Invar® 36
Invar 36 is a 36% nickel-iron alloy notable for its uniquely low coefficient of thermal expansion which is roughly one-tenth that of carbon steel. It maintains nearly constant dimensions across the range of normal atmospheric temperatures up to 400°F (200°C).
- Common Forms: Plate, Round Bar, Sheet, Wire, Forgings.
- Key Feature: Near-Zero Thermal Expansion at Room Temp.
- Cryogenic: High toughness at cryogenic temperatures (-400°F).
- CTE: 0.8 - 0.9 µin/in·°F (Typical 200°F to 400°F).
Invar 36 is indispensable for applications where dimensional changes due to temperature fluctuation must be minimized. From precision laser equipment to aerospace composite molds, Invar 36 ensures that the part shape remains consistent, preventing misalignment, warping, or stress buildup.
Dimensional Stability
The defining characteristic: prevents thermal distortion in sensitive instruments like optical measuring devices and laser benches.
Composite Tooling Match
Its CTE closely matches that of carbon-fiber composites, making it the premier material for aerospace lay-up molds.
Cryogenic Performance
Unlike many steels which become brittle, Invar 36 retains superior toughness and ductility at cryogenic temperatures (LNG/Liquid Oxygen).
| Element | Content (%) |
|---|---|
| Nickel (Ni) | 35.0 - 37.0 |
| Iron (Fe) | Balance |
| Carbon (C) | 0.05 max |
| Manganese (Mn) | 0.60 max |
| Silicon (Si) | 0.40 max |
*Note: The precise 36% Nickel balance is critical for the "Invar Effect".
| Product Form | Standards (ASTM / AMS) |
|---|---|
| Plate, Sheet, Strip | ASTM F1684, ASTM B753, AMS I-23011 (Class 7) |
| Bar, Rod, Forging | ASTM F1684, AMS I-23011 (Class 7) |
| Aerospace Tooling | Boeing BMS 7-320 (Invar 36 Tooling Plate) |
| Temperature Range | CTE (µm/m·°C) | CTE (µin/in·°F) |
|---|---|---|
| 30 - 100°C | 1.3 | 0.7 |
| 30 - 200°C | 2.7 | 1.5 |
| 30 - 300°C | 5.3 | 2.9 |
*Note: Above the Curie point (approx 280°C), expansion rates increase to match standard steels.
Composite Tooling
Molds and dies for curing carbon fiber aerospace parts (Boeing 787 wings, fuselages).
LNG Piping
Transfer piping for Liquefied Natural Gas, preventing shrinkage and leakage at -162°C.
Optical Instruments
Laser housings, telescope supports, and seismic creep gauges requiring zero movement.
Thermostats
The low-expansion side of bimetallic strips used in thermal switches.
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