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Stainless Steel

904L Stainless

904L is a super-austenitic stainless with high nickel, chromium, and notably high molybdenum, engineered for the most severe corrosive media. Its corrosion rating of 5 reflects outstanding resistance to sulfuric and other reducing acids plus chlorides. Mechanically it is a soft austenitic at 520 MPa tensile and 220 MPa yield; its value is chemistry, not strength, and it carries a premium cost.

How 904L Stainless machines

Machinability is poor at 1.7/5. The high nickel and molybdenum make 904L tough, gummy, and prone to work-hardening and built-up edge. Use sharp coated carbide, slow speeds with heavy positive feeds to cut beneath the hardened layer, maximum rigidity, and copious flood coolant; never let tools rub or dwell.

Manufacturing & processing

904L is processed by CNC, sheet metal, and forging in the solution-annealed condition. It is not hardenable by heat treatment. It welds well using matched or higher-alloy filler, but interpass temperatures must be controlled to avoid sensitization and intermetallic precipitation that would degrade its hard-won corrosion resistance.

Typical applications

Best for sulfuric acid and severe corrosion service. Typical uses include sulfuric and phosphoric acid handling, chemical and petrochemical processing, flue-gas scrubbers, pulp-and-paper bleaching, and seawater equipment where ordinary stainless would pit or corrode through.

When to choose it

Reach for 904L only when the chemistry is genuinely aggressive, such as hot sulfuric acid, and cheaper stainless cannot survive. If you need strength too, 2205 duplex is better and cheaper. For pure mechanical duty, 904L's high cost is wasted.

Suitable surface finishes

Common finishes for 904L Stainless: passivation, electropolishing, bead blasting, brushed. Use the finish selector →

FAQ

What makes 904L resist sulfuric acid so well?
Its high molybdenum and copper content, combined with elevated nickel and chromium, provides exceptional resistance to reducing acids like sulfuric. This chemistry is the entire reason to specify 904L, which otherwise has unremarkable mechanical properties.
Is 904L stronger than 316?
No. At 220 MPa yield it is comparable to or slightly below 316. 904L is chosen purely for corrosion resistance, not strength. If you need both strength and corrosion resistance, 2205 duplex is the better and more economical option.
Why is 904L so expensive to machine?
Its high nickel and molybdenum make it gummy and strongly work-hardening, rated 1.7/5. Slow speeds, heavy feeds, rigid tooling, sharp carbide, and heavy coolant are mandatory, all of which raise cycle time and tooling cost.

Property values are typical/nominal for early guidance and vary by temper, grade, supplier and heat treatment. Confirm critical specs against a certified datasheet or with an mfgiq engineer.