What's the difference between hot rolled technique and cold rolled technique?

Hot rolled technique

Using continuous casting slab or blooming slab as raw material, it is heated by a walking heating furnace, and then enters the rough rolling mill after dephosphorization by high-pressure water. The rough rolling material is cut head, tail, and then enters the finishing rolling mill for computer-controlled rolling. After the final rolling, it undergoes laminar cooling (computer-controlled cooling rate) and coiled by a coiler to become a straight hair coil. The head and tail of straight hair curlers are often tongue-shaped and fish-tail-shaped, with poor thickness and width accuracy, and the edges often have defects such as wave shape, hemming, and tower shape. The coil weight is heavier and the inner diameter of the steel coil is 760mm. (Generally used in the pipe making industry.) After the straight hair coil is processed by the head, tail, edge trim, multi-pass straightening, leveling and other finishing lines, then it is cut or recoiled to become: hot rolling Products such as steel plate, flat hot-rolled steel coil, slitting strip, etc. If the hot-rolled finished coil is pickled to remove the oxide scale and coated with oil, it becomes a hot-rolled pickled coil.

Cold rolled technique

Hot-rolled steel coils are used as raw materials, and after pickling to remove the oxide scale, they are cold rolled. The finished product is hard-rolled coils. Cold work hardening caused by continuous cold deformation increases the strength and hardness of the hard-rolled coils and decreases the toughness index. , The stamping performance is deteriorated and can only be used for simple deformed parts. Hard rolled coils can be used as raw materials for hot-dip galvanizing plants, because hot-dip galvanizing lines are equipped with annealing lines. The weight of the rolled hard coil is generally 6 to 13.5 tons, and the inner diameter of the steel coil is 610mm. Generally, cold continuous rolled plates and coils should be de-annealed by continuous annealing (CAPL unit) or bell furnace to eliminate cold work hardening and rolling stress, and meet the mechanical performance indicators specified by the standard. The surface quality, appearance and dimensional accuracy of cold-rolled steel sheets are better than those of hot-rolled steel sheets.