When it comes to choosing stainless steel grade, it is very crucial to understand the differences between similar metals. The two most popular types are 321 vs 316 stainless steel. So, what makes them different? Let’s find out the pros and cons!
316 vs 321 stainless steel have different properties, which is why both have their unique applications. In this article, we will look at the main differences between 316 and 321 in terms of chemical composition, properties, and specific environments to help users make a good choice of the right stainless steel material.
316 Stainless Steel
Grade 316 stainless steel, also known as AISI 316 or UNS S31600, is an austenitic stainless steel with a higher molybdenum content than 304 stainless steel. This additional molybdenum enhances corrosion resistance, especially against chlorides and other aggressive environments.
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.
In summary, 316 stainless steel offers general corrosion resistance and versatility, while 321 stainless steel provides enhanced resistance to intergranular corrosion and is well-suited for high-temperature environments.
321 vs 316 Stainless Steel – What’s the Difference
316 SS is an austenitic stainless steel with higher nickel and molybdenum content compared to 321 stainless, which gives it excellent corrosion resistance even in chlorine environments, which is why it is best suited for marine applications. 321 stainless steel, in addition to its nickel and molybdenum content, also has titanium stabilization, which makes it suitable for high-temperature applications. 321 stainless steel does not allow chromium carbide precipitation during welding, thus preventing intergranular corrosion.
| Feature | 316 Stainless Steel | 321 Stainless Steel |
|---|---|---|
| Core Advantage | Excellent corrosion resistance, especially against chlorides | Excellent high-temperature resistance and resistance to intergranular corrosion |
| Key Alloying Element | Molybdenum | Titanium |
| Best Working Environment | Marine environments, chemical processing, and food processing | High-temperature environments (425–850°C), such as exhaust systems and furnace parts |
| Weldability | Good, but thick sections may require post-weld annealing | Excellent, typically no post-weld heat treatment needed |
| Cost & Versatility | Usually higher (due to expensive molybdenum and nickel) | Usually lower (compared to 316) |
The Equivalents of 321 and 316 Stainless Steel:
| GB/T | 321 | 316 |
|---|---|---|
| ASTM/UNS | 321 / S32100 | 316 / S31600 |
| EN | X6CrNiTi18-10 (1.4541) | X5CrNiMo17-12-2 (1.4401) |
| JIS | SUS 321 | SUS 316 |
| GOST | 08Х18Н10Т | 03Х17Н14М3 |
Chemical Composition of 321 vs 316 Stainless Steel
| Element | Grade 316 Stainless Steel | Grade 321 Stainless Steel |
|---|---|---|
| C | 0.08 max | 0.08 max |
| Mn | 2.00 max | 2.00 max |
| Si | 0.75 max | 0.75 max |
| P | 0.045 max | 0.045 max |
| S | 0.030 max | 0.030 max |
| Cr | 16.00 – 18.00 | 17.00 – 19.00 |
| Ni | 10.00 – 14.00 | 9.00 – 12.00 |
| Mo | 2.00 – 3.00 | – |
| Ti | – | 5 * C – 0.70 |
Physical Properties of 321 vs 316 Stainless Steel:
| Property | Grade 316 | Grade 321 |
|---|---|---|
| Density (g/cm³) | 7.98 | 7.92 |
| Melting Point (°C) | 1398 – 1420 | 1398 – 1420 |
| Specific Heat (J/kg·K) | 500 | 500 |
| Thermal Conductivity (W/m·K) | 16.2 | 16.3 |
| Electrical Resistivity (µΩ·m) | 740 | 720 |
| Modulus of Elasticity (GPa) | 193 | 193 |
| Poisson’s Ratio | 0.3 | 0.3 |
| Thermal Expansion (10^-6/K) | 16.5 – 16.7 | 16.5 – 16.9 |
Mechanical Properties of 321 vs 316 Stainless Steel:
| Property | Grade 316 | Grade 321 |
|---|---|---|
| Tensile Strength (MPa) | 515 – 690 | 515 – 850 |
| Yield Strength (0.2% offset) (MPa) | 205 – 260 | 205 – 230 |
| Elongation (%) | 30 – 40 | 35 – 40 |
| Hardness (Brinell HB) | ≤ 217 | ≤ 217 |
Advantages of 321 vs 316 Stainless Steel
Stainless steel grades 321 and 316 both have their advantages and are suited for different applications. Here are some advantages of grade 321 stainless steel compared to grade 316:
- High-Temperature Stability: Grade 321 stainless steel contains titanium as a stabilizing element, which helps prevent sensitization and grain boundary carbide precipitation during high-temperature exposure. This makes it more suitable for applications involving extended exposure to elevated temperatures, such as in heat exchangers and furnace components.
- Weldability: Grade 321 stainless steel has better weldability compared to 316 due to its titanium content. The titanium forms stable carbides, preventing chromium depletion at the grain boundaries during welding. This minimizes the risk of sensitization and intergranular corrosion after welding.
- Resistance to Intergranular Corrosion: The titanium content in grade 321 also contributes to its improved resistance to intergranular corrosion, especially after welding or exposure to high temperatures. This is important in applications where corrosion resistance is crucial.
- Aerospace and Jet Engine Applications: Grade 321 stainless steel is often used in aerospace and jet engine applications due to its ability to withstand high temperatures and resist corrosion in these demanding environments.
- Cost-Efficiency: Grade 321 is generally less expensive than 316 stainless steel due to its lower nickel content. This can make it a more cost-effective option for certain applications while still providing good corrosion resistance and high-temperature capabilities.
- It’s important to note that the choice between these two grades depends on the specific requirements of the application. While grade 321 has its advantages, grade 316 also offers excellent corrosion resistance and is widely used in various industries, including marine, chemical, and medical, where its performance characteristics are well-suited. The decision should be based on factors such as temperature exposure, corrosion environment, fabrication requirements, and budget considerations.
The Disadvantage of 321 vs 316 Stainless Steel
While stainless steel grade 321 has its advantages, it also has some disadvantages compared to grade 316. Here are a few of the potential disadvantages of grade 321 stainless steel:
- Lower Corrosion Resistance: Grade 316 stainless steel generally offers better overall corrosion resistance compared to grade 321. Grade 316 contains a higher amount of molybdenum, which enhances its resistance to various corrosive environments, including chloride-containing environments such as seawater.
- Reduced Strength at Elevated Temperatures: While grade 321 is designed for high-temperature applications, its mechanical properties, such as tensile strength and yield strength, may be somewhat reduced at elevated temperatures compared to grade 316. This can impact its performance in certain high-stress applications.
- Limited Cold Workability: Grade 321 stainless steel can be less easily cold-worked compared to grade 316. The presence of titanium in grade 321 can lead to increased strain hardening and reduced ductility during cold-forming processes.
- Sensitization at Extreme Temperatures: Although grade 321 is designed to resist sensitization, extreme temperatures or prolonged exposure to certain aggressive environments can still lead to sensitization and subsequent intergranular corrosion. While grade 316 is also susceptible to sensitization, its molybdenum content provides enhanced resistance in this regard.
- Potential for Titanium Nitride Precipitation: In certain environments, titanium nitride precipitation can occur on the surface of grade 321 stainless steel, affecting its appearance. This phenomenon is less likely to occur in grade 316 stainless steel.
- Limited Availability: Grade 321 stainless steel might be less commonly available compared to grade 316, depending on the region and specific suppliers. This can affect the ease of sourcing and lead times.
- It’s important to consider these potential disadvantages in the context of your specific application requirements. Both grade 316 and grade 321 have their strengths and weaknesses, and the choice between them should be based on factors such as corrosion environment, temperature exposure, mechanical properties needed, fabrication considerations, and budget constraints.
Rust Resistance: 321 vs 316 Stainless Steel
321 Stainless Steel: Good rust resistance, but not ideal for marine or high-salt environments.
316 Stainless Steel: Superior rust resistance, especially suited for marine and salt-exposed conditions.
Strength: 321 vs 316 Stainless Steel
321 Stainless Steel: High strength, performs well in high-temperature environments.
316 Stainless Steel: Strong, but its strength decreases at elevated temperatures.
Toughness:
321 Stainless Steel: Good toughness, with stable performance even at low temperatures.
316 Stainless Steel: Excellent toughness, especially in cryogenic (low-temperature) environments.
Heat Resistance:
321 Stainless Steel: Ideal for continuous service in temperatures between 870-925°C.
316 Stainless Steel: Can withstand temperatures up to 870°C, but is not as suitable for prolonged high-heat exposure.
Corrosion Resistance:
321 Stainless Steel: Great resistance to intergranular corrosion but less resistant in acidic or high-salt environments.
316 Stainless Steel: Enhanced corrosion resistance due to molybdenum (Mo), making it perfect for chemical and marine environments.
Fabrication and Welding:
321 Stainless Steel: Good weldability, but careful control of heat zones is required to prevent sensitization and intergranular corrosion.
316 Stainless Steel: Excellent weldability, maintaining corrosion resistance even without post-weld annealing.
Cost of 321 vs 316 Stainless Steel:
Grade 321 Stainless Steel: More cost-effective, ideal for applications with high-temperature demands on a budget.
Grade 316 Stainless Steel: Slightly more expensive due to molybdenum content, better suited for highly corrosive environments.
Magnetism:
Grade 321 Stainless Steel: Non-magnetic, even after cold working.
Grade 316 Stainless Steel: Typically non-magnetic, though cold working may induce slight magnetism.
Which Stainless Steel is Better 316 or 321?
The choice between 321 stainless steel and 316 stainless steel depends mainly on the specific application and environmental conditions. There is no absolute one is better than another.
If you prioritize heat resistance and weld stability, choose 321 stainless steel. If you are concerned about corrosion resistance in chemical or saltwater environments, 316 stainless steel will be a better fit for you.
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