Inconel 625

Inconel 625

Inconel 625 is a solid-solution matrix stiffened face-centered-cubic alloy and a high-performance super alloy that is an amalgam. It has prominent qualities like better mechanical strength, assured thermal creep deformation resistance, brilliant surface solidness, and insurance from corrosion or oxidation. Due to the presence of nickel, this alloy can also be referred to as nickel 625.

Inconel 625 composition has nickel-chromium-molybdenum and addition of niobium contents, its alloy is more beneficial to various other industries. The addition of Niobium with molybdenum stiffens the alloy’s matrix and thus provides better strength without any kind of heat treatment. Inconel 625 manufacturers can produce Inconel 625 bars, Inconel 625 plates, Inconel 625 rod, and Inconel 625 round bars. Some Inconel 625 suppliers can also produce Inconel 625 seamless pipe.

The Inconel 625 astm for rods and bars is ASTM B 446 while the astm for plate is ASTM B 443. 

Inconel 625 Chemical composition
GRADE   Cr Mo Co Nb+Ta Al Ti C Fe Mn Si P S Ni
INCONEL 625 MIN 20 8 3.15 Balance
MAX 30 10 1 4.15 0.4 0.4 0.1 5 0.5 0.5 0.015 0.015
Inconel 625 density and Physical properties
Grade Density
(g/cm3)
Thermal
Conductivity
(W.m -1.°K-1)
Elastic
Modulus
(GPa)
Specific Heat
(J.kg-1.°K-1)
Electrical
Resistivity
(μΩ.cm)
Inconel 625 8.42 1354-1413 207 (0-100°C) 10.3
460

Is Inconel 625 a stainless steel?

No, Inconel 625 is not stainless steel. However, the nickel alloy 625 properties are much better than stainless steel as it provides a higher corrosion resistance. It also possesses more tensile strength and is formulated for use in extremely high temperatures.

Alloy 625 is resistant to oxidation and scaling at elevated temperatures. At 1800°F, scaling resistance becomes an important factor in working conditions. It is better than other high-temperature alloys under cyclic heating and cooling conditions. The combination of the alloying elements in nickel alloy 625 makes it withstand a range of severe corrosive environments.

When talking about Inconel 625 vs 718, the major difference is that Inconel 625 is non-magnetic and oxidation resistant, while Inconel 718 is an austenitic super-alloy.

Inconel 625 Corrosion Resistance

The alloy Inconel 625 is resistant to a wide range of corrosive media from highly oxidizing to medium reducing. Inconel 625 alloy has more alloy content in it due to which it can withstand the effect of severe corrosive environments. In mild environments such as freshwater seawater, atmosphere, neutral salts and even alkaline media, or in more extreme corrosive environments, the mixture of nickel and chromium gives Inconel 625 more strength to resist oxidizing chemicals, whereas the more nickel and molybdenum contents provide resistance to non-oxidizing environments.

The high molybdenum content also provides resistance to pitting and crevice corrosion and niobium stabilizes the alloy while welding against sensitization, thus preventing further intergranular cracking. Also, the high nickel content makes it free from chloride ion stress corrosion cracking. 

Inconel 625 Specifications

GRADE UNS OLD BRITISH G0ST OR AFNOR JIS
INCONEL 625 N06625 BS EN XH60BT ЭИ602 NC22DNB4M NCF 625
NA 21 2.4856

Fabrication and Heat Treatment of Alloy 625

Alloy 625 can be manufactured through various cold and hot working processes. It resists deformation at hot working temperatures; therefore higher loads are required to form the material. Hot forming should be performed within a temperature range of 1700° to 2150°F. During cold working, the material of Inconel 625 hardens faster than traditional austenitic stainless steel.

The alloy has three heat treatments: 1) solution annealing at about 2200°F and air quench or quicker, 2) annealing at about 1900°F and air quenching or quicker and 3) stress-relieving at up to 1500°F and air quenching. Solution annealed (grade 2) material is commonly used for applications above 1500°F where resistance to creep is important. The soft annealed material is mainly used for low temperatures and has the ideal combination of tensile and rupture properties.

Weldability of Inconel 625

Alloy Inconel 625 is ductile and strong at lower temperatures, it has high strength, fatigue and thermal-fatigue strength, better resistance to oxidation, and excellent weldability and brazeability, thus Inconel 625 is used in a wide variety of industries. Inconel 625 tubing is popularly used in the aerospace industry due to its high tensile strength and weldability.

Welding can be done by gas-shielded processes using tungsten electrodes or consumable electrodes. Post Weld heat treatments of the weld are not necessary to maintain corrosion resistance. Heavy restrained sections can be seamlessly welded and it’s mechanical properties follow the same trends as any base metal properties.

Inconel 625 Application

Inconel 625 was developed in the 1960s with the sole purpose of crafting a material that can be used to manufacture steam-line piping. Further changes to the Inconel 625 composition have made it to be even more creep-resistant alloy. The application of Inconel 625 has grown in a variety of industries like chemical processing industry, and for marine and nuclear applications to manufacturing pumps, and valves and other high-pressure equipment. Other areas where the alloy is used are:

  • Aircraft ducting systems
  • Jet engine exhaust systems
  • Engine thrust-reverser systems
  • Specialized seawater equipment
  • Chemical process equipment