I don't know if you fancy doing this but it's the method I use most of the time and I've done this a lot.farm machinery rusty nuts.If you still have a head on the bolt get a small cold chisel and tap it on the edge in the direction you want.sometimes it's a good idea to give it a tap in the wrong direction just to break the bind.use a good weight hammer but fairly gentle taps and you can use quite a steep angle.i can almost guarantee that this will work but if it doesn't it won't stop you trying other options.