Hardening and Tempering with Induction

What is Hardening?

Hardening can be defined simply as any process by which the hardness of a material is increased and ductility is decreased. This can be done in order to strengthen high-wear surfaces and extend the service life of parts. Although there are a number of different methods for hardening which may be more or less suitable depending on the material being used, Induction technology is often utilized in a hardening process known as Quenching and Tempering.

What is Quenching & Tempering?

Quenching and Tempering is a hardening process that can only be performed in medium to high carbon steel. The steel is heated to a high enough temperature for the crystal structure of the iron to change from ferrite to austenite. In this altered crystal state, the steel is able to dissolve much more carbon than it otherwise could. The steel is then quenched using water, oil, or, in the case of induction equipment, a water-polymer solution. This quenching cools the steel rapidly which prevents carbon precipitates from forming which can reduce the final hardness of the steel. Once the steel cools to a low enough temperature, the crystal structure tries to return to its low-temperature state. At this point, the steel has dissolved more carbon than it can hold in its original low-temperature state so it transforms into a different crystal structure called martensite. Martensite is extremely hard due to having distorted crystal structures and a higher saturation of carbon. At this point, the steel is very hard but as a result, it is also very brittle. Tempering involves heating the steel back up to a much lower temperature in order to slightly reduce the hardness and, in turn, reduce the brittleness. The temperature at which the steel is heated depends on how much hardness needs to be retained by the steel. Once the desired hardness is achieved, the steel is quenched again in order to prevent residual heat from tempering the steel further.

Quenching & Tempering with Induction

Induction technology is most often used in Quenching and Tempering procedures where it provides the most distinct advantages. This procedure requires extreme amounts of precision in both the heating and quenching of the steel in order to achieve the desired hardness profile. Even extremely small variations in the procedure such as heating for a second too long or quenching at the wrong temperature can result in large variations from part to part. Because of this, precise control of the process becomes paramount. Induction technology offers more control than any other method of heating.

Automatic handling and fixturing of components for heating and quenching provides for high production rates and helps to produce consistent results part after part. Induction is by far the fastest method of hardening and heat treating. As a result, the process produces minimal distortion, no surface decarburization, fine grain microstructure, and precisely controlled hardness patterns. induction is the perfect solution for any facility looking to step up production to the next level.

Induction Case Hardening

Selective induction case hardening can enhance the performance of parts by providing hybrid mechanical properties, hardness where needed on wear surfaces, and ductility in the core to provide impact resistance.

Selective induction hardening has the ability to specifically target and apply heat rapidly to a localized area of a part. As a result, the part develops a layer, or case, of hardened material. This is ideal for parts that are highly stressed in operation and require a combination of mechanical properties. For example, high yield strength, fatigue resistance, and resistance to wear at the same time.

The precise hardness pattern can be controlled by appropriate adjustment of the frequency used, induction coil geometry, power level, and the location of the part in the coil. The hardness pattern remains highly consistent from part to part due to industry-leading precision in Radyne systems. Rotation during heating assures a uniform case.

Progressive Induction Hardening | Induction Scanning

Frequently, parts require surface hardening in selected areas to provide optimum performance and long service. Induction hardening, using progressive heating and quenching, provides an economical way to process shafts or other parts.

By progressively passing a steel shaft through a heating coil into a water quench, the outer skin can be heated, quenched, and hardened without affecting its core. When a completely uniform case is required it is often necessary to rotate the shaft. The coil and the associate water quench usually form one unit, as the position of the water quench with respect to the inductor is very important. The water supply is often fed through the coil itself, as illustrated. Controlled scanning of shafts through the induction coil and quench ring while rotating produces controlled case depths over adjustable lengths of the shafts, all in on an automated cycle.

Control of the case depth depends upon the power input from the generator and the downward speed of the shaft through the induction coil while the length of the hardened section is controlled by a pyrometer which is set to suit specifications. Once the desired case depth and hardness patterns are found by matching equipment parameters, these settings can be made consistent for a repeatable process across every part.

While the application described involves surface hardening, it is adaptable for other heat-treating operations that require progressive heating, such as annealing and tempering.

Hardening & Tempering Industries & Equipment

Hardening & Tempering is extremely common in many industries. Often, heat-treating procedures are outsourced to a commercial heat treater because traditionally the process can be dirty and can require building modifications or additions and highly specialized equipment to comply with safety and environmental standard. Luckily, induction technology provides a clean, efficient, safe, and cost-effective solution that allows manufacturers to bring their heat-treating back in-house.

Induction Scanners

Induction Scanners are some of the most versatile induction machines offered by Radyne. These machines are used across many industries to heat-treat a large variety of components. Radyne offers two lines of induction scanners to suit our customers’ needs.


ScanMaster is Radyne’s premium line of induction scanners. These are vertical scanners designed for medium to large parts.

FlexScan 12


FlexScan is Radyne’s entry-level pop-up scanner line. Pop-up scanners feature a single spindle extending from the base of the machine and are commonly used for small to medium-sized parts.

These systems are commonly used to heat treat components such as:

  • Bearings
  • Bits
  • Blades
  • Gears
  • Pins
  • Rods
  • Shafts
  • Hand Tools
  • Weapon & Firearm Components

Industries that commonly use induction scanners:

  • Aerospace
  • Ammunition
  • Automotive
  • Heavy Equipment


Hardening & Tempering in the wire industry is most commonly used in the production of spring wire. This usually requires hardening & Tempering to be done in a single, continuously moving line. Induction technology makes it possible to provide a single, high-speed line that performs both the hardening and tempering procedures with extreme accuracy.

Radyne - Spring Wire Line

Spring Wire IT Line

The Radyne Spring Wire IT Line is designed to harden and temper spring wire on a continuously moving line. This all-in-one system is turn-key and includes everything you need from play-off to take-up.

Bolt & Fastener

Bolt & Fastener Hardening System

The Radyne bolt and fastener hardening system is designed to rapidly harden threads or other localized areas of fasteners. The system utilizes a rotary table which is fed by a collator system and then passes the parts through an induction coil before dropping them into a quench solution. This system is the choice of high-quality fastener manufacturers across the globe.