347 Stainless Steel Coil
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What is 347 Stainless Steel? 347 Stainless Steel (UNS S34700) is an austenitic chromium-nickel stainless steel that is stabilized with niobium (columbium) and, sometimes, tantalum. It’s essentially a modified version of 304 stainless steel. The primary purpose of adding niobium is to prevent the formation of chromium carbides at grain boundaries when the material is exposed to temperatures in the sensitization range (typically 427°C to 816°C or 800°F to 1500°F). This phenomenon, known as sensitization, can lead to intergranular corrosion in unstabilized grades like 304, especially after welding. By forming stable niobium carbides instead, 347 maintains its corrosion resistance even after exposure to high temperatures or welding without a post-weld annealing treatment. Like other austenitic stainless steels, 347 is generally non-magnetic in its annealed condition.
Key Properties of 347 Stainless Steel
The niobium stabilization is the defining characteristic of 347 stainless steel, offering critical advantages for specific high-temperature and welded applications.
Intergranular Corrosion Resistance (Stabilization)
- Resistance to Sensitization: This is 347’s most significant property. The addition of niobium ensures that carbon within the alloy preferentially combines with niobium to form stable niobium carbides, rather than with chromium. This prevents chromium from depleting at the grain boundaries, thereby eliminating the susceptibility to intergranular corrosion when exposed to high temperatures, particularly within the sensitization range, or after welding. This is crucial for applications that operate at elevated temperatures or involve heavy welded sections where post-weld annealing is impractical.
Excellent High-Temperature Performance
- Oxidation Resistance: 347 offers excellent resistance to oxidation in continuous service up to approximately 816°C (1500°F) and in intermittent service up to about 899°C (1650°F).
- Creep and Stress-Rupture Properties: Due to the niobium stabilization, 347 exhibits superior creep resistance and higher stress-rupture properties at elevated temperatures compared to unstabilized grades like 304 or even titanium-stabilized 321. This makes it ideal for high-temperature structural components.
Good General Corrosion Resistance
- Similar to 304: In many environments, 347 offers general corrosion resistance comparable to 304 stainless steel. It performs well in atmospheric conditions, fresh water, and a wide variety of organic and inorganic chemicals.
- Enhanced in Specific Conditions: Its resistance to intergranular corrosion after high-temperature exposure makes it superior to 304 in applications involving high-temperature service or welding where sensitization could otherwise be an issue.
- Limited Chloride Resistance: While generally good, 347 does not contain molybdenum and is therefore less resistant to pitting and crevice corrosion in chloride-rich environments (e.g., seawater) compared to molybdenum-bearing grades like 316.
Mechanical Properties
- Good Strength and Ductility: 347 maintains good tensile strength and yield strength, combined with excellent ductility and formability, similar to other austenitic stainless steels. It cannot be hardened by heat treatment but can be strengthened by cold working.
- Good Low-Temperature Toughness: Like other austenitic grades, 347 retains good toughness at cryogenic temperatures.
Weldability
- Excellent Weldability: 347 is readily weldable by all common fusion and resistance welding processes. The niobium stabilization eliminates the need for post-weld annealing to restore corrosion resistance, which is a significant advantage for complex fabrications. It is often used as a filler metal for welding 321 stainless steel.
Non-Magnetic
- Generally Non-Magnetic: In its annealed condition, 347 stainless steel is non-magnetic. However, like other austenitic grades, it can become slightly magnetic after significant cold working.
Detailed Specifications: Dimensions and Parameters
347 Stainless Steel Coil is available in various dimensions and surface finishes, typically conforming to ASTM A240/A240M standards, to meet the requirements of its demanding applications.
| Parameter | Standard Range |
| Thickness | 0.3mm – 10mm (0.012 in – 0.394 in) |
| Width | 1000mm – 2000mm (39.37 in – 78.74 in) |
| Length | Coil form (continuous length) |
| Surface Finish | 2B, No.1, BA, Polished Finishes (e.g., No.4) |
| Edge Condition | Mill Edge, Slit Edge |
| Standard | ASTM A240/A240M, ASME SA-240 |
Note: Specific dimensions, available finishes, and tempers may vary based on current stock and manufacturing capabilities. Always contact your supplier for precise information on required specifications.
Chemical Composition of 347 Stainless Steel
The controlled chemical composition of 347 stainless steel, particularly the crucial addition of niobium, defines its specialized properties.
| Element | Weight Percentage (%) |
| Carbon (C) | |
| Silicon (Si) | |
| Manganese (Mn) | |
| Phosphorus (P) | |
| Sulfur (S) | |
| Chromium (Cr) | 17.0 – 19.0 |
| Nickel (Ni) | 9.0 – 13.0 |
| Niobium (Columbium) + Tantalum |
The presence of Niobium (Columbium), often with Tantalum, is the defining feature, serving to stabilize the alloy against sensitization.
