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UNS S31254 PLATEGSM

UNS S31254 (254 SMO): A Comprehensive Guide for Industrial Applications

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1. Introduction and Overview

UNS S31254 (254 SMO) is a high-alloy austenitic stainless steel known for its exceptional resistance to chloride-induced corrosion, pitting, and crevice corrosion. It was originally developed to address the needs of industries operating in harsh marine and chemical processing environments where conventional stainless steels, like 316L, fall short. With a combination of high molybdenum and nitrogen content, UNS S31254 (254 SMO) offers a superior solution for resisting corrosion, making it ideal for demanding applications in the oil and gas, chemical processing, pulp and paper, and marine industries.

The alloy also provides excellent strength, formability, and weldability, which makes it versatile for various forms of manufacturing, including pipes, tubes, plates, and other product forms.

2. Available Products and Specifications

Equivalent Grades:

  • Common Name: 254 SMO
  • UNS Number: S31254
  • DIN: 1.4547
  • EN: X1CrNiMoCuN20-18-7
  • ISO: X1CrNiMoCuN20-18-7
  • JIS: SUS312L
  • W.Nr.: 1.4547

Related Product Standards:

  • ISO: 15510
  • EN: 10088-1, 10028-7
  • ASTM: A240 (Plates), A312 (Pipes), A479 (Bars), A182 (Forgings)
  • ASME: SA240, SA312, SA479, SA182
  • JIS: G4304 (Plates), G4303 (Bars), G3459 (Pipes)

Available Product Forms:

  • Pipe
  • Tube
  • Plate
  • Sheet
  • Strip
  • Bar
  • Rod
  • Wire
  • Forging Stock

3. Applications

UNS S31254 (254 SMO) is commonly used in industries where high resistance to chloride stress corrosion, pitting, and crevice corrosion is essential. Its applications include:

  • Oil and Gas: Ideal for heat exchangers, flowlines, piping systems, and components exposed to seawater or sour gas environments.
  • Chemical Processing: Excellent in handling aggressive acids, such as sulfuric and phosphoric acid, and equipment exposed to highly corrosive environments.
  • Pulp and Paper: Used in bleaching plants, digesters, and other components exposed to aggressive chemicals like chlorine dioxide and sodium hydroxide.
  • Marine and Offshore: Suited for seawater piping, desalination plants, and marine hardware due to its superior resistance to saline and chloride-rich conditions.
  • Air Pollution Control: Components in flue gas desulfurization (FGD) systems, which operate in acidic and high-temperature environments.
  • Power Generation: In heat exchangers and other high-stress components.
  • Food Processing, Biochemicals, and Pharmaceuticals: Used for sanitary equipment due to its non-reactive surface and corrosion resistance in clean and high-purity environments.

4. Corrosion Resistance Properties

The standout feature of UNS S31254 (254 SMO) is its resistance to several forms of corrosion:

  • Pitting and Crevice Corrosion: Thanks to its high molybdenum (6%) and nitrogen content, it offers superior resistance to pitting and crevice corrosion in chloride-rich environments.
  • Stress Corrosion Cracking: 254 SMO outperforms traditional stainless steels like 304L and 316L in environments with high chlorides, reducing the risk of stress corrosion cracking.
  • General Corrosion: The high chromium and nickel content provide excellent resistance to uniform corrosion in both acidic and neutral solutions.
  • Intergranular Corrosion: The low carbon content helps prevent carbide precipitation, which reduces the risk of intergranular corrosion after welding.

5. Physical and Thermal Properties

  • Density: 8.0 g/cm³
  • Melting Range: 1320–1390°C (2408–2534°F)
  • Thermal Conductivity: 14.5 W/m·K at 20°C
  • Specific Heat: 500 J/kg·K at 20°C
  • Coefficient of Thermal Expansion: 15 x 10^-6/K
  • Electrical Resistivity: 0.85 μΩ·m at 20°C

6. Chemical Composition

The typical chemical composition of UNS S31254 (254 SMO) is:

Element Content (%)
Chromium (Cr) 19.5 – 20.5
Nickel (Ni) 17.5 – 18.5
Molybdenum (Mo) 6.0 – 6.5
Nitrogen (N) 0.18 – 0.22
Copper (Cu) 0.5 – 1.0
Carbon (C) ≤ 0.020
Manganese (Mn) ≤ 1.0
Silicon (Si) ≤ 0.80
Phosphorus (P) ≤ 0.030
Sulfur (S) ≤ 0.010

7. Mechanical Properties

The mechanical properties of UNS S31254 (254 SMO) provide both high strength and ductility:

  • Tensile Strength (MPa): 650 – 850
  • Yield Strength (MPa): ≥ 310
  • Elongation: ≥ 35%
  • Hardness (Brinell): ≤ 210 HB

8. Heat Treatment

Solution annealing at temperatures between 1150°C and 1200°C (2102°F–2192°F) followed by rapid cooling, typically water quenching, restores the alloy’s corrosion resistance and mechanical properties. This process is essential after forming or welding to maintain the austenitic structure and prevent the formation of detrimental phases.

