1.4460 stainless steel is a duplex stainless steel (austenitic-ferritic microstructure) with excellent corrosion resistance, high strength, and good weldability. It is widely recognized in industrial standards, corresponding to UNS S31803 and ASTM A182 F51, and is commonly used in demanding environments such as chemical processing, marine engineering, and oil and gas industries. Below is a detailed overview:
1. Chemical Composition
The chemical composition of 1.4460 is carefully balanced to form its duplex structure and ensure performance, with key elements (wt%) as follows:
Chromium (Cr): 21.00–23.00% (enhances corrosion resistance and ferrite formation)
Nickel (Ni): 4.50–6.50% (stabilizes austenite and improves toughness)
Molybdenum (Mo): 2.50–3.50% (boosts pitting and crevice corrosion resistance)
Nitrogen (N): 0.08–0.20% (strengthens the structure and improves corrosion resistance)
Carbon (C): ≤0.03% (reduces carbide precipitation, minimizing intergranular corrosion risk)
Manganese (Mn): ≤2.00%
Silicon (Si): ≤1.00%
Phosphorus (P): ≤0.030%
Sulfur (S): ≤0.020%
This composition gives it a Pitting Resistance Equivalent Number (PREN) of ~30–35, significantly higher than 304 stainless steel (~18) and comparable to 316L (~25), indicating superior resistance to pitting and crevice corrosion.
2. Microstructure & Physical Properties
Microstructure: A balanced mix of austenite (30–50%) and ferrite (50–70%), which combines the toughness of austenitic steels with the strength and corrosion resistance of ferritic steels.
Density: ~7.8 g/cm³ (slightly lower than austenitic grades like 316L, ~8.0 g/cm³).
Melting Point: 1400–1450°C.
Thermal Conductivity: ~18 W/(m·K) at 20°C (higher than austenitic steels, improving heat transfer efficiency).
Coefficient of Thermal Expansion: ~12 × 10⁻⁶/°C (20–100°C), lower than 304 (~17 × 10⁻⁶/°C), reducing thermal stress in high-temperature applications.
Magnetism: Magnetic due to its ferrite content (unlike fully austenitic grades like 304, which are non-magnetic).
3. Mechanical Properties
1.4460 exhibits high strength, making it suitable for weight-sensitive or high-pressure applications:
Tensile Strength: ≥620 MPa (significantly higher than 316L, ~485 MPa).
Yield Strength: ≥450 MPa (nearly double that of 316L, ~210 MPa).
Elongation: ≥25% (good ductility for forming and fabrication).
Hardness: ≤290 HB (Brinell) or ≤30 HRC (Rockwell C).
Its mechanical properties remain stable across a wide temperature range, from cryogenic conditions to moderate high temperatures (up to ~300°C).
4. Corrosion Resistance
General Corrosion: Resistant to atmospheric corrosion, fresh water, and many organic/inorganic acids (e.g., sulfuric acid, phosphoric acid) due to its high chromium and molybdenum content.
Pitting & Crevice Corrosion: Excellent resistance in chloride-rich environments (e.g., seawater, brines) thanks to molybdenum and nitrogen, outperforming 316L in harsh chloride conditions.
Stress Corrosion Cracking (SCC): Far more resistant to SCC than austenitic steels like 304 or 316, which are prone to SCC in chloride environments.
Intergranular Corrosion: Low carbon content and nitrogen addition minimize carbide precipitation, reducing the risk of intergranular corrosion, even after welding.
5. Weldability & Fabrication
1.4460 has good weldability but requires attention to heat input to maintain its duplex microstructure:
Welding Methods: Compatible with TIG, MIG, and SMAW (stick welding).
Heat Input Control: Excessive heat can promote austenite growth and reduce ferrite, weakening corrosion resistance and toughness. Recommended heat input: 0.5–2.5 kJ/mm.
Filler Metals: Matching duplex fillers (e.g., 1.4462) are used to preserve mechanical properties and corrosion resistance.
Post-Weld Treatment: Generally, no post-weld heat treatment is needed, but cleaning (to remove oxides) is essential.
6. Applications
Due to its combination of high strength, corrosion resistance, and cost-effectiveness (compared to super austenitic steels), 1.4460 is used in:
Marine Engineering: Seawater pipelines, ship hull components, offshore platforms, and desalination plants.
Chemical Processing: Reactors, storage tanks, and pipelines handling corrosive media (acids, chlorides).
Oil & Gas Industry: Downhole equipment, wellhead components, and offshore drilling systems.
Water Treatment: Pumps, valves, and fittings in wastewater treatment plants.
Structural Applications: Bridges, pressure vessels, and heat exchangers where high strength and corrosion resistance are required.
Key Comparisons
vs. 316L: 1.4460 has higher strength (yield strength ~2× that of 316L) and better chloride corrosion resistance but is slightly less ductile.
vs. Super Duplex (e.g., 1.4410): 1.4460 is more cost-effective but has lower PREN (30–35 vs. 40+ for super duplex) and is less suitable for extreme corrosion environments.
In summary, 1.4460 is a versatile duplex stainless steel that balances strength, corrosion resistance, and processability, making it a preferred choice for industrial applications in aggressive environments.