General Properties

Alloy 904L (UNS N08904) is a super austenitic stainless steel that is specifically designed to provide moderate to high corrosion resistance in a wide range of process environments. It offers excellent corrosion resistance due to its high chromium and nickel content, as well as the addition of molybdenum and copper.The high chromium and nickel content of Alloy 904L, combined with 4.5% molybdenum, contribute to its superior corrosion resistance. It offers good to excellent resistance against chloride-induced stress corrosion cracking, pitting corrosion, and general corrosion. In comparison to stainless steels like 316L and 317L, which are also molybdenum-enhanced, Alloy 904L provides superior corrosion resistance.Originally developed to withstand environments containing dilute sulfuric acid, Alloy 904L exhibits good resistance to a range of inorganic acids, including hot phosphoric acid. It also offers good resistance to most organic acids. This makes it suitable for applications in industries such as chemical processing, pharmaceuticals, and pollution control, where exposure to corrosive acids is common.The combination of its highly alloyed chemistry, including 25% nickel and 4.5% molybdenum, makes Alloy 904L a robust stainless steel grade with excellent corrosion resistance properties, particularly in aggressive environments.

Alloy 904L is easily welded and processed by standard shop fabrication practices.

Corrosion Resistance

The high content of alloying elements in Alloy 904L provides exceptional resistance to uniform corrosion. It was originally developed to withstand environments containing dilute sulfuric acid and offers full resistance in such environments within the entire concentration range of 0 to 100% at temperatures up to 95°F (35°C). Additionally, Alloy 904L demonstrates good resistance to other inorganic acids, including phosphoric acid, as well as most organic acids.However, it is important to note that acids and acid solutions containing halide ions can be highly aggressive, and the corrosion resistance of Alloy 904L, as well as other stainless steels like 317L and 317LMN, may be insufficient in such environments.When it comes to fractional distillation of tall oil or hot concentrated caustic solutions, where corrosion resistance is crucial, the nickel content of the material becomes significant. With a nickel content of 25%, Alloy 904L has proven to be a suitable alternative to many conventional stainless steels in these applications.Moreover, conventional stainless steels like 304L and 316L are susceptible to chloride stress corrosion cracking (SSC) under certain conditions. The resistance to SSC increases with higher nickel and molybdenum contents. As a result, high-performance austenitic stainless steels such as Alloy 904L exhibit excellent resistance to SSC. In chloride solutions under evaporative conditions, these high-performance austenitic steels and duplex stainless steels outperform 316L, as shown in the table you mentioned.

*Composition: 20% HNO3 + 4 HF.

Uniform Corrosion in wet process phosphoric acid at 60°C

Composition: 54% P2O5, 0.06% HCI, 1.1% HF, 4,0% H2SO4, 0.27% Fe2O3, 0.17% AI2O3, 0.10% SiO2, 0.20% CaO and 0.70% MgO.
Corrosion rates in fatty acid column for the distillation of tall oil at 253°C

Chemical Analysis

Weight % (all values are maximum unless a range is otherwise indicated)

Mechanical Properties