Learn about the benefits of each type of steel and which one to choose for your project.
Cold rolled steel sheets are stored and sold in coils after rolling.
Bicycle locks are most secure when the size is as small as possible.
Steel comes in many grades, sizes, shapes and finishes – the World Steel Association lists over 3,500 different grades, each with unique properties. The different types mean that steel can be used for a wide range of applications in infrastructure, appliances, vehicles, windmills and many more.
However, optimising the properties of steel for each application involves more than just changing the chemical composition. The steelmaking process can also have a significant impact on the steel product – even when the grades and specifications are the same. A key difference in prefabricated steel products is the difference between hot-rolled and cold-rolled steel.
What is the difference between hot-rolled and cold-rolled steel?
It is worth noting that the main difference between hot-rolled and cold-rolled steel is the process.” Hot rolling” refers to a process that is carried out with heat.” Cold rolling” refers to processes carried out at or near room temperature. Although these techniques affect overall properties and applications, they should not be confused with formal specifications and steel grades, which relate to metallurgical composition and property classification. Different grades and specifications can be hot-rolled or cold-rolled – including basic carbon steels and other alloy steels.
This may seem obvious, but some types of steel are better suited to certain applications. Knowing which type of steel to use can help prevent overspending on raw materials. It can also save time and money on additional processing. Understanding the differences between hot and cold steels is essential to choosing one or the other.
Hot rolled steel
Cold rolled steel being processed by a rolling machine
Cold rolled steel is ideal for products that require precise dimensions and improved surface characteristics.
Hot rolled steel is steel that passes through the rolls at very high temperatures – over 1,700˚F, which exceeds the recrystallisation temperature of most steels. This makes the steel easier to form and results in a product that is easier to process.
To process hot-rolled steel, the steel fabricator starts with a large rectangular sheet of metal called a billet. The billet is heated and sent for pre-treatment, where it is flattened to form a large coil. There it is held at a high temperature and passed through a series of rolls to reach its final size. The white hot strand passes through the rolls at high speed. For sheet metal, the rolled steel is rolled into coils and allowed to cool. For other shapes, such as bars or plates, the material is split and packed.
Hot rolled steel is steel that has been passed through the rolls at very high temperatures.
As it cools, the steel shrinks slightly. Because hot rolled steel cools after processing, there is less control over its final shape, making it less suitable for precision applications. Hot rolled steel is usually used in applications where specific dimensions are not required. Hot rolled steel is often used for railway tracks and construction projects.
Hot rolled steel can usually be identified by the following characteristics
Rough surfaces – residues from cooling at extreme temperatures.
Slightly rounded edges and corners of bar and plate products (due to shrinkage and lower finish)
Slight distortion, cooling results in slight trapezoidal shapes rather than perfectly square corners
What are the benefits of hot-rolled steel?
Hot-rolled steel usually requires less processing than cold-rolled steel, which makes it considerably less costly. As hot-rolled steel is allowed to cool to room temperature, it is effectively normalised, meaning that it has none of the internal stresses that can arise during tempering or mechanical hardening.
Hot rolled steel is ideal where dimensional tolerances are not as important as the overall strength of the material, and where surface finish is not a critical issue. When surface finish is a critical issue, hot rolled steel is the ideal choice.