Duplex SS 2507

Duplex SS 2507

UNS S32750 (F53 / 1.4410 / Alloy 32750 / Alloy 2507)

Duplex stainless steel 2507 is another two-phase alloy with a stable austenite and ferrite grain structure. It is a chromium-nickel-molybdenum alloy with a specifically designed composition for applications that require high strength and highly corrosive environment resistance.

The ferritic portion of the grade provides resistance to cracking under various environments including warm chloride environments. The chromium content (25%) resists general corrosion by forming a protective oxide layer on the surface whilst the Nickel content (7%) provides the required ductility and strength to the alloy.

The Nickel element also promotes its austenite structure. The acidic conditions are also appropriately resisted. Molybdenum (4%) restricts localized corrosion and helps increase its mechanical properties. This chemical composition of the grade along with other alloying elements, like nitrogen provide exceptional resistance to chloride pitting, chloride stress corrosion cracking, better mechanical and thermal properties. The grade has low coefficient to thermal expansion resulting in a stable weld at the heat affected zone, the base metal thus provides better weldability.

High impact and tensile strength are provided along with high thermal conductivity. The grade can be suitably used for structural and dynamic applications. However, it is not recommended to use the grade at elevated temperatures. Using the grade above 320°C is avoided since it might lose its strength, toughness and corrosion resistance on prolonged exposure. The UTS (ultimate tensile strength) at 20°C is 116 KSI and at elevated temperature of 215°C, the UTS becomes 94 KSI. The impact strength of the alloy is somewhat retained at lower temperatures but it is not recommended for lower cryogenic temperatures.

At room temperature, the impact strength is 162 ft. lbs and at -40°C, the impact strength is 140 ft. lbs. While at very low temperatures like -100°C, the impact strength becomes 30 ft. lbs. The grade has low carbon content (0.03%max), due to which carbide precipitation at the heat affected zone is neglected. Hence, inter-granular corrosion due to carbide precipitation at grain boundaries is strongly avoided. Due to the higher strength of the grade, lighter sections of the grade having the same strength and design are often used in replacement of nickel grade alloys to achieve lighter weight products.

Hence, cost of fabrication and machining is also reduced. Duplex SS 2507 is almost 10% lighter than grade 316 and also has a greater life cycle. The grade can be suitably hot worked and cold worked. Hot working can be done around 1020-1230°C, followed by careful solution annealing at 1050°C. Since the grade has very high strength, large forces are required to cold deform the grade, spring back allowances could be required to complete the process. Intermediate solution anneals would be required when 10% cold deformation takes place.

  • Chemical properties
  • Physical properties
  • General data
  • Standards Specifications
  • Forms of Supply
  • Corrosion Resistance
  • Heat Treatment
  • Weldability
  • Machining
  • Applications
  • Possible grade alternatives
Grade   Ni C Cr Mn Si P Cu S Mo N


Min 6 - 24 - - - - - - 0.24
Max 8 0.030 26 1.20 0.80 0.035 0.50 0.020 1.20 0.32
Density kg/cm3) 7.8 g/cm3/0.281 lb/in3
Melting Point 1350°C  2460°F
Specific Heat 0-100°C ( J/kg.K) Btu/lb ºF 0.12
Thermal Conductivity at 20°C (W/m.K) 8.7
Elastic Modulus (GPa) 29
Electrical Resistivity (nW.m) 31.5 Ω-in x 10-6
Quench Rapid Air/Water
Annealing Minimum 1925°F/1050 °C
Standard 2507
UNS S 32750
EN X2 Cr Ni MoN 25.7.4
AFNOR Z3 CN 25.06 Az
Pipes & Tubes
Summary Standards
Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service ASTM A789
Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Pipe ASTM A790
Standard Specification for Ferritic/Austenitic (Duplex) Stainless Steel Pipe Electric Fusion Welded with Addition of Filler Metal ASTM A928
Standard Specification For Seamless Stainless Steel Mechanical Tubing ASTM A511
Fittings & Flanges
Summary Standards
Standard Specification for Stainless Steel Forgings, Ferritic/Austenitic (Duplex), for Pressure Vessels and Related Components ASTM A1049
Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service ASTM A182

Piping and tubing, fittings and flanges, washers.

The grade is specifically used for high strength applications and exceptional corrosion resistance. The grade resists a wide range of aggressive media without losing its mechanical properties. Because of its high alloy content, excellent resistance to chloride stress corrosion cracking is provided. The crevice corrosion temperature when tested against other duplex stainless steels (grade 2304, 2205) and austenitic grades (grade 304L, 316, 316L, 904L), the grade 2507 and grade 254 SMO show the best performance to resist crevice corrosion. Appreciable corrosion resistance to organic acids like formic and acetic acid and inorganic acids like chloride containing acids is provided. On seawater corrosion test, deteriorating phases like sigma phase and nitrides in the microstructure were not found. Very low weight loss and negligible pitting were found. Inter-granular corrosion is avoided in the grade due to its low carbon content.

The grade needs to be thoroughly solution-annealed after hot or cold working. Solution-annealing should be carried around 1050°C, followed by a rapid air cooling or water quenching, such that embrittlement is avoided and maximum corrosion resistance is restored. Time at temperature should be decided upon sections, and every section should be evenly heat treated. The product needs to properly pickled and impurities and oxides removed.

The duplex grade has improved weldability. Welding techniques like gas tungsten arc welding, gas metal arc welding, plasma arc welding, flux cored wire, shielded metal arc welding, and submerged arc welding can be used. Filler metal should be appropriately selected such that resulting weld with duplex structure is produced. The weld needs to be properly cleaned and descaled. If single surface cleaning is not possible, GTAW technique should be used for root passes. Pre-heating and post-heating are normally not required.

The grade possesses a combination of properties of ferrite and austenite structure. It has higher strength, toughness, and mechanical properties. Hence, higher forces are required to deform the grade. Positive feed, adequate lubrication, rigid tooling and powerful machinery is recommended.

Oil and gas industry equipment, Offshore Oil production/technology, Pulp & Paper Mill Equipment, Mechanical and structural components, Desalination plants, Chemical process industries, heat exchangers, vessels, and piping, Marine Applications, Flue Gas Scrubbing Equipment, process and service water systems, fire-fighting systems, injection and ballast water systems, Power industry FGD systems, corrosion-resistant parts, high pressure RO-plant and seawater piping, industrial scrubber systems, absorber towers.

Grade 254 SMO
Grade   C Cr Mo N P Cu Mn S Ni Fe Si
254 SMO Min. - 24 3 0.24 - - - - 6 Bal -
Max. 0.030 26 5 0.32 0.035 0.50 1.20 0.020 8 - 0.80
Grade Hastelloy C276
Grade   Ni C Co Mn Si Cr W S V Fe P Mo
Hastelloy C276 Min. Bal(50.99) - - - - 14.5 3.0 - - 4.0 - 15.0
Max. - 0.010 2.5 1.00 0.08 16.5 4.5 - 0.35 7.0 0.04 17.0

Product Enquiry