They're all plain old cold rolled steel. Flip it over and the heat and weight of the charcoal will form it the other way. Can't wait? pull it out when it's hot and flatten it on the sidewalk using a piece of plywood (it is hot, after all). Or can't wait for it to heat up and bother with leather gloves and handling hot metal, place it on the sidewalk and step on it (though usually you have to go beyond the zero point because it will flex back).. But really, there's not much magic to flattening out a charcoal grate. Whatever's clever.