Thursday 14 June 2018

Rolling Mill Plant

Hot And Cold Rolled Steel - Process and Usages

Customers often want to know the difference between hot rolled steel and cold rolled steel. There are certain typical dissimilarities between these two kinds of metal. The differences between hot rolled steel and cold rolled steel relates to the technique used to process these metals at the mill, and not the product specifics or grade.

Hot Rolled Steel

Hot rolling is a rolling mill plant process which includes rolling the steel at a high temperature (ordinarily at a temperature more than 1700° F), which is above the steel's recrystallization temperature. When steel is above the recrystallization temperature, it can be molded and shaped with ease, and the steel can be made in significantly bigger sizes. Hot rolled steel is basically less expensive, than cold rolled steel because of the fact that its usually produced, with no delays in the process. And thus the reheating of the steel isn't required (as it is with cold rolled). Once the steel cools off it will contract marginally, subsequently giving less control on the size and shape of the finished product as compared to cold rolled.

Usages: Hot rolled items like hot rolled steel bars are used in the welding and construction works, to manufacture railroad tracks and I-beams, for instance. Hot rolled steel is used in the cases where exact shapes and tolerances are not required.

Cold Rolled Steel

Cold rolled steel is basically hot rolled steel that has been put to further processing in a rolling mill plant facility. Further processing of the steel happens in cold reduction mills, where the material is cooled (at room temperature) subsequently undergoing - annealing and temper rolling. The steel produced as a result of this process has closer dimensional tolerances and, a larger range of surface finishes. The term Cold Rolled is erroneously used on all products, when actually the product deals with the rolling of flat rolled sheet and coil products.

Usages: In projects where tolerances, surface condition, concentricity, and straightness are the main considerations.

Conclusion

When talking about bar products, the term used is "cold finishing", which more often than not comprises of cold drawing and/or turning, grinding and polishing. This process begets higher yield points.

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