Works as a blacksmith, I want to tell you a secret: it’s easy to Unscrew the rusted screw connections. Since they have the opportunity — heat the screw a few degrees to about 500-600 (roughly when the metal a little blush). Then dipped in water and hold until cool. While you hear crackles, especially major parts: the water, entering the thread, turns into steam under high pressure crumbles and makes all the debris. Now quiet tapping is enough to nut or stud is easy, often even without the key turned. This method is suitable for pressed parts.
S. DENISOV, state farm “Temp”, the Saratov region