A stabilised austenitic stainless steel, Alloy 347 offers excellent resistance to intergranular corrosion and reliable mechanical performance at high temperatures.
Alloy 347 (also known as 347 stainless steel or UNS S34700) is a niobium and tantalum stabilised austenitic stainless steel developed to reduce the risk of intergranular corrosion after welding or prolonged exposure to high temperatures. The addition of niobium and tantalum helps prevent chromium carbide precipitation, allowing the alloy to maintain its corrosion resistance in welded components.
Alloy 347 is commonly used in the aerospace, oil and gas, chemical processing and power generation industries, where good corrosion resistance, weldability and high-temperature performance are required. It is particularly suitable for heavy welded fabrications that cannot be solution annealed after welding.
Key Benefits of Alloy 800H/AT:
We stock Alloy 347 in a variety of product forms to suit different applications and fabrication methods, including coil, plate, round bar, sheet, and welding wire. To view available sizes and submit an enquiry, use the dropdown selector below.
The following elements in Alloy 347 provide its distinctive balance of intergranular corrosion resistance and high-temperature performance.
| % | Cr | Ni | Cb+Ta | C | Si | Mn | P | S | Fe |
|---|---|---|---|---|---|---|---|---|---|
| Min | 17 | 9 | Cb10xc | 0.04 | - | - | - | - | - |
| Max | 19 | 13 | 1 | 0.08 | 0.75 | 2 | 0.045 | 0.03 | Balance |
Alloy 347 is engineered for service in conditions involving intergranular corrosion risk, elevated temperature, and mechanical load. Key physical and thermal properties include:
Alloy 347 (UNS S34700) is a niobium and tantalum stabilised austenitic stainless steel developed to reduce the risk of intergranular corrosion after welding or prolonged exposure to high temperatures. It is commonly used in the aerospace, oil refining, chemical processing and power generation industries, where corrosion resistance, weldability and high-temperature strength are essential.
It was developed to provide an optimal balance between:
The addition of niobium and tantalum stabilises the alloy by reducing chromium carbide precipitation at grain boundaries during welding and high-temperature service. This helps Alloy 347 retain its corrosion resistance in welded components without the need for post-weld solution annealing in many applications.
Welding can be carried out using GTAW (TIG), GMAW (MIG) and resistance welding methods. Alloy 347 is commonly used for heavy welded fabrications operating between 426.67°C and 815.55°C, where corrosion resistance and high-temperature performance are both required.
| Mechanical & Physical Properties | 21.1°C | 100°C | 500°C |
|---|---|---|---|
| Coefficient of Thermal Expansion, µm/m⁰C | 16.6 | ||
| Thermal Conductivity/ kcal/(hr.m.°C) | 167.4 | 219.8 | |
| Modulus of Elasticity Dynamic/ x105 MPa | 1.93 |
| 75 | Tensile strength, ksi |
|---|---|
| 30 | 0.2% Yield Strength, ksi |
| 40 | Elongation, % |
| 201 | Hardness Max, Brinell |
| Temperature, °C | 20°C | 204.44°C | 426.66°C | 537.77°C | 648.88°C | 732.22°C | 815.55°C |
|---|---|---|---|---|---|---|---|
| Ultimate Tensile Strength, ksi | 93.3 | 73.6 | 69.5 | 63.5 | 52.3 | 39.3 | 26.4 |
| 0.2% Yield Strength, ksi | 36.5 | 36.6 | 29.7 | 27.4 | 24.5 | 22.8 | 18.6 |
Due to its resistance to intergranular corrosion, good weldability and high-temperature strength, Alloy 347 is widely used in oil refineries, aerospace and other industries where welded components are exposed to high operating temperatures.
It is a niobium and tantalum stabilised austenitic stainless steel containing chromium and nickel, with small amounts of carbon, silicon, and manganese to enhance strength and intergranular corrosion resistance.
Alloy 347 retains structural integrity and intergranular corrosion resistance in continuous service between 426.67°C and 815.55°C (800°F to 1500°F).
Primarily in oil refineries and heavy welded assemblies, including fluid catalytic cracking units, hanger rods, recuperator tube sheets, fired heater tubes, and reactor equipment, as well as aircraft exhaust stacks, manifolds, and ring collectors.
They are the same material. "Alloy 347" and "347 stainless steel" both refer to UNS S34700.
NeoNickel supplies Alloy 347 in coil, plate, sheet, round bar, and welding wire.
NeoNickel supplies Alloy 347 stainless steel across the UK and Europe, supporting both urgent requirements and long-term project needs. All material is supplied with full mill certification and traceability, meeting relevant ASTM, AMS and other international standards. Our team can assist with material selection, specifications and product forms.
If you’re unsure which Alloy 347 product form is right for your application, fill out our enquiry form and a member of the team will be in touch.
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