904L stainless steel – UNS N08904
Low-carbon Ni-Cr-Mo-Cu super-austenitic stainless steel
Super-austenitic stainless with 23–28% Ni, 4–5% Mo and 1–2% Cu, designed for dilute sulfuric and phosphoric acid. Pitting and chloride stress corrosion resistance far superior to 316L/317L.
Designations and equivalents
| System | Designation |
|---|---|
| UNS | N08904 |
| W.Nr./EN | 1.4539 (X1NiCrMoCu25-20-5) |
| DIN | X1NiCrMoCu25-20-5 |
| JIS | SUS890L |
| Trade names | 904L, Uranus B6 |
Standards by product form
| Form | Standard |
|---|---|
| Bar | ASTM A479 / B649 |
| Forging/flange | ASTM A182 F904L / B366 (fittings) |
| Plate | ASTM B625 / A240 |
| Tube | ASTM B677 / B673 / B674 |
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 | 7222.30.00 | 7222.30 | 7222.30.0024 | 7222 30 51 |
| Hot-rolled bar | 7222.11.00 | 7222.11 | 7222.11.0059 | 7222 11 11 |
| Plate (> 10 mm, width ≥ 600 mm) | 7219.21.00 | 7219.21 | 7219.21.0020 | 7219 21 10 |
| Seamless pipe | 7304.41.90 | 7304.41 | 7304.41.6045 | 7304 41 00 |
| Welded pipe | 7306.40.00 | 7306.40 | 7306.40.5085 | 7306 40 80 |
| Flange and fitting | 7307.21.00 | 7307.21 | 7307.21.5000 | 7307 21 00 |
Tariff class: stainless steel (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 A479 / B625 (N08904)
| Element | Range (%) |
|---|---|
| C | ≤ 0.020 |
| Mn | ≤ 2.00 |
| P | ≤ 0.045 |
| S | ≤ 0.035 |
| Si | ≤ 1.00 |
| Cr | 19.0 – 23.0 |
| Ni | 23.0 – 28.0 |
| Mo | 4.0 – 5.0 |
| Cu | 1.0 – 2.0 |
| N | ≤ 0.10 |
| Fe | balance |
Mechanical properties
Solution annealed (ASTM B625 / A479)
| Property | Value |
|---|---|
| Yield strength (0.2%) | ≥ 215 MPa |
| Tensile strength | ≥ 490 MPa |
| Elongation | ≥ 35% |
| Hardness | 70 – 90 HRB (typical) |
Typical physical properties
| Property | Value |
|---|---|
| Density | 7.95 – 8.0 g/cm³ |
| Melting range | ≈ 1,300 – 1,390 °C (typical) |
| Modulus of elasticity | 195 GPa |
| Thermal conductivity (20 °C) | ≈ 11.5 – 12 W/m·K |
| Thermal expansion (20–100 °C) | ≈ 15.3 µm/m·K |
Heat treatment, welding and machining
| Item | Usual practice |
|---|---|
| Service temperature | Cryogenic up to ≈ 371 °C in pressure vessels (ASME); above that there is a risk of embrittlement (intermetallic phases). |
| Heat treatment | Solution annealing 1,060 – 1,150 °C with rapid water quench. |
| Welding | Good, with low heat input and interpass ≤ 100 °C (fully austenitic, sensitive to hot cracking). Consumable AWS ER385 / E385; ERNiCrMo-3 for maximum pitting resistance. |
| Machining | Machinability lower than carbon steel: it work hardens quickly; use sharp tools, positive rake, constant feed without 'rubbing' and abundant coolant. Harder than 316L because of the higher Ni content. |
Filler metal for welding
The wire composition is usually not identical to the material: each page explains why.
Typical applications
- Dilute sulfuric acid production and handling
- Phosphoric acid and fertilizers
- Gas scrubbers (FGD)
- Pickling
- Exchangers with brackish water/cooled seawater
- Pulp and paper
- Agrochemicals
- Petroleum and fuel refining
Alternatives: 317L in less severe media; 254 SMO (6Mo) or Alloy 20 in hotter chlorides/sulfuric acid; Alloy 28 (UNS N08028) or Ni alloys (625, C-276) above that.
904L stainless steel: complete guide
What 904L stainless steel is
904L belongs to the family of special stainless steels, in the super-austenitic group. Compared with 317L, it has much more nickel, more molybdenum and a copper addition, and it sits one step below 6Mo alloys such as 254 SMO.
Chemical composition and role of the elements
Nickel (23 – 28%) stabilizes the austenite and gives stress corrosion resistance; molybdenum (4 – 5%) raises the PREN to 32 – 39; copper (1 – 2%) improves resistance to reducing acids, especially sulfuric. Carbon up to 0.020% prevents sensitization after welding.
Corrosion and limits of use
It resists dilute and intermediate sulfuric acid, phosphoric and acetic acid and chloride media up to high concentrations, including those of gas desulfurization. Resistance to hydrochloric acid, however, is limited to very dilute, cold solutions; for HCl the choice is a nickel-molybdenum alloy such as Hastelloy B-2 or C-276. At temperature, the design limit in pressure vessels (ASME) is about 371 °C.
Applications
Sulfuric and phosphoric acid equipment, fertilizer plants, FGD absorbers, pulp bleaching, heat exchangers with moderately aggressive seawater, offshore components, pumps, valves and shafts for the chemical and pharmaceutical industry.
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 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 904L stainless steel?
Per ASTM A479 / B625 (N08904): C ≤ 0.020; Mn ≤ 2.00; P ≤ 0.045; S ≤ 0.035; Si ≤ 1.00; Cr 19.0 – 23.0.
Which standards cover 904L stainless steel?
Bar: ASTM A479 / B649. Forging/flange: ASTM A182 F904L / B366 (fittings). Plate: ASTM B625 / A240. Tube: ASTM B677 / B673 / B674.
Up to what temperature can 904L stainless steel be used?
Cryogenic up to ≈ 371 °C in pressure vessels (ASME); above that there is a risk of embrittlement (intermetallic phases).
Which materials can replace 904L stainless steel?
317L in less severe media; 254 SMO (6Mo) or Alloy 20 in hotter chlorides/sulfuric acid; Alloy 28 (UNS N08028) or Ni alloys (625, C-276) above that.
Is 904L better than 316L?
In corrosion, yes: it has more nickel, molybdenum and copper, and resists dilute sulfuric acid and chloride pitting much better (PREN about 35, versus 25 for 316L). It costs considerably more, so it only pays off where 316L cannot cope.
Is 904L magnetic?
No. It is fully austenitic and non-magnetic in the solution-annealed condition.
Can 904L be welded?
Yes, by TIG, MIG and covered electrode, with ER385 consumable and heat input control, without preheating or post-weld treatment.
Why does 904L cost more than 316L?
Because of its composition: 23 – 28% nickel, 4 – 5% molybdenum and 1 – 2% copper, versus 10 – 14% Ni and 2 – 3% Mo in 316L. The price follows the quotation of those metals, the form (bar, plate, forging) and the quantity. For a figure, request a quote with size and quantity.
