904L stainless steel is a superaustenitic stainless steel grade, alloy 904L (UNS N08904) and contains high levels of chromium and nickel with additions of molybdenum and copper to provide superior corrosion resistance. The combination of high chromium and nickel content, coupled with additions of molybdenum and copper, assures good to excellent corrosion resistance, and moderate to high corrosion resistance in a wide range of process 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.
With high-level alloys of 25% nickel and 4.5% molybdenum, 904L stainless steel provides good chloride stress corrosion cracking resistance, pitting and general corrosion resistance superior to 316L and 317L molybdenum enhanced stainless steels, The copper addition provides resistance to hot phosphoric acid and dilute sulfuric acid. 904L stainless steel is non-magnetic and offers excellent formability, toughness, and weldability.
904L Stainless Steel Composition
The chemical composition of stainless steel 904L contains roughly 19 to 23% chromium, 23 to 28% nickel, 4 to 5% molybdenum, and 1.0-2.0% Cu, which gives the alloy greater corrosion resistance than 316L.
| Grade | Ni | Cr | Mo | Cu | C | Mn | Si | P | S | Fe |
|---|---|---|---|---|---|---|---|---|---|---|
| 904L | 23 – 28 | 19 – 23 | 4.0 -5.0 | 1.0 – 2.0 | 0.02 | 2.00 | 1.00 | 0.045 | 0.035 | Balance |
904L Stainless Steel Mechanical Properties
| Mechanical Properties | Data |
|---|---|
| Yield Strength, min. (Mpa) | 215 |
| Tensile Strength, min. (Mpa) | 490 |
| Elongation, min. | 35% |
| Hardness, max. (HRB) | 90 |
904L Stainless Steel Physical Properties
| Grade | Density (Kg/M 3 ) | Elastic Modulus (GPa) | Mean Co-Eff Of Thermal Expansion (Μm/M/°C) 0-100°C | Thermal Conductivity (W/M.K) At 20°C | Specific Heat 0-100°C (J/Kg.K) | Elec Resistivity (NΩ.M) |
|---|---|---|---|---|---|---|
| 904L | 7900 | 190 | 15 | 11.5 | 500 | 952 |
904L Stainless Steel Equivalents
| AISI | UNS | DIN | EN |
|---|---|---|---|
| 904L | N08904 | 1.4539 | X1NiCrMoCu25-20-5 |
904L, 1.4539 Comparison
| Standard | Grade | C | Mn | Cr | Ni | Mo | N | Other |
|---|---|---|---|---|---|---|---|---|
| ASME II A SA-240 | UNS N08904 | ≤0.020 | ≤2.00 | 19.00-23.00 | 23.0-28.0 | 4.00-5.00 | ≤0.10 | Cu:1.0-2.0 |
| ASTM A240 | 904L | ≤0.020 | ≤2.00 | 19.0-23.0 | 23.0-28.0 | 4.0-5.0 | ≤0.10 | Cu:1.0-2.0 |
| EN 10028-7 | 1.4539 | ≤0.020 | ≤2.00 | 19.0-21.0 | 24.0-26.0 | 4.0-5.0 | ≤0.15 | Cu:1.20-2.00 |
| EN 10088-2 | 1.4539 | ≤0.020 | ≤2.00 | 19.0-21.0 | 24.0-26.0 | 4.0-5.0 | ≤0.15 | Cu:1.20-2.00 |
| EN 10088-3 | 1.4539 | ≤0.020 | ≤2.00 | 19.0-21.0 | 24.0-26.0 | 4.0-5.0 | ≤0.15 | Cu:1.20-2.00 |
| EN 10088-4 | 1.4539 | ≤0.020 | ≤2.00 | 19.0-21.0 | 24.0-26.0 | 4.0-5.0 | ≤0.15 | Cu:1.20-2.00 |
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), provide 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.
Grade 904L stainless steel has excellent resistance to warm seawater and chloride attack. The high resistance of grade 904L against stress corrosion cracking is due to the presence of high amounts of nickel in its composition. Moreover, the addition of copper to these grades develops resistance to sulphuric acid and other reducing agents in both aggressive and mild conditions.
The corrosion resistance of grade 904L is intermediate between super austenitic grades, with 6% molybdenum content, and standard 316L austenitic grades. Grade 904L is less resistant to nitric acid than grades 304L and 310L, which are free of molybdenum. This steel grade needs to be solution-treated following cold working, to achieve maximum stress corrosion cracking resistance under critical environments.
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. The entire workpiece must 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).
Heat Resistance
Grade 904L stainless steels offer good oxidation resistance. However, the structural stability of this grade collapses at high temperatures, particularly above 400°C.
