If, God forbid, someone used red Loctite on the screw, you’ll have to heat the parts to 500 degrees to break the bond but temperatures over 400 degrees are best avoided because steels can lose their temper at temperatures between 400 and 600 degrees. You don’t ever want to put so mu...
The next level involves use of a large commercial air impact wrench for : removal, however, use of heat is still recommended, as if there is Red Loctite in there and it's not softened with heat, you can break things or rip the threads right off the assembly. (Not likely in this case...