5-axis CNC milling drawing: Al 7075-T6 block with pockets, toolpath and dimensions

Invar 36 · FeNi 36

Near-zero thermal expansion. Precision instruments. 1.2 ppm/°C.

Q: Cost comparison?

Invar 36 raw material: $30-50/kg — roughly 5-8× steel cost. Machining cost: 2-3× steel due to difficulty. Super-Invar: $80-150/kg, even harder to machine. For precision applications where dimensional stability enables function or simplifies engineering, Invar cost is typically justified. For general applications where thermal expansion doesn't matter, Invar is overkill.

Q: Weldability?

Invar welds well with TIG or laser. Use matching Invar filler rod — mixing with steel filler loses CTE match in the weld. Standard practice: preheat 100-150 °C, TIG weld with argon, post-weld stress relief at 300 °C for dimensional stability. Our experience includes welded LNG tank sections and composite tool assemblies.

Q: Lead times?

Invar 36: 2-3 week material lead time (not a commodity stocked material). Super-Invar: 4-6 weeks. Kovar: 2-3 weeks. Machining time 1.5-2× steel equivalent due to difficulty. Typical Invar order: 4-6 weeks from PO to ship. Plan ahead for precision Invar projects.

Invar 36 (36% nickel, 64% iron) has the lowest thermal expansion coefficient of any metal — 1.2 ppm/°C, roughly 10× lower than steel. Used where dimensional stability with temperature is critical: precision instruments, composite tooling, LNG tanks, aerospace optics.

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Technical plate for Near-zero thermal expansion. Precision instruments. 1.2 ppm/

At a glance

Density: 8.05 g/cc
Tensile strength: 480 MPa
Yield strength: 275 MPa
Elongation: 30%
CTE @ 20-100 °C: 1.2 ppm/°C
CTE @ 200-300 °C: 3 ppm/°C
Curie point: 279 °C
Magnetic: Ferromagnetic below Tc

Invar 36 · FeNi 36

Key data

Density: 8.05 g/cc
Tensile strength: 480 MPa
Yield strength: 275 MPa
Elongation: 30%
CTE @ 20-100 °C: 1.2 ppm/°C
CTE @ 200-300 °C: 3 ppm/°C
Curie point: 279 °C
Magnetic: Ferromagnetic below Tc

01 · Grades & variants

Invar family.

Invar 36

Fe-Ni36 standard composition. Lowest CTE near room temperature. Workhorse for precision instruments and tooling.

Super-Invar

Cobalt-modified for even lower CTE (0.72 ppm/°C) at room temperature. Premium cost, specialized applications like laser optics mounts.

Kovar

Matched-CTE alloy for glass-to-metal seals. CTE 5 ppm/°C matches borosilicate glass. Used for vacuum tube feedthroughs, sensor packaging.

Invar 42

42% nickel variant. Higher CTE than Invar 36 (4.5 ppm/°C) but matched to Pyrex glass. Used for semiconductor lead frames.

Invar M-93

Sulfur-modified Invar for improved machinability. Slightly reduced properties but much easier to machine.

Free-Cut Invar

Specialty free-machining grade. Similar CTE to standard Invar but with lead or sulfur additions for easier production machining.

Invar 36 is the standard grade. Related alloys offer modified properties — slightly different expansion curves, specific temperature ranges, or improved machinability.

02 · Why this material

Why Invar exists.

10× lower expansion

Steel: 12 ppm/°C. Aluminum: 23. Invar: 1.2. For a 100 mm part changing 100 °C, Invar changes 0.012 mm vs 0.12 mm for steel.

Dimensional stability

Precision measuring devices, optical benches, composite tooling maintain dimensions across ambient temperature variations.

Cryogenic service

LNG containment and cryogenic handling — Invar shrinks minimally when cooled to -196 °C.

Proven reliability

Used since 1896 (discovered by Charles-Édouard Guillaume, Nobel Prize 1920). Century of precision applications.

Invar solves the thermal expansion problem — everywhere temperature changes would disrupt precision.

03 · Applications

Invar applications.

LNG tanker tanks

Primary containment for LNG ships — minimal thermal contraction from ambient to -162 °C

Composite tooling

Layup molds for aerospace carbon fiber — doesn't warp during 150-180 °C autoclave cure cycle

Precision measuring

Gauge blocks, length standards, measuring instruments

Laser optics mounts

Laser bench mounts, optical tables — maintain alignment across temperature

Semiconductor lead frames

IC lead frames for thermally-stable electrical connections

Aerospace optical

Satellite optical mounts, space telescope structures

Precision clocks

Pendulum clock rods (original Invar application) — period doesn't change with temperature

Seismic sensors

Seismometer components — mass doesn't change with temperature

Shadow masks

CRT TV shadow masks (historical) — precision hole pattern stable under heat

04 · Finishing

Invar finishing.

As-machined

Silver metallic. Similar appearance to stainless. Ra 1.6 µm typical.

Polished

Ra 0.4 µm achievable. Invar polishes to bright finish similar to stainless.

Electroplated

Accepts standard plating — nickel, chrome, zinc. Used for corrosion protection.

Passivation

Standard passivation enhances corrosion resistance — Invar is less corrosion-resistant than stainless.

Heat treated

Solution treatment stabilizes Invar for dimensional stability. Critical for precision applications.

Machining-stress relief

Post-machining stress relief at 300 °C removes residual stress that could cause dimensional drift.

Weldable

TIG and laser welding standard. Use Invar filler to maintain CTE match.

Carburized

Surface carburizing possible for improved wear — changes surface CTE however.

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FAQ

Near-zero thermal expansion — questions

Why is Invar difficult to machine?

Invar work-hardens severely during cutting — similar to 304 stainless but worse. Low thermal conductivity means heat concentrates at cutting edge. Result: tool wear rapid, surface finish poor without care. Solutions: sharp carbide tools, slow cutting speeds (40-60 m/min vs 100+ for steel), flood coolant, positive rake geometry, climb milling preferred. Plan for 2-3× longer machining time vs steel.

Invar vs specialty low-CTE alternatives?

Super-Invar: Fe-Ni32-Co5 achieves CTE 0.72 ppm/°C — half of Invar. 3× cost of Invar. Used for extreme precision (laser reference cavities, gravity wave detectors). Zerodur (glass-ceramic): CTE 0.05 ppm/°C — virtually zero. Brittle, cannot be machined conventionally. Used for space telescope primary mirrors. Silicon carbide: CTE 4 ppm/°C but extremely stiff. Used for SiC optical mounts. For metal applications where threading, welding, machining needed, Invar or Super-Invar are the practical choices.

Dimensional stability over time?

Invar can exhibit slow dimensional drift over years if not properly heat-treated. Stabilization treatment: hot-cold cycling between -196 °C and +250 °C multiple times, then final stress-relief anneal. This drives out metastable phases. For long-service precision instruments, specify stabilized Invar. Untreated Invar: up to 5 ppm/year dimensional drift possible. Stabilized Invar: <0.5 ppm/year drift.

Cost comparison?