Difference Between Inconel 718 and Inconel 625

Inconel 718 and Inconel 625 are nickel-based alloys with excellent comprehensive properties, and both belong to the inconel alloy series. They have good high temperature resistance and corrosion resistance. The difference is that the performance of Inconel 718 is more inclined to high strength. Inconel 625 more prone to corrosion resistance.

The following is a comparison of these 2 alloys from several aspects, so that you can have a more comprehensive and clear understanding of the alloy.

1 .Overview

Inconel 718 (UNS N07718, W.Nr. 2.4668) is a high strength, corrosion resistant nickel-chromium alloy for use in temperatures from -423°F to 1300°F. The yield strength below 650 ℃ ranks first in the deformed superalloy, and has good fatigue resistance, radiation resistance, oxidation resistance, corrosion resistance, as well as good processing performance and good welding performance. It can manufacture various parts with complex shapes, and has been widely used in the above temperature range in aerospace, nuclear energy, petroleum industry and extrusion dies. The alloy is a precipitation-strengthened alloy with a density of 8.19g/cm³.

INCONEL 625 (UNS N06625 , W.Nr. 2.4856) is a solid solution strengthened nickel base wrought superalloy with excellent corrosion resistance and high oxidation properties, good tensile and fatigue properties from low temperature to 1800°F , and resistant to stress corrosion in a salt spray atmosphere. Therefore, it can be widely used in the manufacture of aero-engine parts, aerospace structural parts and chemical equipment, with a density of 8.44 g/cm³.

2. Comparison of element content

Si element can improve the corrosion resistance and hardness of the alloy. Adding appropriate Si element to the nickel alloy can promote the formation of a dense silicon oxide protective film in the corrosive medium and improve the corrosion resistance of the material. The silicon ratio of Inconel 625 is higher than that of Inconel. The content of 718 is high, so inconel 625 has better corrosion resistance.

Inconel 718 has a much higher iron content than Inconel 625, and its content of nickel, chromium, and molybdenum is relatively small. Nickel and chromium can improve the corrosion resistance of the alloy, and molybdenum can supplement the reduction resistance of the alloy. Therefore, the corrosion resistance of Inconel 625 is much greater than that of Inconel 718.

Inconel 718 has a higher niobium content than Inconel 625, thus allowing age hardening, allowing annealing and welding without spontaneous hardening during heating and cooling. Inconel 625 does not have this feature.

3. Strengthening method

Inconel 718 is a precipitation strengthened alloy. During production, aluminum and titanium precipitate from the matrix to form the γ' phase. This greatly increases the strength of the alloy. Niobium and tantalum also play a precipitation strengthening role in Inconel 718. But different from aluminum and titanium, a part of niobium and tantalum enter the γ matrix for solid solution strengthening, and a part enters the γ' phase to increase the precipitation strengthening effect, while more niobium and tantalum can form the γ'' precipitation strengthening phase. The strengthening effect of this precipitation-strengthening phase at medium and low temperature is more obvious than that of the γ' phase. But at high temperature, the effect of γ'' phase will be significantly weakened.

Inconel 625 is a solid solution strengthened alloy, mainly through solid solution strengthening. Most of the aluminum and titanium in the alloy dissolve into the alloy matrix (γ-austenite). This has a weaker strengthening effect on the alloy. Due to the large atomic radii of niobium and tantalum, their solid solution strengthening effect on 625 alloy is greater than that of aluminum and titanium.

4. Mechanical properties

It is obvious that the yield strength and tensile strength of Inconel 718 are much higher than those of Inconel 625

5. Heat treatment method

Inconel 718 is a precipitation-strengthened alloy, so it is generally subjected to aging treatment after solution treatment. The purpose is to fully analyze the precipitation strengthening phase and improve the strength of the alloy. There are two heat treatment methods for this alloy:

a. Solution annealing at 1700-1850°F, rapid cooling in water, then precipitation hardening at 1325°F for 8 hours, furnace cooling to 1150°F, holding at 1150°F for a total aging time of 18 hours, Next, air cooling is performed.

b. Solution annealed at 1900-1950°F, then rapidly cooled in water, precipitation hardened at 1400°F for 10 hours, furnace cooled to 1200°F, held at 1200°F for 20 hours total aging time, final Air cooling.

The properties of the alloys obtained by the two heat treatment methods are different and can be selected according to the actual application. The first heat treatment method is performed by default

The standard heat treatment method for 625 alloy is solution treatment, and the 625 alloy after solution treatment can achieve the best performance state.

6. Industry application

Inconel 718 and Inconel 625 can be widely used in aerospace, marine engineering, oil and gas, electric power and other industries. In addition, INconel 718 is also widely used in the automobile manufacturing industry. Due to its high corrosion resistance, Inconel 625 can also be used in pollution treatment, chemical processing and other fields.

7. Suppliers

Wudenalloy has focused on the production and manufacture of nickel alloys for more than ten years. We are a principal worldwide supplier of corrosion-resistant alloys and other superalloy metals. We have a professional technical team and after-sales service, so we can offer high -quality Hastelloy, Incoloy, Inconel, Monel, Duplex Stainless Steel, and other alloy material. These materials are available in wire, bar, sheet&plate, pipe&tube, flange, forging, and other forms to meet the needs of our customers.

Request a quote now to get the competitive special alloy prices, you can also send emails to sales@wudenalloy.com, Wudenalloy is your trusted supplier of special alloy material.