347 Stainless Steel vs. Other Stainless Steel Grades: A Comparative Look
Comparing 347 to other common stainless steels highlights its advantages for high-temperature and welded applications.
| Feature | 347 | 321 | 304L | 316L |
| Stainless Steel Family | Austenitic | Austenitic | Austenitic | Austenitic |
| Stabilizing Element | Niobium (Columbium) + Tantalum | Titanium | None (low carbon for weldability) | None (low carbon for weldability) |
| Resistance to Intergranular Corrosion | Excellent (after high-temp exposure/welding) | Excellent (after high-temp exposure/welding) | Good (due to low carbon, but less than 347/321) | Good (due to low carbon) |
| High-Temperature Strength/Creep | Excellent (superior to 321, 304L) | Good | Moderate | Moderate |
| General Corrosion Resistance | Excellent (similar to 304L) | Excellent (similar to 304L) | Excellent | Superior (due to Molybdenum) |
| Chloride Resistance (Pitting/Crevice) | Moderate | Moderate | Moderate | High |
| Weldability | Excellent (no post-weld anneal needed) | Excellent (no post-weld anneal needed) | Excellent | Excellent |
| Cost | High | High | Low | Moderate to High |
| Typical Use | Aircraft exhaust, boiler tubes, heavy welded equipment, chemical process equipment | Aircraft exhaust, compensators, furnace parts | Food & beverage, general chemical, architectural | Marine, chemical processing, pharmaceutical, medical implants |
347 and 321 are often considered interchangeable, but 347 generally offers slightly better performance in stronger oxidizing conditions and maintains stability during welding better than 321 due to the differing stability of niobium vs. titanium carbides.
Key Industries and Applications for 347 Stainless Steel Coil
The unique properties of 347 Stainless Steel Coil, particularly its intergranular corrosion resistance and high-temperature strength, make it essential for critical applications.
| Industry | Typical Applications |
| Aerospace | Aircraft exhaust manifolds, jet engine parts, collector rings, aircraft firewalls (where high temperatures and reliable weldments are critical) |
| Power Generation | Boiler tubes, superheater tubes, heat exchanger tubing, steam pipes, furnace parts (for high-temperature pressure-containing components) |
| Petrochemical & Chemical Processing | Heavy wall welded equipment, distillation columns, cracking units, liners, transfer lines, storage tanks for organic chemicals (where intergranular corrosion is a risk from high-temperature processing) |
| Food & Beverage | Equipment exposed to high temperatures or demanding cleaning cycles, such as cookers and drying equipment, where integrity after welding is key. |
| General Industrial | Expansion joints, compensators, and other components requiring high-temperature strength and good weldability. |
Global Price Overview: 347 Stainless Steel Coil
The price of 347 Stainless Steel Coil is generally higher than 304L and 316L, reflecting the cost of niobium (columbium) and the specialized processing required for stabilization. Pricing is influenced by global demand, the cost of raw materials (especially nickel, chromium, and niobium), energy prices, and the specific producer. The figures below are illustrative and subject to market fluctuations. For the most accurate and current pricing, please contact us directly.
| Region / Factor | Price Range (USD per Metric Ton) – Illustrative | Notes |
| Asia | $3,500 – $6,500 | Prices may vary based on producer’s quality control and specific alloy surcharges. |
| Europe | $4,000 – $7,500 | Reflects high quality standards, advanced manufacturing, and stricter material specifications. |
| North America | $4,500 – $8,000 | Influenced by domestic demand, import dynamics, and the high-performance nature of its applications. |
| Raw Material Cost (Ni, Cr, Nb) | High Impact | Fluctuations in these commodity markets, especially niobium, are primary cost drivers. |
| Order Volume | Discounts for Bulk | Larger purchase quantities may receive more favorable per-unit pricing. |
| Surface Finish & Thickness | Varies | Specific finishes and very thin gauges can incur slightly higher costs. |
Disclaimer: These are approximate price ranges and should not be considered as definitive quotes. For precise pricing and lead times, please reach out to our sales team.
Frequently Asked Questions (FAQs)
Here are answers to some of the most common questions about 347 Stainless Steel Coil.
Q1: What is the main advantage of 347 stainless steel over 304?
A1: The main advantage of 347 stainless steel over 304 is its resistance to intergranular corrosion (sensitization) after exposure to high temperatures (427°C to 816°C or 800°F to 1500°F) or after welding. This is achieved by the addition of niobium (columbium) and tantalum, which stabilize the carbon, preventing chromium carbide precipitation at grain boundaries. This eliminates the need for post-weld annealing, making 347 ideal for heavy welded fabrications or components used at elevated temperatures.
Q2: Is 347 stainless steel magnetic?
A2: In its annealed condition, 347 stainless steel is generally non-magnetic, similar to other austenitic stainless steels. However, like 304, it can become slightly magnetic after significant cold working.
Q3: How does 347 compare to 321 stainless steel?
A3: Both 347 and 321 stainless steels are stabilized austenitic grades designed to resist intergranular corrosion. The primary difference is the stabilizing element: 347 uses niobium (columbium) and tantalum, while 321 uses titanium.
- 347 (Niobium stabilized): Generally preferred for higher temperature applications (above 537°C or 1000°F) due to niobium’s superior strength at elevated temperatures and better resistance to oxidation in strong oxidizing conditions. Niobium also dissolves less readily during welding, leading to better carbide stability in the weld metal.
- 321 (Titanium stabilized): More widely used for applications up to 537°C (1000°F). Titanium can be lost across the welding arc more easily than niobium, potentially leading to less stable weld deposits in some instances.
In most general corrosion environments, their performance is similar, but 347 often has slightly better overall resistance, especially after exposure to the sensitization range.
Q4: Can 347 stainless steel be heat treated for hardening?
A4: No, 347 stainless steel cannot be hardened by heat treatment. Like other austenitic stainless steels, its microstructure does not allow for martensitic transformation through heating and quenching. It can only be strengthened through cold working.
Q5: What are typical applications for 347 stainless steel coil?
A5: 347 stainless steel coil is commonly used in applications requiring excellent resistance to intergranular corrosion after welding or high-temperature exposure, along with good high-temperature strength and oxidation resistance. Key applications include aircraft exhaust manifolds and jet engine parts, boiler tubes, superheater tubes, chemical process equipment (especially heavy welded sections), and other components operating at elevated temperatures where maintaining corrosion resistance after fabrication is critical.
