Induction hardening is an effective heat treatment process in manufacturing, which increases the hardness and strength of the workpiece. It involves heating a workpiece inside a coil structure. The high-frequency AC passes through the coil and generates an electromagnetic field. Energy generated by the field heats the workpiece. The heating of the workpiece causes phase transformation, and the instant cooling mechanism in the hardening machine stabilizes the phase transformation (Martinistic) to harden the workpiece.

The induction hardening process can harden different material pieces, parts, and products. This article will discuss the common materials used in induction hardening projects in detail.

What are the common material options for induction hardening?

There are a few basic requirements for any materials to be eligible for the Induction hardening process. The material needs to have high thermal & electrical conductivity. However, only a few materials are hardened using induction hardening because of specific microstructure and metallurgical requirements.

The material should have a suitable microstructure that will allow it to harden effectively through a phase transformation, which means a certain amount of carbon content. In addition, the material must hold metallurgical properties that enable it to retain its hardness after cooling. For example, austenitic steels are unsuitable for induction hardening as they have poor hardenability.

The following are the most common materials used in Induction hardening projects;

  • Cast iron (>2% of carbon content)
  • Medium carbon steel (0.3 to 0.6 % of carbon content)
  • High carbon steel (0.6 to 1.4% of carbon content)
  • Alloy steels
  • Tool steel
  • Stainless steel

Aluminum and titanium alloys are also compatible with induction hardening, although these non-ferrous materials are less common than other materials.

Steel induction hardening

Alloy steels, tool steels, stainless steel, or other steels (at least 0.3% carbon content) can be processed with induction hardening. In fact, steel is the most popular material in induction hardening projects. The raw-steel sheets, steel parts, and products are subjected to induction hardening to enhance the desired properties. It is one of the most efficient approaches to customize the strength and hardness of steel items to a desired level.

Most steel parts and products undergo an induction hardening process for surface hardening, such as manufacturing tools, gears, shafts, crankshafts, camshafts, bearings, bushings, axels, cylinders, pipes, connecting rods, and many more. The hardening depth can be controlled by adjusting the current, heating time, quenching rate, and other operational parameters. The hardening depth can range from 0.5 to 10 mm according to the specific requirements and intended use.

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Common grade of steel alloys for induction hardening

Steel that contains additional alloying elements in addition to carbon is known as alloy steel. Chromium, nickel, molybdenum, and Manganese are common alloying elements added to steel to increase its strength, hardness, toughness, and corrosion resistance.

There are several alloy steel grades used in diverse induction hardening projects. A grade of alloy steel refers to a specific standard or classification that defines the composition and properties of the steel.

Grades Description
1045 It is a medium carbon steel alloy with 0.43-0.50% carbon content and other alloying elements. The SAE 1045 steel can be hardened through induction heating to increase its strength and hardness. Although, with lower hardenability, it may not be suitable for specific applications with a very high surface hardness.
1050 Alloy steel 1050 is a medium-carbon steel alloy composed mainly of Manganese, carbon, and iron. It has a lower carbon content than 1045 steel, which means it is softer and less hardenable.
1144 It includes manganese and sulfur in addition to carbon as an alloying element. The ability to be stress-relieved without becoming brittle makes it unique.
4140 A low-alloy steel that is known for its good strength and toughness. The steel can be induction hardened to achieve a surface hardness of up to 58HRC (typical value). It has a relatively low hardenability compared to other high-alloy steel (John Pearson, 2021).
4340 It is a high-alloy steel with high strength and hardness, suitable for crankshafts, connecting rods, and other high-stress parts. Additionally, the addition of nickel in the alloy provides better toughness and ductility at high strength levels.
5210 It is a high-carbon alloy steel, and this high carbon content makes it suitable for induction hardening projects. This grade is used in high-performance applications after induction hardening that requires high surface hardness, such as bearings, gears, and cutting tools.
8620 8620 is a low-alloy steel commonly used in induction hardening projects. It is hardened to achieve different properties, strength, hardness, and fatigue life.
9310 It has a relatively high hardenability compared to other alloy steels, making it an excellent choice for induction hardening in applications with very high hardness.

Other alloy steel grades in induction hardening include 4150, 4350, 5150, 8650, EN25, EN2, XK1340, K245, and many more.

The carbon content of steel & induction hardening

As previously mentioned, the steel must have a certain percentage (0.3%) of carbon content to process with induction hardening. Therefore, the carbon content of steel is closely related to the induction hardening process. The carbon content primarily determines the hardness and depth of the hardened layer. Higher carbon content steels are harder and more brittle and can be hardened to a greater depth. On the other hand, low-carbon steels are softer and more malleable and can only be hardened to a shallower depth. The depth of the hardened layer is vital in induction hardening because it affects the strength and wear resistance of the component.

Additionally, the carbon content affects the transformation temperature of the steel during the induction hardening process. Steels with higher carbon content have a higher transformation temperature, which must be reached to transform the austenite to martensite.

Material selection procedure for induction hardening

The material suitable for your induction hardening projects depends on the specific requirements and constraints of the application, as well as the available materials and processing capabilities. Material selection is an essential aspect of induction hardening since it directly affects the performance of induction-hardened work.

The material selection procedure for induction hardening typically involves the following steps:

  1. Define the application requirements: The first step is to define & determine the specific requirements for the application, such as strength, hardness, wear resistance, toughness, and ductility.
  2. List the material options: Based on the application requirements, create a list of all potential material options, typically including a range of materials & alloys with different carbon content, other alloying elements, and microstructures.
  • Examine the induction hardening capabilities: Examine the capabilities of each material option you listed before considering several factors such as the transformation temperature, hardness, depth of the hardened layer, and susceptibility to cracking.
  1. Evaluate mechanical properties: Compare the mechanical properties of each material option, including strength, hardness, toughness, and ductility. You must ensure that they meet the requirements for the application.
  2. Consider cost and availability: Compare the price & availability of each material option, taking into account factors such as raw material costs, manufacturing costs, and lead time.
  3. Make a final decision: Based on the assessment of induction hardening capabilities, mechanical properties, and cost and availability, make the final decision on the most suitable material for the application.

Conclusion

The common materials used for induction hardening include cast iron, medium and high-carbon steels, alloy steels, tool steel, and stainless steel. However, steel is the most commonly used material in induction hardening projects. Choosing a suitable material is crucial since the material directly affects the quality and performance of induction-hardened parts or products. Therefore, select the material for your project based on the desired properties, intended application, hardening capability, cost, and fatigue life.