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

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.

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.

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.

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.

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.

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.