Hot-rolled steel is a steel that has been heated and rolled at a high temperature. Its strength is not very high, but it is sufficient for our use. Its plasticity and weld-ability are good, so we use it more often; cold-rolled steel is ordinary hot rolling. Steel is strongly drawn beyond the steel in the strain hardening stage, its strength is high, but the toughness and weld-ability are poor, relatively hard and brittle!
Hot rolling is the heating of the material during the rolling process or before rolling. Rolling is generally carried out after heating to a temperature above the crystallization temperature. Such as: 1000 degrees or more, hot rolling is processed at high temperatures. Allow the interior of the steel to recrystallize. Let it be more excellent. However, hot rolling does not change the structural properties of the metal.
Cold rolled steel is steel that has been produced by cold rolling. Cold rolling is a steel sheet in which the No. 1 steel sheet is further rolled to a target thickness at room temperature. Compared with hot-rolled steel sheets, cold-rolled steel sheets are more precise in thickness and have a smooth and beautiful surface, as well as various superior mechanical properties, especially in terms of processability.
Because cold-rolled raw rolls are brittle and hard, they are not suitable for processing. Therefore, cold-rolled steel sheets usually need to be given to customers after annealing, pickling and surface smoothing. The maximum thickness of cold rolling is 0.1--8.0MM or less. For example, the thickness of cold-rolled steel sheets in most factories is 4.5mm or less; the minimum thickness and width are determined according to the equipment capacity and market demand of each factory.
The difference between cold rolled steel and hot rolled steel is not in the smelting process, but in the rolling temperature, or the rolling end temperature. When the finish rolling temperature is lower than the crystallization temperature of the steel, it becomes cold rolled steel. Hot-rolled steel is easy to roll, and the rolling efficiency is high, but the steel is oxidized under hot rolling conditions, and the surface of the product is black and gray.
Cold-rolled steel requires high rolling mill power, low rolling efficiency, and intermediate annealing in order to eliminate work hardening during rolling, so the cost is also high, but the cold-rolled steel surface is bright and of good quality and can be directly used for processing. Finished products, especially the cold rolled steel plate is widely used.