SUS321 Stainless Steel: Titanium-Stabilized Grade Performance

What Is SUS321

SUS321, equivalent to ASTM 321 and UNS S32100, is a titanium-stabilized austenitic stainless steel with 17.0 to 19.0 percent chromium, 9.0 to 12.0 percent nickel, and titanium at least five times the carbon content up to 0.70 percent. The titanium forms stable titanium carbides, preventing chromium depletion at grain boundaries and preserving corrosion resistance in the carbide precipitation range.

Key Performance Characteristics

SUS321 maintains mechanical integrity and creep strength at elevated temperatures better than Type 304. Its corrosion resistance is similar to 304 and 304L but superior in the carbide precipitation range because of titanium stabilization. It welds excellently, with no post-weld annealing typically needed to restore corrosion resistance, resists oxidation up to about 816 degrees C, and retains excellent toughness down to cryogenic temperatures.

Applications

SUS321 is used in aerospace exhaust manifolds, engine components, and hot sections; automotive exhaust systems, heat shields, and bellows; furnace casings, liners, and fixtures; and petrochemical and power plant high-temperature piping, ducting, and boiler components. It is also specified for expansion joints and welded assemblies that cannot be annealed after fabrication.

Limitations

SUS321 is not recommended for decorative purposes because it does not polish as well as 304, and it can still suffer stress corrosion cracking in warm chloride environments above 60 degrees C. For service above about 600 degrees C where creep strength governs, the high-carbon variant 321H is recommended.

Comparison with 304 and 347

Compared with 304, SUS321 offers superior resistance to intergranular corrosion after welding and better high-temperature creep strength. Compared with 347, which uses niobium stabilization, SUS321 uses titanium, which is more economical but can be lost during welding; 347 is preferred for heavy-section welded construction.

Frequently Asked Questions

Q: What is SUS321?

A: A titanium-stabilized austenitic stainless steel, ASTM 321, UNS S32100.

Q: Why is titanium added to SUS321?

A: To bind carbon and prevent chromium carbide precipitation during welding and heating.

Q: What temperature can SUS321 resist?

A: Oxidation resistance up to about 816 degrees C.

Q: Does SUS321 need post-weld annealing?

A: Not normally, thanks to titanium stabilization.

Q: What applications use SUS321?

A: Aerospace exhausts, automotive systems, furnace equipment, and boiler piping.

Q: What is the difference between SUS321 and SUS321H?

A: 321H has higher carbon, 0.04 to 0.10 percent, for better creep strength.

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