Induction Hardening

Induction hardening is a metallurgical surface treatment in which a metal part is heated rapidly by electromagnetic induction and then quenched, producing a hard, wear resistant martensitic surface layer while leaving the softer, tougher core of the part largely unaffected, so specific areas of a component can be selectively hardened. The underlying physics traces to Michael Faraday's 1831 discovery of electromagnetic induction, though practical induction heating for hardening steel did not develop until the early twentieth century, when engineers at Midvale Steel and the Ohio Crankshaft Company built early surface-hardening induction systems using motor generators, drawing on an understanding of how current penetration depth relates to hardening depth. By the late 1950s the technology was in regular industrial use, employing motor generators and thermionic emission triode oscillators, and modern induction hardening equipment, now built with semiconductor and digital control technology, ranges from about one kilowatt up to many megawatts of power.