321 vs 347 Austenitic Stainless Steels: Titanium vs Niobium-Stabilized High-Temp Grades

 

What are their core compositions and key performance differences?

321 contains 17–19% Cr, 9–12% Ni, 0.4–0.8% Ti, with titanium binding carbon to avoid sensitization up to 800°C.347 features 17–19% Cr, 9–13% Ni, 0.7–1.0% Nb (plus Ta), with niobium carbides stable up to 900°C-superior for extreme heat.Both eliminate post-weld heat treatment, critical for high-temp welded parts.

How do their high-temperature capabilities suit distinct applications?

321 is ideal for moderate high-heat parts: boiler tubes, automotive exhaust headers (≤800°C service).347 dominates ultra-high-temp uses: jet engine exhausts, nuclear steam lines (≥800°C, resists creep deformation).

In which scenarios is one grade irreplaceable?

Choose 321 for cost-sensitive high-heat welded assemblies (≤800°C).Opt for 347 for ≥800°C service-321's titanium carbides coarsen, reducing strength.

What are the cost and fabrication trade-offs?

321 is 10–15% cheaper than 347 (titanium is more abundant), making it economical for non-extreme high-heat uses.347 requires tighter welding heat control to avoid niobium carbide agglomeration; 321 is more forgiving.

What are the key guidelines?

Neither grade suits marine environments-upgrade to 316Ti for corrosion + heat resistance.Prioritize 321 for ≤800°C welded parts; select 347 for ≥800°C ultra-high-temp service.