904L Stainless Steel
A Ni-Cr-Mo-Cu super-austenitic stainless steel
Typical values for the temper in the title
904L contains 23–28% nickel, about 20% chromium, 4–5% molybdenum and added copper. The combination of high nickel and copper gives it special resistance in reducing acids, especially sulfuric acid, where 316L fails. Its PREN is about 35.
It is used in the chemical industry, in sulfuric and phosphoric acid equipment and in heat exchangers. It is also known outside industry, as a material for luxury watch cases.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 490–690 MPa | |
| Yield strength Rp0.2 | 220–350 MPa | |
| Elongation A | 35% | |
| Hardness | 140–200 HB | |
| Modulus of elasticity E | 200 GPa | |
| Density ρ | 7.95 g/cm³ | |
| Machinability | 35% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Ni nickel | 23.0–28.0 | austenitic structure and acid resistance |
| Cr chromium | 19.0–23.0 | the protective layer |
| Mo molybdenum | 4.0–5.0 | pitting resistance |
| Cu copper | 1.0–2.0 | sulfuric acid resistance |
| C carbon | max 0.020 | |
| Mn manganese | max 2.00 | |
| Si silicon | max 1.00 | |
| N nitrogen | max 0.10 | |
| Fe iron | balance |
Ranges per ASTM A240 (UNS N08904).
Conditions and heat treatment
Like all austenitic stainless, it is not hardened by heat treatment. The normal delivery condition is annealed.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed | the normal condition: soft, ductile, most corrosion resistant | most applications |
| Cold worked (¼H to full hard) | much higher strength, slightly magnetic | strong springs, sheet and strip |
| Not hardenable by heat treatment | — | austenitic stainless strengthens only by cold work |
Applications
- Sulfuric acid equipment
- Phosphoric acid equipment
- Chemical heat exchangers
- Pharmaceutical equipment
- Watch cases
Fabrication
Welding
Weldable, usually with a matching filler (ER385) or an overalloyed nickel filler. The fully austenitic structure is prone to hot cracking, so heat input is kept low.
Machining
Difficult: strong and work hardening. Sharp tools, low speeds and a steady feed.
Cost
More expensive than 316L because of the nickel.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 316 / 316L | 485–620 / 170–310 MPa | Excellent — ER316L | cheaper, for milder conditions · material page |
| 254 SMO | 650 / 295 MPa | Good — ERNiCrMo-3 | 6Mo: better in seawater and chlorides · material page |
| 2205 Duplex | 620–880 / 450–620 MPa | Good — ER2209 | stronger and cheaper, with similar chloride resistance · material page |
Common mistakes
Choosing 904L for seawater
It is good in acids. In seawater, 254 SMO or super duplex are better.
Welding with high heat input
The structure is prone to hot cracking. Keep heat input low.
Choosing 904L where 316L is enough
The price difference is large. Choose by corrosion data for the environment.
Equivalents, standards and supply
| EN | 1.4539 |
|---|---|
| DIN | X1NiCrMoCu25-20-5 |
| JIS | SUS890L |
| Standards | ASTM A240 / EN 10088-2 |
| Forms | plate · pipe |
| Producers | Outokumpu · Aperam · Valbruna |
Learn more
Values are typical and for comparison only. For design, rely on the standard and on the mill certificate. Sources: ASTM A240, ASTM A276 and EN 10088 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026