Comprehensive Guide to 347 Stainless Steel: Properties, Applications, and Market Insights
In the ever-evolving world of industrial materials, 347 stainless steel stands out as a versatile and highly sought-after alloy. Known…
Durable, versatile, and engineered to withstand extreme conditions, 347 stainless steel is a material that plays a critical role across a wide range of industries. From high-performance aerospace components to corrosion-resistant equipment in chemical and food processing, this alloy is designed to meet the demands of challenging environments. What sets it apart? Its unique composition, stabilized with niobium, offers exceptional resistance to intergranular corrosion and remarkable stability at high temperatures, making it a top choice for applications where strength, reliability, and longevity are non-negotiable.
In this article, we’ll take a closer look at the defining properties of 347 stainless steel, exploring its chemical makeup, mechanical advantages, and resistance to wear and tear. You’ll also discover its many practical applications, from power generation systems to environmental equipment, as well as the forms it’s available in to suit diverse manufacturing needs. Whether you’re an engineer, a manufacturer, or simply curious about advanced materials, this guide will equip you with everything you need to know about why 347 stainless steel is an industry favorite.
347 stainless steel is a highly durable and corrosion-resistant alloy, valued for its exceptional performance in high-temperature and demanding environments. It is a niobium-stabilized version of 304 stainless steel, designed to resist corrosion caused by carbide precipitation. This unique composition provides excellent resistance to high-temperature stress and corrosion, making it ideal for use in challenging industrial settings.
Given these properties, 347 stainless steel has become essential across various industries where strength and durability are paramount. From aerospace and power generation to chemical processing and food production, this alloy offers versatility and reliability in harsh conditions. It is also widely used in environmental systems, contributing to pollution control and waste management.
This guide provides an in-depth look at 347 stainless steel, covering its composition, properties, and applications. By exploring its features and comparing it to similar materials, you will gain valuable insights into its capabilities. Whether you’re selecting materials for industrial projects or seeking to understand its capabilities, this guide will help you make informed decisions.
347 stainless steel is an alloy made of chromium, nickel, and niobium, designed for high corrosion resistance and stability at elevated temperatures. The addition of niobium prevents the formation of chromium carbides, which can reduce corrosion resistance, ensuring the alloy performs well in demanding environments. Niobium stabilizes the alloy by stopping the formation of harmful carbides, especially at high temperatures. Its precise chemical composition includes 17–20% chromium, 9–13% nickel, and small amounts of manganese, silicon, and carbon, all of which work together to enhance durability and resistance to wear.
One of the key advantages of 347 stainless steel is its resistance to intergranular corrosion, a type of deterioration that occurs at grain boundaries in metals. This resistance is critical in environments prone to sensitization, such as those exposed to temperatures between 800–1500°F (427–815°C). By preventing chromium carbide precipitation, the alloy retains its corrosion resistance and structural integrity, making it a reliable material for chemical processing equipment and other corrosive applications.
347 stainless steel is engineered to perform exceptionally well under high-temperature conditions. The niobium-stabilized structure prevents damage caused by carbide formation, maintaining strength and durability under heat stress. It can withstand continuous service temperatures up to 1500°F (815°C) and even higher in intermittent service, making it an excellent choice for heat exchangers, superheaters, and other components exposed to extreme heat.
Thanks to its niobium stabilization, 347 stainless steel has excellent weldability and minimizes the risk of corrosion during welding. It is compatible with most common welding methods like TIG, MIG, and resistance welding. Additionally, post-weld heat treatment is generally not required, making the fabrication process more efficient and cost-effective.
347 stainless steel offers a balance of strength, flexibility, and durability, with a tensile strength of 75 ksi, yield strength of 30 ksi, and excellent elongation of 40%. Its hardness and resistance to wear ensure reliable performance in applications requiring both toughness and ductility.
This alloy is lightweight, with a density of 0.288 lb/in³, and performs well under thermal and mechanical stress, offering good heat transfer and elasticity. Its thermal conductivity and specific heat make it suitable for use in components that experience frequent temperature fluctuations, ensuring stability and efficiency in demanding environments.
With its unique combination of corrosion resistance, high-temperature performance, and mechanical stability, 347 stainless steel is an ideal choice for demanding industrial applications. Its versatility and reliability make it a standout material in industries ranging from chemical processing to power generation.
