As an important metal material, stainless steel plays a key role in many industrial fields. Among the many stainless steel grades, 321 vs 347 stainless steel has attracted much attention due to its unique chemical composition and performance characteristics. This article will compare the performance, characteristics, and application fields of 321 vs 347 stainless steel to help readers better understand these two materials.
Definition of 321 vs 347 Stainless Steel
321 Stainless Steel
321 stainless steel is an austenitic stainless steel alloy that contains titanium as an alloying element. This addition of titanium enhances its resistance to intergranular corrosion, particularly during welding and high-temperature operations. Due to its improved corrosion resistance at elevated temperatures, 321 stainless steel is often employed in applications such as exhaust systems, jet engine components, and high-temperature chemical processing.
347 Stainless Steel
347 stainless steel is a type of austenitic stainless steel that is characterized by its composition and specific properties. It is part of the 300 series stainless steels, which are known for their corrosion resistance, durability, and heat resistance. The distinctive feature of 347 stainless steel is the addition of the element niobium (Nb), also known as columbium, in its composition. This element plays a significant role in enhancing the steel’s performance, particularly in high-temperature and corrosive environments.
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321 vs 347 Stainless Steel – What’s the Difference
Chemical Composition of 347, 321
| Element | Grade 347 Stainless Steel | Grade 321 Stainless Steel |
|---|---|---|
| C | 0.08 | 0.08 |
| Mn | 2.00 | 2.00 |
| Si | 0.75 | 0.75 |
| P | 0.045 | 0.045 |
| S | 0.030 | 0.030 |
| Cr | 17.0-19.0 | 17.00 – 19.00 |
| Ni | 9.0-13.0 | 9.00 – 12.00 |
| Mo | – | – |
| N | – | 0.1 |
Both 347 and 321 stainless steels are part of the austenitic stainless steel family and share many similarities in their chemical compositions. The key differences lie in the additional elements present in each grade. In 347 stainless steel, the addition of niobium improves its resistance to intergranular corrosion and sensitization in high-temperature environments. In 321 stainless steel, the addition of titanium aids in preventing carbide precipitation during welding, reducing the risk of intergranular corrosion.
These slight variations in composition give each stainless steel grade its distinct properties and advantages for specific applications.
Physical Properties of 321 vs 347 Stainless Steel:
| Physical Property | 321 Stainless Steel | 347 Stainless Steel |
|---|---|---|
| Density (g/cm³) | 7.93 | 7.96 |
| Melting Point (°C) | Approx. 1400 | Approx. 1400 |
| Coefficient of Thermal Expansion | 16.5 x 10^-6 /°C | 16.5 x 10^-6 /°C |
| Thermal Conductivity (W/m·K) | 16.3 (100°C) / 21.5 (500°C) | 16.3 (100°C) / 21.5 (500°C) |
| Young’s Modulus (GPa) | 193 | 193 |
| Electrical Resistivity (μΩ·cm) | 72 (20°C) / 86 (500°C) | 72 (20°C) / 86 (500°C) |
In summary, 321 and 347 stainless steels share many similar physical properties due to their common austenitic stainless steel nature. These properties contribute to their overall performance in various applications, especially in high-temperature and corrosive environments.
Mechanical Properties of 321 vs 347 Stainless Steel:
| Mechanical Property | 321 Stainless Steel | 347 Stainless Steel |
|---|---|---|
| Tensile Strength (MPa) | 515 – 730 | 515 – 655 |
| Yield Strength (0.2% offset) (MPa) | ≥205 | ≥205 |
| Elongation (%) | ≥40 | ≥40 |
| Hardness (Brinell HB) | ≤217 (Annealed) | ≤217 (Annealed) |
These mechanical property comparisons highlight the similarity between 321 and 347 stainless steels in terms of their mechanical performance. Both grades have comparable tensile strength, yield strength, elongation, and hardness, which can be attributed to their common austenitic stainless steel structure. These properties make them suitable for various applications, particularly those requiring good strength, ductility, and resistance to deformation.
Advantage of 321 vs 347 Stainless Steel:
Advantages of 321 Stainless Steel:
- Intergranular Corrosion Resistance: The addition of titanium in 321 stainless steel reduces the risk of intergranular corrosion and sensitization during high-temperature operations. This makes it well-suited for applications involving welding and exposure to corrosive environments.
- High-Temperature Performance: 321 stainless steel offers excellent high-temperature oxidation resistance, making it suitable for applications such as heat exchangers, furnace components, and exhaust systems.
- Weldability: The titanium-stabilized composition of 321 stainless steel prevents the formation of harmful carbides during welding, reducing the likelihood of weld decay and sensitization.
- Formability and Ductility: 321 stainless steel retains good formability and ductility even after exposure to elevated temperatures, making it suitable for forming and bending processes.
- Food Processing Industry: Due to its resistance to corrosion and low carbon content, 321 stainless steel is used in equipment for the food and beverage industry.
Advantages of 347 Stainless Steel:
- Intergranular Corrosion Resistance: The addition of niobium in 347 stainless steel provides excellent resistance to intergranular corrosion, particularly in high-temperature applications.
- High-Temperature Performance: Like 321 stainless steel, 347 stainless steel maintains its strength and corrosion resistance at elevated temperatures, making it suitable for high-temperature equipment and components.
- Weldability: The niobium content in 347 stainless steel aids in preventing carbide precipitation during welding, reducing the risk of sensitization and intergranular corrosion.
- Chemical Processing: The corrosion resistance and high-temperature stability of 347 stainless steel make it well-suited for use in chemical processing equipment and applications involving corrosive chemicals.
- Aerospace Industry: The combination of high-temperature resistance and corrosion resistance makes 347 stainless steel a suitable choice for aerospace components subjected to demanding conditions.
Both 321 and 347 stainless steels offer advantages in specific applications. While they share many similarities due to their austenitic nature, their unique alloying elements provide targeted benefits in different scenarios. When selecting between these grades, considering the specific environment, temperature, and performance requirements is crucial to making the optimal choice for a given application.
Application of 321 vs 347 Stainless Steel
Applications of 321 Stainless Steel:
- High-Temperature Equipment: 321 stainless steel’s high-temperature oxidation resistance makes it suitable for manufacturing equipment used in high-temperature environments, such as heat exchangers, furnace parts, and exhaust systems.
- Aircraft Exhaust Systems: The combination of heat resistance and corrosion resistance makes 321 stainless steel a preferred choice for aircraft exhaust systems, where it can withstand the high temperatures and corrosive gases produced during flight.
- Food Processing Equipment: 321 stainless steel’s corrosion resistance and low carbon content make it suitable for equipment used in the food processing industry, where hygiene and resistance to corrosive foods are critical.
- Chemical Processing: Its resistance to chemicals and high temperatures allows 321 stainless steel to be used in various chemical processing applications, including reactors, storage tanks, and pipes.
- Power Generation: 321 stainless steel is utilized in power plants for components exposed to high-temperature steam and gases, such as superheaters and reheaters.
Applications of 347 Stainless Steel:
- Chemical Processing Equipment: The excellent corrosion resistance of 347 stainless steel in high-temperature, corrosive environments makes it suitable for equipment used in chemical processing, including reactors, heat exchangers, and pipelines.
- High-Temperature Piping: 347 stainless steel’s ability to maintain its properties in high-temperature conditions makes it suitable for piping and tubing used in various industries, including petrochemical and power generation.
- Aerospace Industry: 347 stainless steel’s resistance to intergranular corrosion and high-temperature stability make it suitable for aerospace components such as rocket engine parts, where both corrosion resistance and high-temperature performance are critical.
- Automotive Exhaust Systems: Similar to 321 stainless steel, 347 stainless steel can be used in automotive exhaust systems to withstand the high temperatures and corrosive gases generated by internal combustion engines.
- Oil and Gas Industry: 347 stainless steel’s resistance to corrosion and high temperatures makes it a viable choice for components used in the oil and gas industry, including pipelines and processing equipment.
In both cases, the choice between 321 and 347 stainless steel depends on the specific requirements of the application, including the operating temperature, exposure to corrosive environments, and mechanical properties needed for the components. Careful consideration of these factors ensures that the chosen stainless steel grade performs optimally and meets the demands of the intended application.