Is there a way to tell the difference between cold steel and hot rolled steel If so how can you tell?

Answer 1

Why does Hot Rolled Steel have a rough, blue-grey finish, while Cold Finished Steel has a smooth grey finish?

Hot Rolled Steels are just that - They are heated up red-hot and pushed through rollers that squeeze the metal, literally squishing it into a particular profile, depending on the shape of the rollers. The process takes a long time, and because the steel is so hot for so long in the open air of the steel mill, the surface of the metal has has a long time to oxidize, producing a thick, tough oxide scale with the characteristic blue grey finish of the final product.

Cold Finished Steels are just that - the final rolling is done when the steel is cold (room temperature), the whole operation bathed in oil, so the finished product is unoxidized, the grey of the actual steel, and as smooth as the rollers that do the processing.

that was taken from metalrefrence.com