All sheet metal, when it leaves the mill, is hot rolled into big rolls, stored, and shipped that way. Since the roll is flattened and cut into sheets while cold, the memory is still there from when it was wound up hot. The steel on the outside of the roll has less memory because it’s less tightly wound; the steel on the inside has a lot of memory because it’s very tightly wound.
Tread plate has this memory more than slick steel; I assume it’s because of the raised diamonds which are also pressed into the steel while it is hot. But all sheet metal has this memory.
On a QuickLoadz, the deck is made up of 3/16″ tread plate cut into 16″ wide sections and welded to the 10G cross-members. When the plate steel hits the 845° molten zinc, memory in the steel is released. But you also have this 16″ × 42″ wide piece of steel welded in select spots, so the memory has no place to go, and will therefore cause the 16″ wide panels to hump up or down. This isn’t severe and will generally be less than half an inch, but is completely unavoidable unless you dip the trailer, then the deck plates, then weld them together afterwards. If you do that, you get crappy welds because of the zinc, and where you welded, you don’t get the protection of the hot dip galvanizing.
We cut our deck plates into 16″ sections instead of 48″ sections because in 16″ sections, the warp is manageable. Over a 48″ wide section, the stresses become so great that oftentimes it will rip out welds. Also, we are very specific as to where the deck plates are welded, to balance the warp of individual sheets with the strength of the deck overall.
There are odd ball things that will happen. For instance, some plates won’t seem to warp at all, and some warp a full half inch up or down. The reason is that some of those plates were made with outside roll (little memory) and some inside roll (lots of memory). Deck plate warp is noticeable when you’re standing right next to the trailer, but you can’t really see it in pictures. For example, this picture is right down the line of the bed: