In induction hardening, heat is generated by eddy currents into the surface layer of the workpiece. The eddy currents are caused by the field of an induction coil in which a high-frequency alternating current flows. The penetration depth can be adjusted by the alternating frequency of the current. Rotationally symmetrical components are particularly suitable for induction hardening.
The hardening of the edge zone of a workpiece is used when the workpiece requires a hard and wear-resistant edge zone, but a high-strength and tough core. This is necessary for workpieces whose surfaces are subject to wear and which have to bear shock-like and alternating loads, such as shafts, bolts, gear wheels or slideways.During induction hardening of the surface layer, a thin outer layer of the workpiece made of hardenable steel is rapidly heated by a strong supply of heat and hardened by immediate quenching. This produces martensite. The lower workpiece areas are not heated sufficiently in the short heating time and remain unhardened.
For carburizing, steels with a carbon content of 0.1% to 0.2% are used, which are actually not hardenable. The workpieces are annealed for several hours at 880°C to 980°C in carbon releasing materials. Carbon diffuses into the surface layer, which becomes hardenable as a result. Solid substances (coke-charcoal granulate), liquid substances (highly toxic cyanide salt melts) or gases (mixture of CO and H2) are used as input materials.Subsequent induction hardening and tempering then give the carburized workpieces the desired properties for use. Only the surface layer is hardened, the workpiece core remains unhardened and tough.
Induction hardening offers some positive advantages in the series production of components: