Invar® (CarTech® Invar 36® Alloy, NILO® 36, Pernifer® 36)

Invar®  A Controlled Expansion Alloy

Invar® (UNS K93600) is a nickel-iron controlled expansion alloy. This alloy is produced by several companies all which have trademarked their own brand name. The following represents the trade names used: CarTech® Invar 36® Alloy, Pernifer® 36, NILO® 36 and Invar® Steel.

With a composition of 36% Nickel (nominal) and the balance Iron, Invar Alloy has the lowest thermal expansion of any known alloy.  Another key factor is that it exhibits a very low expansivity below its Curie Temperature. This anomaly has been termed the “Invar Effect”.  For this reason, Invar Alloy is particularly beneficial in applications where minimum thermal expansion and high dimensional stability is required.

Available in Standard and Free-Machining Grades

Ed Fagan Inc. is a leading supplier of Invar alloy and is available in various forms and sizes.  A premium controlled expansion alloy, we stock two grades of Invar to meet the needs of our customers:

  • Invar Standard Grade
    • Sheet and plate
    • ASTM B753, ASTM F1684, AMS I 23011 Class 7, UNS  K93603, MIL I 23011 Class 7 (Note: this spec has been de-activated by the US Military and has been replaced by AMS I 23011 Cl 7).
  • Free-Machining Grade (Free-Cut Invar “36”®)
    • Round bar and rod
    • Constituant Selenium of .015% added to aide in machining.
    • ASTM F1684, UNS  K93050

The Discovery and History of Invar

The alloy Invar was discovered by Charles Edouard Guillaume in 1896.  Charles was employed at the International Bureau of Weights and Measures and he was investigating metals that would not change in length when exposed to temperature variations.  He was seeking a cost-effective material with a perfectly defined length for reference bars that could be used as secondary standard throughout the world.

Guillaume was experimenting with nickel-iron heats and discovered that the coefficient of expansion at room temperature was lowest at a nickel level of 36%.  In fact, with 36% nickel, the alloy heats exhibited the least amount of thermal expansion of any alloy known. Guillaume called the alloy expansion “invariable” and hence the name Invar.

This remarkable discovery has evolved to produce many additional alloys and applications that have contributed to major advancements in science.  The impact of Guillaume’s discovery was acknowledged in 1920 by his Nobel Prize.  He is the first and only scientist in history to be so honored for a metallurgical achievement.


Invar® is a registered trademark of Aperam Alloys Imphy, France

CarTech® Invar 36 Alloy® is a registered trademark of CRS Holdings Inc., USA

Free-Cut Invar® “36” is a registered trademark of CRS Holdings Inc., USA

NILO® is a registered trademark of Special Metals Corporation, USA.

Pernifer® is a registered trademark of VDM Metals GmbH, Germany