Alloy X is a nickel-chromium-iron-molybdenum high-temperature alloy. This datasheet presents the material within the American (ASTM / ASME / UNS) standard system.
A solid-solution-strengthened superalloy of the Ni-Cr-Fe-Mo family, Alloy X possesses an exceptional combination of oxidation resistance, fabricability and high-temperature strength, with creep and stress-rupture properties useful to about 1200 °C. The high nickel content improves resistance to carburisation, nitridation and chlorination; chromium provides oxidation and carburisation resistance; and molybdenum and tungsten enhance high-temperature creep strength. It is exceptionally resistant to stress-corrosion cracking in petrochemical applications and retains good ductility after prolonged exposure at 650, 760 and 870 °C. With excellent forming and welding characteristics, it is supplied in the solution heat-treated condition.
Typical applications include gas-turbine combustion-zone components — transition ducts, combustor cans, spray bars and flame holders — afterburners, tailpipes and cabin heaters, and industrial-furnace rolls, retorts, baffles and muffles.
| Property | Value | Unit |
|---|---|---|
| Density | 8.22 | g/cm³ |
| Melting range | 1260–1355 | °C |
| Elastic modulus | 205 | GPa |
| Coefficient of thermal expansion (20–100 °C) | 13.9 | µm/m·°C |
| Thermal conductivity (20 °C) | 9.1 | W/m·K |
| Specific heat (20 °C) | 486 | J/kg·K |
| Structure | Austenitic (FCC), single phase | — |
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Nickel | Ni | Balance | — | Base element; carburisation / nitridation resistance |
| Chromium | Cr | 20.5 | 23.0 | Oxidation / carburisation resistance |
| Iron | Fe | 17.0 | 20.0 | Solid-solution; cost-effectiveness |
| Molybdenum | Mo | 8.0 | 10.0 | High-temperature creep strength |
| Cobalt | Co | 0.50 | 2.50 | High-temperature strength |
| Tungsten | W | 0.20 | 1.0 | Creep / oxidation resistance |
| Manganese | Mn | — | 1.0 | Deoxidiser |
| Silicon | Si | — | 1.0 | Oxidation resistance |
| Carbon | C | 0.05 | 0.15 | Carbide strengthening |
Solution heat-treated condition, typical values for UNS N06002.
| Condition | Property | Value |
|---|---|---|
| Solution annealed | Tensile strength (UTS) | ≥755 MPa (110 ksi) |
| Solution annealed | 0.2% yield strength | ≥385 MPa (56 ksi) |
| Solution annealed | Elongation at break | ≥45 % |
| At elevated temperature | Creep / rupture strength | Useful to ~1200 °C |
| — | Elastic modulus | 205 GPa |
Confirm against the mill test report. The alloy retains good ductility after long-time exposure at high temperature, supporting its use in gas-turbine and furnace service.
| Environment | Performance | Notes |
|---|---|---|
| High-temperature oxidation (to ~1200 °C) | Excellent | Adherent chromia scale |
| Carburisation | Excellent | Best among Ni / Co alloys |
| Reducing / neutral atmospheres | Excellent | Balanced resistance |
| Hot corrosion / molten salts | Very Good | Low attack in tests |
| Stress-corrosion cracking | Excellent | Petrochemical service |
The balanced chromium, molybdenum and nickel content gives an exceptional combination of resistance to oxidizing, reducing and neutral atmospheres at high temperature, with outstanding carburisation resistance and excellent resistance to stress-corrosion cracking.
A single-phase solid-solution alloy; not hardenable by precipitation. Properties are set by solution annealing.
Solution Anneal Solution anneal sheet and tube at approximately 1175 °C (2150 °F) and rapidly cool (air or water). Bar and forgings are held at about 1177 °C long enough to bring the section to temperature, then rapidly cooled. The alloy is not strengthened by heat treatment; all hot- or cold-worked parts should be annealed and rapidly cooled to restore the best balance of properties.
Excellent weldability; welded by shielded-metal-arc, gas-tungsten-arc and gas-metal-arc processes, and resistance welding, with matching filler. Welding is performed on solution-annealed material.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / TIG | Excellent | Matching X filler (ERNiCrMo-2) |
| GMAW / MIG | Good | Matching filler |
| SMAW / stick | Good | Matching electrode (ENiCrMo-2) |
Weld on solution-annealed material with matching filler and clean surfaces.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Machinability | Difficult; work-hardens, rigid setups, sharp tooling |
| Speeds | Slow speeds, positive feeds, no dwelling |
| Coolant | Ample coolant |
Forming Processes
| Process | Notes |
|---|---|
| Cold forming | Good ductility; work-hardens, anneal between heavy operations |
| Hot forming | ~1177 °C (held to temperature); anneal and rapid-cool afterward |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Aero gas turbine | Combustor cans, transition ducts, flame holders | Oxidation + high-temperature strength |
| Propulsion | Afterburners, tailpipes, cabin heaters | Thermal + oxidation resistance |
| Industrial furnaces | Rolls, retorts, baffles, muffles | Oxidizing/reducing/neutral atmospheres |
| Petrochemical | High-temperature equipment | Stress-corrosion-cracking resistance |
| Product Form | ASTM Standard | AMS |
|---|---|---|
| Plate, sheet and strip | ASTM B435 | AMS 5536 |
| Bar and forgings | ASTM B572 | AMS 5754 |
| Seamless pipe and tube | ASTM B622 | AMS 5587 |
| Welded pipe and tube | ASTM B619 | AMS 5588 |
Nickel-chromium-iron-molybdenum high-temperature alloy. UNS N06002.
| Alloy | Cr % | Mo % | Fe % | Best Used For |
|---|---|---|---|---|
| Alloy X | 20.5–23 | 8–10 | 17–20 | Ni-Cr-Fe-Mo high-temp; gas-turbine combustors, furnace parts |
| Alloy S | 14.5–17 | 14–16.5 | ≤3 | Low-expansion high-temp; seal rings, dissimilar filler |
| Alloy N | 6–8 | 15–18 | ≤5 | Molten fluoride salts; molten-salt reactors |
| Alloy W | 4–6 | 23–26 | 4–7 | Dissimilar-metal welding filler |
| Alloy 625 | 20–23 | 8–10 | ≤5 | General Ni-Cr-Mo-Nb corrosion / strength |




