Induction hardening

The resistance of components to wear or to local pressure can be significantly improved by induction hardening. The aim of these processes is to generate wear-resistant casting surfaces with high hardness while allowing the castingcore to keep its good tensile properties. Another important characteristic is that these kinds of measures generate internal compressive stresses within the surface layers, which increase the fatigue strength in the casting.

Induction hardening is based on induction of an eddy current into the surface layers of castings by having alternating current flow through a coil. With increasing frequency, the current penetration depth and thus the achievable hardnesspenetration depths are decreased. Moreover, the hardnesspenetration depth and the surface hardness are determined by the heat-up time (Figures 1 and 2).

In addition to induction hardening, laser hardening takes on more significance. Here, the material is heated up to austenitization temperature by energy supply through a laser beam. Intrinsic quenching due to the steep temperature gradient towards the inside of the material and the resulting high cooling rate causes formation of a martensitic structure with great hardness.

Additional references:

Flame hardening
Case hardening
Electron beam hardening
Torch hardening
Interrupted quenching
Nitriding, Immersion hardening
Hot-bath hardening 
Hardness test  

  • Fig. 1: Effect of the hardening duration on surface hardness and hardness penetration depth (acc. to W. Patterson)
  • Fig. 2:  Effect of heat-up duration on hardness penetration depth 1 = 2.5 s; 2 = 3.0 s; 3 = 3.5 s (acc. to W. Patterson)
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