Cold-rolled sheets generally do not undergo a heating process before rolling. However, due to the small thickness of the strip steel, it is easy to have a shape problem. Moreover, it is a finished product after cold rolling, so in order to control the dimensional accuracy and surface quality of the strip steel, many very cumbersome processes are used.

       The cold rolling production line is long, with many equipments and complicated process. With the improvement of users' requirements for strip dimensional accuracy, shape and surface quality, the control model, l1 and l2 systems, and shape control methods of cold rolling mills are more than those of hot rolling. Moreover, the temperature of the roll and the strip is also one of the more important control indicators.

       By definition, steel ingots or billets are difficult to deform and process at room temperature, and are generally heated to 1100-1250°C for rolling. This rolling process is called hot rolling. Most steel products are rolled by hot rolling method.

       However, because the surface of steel is easy to form oxide scale at high temperature, the surface of hot-rolled steel is rough and the size fluctuates greatly. Therefore, steel with smooth surface, accurate size and good mechanical properties is required. Hot-rolled semi-finished products or finished products are used as raw materials and then cold Production by rolling method.

       Rolling at room temperature is generally understood as cold rolling. From a metallurgical point of view, the boundary between cold rolling and hot rolling should be distinguished by the recrystallization temperature. That is, rolling below the recrystallization temperature is cold rolling, and rolling above the recrystallization temperature is hot rolling. The recrystallization temperature of steel is 450-600°C.

       Simply put:

1. The surface of the cold-rolled plate has a certain glossiness, and it feels smoother to the touch, similar to the very common steel water cup used for drinking water.

2. If the hot-rolled sheet has not been pickled, it is similar to the surface of many ordinary steel sheets on the market. The surface with rust is red, and the surface without rust is purple-black (iron oxide scale).