N08825 is a titanium-stabilised nickel–iron–chromium alloy with additions of molybdenum and copper, designed to provide exceptional resistance to a wide range of corrosive environments. This datasheet presents the material within the American (ASTM / ASME / SAE-AMS / UNS) standard system.
The nickel content is sufficient for resistance to chloride-ion stress-corrosion cracking; together with molybdenum and copper it gives outstanding resistance to reducing environments such as sulphuric and phosphoric acids. Molybdenum also aids resistance to pitting and crevice corrosion, while the chromium content confers resistance to oxidising substances such as nitric acid, nitrates and oxidising salts. The titanium addition, with appropriate heat treatment, stabilises the alloy against sensitisation to intergranular corrosion.
These properties make it especially useful in sulphuric and phosphoric acid service, sulphur-bearing flue gases, sour-gas and oil-field equipment, pickling operations, nuclear fuel reprocessing, propeller shafts, tank trucks and seawater handling. It has good mechanical properties from cryogenic to moderately high temperatures; exposure above about 540 °C can cause phase formation that lowers ductility, so it is not normally used where creep-rupture strength governs. It is listed in NACE MR0175 / ISO 15156 (type 4c) for sour service.
Values per Special Metals official datasheet, annealed condition.
| Property | Value | Unit |
|---|---|---|
| Density | 8.14 | g/cm³ |
| Specific heat capacity (26 °C) | 440 | J/kg·K |
| Thermal conductivity (26 °C) | 11.3 | W/m·K |
| Electrical resistivity (26 °C) | 1.13 | µΩ·m |
| Young's modulus (20 °C) | 196 | GPa |
| Poisson's ratio | 0.32 | — |
| Magnetic permeability (annealed) | <1.005 | Essentially non-magnetic |
| Maximum service temperature | ~540 | °C |
Limiting composition per ASTM B425 (UNS N08825).
| Element | Symbol | Min % | Max % | Role in Alloy |
|---|---|---|---|---|
| Nickel | Ni | 38.0 | 46.0 | Chloride-SCC resistance; reducing-acid resistance |
| Iron | Fe | 22.0 | balance | Base element |
| Chromium | Cr | 19.5 | 23.5 | Oxidising-media resistance; passive film |
| Molybdenum | Mo | 2.5 | 3.5 | Pitting/crevice + reducing-acid resistance |
| Copper | Cu | 1.5 | 3.0 | Sulphuric/phosphoric-acid resistance |
| Titanium | Ti | 0.6 | 1.2 | Stabiliser against sensitisation |
| Carbon | C | — | 0.05 | Low; minimises sensitisation |
| Manganese | Mn | — | 1.0 | Deoxidiser |
| Aluminium | Al | — | 0.2 | Residual |
| Silicon | Si | — | 0.5 | Deoxidiser |
| Sulphur | S | — | 0.03 | Residual impurity |
Typical room-temperature properties, annealed condition.
| Property | Value | Source |
|---|---|---|
| Ultimate tensile strength | 662 MPa (96 ksi) | Special Metals / mill-annealed plate |
| 0.2% proof strength (yield) | 338 MPa (49 ksi) | Special Metals / mill-annealed plate |
| Elongation at break | ≥45 % | Special Metals |
| Hardness | 135–165 HRB | Special Metals |
The alloy retains strength and toughness at cryogenic temperatures and can be substantially strengthened by cold work. It is not age-hardenable. Values are typical; confirm against the mill test certificate for each delivery.
| Environment | Performance | Notes |
|---|---|---|
| Sulphuric acid | Outstanding | Ni + Mo + Cu give resistance across a wide concentration range |
| Phosphoric acid | Outstanding | Suitable for evaporators and process duty |
| Chloride stress-corrosion cracking | Outstanding | High Ni content |
| Pitting and crevice corrosion | Very Good | Molybdenum addition |
| Nitric acid / oxidising media | Very Good | Chromium content |
| Intergranular corrosion | Excellent | Ti-stabilised; resists sensitisation after welding |
| Sour service (H₂S) | Good | NACE MR0175 / ISO 15156 type 4c |
| Seawater | Very Good | Used for propeller shafts and marine hardware |
A solid-solution, titanium-stabilised alloy; not age-hardenable. Heat treatment is for annealing / stabilisation only.
Anneal / Stabilise Anneal Temperature: ~940 °C (1725 °F) Purpose: softening, recrystallisation, and (with the titanium addition) stabilisation against intergranular sensitisation.
Service caution: exposure above ~540 °C can cause phase formation that lowers ductility and impact strength; the alloy is normally limited to ~540 °C in service.
Good weldability by all conventional processes. Welds should be made in the annealed condition; the titanium stabilisation helps resist weld-zone sensitisation.
| Welding Process | Applicability | Filler / Consumable |
|---|---|---|
| GTAW / GMAW | Excellent | AWS A5.14 ERNiFeCr-1 (Filler Metal 65) |
| SMAW / stick | Good | Welding Electrode 135 |
| Higher-alloy / dissimilar joints | — | INCO-WELD 686CPT (AWS ERNiCrMo-14) for higher-alloy joints |
Clean, oxide-free joint preparation is essential for sound welds.
Machining Guidelines
| Parameter | Recommendation |
|---|---|
| Work hardening | Moderate (austenitic behaviour) |
| Tooling | Rigid setup, sharp tools |
| Coolant | Flood coolant recommended |
| Preferred condition | Annealed |
Forming Processes
| Process | Notes |
|---|---|
| Hot forming | Standard hot-working practice for Ni-Fe-Cr alloys |
| Cold forming | Readily formed (austenitic-stainless practice); strengthens by cold work |
| Annealing | ~940 °C after heavy cold work |
| Industry | Typical Components | Key Requirements |
|---|---|---|
| Chemical processing | Phosphoric-acid evaporators, vessels, piping | Sulphuric/phosphoric-acid resistance |
| Oil and gas | Sour-well downhole tubulars, packers, subsurface equipment | H₂S resistance (NACE MR0175 type 4c) |
| Pickling / metal finishing | Pickling tanks and equipment | Acid resistance |
| Nuclear | Spent-fuel reprocessing equipment | Broad corrosion resistance |
| Marine | Propeller shafts, seawater piping, exhaust systems | Chloride-SCC + seawater resistance |
| Pollution control | Flue-gas (sulphur-bearing) handling, waste processing | Mixed acid + oxidising resistance |
| Product Form | ASTM Standard | ASME Code |
|---|---|---|
| Rod, bar and wire | ASTM B425 | ASME SB-425 |
| Forgings | ASTM B564 | ASME SB-564 |
| Plate, sheet and strip | ASTM B424 / B906 | ASME SB-424 / SB-906 |
| Seamless pipe and tube | ASTM B163 / B423 / B829 | ASME SB-163 / SB-423 |
| Welded pipe / tube | ASTM B704 / B705 / B751 / B775 | ASME SB-704 / SB-705 |
| Fittings | ASTM B366 | ASME SB-366 |
| Welding consumables | AWS A5.14 ERNiFeCr-1 (Filler 65) · Electrode 135 | — |
Listed in NACE MR0175 / ISO 15156 (type 4c) for sour service; ASME Code Cases 1936 / N-572.
| UNS | Ni % | Cr % | Other | Best Used For |
|---|---|---|---|---|
| N08825 | 38–46 | 19.5–23.5 | Mo 2.5–3.5, Cu 1.5–3 | Sulphuric/phosphoric acid; sour service; seawater |
| N08800 | 30–35 | 19–23 | Al+Ti | Heat resistance; less aqueous-acid resistance |
| N08020 | 32–38 | 19–21 | Cu 3–4, Nb | Sulphuric acid; lower-cost Fe-base |
| N08028 | 30–32 | 26–28 | Mo 3.5 | Phosphoric/sulphuric acid; higher Cr |
| N06625 | ≥58 | 20–23 | Mo 8–10, Nb | Seawater + higher strength; broader corrosion |




