I have bought many old frames and bicycles over the past decades to rebuild them and several have had problems. Probably one reason why the seller wanted to sell ! One example comes to mind. The lady in Germany couldn't remove the one piece handlebar /stem from the frame [front fork steerer tube] because it was rusted in - so she sawed through the stem, presumably with a hack-saw !
Fortunately I have a friend who owns a local vehicle body repair shop and he will attempt anything that is beyond my capabilities.
He has "straightened bent front fork blades, releases lock-rings, releases bottom bracket cups stuck in the frame, releases seat pins stuck in the seat tube, releases stems from the steerer tube and releases pedal axles from cranks etc., for me many times and it usually takes between a few seconds and a couple of minutes. The cost is never more than a fiver.
He uses a piece of equipment called an impedence something or other and it looks like an oversize washing machine which he plugs into a hefty electrical supply.
There is a thick cable coming from it to what can only be described a big soldering iron with a little spade-shaped tip.
This is what happens - as soon as the tip touches metal it glows red immediately and with one or two touches, that loosens whatever you want loosening, including any of the above difficulties I've mentioned. Impressive and almost unbelievable.
To straighten fork blades, he lays the forks front downwards on the concrete floor, with the head nut on the steerer tube.
He then either puts some very heavy steel weights [they seem to be about 30 cm x 30 cm x 15 cm each one, or he puts his big boot on the steerer tube / fork crown area. He then applies the "magic wand" to the stretched edge of the blades a few times to get them really hot and immediatey throws cold water on them ! The blades then shrink back straight, or virtually straight if they were badly bent backwards.
You'll see on the photos that the front forks are badly bent backwards on the bike photo and reasonably straightened on the photo of the cleaned / rust treated forks.
This gadget works well for my difficult situations, how it works I don't need to know - it saves me a lot of time struggling with paraffin, various oils and brute force. Simple, eh ?

Yes!

keidal, Sounds interesting perhaps the next time that you are in the shop maybe some pics or vid of the Frankenstein at work!
Regards, Ben

It sounds like he's using an induction heater.
Something like this: Portable Induction Brazing Heater-Induction heater,melting furnace,induction brazing machine Manufacturer
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Ragnar

Now you know why it's called Eddy current.