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Inconel alloy 625 – Potential characteristics for high temperature applications

Inconel alloy 625 is known for its supreme characteristics such as high tensile strength and resistance to creep and stress rupture at high temperatures. Moreover, it has proven to become a highly versatile alloy with several significant characteristics such as high strength, fracture hardness, fabricability and corrosion resistance.

Alloy 625 is a versatile alloy comprising of several significant characteristics for example corrosion resistance in seawater, oxidizing and reducing acids and salts, good fatigue strength and supreme weldability and fabricability.

Inconel alloy 625 was made as a nickel-chromium alloy that is solid solution reinforced by molybdenum and niobium elements. It is mainly used for offering resistance to aqueous corrosion at ambient to nominally higher temperatures, high strength as well as resistance to creep, rupture and corrosion at the high temperatures.

Annealing

Inconel is annealed in the range of 1600oF to 1800oF or 871-982oC to attain a fine grain structure. The solution annealed form is for service at temperatures above 1100oF or 593oC when resistance to creep and rupture are required. While ASTM specifications need a nominal annealing limit of 2000oF or 1093oC, products are annealed between 2050- 2150oF and hence attain a coarse grain matrix. It improves alloy’s resistance to creep and rupture at the elevated service temperatures.

A recent grade in the development of Inconel 625 products is a vacuum induction melted, controlled chemistry and fine grain product that attains significantly enhanced fatigue resistance and heat stability. Melting is closely related to develop a specifically clean microstructure. Thermal-mechanical treatment is performed to develop a fine grain size. This structure shows improved resistance to mechanical fatigue and enhanced heat stability.

Precipitation Hardening

Inconel 625 metal is remarked as a solid solution reinforced alloy containing 4% niobium, it is slightly age hardenable. When heated to 1200-1600oF or 649oC – 871oC limit, Inconel 625 can precipitate a fine Ni3Nb dispersoid gamma double prime. Different forms of carbide particles can also be developed. An effect of the combined precipitation of these phases is to noticeably increase the yield and tensile strengths. Inconel 625 products usually attain tensile and yield strength values about 130 ksi and 60 ksi. Although the material aged at 1200oF to 1250oF for prolong time periods get tensile strength more than 160 ksi and yield strength more than 110 ksi.

Applications

Inconel 625 is commonly used for several applications for offering good tensile strength, ductility, impact and hardness characteristics at cryogenic temperatures. Inconel 625 provides supreme weldability and resistance to hot fracturing. It has become a popular welding composition.

It also offers supreme resistance to marine corrosion. So, it is commonly used for fabrication of shipboard components and related support hardware.

Inconel 625 also provides characteristics that make it supreme for service at the high temperatures. Inconel 625 provides a significant combination of strength and resistance to creep and rupture resistance prevention of corrosive attack at service temperatures about 2100oF or 1140oC.

Inconel 625 is a commonly manufactured alloy for which ASME Boiler and Pressure Vessel Code has specified permitted design stresses for application about 1800oF or 982oC.