Both 304 and 321 stainless steels are widely used austenitic grades, yet they differ significantly in composition, properties, and suitable applications. The key distinctions can be summarized across five dimensions:
1. Chemical Composition
304 stainless steel typically contains about 18% chromium (Cr) and 8% nickel (Ni), with a maximum carbon content of ≤0.08%.
321 stainless steel builds on the 304 stainless steel composition by adding titanium (Ti) in the range of 0.3–0.7%. The titanium forms stable TiC compounds, which significantly enhance the material's resistance to intergranular corrosion, especially within the sensitization temperature range of 450–850°C, by inhibiting chromium carbide precipitation.
2. High-Temperature Performance
304 stainless steel can be used continuously up to approximately 870°C, with short-term exposure tolerance around 925°C. However, it is susceptible to sensitization-intergranular corrosion-when held within certain temperature ranges.
321 stainless steel offers superior high-temperature stability due to titanium stabilization, allowing reliable long-term service up to 800°C with notably better resistance to intergranular attack than 304.
3. Mechanical Properties: Room Temperature vs. Elevated Temperature
At room temperature, both grades show similar strength:
304: Yield strength ~205 MPa, tensile strength ~515 MPa, elongation ~40%
321: Yield strength ~220 MPa, tensile strength ~520 MPa, elongation ~35%
At elevated temperatures (e.g., 500°C), 321 stainless steel maintains approximately 15% higher strength retention compared to 304, making it more suitable for load-bearing applications under prolonged heating.
4. Fabrication and Welding
304 stainless steel offers good cold workability and is easily formed by stamping, bending, etc. Welding is commonly performed using 308L-type filler metals.
For 321 stainless steel, welding requires strict control of interpass temperature (recommended <150°C) and the use of titanium-stabilized filler metals such as Type 347 to prevent intergranular corrosion in the heat-affected zone. Its higher work-hardening rate may necessitate intermediate annealing during deep drawing operations.
5. Typical Applications
304 stainless steel is widely used for food processing equipment, chemical tanks, architectural trim, and household products due to its balanced corrosion resistance and cost-effectiveness.
321 stainless steel is preferred for continuous high-temperature service, such as in petrochemical cracking tubes, aero-engine components, heat exchangers, and boiler parts that operate long-term between 500–800°C.
FAQ
Q: Is 304 or 321 stainless steel better?
It depends on the temperature. For applications under 450°C, 304 is more cost-effective. For prolonged use above 500°C or in thermal cycling, 321 performs better due to its titanium content.
Q: What is 321 stainless steel equivalent to?
The main international standards are UNS S32100 (US), EN 1.4541 (Europe), and AISI 321. Its composition is similar to 304 but stabilized with titanium.
Q: What is 321 stainless steel used for?
It is primarily used in high-temperature applications such as exhaust systems, heat exchangers, furnace parts, boiler components, and welded equipment operating above 500°C.
Cost and Selection Guidelines
Current market pricing generally places 304 stainless steel in the range of $1,650–2,500 per metric ton, while 321 stainless steel commands a 15–20% premium (approximately $1,900–3,000 per metric ton) due to the titanium addition.
Selection should follow a temperature-first approach:
- For continuous service below 450°C, 304 offers a cost-effective and reliable solution.
- For prolonged operation above 500°C, especially under thermal cycling or corrosive conditions, 321 should be specified to ensure long-term structural integrity and safety.
We specialize in supplying 304 and 321 stainless steel, offering custom processing and delivery services. For further material inquiries or sample requests, please feel free to contact us anytime.
WhatsApp: +8613572553287
Email: baohui@bhsteelpipe.com
