INVAR 36 Alloy: The Ultimate Low Expansion Material for Precision Engineering — ASTM F1684
INVAR 36 (UNS K93600 / K93603, W.Nr. 1.3912) is a nickel-iron low expansion Alloy containing approximately 36% nickel, with the balance being iron. Discovered by Charles Édouard Guillaume in 1897 — a breakthrough that earned him the 1920 Nobel Prize in Physics — Invar 36 remains one of the most important controlled expansion alloys in modern engineering.
Its defining characteristic is an extremely low coefficient of thermal expansion (CTE) — approximately one-tenth that of carbon steel — maintained from cryogenic temperatures up to around 260°C (500°F). This unique property makes INVAR 36 indispensable in applications where dimensional stability under temperature variation is critical.
Chemical Composition of INVAR 36 (Astm F1684)
| Element | Content (wt. %) | Role |
|---|---|---|
| Nickel (Ni) | 35.5 – 36.5 | Core element for low CTE |
| Iron (Fe) | Balance | Matrix |
| Carbon (C) | ≤ 0.05 | Controlled for stability |
| Manganese (Mn) | 0.20 – 0.40 | Deoxidation |
| Silicon (Si) | ≤ 0.20 | Residual control |
| Sulfur (S) | ≤ 0.002 | Minimized for purity |
| Phosphorus (P) | ≤ 0.020 | Minimized for purity |
| Chromium (Cr) | ≤ 0.15 | Residual limit |
| Cobalt (Co) | ≤ 0.50 | Residual limit |
The precisely controlled nickel content gives INVAR 36 its signature low expansion behavior, while tight limits on residual elements guarantee consistent performance in precision equipment and critical assemblies.
Mechanical Properties of INVAR 36
| Property | Typical Value | Test Standard |
|---|---|---|
| Tensile Strength | 430 – 550 MPa | ASTM F1684 |
| Yield Strength (0.2% offset) | 240 – 350 MPa | ASTM F1684 |
| Elongation | 25 – 40% | ASTM F1684 |
| Hardness | 130 – 180 HB | ASTM E10 |
| Modulus of Elasticity | 141 GPa | — |
| Density | 8.05 g/cm³ | — |
| Curie Temperature | 230 – 279°C | — |
| Melting Point | 1427°C | — |
| Electrical Resistivity | 84 μΩ·cm | — |
INVAR 36 also retains good strength and toughness at cryogenic temperatures, making it suitable for LNG storage and transportation systems operating below −162°C.
Thermal Expansion Properties (CTE)
| Temperature Range | CTE (×10⁻⁶/°C) |
|---|---|
| 20 – 100°C | ≤ 1.5 |
| 30 – 150°C | 1.72 |
| 30 – 200°C | 1.72 |
| 30 – 250°C | 2.53 |
| 30 – 300°C | 4.92 |
| 30 – 400°C | 7.82 |
This near-zero CTE behavior below the Curie temperature is the foundation of INVAR 36's reputation as the premier low expansion alloy for dimensional stability applications.
INVAR 36 vs Alloy 42: Key Differences
Although both are nickel-iron controlled expansion alloys, INVAR 36 and Alloy 42 serve fundamentally different engineering purposes.
| Parameter | INVAR 36 | Alloy 42 |
|---|---|---|
| Nickel Content | ~36% | ~42% |
| UNS Number | K93600 / K93603 | K94100 |
| Primary Standard | ASTM F1684 | ASTM F30 |
| CTE (20–100°C) | ≤ 1.5 × 10⁻⁶/°C | 4.0 – 5.3 × 10⁻⁶/°C |
| CTE (30–300°C) | ~4.9 × 10⁻⁶/°C | 4.0 – 4.7 × 10⁻⁶/°C |
| CTE (30–450°C) | ~8.8 × 10⁻⁶/°C | 6.7 – 7.4 × 10⁻⁶/°C |
| Key Advantage | Ultra-low CTE near room temperature | Matched CTE to silicon & ceramics |
| Primary Use | Dimensional stability tooling, optical benches | Glass-to-metal & ceramic-to-metal seals |
| Typical Applications | Aerospace composite molds, laser systems, LNG piping | Semiconductor lead frames, electronic tubes, thermostats |
Summary: INVAR 36 excels where near-zero thermal expansion is required near ambient temperatures. Alloy 42 delivers a stable, matched CTE over a wider range (20–300°C), making it ideal for hermetic sealing applications with glass and ceramics.
Key Applications of INVAR 36
| Industry | Applications |
|---|---|
| Aerospace | Composite forming tools & dies, satellite structures, antenna dishes |
| Precision Instruments | Laser components, interferometers, optical benches, measuring devices |
| LNG & Cryogenics | Membrane tank support systems, piping anchors, cryogenic components |
| Electronics | Shadow masks for OLED/LCD, photomasks, packaging heat sinks |
| Energy | Wind turbine components, thermostat rods, bimetallic elements |
INVAR 36 is widely specified in sectors where thermal expansion would otherwise degrade accuracy — from aerospace composite tooling to LNG carrier membranes.
ZYTC Alloy: Your Trusted INVAR 36 Partner
ZYTC Alloy has just completed an export order of INVAR 36 Alloy Bar to Turkey, manufactured strictly to ASTM F1684. The order covered specifications of ø210 × 152 mm and ø240 × 75 mm.
Our capabilities at a glance:
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20 years of export experience in nickel-based alloys, cobalt-based alloys, titanium alloys, and related materials
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Independent laboratory — in-house testing for chemical composition, mechanical properties, impact energy, and high-temperature performance
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ISO9001 and AS9120 certified
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Full product range: INVAR 36 plate, strip, wire, bar, tube, forging, and custom-machined parts per drawings
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Strict adherence to ASTM, AISI, ISO, JIS, AMS and other international standards
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Fast lead times, competitive pricing, consistent high quality
Regardless of order quantity, ZYTC Alloy executes a standardized, process-driven, and specialized production and inspection workflow. Every INVAR 36 product passes full tensile, hardness, dimensional, and chemical verification before delivery.
Contact ZYTC Alloy today for your INVAR 36 requirements — whether you need standard stock or custom-machined components, we deliver precision, reliability, and speed.
