Alloy 400,Monel 400 Wire,UNS N04400

Alloy 400,Monel 400 Wire,UNS N04400

Introduction to Alloy 400 (Monel 400 Wire, UNS N04400)

Alloy 400, commercially known as Monel 400 and classified under UNS N04400, is a classic nickel-copper superalloy celebrated for its exceptional corrosion resistance, mechanical stability, and versatility across diverse environments. As the foundational alloy of the Monel family, it features a balanced nickel-copper matrix (typically 63-67% Ni, 28-34% Cu) that delivers robust performance from cryogenic conditions (-253°C/-423°F) up to 480°C/900°F. Unlike its low-carbon derivative (Monel 405), Monel 400 has a slightly higher carbon content (≤0.15 wt%), which provides moderate high-temperature strength but requires careful welding to avoid intergranular corrosion (IGC) in harsh service. Its solid-solution strengthened austenitic microstructure ensures excellent ductility, toughness, and resistance to seawater, brines, organic acids, reducing chemicals (e.g., H₂S), and even molten alkalis—making it a staple in industries where corrosion resilience is non-negotiable. Monel 400 wire, a key form of this alloy, is widely used in chemical processing, marine engineering, oil & gas, and aerospace applications—excelling in components like thermocouple sheaths, valve stems, electrical connectors, and non-welded fasteners that demand long-term durability in aggressive media.

1. Chemical Composition (Typical, wt%)

The chemical composition of UNS N04400 adheres to strict industry standards including ASTM B865 (for nickel-copper alloy wire), ASTM B164 (for nickel-copper alloy sheet/plate), and ASME SB865, with its nickel-copper balance being the primary driver of corrosion performance. The typical composition is as follows:

Element

Content Range (wt%)

Function

Nickel (Ni)

63.0 - 67.0

Serves as the primary matrix element, stabilizing the austenitic structure; enhances resistance to reducing environments (e.g., sour gas, sulfuric acid) and maintains ductility at cryogenic temperatures.

Copper (Cu)

28.0 - 34.0

A core alloying element that boosts corrosion resistance in seawater, brines, and organic acids (e.g., acetic, formic acids); improves workability during wire drawing and reduces alloy cost compared to nickel-only alloys.

Carbon (C)

≤ 0.15

Provides moderate high-temperature strength via limited carbide formation; requires controlled welding (e.g., post-weld annealing) to prevent intergranular corrosion in corrosive service.

Iron (Fe)

≤ 2.5

Improves hot workability (critical for wire rod production) and enhances thermal conductivity; limited to avoid compromising corrosion resistance in marine or chemical environments.

Manganese (Mn)

≤ 1.5

Aids in deoxidation during melting and improves cold workability for fine wire drawing; controlled to avoid brittleness at low temperatures.

Silicon (Si)

≤ 0.5

Reduces oxide formation during hot processing and improves molten alloy fluidity for casting; limited to avoid excessive inclusions that degrade fatigue life.

Sulfur (S)

≤ 0.010

Strictly limited to prevent hot cracking during wire drawing and welding; reduces the risk of pitting corrosion in sulfur-rich environments (e.g., oil refineries).

Phosphorus (P)

≤ 0.015

Controlled to avoid grain boundary embrittlement, especially in components exposed to cyclic loading or cryogenic temperatures.

Cobalt (Co)

≤ 1.0

Trace element that slightly enhances high-temperature strength without interfering with corrosion resistance; limited to avoid increasing alloy cost.

2. Physical Properties

Monel 400 wire exhibits stable physical properties across its operating temperature range, with performance driven by solid-solution strengthening (no age hardening required—simplifying manufacturing). Key properties (measured at room temperature unless specified otherwise) are:

Property

Value

Test Condition

Density

8.80 g/cm³

Room temperature (25°C)

Melting Point Range

1300 - 1350°C

-

Thermal Expansion Coefficient

13.3 × 10⁻⁶/°C

20 - 100°C; 16.0 × 10⁻⁶/°C (20 - 400°C)

Thermal Conductivity

22.7 W/(m·K)

100°C; 29.1 W/(m·K) (400°C)

Electrical Resistivity

0.54 × 10⁻⁶ Ω·m

Room temperature (25°C); 0.62 × 10⁻⁶ Ω·m (400°C)

Modulus of Elasticity

180 GPa

Room temperature (tensile); 155 GPa (400°C)

Poisson’s Ratio

0.32

Room temperature

Curie Temperature

≈ -196°C

Below this temperature, weakly ferromagnetic (irrelevant for most application temperatures).

Tensile Strength

≥ 650 MPa

Room temperature; ≥ 400 MPa (400°C)

Yield Strength (0.2% Offset)

≥ 275 MPa

Room temperature; ≥ 200 MPa (400°C)

Elongation

≥ 40%

Room temperature; ≥ 45% (-196°C, liquid nitrogen)

Hardness (Annealed)

≤ 180 HB

Room temperature

Impact Toughness (Charpy V-Notch)

≥ 120 J

Room temperature; ≥ 80 J (-196°C)

Corrosion Resistance

Passes 1000-hour salt spray test (ASTM B117); Resists 5% H₂SO₄ (room temperature, no pitting)

5% NaCl solution, 35°C (salt spray); Dilute sulfuric acid

3. Production Process of Monel 400 Wire

The manufacturing of Monel 400 wire focuses on preserving its nickel-copper balance, controlling carbon content, and optimizing ductility—with no age hardening required. Key steps include:

3.1 Raw Material Melting & Casting

Melting: High-purity raw materials (nickel, copper, iron, etc.) are melted via vacuum induction melting (VIM) or air induction melting with argon degassing (AIM-AD). This process ensures precise control of nickel-copper ratio and carbon content (≤0.15 wt%), eliminates gaseous impurities (O₂ < 25 ppm, N₂ < 30 ppm), and avoids segregation—critical for consistent corrosion performance.

Casting: Molten alloy is cast into ingots (500 - 2500 kg) or blooms, which undergo homogenization annealing at 1050 - 1100°C for 8 - 10 hours. This step eliminates chemical segregation (especially of nickel and copper), dissolves coarse carbides, and refines the microstructure—preparing the material for hot working while preserving ductility.

3.2 Hot Working & Wire Rod Production

Hot Rolling: Ingots/blooms are hot-rolled at 950 - 1050°C into wire rods (diameter: 8 - 20 mm). Hot rolling is performed at a controlled temperature range to avoid grain coarsening; rods are air-cooled to room temperature at a rate of 50 - 80°C/hour to maintain the austenitic phase and prevent excessive carbide formation.

Descaling: Hot-rolled rods undergo shot blasting (to remove loose oxide scale) followed by acid pickling (nitric-hydrofluoric acid solution) to eliminate residual nickel-copper oxide layers. This step prevents surface defects during cold drawing and ensures a clean surface for subsequent processing (e.g., passivation).

3.3 Cold Drawing (Wire Formation)

Multi-Pass Cold Drawing: Wire rods are cold-drawn through diamond dies in 6 - 10 passes to achieve the desired diameter (typically 0.1 mm - 10 mm). Each pass reduces diameter by 12 - 20%, with intermediate annealing (950 - 1000°C for 30 - 45 minutes, water-quenched) between passes. This annealing step relieves work hardening, restores ductility, and dissolves any unintended carbides—critical for maintaining corrosion resistance and formability.

Dimensional Control: Tension, die alignment, and drawing speed are precisely regulated to maintain tight diameter tolerance (±0.015 mm for precision wire) and roundness (≤0.008 mm). For applications like thermocouple sheaths or electrical connectors, laser diameter monitoring ensures consistency—uneven dimensions can affect temperature measurement accuracy or electrical conductivity.

3.4 Final Heat Treatment (Stability & Corrosion Optimization)

Monel 400 wire undergoes stress-relief annealing to optimize performance, especially for components exposed to cyclic loading or corrosive environments:

Stress Relief: Heating the wire to 850 - 900°C for 1 - 2 hours, followed by air cooling. This step reduces residual stresses from cold drawing, stabilizes the austenitic microstructure, and controls carbide distribution—minimizing the risk of stress corrosion cracking (SCC) in service.

Weld Preparation (Optional): For wire used in welded assemblies, a pre-weld anneal (980 - 1020°C for 1 hour, water-quenched) is performed to dissolve existing carbides. Post-weld annealing (850 - 900°C for 2 hours) is then recommended to prevent intergranular corrosion in the heat-affected zone (HAZ).

3.5 Surface Finishing & Quality Inspection

Surface Treatment:

Pickling: Post-annealing pickling in nitric acid to remove oxide scales and enhance the natural nickel-copper corrosion-resistant film—critical for marine or chemical applications.

Passivation: Optional chromate treatment to further strengthen the surface film, reducing the risk of pitting corrosion in chloride-rich environments (e.g., seawater).

Polishing: For high-precision applications (e.g., medical devices, aerospace sensors), the wire is polished to a smooth surface finish (Ra ≤ 0.2 μm) to avoid contamination and minimize friction.

