UNS S32750 Super Duplex Stainless Steel

S32750 stainless steel, also known as UNS S32750 or SAF2507, is a super duplex stainless steel that combines the advantages of austenite and ferrite. It is a material with excellent corrosion resistance and high strength. It is widely used in chemical industry, offshore platform, papermaking industry and other occasions with extremely high requirements for corrosion resistance and mechanical properties, such as heat exchangers and cold showers and devices that are resistant to seawater, high temperature and concentrated nitric acid.

Main representative grades of duplex stainless steel:
Low alloy type - representative grade: UNS S32304 (23Cr-4Ni-0.1N)
Medium alloy type - representative grade: UNS S31803 (22Cr-5Ni-3Mo-0.1N)
High alloy type - representative grade: UNS S32550 (22Cr-6Ni-3Mo-2Cu-0.2N)

Super duplex stainless steel type - standard grade: UNS S32750 (25Cr-7Ni-3.7Mo-0.3N)

Features:
Low alloy type: UNS S32304 does not contain molybdenum and can replace AISI 304 or 316 in terms of stress corrosion resistance.
Medium alloy type: The corrosion resistance of UNS S31803 is between AISI 316L and 6%Mo+N austenitic stainless steel.
High alloy type: generally contains 25% Cr, also contains molybdenum and nitrogen, some also contain copper and tungsten, this type of steel has higher corrosion resistance than 22% Cr duplex stainless steel
Super duplex stainless steel type: contains high molybdenum and nitrogen, some also contain tungsten and copper, also suitable for harsh media conditions, with good corrosion resistance and mechanical comprehensive properties, comparable to super austenitic stainless steel.

1. Chemical composition
The chemical composition of S32750 is the key to its high performance, mainly including:
· Carbon (C): ≤0.030%
· Silicon (Si): ≤0.80%
· Manganese (Mn): ≤1.20%
· Phosphorus (P): ≤0.035%
· Sulfur (S): ≤0.020%
· Chromium (Cr): 24.00～26.00%
· Nickel (Ni): 6.00～8.00%
· Molybdenum (Mo): 3.00～5.00%
· Nitrogen (N): 0.24～0.32%
· Copper (Cu): ≤0.5%
· Iron (Fe): Balance

The combination of these components gives S32750 excellent resistance to pitting, crevice and uniform corrosion.

2. Mechanical properties
The mechanical properties of S32750 are excellent, including:

· High strength: Due to its duplex microstructure, S32750 exhibits higher strength than austenitic stainless steel.
· Good toughness: It can maintain good toughness even in low temperature environments.
· High temperature and high pressure resistance: S32750 stainless steel can exhibit excellent performance in high temperature and high pressure environments, including stable strength and toughness, good corrosion resistance and resistance to stress corrosion cracking.

3. Corrosion resistance
The corrosion resistance of S32750 is better than many other stainless steel materials, especially in chloride environments. The high chromium, molybdenum and nitrogen contents provide excellent resistance to pitting and crevice corrosion.

4. Processing performance
The processing performance of S32750 is similar to that of ordinary austenitic stainless steel pipes, but due to its high strength and hardness, higher processing forces and more wear-resistant tools may be required.

5. Heat treatment characteristics
S32750 is usually supplied in the solution annealed state to ensure the best corrosion resistance and mechanical properties.

6. Application fields
S32750 stainless steel pipe is suitable for high-strength and corrosion-resistant structural parts and components in the fields of ocean, chemical industry, oil and gas.

· Chemical industry: used to manufacture heat exchangers, reactors and piping systems.
· Seawater system: used for offshore platforms, ships, submarine pipelines, submarine equipment, offshore structures and seawater desalination systems.
· Papermaking industry: used for production equipment such as bleaching equipment.
· Oil and gas industry: S32750 stainless steel is used in oil drilling, oil field development, submarine oil and gas pipelines, oil refining equipment and liquefied natural gas (LNG) processes.

7. Welding performance
S32750 has good welding performance, but appropriate welding process is required to avoid changes in microstructure and performance degradation.

8. Supply status
S32750 is usually supplied in annealed and pickled state to ensure the corrosion resistance of the material.

9. Economy
Although S32750 costs more than ordinary stainless steel, its excellent performance and long life make it economical in many applications.

10. Environmental adaptability
S32750 can maintain stable performance in various harsh chemical and marine environments.

11. Safety
The use of S32750 can improve the safety and reliability of equipment, especially in occasions with high loads and corrosive media.

12. Future development
With the improvement of the performance requirements of corrosion-resistant materials, the application areas of S32750 may be further expanded, including more complex industrial environments and more severe application conditions.

13. Similar grades
S32750 has similar chemical composition and properties to some other grades of steel, for example:

· Chinese standard: 07Cr25Ni7Mo4N
· American standard: ASTM S32750
· Japanese standard: JIS SUS 329J3
· German standard: DIN 1.4410

14. Specifications and dimensions
S32750 is available in a variety of specifications and dimensions, including hot-rolled bars, forged bars, cold-rolled sheets, hot-rolled plates, and forgings of various sizes.

15. Physical properties

The physical properties of S32750 are as follows:
· Melting point: It has a certain melting point range after solution treatment.
· Specific heat capacity: It has a certain specific heat capacity in the range of 0 to 100°C.
· Thermal conductivity: It has a specific thermal conductivity in the range of 100 to 500°C.
· Linear expansion coefficient: It has a certain linear expansion coefficient in the range of 100-500℃.
· Resistivity: It has a certain resistivity at 20℃.
· Elastic modulus: It has a certain longitudinal elastic modulus at 20℃.
· Hardness: It has measurable hardness values, such as HBW and HRB.
· Magnetism: S32750 is a non-magnetic or weakly magnetic material.

16. Mechanical properties
The mechanical properties of S32750 include:

· Tensile strength: ≥550 MPa
· Yield strength: ≥450 MPa
· Elongation: ≥15%

· Sectional shrinkage: ≥5%

Read more: UNS S31803 Duplex Stainless Steel or Stainless Steel Seamless Pipe Manufacturing Process