321 vs 316L Stainless Steel: What’s the Difference?

When it comes to choosing the right stainless steel for demanding applications, small differences in material properties can lead to big impacts on performance, durability, and cost. Two popular contenders—321 and 316L stainless steel—are often compared for their unique strengths, particularly in industries like aerospace, chemical processing, and marine engineering. But how do they really stack up? From corrosion resistance to heat tolerance, and even down to cost-effectiveness, these alloys bring distinct advantages to the table.

In this article, we’ll dive into their chemical compositions, performance in high-temperature and corrosive environments, and suitability for various industrial uses. Whether you’re looking for optimal resistance in harsh conditions or a budget-friendly solution for your next project, understanding the differences between 321 and 316L stainless steel will help you make an informed choice. So, which one is better suited for your needs? Let’s find out.

Chemical Composition Comparison

Overview of 321 Stainless Steel Composition

321 stainless steel is an austenitic alloy known for its resistance to oxidation and corrosion, primarily due to its chromium content of 17-19%. The alloy also contains 9-12% nickel, which enhances its toughness and high-temperature performance. A distinctive feature of 321 stainless steel is the addition of 0.3-0.7% titanium. This element stabilizes the alloy and prevents carbide precipitation during welding or high-temperature exposure. Other elements include a maximum of 0.08% carbon, up to 2.0% manganese, up to 1.0% silicon, and a maximum of 0.030% sulfur.

Overview of 316L Stainless Steel Composition

316L stainless steel is another austenitic alloy known for its high corrosion resistance. This alloy contains 16-18% chromium and 10-14% nickel, providing strong resistance to oxidation and maintaining strength at high temperatures. One of the key differentiators of 316L stainless steel is its molybdenum content (2-3%), which significantly enhances its resistance to pitting and crevice corrosion, particularly in chloride-rich environments. Like 321, 316L also contains a maximum of 0.08% carbon, up to 2.0% manganese, up to 1.0% silicon, and a maximum of 0.030% sulfur.

Key Differences in Chemical Makeup

Molybdenum Content

316L stainless steel includes 2-3% molybdenum, which enhances its resistance to pitting and crevice corrosion, especially in environments with high chloride levels. In contrast, 321 stainless steel does not contain molybdenum, which limits its effectiveness in such corrosive settings.

Titanium Addition

Titanium in 321 stainless steel prevents chromium carbide formation during welding or high-temperature use, reducing the risk of intergranular corrosion. This makes 321 stainless steel particularly suitable for applications involving prolonged exposure to high temperatures, such as in aerospace components or industrial exhaust systems.

Chromium and Nickel Content

While both alloys contain chromium and nickel, their proportions differ slightly. 321 stainless steel has a slightly higher chromium content (17-19% compared to 16-18% in 316L) and a lower nickel content (9-12% compared to 10-14% in 316L). These variations affect their mechanical properties and corrosion resistance differently.

Impact on Material Properties

Corrosion Resistance

The molybdenum in 316L stainless steel offers excellent resistance to corrosion in chloride-rich environments. This makes it ideal for marine and chemical processing applications. Conversely, the titanium stabilization in 321 stainless steel offers robust resistance to intergranular corrosion, particularly in high-temperature environments.

High-Temperature Stability

321 stainless steel’s titanium content enhances its stability and resistance to carbide precipitation at high temperatures. This makes it an excellent choice for applications that involve continuous exposure to temperatures up to 900°C, such as in aerospace and heat exchanger components. On the other hand, while 316L also performs well at elevated temperatures, it is not as stable as 321 in such conditions due to the lack of titanium.

Weldability

The addition of titanium in 321 stainless steel also improves its weldability. It prevents carbide precipitation during welding, maintaining the alloy’s strength and corrosion resistance. 316L stainless steel, although also weldable, may require post-weld annealing to avoid sensitization and maintain its corrosion resistance.

Corrosion Resistance in Different Environments

Corrosion Resistance in General Environments

316L stainless steel is well-known for its excellent corrosion resistance, especially in chloride-rich environments. The 2-3% molybdenum content significantly enhances its resistance to pitting and crevice corrosion, making it ideal for marine and chemical processing applications where it maintains integrity even in harsh, salty conditions.

321 stainless steel also provides strong corrosion resistance, though it lacks molybdenum. Titanium in 321 stainless steel stabilizes the alloy and prevents intergranular corrosion, especially useful in high-temperature applications. While 321 may not match 316L’s performance in chloride-rich environments, its high-temperature stability makes it a reliable choice for specific use cases.

Specific Environmental Performance

Chloride-Rich Environments

• 316L Stainless Steel: With its molybdenum content, 316L demonstrates exceptional resistance to chloride-induced corrosion, including pitting and crevice corrosion. This makes it highly effective in environments like seawater exposure and chemical plants, where chloride levels can compromise other materials.
• 321 Stainless Steel: While resistant to general corrosion, 321 is less effective in chloride-rich environments due to the absence of molybdenum. It is better suited for applications where high temperatures take precedence over exposure to chlorides.

High-Temperature Environments

• 316L Stainless Steel: Although 316L stainless steel offers good heat resistance, it can experience carbide precipitation at high temperatures, which may reduce its corrosion resistance. This limits its suitability for prolonged exposure to elevated temperatures, though it remains effective in moderately high-temperature conditions.
• 321 Stainless Steel: The titanium content in 321 provides excellent resistance to carbide precipitation, preserving its corrosion resistance even under sustained high-temperature conditions. This makes it an excellent choice for applications such as aerospace components, industrial furnaces, and exhaust systems.

Comparative Analysis

Heat Resistance and High-Temperature Applications

321 stainless steel is engineered for high-temperature environments. Its key attribute lies in its ability to resist oxidation and maintain structural integrity during prolonged exposure to elevated temperatures. The addition of titanium enhances its thermal stability by preventing the formation of chromium carbides at grain boundaries, which can otherwise lead to intergranular corrosion. This characteristic makes 321 stainless steel ideal for demanding applications such as exhaust systems, heat exchangers, and aerospace components.

316L stainless steel, while effective in high-temperature environments, offers slightly different thermal properties. It can withstand continuous temperatures up to 870°C and intermittent exposure up to 925°C. However, due to the absence of stabilizing elements like titanium, 316L is more prone to carbide precipitation at elevated temperatures. This can compromise its corrosion resistance during prolonged high-temperature service. Despite this limitation, 316L remains a reliable choice for applications that prioritize general corrosion resistance, such as chemical processing equipment and marine environments.

Performance Comparison in High-Temperature Applications

Let’s compare the performance of these two types of stainless steel in high-temperature applications:

• Temperature Limits and Thermal Stability:
  321 stainless steel can endure continuous temperatures up to 900°C and intermittent exposure up to 925°C, thanks to its titanium stabilization. This provides enhanced thermal stability, making it suitable for sustained high-temperature applications. In contrast, 316L stainless steel is suitable for continuous use up to 870°C and intermittent exposure up to 925°C but lacks the stabilization benefits of titanium, making it less resistant to carbide formation.
• Structural Integrity and Corrosion Resistance:
  321 stainless steel maintains superior structural integrity and corrosion resistance at elevated temperatures due to its titanium content, which prevents chromium carbide formation. Meanwhile, 316L, though effective in moderate high-temperature conditions, may experience reduced corrosion resistance over time due to carbide precipitation, limiting its use in prolonged high-heat applications.

Application Suitability

321 stainless steel is preferred for high-temperature environments like aerospace components, automotive exhaust systems, and industrial furnaces. Its ability to resist intergranular corrosion and maintain mechanical properties under high heat makes it the material of choice for these applications. On the other hand, 316L stainless steel is better suited for environments emphasizing corrosion resistance, such as marine and chemical processing applications, where its molybdenum content provides added protection against pitting and crevice corrosion.

Thermal Properties Comparison

Here is a comparison of the thermal properties of 316L and 321 stainless steel:

Both materials exhibit similar thermal properties, but their suitability for high-temperature applications is influenced by their composition, particularly the presence of stabilizing elements in 321 stainless steel.

Heat Resistance

Heat resistance is the ability of a material to retain its mechanical properties and resist oxidation when exposed to elevated temperatures. The alloying elements in stainless steel play a crucial role in enhancing or reducing its stability and corrosion resistance under high heat.

Mechanical Properties and Machinability

Strength and Ductility Comparison

The mechanical properties of stainless steel are critical in determining their suitability for various applications. Both 321 and 316L stainless steels exhibit robust mechanical properties but have some differences.