347 stainless steel is a versatile material renowned for its resilience in high-stress environments, making it a staple in several industries. In aerospace engineering, it is indispensable due to its ability to maintain structural integrity under extreme temperatures and pressures. This makes it an ideal choice for critical components like jet engine parts, exhaust manifolds, gas turbines, and collector rings. Its excellent weldability allows for the easy fabrication of complex structures, further enhancing its utility in this demanding field.
In the chemical processing industry, 347 stainless steel stands out for its exceptional resistance to intergranular corrosion and high-temperature oxidation. These properties make it ideal for handling aggressive chemicals in reactors, heat exchangers, distillation columns, and storage tanks. The addition of niobium to the alloy ensures long-term durability even in environments where acidic or oxidizing substances are prevalent, safeguarding critical equipment and reducing maintenance needs.
In the food industry, 347 stainless steel is valued for its non-magnetic properties, corrosion resistance, and ease of cleaning, making it perfect for cookers, drying equipment, storage tanks, and conveyor systems. Its durability under frequent cleaning cycles and exposure to varying temperatures ensures compliance with stringent food safety regulations while maintaining long-term operational efficiency.
Power plants rely on 347 stainless steel for its ability to perform under high-temperature and high-pressure conditions. This alloy withstands temperatures over 1000°F (538°C), resisting creep and stress rupture, ensuring power plants operate safely and efficiently. It is commonly used in boilers, radiant superheaters, heat exchangers, and steam piping, where reliability and durability are paramount.
Environmental systems benefit greatly from the durability and high-temperature stability of 347 stainless steel. Its resilience in harsh conditions, such as exposure to corrosive gases, makes it essential for waste gas treatment systems, solid waste processing equipment, and pollution control devices. These applications demand materials that can endure severe environmental stress while maintaining consistent performance over time.
In heavy-duty exhaust systems and refinery piping, 347 stainless steel proves its worth through its robustness against thermal fatigue, oxidation, and corrosion. These qualities make it ideal for exhaust manifolds, catalytic converter components, and refinery piping systems, where reliability is crucial in maintaining uninterrupted operations in challenging environments.
347 stainless steel sheets and plates are essential in industries where strength and corrosion resistance are critical. Sheets are thin and flexible, whereas plates are thicker, offering greater durability and strength. These forms are easily cut, bent, and welded, making them ideal for precise component fabrication.
Sheets are commonly used in chemical processing equipment, including reactor linings and heat exchangers, while plates excel in heavy-duty applications like pressure vessels and boiler components.
347 stainless steel bars come in various shapes, such as round, square, and hexagonal, making them versatile for engineering applications.
347 stainless steel tubes and pipes are crucial for safely transporting fluids and gases in extreme conditions. Available in seamless and welded forms, they are designed to handle high pressures and temperatures.
Coil, wire, and foil forms provide lightweight flexibility and precision for specialized applications.
347 stainless steel mesh is durable and corrosion-resistant, ideal for filtration and screening across industries.
Casting enables 347 stainless steel to be shaped into complex, specialized components.
347 stainless steel welding and filler rods are vital for joining parts in high-temperature, corrosive settings.
The UNS designation for 347 stainless steel, S34700, specifies its unique chemical composition and properties. This grade has several international equivalents, including WNR 1.4550 (Germany), DIN X10CrNiNb18-9 (Europe), BS 347S17 (UK), and SAE 30347 (USA). These equivalents facilitate global standardization, ensuring compatibility across industries and regions.
347 stainless steel is governed by a variety of ASTM and ASME specifications that define its production and application. These standards are categorized as follows:
Plates, Sheets, and Strips:
ASTM A240: Covers stainless steel plates, sheets, and strips for pressure vessels and general use.
Piping and Tubing:
ASTM A312: Specifies seamless and welded austenitic stainless steel pipes.
ASTM A358: Applies to electric-fusion-welded austenitic stainless steel pipes for high-temperature service.
Fittings and Components:
ASTM A182: Pertains to forged or rolled alloy and stainless steel pipe flanges, fittings, and valve parts.
ASTM A403: Covers wrought stainless steel piping fittings.
Bars and Shapes:
ASTM A276: Defines stainless steel bars and shapes for structural and mechanical applications.
These standards guarantee the material meets the necessary properties for applications like piping and structural components.
In European and German systems, 347 stainless steel is classified as EURONORM FeMi35Cr20Cu4Mo2 and DIN 2.4660, which define its composition and high-performance capabilities. These classifications harmonize with global standards to ensure consistent quality and performance.
