1. Density

Hot rolled steel sheet has low hardness, good ductility, low oxide finish, but the plasticity is good. It is generally thin sheet, can be used as punching sheet. Hot rolled steel sheet is divided into structural steel, low-carbon steel, welded steel, and then check the specific steel density and composition according to different steel that you need. 

Cold rolled steel sheet has high hardness and high strength, is relatively difficult to processing, but not easy to deform.

2. Carbon content

Hot rolled steel sheet has higher carbon content than cold rolled steel sheet. The density is the same in the case of similar component. However, if the composition is different, such as stainless steel, regardless of cold rolling, hot rolling, the density is 7.9g/cm3 or so. The specific depends on the composition.

3. Production process 

Hot rolled steel sheet has lower mechanical properties than cold processing, also inferior to forging processing, but with good toughness and ductility.

The hot rolled steel sheet is rolled at high temperature, and cold rolling is carried out at normal temperature. In general, cold rolled steel sheet has better strength, hot rolled steel sheet has better ductility. The general thickness of cold rolling is relatively small, hot rolling can have a greater thickness. The surface quality, appearance and dimensional accuracy of the cold rolled steel sheet are better than those of hot rolling, and the thickness can be about 0.18mm, which is popular. 

Cold rolled steel sheet can be used for cold bendin and other parts due to a certain degree of work hardening. Because the yield point is  close to the tensile strength, so the risk of using can not be foreseeable, prone to accidents when the load exceeds the allowable load.