What is the difference between hot rolling and cold rolling of steel plates?

Hot rolled steel is rolled by high-temperature heating. Its strength is not very high, but it is enough to meet our use. It has good plasticity and weldability, so we use it more often. Cold rolled steel is the steel of ordinary hot-rolled steel which has passed the stage of strain hardening by strong drawing. Its strength is very high, but its toughness and weldability are poor, and it is hard and brittle!

Hot rolling is to heat the material in the process of rolling or before rolling. Generally, rolling can only be carried out after heating to the recrystallization temperature.
Ironmaking → steelmaking → continuous casting (or die casting) → hot rolling (out of hot rolling products) → cold rolling (out of cold rolling products)
Cold rolled steel is the steel produced by cold rolling. Cold rolling is to further thin the steel plate to the target thickness at room temperature. Compared with hot-rolled steel plate, cold-rolled steel plate is more accurate in thickness, smooth and beautiful in surface, and has various superior mechanical properties, especially in processing performance.

The hot-rolled steel has low strength, good extension and poor appearance color.
Cold rolled steel has high strength, high hardness and bright surface.
In addition to the size factor, it can also be distinguished from the surface color and quality. Hot rolled steel has obvious oxidation color, and cold rolled steel has bright and clean surface. It can also be distinguished simply by using hard object to depict the surface. Hot rolled steel is relatively easy to be scratched, and cold rolled steel (with higher hardness) is not easy to be scratched.