hot rolled steel plate hardness is low, easy processing, ductility is good. Cold rolled sheet hardness is high, processing is relatively difficult, but not easy to deformation, high strength. Hot rolled plate strength is relatively low, surface quality almost (low oxidation finish), but good plasticity, generally medium thick plate, cold rolled plate: high strength and high hardness, high surface finish, generally thin plate, can be used as a stamping plate. Far less cold hot rolled steel plate, mechanical properties, but also is inferior to the forging processing, but has good toughness and ductility cold-rolled steel sheet due to a certain degree of strain hardening, toughness is low, but can reach better showed, used for cold bending spring pieces and parts, at the same time due to the yield point is close to the tensile strength, so no foresight to danger, in use process When the load exceeds the allowable load, accidents are likely to occur. Hot rolling is rolling the steel plate into relatively thin steel plate at a higher temperature. Cold rolling is rolling steel plate at room temperature. Generally, hot rolling is carried out first, and then cold rolling. When the steel plate is thicker, it can only be hot rolled, and then cold rolled after it is rolled into thinner plate. Hot rolled steel plate is divided into thick plate (thickness > 4mm) and thin plate (thickness 0.35~4mm). Cold rolled steel plate only thin plate (thickness of 0.2 ~ 4mm). The termination temperature of hot rolling is generally 800 ~ 900℃, and then it is generally cooled in the air, so the hot rolling state is equivalent to normalizing treatment. The metal materials delivered in hot rolling state are covered with a layer of oxide film on the surface, so they have certain corrosion resistance. The requirements for storage, transportation and storage are not as strict as those delivered in cold drawing (rolling). For example, large and medium-sized section steel and medium thick steel plate can be stored in the open cargo yard or be covered with rayon. Compared with hot rolling, cold rolling metal materials have higher dimensional accuracy, better surface quality, lower surface roughness and higher mechanical properties. But prone to corrosion or rust, its packaging, storage and transportation have more stringent requirements, need to be kept in the warehouse, and should pay attention to the temperature and humidity control in the warehouse.