In the field of heat treatment, there are usually two heating methods for induction hardening, simultaneous heating hardening and scanning hardening. Using the correct heating method is beneficial to improve the effect and production efficiency of steel induction hardening. Many automotive and industrial metal parts require induction hardening to increase the surface hardness of the workpiece. After induction heating, the surface hardness of the workpiece increases, and the service life will be longer.

Read on to learn about two heating methods to benefit your induction hardening process.

Two induction hardening methods

Due to the different shapes of metal parts and different areas that need to be hardened, we must use different heating methods to achieve the best results. These methods usually include the following two types.

1. Simultaneous Heating and Hardening

In this heating method, we heat the entire surface of the metal part at the same time. This means that the induction coil covers the entire steel part (in the case of local hardening, the induction coil only needs to cover the area to be hardened). After reaching the target temperature, turn off the heat and let it cool down immediately. Generally, we use cooling water to spray parts.

During the simultaneous heating and hardening of the gear, the relative position of the induction coil and the gear is constant. That is, the coil does not move from one end of the part to the other. But the gear itself can turn. For more even heating, we place it on a rotatable base. While heating, rotate the gear quickly to maintain the consistency of the surface temperature of the gear.

In the water cooling process of parts, there are two methods available:

  • The gear falls straight into the pool
  • The sprinkler sprays water on the gear

The effect of both methods is very good. When choosing, it is necessary to consider the size and shape of the steel part to ensure that the entire surface can achieve a good cooling effect.

2. Scanning Hardening

Scanning hardening is also called continuous hardening. This method is often used for shaft hardening. In this method, the scanner controls the induction coil to move at a constant speed. The induction coil starts at one end of the shaft for surface heating and it slowly moves to the other end of the shaft.

Like simultaneous heating hardening, in the process of scanning hardening, the shaft can also rotate at a constant speed to ensure temperature consistency.

Induction coils are usually equipped with a water spray that will immediately spray the heated area. The water spray will be set to start after 1 second or 2 seconds of heating.

Application of scanning hardening

When the surface hardening area is relatively large and the power of the power supply equipment is insufficient, we usually use scanning hardening.

Common scanning heating induction hardening applications:

  • Circumferential scanning hardening of the outer surface of camshaft
  • Scanning hardening of track surface
  • Scanning hardening of automobile shaft
  • Scanning hardening of single tooth of large gear

When the surface hardening area is relatively large and the power of the power supply equipment is insufficient, we usually use scanning hardening. Extensive production experience shows that under the condition of the same power supply, the production efficiency of parts by the simultaneous heating method is higher than that by the scanning hardening method, and the hardening equipment occupies less floor space.

Hardening of stepped shaft parts

During the scanning heating process, the temperature will be low in the transition zone from the large-diameter step to the small-diameter step. This is because the transition zone creates an offset in the electromagnetic field of the inductor, causing a discontinuity in the quenched layer along the entire length of the shaft.

At present, the method of simultaneous heating with longitudinal current is generally used to keep the hardened layer of the stepped shaft continuous throughout the entire length, thereby improving the torsional strength of the shaft.

Equipment for two induction hardening methods

Generally, high-power induction heating machines are usually used for simultaneous heating and hardening, and induction hardening machine tools are used for scanning quenching, including vertical induction hardening machine and horizontal induction hardening machine.


Two methods of induction hardening, simultaneous heat hardening and scanning hardening, are suitable for different parts. In actual use, we have to consider comprehensively according to the shape, size and area of the hardened area of the steel part.