Incoloy 825 – UNS N08825
Titanium-stabilized nickel-iron-chromium alloy with molybdenum and copper
Ni-Fe-Cr alloy with Mo, Cu and Ti, developed for aqueous corrosion: sulfuric and phosphoric acids, chloride stress corrosion cracking and intergranular corrosion (Ti-stabilized). It is the reference material for sour-well tubing and pickling equipment. Pitting resistance is moderate (PREN ≈ 31).
Designations and equivalents
| System | Designation |
|---|---|
| UNS | N08825 |
| W.Nr./EN | 2.4858 – NiCr21Mo |
| DIN | NiCr21Mo |
| JIS | NCF 825 |
| Trade names | Incoloy 825 (Special Metals), Nicrofer 4221 (VDM), Alloy 825 |
| Others | ISO NiFe30Cr21Mo3 |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM B425 |
| Forging | ASTM B564 |
| Plate | ASTM B424 |
| Tube | ASTM B423 (seamless), B163, B705 (welded) |
Tolerances and HS codes
- Forged bars (round and square): machining allowance from 2 mm (Ø 6–16 mm) to 24 mm (Ø 400–500 mm) on the diameter. E.g. Ø 100–125 mm finished: +7 mm, tolerance +6 / −0 (length up to 3,500 mm).
- Forged discs: allowance of 4 to 9 mm on the diameter and 3 to 11 mm on the height, plus-only tolerance.
- Cutting and machining: band saw −0 / +5 to +15 mm on length; waterjet +10 % of thickness on the diameter (min. 2 mm); machined parts −0 / +2 to +5 mm on the diameter. See the full tables (INF 002 and INF 003, the same for every alloy).
| Form | NCM (Brazil, 8 digits) | HS (international, 6 digits) | HTS (USA, 10 digits)* | CN (European Union, 8 digits)* |
|---|---|---|---|---|
| Forged bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Hot-rolled bar | 7505.12.10 | 7505.12 | 7505.12.3000 | 7505 12 00 |
| Plate (> 10 mm, width ≥ 600 mm) | 7506.20.00 | 7506.20 | 7506.20.3000 | 7506 20 00 |
| Seamless pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 12 00 |
| Welded pipe | 7507.12.00 | 7507.12 | 7507.12.0000 | 7507 12 00 |
| Flange and fitting | 7507.20.00 | 7507.20 | 7507.20.0000 | 7507 20 00 |
Tariff class: nickel alloy (by chemical composition, under the Chapter 72 Notes and Section XV Note 5).
*: US and EU codes for reference. NCM per current legislation (General Rules of Interpretation, Notes to Chapters 72, 74 and 75 and Section XV Note 5). Confirm the final code with your customs broker according to the item size and finish. HS = first 6 digits of the NCM.
Chemical composition (%)
ASTM B425 / B564 (UNS N08825)
| Element | Range (%) |
|---|---|
| Ni | 38.0 – 46.0 |
| Fe | ≥ 22.0 |
| Cr | 19.5 – 23.5 |
| Mo | 2.5 – 3.5 |
| Cu | 1.5 – 3.0 |
| Ti | 0.6 – 1.2 |
| C | ≤ 0.05 |
| Mn | ≤ 1.0 |
| Si | ≤ 0.5 |
| Al | ≤ 0.2 |
| S | ≤ 0.03 |
Mechanical properties
annealed (ASTM B564 / B425)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 241 MPa |
| Tensile strength | ≥ 586 MPa |
| Elongation | ≥ 30% |
Typical physical properties
| Property | Value |
|---|---|
| Density | 8.14 g/cm³ |
| Melting range | 1,370 – 1,400 °C |
| Modulus of elasticity | 196 GPa |
| Thermal conductivity (20 °C) | 11.1 W/m·K |
| Thermal expansion (20–100 °C) | 14.0 µm/m·K |
| Electrical resistivity | 113 µΩ·cm |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | From cryogenic up to ~540 °C (usual limit in ASME pressure vessels). Not indicated for creep service. |
| Heat treatment | Stabilizing anneal at ≈ 940 °C (range 920 – 980 °C), with rapid cooling. Forms Ti carbides and prevents sensitization. Not age hardenable. |
| Welding | Good weldability. Most used consumable: AWS ERNiCrMo-3 / ENiCrMo-3 (625, over-alloyed); alternative ERNiFeCr-1 (FM 65 type). |
| Machining | Similar to high-alloy austenitic stainless: work hardens; use carbide, moderate speed and coolant. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Well tubing and components with H₂S/CO₂ (oil and gas)
- Sulfuric and phosphoric acid equipment
- Pickling tanks, baskets and coils
- Gas scrubbers (FGD)
- Heat exchangers cooled with brackish water
- Nuclear fuel reprocessing
Alternatives: 904L or Alloy 20 (N08020) in sulfuric acid at lower cost; 625, C276 or 6Mo super-austenitic when there is a risk of pitting or crevice corrosion in chlorides; 28 (N08028) as a similar option.
Incoloy 825: complete guide
What Incoloy 825 is
Incoloy 825 belongs to the family of nickel alloys, in the nickel-iron-chromium group for aqueous corrosion. It derives from Incoloy 800 by adding molybdenum, copper and titanium and increasing the nickel: molybdenum gives resistance to pitting and reducing media, copper protects in sulfuric acid, titanium stabilizes the alloy against intergranular corrosion and the high nickel makes it practically immune to chloride stress corrosion cracking.
Mechanical properties
Annealed, ASTM B425 requires a minimum yield strength of 241 MPa, minimum tensile strength of 586 MPa and minimum elongation of 30%. The alloy does not harden by heat treatment.
Corrosion and limits of use
825 resists sulfuric and phosphoric acid over a wide concentration range, organic acids, moderate chlorides and stress corrosion cracking, with a PREN of 28 to 35, and is qualified by NACE MR0175 for H2S wells. It is limited in hydrochloric acid and in crevices in stagnant seawater, where Inconel 625 or C-276 are indicated.
Applications
Sulfuric and phosphoric acid tanks, heat exchangers and piping, pickling equipment, production tubing and oil and gas well components in sour service, desulfurization absorbers, nuclear fuel reprocessing equipment and valve and pump components for the chemical industry. Alternatives: Alloy 20 for sulfuric acid and Alloy 28 (UNS N08028) for phosphoric acid and wells.
Supply forms and Dustre services
Round bars and blocks forged in open die, cut to size on a band saw, with rough or finish machining, solution annealing or annealing in our own furnaces and hardness, tensile and impact testing. All material is supplied with a 3.1 inspection certificate and heat traceability.
Frequently asked questions
What is the chemical composition of Incoloy 825?
Per ASTM B425 / B564 (UNS N08825): Ni 38.0 – 46.0; Fe ≥ 22.0; Cr 19.5 – 23.5; Mo 2.5 – 3.5; Cu 1.5 – 3.0; Ti 0.6 – 1.2.
Which standards cover Incoloy 825?
Bar: ASTM B425. Forging: ASTM B564. Plate: ASTM B424. Tube: ASTM B423 (seamless), B163, B705 (welded).
Up to what temperature can Incoloy 825 be used?
From cryogenic up to ~540 °C (usual limit in ASME pressure vessels). Not indicated for creep service.
Which materials can replace Incoloy 825?
904L or Alloy 20 (N08020) in sulfuric acid at lower cost; 625, C276 or 6Mo super-austenitic when there is a risk of pitting or crevice corrosion in chlorides; 28 (N08028) as a similar option.
