What is the Difference Between Hot Rolled and Cold Formed Steel Sections?
Steel is one of the most common metals on the market and is used by almost every person every single day. From stainless steel kitchen appliances to structural steel beams in buildings, steel is extremely versatile and can be found everywhere, whether you realise it or not. There are many different types of steel, over 3,000 in fact, and each of them can be classified into either hot rolled or cold rolled.
Depending on your metalwork needs, it’s important to know the difference between hot rolled and cold formed steel sections as this can greatly affect the overall finish and properties of the steel. If you’re unsure, keep reading as we explain the differences between the two manufacturing processes.
What is hot rolled steel?
Steel can be formed in one of two ways, with the most common being hot rolled. This refers to the process in which the steel is made from, with hot rolling using heat. During the hot rolling process, the steel is heated to 1700˚. This is above the recrystallization temperature for steel, resulting in it being far easier to mould and form.
First, the steel starts off as a billet. This is a big rectangle of metal. It is heated and pre-processed (this essentially means the billet is flattened down into a roll). The high temperatures are maintained as the metal is pushed at speed through rollers until it reaches the shape and form required. Coils are used to create sheet metal, whilst plates and bars are separated into sectioned.
Once the final dimensions have been achieved, the steel is left to cool down.
What is cold rolled steel?
Cold rolled steel is the other main process used to form steel. Like hot rolled steel, during the cold rolling process, the steel is heated to a temperature above its recrystallization point. From there, it goes through the hot rolling process. This means a billet of metal is flattened out, and it is then pushed through rollers at a high speed and high temperature until the final dimensions and shape is achieved.
Once the steel has cooled down, it is pushed through the rollers again to refine the finish.
What are the differences between hot and cold rolled steel?
With the processes being so similar, you might be wondering what the differences are between the steels that are hot and cold rolled. Generally speaking, hot rolled steel is easier to work with, but when it cools down it shrinks. This means exact dimensions are difficult to achieve. The surface is also scaly and the edges can be rounded, with further distortions sometimes being found within the metal.
For applications where straight edges and exact dimensions are required, as well as a smoother, cleaner finish, cold rolling works better. Whilst the steel is harder to form when it’s at room temperature or just below, there’s no risk of shrinkage due to cooling. This is where most of the imperfections in steel come from during the hot rolling process.
When is hot rolled steel better?
Hot rolled steel has many benefits. Firstly, it’s faster to manufacture and is easier, too. With it being faster, this also means it’s cheaper. It’s perfect for large scale applications where the overall finish and exact dimensions are not of as much concern. This is why hot rolled steel is commonly used within the transportation industry in the form of railway tracks, as well as within the construction and architectural industries. If the overall look of the steel doesn’t matter too much, hot rolled steel is the better option. It’s also ideal when you need steel with no internal stresses. When it cools down the steel normalises, therefore removing any internal stresses and bettering the tensile strength.
When is cold rolled steel better?
Cold rolled steel is generally stronger and harder than hot rolled steel, and it’s more precise. If you need an accurate shape with a shiny, smooth, tidy finish, cold rolled steel is the better option. The metal ends up straighter and true to the dimensions you need, but there are internal stresses than can cause unforeseen warping. To prevent this, you will need to relieve the stress before you begin working with the cold rolled steel.
Cold rolling, although more precise, is more expensive and the process takes a lot longer to complete.
Which is better overall?
There is no clear answer as to which process is better overall – it depends on your project and needs. For standard projects where precision isn’t top of the list, hot rolled steel is ideal, but if you need something a bit more refined and that is harder and stronger, cold rolled steel is better.
Buy steel online
Here at Rapid Metals, we are one of the UK’s leading suppliers of steel. We provide a wide selection available to buy online, but if you can’t find what you need, or if you have questions about sourcing the correct type of steel for your project, please contact us and we’ll be happy to help.