Alloy 39，Low Expansion 39 Alloy Forgings，

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Alloy 39 (Low Expansion 39 Alloy Wire) - Introduction with Composition, Properties, Applications and Product Forms

Alloy 39, commercially known as Low Expansion 39 Alloy, is a specialized iron-nickel alloy celebrated for its extremely low coefficient of thermal expansion, making it a cornerstone material in applications where dimensional stability across wide temperature ranges is critical. This high-performance alloy combines low thermal expansion with good mechanical strength, corrosion resistance, and excellent fabricability, and is available in a comprehensive range of forms to meet diverse industrial needs, including Bar (Round bar, Flat bar), Ribbon, Wire, Rods, Tube, Pipe, Foil, Plate, Sheet, Strip, and Forging Stock. Low Expansion 39 Alloy Wire, in particular, is valued for its precision, flexibility, and consistent low expansion properties, making it ideal for intricate components in aerospace, electronics, and precision instrumentation. Below is a detailed overview of its chemical composition, key properties, practical applications, and available product forms.

Chemical Composition

The precisely engineered chemical composition of Alloy 39 (Low Expansion 39 Alloy) is the foundation of its exceptional low thermal expansion and mechanical performance. The typical composition (by weight) is as follows:

Iron (Fe): 59-61% (primary matrix element, providing structural strength and stability)

Nickel (Ni): 38-40% (critical for achieving low thermal expansion, forming a face-centered cubic structure that minimizes dimensional changes with temperature)

Carbon (C): ≤ 0.05% (controlled to avoid carbide formation, which could increase thermal expansion and reduce ductility)

Manganese (Mn): ≤ 0.5% (assists in deoxidation during manufacturing and improves weldability)

Silicon (Si): ≤ 0.3% (minimized to prevent the formation of brittle silicides, preserving ductility)

Sulfur (S): ≤ 0.01% (kept at very low levels to ensure good ductility and prevent hot shortness during fabrication)

Phosphorus (P): ≤ 0.02% (controlled to maintain low expansion properties and avoid embrittlement)

Other trace elements: ≤ 0.3% total (including chromium and copper, all minimized to preserve the alloy’s low expansion characteristics)

This carefully balanced composition synergistically delivers the alloy's signature low thermal expansion, good mechanical strength, and formability, making it suitable for precision applications requiring dimensional stability.

Key Properties

Alloy 39 (Low Expansion 39 Alloy Wire) and its various forms exhibit a unique set of properties that make them indispensable in applications demanding dimensional stability and reliability:

Mechanical Properties (room temperature, annealed condition):

Tensile strength: 420-550 MPa (60,900-79,800 psi)

Yield strength (0.2% offset): 140-230 MPa (20,300-33,400 psi)

Elongation (in 50 mm): 35-50% (excellent ductility, enabling complex forming, bending, and drawing into wire and thin forms)

Hardness: 110-150 HB (Brinell hardness, indicating good machinability and workability)

Thermal Properties (key for low expansion applications):

Coefficient of thermal expansion (CTE): Extremely low CTE of 4.5-5.5 μm/(m·K) over the temperature range of -50°C to 200°C (-58°F to 392°F), ensuring minimal dimensional changes with temperature fluctuations

Curie temperature: 160-180°C (320-356°F), below which the alloy retains its low expansion properties

Thermal conductivity: 17 W/(m·K) at 20°C (68°F), suitable for applications requiring controlled heat transfer

Specific heat capacity: 460 J/(kg·K) at 20°C (68°F)

Corrosion Resistance:

General corrosion resistance: Good resistance to atmospheric corrosion, freshwater, and mild industrial environments

Chemical resistance: Resistant to dilute acids, alkaline solutions, and organic chemicals; less suitable for strong oxidizing acids and saltwater

Wet corrosion: Resistant to oils, solvents, and mild detergents, ensuring durability in precision equipment

Oxidation resistance: Moderate resistance to oxidation in air up to 350°C (662°F), forming a thin oxide layer that prevents rapid degradation

Physical Properties:

Density: 8.0 g/cm³ (0.289 lb/in³)

Melting point: 1440-1480°C (2624-2696°F)

Modulus of elasticity: 145 GPa (21,000 ksi) at room temperature

Electrical resistivity: 0.50-0.60 μΩ·m at 20°C (68°F)

Product Forms

Alloy 39 (Low Expansion 39 Alloy) is manufactured in a diverse range of forms to accommodate specialized industrial processes across aerospace, electronics, and precision engineering sectors:

Bar: Available as Round bar (diameters from 6 mm to 200 mm) and Flat bar (thickness 5 mm to 100 mm, width 15 mm to 500 mm), ideal for machining into precision components such as optical mounts, sensor housings, and aerospace hardware.

