Hi there,
what you could do is get a cold chisel, and split the nut in line with the axle its on. There are tools called, "nut splitters", that work with a screw and a blade like a cold chisel but the chisel works just as well. Generaly you don't have to split the nut entirely, just enough to expand it around the threads.
Hope that makes sense to you, it's the approved mechanics way and much better than heating the axle/bearings.