Stainless steel 321, also known as SS 321 alloy, is a heat-resistant austenitic stainless steel stabilized with titanium. It was developed to combat the problem of intergranular corrosion after exposure to temperatures in the chromium carbide precipitation range of 427–816 °C (800–1500 °F). Known for its excellent corrosion resistance, good mechanical strength, and superior resistance to oxidation at elevated temperatures, SS 321 is widely used in high-temperature industrial applications.
The alloy is a modified version of Type 304 stainless steel, with the addition of titanium (Ti) as a stabilizing element. The titanium forms stable carbides, preventing chromium depletion in the heat-affected zones, which makes 321 stainless steel sheet suitable for continuous use in the 538–870 °C (1000–1600 °F) range.
In industries such as aerospace, petrochemical, power generation, heat treatment, and food processing, 321 stainless steelis a material of choice when consistent performance under high heat is essential.
2. Chemical Composition of SS 321 Alloy
The chemical composition of SS 321 alloy is carefully controlled to ensure long-term durability and heat resistance.
Role of Titanium
Titanium is crucial in SS 321 stainless steel. It reacts with carbon to form titanium carbides, preventing chromium carbides from forming. This ensures that chromium remains in solid solution and available to form a passive oxide layer for corrosion resistance.
3. Mechanical Properties of 321 Stainless Steel Sheet
The mechanical performance of 321 stainless steel sheet is excellent across a range of temperatures.
321 SS maintains these properties even at elevated temperatures, making it ideal for furnace components, exhaust systems, and heat shields.
321 SS maintains these properties even at elevated temperatures, making it ideal for furnace components, exhaust systems, and heat shields.
4. Corrosion Resistance of Heat-Resistant SS 321
General Corrosion Resistance
The corrosion resistance of austenitic stainless steel 321 is similar to 304 stainless steel, with improved performance in high-temperature and oxidizing environments.
Intergranular Corrosion Resistance
Unlike 304 stainless steel, 321 is not prone to intergranular corrosion after exposure to high temperatures due to titanium stabilization.
Oxidation Resistance
SS 321 alloy resists oxidation up to 870 °C (1600 °F) in continuous service and up to 925 °C (1700 °F) in intermittent service. This makes it suitable for:
- Thermal oxidizers
- Furnace muffles
- Exhaust manifolds
5. Physical Properties of 321 Stainless Steel
6. Fabrication & Welding of 321 Stainless Steel Sheet
321 stainless steel sheet can be fabricated by standard methods used for other austenitic stainless steels:
Cold Working
- High ductility allows for deep drawing and cold bending.
- Work hardens rapidly, requiring intermediate annealing.
Hot Working
- Forging temperature: 1149–1260 °C (2100–2300 °F)
- Rapid cooling after hot working to avoid sensitization.
Welding
- TIG and MIG welding are commonly used.
- Use filler metal ER321 or ER347 to maintain corrosion resistance.
- Post-weld annealing not typically required unless in highly corrosive environments.
7. Applications of SS 321 Alloy
Thanks to its excellent mechanical properties and heat resistance, SS 321 alloy is found in many demanding industries:
Aerospace Industry
- Jet engine parts
- Exhaust ducts
- Firewalls
Chemical & Petrochemical Processing
- Heat exchangers
- Reactors
- Pressure vessels
Power Generation
- Superheater and reheater tubes
- Boiler baffles
- Ducting
Automotive
- Manifolds
- Mufflers
- Turbocharger components
Food & Beverage Industry
- Brewery equipment
- Pasteurization lines
- Commercial ovens
Architectural Uses
- Wall cladding
- Elevator panels
- Railings (No. 4 or BA finish)
8. Available Forms: 321 Stainless Steel Sheet and More
321 stainless steel is available in multiple product forms:
Sheet and Coil
- Thickness: 0.4 mm – 6 mm
- Width: Up to 1500 mm
- Finish: 2B, BA, No.4, No.1
Plate
- Thickness: 6 mm and above
- Used in heavy structural and high-pressure equipment
Bar, Rod, Wire
- For machining and welding consumables
Pipe and Tube
- Seamless and welded options for heat-exchange and chemical industries
9. Surface Finishes of 321 Stainless Steel Sheet
The most popular finishes include:
10. 321 vs. Other Stainless Steels
11. Standards & Specifications
321 stainless steel conforms to several global standards:
- ASTM A240: Plate, sheet, and strip for pressure vessels
- AMS 5510/5512: Aerospace-grade sheet and strip
- EN 1.4541: European designation
- ISO 15510: Stainless steel grades
- UNS S32100: Unified Numbering System code
Conclusion
Stainless steel is 100% recyclable. SS 321 alloy maintains its performance over decades, reducing replacement frequency. Most suppliers offer 60–90% recycled content in new 321 stainless steel sheet products.
