347 / 347H Stainless Steel (1.4550 / 1.4912)

347/347H stainless steel is a high-performance, austenitic alloy designed for strength and stability in high-temperature, corrosive environments.

347/347H Stainless Steel

347 stainless steel is a titanium- and niobium-stabilised austenitic stainless steel alloy that offers excellent corrosion resistance, especially against intergranular attack after exposure to high temperatures. It is widely used in applications where welding or thermal stress is a factor, thanks to its stability and resistance to carbide precipitation.

347H stainless steel is the high-carbon variant of 347. The increased carbon content (typically 0.04–0.10%) improves its strength, creep resistance, and overall performance at elevated temperatures, making it a preferred choice for components subjected to long-term heat and pressure.

Both alloys are non-magnetic and provide strong oxidation and corrosion resistance, even in high-chloride or acidic environments. Typical applications include heat exchangers, boilers, furnace parts, and high-temperature fasteners. 347 tubes & pipes, sheets & plates, round bar, and custom-formed products are frequently used in sectors such as aerospace, petrochemical, chemical processing, and power generation.

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AVAILABLE FORMS

Intamet offers 347 in a wide range of forms, including the below:

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What is the Chemical Composition of 347 / 347H Stainless Steel?

347 stainless steel (UNS S34700 / 1.4550) typically includes:

Carbon (C): ≤ 0.08%
Manganese (Mn): ≤ 2.00%
Phosphorus (P): ≤ 0.045%
Sulfur (S): ≤ 0.030%
Silicon (Si): ≤ 1.00%
Chromium (Cr): 17.00–20.00%
Nickel (Ni): 9.00–13.00%
Nitrogen (N): ≤ 0.10%
Columbium + Tantalum (Nb + Ta): ≥ 10×(C + N)
Iron (Fe): Balance

347H stainless steel (UNS S34709 / 1.4912) differs primarily in carbon content:

Carbon (C): 0.04–0.10%

All other elements are generally the same, though 347H may include small amounts of columbium and tantalum to enhance stability at high temperatures.

What are the Physical Properties of 347 / 347H Stainless Steel?

Physical properties common to both grades include:

Density: 8.0 g/cm³

Melting Point: 1454–1495 °C

Specific Heat: 0.5 J/g·K

Thermal Conductivity: ~16 W/m·K

Thermal Expansion: ~16 × 10⁻⁶/K

Modulus of Elasticity: 193 GPa

These properties ensure 347 / 347H maintains structural integrity under long-term thermal cycling and pressure, ideal for use in boilers, heat exchangers, and superheater tubes.

Are There Variants of 347 Stainless Steel?

Several variants of 347 exist to support specialised manufacturing or operational needs:

347H: High-carbon version for improved strength and creep resistance at high temperatures
347L: Low-carbon version for improved weldability and reduced carbide precipitation
347F: Improved formability and toughness, often used in cold-working and cryogenic applications
347S: Stabilised variant for enhanced resistance to intergranular corrosion in thermal cycling
347N: Nitrogen-strengthened for added tensile and yield strength in aggressive service conditions

What are the mechanical properties of 347 / 347H stainless steel?

Both 347/347H stainless steels offer strong mechanical performance, but 347H provides superior strength at elevated temperatures due to its higher carbon content. Typical values include:

Tensile Strength: 515–655 MPa (75–95 ksi)
Yield Strength: 205–345 MPa (30–50 ksi)
Elongation: 40–50%
Hardness (Brinell): 217–269 HB
Modulus of Elasticity: 193 GPa (28 × 10⁶ psi)
Density: 8.0 g/cm³
Melting Point: 1454–1495 °C (2650–2750 °F)

347H is preferred in high-temperature applications where creep strength and stress rupture resistance are required over long service periods.

Where is 347 / 347H Stainless Steel Used?

Due to their excellent combination of strength, corrosion resistance, and weldability, 347 and 347H stainless steels are used in:

Power generation — superheaters, boiler tubes, pressure vessels

Aerospace — exhaust manifolds, turbine engine parts

Petrochemical and chemical processing — high-pressure piping and heat exchangers

Industrial heating — furnace parts and radiant tubes

Fasteners — high-temperature nuts, bolts, and screws

Available in forms such as 347H stainless steel tubes & pipes, sheets & plates, round bar, and fittings, these grades are ideal for applications exposed to long-term thermal stress and corrosive conditions.

347 / 347H Stainless Steel (1.4550 / 1.4912)