Steels and superalloys · Workhorse

Invar 36

Invarvalues describe: Invar 36

Why it wins

Near-zero expansion iron: metrology frames, laser resonators, mask and reticle structures, optical benches that must not breathe with temperature.

Why not the alternative

Stainless moves 10x more per kelvin; ULE and Zerodur are glass, not structure.

Watch out

Ferromagnetic, rusts, welds shift its CTE locally.

Properties

The values below are candidate: compiled from the sources named, not yet individually validated. Provisional provenance: ASM Handbook: properties, corrosion, heat treatment; NIST cryogenic material properties database; Kurt J. Lesker materials notes.

Wet cleaning

Recipe	degrease, DI rinse, dry immediately
Forbidden	aqueous soaking: it rusts
Limit	stress relief after machining matters more than cleaning

Vacuum and outgassing

Outgassing, unbaked (10 h)	3e-9 mbar·L/s/cm²
Outgassing, baked	2e-11 mbar·L/s/cm²
Vapour pressure	negligible

Temperature

Bake, assembled	230 °C
Vacuum degas	830 °C
Braze / H2 firing	1000 °C
Metallurgical limit	Curie 230 °C: the anomaly ends there

Thermal

CTE	1.5 ppm/K
Thermal conductivity	13 W/m·K
Specific heat	515 J/kg·K
Emissivity	0.2–0.3
Melting / softening	1427 °C

Mechanical

Strength	275 ys MPa
Tensile	450–500 MPa
Elongation	30 %
Young's modulus	141 GPa
Hardness	130–150 HV
Density	8.1 g/cm3

Electrical and magnetic

Relative permeability	ferromagnetic
Resistivity	82 µΩ·cm

Engineering

Corrosion	moderate; rusts, usually plated
Joining	weldable; the expansion match is lost at the weld
Process notes	stress-relieve after machining or it moves
Availability and cost	stock, moderate premium

Grades

Invar 36 (K93600, 1.3912)	the standard low-CTE grade
Super Invar	lower CTE still, narrower temperature window

Sources · 2

1. O Hanlon, A Users Guide to Vacuum Technology
2. Kurt Lesker materials notes

← The Matter