No matter what you use you will not be able to convert the oxidixed metal back to its base. Using an acid to further etch the surface can only remove more material. Instead of soaking in Acid (citric, HCl or whatever) or using a penetrating spray, WD-40 is your best bet to save as much of the tool as possible.

Mechanically removing the rust to clean it up after will help it look pretty again.

After cleaning coat it with a surface protector like Boeshield T-9.

I use it on my jointer and table saw surfaces and all other exposed steel.

Tim