Hot rolling and cold rolling are the two basic methods of producing structural steel such as sheet steel, flat-steel, steel rods and steel plates. Each method has advantages metal workers can use to make their projects better or more efficient.
Hot rolled steel is formed to shape while it is red-hot then allowed to cool. Since red-hot steel shrinks as it cools, the final product is not perfectly uniform. The surface of the metal is slightly rough and the thickness may vary a few thousandths of an inch; as a result, metal work which is structural only is commonly done with hot-rolled steel.
Cold rolled steel is made by passing cold steel material through heavy rollers which compress the metal to it's final shape and dimension. The result is a very uniform, smooth surfaced product. Cold rolled steel is suited for steel products such as railings or machinery which will be painted and put to use.
It's commonly thought that the strength of cold-rolled steel is greater than hot-rolled steel. The strength is more a factor of the specific metals and amount of carbon used to produce the alloy, than the manufacturing method used to create it.
Hot rolled steel is less costly to manufacture and is generally priced less than similar cold rolled steel products.