The difference between cold rolled sheet and hot rolled sheet

Cold-rolled sheets generally do not have a heating process before rolling. However, due to the small thickness of the strip steel, plate shape problems are prone to occur. Moreover, after cold rolling, it is a finished product. Therefore, in order to control the dimensional accuracy and surface quality of the strip steel, many cumbersome processes are used. The cold rolling production line is long, the equipment is many, and the process is complicated. With the improvement of users' requirements for strip dimensional accuracy, strip shape and surface quality, there are more control models, l1 and l2 systems, and strip shape control methods for cold rolling mills than for hot rolling. Moreover, the temperature of rolls and strip steel is also one of the more important control indicators.

By definition, steel ingots or billets are difficult to deform and process at room temperature. They are generally heated to 1100 to 1250°C for rolling. This rolling process is called hot rolling. Most steels are rolled by hot rolling. However, because iron oxide scale is easily formed on the surface of steel at high temperature, the surface of hot-rolled steel is rough and the size fluctuates greatly. Therefore, the steel with smooth surface, precise size and good mechanical properties is required. Hot-rolled semi-finished or finished products are used as raw materials and then cold Rolling method production.

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 to 600°C.

Simply put:

1. The surface of the cold-rolled sheet has a certain degree of gloss, and it feels smooth to the touch, similar to the common steel cup used to drink water.

2. If the hot-rolled plate is not pickled, the surface is similar to many ordinary steel plates on the market. The rusted surface is red, and the unrusted surface is purple-black (oxidized iron scale).