Invar 36 Nickel-Iron Alloy Wire

Invar 36 Wire (UNS K93603, Nilo 36, Fe-Ni36, Alloy 36) is a low-expansion iron-nickel alloy wire with a face-centered cubic austenitic structure and 36% nickel.

As a high-precision wire product, Invar 36 wire has an extremely low coefficient of linear thermal expansion (averaging 1.5 × 10⁻⁶/°C) from -100°C to +200°C. It also offers good ductility, toughness, and weldability, along with excellent dimensional stability, making it a core material for manufacturing high-precision electronic instruments, support wires for optical equipment, cryogenic sensors, and specialty cables.

Invar 36 wire is primarily supplied in annealed (soft), light cold-drawn, or hard cold-drawn tempers. Standard diameters range from approximately 0.05 mm to 5.00 mm, with products available in coils or as cut-to-length straight wires. For precision electronic components, optical instruments, and micro-structural parts, specifications regarding diameter tolerance, roundness, surface finish, and straightness can be controlled according to customer drawings. The reference price range for Invar 36 wire is $30.00–$60.00 USD/kg; the minimum order quantity (MOQ) for standard stock wire is 30 kg, and the lead time for custom production is typically 15–20 working days.

Data is based on ASTM F1684.

Final mechanical properties shall be determined based on wire diameter, cold-working rate, and delivery condition.

The coefficient of thermal expansion of Invar 36 varies depending on the temperature range, heat treatment condition, degree of cold work, and testing method.

 Invar 36 is a controlled-expansion alloy designed to match the coefficient of thermal expansion of sealing materials or specific application requirements; it is not intended for high-temperature strength or corrosion resistance. The alloy loses its low-expansion characteristics during long-term service above 230°C and lacks high-temperature load-bearing capacity; furthermore, its corrosion resistance in corrosive media is limited, making it unsuitable for chemically corrosive environments.

Temperature Conditions: The low-expansion characteristics of Invar 36 wire are most stable within the range of -250°C to +200°C. Its Curie temperature is approximately 230°C; above this temperature, ferromagnetism is lost, the low-expansion effect diminishes sharply, and the coefficient of thermal expansion rises rapidly. Consequently, this alloy is unsuitable for long-term high-temperature service.

 

Atmospheric and Environmental Conditions: Invar 36 exhibits basic corrosion resistance in dry atmospheric environments but is prone to rusting in humid or corrosive media; its corrosion resistance is far inferior to that of stainless steel. Surface protective treatment is recommended for long-term use or outdoor applications.

 

Stress Conditions: Invar 36 is highly sensitive to residual stress. Stresses introduced during cold working and machining can alter the material's dimensional stability and expansion behavior. For precision applications, stress-relief annealing must be performed after processing to stabilize its properties.

 

Operating conditions to avoid: Heating in a sulfur-containing atmosphere (which causes hot shortness) and prolonged use above the Curie temperature. Finished parts after annealing are sensitive to mechanical stress; re-annealing is required after machining to restore dimensional stability.

Lork Group
Marketing Operations Department

Email: claire@lorkgroup.com
WhatsApp: +86 199 3707 5488

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