Good to hear that someone else is etching steel. First, you need to be using the right kind of steel. The steel you want to be using is mild steel or cold-rolled steel. Galvanized doesn't work well for obvious reasons; it doesn't corrode well. I have had success with Dutch Mordant and I have also had good results with Nitric Acid. The Dutch Mordant for steel is mixed as follows: You'll need 20 ounces of water, 5 ounces of Hydrochloric Acid and 1 ounce of Potassium Chlorate. Boul about 8 ounces of the water and pour it over the potassium chlorate crystals. Stir in the remainder of the water, and when cool, add the acid. Always pour acid into water, never water into acid.
You probably know this but don't use different metals in the same acids. Keep copper plates in a bath for copper only; keep a separate bath for steel. Also, be very careful with the Dutch bath especially while mixing, it gives off chlorine gas which is dangerous. I have used it for several years with no ill effects.
The Dutch bath will bite cleanly but if you need a very deep etch, you may want to try Nitric Acid. Nitric will bite in a more irregular way and you'll need to feather air bubbles frequently.