Excellent Corrosion Resistance of 904L Stainless Steel
904L is a high-alloy austenitic stainless steel designed for exceptional resistance to strong reducing acids, especially sulfuric acid. It also resists corrosion from chloride-induced environments, making it highly suitable for aggressive chemical and marine applications. With a low carbon content and high alloying elements like molybdenum and copper, 904L maintains excellent toughness and formability.
This article introduces the composition, properties, and industrial applications of 904L to support better material selection in engineering.
What is 904L Stainless Steel?
904L (UNS N08904) is a superaustenitic stainless steel originally developed for corrosion resistance in dilute sulfuric acid. It is non-stabilized and has low carbon content, offering improved weldability and resistance to intergranular corrosion.
With high nickel and molybdenum content, 904L outperforms 316L in many aggressive environments and offers excellent performance in both oxidizing and reducing acids.
904L Equivalent Grades
| Standard / System | Equivalent Designation |
| UNS | N08904 |
| ASTM / ASME | ASTM A240, A312, A479, B625 |
| EN / DIN | 1.4539 (X1NiCrMoCu25-20-5) |
| ISO | X1NiCrMoCu25-20-5 |
| JIS | SUS 890L |
904L Chemical Composition
| Element | Content (%) |
| Chromium (Cr) | 19.0 – 23.0 |
| Nickel (Ni) | 23.0 – 28.0 |
| Molybdenum (Mo) | 4.0 – 5.0 |
| Copper (Cu) | 1.0 – 2.0 |
| Carbon (C) | ≤ 0.020 |
| Manganese (Mn) | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 |
| Phosphorus (P) | ≤ 0.045 |
| Sulfur (S) | ≤ 0.035 |
904L Mechanical Properties
| Property | Typical Value |
| Tensile Strength | 490 – 710 MPa |
| Yield Strength | ≥ 220 MPa |
| Elongation | ≥ 35% |
| Hardness (HBW) | ≤ 220 |
904L Physical Properties
| Property | Value |
| Density | 8.0 g/cm³ |
| Melting Point | 1300 – 1390 °C |
| Thermal Conductivity | 12 – 15 W/m·K (at 20 °C) |
| Electrical Resistivity | ~0.95 µΩ·m |
| Modulus of Elasticity | ~195 GPa |
| Service Temperature Range | -50 °C to ~400 °C |
Applications of 904L Stainless Steel
- Sulfuric Acid Plants: Highly suitable due to superior resistance to dilute sulfuric acid.
- Chemical Processing Equipment: Used in reactors, tanks, and pipelines exposed to acids and chlorides.
- Pharmaceutical and Food Industry: Low metal ion leaching makes it safe for hygienic applications.
- Heat Exchangers: Withstands aggressive, high-temperature corrosive media.
- Seawater Systems: Good resistance to chlorides and saltwater conditions.
- Pulp & Paper Industry: Resists corrosive bleaching agents.
Advantages of 904L
- Excellent resistance: Particularly to sulfuric acid, phosphoric acid, and chloride pitting.
- Low carbon content: Minimizes intergranular corrosion risk after welding.
- Better than 316L and 317L: Stronger resistance to stress corrosion cracking.
- Non-magnetic: In the annealed condition, suitable for sensitive instrumentation.
- Good weldability and formability: Performs well with standard fabrication practices.
Limitations of 904L
- Higher cost: Due to high nickel and molybdenum content.
- Moderate strength: Lower yield strength compared to duplex or super duplex steels.
- Challenging machining: Work hardens quickly and needs appropriate tooling.
- Not ideal for high-chloride immersion: Still vulnerable to crevice corrosion under stagnant conditions.
904L vs Other Stainless Steels
| Feature | 316L | 904L | 254 SMO |
| PREN (Pitting Index) | ~25 | ~34–36 | ~43–45 |
| Molybdenum Content | ~2.0% | ~4.5% | ~6.5% |
| Chloride Resistance | Moderate | High | Very High |
| Strength | Medium | Medium | High |
| Cost | Low | High | Very High |
Summary
This article introduces 904L stainless steel, highlighting its chemical composition, corrosion resistance, mechanical strength, and key applications. As a super austenitic stainless steel, 904L offers excellent performance in harsh chemical and chloride-rich environments.
MT.BOLTS supplies 904L fasteners and components for industrial, marine, and chemical systems. Contact our team or visit our website for more details or to request a customized quote.
