The difference between cold rolling and hot rolling

The difference between cold rolling and hot rolling is mainly the temperature of the rolling process. “Cold” means normal temperature, and “hot” means high temperature. From a metallographic 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. The main differences between hot rolling and cold rolling are: 1. Appearance and surface quality: Since the cold plate is obtained after the cold rolling process of the hot plate, and some surface finishing will be carried out at the same time, the surface quality of the cold plate (such as Surface roughness, etc.) is better than hot plate, so if there is a higher requirement for the coating quality of the product, such as post-painting, cold plate is generally selected, and hot plate is divided into pickling plate and non-pickling plate. The surface of the pickled plate has a normal metallic color due to pickling, but the surface is not as high as the cold plate because it is not cold-rolled. The surface of the unpickled plate usually has an oxide layer, a black layer, or a black iron tetroxide layer. In layman’s terms, it looks like it’s been roasted, and if the storage environment is not good, it usually has a little rust. 2. Performance: In general, the mechanical properties of the hot plate and the cold plate are considered to be indistinguishable in the engineering, although the cold plate has a certain degree of work hardening during the cold rolling process, (but it does not rule out the strict requirements for mechanical properties. , then it needs to be treated differently), the yield strength of the cold plate is usually slightly higher than that of the hot plate, and the surface hardness is also higher, depending on the degree of annealing of the cold plate. But no matter how annealed, the strength of cold plate is higher than that of hot plate. 3. Forming performance Since the performance of cold and hot plates is basically not too different, the influencing factors of forming performance depend on the difference in surface quality. Since the surface quality is better from cold plates, generally speaking, steel plates of the same material are of the same material. , the forming effect of cold plate is better than that of hot plate.