What is the difference between hot rolled steel vs cold finish steel?

Cold rolling is a metal working process in which metal is deformed by passing it through rollers at a temperature below its recrystallization temperature. Cold rolling increases the yield strength and hardness of a metal by introducing defects into the metal's crystal structure. These defects prevent further slip and can reduce the grain size of the metal, resulting in Hall-Petch hardening.

Cold rolling is most often used to decrease the thickness of plate and sheet metal.

Cold Formed Steel

The metallurgical process of Hot rolling, used mainly to produce sheet metal or simple cross sections from billets describes the method of when industrial metal is passed or deformed between a set of work rolls and the temperature of the metal is generally above its recrystallization temperature, as opposed to cold rolling, which takes place below this temperature. Hot rolling permits large deformations of the metal to be achieved with a low number of rolling cycles.

The hot-rolled steel shapes are formed at elevated temperatures while the cold-formed steel shapes are formed at room temperature. Cold-formed steel structural members are shapes commonly manufactured from steel plate, sheet or strip material. The manufacturing process involves forming the material by either press-braking or cold roll-forming to achieve the desired shape. Examples of the cold-formed steel are corrugated steel roof and floor decks, steel wall panels, storage racks and steel wall studs.

The differences between cold-formed and hot-rolled steel are not just in the thickness and the shapes. Since cold-formed steel members are formed at room temperature, the material becomes harder and stronger. Its lightweight makes it easier and more economical to mass-produce, transport and install.

One of the main differences between designing with cold-formed steel shapes and with hot-rolled structural shapes is that with the hot-rolled, one is primarily concerned about two types of instability: column buckling and lateral buckling of unbraced beams. The dimensions of hot-rolled shapes are such that local buckling of individual constituent elements generally will not occur before yielding.

This is not the case with cold-formed members. Here local buckling must also be considered because, in most cases, the material used is thin relative to its width. This means that the individual flat, or plate, elements of the section often have width to thickness ratios that will permit buckling at stresses well below the yield point.

Hot Rolled Steel