Bar and Rod
Plate and Sheet
Strip
Pipe and Tube
Wire
Welding
Powder Material
Cast Products
Forged Products
Fittings
Fastening
Round Bar:
φ2–500 mm, 1–6 m length
Flat/Square Bar:
4–100 mm thickness/width
Hex Bar:
A/F 3–100 mm
Hollow Bar:
OD 20–300 mm
Sheet:
0.3–6 mm thickness
Medium Plate:
6–25 mm thickness
Heavy Plate:
25–100 mm thickness
Standard Strip:
0.05–3 mm thick,
10–600 mm wide
Precision strip:
0.01–0.5 mm thick,
tight tolerance ±0.005 mm
Foil:
0.005–0.1 mm thick
Seamless Tube:
OD 6–450 mm,
WT 1–50 mm,
1–12 m length
Welded Tube:
OD 10–600 mm,
WT 1–20 mm
Capillary Tube:
OD 1–10 mm,
WT 0.1–2 mm
Wire Form:
Cold Drawn Wire,
Bright Wire,
Spring Wire,
Fine Wire,
Ultra-fine Wire
General Diameter:
φ0.1–10 mm
Coil Weight:
50–500 kg,
customizable tolerance
Solid Wire:
φ0.8–4.0 mm
Flux-cored Wire:
φ1.2–4.0 mm
Welding Rod:
φ2.0–5.0 mm
Powder Form:
AM 3D Printing Powder,
Spherical Powder,
Gas-atomized Powder,
Water-atomized Powder
Particle Size:
10–150 μm
Sphericity:
≥90% for AM grade
Cast Ingot:
φ200–800 mm
Precision Casting:
min wall 0.5 mm
Cast Pipe:
OD 100–600 mm,
WT 10–50 mm
Forged Bar:
Φ35–500 mm
Forged Ring:
OD 200–2000 mm
Forging Weight:
1–5000 kg
Fittings Form:
Elbow, Tee, Reducer, Flange, Cap, Outlet, Lap Joint
Size range:
1/2''–24'' (DN15–DN600)
Wall thickness:
Sch10–Sch160, STD, XS, XXS
Pressure Class:
150–2500 LB
Fastening Form:
Bolt, Nut, Screw, Stud, Washer, Pin, Rivet
Metric: M3–M64
Imperial: #4–2.5''
Length: 6–500 mm
Incoloy 903 is an age-hardenable nickel-iron-cobalt controlled-expansion alloy. This datasheet presents the material within the American (ASTM / ASME / UNS) standard system.
Developed by Special Metals, Incoloy 903 is distinguished by an unusual combination of properties: a constant low coefficient of thermal expansion, a constant modulus of elasticity over a range of temperature, and high strength. It is strengthened by precipitation of γ′ / γ″ (Ni₃(Nb,Ti,Al)) phases during ageing, with the nickel, cobalt and iron together controlling the Curie temperature and the low-expansion behaviour and the niobium, titanium and aluminium providing precipitation hardening. The result is precise dimensional stability with temperature combined with high strength, making the alloy valuable where close clearance control or constant elastic modulus is required. It is used in the solution-treated and aged condition.
Typical applications include rocket-engine thrust chambers, gas-turbine rings and casings for clearance control, steam-turbine bolts, springs, gage blocks and ordnance hardware.
| Property | Value | Unit |
|---|---|---|
| Density | 8.14 | g/cm³ |
| Inflection temperature | ~427 | °C |
| Elastic modulus | 148 | GPa |
| Coefficient of thermal expansion (20–425 °C) | 7.6 | µm/m·°C |
| Thermal conductivity (20 °C) | 16.9 | W/m·K |
| Specific heat (20 °C) | 442 | J/kg·K |
| Structure | Austenitic (FCC) | — |
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Iron | Fe | Balance | — | Base element; low-expansion matrix |
| Nickel | Ni | 36.0 | 40.0 | Controls expansion / Curie temperature; γ′ matrix |
| Cobalt | Co | 13.0 | 17.0 | Controls expansion; raises inflection temperature |
| Niobium | Nb | 2.40 | 3.50 | γ′ / γ″ precipitation strengthening |
| Titanium | Ti | 1.00 | 1.85 | γ′ precipitation strengthening |
| Aluminium | Al | 0.30 | 1.15 | γ′ formation |
| Silicon | Si | — | 0.35 | Deoxidiser |
| Carbon | C | — | 0.10 | Carbide formation |
Age-hardened condition, typical values for UNS N19903.
