Difference between cold rolled steel and hot rolled steel

COLD ROLLED STEEL:The most common of the metals encountered by the jobshop powdercoater, this product is roll formed to a close tolerance and a fine surface finish, suitable for stamping, forming, and moderate drawing operations.  This material can be bent flat upon itself without cracking.  Good base for phosphate conversion coating.  Pretreatment recommendations are Clean, Phosphate, rinse, and seal or deionize rinse.

HOT ROLLED STEEL:A low carbon steel suitable for forming, punching, welding, and shallow drawing.  Surface has normal mill scale that must be mechanically or chemically removed prior to the application of any conversion coating or any organic topcoat.  This mill scale adheres weakly to the metal and forms a layer between the desired finishing material and the steel substrate.  Thus, the total adhesion properties of the finish over mill scale would depend on the weak adhesion of the mill scale to the base metal.  

HOT ROLLED STEEL PICKLE AND OIL: A low carbon material from which the mill scale has been removed by acid pickling.  The light oil is applied after the acid pickling to prevent corrosion from forming on the steel.  This material has a smooth surface, suitable for stamping, drawing, and pretreatment prior to coating.