321 vs 304 Stainless Steel: The Ultimate Comparison Guide for High-Temperature and Welding Applications
When buyers search for 321 vs 304 stainless steel, they are usually facing a practical decision: standard 304 is economical and widely available, but 321 can prevent costly failures in welded, heat-exposed service. If your project includes exhaust systems, furnace parts, bellows, or hot-side piping, choosing the wrong grade can lead to premature corrosion at weld zones, unplanned shutdowns, and expensive rework.
At LYHSteel, we frequently receive RFQs asking whether 321 stainless steel is worth the premium over 304, and whether 304 can be used safely for high-temperature components. This guide provides a procurement-focused, engineering-aligned answer—supported by clear selection rules, specification tips, and an RFQ checklist that helps you quote faster and buy with fewer surprises.
Quick Decision Summary
If you want the short, decision-ready version:
Choose 304 stainless steel for general fabrication and ambient-to-moderate temperature service where long heat exposure is not a concern.
Choose 321 stainless steel when the part is welded and will experience continuous or repeated heating through the sensitization temperature range (typical reference: 425–815°C / 800–1500°F).
Do not choose 321 as a “chloride upgrade.” If chlorides are the problem, evaluate 316/316L or duplex instead.
The Core Difference: Titanium Stabilization (Why 321 Exists)
The most important difference between 304 and 321 is titanium (Ti).
304 Stainless Steel: The industry standard “18/8” austenitic stainless steel (approximately 18% Cr and 8% Ni). It offers strong general corrosion resistance, excellent formability, and competitive cost.
321 Stainless Steel: A 304-type stainless steel stabilized with titanium. Titanium is added to reduce susceptibility to sensitization and intergranular corrosion in heat-affected zones (HAZ), especially after welding.
Why titanium matters
When austenitic stainless steel is held or repeatedly cycled through a temperature window commonly referenced around 425–815°C (800–1500°F), chromium carbides can precipitate at grain boundaries. This locally depletes chromium, reducing corrosion resistance at those boundaries and creating risk of intergranular corrosion—often described in fabrication as “sensitization” or “weld decay.”
Titanium preferentially combines with carbon (forming stable titanium carbides), which helps protect chromium from being tied up in chromium carbides. The practical outcome is simple:
321 is designed to stay more corrosion-resistant around weld zones in heat-exposed service, even when post-weld solution annealing is not performed.
Chemical Composition Comparison (ASTM A240 Reference Ranges)
Below is a practical comparison commonly referenced for procurement to ASTM A240 stainless plate/sheet/strip requirements. Always verify the latest revision and your project specification requirements.
| Element | 304 Stainless Steel (%) | 321 Stainless Steel (%) |
|---|---|---|
| Chromium (Cr) | 18.0 – 20.0 | 17.0 – 19.0 |
| Nickel (Ni) | 8.0 – 10.5 | 9.0 – 12.0 |
| Carbon (C) | 0.08 max | 0.08 max |
| Titanium (Ti) | — | min = 5×(C+N), max = 0.70 |
| Manganese (Mn) | 2.00 max | 2.00 max |
| Silicon (Si) | 0.75 max | 0.75 max |
Key takeaway: Titanium stabilization is the “insurance policy” you pay for in 321—mainly to protect welded assemblies and heat-cycled components.
Official reference for product form standards: ASTM A240/A240M (plate, sheet, strip).
High-Temperature Performance: Where the Grades Separate
For many industrial buyers, temperature is the deciding factor—not because 304 “melts,” but because weld zones and grain boundaries become vulnerable during prolonged or repeated heating.
304 stainless steel at elevated temperature
304 can offer good oxidation resistance at elevated temperatures. However, if it is held in the sensitization range for sufficient time—especially after welding—it may become vulnerable to intergranular corrosion in certain environments, particularly near welds and HAZ regions.
321 stainless steel at elevated temperature
321 is commonly selected for service that repeatedly cycles through, or operates within, the sensitization range. Thanks to titanium stabilization, it is typically favored for:
better resistance to intergranular corrosion after exposure,
improved reliability for welded assemblies,
stronger performance for heat-cycled components where HAZ durability is critical.
Practical rule: If your component operates continuously above ~500°C and includes welds (or will be heavily formed and then welded), 321 is frequently the safer and more specification-aligned choice.
Corrosion Resistance: What 321 Improves (and What It Does Not)
General corrosion (ambient service)
In typical ambient environments—architecture, food processing, general fabrication—304 and 321 perform similarly. If heat is not a factor, 321 rarely provides meaningful additional corrosion value versus 304.
Intergranular corrosion (the real differentiator)
321 is selected primarily to reduce risk of sensitization-related corrosion in welded zones after heat exposure. If your application includes hot-side cycling or prolonged elevated temperature, this can be the difference between stable service life and early failure.
Chlorides and pitting
Neither 304 nor 321 is designed as a “marine grade.” If pitting/crevice corrosion in chloride environments is the concern, evaluate 316/316L or duplex grades.
If you need a quick comparison tool for pitting resistance screening, you can use a PREN calculation as a directional reference:
Internal tool: PREN Calculator (LYHSteel)
https://lyhsteel.com/pren-calculator/
Weldability and Fabrication Behavior
Both grades weld well, but the post-weld risk profile differs.
304: excellent weldability, but sensitization risk in heat-exposed service
304 is straightforward to weld. The risk arises when welded components operate in sensitization conditions without appropriate grade selection (e.g., 304L) or heat treatment, depending on service and environment.
321: designed for welded, heat-exposed assemblies
321 was developed to reduce sensitization-related corrosion issues around weld zones. In many industrial projects, it is specified to avoid mandatory post-weld solution annealing while maintaining HAZ reliability.
Fabrication note (appearance): 321 may produce a less uniform polish than 304 because titanium stabilization can contribute to “streaking” or a slightly duller aesthetic finish. For highly cosmetic architectural cladding, 304 often remains the preferred choice.
For surface finish selection and finish terminology, you can reference:
Internal resource: Surface Finish Chart
https://lyhsteel.com/surface-finish-chart/
Cost Analysis: Is 321 Worth the Premium?
In many markets, 321 stainless steel often carries a premium versus 304 due to:
titanium alloying cost,
production complexity,
lower overall availability compared with 304.
A reasonable procurement mindset is:
Do not specify 321 “just to be safe.”
Specify 321 when the service temperature + welding + reliability risk justify it.
If your service is below ~500°C and does not involve sensitization-critical exposure, 304 (or 304L where appropriate) is typically the more economical engineering choice.
Application-Based Selection: When to Choose Which Grade
Choose 304 stainless steel for:
kitchen equipment and appliances,
architectural panels and railing systems,
food and beverage tanks and general processing equipment,
chemical containers in low-to-moderate temperature service.
Choose 321 stainless steel for:
aircraft and industrial exhaust stacks/manifolds,
expansion joints, bellows, and vibration-prone hot assemblies,
furnace parts and heating element tubing,
heat exchangers on the hot side in refineries or thermal systems,
welded pressure-containing components operating at elevated temperature.
Buyer-Friendly Selection Rules
Use these rules in procurement meetings and RFQ reviews:
If the part is welded and will run through 425–815°C / 800–1500°F repeatedly, choose 321.
If the part is primarily ambient service with general corrosion requirements, choose 304.
If chloride pitting is the concern, evaluate 316/316L or duplex, not 321.
If appearance and polishing consistency are critical, 304 is typically easier to finish aesthetically.
If the project spec references stabilized grades (e.g., SUS321 / 1.4541), align with 321 to avoid nonconformance risk.
For grade equivalency support (JIS/EN/ASTM mapping), you can reference:
Internal resource: Steel Grade Equivalent Chart
https://lyhsteel.com/steel-grade-equivalent-chart/
How to Specify on a Purchase Order
If you want accurate pricing and fewer back-and-forth emails, include the following in your inquiry:
Grade: 304 / 304L / 321
Product form: coil / sheet / plate / strip
Standard: ASTM A240 (or EN/JIS equivalent)
Size: thickness × width × length (or coil ID/OD and coil weight)
Surface finish: 2B / BA / No.4 / HL (plus protective film requirement)
Quantity: total tons and preferred split per coil/sheet
Mechanical / testing: MTC/MTR, PMI if required, third-party inspection if required
Tolerances: thickness/width/flatness expectations
Internal tool: Dimensional Tolerance Calculator
https://lyhsteel.com/dimensional-tolerance-calculator/Packing: seaworthy export packing, pallet/crate preference, container loading notes
Destination: port and delivery term (EXW/FOB/CIF, etc.)
Why Source 304/321 Through LYHSteel
LYHSteel supports industrial buyers with specification-driven supply and export execution, including:
coil, sheet, and plate sourcing aligned to common standards,
processing coordination (slitting, shearing, surface finish control as required),
export packing discipline and documentation support (MTC, packing lists, traceability).
Ready to quote: Send grade + size + finish + quantity + destination port, and we will respond with a specification-based quotation and practical packing plan.
Contact page (replace with your actual LYHSteel contact URL if different):
https://lyhsteel.com/contact-us/
FAQ
1) Is 321 stainless steel always better than 304?
No. 321 is purpose-built for welded, heat-exposed service where sensitization risk matters. For standard ambient applications, 304 is typically the best value.
2) Can I use 304 for furnace parts or exhaust components?
It depends on temperature profile and exposure time. If the component spends meaningful time in the sensitization range and includes welds, 321 is frequently the more reliable choice.
3) Does 321 resist rust better than 304 at room temperature?
In many ambient environments, corrosion performance is very similar. 321’s advantage is mainly in weld/HAZ stability after heat exposure.
4) Is 321 a substitute for 316 in marine environments?
No. 321 is not a chloride upgrade. If chlorides drive pitting/crevice corrosion risk, evaluate 316/316L or duplex grades.
5) Should I consider 304L instead of 304?
304L (lower carbon) is often used to reduce sensitization risk in welded fabrication. For heat-exposed welded assemblies, 321 is still commonly specified.
6) Why does 321 sometimes look less “bright” after polishing?
Titanium stabilization can influence finishing appearance and may produce streaking or a slightly less uniform polished look versus 304 in certain decorative applications.
7) What standards should I reference for ordering sheet/plate?
ASTM A240/A240M is commonly referenced for stainless plate, sheet, and strip, but always follow your project specification and regional requirements.
8) What information do you need for a fast quote?
Grade, product form, thickness/width/length (or coil specs), finish, quantity, destination port, inspection requirements, and packing requirements.