Just mentioning, a company called Ohio Crankshaft was a pioneer in
this a long time ago. Induction heating was used for hardening, mainly
case hardening steel. It was called the TOCCO process.

In the old days the flux wasn't all that well controlled and there was
plenty of power. The olman told me that the machine pulled 700 amps a
700 volts. This brought cranks and cams up to quenching temperature in
seconds, maybe sooner. After all 49 Kw can do that. About the flux,
when they said get everything metal out of your pockets they meant it.
One guy had a lighter on him working with the machine and got burned
really badly.

Some minor info available here : http://papers.sae.org/370166/

There is not a whole lot of info on it available on the net searching
directly for TOCCO. But then as good as it is, they screwed up a whole
lot of Chevy camshafts about 25 years ago or so. ALOT of them. I got a
buddy who actually knows how to work on those things, but there are
only so many. There doesn't need to be that many. At 49 Kw I'm sure
the process goes pretty fast. That was kinda the idea.

Anyone want to buy an induction cooktop ? I got one stashed somewhere,
just because I figured it could be dangerous.

To build the box that feeds the coils should not be all that
difficult. It does not use microwave frequencies, it's just RF. Some
switched mode power supplies run higher frequencies these days.

J