovar-H has a typical yield strength of 760 MPa (110 ksi) and a tensile strength of 860 MPa (125 ksi) — stronger than 83% of nickel alloy grades. Strength varies by condition: see the 6 listed tempers.
Is Kovar-H easy to machine?
Not especially — machinability is rated fair (40/100, better than 98% 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-H be welded?
Yes — weldability is rated very good (70/100). 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-H?
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-H 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-H?
Kovar-H is rated for continuous use to about 200°C (392 °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-H?
Yes — Kovar-H 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.