Cold rolled steels are hot rolled steels that have then been subjected to further rolling at room temperature. This process further refines the dimensions and surface quality of the finished product. The term “cold rolled” is sometimes also used interchangeably to describe product finishes such as polishing, turning and grinding, but the industry definition of cold rolling refers to steel products that are subjected to compression in a cold rolling mill.
There are several characteristics that determine whether a bar of steel is hot rolled or cold rolled. Cold rolled steel has a smooth surface that is oily to touch. The corners and edges of cold worked steel bars are sharper and more precise. Cold rolled products are straighter, more concentrated and stronger than hot rolled products. They also have a superior surface finish. Cold rolled steel is up to 20% more resistant to tension breaking and deformation and is harder than hot rolled steel.
Once steel has been hot rolled through a rolling mill at a temperature above the metal recrystallization temperature of 1100°F, it is left to cool and then re-rolled at room temperature. The tandem rolling stands used for cold rolling require more strength than hot rolling mills, as the steel’s malleability is affected by the processes and it becomes harder. Cold rolling mills produce steel products in specific shapes – round, square and flat steel products such as strips, bars, plates and rods. The dimensions of these products can be smaller and much more precise than those of hot rolled steel products.
Cold rolled steel strips, bars, rods and plates are typically used for construction processes in which a high level of technical precision and dimensional tolerance is required. Smaller steel products that need to be durable and dimensionally tolerance are typically cold rolled. End products include office furniture such as chairs, filing cabinets and computer components, exhaust pipes for smaller vehicles, fan blades, and household appliances and their components.