Hot rolled steel is above 1000 degrees with rolls pressed out, usually plate small to 2mm thick, high-speed processing of steel deformation heat is not offset by the increased area of steel heat dissipation, i.e., difficult to maintain the temperature above 1000 degrees to process, only to sacrifice the hot rolling of this efficient and cheap processing method, rolling at room temperature, that is, the hot-rolled material and then cold rolled to meet the market requirements for thinner thickness.Of course, cold-rolled and bring new benefits, such as work hardening, so that the strength of steel, but should not be welded, at least the weld work hardening is eliminated, high strength is no longer, back to the strength of its hot-rolled material, cold-formed steel can be used for hot-rolled material, such as steel pipe, can also be used for cold-rolled material, cold-rolled material or hot-rolled material, 2mm thick is a criterion for hot-rolled material is the thinnest 2mm thick, the cold-rolled material is the thickest 3mm.