Do You Know the Exact Process of Induction Hardening?

Induction hardening is a heat treatment in which metal parts are heated by electromagnetic induction and then quenched. It is also a form of surface hardening and can be used on many steels and steel alloys. Induction heating was first developed and introduced in 1831 by Michael Faraday. He could demonstrate that an electric potential could be generated by winding two copper coils around a magnetic core, turning one winding on and off at the same time would affect the other winding. These currents are generated by the alternating magnetic field around the core. As neither coil is in contact, the second coil induces an electric potential, a process known as induction heating.

Process

Induction hardening can be divided into two steps. The first step is heating, in which an electromagnet is used to heat the conductive metal. This is followed by quenching to change the surface structure of the material.

Induction heating

In induction heat treatment facilities, materials such as steel are usually placed in water-cooled copper coils where they are subjected to an alternating magnetic field. They are subjected to electromagnetic induction via an electromagnetic body and an electronic oscillator. This oscillator sends an alternating current through the electromagnet, which creates an alternating magnetic field that penetrates the material. The result is an eddy current (current loop) that heats the object inside the inductor coil.

Steels with a ferromagnetic structure can also be heated by hysteresis losses. Hysteresis losses generate heat by rearranging the magnetic domains, although this depends on the frequency of the current, the depth of penetration and the properties of the material (size, density, alloy) as to how much heat can be generated.

Quenching

Immediately after the induction heating process, the object must be quenched, which means that it must cool down extremely quickly. For this purpose, the workpiece is usually placed in a tank of oil or water, but sometimes cold air is used. Quenching ensures that only the surface hardens and that the heat does not spread to the core of the material, thus avoiding phase changes. These structures show higher tensile strength and lower initial yield stress than pure ferrite structures. Quenching also reduces grain size, which is a key factor in increasing the hardness of the material.

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Improved properties

Deeper surface depth: Induction hardening can penetrate surfaces up to 0.31" (8 mm). This depends on the induction hardening process and the properties of the material.

Finer grain size: As mentioned above, induction hardening changes the grain size of the material surface. Finer grain size increases hardness as the surface is more difficult to penetrate.

Higher wear resistance and fatigue resistance: Induction hardening increases wear resistance because the structure of the surface layer is changed. Ferritic steels acquire a martensitic structure, providing improved wear resistance.

Induction hardening is a good alternative to boriding and if you are looking for a treatment that also improves adhesion, wear resistance, high temperature stability and acid resistance, the certified BoroCoat treatment is a better choice. However, it depends on the application area and other factors as to which hardening technology is better suited to your needs. If you need any help deciding, please contact us here.