Alloy 926, often referred to as UNS N08926 or 1.4529, is a super austenitic stainless steel renowned for its excellent general corrosion resistance, especially in environments that are highly aggressive or rich in chlorides. Developed to combat pitting, crevice corrosion, and chloride-induced stress corrosion, this alloy is widely used in demanding applications across numerous industries. Its unique blend of mechanical properties, high alloying elements, and versatility make it a highly reliable material in harsh operational conditions.
Chemical composition and physical properties
The exceptional corrosion resistance of Alloy 926 is attributed to its chemical composition, which includes high levels of chromium, nickel, and molybdenum. These elements work synergistically to provide resistance to aggressive chemical substances, while nitrogen enhances the material’s mechanical properties.
Chemical composition
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Chromium (Cr): 19.0–21.0%
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Nickel (Ni): 24.0–26.0%
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Molybdenum (Mo): 6.0–7.0%
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Nitrogen (N): 0.15–0.25%
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Iron (Fe): Balance
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Manganese (Mn): ≤ 2.0%
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Copper (Cu): 0.5–1.5%
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Silicon (Si): ≤ 0.5%
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Carbon (C): ≤ 0.02%
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Phosphorus (P): ≤ 0.03%
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Sulfur (S): ≤ 0.01%
This composition offers increased resistance to pitting and crevice corrosion, even in highly acidic environments, including phosphoric acid, sulfuric acid, and sea water filtration systems.
Physical properties
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Density: ~8.1 g/cm³
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Melting Range: 1350–1390°C
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Elastic Modulus: ~200 GPa
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Thermal Conductivity: ~12 W/m·K
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Specific Heat Capacity: ~500 J/kg·K
These properties make Alloy 926 suitable for use in high-temperature and high-pressure environments.
Mechanical properties
Alloy 926 is a ductile material with a high strength-to-weight ratio, which is further enhanced by the presence of nitrogen. Its mechanical properties include:
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Tensile Strength: 650–800 MPa
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Yield Strength: ≥ 290 MPa
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Elongation: ≥ 35%
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Hardness: Approximately 220 HBW
These characteristics ensure durability under mechanical strain, even in modest corrosion strain facilities such as flue gas desulfurization plants, power plants, and offshore industry tanks.
Corrosion resistance
One of the standout qualities of Alloy 926 is its excellent general corrosion resistance, especially against pitting, crevice corrosion, and chloride stress corrosion. Its high molybdenum and chromium content create a protective oxide layer that prevents localized corrosion in:
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Sea water filtration systems
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Salt extraction processes
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Diluted sulfuric acid environments
In addition, the material performs exceptionally well in reducing and oxidizing media, such as phosphorus acid and other aggressive chemicals.
Pitting and crevice corrosion resistance
Alloy 926 has a high PREN (Pitting Resistance Equivalent Number), making it highly effective in environments with high chloride content, such as seawater and chemical processing facilities.
Stress corrosion cracking
Its resistance to chloride-induced stress corrosion is particularly valuable in applications like heat exchangers, injection systems, and pulp industry flexible pipes, where other austenitic stainless steels may fail.
Applications of alloy 926
The robust characteristics of Alloy 926 make it a preferred material in industries that demand reliability in corrosive or high-stress environments. Below are some of its primary applications:
Chemical processing industry
Alloy 926 is used in crystallization plants, pressure vessels, and tank housings exposed to highly aggressive chemicals such as phosphoric acid and sulfuric acid. Its durability ensures extended service life under harsh chemical conditions.
Oil and gas sector
The alloy is critical for offshore industry tanks, oil extraction pumps, and wire lines, where it resists both mechanical stress and corrosive substances found in oil reservoirs.
Power generation
In flue gas desulfurization systems and heat exchangers, Alloy 926 offers increased resistance to the acidic and chloride-rich environments produced during power generation processes.
Marine applications
Thanks to its superior performance in saline environments, Alloy 926 is commonly used in:
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Sea water filtration systems
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Salt extraction equipment
Its ability to withstand high chloride concentrations ensures reliable operation over long periods.
Pulp and paper industry
During the bleaching phase, Alloy 926 proves invaluable in resisting corrosive chemicals while maintaining its structural integrity.
Fabrication and processing
Welding
Alloy 926 is suitable for welding using standard techniques. It exhibits minimal susceptibility to the formation of intermetallic phases, which can otherwise weaken the alloy during welding or prolonged exposure to high temperatures.
Cold and hot working
The material can be formed using cold rolling or hot working techniques, allowing manufacturers to create components such as pipes, tubes, and sheets. Cold working further enhances its mechanical properties, including its yield strength and hardness.
Heat treatment
To maintain its mechanical and corrosion-resistant properties, Alloy 926 is typically solution-annealed at 1150–1180°C, followed by rapid cooling.
Comparison with other austenitic stainless steels
Compared to other austenitic stainless steels such as Alloy 316 or 317, Alloy 926 offers superior performance in chloride-rich and acidic environments. Its higher molybdenum and chromium content provide additional protection against localized corrosion mechanisms like pitting and crevice corrosion.
Why choose alloy 926?
With its good resistance to aggressive environments, superior mechanical properties, and ease of fabrication, Alloy 926 stands out as an ideal choice for demanding industrial applications. It is especially well-suited for projects requiring long-term durability in corrosive settings, such as chemical processing plants, power generation facilities, and offshore oil extraction.
For manufacturers, the alloy offers flexibility in production, thanks to its compatibility with standard forming, welding, and machining techniques. Its broad temperature range and resistance to intermetallic phases ensure consistent performance across diverse conditions.
Conclusion
Alloy 926 is a special stainless steel that excels in environments where both high strength and exceptional corrosion resistance are paramount. Its versatility and reliability make it a vital material across industries such as chemical processing, oil and gas, power generation, and marine applications. By understanding its unique properties and processing requirements, engineers and manufacturers can harness the full potential of Alloy 926 to create durable, high-performance components that stand the test of time.
