S31635 Stainless Steel

S31635 is a titanium-stabilized austenitic stainless steel, corresponding to SUS316Ti. It contains 2-3% molybdenum and 0.10-0.30% titanium, combining excellent chloride corrosion resistance with high-temperature intergranular corrosion resistance. Titanium binds with carbon to prevent chromium carbide precipitation, making it ideal for long-term high-heat service in harsh environments.

Chemical Composition (wt%): C ≤0.08, Si ≤1.00, Mn ≤2.00, P ≤0.045, S ≤0.030, Cr=16.00-18.00, Ni=10.00-14.00, Mo=2.00-3.00, Ti=0.10-0.30, Fe=Balance

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

Performance Advantages: Titanium stabilization avoids high-temp intergranular corrosion; Mo enhances pitting resistance in chlorides; good creep resistance at 400-900°C; weldable without post-heat treatment.

Equivalent Grades: ASTM A240 316Ti, EN 1.4571, SUS316Ti

Applications: High-temperature heat exchanger tubes, chemical reactor linings, nuclear power secondary circuit parts, exhaust systems of marine engines.

FAQ

1. Q: Why is S31635 better than S31600 for high-temperature service? A: S31635's titanium binds carbon to form TiC, preventing chromium carbide precipitation at 400-900°C. S31600 (SUS316) lacks titanium, so chromium carbides form at grain boundaries, causing intergranular corrosion. For furnace tubes operating 24/7 at 600°C, S31635 maintains corrosion resistance for 10+ years, while S31600 may fail in 3-5 years.

2. Q: Can S31635 be used in seawater heat exchangers? A: Yes, it's excellent for this. Molybdenum resists seawater pitting, and titanium ensures weld zone corrosion resistance. Seawater heat exchangers have welded tube-to-header joints-S31635's stabilization avoids intergranular corrosion here, unlike S316L which may need passivation. It balances high-temp performance (for heated seawater) and corrosion resistance.

3. Q: What welding filler metal matches S31635? A: Use ER316Ti filler to retain titanium content. ER316L (no Ti) or ER316 (low Ti) will reduce the weld zone's high-temp corrosion resistance. Weld with TIG at 100-140A, controlling heat to avoid titanium burnout (over 1200°C). No post-weld annealing is needed, simplifying heat exchanger fabrication.

4. Q: Does S31635 have sigma phase risk at high temps? A: Low risk. Its high Ni (10-14%) stabilizes the austenitic structure, preventing sigma phase (brittle intermetallic) formation below 900°C. Above 900°C, hold time should be limited (≤2 hours) to avoid sigma phase. For long-term service at 800-900°C, it's safer than ferritic steels, making it suitable for high-temp chemical equipment.

5. Q: How to inspect S31635 for titanium uniformity? A: Use spark test-uniform titanium content produces consistent orange sparks. For critical parts, use X-ray fluorescence (XRF) to measure Ti (0.10-0.30%). Too low Ti causes carbide precipitation; too high reduces ductility. XRF is non-destructive and ensures material meets specs for high-temp use.