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Super Invar 32-5/UNS K93500/Alloy 32-5 bar

Super Invar 32-5 bar, designated as UNS K93500 and commonly known as Alloy 32-5, is a nickel-iron-cobalt alloy renowned for its exceptionally low and …

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1 Introduction to Super Invar 32-5 (Alloy 32-5)

2 Chemical Composition of Super Invar 32-5 Bar

3 Mechanical and Thermal Properties of Super Invar 32-5 Bar

4 Standard Specifications, Bar Forms, and Available Sizes

5 Primary Applications of Super Invar 32-5 Bar Stock

Super Invar 32-5 bar, designated as UNS K93500 and commonly known as Alloy 32-5, is a nickel-iron-cobalt alloy renowned for its exceptionally low and stable coefficient of thermal expansion (CTE) at temperatures around room temperature. This bar stock form is a specialized material engineered for dimensional stability in precision instruments, scientific equipment, and aerospace components where minimal expansion or contraction with temperature change is critical.

Super Invar 32-5

Introduction to Super Invar 32-5 (Alloy 32-5)

Super Invar 32-5 is an advanced version of the traditional Invar (Fe-36Ni) alloy, with the addition of approximately 5% cobalt. This modification further reduces and stabilizes the thermal expansion coefficient over a specific temperature range, typically from about -50°C to 100°C (-58°F to 212°F). The bar stock is primarily used for machining components such as optical mounting frames, laser cavity resonators, precision gauge blocks, satellite structures, and metrology equipment where thermal drift must be minimized.

Chemical Composition of Super Invar 32-5 Bar

The unique near-zero expansion property of Super Invar 32-5 bar is achieved through its precise composition. Supplied by Shanghai NC Metal Materials Co., Ltd., the bar stock is produced to tight compositional tolerances to ensure predictable and consistent thermal behavior.

Element	Percentage (%) – Typical Range	Primary Function in the Alloy
Iron (Fe)	Balance	Base element of the alloy matrix.
Nickel (Ni)	31.0 – 33.0	Primary element responsible for the low thermal expansion characteristic when combined with iron in this specific ratio.
Cobalt (Co)	4.0 – 6.0	Key addition in Super Invar; further reduces and stabilizes the coefficient of thermal expansion compared to standard 36% Nickel Invar.
Carbon (C)	0.10 max	Residual element; kept low to maintain good ductility and machinability.
Manganese (Mn)	0.50 max	Residual element, deoxidizer.
Silicon (Si)	0.30 max	Residual element.
Phosphorus (P)	0.025 max	Impurity control.
Sulfur (S)	0.025 max	Impurity control.

Mechanical and Thermal Properties of Super Invar 32-5 Bar

The defining property of Super Invar 32-5 bar is its ultra-low thermal expansion, not its mechanical strength. Its mechanical properties are adequate for precision structural applications.

Property	Typical Value / Characteristic	Condition / Notes
Mean Coefficient of Thermal Expansion (CTE)	≈ 0.3 x 10^-6 /°C	Over the range 20°C to 100°C (68°F to 212°F). This is roughly 1/40th that of carbon steel.
Expansion Minimum Temperature	≈ 0.0 x 10^-6 /°C	The CTE goes through a minimum (near zero) typically around room temperature.
Tensile Strength	450 – 550 MPa (65 – 80 ksi)	Annealed condition
Yield Strength (0.2% Offset)	240 – 340 MPa (35 – 49 ksi)	Annealed condition
Elongation	≥ 30%	Annealed condition
Modulus of Elasticity (Young’s Modulus)	≈ 145 GPa (21 x 10^6 psi)	At room temperature
Density	8.13 g/cm³ (0.294 lb/in³)	–
Curie Temperature	≈ 230°C (450°F)	Above this temperature, the alloy loses its low expansion property.

Standard Specifications, Bar Forms, and Available Sizes

Shanghai NC Metal Materials Co., Ltd. supplies Super Invar 32-5 bar in forms suitable for precision machining of stable components.

Product Form	Standard Size Range	Key Standard Specifications	Common Supply Conditions
Round Bar (Cold Drawn/Forged)	5mm (0.2″) to 150mm (6″) Diameter	ASTM F1684 (UNS K93500), Proprietary specifications, Customer-specific thermal expansion guarantees.	Annealed, Stress-Relieved, Cold Drawn & Stress-Relieved
Square Bar	5mm to 80mm Width	Customer specifications	Annealed
Ground & Polished Bar	3mm to 50mm Diameter	For precision instrument use	Precision ground, Stress-Relieved
Forging Billet	100mm to 300mm Diameter	For large, near-net-shape aerospace components	As-Forged, Annealed

Primary Applications of Super Invar 32-5 Bar Stock

Machined components from Super Invar 32-5 bar are used in fields where dimensional stability is paramount: Aerospace & Satellites: Structural members, optical benches, and support frames for space-based telescopes and sensors where temperature fluctuations are extreme.

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