I have crafted several steels made of mild steel. Thickness 1/2, 3/8 and 1/4 inch. On a couple of the thicker ones I have put a groove around the edge so it could be used as a griddle. I have very good success in a convection oven, using the double steel method. I'm still working on perfecting my method on the grill. The biggest issue has been getting a nice char om the top of the crust. I have used 2 steels on the grill with the temperature one the top steel in the 400° and 700° range on the bottom steel. I'm going to try keeping the lower steel temperature around 500° using the Kettlepizza attachment I just picked up and see how that works. I do like the steel over stone in the oven. Still working on the grill method.
I grilled a chicken spatchcock style on the griddle side, turned out very good, with a nice crispy skin.