Stainless Steel 347 (UNS S34700)
Stainless Steel 347 is a columbium (niobium) stabilized austenitic stainless steel designed for use in high-temperature environments where sensitization and intergranular corrosion are primary concerns. By adding Niobium (and occasionally Tantalum), this alloy prevents chromium carbide precipitation during welding and long-term exposure to temperatures between 800° F and 1500° F (427° C to 816° C). While very similar to Type 321, 347 is often preferred for more demanding applications due to its slightly higher creep and stress-to-rupture properties.
At Aries Alloys, we supply Stainless Steel 347 to sectors that require extreme reliability in thermal processing. Our material is chosen for its ability to maintain high structural integrity and corrosion resistance in the most grueling "as-welded" conditions.
Key Performance Benefits
- Niobium Stabilization: The addition of Niobium (10 times Carbon content minimum) ensures the chromium remains in the matrix, protecting the grain boundaries from corrosion after welding.
- Superior High-Heat Strength: Offers slightly better mechanical strength and creep resistance at elevated temperatures compared to Titanium-stabilized Type 321.
- Corrosion Resilience: Excellent resistance to strong oxidizing environments and organic chemicals, as well as high-temperature gases.
- Weldability & Fabricability: Highly adaptable to standard welding techniques; unlike Type 304, it does not require post-weld annealing to retain its corrosion properties.
- Cryogenic Toughness: Maintains exceptional ductility and impact strength at sub-zero temperatures.
Technical Profile & Composition
The Niobium Advantage:
In Type 347, Niobium (Cb/Nb) acts as a stabilizer by forming stable carbides that are more robust than Chromium carbides. This metallurgical process is particularly effective for heavy-wall welded components that stay in the 800° F to 1500° F range for extended periods, where other alloys would typically fail.
Mechanical & Physical Data:
- Density: 7.96 g/cm^3
- Non-Magnetic: Remains non-magnetic in the annealed condition.
- Maximum Service Temperature: Resists oxidation and scaling up to 1600° F (871° C).
- Note on High Carbon: For even greater load-bearing capacity at temperatures above 1000° F, the high-carbon version (347H) is available to provide maximum creep strength.
Primary Industrial Use Cases
Aries Alloys is a strategic supplier of Stainless Steel 347 for high-performance hardware:
- Aerospace Propulsion: Aircraft exhaust stacks, collector rings, jet engine parts, and manifold systems.
- Oil & Gas Refineries: High-temperature catalytic cracking units, heater tubes, and equipment for handling polythionic acid.
- Power Generation: High-pressure steam pipes, boiler tubes, and superheater headers.
- Chemical Industry: Equipment for the production of specialized chemicals involving high-heat cycling and aggressive acids.
- Waste Treatment: Thermal oxidizers and components for high-temperature exhaust systems.
Product Availability at Aries Alloys
We stock and supply Stainless Steel 347 in accordance with ASTM A240, A276, and AMS 5512:
- Sheets & Plates: Precision-cut flat products for the fabrication of aerospace manifolds and heat shields.
- Round & Hex Bars: High-strength bars for machining high-temperature fasteners and structural hardware.
- Seamless & Welded Tubes: For use in high-pressure heat exchangers and exhaust ducting.
- Custom Forgings: Flanges, rings, and specialized blocks for high-heat connectivity.