While there is chromium in stainless steel, it becomes chromium +3 once it oxidizes on the surface. Since the steel is connected to the anode in electrolysis, I would think you are more likely to get chromium hydroxide (which is still chromium in the +3 state); since, most electrolysis is done at higher pH. Chrome +6 is readily soluble in acidic solutions. Try soaking your iron in a vinegar or citric acid bath after electrolysis if you are that concerned. If you think stainless steel that has been welded contains chromium +6, don’t use welded stainless steel in your electrolysis tank. Do you think chromium +6 is bonding with the cast iron somehow during electrolysis?
I have a bigger concern for lead contamination in used cast iron. You never know the use history for an old piece of cast iron.
Sorry I don’t have any links for you, but reddit has threads on this subject. Try searching there.
