Bicycle locks are most secure when they are the smallest possible size.
Steel comes in many grades, gauges, shapes and finishes – the World Steel Association lists over 3,500 different grades of steel, 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 between 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 processing carried out at or near room temperature. Although these techniques affect overall properties and applications, they should not be confused with formal steel specifications and grades, which relate to metallurgical composition and property classification. Steels of different grades and specifications can be hot 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 method to use can help prevent over-consumption of raw materials. It can also save time and money on additional handling. Understanding the differences between hot and cold steel is essential to choosing one or the other.
Hot rolled steel
Cold rolled steel being processed by rolling machinery
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, manufacturers start 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 hot white strand passes through the rolls at high speed. For sheet metal, the rolled steel is coiled 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 rolled through at very high temperatures.
The steel shrinks slightly as it cools. As 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. