Titanium-Stabilized Stainless Steel 321

Stainless Steel 321 is a titanium-stabilized austenitic grade derived from 304, solving intergranular corrosion in welded or high-heat applications. Titanium (5×C–0.70%) binds carbon, ensuring stability in 425–815°C, making it ideal for aircraft exhausts and cryogenic vessels.

Chemical Composition (Key, % ASTM A240): C≤0.08; Cr17.0–19.0; Ni9.0–12.0; Ti5×C–0.70 (min0.10); Mn≤2.0

Mechanical Properties (Annealed): Tensile Strength≥515MPa; Yield Strength≥205MPa; Elongation≥40%; Hardness≤217HB

Performance Advantages: Titanium-stabilized corrosion resistance; 870°C service temp; excellent cryogenic ductility; cost-effective vs. Mo-containing grades.

Applications: Aircraft exhausts, heat exchangers, rocket fuel tanks, food ovens.

Equivalent Grades: EN1.4541, JIS SUS321, DIN X6CrNiTi18-10

Comparison with 316Ti: 321 lacks Mo (poor chloride resistance) but is cheaper; 316Ti suits marine, 321 for dry high heat.

FAQs

How does titanium stabilize 321? Titanium has stronger carbon affinity than chromium. When heated (welding/870°C service), it forms titanium carbides, preventing chromium carbide formation that depletes Cr and causes corrosion. This keeps Cr evenly distributed, maintaining the oxide layer even in the HAZ. Unlike 304, 321 needs no post-weld annealing, saving production time.

 

Can 321 be used in cryogenics? Yes-its austenitic structure stays stable below -150°C, unlike brittle ferritic grades. It retains ≥40% elongation at -196°C (liquid nitrogen temp), preventing catastrophic failure. Titanium carbides refine grains, boosting low-temp toughness. Welded cryogenic vessels (rocket fuel tanks) use 321 because it avoids intergranular corrosion, unlike 304.

 

What is "weld decay," and how does 321 avoid it? Weld decay is intergranular corrosion in 304's HAZ: 425–815°C heating forms chromium carbides, creating Cr-depleted zones. 321's titanium binds carbon first, even in the HAZ, so no Cr-depleted zones form. 304 needs 1010–1120°C annealing to fix this, but 321 welds are corrosion-resistant immediately post-welding.

How does 321 perform vs. 304 at high temps? 304 corrodes above 425°C (welded), but 321 stays stable up to 870°C. At 700°C, 321 retains 85–90% yield strength (304 loses 20%). Titanium carbides resist thermal cycling, reducing fatigue in furnace parts. 304 suits low temps; 321 is superior for high-heat/welded components.

 

What heat treatment is best for 321? Anneal at 925–1100°C (30–60 mins/25mm thickness) to eliminate work hardening and form fine titanium carbides. Water quench rapidly-slow cooling lets carbon react with Cr, negating titanium's effect. Avoid overheating above 1100°C (dissolves titanium carbides). No post-weld treatment is needed, but annealing restores ductility if the HAZ work-hardens.