Mechanical properties of INCONEL alloy 625

We strip back this high-performance nickel alloy and explore the impressive mechanical properties that make it such a well-used material

As the flagship nickel alloy in the impressive line-up of materials that we supply, INCONEL alloy 625 is somewhat of a wonder product among the INCONEL alloy Grades. Its many positive properties mean that it lends itself to so many different industrial uses, making it an exceptionally versatile alloy.

This high-performance material is often lauded for its remarkable corrosion resistance, even in the most aggressive of environments and the highest of temperatures. But this is not its only defining feature; the alloy has been carefully crafted to offer an abundance of physical and mechanical properties to help solve common design engineering problems.

Over the years, INCONEL alloy 625 has developed to enhance these properties further. From when it was first introduced in the 1960s, as a material for steam-line piping, it has been modified to improve its creep resistance and weldability, which has in turn increased its number of industrial applications.

Defining mechanical properties

There are a lot of considerations to make when it comes to material selection. It’s important to evaluate an alloy’s physical and mechanical properties and look at how these measure up against the intended end use.

Physical properties are those properties that are measurable, for example an alloy’s conductivity or melting point. These properties are facts of an alloy’s composition and are useful points to take into consideration.

However, an alloy’s mechanical properties are even more useful for design engineers for comparing the performance of different metal alloys to meet their requirements. Mechanical properties are indicators of how a material performs under the application of different forces. This includes strength (tensile, rupture, fatigue, etc), ductility and resistance to wear over time.

Key mechanical properties of INCONEL alloy 625

While a lot of tests are performed on nickel alloys to determine their mechanical properties, one of the most important is to test for tensile strength. This property relates to the amount of load a metal can withstand before it breaks. Metals go through a number of important strength points before the final fracture. The material will first begin to deform and stretch, until it reaches the point where it retains this deformation (as opposed to returning to its original shape). This is the yield strength. When the material reaches the load at which it ultimately breaks, this is the tensile strength. The more a material can resist a permanent deformation in its shape is known as the alloy’s hardness.

INCONEL alloy 625 has high strength and hardness across the board. It is possible to work the material to offer increased tensile strength in moderate-temperature working conditions by cold working the alloy. When exposed to intermediate temperatures, some hardening does happen within the alloy.

Another key test that is performed on alloys to determine its strength is to look at its fatigue strength. This is how much repeated stress a metal can withstand, though this is very much dependant on the level of stress the metal is placed under, and the frequency and the duration that the stress is applied for. The fatigue limit is usually expressed in the number of ‘cycles’ that the metal can endure. INCONEL alloy 625 exhibits good room-temperature fatigue strength, as well as solid performance at elevated temperatures – variations occur depending on whether the metal has been solution-treated or annealed.

As an example of its exceptional fatigue strength, INCONEL alloy 625’s endurance limit of 108 cycles at room temperature using cold-rolled annealed sheet tested in completely reversed bending was found to be 90,000 psi for smooth bar. A material’s toughness is usually measured with an impact test, to see how much an alloy can absorb the impact without fracturing. This is usually performed at a range of different temperatures. Ductility is also tested, to see how much a material can stretch without fracturing, as well as retain its new shape once the force is removed. Both toughness and ductility can be impacted at very low temperatures, when materials are more prone to cracking. However, INCONEL alloy 625 has the ability to retain its already excellent toughness and ductility properties at temperatures as low as -320°F.

Processing INCONEL alloy 625

In order to get the best mechanical properties out of INCONEL alloy 625, it is usually processed to be either hot worked, cold worked or annealed for conditions under 1200°F. For hotter temperatures, it offers the best performance when annealed or solution treated. Often the material is solution treated if it’s required for components that need the optimum resistance to creep or rupture.

It does need to be processed by expert hands to retain these impressive mechanical properties. Due to the fact that this material was developed to stay very strong under high-temperature conditions, care must be taken when being hot worked. It is easily fabricated by hot forming, but it needs very powerful equipment to do so. However, the material can be cold formed by standard processes and this can have an advantageous impact on the mechanics of the alloy, for example the increased tensile strength as mentioned above.

Find out more about INCONEL alloy 625 on its product page.