This is my first post to this forum - not sure if this is the right forum, but I have an interesting problem regarding metal that I'm hoping someone can educate me on. Recently, I decided that I would like to make my own plow disc grill. I've had one that I purchased from a company that specializes in making these for cooking, and I wanted a second one. I had read that people used to get used plow discs (also called harrow discs) from farms, plug weld the center hole, then grind all the rust and paint off, then season the disc like you would a cast iron pan, then they would cook off of them. I though I'd give it a try - seemed easy. I found a source for used plow discs and got one. I'm attaching pix below to show what I'll describe. I brushed and ground all the rust and scale off the disc, and polished it to a shiny finish. When I put it over a propane burner to start seasoning it, I just happened to wipe the cooking surface with a paper towel and I noticed a orangish yellow reside on the paper towel. I thought I had left a layer of simple green or dish soap on the surface so I filled up the disc with water and boiled it, thinking I'd get the reside off. When I did that, the metal started "weeping" a dark gray residue that would partially wipe off the surface, but discolored the metal on the surface. Also, the side of the metal facing the burner developed a fine sheen of rust after being exposed to the propane flame. I reground the disc with 120 grit fiber disc and shined it up again, removing the discoloration, and repeated the process. The same thing happened, but there was substantially less residue. I then tried boiling vinegar and water in the pan, and that took the discoloration off the surface, but when I boiled it again with just water the reside reappeared. I'm wondering what is happening with this metal. I'm attaching pix of the marks on the back side of the disc. This appears to be a Case IH Earth Metal harrow disc - the website says it's a boron/steel alloy. Obviously, I'm not going to eat off of this thing, but I'm wondering that is happening here, and if it is even possible to get it completely clean so it no longer "weeps."
