Understand the differences between Inconel and stainless steel

When manufacturing a new part, one important question is what metal material to use. What will it be used for?

If a part needs to have superior strength and corrosion resistance at high temperatures, Inconel alloys are best.

If a part needs for handling medical supplies may be better suited for an alloy of stainless steel.

Inconel alloys tend to be better for heat treating applications and other high-temperature processes. Meanwhile, stainless steel alloys are often suitable for sterile manufacturing or medical applications (or any application involving corrosives).

 

In this article, we examine the properties of Inconel and stainless steel and the applications for which they’re well-suited so you can make the best decision based on your project requirements.

 

When comparing stainless steel vs Inconel, it is important to remember that there are different formulations for each. The variants of stainless steel have drastically different tensile strength, recommended operating temperature, and resistance to specific corrosives. For example, grade 316 stainless steel tends to have a higher resistance to chlorides than 304 stainless steel (but also has a higher cost on average).

 

Additionally, certain treatment and forming methods may affect the tensile strength of a metal. For example,the tensile strength of an “as-rolled” bar of Inconel 625 is 120-160 ksi (827-1103 MPa), while a “Solution-Treated” bar has 103-130 ksi (714-896 MPa) of tensile strength.

 

That both of these tensile strength ratings are given as a range instead of a specific number. This is because the strength of a metal may vary somewhat depending on the precise proportion of ingredients in it a slight variation in carbon, nickel, or iron content can significantly alter the final product's strength.

Inconel is a nickel-chrome-based superalloy known for displaying an excellent strength profile at high temperatures of about 2,000°F under harsh corrosive environments. Because of these unique properties, Inconel is used in jet engines, oil and gas extractions, saltwater applications, and heat treat applications. Some popular applications of Inconel include:

However, Inconel alloys are much more expensive than stainless steel alloys.

Chromium is the main alloying element in stainless steel (about 10%-20%), which gives stainless steel alloy 200 times more corrosion resistance than even mild steel. It can be classified into five different groups, as follows:

Most commonly used

Weldable, non-magnetic, and non-heat-treatable

Contains 12-17% chromium, less than 0.1% carbon, and molybdenum, aluminum, and titanium

Offers good ductility and formability

Has poor strength in high temperatures

Magnetic and non-heat-treatable

Cheapest grade

Contains 11-17% chromium, 1.2% carbon, and less than 0.4% nickel

Higher carbon content affects forming and welding

Pre- and post-heat treatment is required to obtain other reliable properties

Contains 20-25% chromium, 5% nickel, molybdenum, and nitrogen

Higher yield strength and greater chloride stress corrosion cracking

Precipitation heat treatment to reduce plasticity

Easy to machine, highly durable, and high on yield strength and tensile strength

Four times tougher than austenitic steel

While it's important to understand the differences between Inconel vs. stainless steel, it's just as essential to understand how the unique properties of each contribute to its machinability.

For example, the strength of Inconel makes it hard to machine, as it is prone to work hardening and can therefore damage tools or deform the workpiece. One of the best ways to overcome this is to solutionize Inconel alloys before machining to release the stress. It is also advisable to use ceramic tools for achieving continuous cuts and reducing work hardening while cutting Inconel blocks.

Cutting stainless steel with precision is also a challenge owing to it's high nickel content, which leads to severe plastic deformation during the machining process. The surface gets hard to penetrate with subsequent attempts. As a result, the alloy requires more cutting force, which leads to tool failure due to excess frictional heat. Using industrial band saws and following the proper cutting process can help you achieve precision faster and more easily.