347 (UNS S34700 / W.Nr. 1.4550)
347 (UNS S34700 / W.Nr. 1.4550) stainless steel is a columbium/tantalum stabilized austenitic chromium-nickel stainless steel. Type 347 has excellent intergranular corrosion resistance and oxidation resistance. at high temperatures. This material is stabilized against chromium carbide formation by the addition of columbium and tantalum. Since these elements have a stronger affinity for carbon than chromium, columbium-tantalum carbides precipitate within the grains instead of forming at the grain boundaries. 347 should be considered for applications requiring intermittent heating between 800ºF (427ºC) and 1650ºF (899ºC) or for welding under conditions which prevent a post-weld anneal. 347 is non-magnetic.
Equivalent Grades
| Trademark | GB | GOST | ASTM | UNS | DIN | W.Nr. | NF | BS | JIS | SS |
| – | – | – | AISI 347 | S34700 | X6CrNiNb 18-10 | 1.4550 | – | – | – | – |
Chemical Composition, %
| Alloy | C | Si | Mn | P | S | Cr | Ni | Mo | Nb+Ta | Fe |
| 347 | ≤0.08 | ≤0.75 | ≤2.00 | ≤0.045 | ≤0.030 | 17.0-19.0 | 9.0-13.0 | – | 10(C+N) | Bal |
Typical Physical and Mechanical Properties (RT, Annealed)
| Density, g/cm3 | Melting Point, ℃ | Tensile Strength, MPa | Yield Strength, MPa | ELongation, % | Hardness, HB |
| 7.9 | 1030-1180 | 510-740 | ≥205 | ≥40 | / |
Available Products and Specifications
| Rod, Bar, Wire and Forgings | ASTM A276, ASTM A479 |
| Plate, Sheet and Strip | ASTM A167, 240 |
| Pipe and Tube | ASTM A312 |
| Welding Product | – |
| Others | ASTM A193, ASTM A193 |
Features
- Good creep strength up to 1500°F
- Maintains good corrosion resistance in applications where the temperature is between 800°F and 1500°F.
- Good resistance to intergranular corrosion in the as welded condition.
Applications
- Oil Refineries
- Fluid catalytic cracking units (FCC)
- Firearms production
- Hanger rods
- Recuperator tube sheets, shell, supports
- Especially where temperatures exceed 550°F and resistance to sulfidation is needed
- Fired heater tubes
- Distributor trays and thermowells
- Equipment in and around reactors (good resistance to polythionic acid)
