321 Stainless Steel - AMS 5510, AMS 5645
321 stainless steel (UNS S32100) is a titanium-stabilized austenitic stainless steel that features improved resistance to intergranular corrosion. This grade is suitable for high-temperature applications up to 1500°F (815°C), where the addition of titanium stabilizes the material against chromium carbide formation. Since titanium has a stronger affinity for carbon than chromium, titanium carbide precipitates within the grain instead of forming at the grain boundaries. While corrosion resistance is similar to 304 and 304L in the annealed condition, it features higher creep and stress rupture properties. 321 stainless steel is non-magnetic and heat resistant for continuous service at elevated temperatures.
- Inventory & Specs
- Chemical Composition
- Physical Properties
- Mechanical Properties
- Datasheet
- Additional Info
- FAQs
Inventory Size Ranges for 321
| Type | Thickness | AMS Standards | ASTM | UNS | ASME | Get a Quote |
|---|---|---|---|---|---|---|
| Coil | 0.012" - 0.125" | AMS 5510, AMS 5645 | ASTM A 167, ASTM A 240, ASTM A 276, ASTM A 479 | UNS S32100, UNS S32109 | ASME SA 167, ASME SA 240 | Get a Quote |
| Sheet | 0.012" - 0.125" | AMS 5510, AMS 5645 | ASTM A 167, ASTM A 240, ASTM A 276, ASTM A 479 | UNS S32100, UNS S32109 | ASME SA 167, ASME SA 240 | Get a Quote |
| Plate | 0.1875" - 0.250" | AMS 5510, AMS 5645 | ASTM A 167, ASTM A 240, ASTM A 276, ASTM A 479 | UNS S32100, UNS S32109 | ASME SA 167, ASME SA 240 | Get a Quote |
| Bar | 0.375" - 9.000" | AMS 5510, AMS 5645 | ASTM A 167, ASTM A 240, ASTM A 276, ASTM A 479 | UNS S32100, UNS S32109 | ASME SA 167, ASME SA 240 | Get a Quote |
| Hex Bar | 0.250" - 1.125" | AMS 5510, AMS 5645 | ASTM A 167, ASTM A 240, ASTM A 276, ASTM A 479 | UNS S32100, UNS S32109 | ASME SA 167, ASME SA 240 | Get a Quote |
| Precision Reroll Strip | 0.0008" - 0.015" | Get a Quote |
Characteristics of 321
321 stainless steels offers similar resistance to general, overall corrosion as the unstabilized chromium-nickel 304 stainless. Heating for long periods of time in the chromium carbide precipitation range may affect the general resistance of 321 stainless in severe corrosion media. 321 alloy in the annealed condition is somewhat less resistant to general corrosion in strongly oxidizing environments compared to annealed 347. For this reason, 347 stainless is preferable for aqueous and other low temperature environments. Exposure in the 800 to 1500°F (427 to 816°C) temperature range lowers the overall corrosion resistance of 321 alloy to a much greater extent than 347 alloy. When the unstabilized chromium-nickel steels are held in or slowly cooled through the range of 800 to 1500°F (427 to 816°C), chromium carbide is precipitated at the grain boundaries. In the presence of certain strongly corrosive media, these grain boundaries are preferentially attacked, a general weakening of the metal results, and a complete disintegration may occur.
Working with 321
Machining 321 stainless steel is similar to that of 304, but slightly tougher. 321 work-hardens quickly, so it is important to use sharp tooling and keep consistent, aggressive feed rates. 321 is known for its weldability due to its titanium and carbon composition which prevents carbine precipitation. Additionally, 321's heat-affected zones stay corrosion resistant and there is no need for post-weld annealing in a majority of cases. 321 offers similar formability to 304, demonstrating good ductility and deep-draw performances. If better formability is required, stainless grades 305 and 304 are recommended.
Other industry standards we comply with:
- PWA-LCS
- GE Aircraft Engine (GT193)
- RR SABRe Edition 2
- DFARS Compliant
Common Trade Names
- ATI 321 (™ Allegheny Technologies)
- Alloy 321
- Type 321 steel
Industry Applications for 321
- Useful in the chromium carbide precipitation range (800-1500°F, 427-815°C)
- Aircraft exhaust stacks
- Manifolds
- Chemical processing equipment
- Welded equipment
- Jet engine parts
- Heat Exchangers
- Expansion joints
Chemical Composition
| Element | Min | Max | |
|---|---|---|---|
| C | Carbon | - | 0.08 |
| Mn | Manganese | - | 2.00 |
| P | Phosphorus | - | 0.045 |
| S | Sulfur | - | 0.030 |
| Si | Silicon | - | 0.75 |
| Cr | Chromium | 17.00 | 19.00 |
| Ni | Nickel | 9.00 | 12.00 |
| Ti | Titanium | 5x(C+N) | 0.70 |
| N | Nitrogen | - | 0.1 |
| Fe | Iron | - | Balance |
Physical Properties
- Magnetic Permeability: H/m Anneal 1.02 Max
| Grade | Density | Modulus of Elasticity in Tension | Melting Range | |||
|---|---|---|---|---|---|---|
| g/cm3 | lb/in3 | psi | GPa | °C | °F | |
| 321 | 7.92 | 0.286 | 28 x 106 | 193 | 1398-1446 | 2550-2635 |
| 347 | 7.96 | 0.288 | 28 x 106 | 193 | 1398-1446 | 2550-2635 |
| Temperature Range | Coefficients | ||
|---|---|---|---|
| °C | °F | cm/cm/°C | in/in/°F |
| 20-100 | 68-212 | 16.6 x 10-6 | 9.2 x 10-6 |
| 20-600 | 68-912 | 18.9 x 10-6 | 10.5 x 10-6 |
| 20-1000 | 68-1832 | 20.5 x 10-6 | 11.4 x 10-6 |
| Temperature Range | W/m·K | Btu · in / hr · ft2 · °F | |
|---|---|---|---|
| °C | °F | ||
| 20-100 | 68-212 | 16.3 | 112.5 |
| 20-500 | 68-932 | 21.4 | 147.7 |
| Temperature Range | J/kg K | Btu/lb · °F | |
|---|---|---|---|
| °C | °F | ||
| 0-100 | 32-212 | 500 | 0.12 |
| Temperature Range | microhm·cm | |
|---|---|---|
| °C | °F | |
| 20 | 68 | 72 |
| 100 | 213 | 78 |
| 200 | 392 | 86 |
| 400 | 752 | 100 |
| 600 | 1112 | 111 |
| 800 | 1472 | 121 |
| 900 | 1652 | 126 |
Mechanical Properties
| Property | Type 321 | Type 347 |
|---|---|---|
| Yield Strength 0.2% Offset, psi (MPa) | 30,000 (205) | 30.000 (205) |
| Ultimate Tensile Strength, psi (MPa) | 75,000 (515) | 75,000 (515) |
| % Elongation in 2 in. or 51 mm | 40.0 | 40.0 |
| Hardness Max., Brinell (Plate) | 217 | 201 |
| Hardness Max., RB (Sheet & Strip) | 95 | 92 |
Datasheet
Additional Info
A Brief History of 321
321 stainless steel emerged from the early development of 18‑8 austenitic stainless steels in the 1920s–1930s. Engineers discovered that standard 304 suffered chromium carbide precipitation when exposed to temperatures around 800–1500 °F, especially during welding. To solve this, metallurgists added titanium, which bonds with carbon and prevents chromium depletion. This stabilized alloy became known as Type 321 (UNS S32100) and was adopted for high‑temperature and welded applications.
How 321 Was Developed
304 stainless steel offered good corrosion resistance but failed in high‑temperature or welded environments due to intergranular corrosion. Researchers introduced titanium (Ti) at levels ≥5× the carbon content, forming stable titanium carbides instead of chromium carbides. This innovation preserved chromium in solution, maintaining corrosion resistance even after prolonged heating. The result was a stainless steel with excellent resistance to carbide precipitation, strong high-temperature stability, good weldability, and improved creep resistance.
Early Applications of 321
Early uses focused on industries that needed stainless steel that could withstand heat, welding, and thermal cycling. Some of these applications included aircraft exhaust systems, chemical processing equipment, boilers and heat exchangers, refinery and petrochemical piping, furnace components, and expansive joints and bellows. These applications leveraged 321's ability to resist intergranular attack and maintain strength at elevated temperatures.
How 321 is Used Today
321 remains a major high-temperature stainless steel, especially where welding and thermal stability are critical. Modern applications include:
- Aerospace: Jet engine components, exhaust manifolds, thermal shields
- Automotive: High temperature exhaust parts, catalytic converter shells
- Petrochemical: High temperature piping, furnace tubes, reformer components
- Thermal Processing: Heat exchangers, annealing covers, furnace parts
- Power Generation: Boiler casings, superheater tubes
- Industrial Manufacturing: Expansion joints, bellows, welded assemblies
Your Trusted Supplier for 321 Stainless
United Performance Metals carries 321 coil and sheet 0.012" - 0.125", 321 plate 0.1875" - 0.250", 321 bar 0.375" - 9.000", 321 hex bar 0.250" - 1.125", and precision rerolled strip 0.0008" - 0.015". 321 material is ideal for pressure vessels and boiler applications.
Product FAQs
321 stainless steel demonstrates superior high temperature performance, excellent weldability, resistance to intergranular corrosion, and stability under thermal stress.
321 stainless steel is essentially the same as 304 but has the addition of titanium for stabilization. This makes 321 better at high temperatures and in weld-critical environments.
While 316 has better chloride corrosion resistance, 321 has better high-temperature stability, making it preferred for thermal cycling and welding.
Titanium binds with carbon to form titanium carbides, which prevents chromium from forming chromium carbides. This improves resistance to intergranular corrosion, especially in the 800–1500 °F (425–815 °C) range.