Looking at your pics it appears to me that the steel has been chemically treated. Don't freak out with that terminology. I say this as it appears your steel has an iridescent color from what I can see in the pics. It appears to be a phosphate coating or treatment. Some of it may also be milling marks from where it was rolled. Naval Jelly is a thick jell of Phosphoric acid, so I think you're going to end up in the same place. Personally, I think I'd clean it well, maybe in the dishwasher a few times, and bake it numerous times getting hot as you can a few times. Maybe do numerous crust only bakes before you start loading pies for eating.