904L (N08904, 14539) super austenitic stainless steel contains 14.0-18.0% chromium, 24.0-26.0% nickel, 4.5% molybdenum. 904L super austenitic stainless steel is a low-carbon, high-nickel, molybdenum austenitic stainless acid-resistant steel, which is a proprietary material imported from French H·S Company. It has good activation-passivation transformation ability, excellent corrosion resistance, good corrosion resistance in non-oxidizing acids such as sulfuric acid, acetic acid, formic acid, phosphoric acid, and good corrosion resistance in neutral chloride-containing media Excellent pitting corrosion resistance, as well as good crevice corrosion resistance and stress corrosion resistance. It is suitable for various concentrations of sulfuric acid below 70 °C, and has good corrosion resistance in acetic acid of any concentration and temperature under normal pressure, as well as in the mixed acid of formic acid and acetic acid.
Super austenitic stainless steel 904L (00Cr20Ni25Mo4.5Cu; UNS: N08904; EN: 1.4539) is a high-alloy austenitic stainless steel with low carbon content. It has good corrosion resistance in dilute sulfuric acid and is specially designed for corrosion conditions. Designed for harsh environments. It has high chromium content and sufficient nickel content. The addition of copper makes it have strong acid resistance, especially for chloride crevice corrosion and stress corrosion cracking. The corrosion ability is slightly better than other steel grades, and it has good machinability and weldability, and can be used for pressure vessels.
Grades and Standards:
UNS N08904 (standard co-designed by SAE and ASTM in 1967), DIN1.4539 (German standard), ASTM A240 (ASTM standard; the new standard classifies it as a stainless steel series, The original standard ASME SB-625 classifies it as a series of nickel-based alloys), SUS890L.
Metallographic structure of 904L stainless steel:
904L is a completely austenitic structure. Compared with the general austenitic stainless steel with high molybdenum content, 904L is not sensitive to the precipitation of ferrite and α phase.
Physical and Mechanical Properties:
Density: 8.0g/cm3. Tensile strength: σb≥520Mpa. Elongation: δ≥35%.
Corrosion resistance of 904L stainless steel:
Because the carbon content of 904L is very low (0.020% maximum), there will be no carbide precipitation in the case of general heat treatment and welding. This eliminates the risk of intergranular corrosion that normally occurs after heat treatment and welding. Due to the high chromium-nickel-molybdenum content and the addition of copper, 904L can be passivated even in reducing environments such as sulfuric and formic acids. The high nickel content also results in a lower corrosion rate in the active state. In pure sulfuric acid in the concentration range of 0~98%, the operating temperature of 904L can be as high as 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 effect on the corrosion resistance. Of all the various phosphoric acids, 904L is more corrosion resistant than ordinary stainless steel. In strong oxidizing nitric acid, 904L has lower corrosion resistance than highly alloyed steel grades that do not contain molybdenum. In hydrochloric acid, the use of 904L is limited to lower concentrations of 1-2%. in this concentration range. The corrosion resistance of 904L is better than that of conventional stainless steel. 904L steel has high resistance to pitting corrosion. Its resistance to crevice corrosion in chloride solutions is also very good. The high nickel content of 904L reduces the rate of corrosion in pits and crevices. Ordinary austenitic stainless steels may be susceptible to stress corrosion in a chloride-rich environment at temperatures above 60°C, and this sensitization can be reduced by increasing the nickel content of the stainless steel. Due to the high nickel content, 904L is highly resistant to stress corrosion cracking in chloride solutions, concentrated hydroxide solutions and hydrogen sulfide rich environments.
Supporting welding consumables: welding rod (E385-16/17), welding wire (ER385).
Application Notes for 904L:
1. Processing performance
1.1 Welding performance
Like general stainless steel, 90 4 L can be welded by a variety of welding methods. The most commonly used welding methods are manual arc welding or inert gas shielded welding. The electrode or wire metal is based on the composition of the base metal and has a higher purity. The content of molybdenum is higher than that of the base metal. Preheating is generally not required before welding, but in cold outdoor operations, in order to avoid condensation of water vapor, the joints or adjacent areas can be heated evenly. Note that the local temperature should not exceed 100 ºC, so as not to cause carbon agglomeration and cause intergranular corrosion. When welding, it is advisable to use small line energy, continuous and fast welding speed. Generally, no heat treatment is required after welding. If heat treatment is required, it must be heated to 1100-1150°C and then cooled rapidly.
1.2 Machinability
The machining characteristics of 904L are similar to those of other austenitic stainless steels, and there is a tendency for tool sticking and work hardening during machining. Positive rake angle cemented carbide tools must be used, and vulcanized and chlorinated oil is used as cutting coolant. The equipment and process should be based on the premise of reducing work hardening. During the cutting process, slow cutting speed and feed amount should be avoided.
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