Electrolytic removal of rust

I'm sorry that i post a little off topic (this is not a sudden-release-of-a-lot-of-energy topic)
I've been playing a little with electrolytic rust-removing after reading the decription at http://www.relicman.com/artresto.htm and http://www.civilwaroutpost.com/Cleaning%20Shells.htm
I cleaned an old wrench, a fox-trap and a few other things, and compared to sandpaper and a wire-brush, it's a gift from the Great Chemist in the Sky.
The rust can be scrubbet off with a piece of scotch-brite, dry the piece and oil it!
But what happens? I have a theory that part of the effect is a physical effect of hydrogen forming under the rust an flaking it off, partly that Fe(III) is reduced to the more soluble Fe(II). The last is based on the observation that the oxide layer turns black.
(The method: A piece of stainless steel as plus, 6 V and a solution og Na2CO3 in water)