9. Forming

UNS S31254 (254 SMO) has good formability and can be formed using conventional cold and hot forming techniques. However, due to its higher strength, more powerful equipment may be needed for cold forming. Post-forming annealing is recommended to restore the material’s properties, especially after severe cold work.

10. Welding

UNS S31254 (254 SMO) is highly weldable using standard welding methods such as TIG, MIG, and manual arc welding. Low heat input is advised to prevent overheating and potential phase formation. Filler materials that match the composition of 254 SMO, such as AWS A5.9 ERNiCrMo-3, are recommended to maintain the alloy’s corrosion resistance and strength.

11. Corrosion of Welds

Welds in UNS S31254 (254 SMO) are resistant to corrosion when proper welding procedures are followed. However, it’s essential to minimize heat input to avoid carbide precipitation, which can lead to sensitization and increased susceptibility to intergranular corrosion.

12. Descaling, Pickling, and Cleaning

Due to its high alloy content, proper descaling and pickling are necessary after heat treatment and welding to remove oxides and restore corrosion resistance. A combination of nitric and hydrofluoric acids is typically used for pickling. After pickling, thorough rinsing with clean water is required to remove any residual acids.

13. Surface Hardening

Like most fully austenitic stainless steels, UNS S31254 (254 SMO) cannot be surface-hardened using traditional methods such as carburizing or nitriding. However, cold working can increase its strength through work hardening, which may be beneficial for certain applications requiring higher surface strength.

Conclusion

UNS S31254 (254 SMO) is a superior choice for demanding environments that require high corrosion resistance and strength. Its ability to withstand chloride-induced corrosion, pitting, and crevice corrosion makes it the go-to material for industries such as oil and gas, chemical processing, pulp and paper, and marine applications. With excellent formability, weldability, and corrosion resistance properties, 254 SMO provides long-lasting, reliable solutions for components exposed to harsh environments.

For users needing a material that excels in extreme conditions while maintaining its structural integrity and corrosion resistance, UNS S31254 (254 SMO) delivers the perfect balance of performance, reliability, and ease of use.

UNS S32760 ZERON® 100

UNS S32760 (Zeron 100): A Super Duplex Stainless Steel (SDSS)

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1. Introduction

UNS S32760 (Zeron 100) is a super duplex stainless steel (SDSS) with a mixed microstructure of austenite and ferrite, giving it superior strength and corrosion resistance. It contains significant amounts of chromium, molybdenum, and nitrogen, providing excellent resistance to chloride-induced pitting, crevice corrosion, and stress-corrosion cracking (SCC). Its high strength-to-weight ratio makes it a preferred choice for various industries, offering substantial cost savings in design and fabrication. In this blog post, we will explore UNS S32760 in detail, covering its specifications, applications, corrosion resistance, and more to clearly understand why this alloy is highly valued in critical industries.

Key Features:

  • High Strength: Superior tensile and yield strength compared to standard austenitic stainless steels.
  • Corrosion Resistance: Exceptional performance in chloride-rich environments.
  • Cost-Effective: Lower material costs compared to more expensive nickel-based alloys.

2. UNS S32760 (Zeron 100) Product Forms and Specifications

  • UNS Number: S32760
  • Common Name: Super Duplex Stainless Steel, Zeron 100
  • W.Nr.: 1.4501
  • ASTM/ASME Standards: A240, A182, A276, A789, A790, B649

Available Product Forms:

  • Pipe
  • Tube
  • Plate
  • Sheet
  • Strip
  • Bar
  • Rod
  • Wire
  • Forging Stock

These product forms provide versatility, making UNS S32760 suitable for various industrial applications requiring mechanical and corrosive stress resistance.

UNS S32760 ZERON 100

UNS S32760 ZERON 100

3. Applications of UNS S32760 (Zeron 100)

Due to its exceptional corrosion resistance and high strength, UNS S32760 is widely used in the following industries:

  • Chemical Processing: Ideal for processing equipment that handles aggressive chemicals like sulfuric and phosphoric acids.
  • Oil and Gas: Used extensively in subsea pipelines, pumps, valves, and manifolds due to its resistance to chloride and hydrogen sulfide environments.
  • Marine and Offshore: These are excellent for seawater applications such as heat exchangers, seawater cooling systems, and marine hardware.
  • Pulp and Paper: Resistant to the corrosive chemicals used in pulp bleaching processes.
  • Air Pollution Control: Suitable for scrubbers, flue gas desulfurization (FGD) systems, and other pollution control systems that handle acidic gases.
  • Power Generation: Used in systems that deal with brackish water and steam, such as condensers and feedwater heaters.

