Hot rolling is thin steel plate rolled in high temperature. Cold rolling is the steel plate rolled in normal temperature. Generally, hot rolling is operated first, then is the cold rolling. For the thick steel plate to be rolled into thin ones, hot rolling is the only solution. After the steel plate becomes thin steel plate, we operate the cold rolling. 

Hot Rolling

Hot rolling is divided into thick steel plate (≧4mm) and thin steel plate(0.35~4mm). Cold rolling steel plate thickness is usually 0.2 ~ 4 mm.The advantages of hot rolling, destroy the forging organization of steel ingot, refine steel grain, eliminate the defects of the microstructure, in order to get close-grained steel structure, and improve the mechanical property. This improvement is mainly on the rolling direction, then steel plate is not longer isotropic body. Shape bubble, crack and porosity, and the steel plate could be seamed in the high temperature and pressure.

Cold Rolling

At room temperature, it is usually be the cold rolling. And from the point of metallography, cold rolling is below crystallization temperature. Advantages of cold rolling, quick shaping speed, high production output, without damaging the coating, a variety of crossing section, and meet the needs of the using conditions. Cold rolling could can produce plastic deformation to increase the yielding point of steel.