Hot Rolled Steel vs. Cold Rolled Steel
June 15, 2021 | Categorised in: Steel 101
Rolled steel is categorized by the temperature and processing it goes through, usually dependent on its use and purpose in a construction or manufacturing project. The variety of applications is helped by the vast number of different steel grades and shapes as well. This means that it’s very versatile and can be used for a wide range of implementations. Not only do the grades, sizes, and chemical makeup of steel products determine what it can be used for, but also the processing can make it more suitable for a certain project or situation.
What is Rolled Steel?
Rolling steel involves running the metal through a pair, or pairs, of rollers to flatten and thin out the steel, or to make the thickness more uniform. This can be done using one pair of rollers, but usually uses three to six pairs that gradually reduce the thickness of the steel. The general reason for rolling steel is largely dimension specifications and to get a piece of steel that is thin enough for its application. However, there are differences in the processes for actually accomplishing this.
Hot vs. Cold Rolled Steel
Hot Rolled Steel
As one might have assumed, the primary difference between hot and cold rolled steel is the temperature at which they are worked on. Hot rolled steel is processed at over 1,700°F and is easier to work with because steel recrystallizes between 750°F and 1,300°F. This means it can be reshaped and altered before it hardens again. Requiring less processing and being able to shape the steel much easier means that it’s less labor-intensive and more cost-effective to process this way.
However, there are drawbacks, such as cooling shrinkage. Steel will shrink as it cools and because this is unpredictable, the amount and direction the steel shrinks can mean that final sizes and dimensions are difficult to plan for. In addition to the measurements, hot rolled steel will also have flaky scale on the surface that needs to be removed through grinding, sand blasting, or acid-bath pickling to get a clean finish.
Cold Rolled Steel
On the other hand, cold rolled steel actually occurs after hot rolling. After this, it’s allowed to cool to room temperature, where it will be further processed without more heat (hence the “cold” rolled steel). This extra processing is significantly more difficult due to the extra power that is needed to shape steel below its crystallization temperature. However, the cold rolled steel is not only much more accurate in terms of dimensions because it doesn’t cool and shrink further, but also has a smooth surface finish. Even better, cold rolled steel’s tensile and yield strength can be increased by around 25% (or even 40-50% in certain situations) greater than hot rolled steel.
Of course with so many benefits there are going to be downsides, the primary one being cost. The extra processing that cold steel requires means that it’s much more labor-intensive and significantly more expensive.
The most significant differences between these two is that hot rolling can get a roughly accurate and thin piece of steel that is functional but much less refined. With cold rolling, an extra processing step is added that improves the dimensional accuracy, overall strength, and visual aesthetics of the steel. To keep a smooth surface and prevent rust, however, steel should be galvanized after being produced. Because of the extra resources and time that are spent, cold rolling is, unsurprisingly, going to be more expensive as well.
Which is Right for You?
Depending on your project, certain aspects of one may push you towards a choice. If how the steel looks and feels doesn’t matter, hot rolling might be the way to go so you don’t have to pay for aspects that won’t really be necessary. If the steel does have to look more presentable, the extra strength is needed, or the size specifications of the pieces of steel are very precise, then the extra money spent on cold steel is probably worth it. It all comes down to what your project involves and what the steel is being used for. If you want assistance choosing what types of steel you might need, reach out and get a quote for how we can help you today.