What’s the difference between hot and cold rolling?

Rolling is one of the key processes in metal manufacturing, but there are two ways to ‘roll’ steel: hot rolling and cold rolling. It is a common misconception that these processes relate to a metal’s specification or grade; instead they refer to how a metal is processed at the mill.

Hot rolling

Hot rolling is the process of rolling the steel at a high temperature (usually over 935°C). These extreme temperatures are higher than the steel’s recrystallisation temperature, meaning it can be shaped and formed more easily. Hot rolling is more common than cold rolling as it is cheaper and less time consuming. Hot rolling has less manufacturing delays due to the fact steel does not need to be reheated, as is the case with cold rolled steel.

When cooling steel after hot rolling, you should expect the steel to shrink slightly. You may find that you have less control over the final size and shape of your steel when using a hot rolling method. Hot rolling, however, allows steel to be formed into much larger sizes than cold rolling.

Cold rolling

Cold rolling involves a similar process to hot rolling, however the steel is subjected to further processing. After being rolled, the steel is cooled at room temperature in cold reduction mills. After the steel has cooled, it is subjected to annealing and/or tempers rolling, in order to provide a wide range of surface finishes and more accurate dimensional tolerances.

Cold rolled steel is often erroneously used to refer to all products, when the product name refers specifically to flat rolled sheet and coil products. When referring to bar products, the process is referred to as cold finishing, a process that instead involves cold drawing, grinding and/or polishing. Generally speaking, cold treated steel and metals have a superior surface finish, tolerance, concentricity, and rigidity when compared to hot rolled products.

If you need help with metal processing or machining for your next project, why not utilise our network of trusted metal processing providers? At ShapeCUT we use plate rollers that can roll steel up to 3,000mm wide and 32mm thick. If you require fast and reliable steel rolling services, contact ShapeCUT today.