| Condition | Property | Value |
|---|---|---|
| Solution treated & aged | Tensile strength (UTS) | ≥1310 MPa (190 ksi) |
| Solution treated & aged | 0.2% yield strength | ≥1035 MPa (150 ksi) |
| Solution treated & aged | Elongation at break | ≥12 % |
| Solution treated & aged | Reduction of area | ≥30 % |
| — | Elastic modulus | 148 GPa |
Confirm against the mill test report. The alloy maintains a low, constant coefficient of thermal expansion to the inflection temperature (~427 °C) with high strength.
| Environment | Performance | Notes |
|---|---|---|
| Dimensional / thermal stability | Excellent | Constant low CTE; key design feature |
| High-temperature oxidation | Limited | Low chromium; not for severe oxidation |
| Aqueous / general | Moderate | Low chromium content |
| Hydrogen environments | Use with care | Subject to standard precautions |
| Elevated-temperature strength | Excellent | Combined with low expansion |
The alloy is selected for its controlled expansion, constant modulus and high strength rather than for corrosion resistance; the low chromium content limits high-temperature oxidation resistance, and protective measures may be needed for severe oxidising service.
A γ′ / γ″ precipitation-hardenable controlled-expansion alloy; strengthened by solution treatment followed by ageing.
Solution Treatment Solution anneal at approximately 845 °C (1550 °F) for about 1 hour and air cool, or per the applicable specification for the product form.
Precipitation Hardening (Ageing) Age at approximately 720 °C (1325 °F) for 8 hours, furnace cool to about 620 °C (1150 °F), hold for a total ageing time of about 18 hours, and air cool — precipitating γ′ / γ″ (Ni₃(Nb,Ti,Al)). A stress-relief and stabilisation cycle may be applied for welded assemblies.
Good weldability; can be welded by gas-tungsten-arc, gas-metal-arc, submerged-arc and shielded-metal-arc processes. Welding is done in the solution-annealed condition with post-weld ageing.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Good | Matching alloy 903 filler |
| GMAW / MIG | Good | Matching filler |
| SAW / SMAW | Acceptable | Matching consumable |
Weld in the solution-annealed condition; apply post-weld stress relief and ageing to develop properties.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Preferred condition | Solution-annealed for machining, then age |
| Machinability | Difficult; rigid setups, carbide tooling, slow speeds |
| Coolant | Ample coolant |
Forming Processes
| Process | Notes |
|---|---|
| Cold forming | Conventional techniques; heavy-duty lubricants required |
| Hot forming | Readily forged; solution and age afterward |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Aerospace / propulsion | Rocket-engine thrust chambers | Low expansion + high strength |
| Gas turbine | Rings, casings, seals (clearance control) | Dimensional stability |
| Precision | Gage blocks, springs, constant-modulus parts | Constant CTE / modulus |
| Power / ordnance | Steam-turbine bolts, ordnance hardware | Strength + stability |
| Product Form | Standard / Designation | AMS |
|---|---|---|
| Bar, rod and forgings | UNS N19903 | AMS 5803 |
| Sheet, strip and plate | UNS N19903 | — |
| Wire | UNS N19903 | — |
| Material designation | UNS N19903 | Special Metals product |
Nickel-iron-cobalt controlled-expansion alloy. UNS N19903.
| Alloy | Type | CTE Trend | Strengthening | Best Used For |
|---|---|---|---|---|
| Incoloy 903 | Ni-Fe-Co controlled expansion | Low, constant (to ~427 °C) | γ′ / γ″ (Nb, Ti, Al) | Constant CTE + modulus + strength; thrust chambers, clearance control |
| Incoloy 907 | Fe-Ni-Co controlled expansion | Low, constant | γ′ (Nb, Ti) | Higher-strength low-expansion rings and shafts |
| Incoloy 909 | Fe-Ni-Co controlled expansion | Low, constant | γ′ (Nb, Ti) | Silicon-bearing low-expansion gas-turbine parts |
| Inconel 783 | Ni-Co-Fe + Al | Low (~20% < 718) | γ′ + β (NiAl) | Oxidation-resistant low-expansion clearance control |
| Inconel 718 | Ni-Cr-Fe | Standard | γ′ + γ″ (Nb, Ti) | Most-used high-strength superalloy |
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