ASTM 310S Stainless Steel: High-Temperature Resistant Austenitic Alloy for Oxidizing Environments

ASTM 310S stainless steel (UNS S31008) is a low-carbon, high-chromium-nickel austenitic alloy engineered for superior oxidation resistance at elevated temperatures up to 1150°C (2100°F). With a nominal composition of 25% chromium and 20% nickel, this grade outperforms standard 304/316 in cyclic heating applications while maintaining excellent creep strength and thermal stability. This technical guide covers its metallurgical properties, heat treatment protocols, industrial applications, and comparative advantages over alternative high-temperature alloys.

1. Chemical Composition (ASTM A240/A480 Specifications)

2. Mechanical Properties at Elevated Temperatures

3. Thermal and Physical Characteristics

• Melting Range: 1399-1446°C (2550-2635°F)
• Thermal Conductivity (100°C): 14.2 W/m·K (vs 16.2 for 304)
• Coefficient of Thermal Expansion (0-100°C): 15.9 μm/m·K
• Specific Heat Capacity (0-100°C): 500 J/kg·K
• Electrical Resistivity: 0.89 μΩ·m at 20°C
• Magnetic Permeability: ≤1.02 (non-magnetic in annealed condition)

4. Manufacturing and Heat Treatment

1. Melting Practice: Electric arc furnace (EAF) followed by argon-oxygen decarburization (AOD) to achieve ultra-low carbon content and precise alloy composition control.
2. Hot Working: Perform at 1150-1260°C with rapid water quenching to prevent sigma phase formation. Avoid working below 900°C to prevent cracking.
3. Cold Working: Limited to moderate deformations due to high work hardening rate. Intermediate annealing required for complex forming operations.
4. Solution Annealing: Heat to 1040-1150°C followed by rapid cooling (water quench or forced air) to dissolve precipitates and restore corrosion resistance.
5. Descaling: Pickling in nitric-hydrofluoric acid bath (20-30% HNO₃ + 2-5% HF at 60-80°C) to remove high-temperature oxide scales.
6. Surface Finishes: Standard mill finishes include 2B (cold rolled, bright annealed), No.1 (hot rolled, annealed, pickled), and specialized high-temperature oxide finishes for furnace applications.

5. Primary Industrial Applications

6. Comparison with Alternative High-Temperature Alloys

7. Fabrication and Service Recommendations

• Welding Procedures: Use ER310 or ER310S filler metal with low heat input (≤1.5 kJ/mm). Preheat not required for thin sections; maintain interpass temperature below 150°C. Post-weld annealing recommended for critical applications.
• Machining Considerations: Use carbide tooling with positive rake angles. Reduce speeds by 30% compared to 304 due to higher work hardening rate. Flood cooling essential to prevent tool wear.
• Corrosion Limitations: Avoid prolonged exposure to reducing acids (HCl, H₂SO₄) or chloride salts above 60°C. Not recommended for wet corrosion environments—consider 316L for such applications.
• Thermal Cycling: Design components to accommodate thermal expansion (15.9 μm/m·K). Use expansion joints for long runs of piping or ductwork.
• Quality Certification: Verify material test reports (MTR) confirm compliance with ASTM A240, A276, or A312 standards. Request PMI testing for critical applications to prevent alloy mixing.