High Carbon 316H Stainless Steel Plate / UNS S31609 SS Plate Thickness 3.0 30

316H Stainless Steel: A High-Temperature Austenitic Alloy

1. Definition & Key Distinction:
316H is a high-carbon variant of the popular 316 austenitic stainless steel. The "H" suffix denotes its suitability for high-temperature service (typically above 500°C / 932°F), where enhanced strength is required.

2. Chemical Composition (Typical):

• Carbon (C): 0.04–0.10% (Higher than standard 316/L to boost high-temperature strength).

• Chromium (Cr): 16–18% (Provides oxidation/corrosion resistance).

• Nickel (Ni): 10–14% (Maintains austenitic structure, improves ductility & corrosion resistance).

• Molybdenum (Mo): 2–3% (Key for pitting/crevice corrosion resistance, especially in chlorides).

• Manganese (Mn): ≤2%

• Silicon (Si): ≤1%

• Phosphorus (P): ≤0.045%

• Sulfur (S): ≤0.03%

• Iron (Fe): Balance

3. Key Properties & Advantages:

• Excellent High-Temperature Strength: Superior creep strength (resistance to slow deformation under stress at high temps) compared to 316/L due to controlled higher carbon content.

• Good Oxidation Resistance: Resists scaling in continuous service up to ~870°C (1600°F) and intermittent service up to ~925°C (1700°F).

• Superior Corrosion Resistance: Inherits excellent general corrosion and pitting/crevice corrosion resistance from its base 316 chemistry, particularly in chloride environments (thanks to Molybdenum).

• Austenitic Structure: Non-magnetic, good ductility, toughness, and formability in the annealed condition.

• Fabricability: Can be readily welded and formed using standard methods for austenitic stainless steels (though post-weld annealing is often recommended).

4. Trade-offs:

• Sensitization Risk: The higher carbon content increases susceptibility to sensitization (chromium carbide precipitation at grain boundaries) during welding or slow cooling through 425–815°C (800–1500°F). This can reduce corrosion resistance in the heat-affected zone. Solution annealing (rapid quenching from 1040–1150°C / 1900–2100°F) is crucial after high-temp exposure to dissolve carbides.

• Lower Corrosion Resistance than 316L: In severely corrosive environments, especially after welding, standard 316L (low carbon) is often preferred to avoid sensitization issues.

5. Primary Applications:
316H is specifically engineered for demanding elevated temperature environments requiring both corrosion resistance and mechanical strength:

• Power Generation: Boiler tubes, superheater tubes, heat exchangers, high-temperature piping in fossil fuel and nuclear plants.

• Chemical & Petrochemical Processing: Furnace parts, catalyst grids, reactor vessels, piping handling hot corrosive fluids.

• Heat Treating Equipment: Retorts, baskets, fixtures.

• Oil & Gas Refining: High-temp piping and components.

• Pressure Vessels designed for sustained high-temperature operation.

6. Common Specifications (Examples):

• ASTM A213 / ASME SA213 (Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, and Heat-Exchanger Tubes)

• ASTM A249 / ASME SA249 (Welded Austenitic Steel Boiler, Superheater, Heat-Exchanger, and Condenser Tubes)

• ASTM A312 / ASME SA312 (Seamless and Welded Austenitic Stainless Steel Pipes)

• ASTM A358 / ASME SA358 (Electric-Fusion-Welded Austenitic Chromium-Nickel Stainless Steel Pipe for High-Temperature Service)

• UNS S31609

7. Comparison Summary:

• vs. 316: Higher carbon (0.04-0.10% vs. max ~0.08%) for better high-temp strength.

• vs. 316L: Significantly higher carbon (316L max is 0.03%) for strength at temp, but greater sensitization risk. 316L excels where welding or maximum corrosion resistance is critical.

• vs. 316Ti/321: 316H relies on carbon for strength; 316Ti/321 use Titanium or Niobium to stabilize against sensitization (better for welded corrosive service, but may have slightly lower creep strength at very high temps).