Hot rolling has the following characteristic, low intensity, good extension, the surface is not shinning.
Cold rolling has the following characteristic, high intensity, high hardness, shining surface.
Hot rolling mill: though high heating, then rolling it to the certain structure.
Cold rolling mill: not heating, in common temperature, normally below critical point.
The mechanical property through hot rolling and cold rolling is different.
Cold rolling is in low hardness, easy to process, with good intention, easy to form cold stress, hot rolling is for high hardness, high intention, difficult to process, not easy to deformation.
Hot rolling needs to be heated, normally temperature should above the critical point, the processing is under high temperature, make the steel recrystallization happen, but not changing the steel structure.
Cold rolling is under normal temperature, roll it into aiming thickness, compare with hot rolling , cold rolling has high accuracy, smooth surface, better mechanic characteristic, especially processability, because the raw material of cold rolling is very crisp and hard, not suitable for processing, normally, cold rolling steel plate should be acid pickling and surfacing, then can send them to final customer.
The difference between cold rolling and hot rolling is not in the process, but the temperature, hot rolling is easy to roll, and high efficiency, but hot rolling makes steel oxidation, surface gray and not shining; cold rolling requires high power motor, low efficiency, high cost, but with very shining surface, can be used as the final product directly, widely used.