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Sandmeyer Steel Company stocks Alloy 904L stainless steel plate in thicknesses from 3/16" through 2". Alloy 904L (UNS N08904) is a superaustenitic stainless steel designed for corrosion and pitting resistance in a wide range of process environments. It is used extensively in the chemical process industry including the production of phosphate-based fertilizers.

Available thicknesses for Alloy 904L:

3/16" 1/4" 3/8" 1/2" 5/8" 3/4"
4.8mm 6.3mm 9.5mm 12.7mm 15.9mm 19mm
1" 1 1/4" 1 1/2" 1 3/4" 2"
25.4mm 31.8mm 38.1mm 44.5mm 50.8mm

General Properties

Alloy 904L (UNS N08904) is a superaustenitic stainless steel that is designed for moderate to high corrosion resistance in a wide range of process environments. The combination of high chromium and nickel content, coupled with additions of molybdenum and copper, assure good to excellent corrosion resistance.

With its highly alloyed chemistry — 25% nickel and 4.5% molybdenum, 904L provides good chloride stress corrosion cracking resistance, pitting and general corrosion resistance superior to 316L and 317L molybdenum enhanced stainless steels.

Alloy 904L was originally developed to withstand environments containing dilute sulfuric acid. It also offers good resistance to other inorganic acids such as hot phosphoric acid as well as most organic acids.

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


  • Air Pollution Control — scrubbers for coal-fired power plants
  • Chemical Processing — process equipment for the production of sulfuric, phosphoric, inorganic and organic acids and the production of phosphate-based fertilizers
  • Metallurgical Processing — pickling equipment using sulfuric acid
  • Oil and Gas Production — offshore process equipment
  • Pharmaceutical Industry — process equipment
  • Pulp and Paper — processing equipment
  • Seawater and Brackish Water — condensers, heat exchangers and piping systems


ASTM........A 240, B 625
ASME........SA 240, SB 625

Corrosion Resistance

The high content of alloying elements in 904L gives the alloy exceptionally good resistance to uniform corrosion.

904L was originally developed to withstand environments containing dilute sulfuric acid, and is one of the few stainless steels that, at temperatures up to 95°F (35°C), provides full resistance in such environments within the entire concentration range of 0 to 100%. 904L also offers good resistance to a number of other inorganic acids, such as phosphoric acid and most organic acids. However, acids and acid solutions containing halide ions can be very aggressive, and the corrosion resistance of 317L, 317LMN and 904L may be insufficient.

Fractional distillation of tall oil often needs better material than 316L or even the more frequently used 317LMN. In these hot concentrated caustic solutions, the corrosion resistance is mainly determined by the nickel content of the material. With a nickel content of 25%, 904L has proven to be a good alternative to most conventional stainless steels.

Conventional stainless steels such as 304L and 316L are susceptible to chloride stress corrosion cracking (SSC) under certain conditions. Resistance to SSC increases with the increased content of nickel and molybdenum. Therefore, the higher performance austenitic stainless steels such as 904L have very good resistance to SSC. The table in the upper right corner shows resistance to SSC in a chloride solution under evaporative conditions. High performance austenitic steels and duplex stainless steels clearly outperform 316L.

Corrosion Resistance

Corrosion Resistance

Uniform Corrosion in pickling acid* at 25°C

ALLOY Corrosion Rate, mm/year
316L >6
904L 0.47
254 SMO® 0.27
654 SMO® 0.06

*Composition: 20% HNO3 + 4 HF.

Uniform Corrosion in wet process phosphoric acid at 60°C

ALLOY Corrosion Rate, mm/year
316L >5
904L 1.2
254 SMO® 0.05

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

ALLOY Corrosion Rate, mm/year
316L 0.88
317LMN 0.29
904L 0.056
254 SMO® 0.01

Chemical Analysis

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

Nickel 23.0 min.-28.0 max. Silicon 1.00
Chromium 19.0 min.-23.0 max. Phosphorus 0.045
Molybdenum 4.0 min.-5.0 max. Sulfur 0.035
Copper 1.0-2.0 max. Iron Balance
Manganese 2.00

Physical Properties


0.287 lbs/in3
7.95 g/cm3

Specific Heat

0.11 BTU/lb-°F (32 – 212°F)
450 J/kg-°K (0 – 100°C)

Modulus of Elasticity

28.0 x 106 psi
190 GPa


Thermal Conductivity 212°F (100°C)

6.8 BTU/Ft-hr°F
12.9 W/m-°K

Melting Range

2372 – 2534°F
1300 – 1390°C

Electrical Resistivity

33.5 Microhm-in at 68°C
95.2 Microhm-cm at 20°C

Mean Coefficient of Thermal Expansion

Temperature Range  
°F °C in/in °F cm/cm °C
68-212 20-100 8.5 x 10-6 15.3 x 10-6

Mechanical Properties

Typical Values at 68°F (20°C) (minimum values, unless specified)

Yield Strength
0.2% Offset
Ultimate Tensile
in 2 in.
psi (min.) (MPa) psi (min.) (MPa) % (min.) (max.)
31,000 220 71,000 490 36 70-90 Rockwell B

Fabrication Data


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

Cold Forming

904L is quite ductile and forms easily. The addition of molybdenum and nitrogen implies more powerful processing equipment may be necessary when compared with the standard 304/304L grades.

Hot Forming

Working temperatures of 1562 – 2102°F (850 –1150°C) are recommended for hot working processes. Normally hot working should be followed by a solution anneal and quench, but for 904L, if hot forming is discontinued at a temperature above 2012°F (1100°C) and the material is quenched directly thereafter, the material may be used without subsequent heat treatment. It is important that the entire workpiece be quenched from temperatures above 2012°F (1100°C). In the event of partial heating or cooling below 2012°F (1100°C), or if the cooling has been too slow, hot working should always be followed by a solution anneal and quenching. 904L should be solution annealed at 1940 – 2084°F (1060 –1140°C).


The cold work hardening rate of Alloy 904L makes it less machinable than 410 and 304 stainless steels.


Alloy 904L can be readily welded by most standard processes. Austenitic plate materials have a homogeneous austenitic structure with an even distribution of alloying elements. Solidification after welding causes the redistribution of certain elements such as molybdenum, chromium and nickel. These segregations remain in the cast structure of the weld and can impair the corrosion resistance in certain environments. Segregation is less evident in 904L, and this material is normally welded using a filler metal of the same composition as the base metal and can even be welded without filler metal.

The welding consumables for 904L are 20 25 CuL covered electrode and 20 25 CuL wire.

LDX 2101 and 254 SMO are registered trademarks of Outokumpu Stainless, Inc.

NOTE: The information and data in this product data sheet are accurate to the best of our knowledge and belief, but are intended for informational purposes only, and may be revised at any time without notice. Applications suggested for the materials are described only to help readers make their own evaluations and decisions, and are neither guarantees nor to be construed as express or implied warranties of suitability for these or other applications.