Steel is rolled using two types of processes – cold rolling and hot rolling. Well, when steel is rolled at more than the temperature of re-crystallisation, it is called hot rolled steel. When steel is rolled at a lower temperature, it is called cold rolled steel. While hot rolled steel is obtained at a temperature of 1000 degrees, the cold rolled steel is obtained at 50 degrees. The hot rolled steel loses its hardness, and softens, once it is heated at a high temperature. The hot rolled steel has to then be treated to strengthen it. On the other hand, the cold rolled steel is obtained by beating it with heavy hammers, as it does not soften like the hot rolled steel. When steel undergoes the cold rolling process, it becomes harder and stronger. When steel is hot rolled, the finished tolerances are loose. With cold rolled steel, the tolerances are much closer. In terms of finishing as well, both the hot rolled steel and the cold rolled steel are different. The Hot rolled steel comes with a rough blue-grey finish, and rounded corners. On the other hand, the cold rolled steel comes with a shiny blue-grey surface, and square corners. In size as well, the hot rolled and the cold rolled steel are different. The hot rolled steel comes in plus minus 0.01 inches, or even more than that. On the contrary, the cold rolled steel comes in less than 0.01 inches. Another difference that can be seen between cold rolled and hot rolled steel, is that cold rolled steel has fewer carbon inclusions. Summary 1. Hot rolled steel is obtained at a temperature of 1000 degrees; the cold rolled steel is obtained at 50 degrees. 2. When steel is hot rolled, the finished tolerances are loose, unlike cold rolled steel. 3. The hot rolled steel comes with a rough blue-grey finish, and rounded corners. On the other hand, the cold rolled steel comes with a shiny blue-grey surface, and square corners. 4. The hot rolled steel comes in plus minus 0.01 inches, or even more than that. The cold rolled steel comes in less than 0.01 inches. 5. The cold rolled steel is harder and stronger than the hot rolled 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. *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.
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