Understand the differences between Inconel and stainless steel

When manufacturing a new part, an important question is which metal material to use. What will it be used for?
If the part needs to have excellent strength and corrosion resistance at high temperatures, then Inconel alloy is the best choice.
If the part needs to handle medical supplies, stainless steel alloys may be more suitable.
Inconel alloys are generally better suited for heat treatment applications and other high-temperature processes. Meanwhile, stainless steel alloys are generally suitable for sterile manufacturing or medical applications (or any application involving corrosive substances).

In this article, we will examine the characteristics of Inconel and stainless steel and the applications they are suitable for so that you can make the best decision based on the needs of your project.

When comparing stainless steel and Inconel, it is important to remember that each has different formulations. The tensile strength, recommended operating temperature, and resistance to specific corrosion of different stainless steels vary greatly. For example, 316 grade stainless steel tends to resist chlorides better than 304 grade stainless steel (but it also costs more on average).

In addition, certain processing and forming methods can affect the tensile strength of the metal. For example, Inconel 625 has a tensile strength of 120-160 ksi (827-1103 MPa) for "as rolled" bars, while "solution treated" bars have a tensile strength of 103-130 ksi (714-896 MPa).

Both of these tensile strength grades are ranges, not specific values. This is because the strength of a metal can vary slightly depending on the exact proportions of its components, and even slight changes in the carbon, nickel, or iron content can significantly change the strength of the final product.

Inconel Alloy
Inconel is a nickel-chromium-based high-temperature alloy known for its ability to maintain excellent strength in harsh corrosive environments up to about 1000°C. Due to these unique properties, Inconel alloys are used in jet engines, oil and gas production, seawater applications, and heat treatment. Some common applications of Inconel alloys include:
Turbines.
Heavy machinery parts.
Turbojet engine parts.
Metal die casting.
Gas pipelines.
3D printing.
However, the price of Inconel alloys is much higher than that of stainless steel alloys.
Stainless Steel
Chromium is the main alloying element in stainless steel (about 10%-20%), which makes stainless steel alloys 200 times more corrosion resistant than mild steel. Stainless steel can be divided into the following five categories:
1.) Austenitic stainless steel
Most commonly used
Weldable, non-magnetic, non-heat treatable
Used in food processing equipment, kitchenware and medical equipment
2.) Ferritic stainless steel
Contains 12-17% chromium, less than 0.1% carbon, as well as molybdenum, aluminum and titanium
Has good ductility and formability
Lower high temperature strength
Magnetic, non-heat treatable
Cheapest grade
Used in the manufacture of automotive parts, industrial machinery and kitchenware because they are easy to cold work and deep drawing operations.
3.) Martensitic Stainless Steel
Contains 11-17% Chromium, 1.2% Carbon, and less than 0.4% Nickel
Higher carbon content affects forming and welding
Requires preheating and post heat treatment for other reliable properties
Used in dental, surgical equipment, knives, and other cutting tools
4.) Duplex Stainless Steel
Contains 20-25% Chromium, 5% Nickel, Molybdenum, and Nitrogen
Has higher yield strength and greater resistance to chloride stress corrosion cracking
Used in chemical plants and pipelines
5.) Precipitation Hardening Stainless Steel
Reduced plasticity through precipitation heat treatment
Easy to machine, highly durable, with high yield and tensile strengths
Four times tougher than austenitic steels
Used in oil and gas, nuclear, and aerospace industries
Machining
It is important to understand the difference between Inconel and stainless steel, but it is also important to understand how each material's unique properties determine its machinability.
For example, Inconel's strength makes it difficult to machine because it is prone to work hardening, which can damage the tool or deform the workpiece. One of the best ways to overcome this problem is to solution treat the Inconel alloy to relieve stress before machining. In addition, it is recommended to use ceramic tools to achieve continuous cutting and reduce work hardening when cutting Inconel blocks.
Precision cutting of stainless steel is also challenging due to its high nickel content, which causes severe plastic deformation during machining. The surface becomes difficult to penetrate during subsequent machining. Therefore, this alloy requires greater cutting forces, and excessive frictional heat can cause tool failure. Using an industrial band saw and following the correct cutting process can help you achieve high-precision cuts faster and easier.