Hot rolling is to roll the steel plate to a relatively thinner steel plate at a higher temperature; cold rolling is to roll the steel plate under normal temperature conditions.
Generally, hot rolling is performed first, followed by cold rolling. In the case of thick steel plates, only hot rolling can be used. After rolling into thinner plates, cold rolling is carried out. Hot-rolled steel plates are divided into two types: thick plates (thickness greater than 4mm) and thin plates (thickness 0.35~4mm); cold-rolled steel plates only have thin plates (thickness 0.2-4mm).
The termination temperature of hot rolling is generally 800 to 900°C, and then it is generally cooled in air, so the hot rolling state is equivalent to normalizing treatment. The metal materials delivered in the hot-rolled state have a certain degree of corrosion resistance because the surface is covered with a layer of oxide film. The requirements for storage, transportation and storage are not as strict as those of cold-rolled delivery materials, such as large and medium-sized steels, and medium-thick steel plates. It can be stored in the open yard or after being covered.
Compared with the hot-rolled state, the metal material in the cold-rolled state has high dimensional accuracy, good surface quality, low surface roughness, and higher mechanical properties. However, it is prone to corrosion or rust, and its packaging, storage and transportation have strict requirements. It must be kept in the warehouse, and attention should be paid to the temperature and humidity control in the warehouse.
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