904L Stainless Steel Equivalent Standards: UNS N08904, EN 1.4539 and More
May 21, 2025
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What 904L Stainless Steel Is
904L is a super-austenitic stainless steel alloyed with roughly 25% nickel, 20% chromium, 4.5% molybdenum and 1.5% copper. The combination of high nickel and molybdenum gives it corrosion resistance well beyond conventional 316L, particularly in sulfuric, phosphoric and acetic acid service, and in chloride environments where pitting, crevice attack and stress corrosion cracking would otherwise limit material life.
Copper is the element that separates 904L from the simpler molybdenum grades: it is added specifically to improve performance in reducing acids. The alloy is fully austenitic and therefore non-magnetic in every condition, and it retains good toughness and weldability, which is why it appears in chemical storage, seawater handling and pharmaceutical equipment as well as in high-end watch cases.
Equivalent Standards and Grades
904L is standardized under several national systems. The table below lists the widely used equivalents and the ASTM product standards that apply to each form.
| Standard system | Grade / material designation |
|---|---|
| UNS (ASTM) | N08904 |
| EN / DIN | 1.4539, X1NiCrMoCu25-20-5 |
| ISO | X1NiCrMoCu25-20-5 |
| JIS (Japan) | SUS 890L |
| AFNOR (France) | Z2NCDU25-20 |
| BS (UK) | 904S13 |
| Product form | ASTM standard |
|---|---|
| Plate, sheet and strip | ASTM B625 |
| Rod and bar | ASTM B649 |
| Welded pipe and tube | ASTM B673, ASTM B674 |
| Seamless pipe and tube | ASTM B677, ASTM B829 |
The grade is also covered as UNS N08904 in ASTM A240 for flat products used as pressure-vessel material, which is the specification most often quoted when 904L plate is ordered for a chemical vessel.
Why 904L Outperforms 316L and 317L
The improvement comes directly from alloy content, not from any special processing route. The table compares typical composition ranges.
| Element | 904L, UNS N08904 | 316L, UNS S31603 |
|---|---|---|
| Nickel (Ni) | 23.0–28.0 | 10.0–14.0 |
| Chromium (Cr) | 19.0–23.0 | 16.0–18.0 |
| Molybdenum (Mo) | 4.0–5.0 | 2.0–3.0 |
| Copper (Cu) | 1.0–2.0 | Not specified |
| Carbon (C) | 0.020 max | 0.030 max |
Alloying at this level is what produces the practical advantages that buyers are paying for:
Resistance to sulfuric, phosphoric and acetic acids across a wider concentration and temperature range than 316L.
High resistance to pitting and crevice corrosion in chloride-bearing media.
Improved resistance to stress corrosion cracking in chloride and caustic environments.
Non-magnetic in all conditions, with good toughness retained at low temperature.
Good weldability by conventional arc processes using matching high-alloy filler metal.
904L Compared with 2507 Super Duplex
The two grades are often compared for seawater and process duty, but they solve different problems. 904L is chosen for acid resistance and weldability; 2507 is chosen for strength and chloride performance.
| Property | 904L | 2507 super duplex |
|---|---|---|
| Microstructure | Fully austenitic | Austenitic plus ferritic, duplex |
| Corrosion resistance | Excellent in acids and general chloride service | Superior in chlorides and seawater |
| Strength | Moderate | Very high, roughly twice the yield strength |
| Weldability | Good, with matching filler metal | Moderate, requires controlled heat input |
| Magnetic behaviour | Non-magnetic | Slightly magnetic |
| Typical duties | Chemical, pharmaceutical, acid storage | Oil and gas, desalination, offshore |
Availability, Market Prices and Selection Notes
904L costs substantially more than 304 or 316 for three reasons: the high alloy content, especially nickel and molybdenum; the limited number of mills that produce it; and the lower production volume, which spreads processing cost over fewer tonnes.
| Product form | Indicative range, 2024–2025 |
|---|---|
| 904L plate and sheet | USD 10–20 per kg |
| 904L seamless pipe | USD 15–30 per kg |
| 904L round bar | USD 12–25 per kg |
| 904L welded tube | USD 14–28 per kg |
These ranges are indicative market levels for reference only; actual prices move with nickel and molybdenum surcharges, quantity, size range, delivery condition and testing requirements, so a specific quotation should always be obtained for project budgeting. When evaluating whether 904L is justified, compare it against the cost of downtime and replacement in 316L rather than against the purchase price alone. Where the service is mainly chloride-related, a duplex or super duplex grade often gives better value; where reducing acids dominate, 904L or a higher nickel alloy is usually the correct choice.
Frequently Asked Questions
Q: What is the UNS number for 904L stainless steel?
904L is UNS N08904. Its European equivalent is EN 1.4539, written as X1NiCrMoCu25-20-5.
Q: Is 904L better than 316L?
Yes for acid service and chloride-bearing environments, because of its higher nickel, chromium and molybdenum content together with copper. The trade-off is a much higher price and more limited availability.
Q: Is 904L magnetic?
No. The alloy is fully austenitic and remains non-magnetic in the annealed, cold-worked and welded condition.
Q: What filler metal is used for welding 904L?
A matching high-alloy austenitic filler such as ER385 (UNS N08904) is typical, with low heat input and controlled interpass temperature to preserve corrosion resistance.
Q: Which standards cover 904L pipe and plate?
ASTM B625 covers plate, B649 rod and bar, and B673 with B674 for welded tube or pipe. Seamless tubular product is specified under ASTM B677 or ASTM B829.
Q: Why is 904L so expensive?
Because it contains around 25% nickel, 4.5% molybdenum and copper, is produced by relatively few mills, and has lower production volumes than mainstream austenitic grades.
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