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Mar 21 2024904L (UNS N08904, W.Nr. 1.4539) is an austenitic stainless steel with a high alloy composition and low carbon content. It is specifically designed to offer moderate to high corrosion resistance in various process environments. The inclusion of copper in this grade significantly enhances its ability to withstand strong reducing acids, especially sulfuric acid. The high levels of nickel and molybdenum in the alloy provide excellent resistance to chloride-induced stress corrosion cracking, including issues like pitting, crevice corrosion, and stress corrosion cracking. Moreover, the austenitic structure of 904L stainless steel ensures exceptional toughness even at cryogenic temperatures. It can be easily welded and processed using standard fabrication techniques.
Chemical Processing: Reactors, tanks, heat exchangers, and piping systems
Oil and Gas: Offshore platforms, subsea equipment, and pipelines
Desalination Plants: Heat exchangers, evaporators, and brine heaters
Pharmaceutical Industry: Tanks, vessels, and process piping systems
Food Processing: Storage tanks, mixing vessels, and piping systems
Power Generation: Flue gas desulfurization (FGD) systems, cooling water systems, and boilers
Marine Applications: Seawater piping, heat exchangers, and offshore structures
|
Material |
Cr |
Mo |
S |
Ni |
Si |
C |
Mn |
N |
|
N08904 |
19.0-23.0 |
4.00-5.00 |
0.035max |
23.0-28.0 |
1.00max |
0.02max |
2.00max |
0.10max |
|
Material |
Tensile strength |
Yield strength 0,2 |
Elongation |
Hardness HB30 |
|
490N/mm² |
220N/mm² |
36% |
70-90HB |
Initially developed for its resistance to sulfuric acid, 904L stainless steel exhibits outstanding resistance to uniform corrosion due to its high content of alloying elements. It also demonstrates remarkable resistance to a wide range of environments, including warm seawater and high-chloride conditions. In most situations, the corrosion performance of 904L falls between that of standard austenitic grade 316L and highly alloyed grades such as those containing 6% molybdenum, often referred to as "super austenitic" grades. As a result, 904L has emerged as a viable alternative to conventional stainless steels. It is worth noting that 904L should undergo a solution treatment after cold work to maximize its resistance to stress corrosion cracking in critical environments.
Solution Treatment (Annealing): Heat to 1090-1175°C and cool rapidly. 904L cannot be hardened by thermal treatment.
The heat treatment of 904L stainless steel is a commonly employed method that involves subjecting the material to specific temperatures for a designated duration in controlled atmospheres, followed by air cooling or quenching. This process serves various purposes, including stress relief, solution annealing, and precipitation hardening.
To remove surface impurities and oxide layers from 904L, pickling is a widely used technique. It entails immersing the material in a pickling solution, typically an acid-based solution, to dissolve contaminants and restore the material's corrosion resistance. Careful control of the concentration and temperature of the pickling solution is essential during the pickling process to prevent excessive etching or corrosion of the stainless steel surface.
Hot Forming: The recommended temperature range for hot working of 904L stainless steel is between 1562 and 2102°F (850 to 1150°C). After hot forming, it is generally recommended to follow up with a solution annealing process and quenching. However, if the hot forming process is halted at a temperature above 2012°F (1100°C) and the material is immediately quenched, subsequent heat treatment may not be necessary. In cases where the material undergoes partial heating or cooling below 2012°F (1100°C), it is important to perform a solution annealing process and quenching after hot working. The recommended temperature range for solution annealing of 904L is 1940–2084°F (1060–1140°C).
Cold Forming: 904L stainless steel exhibits good ductility and can be easily formed. However, due to the presence of molybdenum and nitrogen, more robust processing equipment may be required compared to standard grades like 304/304L.
904L stainless steel is a high purity, low sulfur grade that can be machined using standard techniques. However, its machinability is not as optimized as other grades specifically designed for enhanced machinability. The cold work hardening rate of 904L is higher compared to stainless steels like 410 and 304, which makes it less machinable.
904L stainless steel can be welded using common processes such as manual arc welding and tungsten-argon arc welding. It is recommended to use a filler metal with the same composition as the base metal, such as 20 25 CuL covered electrodes and 20 25 CuL wire, to ensure optimal corrosion properties in welds. Care should be taken to avoid hot cracking, particularly in constrained weldments, as 904L solidifies fully austenitic. Pre-heating is not required, and post-weld heat treatment is generally unnecessary.
Ø Bar & Rod
Ø Plate & Sheet
Ø Coil & Strip
Ø Pipe & Tube
Ø Fitting: Flange, Tee, Elbow, Reducer etc.
Ø Forging: Ring, Shaft, Circle, Block etc.
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