What is Cold Rolled Steel? Steel Foundations
A cold rolled coil (CR or CRC) is the flat product of the cold rolling mill.
Starting with a pickled and oiled hot rolled coil, the cold rolling process unrolls the metal coil and passes it between a set of work rolls, where the compressive force of the rolls reduces the thickness of the metal. Unlike hot rolling where the metal is red hot, this process is done at room temperature, which is why it is referred to as “cold” rolling.
The reduction in thickness hardens the metal, which increases the dislocation density of the metal’s internal microstructure. This increases the strength of the metal, but it also increases its brittleness. Therefore, many cold roll processes are followed by an annealing process to soften or “temper” the metal’s microstructure and to relieve the internal stresses created during the process.
Cold rolling is done on a cold roll mill, which is composed of an entry end uncoiler, a cold rolling mill stand or stands, advanced metal thickness control equipment, oiling equipment, and an exit end recoiler. In addition to steel, the cold rolling process can be done to any metal (stainless steel, aluminum, copper, etc.).
The primary purpose of cold rolling is to improve the surface appearance and mechanical properties of a metal coil.
The physical and mechanical properties that are changed during cold rolling include:
- Decreased material thickness
- Improved thickness accuracy and repeatability
- Improved product surface finish
- Improved product shape and flatness
- Decreased coil memory
- Increased material strength to the desired hardness or temper