Ribbon: Thin, flat strips (thickness 0.05 mm to 1 mm, width 5 mm to 100 mm) used in thermostats, bimetallic strips, and precision electrical components requiring low expansion.

Wire: Low Expansion 39 Alloy Wire (diameters 0.05 mm to 8 mm) offers excellent flexibility and dimensional stability, making it suitable for thermocouple leads, precision springs, and wiring in high-precision instruments.

Rods: Solid cylindrical rods (diameters 3 mm to 50 mm) suitable for structural supports in optical systems, aerospace components, and precision machinery.

Tube and Pipe: Seamless options (outer diameter 5 mm to 150 mm, wall thickness 0.5 mm to 8 mm) for thermal management systems, sensor housings, and fluid transport in precision equipment.

Foil: Ultra-thin sheets (thickness 0.005 mm to 0.1 mm) used in lightweight bimetallic components, thermal shields, and precision electrical contacts.

Plate and Sheet: Flat forms (plate: thickness 4 mm to 80 mm; sheet: 0.2 mm to 4 mm) for fabricating optical benches, laser components, and aerospace structural parts requiring dimensional stability.

Strip: Narrow, flat strips (thickness 0.05 mm to 2 mm, width 10 mm to 200 mm) for precision manufacturing in thermostats, relays, and sensor components.

Forging Stock: Billets and ingots for hot forging into complex shapes such as aerospace brackets, optical mounts, and precision mechanical components.

Applications

The exceptional low thermal expansion properties of Alloy 39 (Low Expansion 39 Alloy Wire) across its various forms make it a critical material in industries requiring dimensional stability and precision:

Aerospace and Aviation:

Aircraft instrumentation: Optical mounts, gyroscope components, and sensor housings (from bar and plate) that maintain alignment across extreme temperature ranges.

Aerospace structures: Components in satellite systems and missile guidance systems (from forging stock and sheet) where dimensional stability under thermal cycling is critical.

Thermal management: Tubes and pipes for coolant lines in avionics, ensuring consistent flow rates despite temperature fluctuations.

Electronics and Optics:

Optical equipment: Laser housings, mirror mounts, and optical benches (from plate and bar) that preserve alignment in temperature-varying environments.

Semiconductor manufacturing: Precision tools and fixtures (from sheet and rod) used in lithography systems, where micron-level accuracy is essential.

Electrical components: Thermostats, bimetallic switches, and relay contacts (from ribbon and strip) that respond reliably to temperature changes.

Precision Instrumentation:

Scientific instruments: Components for spectrometers, atomic clocks, and navigation systems (from wire and bar) requiring high accuracy across temperature ranges.

Medical devices: MRI machine components, laser surgical tools (from foil and sheet), and diagnostic equipment that maintain calibration in varying temperatures.

Metrology equipment: Calibration standards and measurement tools (from bar and rod) that provide consistent results regardless of ambient temperature.

Specialized Applications by Form:

Wire: Thermocouple leads in high-precision temperature sensors, precision springs in instruments, and wiring in electronics where minimal dimensional change is critical.

Ribbon and Strip: Bimetallic strips in thermostats, electrical contacts in precision relays, and connectors in aerospace electronics.

Plate and Sheet: Optical benches, laser housings, and structural components in precision machinery.

Bar and Rod: Machined sensor housings, optical mounts, and fasteners in aerospace and scientific equipment.

In summary, Alloy 39 (Low Expansion 39 Alloy Wire) — available in forms from Bar and Wire to Plate and Forging Stock — delivers exceptional low thermal expansion, good mechanical strength, and formability. Its diverse product forms enable tailored solutions across aerospace, electronics, and precision instrumentation sectors, establishing it as a critical material in applications demanding dimensional stability.

Packing of Standard Packing:

 Typical bulk packaging includes palletized plastic 5 gallon/25 kg. pails, fiber and steel drums to 1 ton super sacks in full container (FCL) or truck load (T/L) quantities. Research and sample quantities and hygroscopic, oxidizing or other air sensitive materials may be packaged under argon or vacuum. Solutions are packaged in polypropylene, plastic or glass jars up to palletized 2764 gallon liquid totes Special package is available on request.