Alloy 725 (UNS N07725)


Alloy 725 is a nickel-chromium alloy with significant additions of molybdenum, niobium and titanium, supplied in the hot worked, annealed and age-hardened condition. It is age-hardened to achieve extremely high strength, approximately twice that of Alloy 625 in the annealed condition, through the precipitation of ϒ” phase during a controlled heat treatment process. As this high strength is achieved by ageing rather than cold working, it retains excellent ductility and toughness, and this approach is useful for large or non-uniform sections that cannot be strengthened through cold working.

Alloy 725 has very similar corrosion resistance to Alloy 625, and so is utilised in a wide range of very corrosive environments. The high nickel content ensures resistance to stress corrosion cracking, combined with molybdenum to strongly resist reducing environments such as sulphuric and phosphoric acids, chromium to resist oxidising environments such as nitric acid, titanium to inhibit intergranular corrosion, and overall resistance to pitting and crevice corrosion. The overall combination of alloying elements provides excellent resistance to conditions found in sour oil and gas wells, containing carbon dioxide, chlorides and hydrogen sulphide, and is approved under NACE MR 1075 for such applications.

Key Features:

  • Suitable for use in highly corrosive sour oil and gas wells, approved under NACE MR 1075
  • Excellent corrosion resistance in a wide variety of corrosive environments including seawater and industrial acids
  • Age hardened for extremely high strength
  • Good ductility and toughness
  • Excellent resistance to stress corrosion cracking


  • Downhole equipment for corrosive/sour service
  • Oil and gas hangers, connectors
  • Fasteners, especially in marine applications
  • Chemical process equipment
  • Agitators
  • Valve stems

Chemical Composition:

Cr Ni Mo Co Nb (+Ta) Ti W Cu C Mn N Si P S Fe Al
Min 19.00 55.00 7.00 2.75 1.00
Max 22.50 59.00 9.50 4.00 1.70 0.03 0.35 0.20 0.015 0.01 Bal 0.35

Mechanical Properties:

Bars up to 3” (76mm) diameter or section Bars greater than 10” (254mm) diameter or section Bars greater than 10” (254mm) diameter or section
0.2% Proof Stress, min 827 N/mm2 120 ksi 827 N/mm2 120 ksi 827 N/mm2 120 ksi
Tensile strength, min 1034 N/mm2 150 ksi 1034 N/mm2 150 ksi 1034 N/mm2 150 ksi
Elongation, 5.65√S0 and 4D 20% 20% 20%
Reduction of Area 35% 35% 35%
Hardness (Rockwell C) <43 <43 <43
Impact Strength (-60oC) Longitudinal, Typical 54J av (47J min) 40 av (35 min)
Impact Strength (-60oC) Transverse, Typical 50J av (43J min) 37 av (32 min) 43J av (37J min) 32 av (27 min)


  1. Tensile testing shall be carried out in accordance with ASTM A370 or EN10002-1
  2. Minimum properties quoted (tested at room temperature in a longitudinal direction)
  3. Testing performed on each melt of material per heat treatment batch

Physical Properties:

Density (Kg.m-1) 8310
Magnetic Permeability (20°C) < 1.001
Young’s Modulus (kN/mm2) 204
Poissons Ration 0.31
Specific Heat, 20°C (J/(g.K)) 0.43
Electrical Resistivity, 20°C (µΩ-m) 1.144
Thermal conductivity, 20°C (W/(m.K)) 10.6
Mean coefficient of thermal expansion, 20-100°C (/K)  13 x 10-6


Datasheet - NA-Alloy 725

Datasheet - NA-Alloy 725