Introduction to Super Austenitic Stainless Steel (904L)

Super austenitic stainless steel (904L) has excellent cold and hot working properties, similar to other commonly used Cr-Ni austenitic steels.

Hot Forging: The maximum heating temperature is 1180°C, and the minimum forging stop temperature is 900°C.
Hot Forming: This steel can be hot formed at temperatures between 1000°C and 1150°C.
Heat Treatment: The heat treatment process involves heating to 1100-1150°C and then cooling quickly.
Welding:
- General welding techniques can be used.
- Manual arc welding and tungsten arc welding are recommended.
- For plates up to 6 mm thick, use an electrode diameter of 2.5 mm or less; for plates over 6 mm thick, use an electrode diameter of less than 3.2 mm.
- Post-welding heat treatment involves heating to 1075-1125°C followed by rapid cooling.
- Tungsten arc welding requires the same material for filler metal as the electrode, with the weld needing pickling and passivation after welding.

904L stainless steel, also known as 00Cr20Ni25Mo4.5Cu, is designed to resist sulfuric acid corrosion.

Acid Resistance: It is also resistant to acetic acid at any concentration and temperature under normal pressure. Additionally, it has good corrosion resistance in formic acid, phosphoric acid, and mixed acids of formic and acetic acids.
Intergranular Corrosion: Tests using the T method in GB1223-75 show that steel with 0.038% carbon content requires over an hour of sensitization to develop intergranular corrosion. Thus, with proper welding procedures, there is no risk of intergranular corrosion for components up to 30 mm thick.
Pitting Corrosion: 00Cr20Ni25Mo4.5Cu is more resistant to pitting corrosion than lower-grade Cr-Ni austenitic steels like 00Cr18Ni10 and 00Cr18Ni14Mo2.
Stress Corrosion: With a Ni content of 25%, 00Cr20Ni25Mo4.5Cu has better stress corrosion resistance than general Cr-Ni austenitic steels. It is particularly effective in preventing stress corrosion cracking in water media containing chloride ions, where other stainless steels such as 18-8 and 18-12-Mo might fail.