Stainless Steel 309S

Stainless Steel 309S is a low-carbon austenitic alloy with high Cr (22–24%) and Ni (12–15%). It resists oxidation up to 980°C and avoids intergranular corrosion, making it perfect for high-heat, moderate-corrosion settings.

Chemical Composition (Key, % ASTM A240)

C: ≤0.08; Cr: 22.0–24.0; Ni: 12.0–15.0

Mn: ≤2.00; Si: ≤1.00

Mechanical Properties (Annealed)

Tensile Strength: ≥515 MPa; Yield Strength: ≥205 MPa

Elongation: ≥40%; Hardness: ≤217 HB

Performance & Uses

Advantages: Oxidation resistance at 980°C, low carbon prevents intergranular corrosion, stable under thermal cycling.

Applications: Furnace liners, exhaust systems, welding fillers, thermal processing gear.

Equivalent Grades

EN 1.4958, JIS SUS309S, DIN X2CrNi23-13

Q&As

Why handle 980°C?Cr (22–24%) forms a dense Cr₂O₃ layer that blocks oxidation. Ni stabilizes the austenitic structure (stays ductile at high temps). Low C avoids weakening the oxide layer, unlike high-C steels.

What does "S" mean?"S" = low carbon (≤0.08%). It stops carbon from reacting with Cr to form carbides (which cause intergranular corrosion). No post-weld heat treatment is needed, simplifying fabrication.

Corrosion-resistant beyond high heat?Yes, for mild corrosives: atmospheric rust, dilute acids, alkalis. But no Mo, so it pits in saltwater (worse than 316Ti). Use it for oven parts or dilute acid equipment, not marine settings.

Compare to 310S?310S has higher Cr/Ni (24–26%/19–22%) and handles 1150°C, but costs more. 309S is cheaper and suffices for ≤980°C (e.g., furnace liners). Both resist intergranular corrosion, but 310S is better for ultra-high heat.

Fabrication tips?Weld with TIG/MIG (309S filler). Bend with more force than 304 (higher strength). Cut with laser/plasma (more sparks, use shields). Machine slowly-avoids work hardening.