Stainless Steel 347H

Stainless Steel 347H is a high-carbon variant of 347 (C: 0.04–0.10%). It retains Nb stabilization (10×C–1.00%) but boosts 900–980°C strength/creep resistance, ideal for high-pressure, long-term high-heat parts.

Chemical Composition (Key, % ASTM A240)

C: 0.04–0.10; Cr: 17.0–19.0; Ni: 9.0–13.0

Nb+Ta: 10×C–1.00 (min 0.70)

Mechanical Properties (Annealed)

Tensile Strength: ≥550 MPa; Yield Strength: ≥220 MPa

Elongation: ≥35%; Hardness: ≤235 HB

Performance & Uses

Advantages: 980°C service temp, excellent creep resistance, no intergranular corrosion.

Applications: Power plant superheaters, turbine components, cracking furnace tubes.

Equivalent Grades

EN 1.4551, JIS SUS347H, DIN X10CrNiNb18-10

Q&As

Why higher C than 347?More C forms extra Nb carbides, boosting tensile strength (550 vs. 515 MPa) and creep resistance. At 900°C, 347H creeps 60% less than 347-vital for superheaters under 100+ bar pressure.

Still corrosion-resistant?Yes. Nb content scales with C (10×C min). For 0.10% C, Nb needs ≥1.00% to bind all carbon. No Cr carbides form, so it resists intergranular corrosion as well as 347.

Max temp vs. 321H/310S?980°C (80°C higher than 321H, 170°C lower than 310S). Cheaper than 310S and better for 900–980°C (e.g., turbine parts) where 321H would fail.

Machining tips?Use carbide tools (HSS wears fast, 235 HB hardness). Cut 10–15% slower than 347 (130 vs. 150 m/min) to avoid work hardening. Use water-soluble coolant-reduces heat and tool wear.

Choose over 310S?310S handles 1150°C but no stabilizer (needs post-weld treatment). 347H is cheaper, resists intergranular corrosion, and suffices for ≤980°C. Better for welded high-pressure parts (e.g., reactors) vs. 310S.