Invar, also known generically as FeNi36 (64FeNi in the US), is a nickel–iron alloy notable for its uniquely low coefficient of thermal expansion (CTE or α). The name Invar comes from the word invariable, referring to its relative lack of expansion or contraction with temperature changes.

Common grades of Invar have a coefficient of thermal expansion (denoted α, and measured between 20 °C and 100 °C) of about 1.2 × 10−6 K−1 (1.2 ppm/°C), while ordinary steels have values of around 11–15 ppm. Extra-pure grades (<0.1% Co) can readily produce values as low as 0.62–0.65 ppm/°C. Some formulations display negative thermal expansion (NTE) characteristics. Though it displays high dimensional stability over a range of temperatures, it does have a propensity to creep.


Density :

lb/cu in

Specific Gravity :
  • Curie Temp :°F,°c
  • Melting Point :°F, °C
  • Electrical Resistivity :Micro-ohm-cm
  • Specific Heat :Cal/g- °C
  • Mechanical Properties :
  • Tensile Strength:ksi 75
    MPa 518
  • Elongation:% in 2 in. 34
  • Typical Hardness Ann.: Rockwell HRB 80
  • Applications :
  • Invar is used where high dimensional stability is required, such as precision instruments, clocks, seismic creep gauges, television shadow-mask frames, valves in motors, and antimagnetic watches.
  • In land surveying, when first-order (high-precision) elevation leveling is to be performed, the Level staff (leveling rod) used is made of Invar, instead of wood, fiberglass, or other metals.
  • Invar struts were used in some pistons to limit their thermal expansion inside their cylinders
  • Chemical Composition Limits of INVAR 36

    Weight % Ni Fe C Mn P S Si Cr Mo Co
    Invar 36 35-38 Rem 0.10 max 0.06 max 0.025 max 0.025 max 0.35 max 0.50 max 0.50 max 1.0 max

    Alloy 36 (NILO 36, INVAR 36) is a Nickel-Iron, low expansion alloy which contains 36% Nickel. Invar 36 has a low coefficient of expansion from cryogenic temperatures to about +500°F (260°C). Invar 36 also retains good strength and toughness at cryogenic temperatures. Common applications include tooling for aerospace composites, standards of length, measuring devices, thermostat rods, laser components and tanks and piping for the storage and transportation of liquefied gases.

    Typical Mechanical Properties of INVAR 36

    Material Condition Ultimate Tensile Strength Yield Strength 0.2 % Elongation (%)
    psi MPa psi MPa
    Invar 36 Annealed 71,000 490 35,000 240 42