Grades 309, 309S, and 309H are austenitic heat-resistant alloys designed for:
• Excellent oxidation resistance up to 1038°C (1900°F) under non-cyclic conditions.
• Good corrosion resistance at high temperatures.
• Easy weldability and machinability using standard shop practices.
309S is the low-carbon version for improved weldability and reduced sensitization.
309H has a higher carbon content for greater creep resistance at high temperatures.

Reference standards:

• ASTM A240
• ASME SA240
• AMS 5523
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Chemical composition (%)

Element 309 309S 309H
Chromium (Cr) 22.0–24.0 22.0–24.0 22.0–24.0
Nickel (Ni) 12.0–15.0 12.0–15.0 12.0–15.0
Carbon (C) ≤0.20 ≤0.08 0.04–0.10
Manganese (Mn) ≤2.00 ≤2.00 ≤2.00
Phosphorus (P) ≤0.045 ≤0.045 ≤0.045
Sulfur (S) ≤0.030 ≤0.030 ≤0.030
Silicon (Si) ≤0.75 ≤0.75 ≤0.75
Iron (Fe) Balanced Balanced Balanced
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Mechanical properties

(at 20°C)
Property Value
Tensile Strength (UTS) ≥515 MPa
Yield Strength 0.2% ≥205 MPa
Elongation over 2″ ≥40%
Brinell Hardness (HB) ≤217
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Physical properties

Property Value
Density 7.89 g/cm³
Modulus of elasticity 196 GPa
Melting range 1480–1530°C
Specific heat (0–100°C) 502 J/kg·K
Thermal conductivity (100°C) 15.6 W/m·K
Electrical resistivity (20°C) 78 µΩ·cm
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Corrosion resistance

• Not ideal for aqueous environments (possibility of intergranular corrosion).
• Excellent oxidation resistance up to:
o 1050°C in continuous service at low sulfur content.
o 950°C in oxidizing atmospheres at high sulfur content.
o 850–950°C in fuel or nitriding atmospheres.
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Heat treatments

• Solution annealing: 1100–1150°C followed by rapid cooling.
• Avoid prolonged exposure to 650–950°C to prevent formation of the sigma phase.
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Weldability

• Weldable with TIG, MIG, SMAW, SAW, FCAW processes.
• May require preheating and post-weld treatment in critical environments.
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Industrial applications

• Furnace supplies: burners, doors, fans, piping.
• Paper industry: components exposed to high temperatures.
• Petroleum refining: catalytic recovery systems.
• Power generation: tube supports in coal-fired boilers.
•

Heat treatments

: retorts, muffles, annealing covers.
• Waste treatment plants: incinerators, rotary kilns.