S30908 Stainless Steel

S30908 is a low-carbon high-chromium-nickel austenitic stainless steel (UNS S30908), corresponding to SUS309S. With 22-24% Cr and 12-15% Ni, it offers excellent high-temperature oxidation resistance, suitable for continuous service at 900-1100℃, widely used in heat treatment equipment.

: C <=0.08, Si <=1.00, Mn <=2.00, P <=0.045, S <=0.030, Cr=22.00-24.00, Ni=12.00-15.00, Fe=Balance

: Tensile Strength >=515MPa, Yield Strength >=205MPa, Elongation >=40%, Hardness (HB) <=217

: Superior oxidation resistance at 900-1100℃; good thermal shock resistance; low carbon reduces intergranular corrosion risk; weldable with matching filler.

: ASTM A240 309S, EN 1.4828, SUS309S

: Furnace linings, heat treatment baskets, high-temperature conveyor belts, boiler fireboxes, welding electrodes for high-temp joints.

1. Q: Why is S30908 suitable for heat treatment baskets? A: Heat treatment baskets face cyclic heating (900℃) and cooling, plus load-bearing. S30908's high Cr forms a dense Cr₂O₃ layer, resisting oxidation and scaling. Its austenitic structure retains ductility during thermal cycles, avoiding cracking. Low carbon prevents intergranular corrosion after welding (baskets are often welded), ensuring 5+ years of service vs 1-2 years for carbon steel baskets.

2. Q: How does S30908 perform in reducing atmospheres? A: Limited performance. It's optimized for oxidizing atmospheres (air, oxygen). In reducing environments (hydrogen, carbon monoxide) at 800℃+, the oxide layer breaks down, causing carburization (surface hardening). For mixed oxidizing-reducing atmospheres, ensure oxidizing conditions dominate. For pure reducing temps, use nickel-based alloys like Inconel 600.

3. Q: What's the difference between S30908 and S30900? A: S30908 (309S) has C <=0.08%, while S30900 (309) has C <=0.15%. Lower carbon in S30908 reduces intergranular corrosion risk after welding, eliminating post-weld annealing. For welded furnace parts, S30908 is preferred. S30900 has slightly higher high-temp strength but worse weld corrosion resistance, used for non-welded high-temp components.

4. Q: How to maintain S30908 furnace linings? A: Remove oxide scale quarterly with wire brushes-thick scale reduces heat transfer. Avoid rapid cooling (e.g., spraying water on hot linings) to prevent thermal shock cracking. After welding, passivate with 20% nitric acid to restore the oxide layer. Inspect welds for cracks annually; repair with ER309L filler if defects are found.

5. Q: When to choose S30908 over S31008? A: S30908 is cost-effective for 900-1100℃ oxidizing environments (e.g., heat treatment furnaces). S31008 (310S) has higher Cr/Ni (24-26% Cr, 19-22% Ni) for 1000-1200℃ service (e.g., incinerators). If temps stay below 1100℃, S30908 saves 20-30% cost without performance loss. For temps above 1100℃, S31008 is necessary for oxidation resistance.