347 vs 347H Austenitic Stainless Steels: Stabilized vs High-Carbon High-Temp Grades

 

What are their core compositions and performance differences?

347 contains 17–19% Cr, 9–13% Ni, 0.7–1.0% Nb, ≤0.08% C. It maintains stability up to 800°C, ideal for general high-heat welded parts.347H has the same Cr/Ni/Nb content but 0.04–0.10% C. Higher carbon forms more niobium carbides, boosting creep resistance at 800–900°C (critical for steam turbine components).Both eliminate post-weld heat treatment, a key advantage over non-stabilized grades.

How do their high-temperature capabilities differ?

347 performs well in moderate high-heat service (e.g., industrial furnace trays, exhaust headers) but softens above 800°C.347H's higher carbon content resists creep deformation at 800–900°C, making it the top choice for nuclear power plant steam lines and gas turbine combustion chambers.

In which applications is one grade irreplaceable?

Choose 347 for general high-heat welded assemblies (≤800°C): boiler tubes, chemical reactor internals.Opt for 347H for ultra-high-temperature, high-pressure service: nuclear steam generators, aircraft engine exhaust components.

What are the cost and fabrication trade-offs?

347H costs 5–8% more than 347 (tighter carbon control adds expense), so it's only used for 800+°C applications.Both weld well with 347 filler metals, but 347H requires stricter heat input control to avoid carbide coarsening.

What are the key guidelines?

347 is over-specified for low-temperature uses-use 321 or 304H to save cost.347H is unsuitable for low-temperature corrosive assemblies-its higher carbon increases sensitization risk without heat treatment.