S34700 Stainless Steel

S34700 is a niobium-stabilized austenitic stainless steel (UNS S34700), corresponding to SUS347. With 17-19% Cr, 9-12% Ni, and 8xC-1.0% Nb (niobium), it prevents intergranular corrosion at 400-900°C, offering better high-temperature stability than titanium-stabilized grades like S32100.

Chemical Composition (wt%): C ≤0.08, Si ≤1.00, Mn ≤2.00, P ≤0.045, S ≤0.030, Cr=17.00-19.00, Ni=9.00-12.00, Nb+Ta=8xC-1.0, Fe=Balance

Mechanical Properties (Annealed): Tensile Strength ≥515MPa, Yield Strength ≥205MPa, Elongation ≥40%, Hardness (HB) ≤217

Performance Advantages: Niobium stabilization resists high-temp carbide precipitation; better creep resistance than S32100; excellent weldability; suitable for long-term 800-900°C service.

Equivalent Grades: ASTM A240 347, EN 1.4550, SUS347

Applications: Nuclear power plant components, high-temperature heat exchangers, aircraft engine parts, chemical reactor tubes, boiler superheaters.

FAQ

1. Q: Why is niobium better than titanium for stabilization? A: Niobium has higher affinity for carbon than titanium, forming more stable NbC. NbC remains intact up to 900°C, while TiC dissolves above 870°C. For long-term service at 850°C (e.g., nuclear heat exchangers), S34700 maintains corrosion resistance for 20+ years, vs 10-15 years for S32100. Niobium also improves creep resistance, a key advantage.

2. Q: What makes S34700 suitable for nuclear power plants? A: It meets nuclear safety standards (ASME BPVC III). Niobium stabilization ensures corrosion resistance in high-temp water/steam (300-350°C) and welded joints. It has low radioactivity absorption and good mechanical stability under radiation. Unlike S30400, it avoids intergranular corrosion in nuclear secondary circuits, reducing leakage risks.

3. Q: How does S34700 perform in welding? A: Excellent weldability. Use ER347 filler to match niobium content. No pre-heat or post-heat treatment is needed for most applications. Weld zone corrosion resistance is equivalent to the base metal, unlike S30400 which needs passivation. For thick-walled reactor tubes, it's easier to weld than titanium-stabilized grades, reducing fabrication time.

4. Q: Can S34700 be used in acidic environments? A: Yes, for mild to moderate acids (5-20% sulfuric acid, organic acids) at 20-800°C. Its austenitic structure and niobium stabilization resist acid corrosion. It's not suitable for high-chloride acids-use S31635. For non-chloride high-temp acids, it's a cost-effective alternative to nickel-based alloys, balancing corrosion resistance and strength.

5. Q: What's the maximum operating temperature of S34700? A: Continuous service up to 900°C; short-term up to 950°C. Above 900°C, NbC dissolves, and sigma phase may form. For temps ≥900°C, use S31008. S34700 is ideal for 400-900°C critical welded parts (e.g., aircraft engine exhaust manifolds), where its stability and strength are essential.