On Tue, 08 Jan 2013 23:41:35 +0200, Kristian Ukkonen
wrote:

[...]

Perhaps immerse it in hot citric acid solution for a while
at the end to get rid of rust and flux remains. I've noticed
citric acid is the wonder cleaning stuff - nonpoisonous,
water based, cheap and cleans rust and flux away really well.
Works fine for brazing fluxes too. It is the same stuff you
use for cleaning your coffee making machine!

I even cleaned my WEDM water container with citric acid.. It was
all green, rusty and dirty in the beginning with who knows what
metal remains on the walls there. Few times of hot citric acid
(as hot as water comes from tap, around 60C, and some citric
acid to it) and it is the normal clean stainless steel colour on
all walls again. Totally amazing!

No doubt excellent for stainless steel. Unfortunately with mild steel
all you are doing is activating the steel surface for further rusting.

Michael Koblic,
Campbell River, BC