Tensile Strength

• 316L Stainless Steel: 316L stainless steel has a tensile strength of 515 to 690 MPa, making it a durable material capable of handling high stress levels.
• 321 Stainless Steel: The tensile strength ranges from 515 to 850 MPa. This broader range suggests that 321 stainless steel can potentially offer higher strength, making it suitable for applications requiring superior mechanical performance.

Yield Strength

• 316L Stainless Steel: 316L stainless steel’s yield strength ranges from 205 to 260 MPa, which marks the point where it starts to deform permanently.
• 321 Stainless Steel: The yield strength ranges from 205 to 230 MPa. Although slightly lower than the upper limit of 316L, it still provides adequate strength for many applications.

Elongation and Hardness

Both materials have similar elongation at break:

• 316L Stainless Steel: Elongation ranges from 30 to 40%.
• 321 Stainless Steel: Elongation ranges from 35 to 40%.

Both materials have similar Brinell hardness values, up to 217 HB, meaning they can endure significant deformation before breaking and are suitable for engineering applications.

Ease of Fabrication and Machining

Machinability is a key consideration for manufacturers, affecting production efficiency and costs.

Machining Challenges

• 316L Stainless Steel: Known for being tougher to machine due to its higher hardness and strength. This material requires robust machining equipment and techniques, which can increase manufacturing costs.
• 321 Stainless Steel: Slightly easier to machine than 316L but still presents challenges due to its increased strain hardening from the titanium content. Proper machining techniques and equipment are essential to achieve desired results.

Weldability

Weldability is an important factor for applications requiring material joining:

• 316L Stainless Steel: May require post-weld annealing to restore corrosion resistance. This is because the absence of stabilizing elements like titanium can lead to sensitization and reduced resistance to intergranular corrosion.
• 321 Stainless Steel: Offers superior weldability due to its titanium content, which prevents chromium depletion and intergranular corrosion during welding. This makes it a preferred choice for applications requiring extensive welding.

Suitability for Various Engineering and Manufacturing Processes

When selecting materials for specific applications, engineers consider mechanical properties and machinability:

• High-Strength Applications: 321 stainless steel, with its potential for higher tensile strength, is well-suited for high-strength applications such as aerospace components and industrial furnaces.
• Corrosion-Resistant Applications: 316L stainless steel, with its excellent corrosion resistance, is ideal for environments exposed to harsh chemicals or marine conditions, such as chemical processing equipment and marine structures.
• High-Temperature Environments: 321 stainless steel is ideal for high-temperature applications because of its thermal stability and resistance to carbide buildup.

Each material’s unique properties make them suitable for different engineering and manufacturing processes, ensuring optimal performance and longevity in their respective applications.

Cost and Availability Considerations

Cost Considerations

When evaluating the cost of stainless steels, 316L and 321 present distinct differences primarily due to their composition.

316L Stainless Steel

316L stainless steel is generally more expensive than 321 stainless steel. Its higher cost comes from the greater nickel content (10-14%) and the inclusion of 2-3% molybdenum. These elements significantly enhance the alloy’s corrosion resistance, especially in environments with high chloride concentrations, such as marine and chemical processing settings. The premium price reflects the superior corrosion protection and resilience against pitting and crevice corrosion that 316L stainless steel provides.

321 Stainless Steel

321 stainless steel, on the other hand, is more cost-effective. Its lower nickel content (9-12%) and the absence of molybdenum reduce its production costs. Instead, 321 contains titanium (0.3-0.7%), which stabilizes the alloy and prevents carbide precipitation during welding or high-temperature exposure. Although it lacks the same corrosion resistance as 316L, its lower cost makes it a practical choice for applications prioritizing high-temperature stability over corrosion resistance.

Availability Considerations

316L Stainless Steel

316L stainless steel is extensively used across various industries, including marine, chemical processing, food processing, and pharmaceuticals. Its widespread application ensures that 316L is readily available from numerous suppliers globally. This widespread availability simplifies sourcing for both large-scale industrial projects and smaller applications, making 316L a convenient choice for many engineers and manufacturers.

321 Stainless Steel

321 stainless steel, often used in aerospace and automotive industries for its high-temperature performance, may be less widely available than 316L. This is particularly true in regions or industries where high-temperature applications are less prevalent. While it is not as universally available as 316L, it can still be sourced relatively easily in sectors where its specific properties are required.