The physical and mechanical properties of 347 stainless steel are standardized to ensure reliable performance. Key properties include:
These specifications ensure the material delivers reliable performance in even the most demanding industrial settings.
Manufacturers must adhere to relevant standards to ensure the quality and performance of 347 stainless steel. Certification involves thorough testing of chemical composition, mechanical properties, and corrosion resistance. This rigorous process guarantees the material’s reliability for critical applications across industries such as aerospace, power generation, and chemical processing.
347 stainless steel is highly weldable and supports various welding techniques. Common techniques like TIG, MIG, and resistance welding ensure efficient fabrication, while using 347 filler metals helps maintain corrosion resistance at weld joints.
Niobium prevents chromium carbides from forming, ensuring the steel remains resistant to corrosion. This makes 347 stainless steel particularly suitable for environments prone to corrosive challenges, especially after welding.
In many cases, 347 stainless steel can be used in the as-welded condition, simplifying the fabrication process. For high-temperature applications, post-weld stabilizing treatments can improve performance, enhancing the alloy’s resistance to intergranular corrosion.
Several heat treatment methods are used to enhance the properties of 347 stainless steel, including annealing, stress relief, and solution treatment.
The alloy is heated to 1010°C to 1193°C (1850°F to 2000°F) and rapidly cooled, typically through water quenching, to prevent chromium carbide formation. This process maximizes corrosion resistance and mechanical properties.
Stress relief heat treatment is performed within the range of 800°C to 870°C (1470°F to 1600°F). This process ensures the material’s integrity, especially in applications prone to stress-related failures.
Solution treatment involves heating the steel to 1065°C to 1150°C (1950°F to 2100°F), followed by rapid cooling. This treatment prevents corrosion and ensures the material performs well over time.
Although 347 stainless steel is not typically age-hardened, it can be strengthened through cold working or moderate-temperature aging.
By applying the appropriate welding and heat treatment methods, 347 stainless steel can deliver exceptional performance in demanding environments.
Both 347 and 321 stainless steels are austenitic alloys designed to resist intergranular corrosion, but their stabilizing elements set them apart. 347 uses niobium, while 321 relies on titanium. This distinction directly impacts their performance, especially in high-temperature environments.
High-Temperature Applications
347 stainless steel outperforms 321 in prolonged high-temperature conditions. Its niobium stabilization ensures better structural integrity and resistance to deformation when exposed to temperatures up to 1500°F (815°C). For example, 347 is commonly used in components like exhaust manifolds and high-temperature chemical reactors, where consistent strength over time is critical.
Corrosion Resistance
Both alloys resist oxidation and general corrosion effectively. However, 347 performs better in environments where prolonged exposure to moisture or chemicals occurs, such as in marine and industrial processing systems. On the other hand, 321 is often sufficient for short-term or lower-intensity applications.
Mechanical Properties
While the tensile strength and ductility of 347 and 321 are similar, 347 offers superior creep resistance. This means it can withstand long-term stress at elevated temperatures without significant deformation, making it ideal for demanding industrial equipment.
Composition Comparison
304 stainless steel is a versatile and widely used alloy, but it lacks the niobium stabilization found in 347. This stabilization gives 347 a distinct edge in environments where high temperatures or welding processes could otherwise weaken the material.
Intergranular Corrosion Resistance
304 is prone to sensitization, a condition where chromium carbides form at grain boundaries, leading to intergranular corrosion. In contrast, 347’s niobium prevents this issue, making it a superior choice for welded structures or components exposed to temperatures between 800–1500°F (427–815°C).
High-Temperature Performance
In applications requiring consistent performance under heat, such as furnace parts or heat exchangers, 347 outshines 304. Its enhanced creep resistance ensures durability and stability in environments where 304 may lose strength over time.
Cost Considerations
While 304 is more economical, the added cost of 347 is often justified for critical applications. For example, industries that rely on heat-intensive processes or frequent welding benefit from the long-term reliability of 347, reducing maintenance and replacement costs.
Key Differences
The main distinction between 347 and 316 lies in their resistance to specific types of corrosion and their high-temperature performance. 316 contains molybdenum, which provides excellent resistance to pitting and crevice corrosion in chloride-rich environments, such as seawater. Meanwhile, 347 excels in high-temperature stability and intergranular corrosion resistance.
Application Suitability
For marine settings or environments with high chloride exposure, 316 is the preferred choice. However, for applications involving sustained high temperatures, such as aerospace components or chemical reactors, 347 is the better option due to its superior thermal stability.