4. Corrosion Resistance Properties of UNS S32760 (Zeron 100)

UNS S32760 offers outstanding corrosion resistance in various environments, making it ideal for harsh industrial applications. Its corrosion resistance properties include:

  • Pitting and Crevice Corrosion Resistance: With high chromium (25%) and molybdenum (3.5%) content, S32760 provides superior resistance to localized corrosion in chloride-rich environments.
  • Stress Corrosion Cracking (SCC) Resistance: Its duplex structure offers significant resistance to SCC, a common issue in austenitic steels when exposed to chloride and high-temperature environments.
  • General Corrosion Resistance: Excellent performance in acidic and alkaline environments, including exposure to seawater, acids, and harsh industrial chemicals.

5. Physical and Thermal Properties of UNS S32760 (Zeron 100)

UNS S32760 maintains its mechanical and corrosion-resistant properties over a wide range of temperatures:

  • Density: 7.8 g/cm³
  • Thermal Conductivity: 14 W/m·K (at 100°C)
  • Thermal Expansion: 13 × 10⁻⁶/°C (at 100°C)
  • Melting Range: 1350°C to 1450°C (2462°F to 2642°F)

These properties make S32760 suitable for applications requiring thermal stability and resistance to temperature fluctuations.

6. UNS S32760 (Zeron 100) Chemical Composition

The chemical composition of UNS S32760 is carefully balanced to enhance both its corrosion resistance and mechanical strength:

  • Chromium (Cr): 24.0 – 26.0%
  • Nickel (Ni): 6.0 – 8.0%
  • Molybdenum (Mo): 3.0 – 4.0%
  • Copper (Cu): 0.5 – 1.0%
  • Tungsten (W): 0.5 – 1.0%
  • Nitrogen (N): 0.2 – 0.3%
  • Iron (Fe): Balance
  • Others: Trace elements such as carbon, silicon, and manganese are kept at minimal levels to prevent precipitation of secondary phases that can reduce corrosion resistance.

7. UNS S32760 (Zeron 100) Mechanical Properties

UNS S32760 offers excellent mechanical strength, making it suitable for high-stress environments:

  • Tensile Strength: 750 MPa (109 ksi)
  • Yield Strength: 550 MPa (80 ksi)
  • Elongation: 25%
  • Hardness: 28 HRC (Rockwell)

This high tensile and yield strength combination makes S32760 ideal for applications where mechanical stress and corrosion are simultaneous concerns.

8. Heat Treatment

To achieve optimal mechanical and corrosion-resistant properties, UNS S32760 undergoes a solution annealing process:

  • Solution Annealing Temperature: 1100°C to 1150°C (2012°F to 2102°F), followed by rapid quenching.

This heat treatment prevents the formation of detrimental secondary phases and ensures the alloy maintains its duplex microstructure.

9. Forming

UNS S32760 can be hot or cold-formed using standard techniques:

  • Cold Forming: Suitable for cold-forming applications due to its good ductility.
  • Hot Forming: Hot-working should be done at temperatures between 1000°C and 1100°C (1832°F to 2012°F) and followed by a solution anneal to restore corrosion resistance.

It is important to note that heat treatment may be necessary after significant cold work to restore the alloy’s balance of strength and corrosion resistance.

10. Welding

UNS S32760 offers excellent weldability using standard welding techniques, including TIG, MIG, and SMAW. Key considerations for welding include:

  • Preheat: Not required.
  • Post-Weld Heat Treatment: In certain applications, solution annealing may be necessary to restore full corrosion resistance.
  • Filler Metal: Use over-matching filler metals like ER2594 or E2594 for optimal weld performance.

Proper welding procedures ensure the alloy’s duplex microstructure remains intact and prevents the formation of unwanted phases that could compromise corrosion resistance.

11. Corrosion of Welds

Welds are often more susceptible to corrosion if not properly treated. However, UNS S32760’s low carbon and high nitrogen content reduce the risk of carbide precipitation, which can lead to intergranular corrosion. Proper heat input control and post-weld cleaning, including pickling and passivation, are crucial for maintaining weld integrity.

12. Descaling, Pickling, and Cleaning

Post-weld cleaning is essential to ensure maximum corrosion resistance. Descaling and pickling can be done using a nitric-hydrofluoric acid solution followed by thorough rinsing. This process removes oxides and surface contamination that could otherwise initiate localized corrosion.

13. Surface Hardening

Surface hardening processes like nitriding are generally not recommended for UNS S32760 as they can negatively affect the alloy’s corrosion resistance. The high inherent strength of the alloy usually eliminates the need for additional hardening treatments.

Conclusion

UNS S32760 (Zeron 100) is a highly versatile and cost-effective super duplex stainless steel that excels in extreme environments where both corrosion and mechanical stress are prevalent. Its excellent corrosion resistance, high strength, and weldability make it a preferred choice across various industries, including chemical processing, oil and gas, marine, and power generation. For industries looking for a reliable material with long service life and low maintenance, UNS S32760 is a top-tier option.

For more information or assistance in selecting UNS S32760 for your application, feel free to contact our expert team at [email protected]. We are here to provide the best material solutions tailored to your needs.