Key Factors Influencing Choice

Application Requirements

The decision between 316L and 321 stainless steel largely depends on the specific requirements of the application. In environments rich in chlorides, such as marine settings, 316L is preferred due to its enhanced corrosion resistance. Conversely, for high-temperature applications, 321 is more suitable because its titanium content prevents carbide precipitation, maintaining stability and performance.

Budget Constraints

When cost is a concern, 321 stainless steel is often the better choice for high-temperature applications where extreme corrosion resistance isn’t required. Its lower cost can provide substantial savings without compromising the required performance in high-temperature conditions.

Material Properties

Knowing the mechanical and thermal properties of each material is key to making the right choice. Both 316L and 321 have similar tensile strengths, but 321 offers slightly higher strength at high temperatures, making it advantageous for applications involving prolonged heat exposure. Meanwhile, 316L excels in toughness at lower temperatures, which is beneficial for applications where both corrosion resistance and mechanical resilience are critical.

Compliance with Global Standards

Overview of Compliance Standards for 321 and 316L Stainless Steel

Both 321 and 316L stainless steels are highly regarded for their versatility and performance in industrial applications. Their compliance with global standards ensures that they meet stringent requirements for chemical composition, mechanical properties, and corrosion resistance, making them suitable for diverse uses.

Common Standards

• ASTM (American Society for Testing and Materials):
  Both materials adhere to ASTM standards, which define their chemical composition and mechanical properties. 316L corresponds to ASTM/UNS S31603, while 321 aligns with ASTM/UNS S32100. These designations ensure consistency in performance across industries.
• ISO (International Organization for Standardization):
  ISO standards, such as ISO 15510, specify grades for stainless steels based on their chemical makeup. Both 316L and 321 meet ISO requirements, ensuring global usability.
• EN (European Norm):
  In the European market, 316L is classified as EN 1.4404, and 321 is classified as EN 1.4541. These standards ensure compatibility with European engineering specifications.
• JIS (Japanese Industrial Standards):
  For applications in Japan, 316L is identified as SUS316L, and 321 is identified as SUS321. These designations ensure compliance with Japan’s unique industrial requirements.
• GOST (Russian Standards):
  In Russia, 316L is often classified under GOST standards as 03Х17Н13М2, while 321 is recognized as 08Х18Н10Т. These classifications are critical for applications in the Russian market.

Key Differences in Compliance Criteria

Chemical Composition Tolerances

321 stainless steel uses titanium to prevent carbide formation, whereas 316L uses molybdenum to improve corrosion resistance. Compliance standards reflect these differences, with specific tolerances for titanium in 321 and molybdenum in 316L. For example, ASTM standards ensure that 321 contains sufficient titanium to be five times the carbon content, whereas for 316L, the molybdenum content must fall within 2-3%.

Performance Testing Requirements

Standards for 321 stainless steel often include additional requirements for high-temperature performance due to its intended applications in aerospace and industrial furnaces. ASTM and EN standards specify tests for oxidation resistance and mechanical stability at elevated temperatures. These tests are less critical for 316L, which is more often used in moderate-temperature environments.

For 316L stainless steel, compliance involves rigorous testing for pitting and crevice corrosion resistance, particularly in chloride-rich environments. ASTM G48 tests measure how well it performs in harsh chemical environments. For 321 stainless steel, the focus is more on intergranular corrosion resistance, with tests like ASTM A262 ensuring that it performs well in high-temperature, oxidizing conditions.

Industry-Specific Compliance Considerations

Aerospace Industry

321 stainless steel is widely used in aerospace for its high-temperature performance, as specified by AMS 5510 (Aerospace Material Specification). These standards emphasize its ability to withstand prolonged exposure to elevated temperatures without compromising structural integrity.

Marine and Chemical Processing Industries

316L stainless steel is preferred in marine and chemical applications due to its compliance with standards like NACE MR0175, which ensures resistance to stress corrosion cracking in chloride-rich environments. Its molybdenum content is a key factor in meeting these requirements.

Food and Pharmaceutical Industries

316L stainless steel complies with food-grade standards such as FDA (Food and Drug Administration) and 3-A sanitary standards, making it ideal for food processing and pharmaceutical applications. These standards focus on corrosion resistance, ease of cleaning, and non-reactivity with food and drugs.