Fabrication
Grade 904L stainless steels are high-purity steels with low sulfur content. They can be machined using any standard methods. These grades can be readily bent to a small radius under cold conditions. Although subsequent annealing is not required in most cases, it should be carried out when the fabrication is performed under severe stress corrosion cracking conditions.
Heat Treatment
Grade 904L stainless steels can be solution heat-treated at 1090 to 1175°C, followed by rapid cooling. Thermal treatment is suitable for hardening these grades.
Welding
Alloy 904L can be readily welded by most standard processes. 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.
Welding of grade 904L stainless steels can be performed using all conventional methods. This grade does not require pre-heat and post-weld heat treatments. Grade 904L can be subjected to hot cracking in constrained weldment.
904L Stainless Steel Specifications
- B625/SB625, Standard Specification for UNS N08925, UNS N08031, UNS N08034, UNS N08932, UNS N08926, UNS N08354, UNS N08830, and UNS R20033 Plate, Sheet, and Strip
- B673/SB673, Standard Specification for UNS N08904, UNS N08925, and UNS N08926 Welded Pipe
- B674/SB674, Standard Specification for Nickel-Iron-Chromium-Molybdenum and Iron-Nickel-Chromium-Molybdenum-Copper Welded Tube
- B677/SB677, Standard Specification for Nickel-Iron-Chromium-Molybdenum and Iron-Nickel-Chromium-Molybdenum-Copper Seamless Pipe and Tube
- B649/SB649, Standard Specification for Ni-Fe-Cr-Mo-Cu-N Low-Carbon Alloys (UNS N08925, UNS N08031, UNS N08034, UNS N08354, and UNS N08926), and Cr-Ni-Fe-N Low-Carbon Alloy (UNS R20033) Bar and Wire, and Ni-Cr-Fe-Mo-N Alloy (UNS N08936) Wire
Forms
Disadvantages of 904L Stainless Steel
- Oxidation at high temperature: 904L stainless steel is easy to oxidize at high temperatures, especially at more than 600°C, the surface is easy to form an oxide film, which will affect its corrosion resistance.
- Processing difficulty: Because 904L stainless steel contains high chromium, nickel, copper, and other elements, its processing difficulty is greater than ordinary stainless steel. Higher technical and operational skills are required in welding, bending, cutting and other processing.
- High cost: The price of 904L stainless steel is much higher than that of ordinary stainless steel, which makes its application range limited. In addition, due to its processing difficulty, the processing cost is also relatively high.
- Magnetism: Compared with ordinary stainless steel, 904L stainless steel has weak magnetism. This may affect the performance of certain applications, such as parts or equipment used in magnetic fields.
- Brittleness: 904L stainless steel may exhibit brittle behavior under certain conditions, particularly at low temperatures. This may reduce its toughness and make it more susceptible to rupture.
Applications Of 904L Stainless Steel
- Process equipment in the chemical industry
- Petrochemical industry
- Bleaching equipment in the pulp and paper industry
- Flue gas cleaning
- Desalination
- Seawater handling
- Hydrometallurgy
- Food and beverage
- Pharmaceuticals
- Heat exchangers
904L Stainless Steel vs 316L
The main differences between 904L stainless steel and 316L stainless steel are composition, corrosion resistance, physical properties and application areas.
Firstly, in terms of composition, 904L stainless steel contains more chromium, nickel and molybdenum, and a small amount of copper is also added, which makes its alloy content about 1.7 times higher than that of 316L stainless steel. In addition, 316L stainless steel does not contain copper, while 904L stainless steel contains copper, so the 904L is more expensive than 316L.
In terms of corrosion resistance, 904L stainless steel is superior to 316L stainless steel due to its high content of chromium, nickel and molybdenum, especially the addition of copper. Especially in chloride environments, 904L stainless steel shows better corrosion resistance.316L stainless steel, although it also has a certain degree of corrosion resistance, 904L stainless steel performs better under strong acids, alkalis and chloride media.
Physically, 904L stainless steel has higher tensile and yield strengths, which makes it superior to 316L stainless steel in terms of wear, pressure and impact resistance. 904L stainless steel’s austenitic lattice structure gives it excellent plasticity and toughness, making it perform well in a variety of engineering applications.
Finally, in terms of applications, 904L stainless steel is widely used in chemical, petrochemical, pharmaceutical, and food processing industries due to its excellent corrosion resistance and mechanical properties. Common applications include equipment such as reactors, tanks, pipelines, heat exchangers, and so on. While 316L stainless steel is widely used in medical devices, food processing equipment, ships and construction, etc.