Invar 36 spotlight

Invar 36[1], also known within the industry as Nilo 36[2], is a nickel-iron superalloy known for its low coefficient of thermal expansion. Containing 36% nickel, it maintains nearly constant dimensions as well as excellent strength and hardness over a wide range of temperatures. Invented in 1896 by Swiss physicist Charles Edouard Guillaume, Invar was created as a low-cost solution for a meter once made of platinum and iridium. Guillaume’s work led to the discovery of a relatively inexpensive iron-nickel alloy—a steel-like material—that expands very little when heated. He named the alloy Invar because it was almost unchanging or “invariable.”

Invar [3] is typically machined. But did you know it can be cast too?

Invar 36 Success

One of our customers came to us specifically wanting to use INVAR 36 for a component requiring the near constant dimensions and long-term dimensional stability this alloy is known for. Due to confidentially agreements, we cannot name the customer. But what we can tell you, is that like with many other projects, CIREX engineers rose to the challenge. They not only cast Invar 36 successfully but completely exceeded the customers’ expectations and saved them money. Once again, we achieved the end goal: Create a quality component at the lowest total cost.

Why did our customer need Invar 36? The slightest change in dimension or shape of their component could alter their end product. Even though they operated in a temperature-controlled room, a temperature change of a few degrees could alter the functioning of the part. They knew they needed to work with a material like Invar 36, but solid machining was too expensive.

How did CIREX help? We had never worked with Invar 36 before, but our engineers had the expertise to take on the challenge. Through research and testing, we came up with a casting material that performed as well if not better than the solid material, and we could cast net-shape successfully. Our methods were so efficient that the final part cost was cheaper than their original block of metal before machining.

The end result? A delighted customer who made considerable savings and a new material we could offer other customers too. Invar 36 maintains almost constant dimensions from -150 degrees Celsius up to 260 degrees Celsius.

Who Should Use Invar 36?

Customers who need to work under strict temperature constraints will probably benefit from using Invar 36. Unfortunately, customers who currently use solid machining do not even realise that casting net-shape is an option. Invar 36 is often used in measuring devices, precision mechanical systems, laser components, thermostat rods, meters and components that transport liquefied gases—to name a few.

Young’s ModulusGPa141 193
Poisson’s Ratio0.26 0.27
Microyield StrengthMPa 70 >300
Thermal Expansion Coefficientx 10-6 K-1114.70
Thermal ConductivityW/m K10.4016.20
Specific HeatW s/kg K515500
Specific Stiffness17.5024.10
Thermal Diffusivity10-6 m2/s 2.604.10
Thermal Distortion (Steady State)µm/W 0.100.91
Thermal Distortion (Transient)s/m2K 0.38 3.68

Advantages of Invar 36

The most obvious advantage of Invar 36 is its ability to retain dimensions at cryogenic temperatures. Aside from that, Invar 36 looks and feels similar to steel. It also has outstanding weldability and machinability. Invar can also be created with customised chemistries to meet customers’ strength and hardness requirements better.

Whatever your situation, our expert engineering staff are ready to listen. With in-house engineers, we partner with you on every project to ensure the highest possible quality for your component. Contact our engineering team today to discuss your possibilities.

1* Invar 36 is a trademark of Carpenter Technology, Reading PA

2* Nilo 36 is a trademark of Special Metals Corporation, USA

3* Invar is a trademark of Imphy Alloys, France