1. Equivalent Grades in Different Standards
- UNS: S34700
- ASTM: TP347
- EN: 1.4550
- GB: 06Cr18Ni11Nb
- JIS: SUS347
2. Chemical Composition (wt%, typical value)
C ≤0.08%, Cr:17.00～19.00%, Ni:9.00～12.00%, Nb ≥10×C% (Nb:0.30~1.00%), Mn ≤2.00%, Si ≤1.00%, P ≤0.045%, S ≤0.030%, balance Fe.
Niobium stabilizes carbon to prevent intergranular corrosion after welding or high-temperature service.
3. Production Process of Seamless Pipe
3.1 Round Billet Melting & Inspection
Raw scrap melted by EAF+AOD refining to control chemical composition; continuous casting into solid round billets. Billets are inspected, surface ground to remove cracks and surface defects.
3.2 Hot Piercing & Hot Rolling
Round billet heated at 1120~1220℃ → rotary piercing to hollow bloom → hot continuous pipe rolling → sizing & straightening → hot finished seamless tube.
3.3 Cold Finishing (for precision cold-drawn seamless tube)
Hot finished tube → pickling to remove oxide → cold drawing / cold pilger rolling → solution annealing → straightening → nondestructive testing (ET/UT/PT) → cutting, final inspection & packaging.
4. Surface Finishes
- Hot Finished (HF / No.1):Black oxide or pickled grey surface for thick-wall industrial piping.
- Pickled Bright Surface:Pickled after heat treatment, uniform silver finish for conventional fluid pipeline.
- Cold Drawn Bright Finish:Smooth bright surface for precision instrument piping and high-purity medium pipeline.
5. Product Features & Physical-Mechanical Properties
Mechanical Properties (Solution Annealed Condition)
Yield Strength Rp0.2 ≥205 MPa, Tensile Strength ≥515 MPa, Elongation ≥40%, HB ≤201.
Physical Parameters
Thermal expansion coefficient close to 304; fully annealed state is basically non-magnetic, slight magnetism generated after cold working.
Core Advantages
- Nb-stabilized grade, excellent anti-intergranular corrosion performance after long-time high-temperature exposure or post-weld heating; superior to 304 for high-temperature welding service.
- Excellent creep resistance and high-temperature oxidation resistance, stable mechanical property under 425~815℃ continuous working temperature.
- Good forming, bending and welding performance, suitable for high-temperature welded pipeline system.
6. Main Applications
- Power Industry:Boiler superheater tube, steam pipeline, thermal power furnace tube, nuclear power auxiliary high-temperature piping.
- Petrochemical Industry:High-temperature reactor piping, cracking furnace tube, heat exchanger tube, refining high-temperature process pipeline.
- Energy & Chemical Equipment:High-temperature furnace accessories, thermal cycling pipeline, equipment nozzle under alternating high temperature.
- Aerospace & Heavy Machinery:High-temperature hydraulic pipeline, engine exhaust manifold pipe, high-temperature instrument tubing.
