Alloy 725, often referred to as Inconel 625 (where Inconel is a trademark of Special Metals Corp), is a nickel-chromium alloy with significant additions of molybdenum, niobium and titanium.
Alloy 725/Inconel 625 can be supplied in the hot worked, annealed and age-hardened conditions. It is age-hardened to achieve extremely high strength, approximately twice that of Alloy 625 in the annealed condition. This is through the precipitation of the 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.
|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 ft.lb av (35 ft.lb min)|
|Impact Strength (-60oC) Transverse, Typical||50J av (43J min)||37 ft.lb av (32 ft.lb min)||43J av (37J min)||32 ft.lb av (27 ft.lb min)|
|Magnetic Permeability (20°C)||< 1.001|
|Young’s Modulus (kN/mm2)||204|
|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|