Material Selection Based on Compliance

When selecting between 321 and 316L, compliance with global standards should align with the operational and environmental demands of the application. For high-temperature applications requiring resistance to intergranular corrosion, 321 stainless steel is often the preferred choice due to its titanium stabilization. Conversely, 316L is better suited for environments with high chloride exposure, thanks to its molybdenum-enhanced corrosion resistance.

Knowing the standards relevant to your industry helps ensure the chosen material meets both performance and regulatory needs.

Applications of 321 and 316L Stainless Steel

Applications of 321 Stainless Steel

321 stainless steel is renowned for its high-temperature stability, making it ideal for applications where prolonged exposure to elevated temperatures is common.

Aerospace Industry

In the aerospace industry, 321 stainless steel is frequently used for components such as jet engine parts, exhaust systems, and high-temperature brackets. Its resistance to oxidation and ability to maintain structural integrity under extreme heat ensure reliability and longevity in critical aerospace applications.

Industrial Furnaces and Heat Exchangers

321 stainless steel, widely used in industrial furnaces and heat exchangers, benefits from titanium content that prevents carbide precipitation and maintains mechanical properties. This makes it suitable for environments where temperatures consistently exceed 800°C.

Chemical Processing Equipment

While not as corrosion-resistant as 316L in chloride-rich environments, 321 stainless steel still finds applications in chemical processing equipment that operate at high temperatures. Its stability and resistance to intergranular corrosion under thermal stress make it a viable option for specific high-temperature chemical processes.

Applications of 316L Stainless Steel

316L stainless steel is prized for its excellent corrosion resistance, particularly in environments with high chloride concentrations.

Marine and Coastal Environments

316L stainless steel is commonly used in marine applications, including boat fittings, dock hardware, and coastal architectural structures. Its molybdenum content significantly enhances resistance to pitting and crevice corrosion caused by saltwater, making it ideal for prolonged exposure to marine environments.

Chemical Processing Industry

In the chemical processing industry, 316L stainless steel is utilized for tanks, piping, and reactor vessels. It withstands corrosive chemicals and maintains integrity in harsh conditions, ensuring safe and efficient operations.

Medical Devices and Equipment

The biocompatibility and corrosion resistance of 316L stainless steel make it ideal for medical implants, surgical instruments, and hospital equipment. It is used in applications where both strength and resistance to body fluids are crucial.

Food and Beverage Industry

The food and beverage industry benefits from 316L stainless steel in equipment such as processing machinery, storage tanks, and kitchen utensils. Its ease of cleaning and resistance to food acids and salts ensure hygiene and longevity.

Comparative Analysis of Applications

When comparing the applications of 321 and 316L stainless steels, several key factors come into play:

• Corrosion Resistance: 316L stainless steel excels in environments with high chloride concentrations, making it ideal for marine and chemical processing applications. In contrast, 321 stainless steel, while still resistant to corrosion, is better suited for high-temperature environments.
• High-Temperature Stability: 321 stainless steel is superior in high-temperature applications due to its titanium stabilization, which prevents carbide precipitation and maintains structural integrity. This makes it the preferred choice for aerospace, industrial furnaces, and heat exchangers.
• Cost-Effectiveness: Generally, 321 stainless steel is more cost-effective than 316L, particularly for high-temperature applications where extreme corrosion resistance is not as critical. For budget-sensitive projects requiring high-temperature performance, 321 offers a practical solution.
• Specific Use Cases: The choice between these materials should be based on specific environmental conditions and operational requirements. For instance, 316L is optimal for marine and chemical processing with its superior corrosion resistance, while 321 excels in applications involving sustained high temperatures.

Each stainless steel variant offers unique advantages that cater to distinct industrial needs, ensuring that engineers and manufacturers can select the best material for their specific applications.

Frequently Asked Questions

Below are answers to some frequently asked questions:

What are the main differences in corrosion resistance between 321 and 316L stainless steel?

The primary differences in corrosion resistance between 321 and 316L stainless steel stem from their distinct chemical compositions.

316L stainless steel contains 2-3% molybdenum, which significantly enhances its resistance to chloride-induced corrosion, making it particularly effective in environments with high chloride concentrations such as marine atmospheres and chemical processing facilities. This molybdenum content helps prevent localized corrosion attacks like pitting and crevice corrosion, which are common in chloride-rich environments.

In contrast, 321 stainless steel lacks molybdenum but includes titanium. While this titanium addition provides excellent resistance to intergranular corrosion and better stability at high temperatures, it does not offer the same level of protection against chloride-induced corrosion as 316L. Consequently, 321 stainless steel is less suitable for environments with high chloride concentrations.

