Hardening with Induction

About Induction Hardening

Induction hardening is a form of heat treatment in which a metal part with sufficient carbon content is heated in the induction field and then quenched (rapidly cooled). The quenched metal undergoes a martensitic transformation, increasing the hardness and brittleness of the part. The induction process can be used to selectively harden an area of a part or assembly without affecting the properties of the part as a whole. Heating is both rapid and selective and lends itself to control the thermal gradient. This controls the depth of hardening (case or through) since the penetration is inversely proportional to the frequency. Typically, hardening systems use higher frequencies of 50 kHz to 400 kHz depending on the target or billet diameter to be processed. Common materials for hardening are carbon steel and stainless steel. Induction heating provides a number of benefits for hardening over other heating methods, including:

• Selective heating a specific area of the part for induction hardening
• Power on-demand, providing rapid heat cycles and eliminating time-consuming preheat cycles
• Finite process control with precise surface temperature control of the part
• Reduced operating costs versus ovens by eliminating the need for continuous power to heat a large ambient area
• Reducing work-in-process inventory by eliminating ovens which require batch processing, in favor of one-piece-flow heating

Typical applications for induction hardening include:

• Surface hardening to specific case depths (maintaining the integrity of the inner core material)
• Shaft hardening
• Selective areas on trigger assemblies and firearms
• Hardening ball screws
• Selective gear-teeth hardening
• Medical tools
• Hand tools, such as hammers, axes, screwdrivers, pliers, etc.
• The manufacture of automotive parts