Quality Control:

Chemical Analysis: Optical emission spectroscopy (OES) to verify nickel-copper ratio and carbon content—critical for corrosion resistance and mechanical performance.

Mechanical Testing: Tensile testing (strength/elongation), hardness testing (HB), and bend testing (to confirm ductility).

Corrosion Testing: Salt spray testing (ASTM B117), immersion testing in 5% H₂SO₄ (room temperature), and stress corrosion cracking testing (ASTM G36) to validate resistance to harsh media.

Non-Destructive Testing: Eddy current testing (for surface defects like cracks or pits) and ultrasonic testing (for internal flaws)—essential for safety-critical components like downhole cables.

Dimensional Inspection: Laser measurement to confirm diameter, straightness (≤0.1 mm/m), and roundness—ensuring compliance with application-specific tolerances.

4. Product Applications

Monel 400 wire’s unique combination of corrosion resistance, ductility, and temperature versatility makes it indispensable in industries requiring reliability in aggressive environments:

4.1 Chemical & Petrochemical Industry

Corrosion-Resistant Components: Fine wire (0.2 - 1.0 mm) for manufacturing thermocouple sheaths, sensor probes, and wire mesh filters in sulfuric acid (H₂SO₄), acetic acid, and ammonia production—resists both oxidizing and reducing acids.

Process Equipment: Wire for valve stems, pump shafts, and agitator springs in chemical reactors—maintains integrity in molten alkalis (e.g., sodium hydroxide) and organic solvents (e.g., methanol).

Pharmaceutical Manufacturing: Sanitary wire for mixing blades and filtration systems—complies with FDA standards (21 CFR Part 177) for food/drug contact and resists cleaning agents like hydrogen peroxide.

4.2 Marine Engineering

Subsea Components: Wire (0.5 - 2.0 mm) for subsea electrical cables, ROV (Remote Operated Vehicle) manipulator parts, and mooring line tensioners—resists seawater corrosion and biofouling, even at depths up to 3000 meters.

Naval Vessels: Wire for hull fasteners, heat exchanger tubes, and propeller shaft components—outperforms stainless steel in saltwater, reducing maintenance costs and extending service life.

Coastal Infrastructure: Wire for corrosion-resistant fencing, bridge cables, and seawater intake screens—resists salt spray and tidal corrosion.

4.3 Oil & Gas Industry

Downhole Tools: Wire for logging tool sensors, electrical conductors, and valve actuators in sour gas wells—resists H₂S (up to 1000 ppm) and brine corrosion at temperatures up to 400°C.

Refining Equipment: Wire for catalyst support grids and flue gas sensor probes in crude oil refining—resists sulfur-induced corrosion and hydrocarbon fouling.

Offshore Platforms: Wire for structural fasteners and firewater system components—maintains strength in marine atmospheric corrosion.

4.4 Aerospace & Cryogenic Applications

Cryogenic Systems: Wire for liquid oxygen (LOX) and liquid hydrogen (LH₂) tank components—maintains ductility at -196°C to -253°C without brittle fracture, critical for rocket propulsion.

Aerospace Electrical Components: Wire for high-reliability electrical connectors in aircraft fuel systems—resists jet fuel corrosion and temperature cycles (-50°C to 150°C).

Satellite Hardware: Wire for antenna components and sensor cables—resists space vacuum and atomic oxygen corrosion.

4.5 Industrial & Consumer Goods

Electrical Engineering: Wire for high-temperature electrical resistors and thermocouple extensions—maintains conductivity at 400 - 480°C.

Food Processing: Wire for mixing blades and conveyor components—resists organic acid corrosion (e.g., tomato paste, citrus juices) and complies with food safety standards.

Marine Hardware: Wire for boat rigging components and corrosion-resistant fasteners—outperforms brass and stainless steel in saltwater.

Conclusion

Alloy 400 (Monel 400 Wire, UNS N04400) is a timeless nickel-copper superalloy wire, distinguished by its exceptional corrosion resistance, ductility, and versatility across extreme temperatures. Its balanced chemistry and solid-solution strengthening make it a reliable choice for critical applications in chemical processing, marine engineering, and aerospace—where corrosion resilience and mechanical stability are non-negotiable. While its slightly higher carbon content requires careful welding, its performance in non-welded or properly post-welded assemblies remains unmatched. For custom requirements—such as ultra-precision wire (down to 0.01 mm diameter), food-grade surface finishes, or large-diameter wire (up to 12 mm) for structural components—manufacturers offer tailored solutions to meet the most demanding corrosion challenges. As the foundational Monel alloy, it continues to be a go-to material for industries where long-term durability in harsh environments is essential.

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 670 gallon liquid totes Special package is available on request.