Induction hardening is a fast, clean, and repeatable process that creates a wear- and fatigue‑resistant case on a steel part. Unlike other case hardening methods, it does not involve a furnace or specialized atmospheres, but instead, uses electricity. This allows for precise control over the hardening results.
However, induction hardening is not suitable for all components or steel grades. Success requires a part design that lends itself to the process and a considered selection of material.
Typically, a component is through‑hardened before induction hardening in order to prepare the core. Then, the part can undergo induction hardening, which follows two basic steps.
First, in the induction‑heating stage, an alternating current passes through a copper coil surrounding the part. The current generates a magnetic field that induces eddy currents in the surface of the part; the steel’s electrical resistance turns the eddy currents into heat until the metal’s surface is brought into the austenite range.
In the second stage, quenching (with water, oil, air, or a polymer quenchant) rapidly cools the heated area, and the austenite transforms to hardened martensite.
Process design is often the most challenging aspect of induction hardening because each coil is custom engineered to a specific part. It’s a complex undertaking. Modern simulation tools, however, can streamline design and minimize trial and error by determining temperature, case depth, and final hardness profile.
Process variables encompass the copper coil design (number of turns, how closely coils are spaced, how far the coil sits from the surface of the part), the frequency of the magnetic field (the lower the frequency, the deeper the case; the higher the frequency, the shallower the case), and the speed and severity of quenching (which locks in the martensitic structure and final hardness profile).
Three approaches to induction hardening include:
For single shot induction hardening, the entire setup (both the part and coil) remains stationary while the area to be treated is heated and then quenched.
The coil travels horizontally or vertically along a stationary part. Induction scanning is especially useful for long shafts that are difficult to fit into a heat treatment furnace.
When spin hardening, the metal part is placed within a coil and rotated to average out the eccentricity, which helps ensure uniform circumferential heating.
Once the setup and coil design are satisfactory, induction hardening is extremely reliable and repeatable, making it well suited for high-volume components such as automotive or power‑transmission parts. Due to upfront costs, the process is usually amortized over years of production, rather than for one‑off projects or very small batches.
Not all grades respond well to induction hardening. The steel must have particular electrical resistance and magnetic properties to generate the necessary heat.
In general, the more carbon in a steel, the harder the case. For example, high or medium carbon steels are better candidates for induction hardening than low-carbon steels.
Alloy steels, particularly those that contain chromium, molybdenum, and nickel, are induction-friendly. Sullivan’s induction hardening grades include:
As it allows you to target certain areas of a part, induction hardening could be a good choice for parts that will experience localized high wear, rolling or sliding contact, or cyclic loading.
Examples of selective hardening include:
Journals (only)
Gear teeth (only)
Spline flanks (no roots)
Specific wear bands along a shaft
Typical components include:
Gear teeth
Bearings
Bearing races
Ball screws
Axles
Camshafts
Crankshafts
While methods such as carburizing can reduce corrosion resistance, induction hardened components retain 100% of their corrosion properties, as no carbon is ever added to the part.
There’s a lot to like about induction hardening. It’s clean, repeatable, reliable, and fast. But not all steels are suitable for induction hardening; Sullivan sells several proven grades, including N360, XD15NW, and XD16N.
See our Line Card for more details.
We stand by the steel we sell. If you require guidance, don’t hesitate to reach out to Sullivan’s experts. We’re committed to supporting each customer’s unique application. Start a live chat or contact Sullivan today!
https://gearsolutions.com/departments/hot-seat/basic-principles-of-induction-hardening-of-steels/
https://material-properties.org/what-is-induction-hardening-advantages-and-application-definition/
https://proleantech.com/induction-hardening/
https://www.simscale.com/blog/induction-hardening-from-basics-to-optimization/
https://www.heattreattoday.com/equipment/heat-treating-equipment/induction-heating-equipment/induction-heating-equipment-technical-content/induction-hardening-understanding-the-basics/
https://www.sdbksteel.com/what-grades-of-steel-can-be-induction-hardened/