Inconel Vs Stainless Steel

Inconel and stainless steel are highly popular metal alloys that offer superior dimensional stability under extremely corrosive environments. However, each has different application areas. When it comes to Inconel vs. stainless steel, three major deciding factors come into play: cost, temperature tolerance, and strength.

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.

Inconel

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:

• Turbines.

• Heavy machinery parts.

• Turbojet engine parts.

• Metal die casting.

• Natural gas piping.

• 3D printing.

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

Stainless Steel

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:

1.) Austenitic

• Most commonly used

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

• Used in food processing equipment, kitchen utensils, and medical equipment

2.) Ferritic

• 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

3.) Martensitic

• 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

• Used for dental, surgical equipment, knives, and other cutting tools

4.) Duplex

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

• Higher yield strength and greater chloride stress corrosion cracking

• Used in chemical plants and piping

5.) Precipitation-Hardenable

• 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

• Used in the oil and gas, nuclear, and aerospace industries

Inconel vs. Stainless Steel: Application Differences

Although both metals may have a similar physical appearance, they are different in many other aspects. Moreover, both metals come in different grades, and no two alloys of the same metal have similar properties. For instance, grade 316 stainless steel alloys can perform better under chloride solutions than grade 304 stainless steel alloys. Moreover, the strength of the alloy may change depending upon the heat treatment received. For example, the tensile strength of “as-rolled” Inconel bars is more than solution-treated bars. Even a slight variation in the secondary elements can alter the final strength profile.

The table below compares the essential properties of the two most popular alloys, Inconel 625 and 304 stainless steel.

Inconel 625 304 Stainless Steel  Tensile strength 135,000 psi (930 MPa) 75,000 psi (515 MPa) Melting point 2,460°F (1350°C) 2,550°F (1400°C) Operating temperature 1,800°F (982°C) 1,697°F (952°C) Yield strength 75,000 psi (517 MPa) 30,000 psi (205 MPa) Elongation 42.5% 35% Machinability Poor Poor Corrosion resistance Good, especially resistant to pitting and crevice corrosion Good, offers excellent resistance to most oxidizing acids

According to the comparison above, applications requiring high tensile strength at high temperatures, Inconel 625 would be an ideal choice over 304 stainless steel; therefore, Inconel 625 is used in heat exchangers and gas turbines. On the other hand, 304 stainless steel, due to its low operating temperature range, is good for applications requiring dimensional stability coupled with high corrosion resistance at low temperatures.

When it comes to corrosion resistance, both have specific application areas. Inconel 625 offers outstanding corrosion resistance to chloride-ion and sea waters. Due to its high-corrosion fatigue strength, the alloy offers protection against pitting and crevice corrosion; thus, it’s used as wiring rope for mooring cables, exhaust ducts for Navy utility boats, and steam line bellows. On the other hand, 304 stainless steel resists corrosion from oxidizing acids such as sulphuric acids and is often used in chemical containers, including those for transport, and automotive and aerospace components.

However, it’s important to note that both alloys have poor machining characteristics. Overcoming the machining challenges of Inconel vs. stainless steel is imperative to keeping material waste and costs under control.

Challenges With Machining Inconel and Stainless 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 its 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.

Unless you have the right setup and expertise to deal with these challenging metals, it’s better to outsource the task to a knowledgeable service provider.

Your Local Metal Supplier for Inconel, Stainless Steel, and Other Alloys

Industrial Metal Service has been supplying a wide range of metals, including Inconel and stainless steel, to the San Francisco Bay Area and beyond for more than two decades. We offer new metals sourced straight from U.S. mills, but for those who wish to save on costs, we also provide metal remnants verified using x-ray fluorescence technology.