SS 904L Material Specification: Composition and Data
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What Is 904L Stainless Steel?
904L, designated UNS N08904, is a low-carbon, high-alloy austenitic stainless steel widely used in applications where the corrosion properties of AISI 316L and AISI 317L are inadequate. Its nickel content of 23.0 to 28.0 percent places it in the high-nickel austenitic family, and the combination of chromium, molybdenum and copper gives it outstanding resistance to reducing acids, chloride pitting and stress corrosion cracking. The material can be processed into plates, coils, pipes, bars and wires, and is a standard choice for sulfuric and phosphoric acid service, seawater systems and pulp bleaching plants.
International Grade Equivalents
The table below shows the equivalent designations of grade 904L in the principal national and international systems.
| Grade | UNS No | Old British | Euronorm | Swedish SS | Japanese JIS |
|---|---|---|---|---|---|
| 904L | N08904 | 904S13 | 1.4539 | 2562 | SUS 890L |
The Euronorm material name for 1.4539 is X1NiCrMoCuN25-20-5, which describes the nominal composition: nickel 25, chromium 20, molybdenum 5 and copper. All these designations refer to the same alloy, so a 904L order placed under any of them should be traceable to the same UNS number on the mill certificate.
Chemical Composition
The composition ranges of grade 904L are listed below.
| Element | Composition, % |
|---|---|
| Carbon, max | 0.02 |
| Manganese, max | 2.00 |
| Silicon, max | 1.00 |
| Phosphorus, max | 0.045 |
| Sulfur, max | 0.035 |
| Chromium | 19.0 - 23.0 |
| Molybdenum | 4.0 - 5.0 |
| Nickel | 23.0 - 28.0 |
| Copper | 1.0 - 2.0 |
The extremely low carbon limit of 0.02 percent maximum keeps the material resistant to intergranular corrosion in the as-welded condition, and the copper addition is the key to its resistance to sulfuric acid and other reducing acids.
Mechanical and Physical Properties
Minimum mechanical properties in the solution-annealed condition are a tensile strength of 490 MPa, a 0.2 percent proof strength of 220 MPa and an elongation of 35 percent in 50 mm, with a typical hardness of 70 to 90 HRB. Typical physical properties are: density 8000 kg/m3, elastic modulus 190 GPa at 20 C, mean coefficient of thermal expansion 15.0 x 10-6 per C between 0 and 100 C, thermal conductivity about 11.5 W/(m.K) at 20 C, specific heat 500 J/(kg.K) between 0 and 100 C and electrical resistivity about 950 nano-ohm-metres. These values are used for design calculations and should be checked against the relevant edition of the standard for the exact product form.
904L vs 304L and 316L
304L is a general-purpose austenitic grade with lower alloy content, suitable for mild corrosive environments and general service. 316L adds molybdenum for chloride resistance and is the economical choice for marine and many chemical duties. 904L is a premium high-alloy grade with significantly higher nickel, chromium and molybdenum plus added copper, which gives superior resistance in hot sulfuric and phosphoric acids, seawater and chloride-contaminated process streams. For most common applications 316L is sufficient; 904L is justified only where 316L has been shown to fail, for example in acid plants, bleach plants and aggressive cooling water systems. The selection should be based on corrosion testing and life-cycle cost, not on alloy content alone.
Fabrication and Selection Points
904L can be formed, welded and machined by standard processes. Welding should use matching austenitic filler metal with a nickel content at least as high as the base metal, and the recommended solution annealing temperature is about 1090 to 1150 C followed by rapid cooling or water quenching, which restores full corrosion resistance after cold work. The material is available as plate, coil, sheet, pipe, tube, bar, wire and fittings, and should be ordered with a mill certificate recording the heat number, chemical analysis and mechanical test results.
Frequently Asked Questions
Q: What is the equivalent material of 904L?
904L is equivalent to UNS N08904, EN 1.4539, X1NiCrMoCuN25-20-5, the old British designation 904S13 and Swedish SS 2562. All designate the same alloy.
Q: Why does 904L contain copper?
Copper in the range of 1.0 to 2.0 percent markedly improves resistance to reducing acids, particularly sulfuric acid, which is the main reason 904L is selected for acid handling plants.
Q: Is 904L better than 316L?
In aggressive media such as hot sulfuric acid, phosphoric acid and chloride-rich process streams, 904L is clearly superior and lasts longer. In general and marine service, 316L gives good performance at much lower cost, so the choice depends on the environment and design life.
Q: What is 904L used for?
Typical uses include sulfuric and phosphoric acid plants, seawater heat exchangers and desalination, pulp and paper bleaching equipment, pharmaceutical reactors and chemical tankers.
Q: Can 904L be welded?
Yes, with matching high-nickel austenitic filler metal. The very low carbon content avoids sensitisation, and solution annealing after severe forming restores maximum corrosion resistance.
Q: What heat treatment is required for 904L?
The standard treatment is solution annealing at about 1090 to 1150 C followed by rapid cooling or water quenching, which keeps all alloying elements in solution and gives the best corrosion resistance.
