904L Super Austenitic Stainless Steel: Comprehensive Guide to High-Performance Corrosion Resistance
Material Overview

904L (UNS N08904) is a low-carbon, highly alloyed super austenitic stainless steel designed for extreme corrosive environments. Its key advantages lie in the combination of high chromium (Cr), nickel (Ni), molybdenum (Mo), and copper (Cu), significantly enhancing resistance to acids, chloride-induced corrosion, and stress cracking. Widely used in chemical processing, marine engineering, and pharmaceuticals.

Chemical Composition & Physical Properties

Chemical Composition (Typical)

Carbon (C): ≤0.02% (prevents intergranular corrosion)

Chromium (Cr): 19.0-23.0% (excellent oxidation resistance)

Nickel (Ni): 23.0-28.0% (enhances stress corrosion cracking resistance)

Molybdenum (Mo): 4.0-5.0% (superior pitting/crevice corrosion resistance)

Copper (Cu): 1.0-2.0% (optimizes performance in reducing acids).

Physical Properties

Density: 8.0-8.24 g/cm³

Melting Point: 1300-1390℃

Thermal Conductivity: 15 W/(m·K)

Non-magnetic at room temperature.

Mechanical Properties

Tensile Strength: ≥490 MPa
Yield Strength: 215-220 MPa
Elongation: ≥35%
Hardness: HB200-240

Ideal for pressure vessels and complex structures due to high ductility.

Key Advantages

Acid Resistance

Superior performance in dilute sulfuric acid (0-98%, ≤40°C) and phosphoric acid (0-85%).

Chloride Resistance

Excellent resistance to pitting, crevice corrosion, and SCC in seawater/chloride solutions.

Limitations

Avoid in strong nitric acid or hydrochloric acid (>2% concentration).

Performance Comparison

Property	904L	316L	317L
Sulfuric Acid	Excellent (≤40°C)	Moderate (low conc.)	Moderate
Chloride Resistance	Excellent (marine use)	Poor (prone to pitting)	Good
Copper Content	1.0-2.0% (acid resistance)	None	None
Cost-Effectiveness	High	Low	Moderate