I'm trying to remove a fork from a steel track frame with standard type threaded headset. I am holding the bottom nut above the headtube with a headset spanner, and trying to remove the top locknut with a large strong headset wrench. both are 32mm and fit the nuts.

No luck.

Feels like the top lock nut is stuck to the steel fork. It doesn't seem damaged as the headset and steering work fine. Im afraid to grab the fork from underneath the headtube to apply more pressure as I don't want bend the fork.

Lock nut is aluminum and fork is steel.

Any suggestions?

I think that's what you do when you have tried to undo the locknut with two wrenches. Plenty of WD40 might, of course, eventually help free the locknut.

A standard open-ended headset wrench is not the best thing for a locknut. You get proper locknut wrenches which provide more all-round grip, and your local bike mechanic might have one of these.

Plusgas is alot better than WD-40. Why even let WD-40 with 100ft of a bike.

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www.thecycleclinic.co.uk

for seized bolts you could:

-Spray with penetrating oil (wd40 is not a good on at that, use PB blaster)
-"scare" it free, by tapping it
-using "reverse psychology", sometimes a bolt will go tighter and then free itself up
-use heat
-use ammonia when corrosion is the possible culprit

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2011 Cannondale Flash F1
2010 Cannondale Caad9
2000 Cannondale Caad 4 aero
1999 Cannondale Caad1
???? Concorde SS

Good ol' Galvanic corrosion. It used to be quite common during the stell frame/ alloy seatpost era.
If you don't require the headset, use heat. Mind you, if it's corroded in place, the headset's likely toast anyways. So yeah, heat. Keep in mind if you're using a torch to be aware of any previous chemicals you might have already poured into it. You might not like the end result if not.

Thanks all. Sprayed it with some lube and bought a good park wrench and spanner and got it off finally.