How do 321 and 316L stainless steels perform in high-temperature applications?

321 stainless steel performs exceptionally well in high-temperature applications due to its titanium stabilization, which prevents chromium carbide precipitation. This allows it to maintain strength and resistance to intergranular corrosion at continuous temperatures up to 900°C and intermittent temperatures up to 925°C. It is thus ideal for prolonged high-heat environments such as aerospace components and industrial furnaces.

On the other hand, 316L stainless steel, while also suitable for high-temperature use, excels in applications with intermittent high temperatures, up to 870°C continuously and 925°C intermittently. However, it is less effective for sustained high-heat exposure due to a higher risk of carbide precipitation, which can degrade its corrosion resistance over time. Therefore, 316L is more suitable for environments requiring excellent corrosion resistance, particularly in chloride-rich conditions.

Which stainless steel is more cost-effective for specific industrial applications?

When evaluating cost-effectiveness for specific industrial applications, 321 stainless steel is generally more economical due to its lower nickel content and the absence of molybdenum, which makes it less expensive than 316L. This makes 321 a suitable choice for high-temperature applications like aerospace and automotive industries, where its titanium content provides stability and prevents intergranular corrosion.

On the other hand, 316L stainless steel, with its higher nickel and molybdenum content, offers superior corrosion resistance, particularly in chloride-rich environments such as marine and chemical processing applications. While it may be more expensive, its exceptional corrosion resistance makes it a cost-effective choice in environments where such properties are critical.

Are 321 and 316L stainless steels compliant with global standards like ASTM and ISO?

Yes, both 321 and 316L stainless steels are compliant with major global standards such as ASTM and ISO. For ASTM standards, both are covered under ASTM A240, which specifies requirements for chromium and chromium-nickel stainless steel plate, sheet, and strip for pressure vessels and general applications. Specifically, 316L is often referenced as UNS S31603, and 321 as UNS S32100, ensuring they meet ASTM criteria for chemical composition and mechanical properties.

ISO standards focus on quality management and specific material properties, and both 321 and 316L stainless steels conform to these international standards due to their extensive use and acceptance globally. This compliance guarantees their reliability and performance in various industrial applications, from marine environments to high-temperature scenarios, aligning with global standards for quality and safety.

Which material is better for marine environments?

For marine environments, 316L stainless steel is the better choice compared to 321 stainless steel. The primary reason lies in the chemical composition and corrosion resistance properties of 316L. It contains 2-3% molybdenum, which significantly enhances its resistance to pitting and crevice corrosion in chloride-rich environments like seawater. This makes 316L stainless steel particularly suitable for marine applications where exposure to saltwater can cause severe corrosion issues.

On the other hand, 321 stainless steel lacks molybdenum and instead includes titanium, which stabilizes the material against intergranular corrosion at high temperatures. While 321 offers good general corrosion resistance and better high-temperature stability, it does not perform as well as 316L in chloride-rich conditions.

Therefore, for applications involving marine environments, 316L stainless steel is the preferred material due to its superior corrosion resistance and durability in the presence of chlorides.

How do I choose between 321 and 316L stainless steel for my application?

To choose between 321 and 316L stainless steel for your application, consider the specific environmental conditions, temperature requirements, and mechanical properties needed.

316L stainless steel is ideal for environments with high chloride content, such as marine and chemical processing industries, due to its excellent corrosion resistance enhanced by molybdenum. Its low carbon content minimizes carbide precipitation during welding, making it suitable for applications requiring high weldability and corrosion resistance. This makes 316L a preferred choice for medical devices and food processing equipment.

On the other hand, 321 stainless steel contains titanium, which stabilizes the material against carbide precipitation at high temperatures, making it suitable for high-temperature applications like aerospace and industrial furnaces. It performs well under thermal stress and is ideal for welding-intensive tasks where maintaining strength and corrosion resistance during welding is critical.

In terms of cost, 316L tends to be more expensive due to its higher nickel and molybdenum content, while 321 is generally more cost-effective but less resistant in chloride-rich environments.

Ultimately, if your application involves high temperatures or requires resistance to thermal stress, 321 is the better choice. If corrosion resistance, especially in chloride-rich environments, and weldability are paramount, 316L is more suitable.