Alloy 904L is a low carbon version of Type 904 stainless steel. It has good resistance to sulphuric, phosphoric and acetic acids. It also has good resistance to crevice and stress corrosion cracking. 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.
Alloy 904L is a nickel-chromium-iron alloy that has good corrosion resistance, mechanical properties and thermal stability. It has excellent corrosion resistance to seawater, brine, steam and most industrial chemicals.
Austenitic structure gives the material its excellent corrosion resistance. The chromium content in this alloy makes it more resistant to pitting than similar alloys with less chromium (e.g., Alloy 6061).
It can be used as structural materials in service temperatures up to 1000°C (1832°F) with little loss of mechanical properties or other problems such as stress cracking occur due to thermal fatigue when exposed at higher temperatures for an extended period of time.
SS 904L Equivalent Grade
The datasheet below summarizes Rolex 904L stainless steel equivalent grade such as European EN (German DIN EN, British BS EN, French NF EN…), Chinese GB, ISO, Japanese JIS standard.
AISI 904L equivalent material
Grade (Steel Number)
ISO Name (ISO Number)
AISI SAE; ASTM
904L (UNS N08904)
EN 10088-2; EN 10088-3
GB/T 20878; GB/T 4237; GB/T 3280
Datasheet and Specification of 904L
The following data sheet summarizes the chemical composition, properties, heat treatment and equivalent grade of 904L stainless steel (SS904L).
Chemical Composition of 904L
The following data sheet gives SS 904L stainless steel chemical composition.
Chemical Composition, %
Bars and Shapes
Plate, Sheet, and Strip
Mechanical Properties of 904L
The following table lists Rolex 904L stainless steel (SS904L) mechanical properties such as yield strength, tensile strength, elongation and hardness.
AISI ASTM 904L Steel Mechanical Properties
Tensile Strength, MPa (ksi), ≥
0.2% Yield Strength, MPa (ksi), ≥
Elongation in 50 mm (2 in.), %, ≥
Rockwell Hardness (HRBW), ≤
904L (UNS N08904)
Bars and Shapes
Annealed, Hot-finished or cold-finished
Plate, Sheet, and Strip
Heat Treatment of 904L
Annealing: The recommended annealing temperatures for 904L wrought steel is 1095 °C (2000 °F).
Corrosion resistance of 904L stainless steel
Since the carbon content of 904L is very low (max. 0.020%), there is no carbide precipitation under general heat treatment and welding. This eliminates the risk of intergranular corrosion that occurs after general heat treatment and welding. Due to the high chromium-nickel-molybdenum content and the addition of copper elements, 904L can be passivated even in reducing environments such as sulfuric acid and formic acid. The high nickel content gives it a low corrosion rate even in the active state. In the concentration range of 0-98% pure sulfuric acid, 904L can be used at temperatures up to 40 degrees Celsius. In pure phosphoric acid in the concentration range of 0-85%, its corrosion resistance is very good. In industrial phosphoric acid produced by the wet process, impurities have a strong influence on the corrosion resistance. In all kinds of phosphoric acid, 904L corrosion resistance is better than ordinary stainless steel. In strongly oxidizing nitric acid, 904L has lower corrosion resistance compared to highly alloyed steel grades without molybdenum. In hydrochloric acid, the use of 904L is limited to a lower concentration of 1-2%. In this concentration range. 904L has better corrosion resistance than conventional stainless steels. 904L steel has a high resistance to pitting corrosion. Its resistance to crevice corrosion is also good in chloride solutions. 904L’s high nickel content reduces the rate of corrosion at pits and crevices. Ordinary austenitic stainless steels may be sensitive to stress corrosion in a chloride-rich environment at temperatures above 60 degrees C. This sensitization can be reduced by increasing the nickel content of the stainless steel. Due to the high nickel content, 904L has a high resistance to stress corrosion rupture in chloride solutions, concentrated hydroxide solutions and hydrogen sulfide-rich environments.
Processing performance of 904L
Welding performance of 904L
As with general stainless steel, 904L can be welded using a variety of welding methods. The most commonly used welding method for manual arc welding or inert gas shielded welding, welding rod or wire metal based on the composition of the base metal material and higher purity, molybdenum content requirements than the base material. Preheating is generally not necessary before welding, but in cold outdoor work, to avoid condensation of water vapor, the joint or the adjacent area can be uniformly heated. Note that the local temperature should not exceed 100 ℃, so as not to lead to carbon agglomeration, causing intergranular corrosion. Welding should use a small linear energy, continuous and fast welding rate. After welding generally do not need heat treatment, if heat treatment, must be heated to 1100-1150 ℃ after rapid cooling.
Matching welding consumables: welding rod (E385-16/17), welding wire (ER385).
Machinability of 904L 904L machining characteristics similar to other austenitic stainless steel, the process has a tendency to sticky tool and work hardening. Must use positive front angle carbide tools, sulfide and chlorinated oil as cutting coolant, equipment and process should be to reduce the premise of machining hardening. Slow cutting speed and tool feed should be avoided in the cutting process.
Tube platesare used on steam boilers to seal the tubes in place. The tube plate is usually made from forged steel, and is usually drilled or punched to leave a clearance hole for the tubes to be inserted into the tube plate. Tubing or pipe carries liquid or gas through a system of valves and connections until it reaches its destination where it is often cooled using cold water. Tube plates are notched around their perimeter so that they can accommodate each length of tube installed within them; this makes tube plates highly versatile and applicable across many industrial sectors including power generation, petrochemical processing plants, pharmaceuticals production facilities and more. By using a tube plate, it allows the tubes to be easily installed and removed in case of repair or replacement. Tube plates are used to support tubes in a boiler. They can be installed on the ends of tubes, or between them if there is not enough room for a full plate. The reason why tube plates are so useful is that they allow for easy installation and removal of tubes in case of repair or replacement. Without them, it would be much more difficult to remove a damaged tube without causing damage to the other parts nearby. Tube plates are usually made from forged steel and will have holes drilled through that can accommodate different sizes of bolts to hold the tubes together safely during operation. The most common type of thread used for tubes is the NPT thread, which stands for National Pipe Thread. NPT threads have a 60 degree angle and have flattened peaks and valleys. The term “pipe” refers to the shape of the threads on both sides of the pipe: one side has a flat top, and the other side has a flat bottom (hence “pipe”). This shape allows for easy tightening with wrenches or hand tools. Tubes are thin-walled piping used in boilers to condense steam and transfer heat from hot gases or fluids that pass through them to the water in the boiler. They are usually made from steel, copper or aluminum.
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