Overview of 4140
4140 is a chromium-molybdenum low-alloy steel primarily used for its strength and toughness in mechanical applications. It is commonly found in gears, shafts, and heavy-duty machinery, where its high strength-to-weight ratio is essential.
Corrosion Resistance
Unlike 347, 4140 lacks inherent corrosion resistance. While suitable for dry or controlled environments, it is not ideal for conditions involving moisture, chemicals, or high humidity. In contrast, 347 thrives in such environments, offering long-term resistance to rust and oxidation.
Strength and Toughness
4140’s mechanical strength makes it a go-to material for applications like crankshafts and hydraulic cylinders. However, it cannot withstand high temperatures or corrosive environments like 347, limiting its use in industries such as chemical processing or aerospace.
347 stainless steel stands out for its exceptional high-temperature stability, intergranular corrosion resistance, and overall durability. Compared to 321 and 304, it offers better long-term performance under heat and stress. While 316 is better suited for chloride-rich environments, 347 excels in applications requiring consistent strength and reliability at elevated temperatures. Finally, while 4140 is unmatched in mechanical strength, it lacks the corrosion resistance and thermal stability that make 347 indispensable in industries like aerospace, chemical processing, and power generation.
The aerospace industry depends on 347 stainless steel for its unmatched strength and resilience in extreme thermal conditions. With components routinely exposed to high temperatures and intense stress, this alloy ensures safety and durability where failure is not an option. Its resistance to oxidation and thermal fatigue makes it a preferred material for critical parts such as exhaust manifolds, jet engine components, and high-temperature ducts. Additionally, its excellent weldability enables the creation of intricate structures essential for lightweight yet robust aerospace designs.
While aerospace applications demand thermal resilience, the chemical processing industry values 347 stainless steel for its exceptional ability to withstand corrosive environments. Niobium stabilization prevents carbide precipitation, making the alloy highly resistant to aggressive chemicals such as acids and oxidizing agents. This unique property ensures the longevity of vital equipment like reactor vessels, heat exchangers, and distillation columns. By offering reliable performance in the face of harsh chemical exposure, 347 stainless steel reduces maintenance needs and enhances operational efficiency.
In the food processing sector, where hygiene and durability are critical, 347 stainless steel stands out as an ideal choice. It resists corrosion caused by frequent cleaning cycles and exposure to food acids, ensuring the integrity of cookers, drying equipment, and storage tanks. The alloy’s non-magnetic properties and ease of cleaning help manufacturers meet strict food safety standards. Whether in high-temperature cooking or low-temperature storage, 347 stainless steel ensures consistent performance, making it indispensable for maintaining quality and safety in food production.
The power generation industry requires materials that can endure prolonged exposure to high pressure and temperature. 347 stainless steel delivers on this demand by resisting creep—the tendency of materials to deform under constant stress—and stress rupture, which refers to failure after extended stress exposure. These properties make it a reliable choice for critical components such as boilers, radiant superheaters, and steam piping. For example, in fossil fuel and nuclear power plants, where consistent performance is paramount, 347 stainless steel ensures uninterrupted energy production and minimizes the risk of costly failures.
Environmental systems, such as pollution control and waste management, benefit significantly from the resilience of 347 stainless steel. Its ability to withstand corrosive gases and harsh chemicals makes it suitable for equipment like waste gas treatment units and flue gas desulfurization systems. By maintaining structural integrity in challenging conditions, the alloy plays a crucial role in reducing environmental impact and supporting sustainability efforts.
In the oil and gas sector, where materials face both high temperatures and corrosive substances, 347 stainless steel provides a dependable solution. It is commonly used in refinery piping, catalytic reformers, and heat exchangers, ensuring the safe and efficient processing of hydrocarbons and other chemicals. The alloy’s resistance to thermal fatigue and oxidation makes it particularly valuable in applications where operational reliability is critical to productivity and safety.
High-performance automotive systems and heavy-duty exhaust applications demand materials that can withstand extreme heat and thermal cycling. 347 stainless steel excels in this role, offering durability and stability in components like catalytic converters and exhaust manifolds. Its ability to maintain performance under intense conditions ensures long-lasting functionality, making it a go-to material for manufacturers aiming to enhance efficiency and reduce emissions.
In pharmaceutical and biotech applications, where cleanliness and chemical resistance are essential, 347 stainless steel proves to be a reliable choice. It resists corrosion from sterilization processes and harsh cleaning agents, ensuring the durability of critical equipment like reactors, mixers, and storage tanks. Its ability to maintain structural integrity under high-temperature steam sterilization further solidifies its role in meeting stringent hygiene and safety requirements in these industries.
