The difference between 304 stainless steel and 321 stainless steel
The main difference lies in the addition of titanium to 321 stainless steel, while 304 stainless steel does not. This addition makes 321 stainless steel more suitable for high-temperature applications because it prevents carbide precipitation during welding, which would cause 304 stainless steel to corrode at high temperatures. Both have corrosion resistance, but 321 stainless steel has better high-temperature strength and thermal stability.
What is 321 stainless steel?
Type 321 stainless steel is a stabilized austenitic stainless steel, similar to type 304 stainless steel, but with the addition of titanium. The addition of titanium reduces or prevents carbide precipitation during welding and at high temperatures of 800-1500°F (427-816°C). Furthermore, it improves the alloy's high-temperature properties.
304 Stainless Steel
Composition: Contains approximately 18% chromium and 8% nickel.
Applications: Suitable for general corrosion-resistant applications in a variety of fields, including food processing equipment and general manufacturing.
Limitations: When exposed to high-temperature environments after welding, it is prone to intergranular corrosion ("weld corrosion") due to the formation of chromium carbides.
321 Stainless Steel
Composition: Similar to 304 stainless steel, but with added titanium.
Applications: Specifically designed for high-temperature applications such as boiler components, heat exchangers, and exhaust systems.
Advantages: Titanium preferentially reacts with carbon to form carbides, thus preventing the formation of chromium carbides at grain boundaries, giving it high resistance to intergranular corrosion, especially after welding.
| 304 VS. 321 | 304 Stainless Steel | 321 Stainless Steel |
| Features | Corrosion resistance, good toughness | Abrasion resistance, high temperature resistance, creep resistance |
| Grade | 0Cr18Ni9 (0Cr19Ni9) 06Cr19Ni9 S30408 | X10CrNiTi189 321, S32100, TP321 SUS321 |
| Chemical composition |
C: ≤0.08, Si: ≤1.0, Mn: ≤2.0, Cr: 18.0～20.0, Ni: 8.0～10.5, S: ≤0.03, P: ≤0.035, N≤0.1 |
S: 0.030, Ni: 9.00-12.00, Cr: 17.00-19.00, Ti: 5C-0.70 |
| Tensile strength (Mpa) | 520 | ≥520 |
| Conditional yield strength (MPa) | 205-210 | ≥205 |
| Elongation (%) | 40% | ≥40 |
| Hardness | HB187 HRB90 HV200 | ≤187HB; ≤90HRB; ≤200HV |
| Density | 7.93 g/cm3 | 7.93 g/cm3 |
| Theoretical weight | Weight (kg) = thickness (mm) * width (m) * length (m) * density value | Weight (kg) = thickness (mm) * width (m) * length (m) * density value |
| Uses |
Tableware, cabinets, indoor pipelines, water heaters, boilers, bathtubs, auto parts, medical appliances, building materials, chemicals, food industry, agriculture, and ship parts. |
Outdoor machines for the chemical, coal, and petroleum industries. |
Temperature Resistance
| Property | 304 Stainless Steel | 321 Stainless Steel |
|---|---|---|
| Maximum Continuous Use Temp | ~870°C | ~925°C |
| Thermal Stability | Moderate | High (improved resistance to intergranular corrosion) |
Mechanical and Corrosion Properties
| Property | 304 SS | 321 SS |
|---|---|---|
| Tensile Strength | ~515 MPa | ~505 MPa |
| Elongation | ≥ 40% | ≥ 40% |
| Corrosion Resistance | Excellent in most environments | Similar to 304, but better at high temps |
Applications Comparison
| Application | 304 Stainless Steel | 321 Stainless Steel |
|---|---|---|
| Food Processing Equipment | ✓ | ✓ (less common) |
| Chemical Containers | ✓ | ✓ |
| Heat Exchangers / Boilers | ✗ (limited by temp) | ✓ |
| Jet Engine Parts / Exhausts | ✗ | ✓ (preferred) |
| Welding Environments | ✓ | ✓ (preferred if post-weld heat is high) |
