Putting too much power into the rust bolt is going to ruin the bolt or snap it. WD40 is useless. WD40 is a lubricating oil. It works for light rust and has many other uses, but it does nothing in terms of seized bolts. Penetrating oil is one option. Another method is freezing the part, this will make the parts contract and break the rust seal. I saw a freezing thing at Eurocar parts a while back. I haven't personally tried it but it should work too. And remember, if you heat it you don't want to heat the bolt much instead you need to heat the area around the bolt where the coils will be so they can expand, expanding the screw is not going to do much. (At your own risk ) A desi method we use is set it alight with petrol(My dad used this method on old Imports). Just be prepared to put out the fire should it get out of control.