UNS N08904 (904L) Super Austenitic Stainless Steel
ASTM A240/B625 · Updated: 2026-05-25
UNS N08904 (904L) is a high-alloy austenitic stainless steel with elevated nickel (23-28%), chromium (19-23%), molybdenum (4-5%), and copper (1-2%)—designed to resist reducing acids like sulfuric, phosphoric, and acetic acid. Its PREN of 36-38 surpasses 316L and approaches duplex 2205 territory, but unlike duplex, 904L maintains excellent toughness and formability at all temperatures. Standard material for chemical processing equipment, pulp and paper digesters, seawater heat exchangers, and pollution control scrubbers. The high nickel content makes it one of the most expensive stainless grades.
Quick Facts
| Category | Stainless Steel |
| Standard | ASTM A240/B625 |
| Density | 8.00 g/cm³ |
| Yield Strength | 220 MPa (32 ksi) |
| Tensile Strength | 490 MPa (71 ksi) |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN 1.4539 | Compare |
| X1NiCrMoCu25-20-5 | Compare |
| SUS890L | Compare |
| 00Cr20Ni25Mo4.5Cu | Compare |
| 904L | Compare |
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Frequently Asked Questions
When should 904L be chosen over 316L?
Choose 904L when the environment contains: (1) sulfuric acid above 10% concentration, (2) phosphoric acid at elevated temperatures, (3) severe pitting conditions where 316L has failed, or (4) simultaneous chloride and acid exposure. 904L costs 3-5× more than 316L, so it is only justified when 316L or 2205 have proven inadequate. For most seawater applications, 2205 duplex is a more economical choice.