What is 1.4550 Stainless Steel?
Jan 26, 2026
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1.4550 stainless steel, commonly known as 347 or UNS S34700, is a niobium (columbium)-stabilized austenitic stainless steel. Similar to 321, it is designed to resist intergranular corrosion after exposure to high temperatures, but uses niobium instead of titanium as the stabilizing element. This grade is particularly valued for its excellent high-temperature properties and is commonly used in welded assemblies, aircraft components, and high-temperature industrial equipment.
This niobium-stabilized grade is standardized under major international systems.
| Standard | Equivalent Grade |
|---|---|
| EN (Europe) | 1.4550 |
| ASTM/AISI (USA) | 347, UNS S34700 |
| JIS (Japan) | SUS347 |
| KS (Korea) | STS347 |
Niobium (Nb) is the key stabilizing element in its composition.
| Element | C | Si | Mn | P | S | Cr | Ni | Nb |
|---|---|---|---|---|---|---|---|---|
| Content (%) | ≤ 0.08 | ≤ 1.0 | ≤ 2.0 | ≤ 0.045 | ≤ 0.03 | 17.0 - 19.0 | 9.0 - 12.0 | ≥ 10xC% |
It provides good strength and ductility across a range of temperatures.
| Property | Yield Strength (Rp0.2) | Tensile Strength (Rm) | Elongation (A) | Hardness (HB) |
|---|---|---|---|---|
| Typical Value | ≥ 205 MPa | 500 - 750 MPa | ≥ 40% | ≤ 215 |
Key Characteristics and Applications of 1.4550 / 347
Intergranular Corrosion Resistance: Niobium forms stable carbides, preventing chromium depletion at grain boundaries during exposure to temperatures between 450-850°C, making it highly resistant to sensitization.
Good High-Temperature Strength: Maintains excellent creep and stress rupture strength at elevated temperatures, suitable for continuous service up to about 870°C.
Excellent Weldability: Can be welded using all common methods without subsequent heat treatment, making it ideal for fabricated high-temperature components.
Primary Applications:
Aerospace: Jet engine components, afterburner parts, and high-temperature fasteners.
Chemical Processing: Welded vessels, heat exchangers, and piping systems that operate at elevated temperatures.
Power Generation: Superheater tubes, boiler components, and turbine parts.
Heat Treatment Equipment: Retorts, muffles, and radiant tubes.
What is the difference between 347 (1.4550) and 321 (1.4541) stainless steel?
Both are stabilized grades, but they use different stabilizing elements: 347 uses niobium (Nb), while 321 uses titanium (Ti). Niobium-stabilized 347 generally offers better high-temperature strength and is often preferred for heavy welded sections because niobium carbides are less likely to segregate or oxidize during welding than titanium carbides. 321 may be chosen for its slightly better formability in certain cold-working applications.
Why is 347 stainless steel often used in aerospace applications?
Grade 347 is favored in aerospace due to its reliable performance in high-temperature, high-stress environments. Its stabilization provides consistent resistance to intergranular corrosion after prolonged exposure to operating temperatures, and its good creep strength makes it suitable for components like exhaust systems, engine mounts, and thermal protection systems where both strength and corrosion resistance are critical.
Looking for a Reliable Supplier of 1.4550 / 347 Stainless Steel?
GNEE Steel supplies high-quality 347 (1.4550) stainless steel in plate, sheet, pipe, and bar forms for high-temperature and corrosion-resistant applications. We provide full material certification and processing support. If you have any requirements, please feel free to contact us.
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