From aerospace to pharmaceuticals, 347 stainless steel demonstrates remarkable versatility and reliability. Its unique combination of strength, durability, and resistance to extreme conditions makes it indispensable across a wide range of industries. Whether enabling the safe exploration of the skies or ensuring the purity of life-saving medications, 347 stainless steel continues to set the standard for performance in demanding environments.
Below are answers to some frequently asked questions:
The chemical composition of 347 stainless steel includes a balance of iron as the primary element, with key alloying elements such as 17.0-19.0% chromium, 9.0-13.0% nickel, and a maximum of 0.08% carbon. It also contains up to 2.0% manganese, 1.0% (or 0.75% in some specifications) silicon, 0.045% phosphorus, and 0.030% sulfur. The defining feature of 347 stainless steel is its stabilization with niobium (and tantalum), where the niobium content is at least 10 times the carbon content but does not exceed 1.0%. This stabilization enhances its resistance to intergranular corrosion and improves performance in high-temperature environments.
347 stainless steel is an austenitic chromium-nickel alloy stabilized with niobium, offering excellent resistance to intergranular corrosion by preventing carbide precipitation. It exhibits superior high-temperature stability, maintaining mechanical integrity up to 1500°F (816°C), and demonstrates strong creep and stress rupture properties under prolonged stress. Its corrosion resistance is comparable to 304 stainless steel, with enhanced performance in strongly oxidizing environments and good resistance to chloride-induced stress corrosion. The material is easily weldable using standard techniques without requiring post-weld heat treatment and offers good strength, ductility, and processability, making it suitable for cold working and complex fabrications.
347 stainless steel is typically used in various industries due to its excellent corrosion resistance and high-temperature stability. Key applications include petrochemical and chemical processing equipment, such as reactors and storage tanks, where it withstands high-pressure and corrosive environments. In power generation, it is utilized in high-pressure steam components like heat exchangers and boilers. The aerospace industry employs 347 stainless steel for engine parts and gas turbines due to its performance under high temperatures and pressures. It is also used in food processing equipment for its non-magnetic and corrosion-resistant properties, as well as in environmental equipment for waste gas and solid waste processing. Additionally, 347 stainless steel is found in boiler tubes, heat exchangers, high-temperature steam services, and some household and industrial appliances. Its good intergranular corrosion resistance and high-temperature performance make it suitable for demanding industrial applications.
347 stainless steel differs from 304 and 316 stainless steels primarily in its high-temperature performance and resistance to intergranular corrosion. Stabilized with niobium, 347 resists sensitization, making it ideal for prolonged exposure to elevated temperatures (up to 850°C), such as in aerospace, power generation, and chemical processing applications. In comparison, 304 lacks stabilizing elements, making it more prone to intergranular corrosion at high temperatures, while 316, though offering superior corrosion resistance in environments with chlorides and moisture due to molybdenum, is less stable than 347 under extreme heat. Additionally, 347 offers better creep and stress rupture properties than both 304 and 316, though it requires more careful welding techniques. Each alloy is suited to specific environments, with 347 excelling in high-temperature and corrosive conditions.
For welding 347 stainless steel, TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas) welding processes are recommended due to their precision and ability to maintain weld quality without requiring post-weld heat treatment. Resistance welding is also suitable, providing satisfactory results without special post-weld treatments. It is crucial to use AWS E/ER347 filler metals to match the properties of the base material and reduce the risk of hot cracking. Post-weld heat treatment is generally unnecessary, but if needed, stress relief can be performed between 800°C to 870°C (1470°F to 1600°F) to prevent intergranular corrosion. Avoid oxyacetylene welding as it may lead to carbon pickup, compromising the material’s properties. The niobium content in 347 stainless steel ensures excellent intergranular corrosion resistance, preserving weld integrity and toughness.
347 stainless steel is available in several forms and shapes to meet diverse industrial needs. These include sheets and sheet coils for versatile fabrication processes, plates for applications requiring thicker material, and round bars used in machinery parts and fasteners. It is also available as processed flat bars for specific dimensions, and tubular products like pipes and tubes, which are essential in heat exchangers and high-pressure steam applications. These varied forms make 347 stainless steel adaptable for industries such as petrochemical, power engineering, food processing, aerospace, and environmental equipment.
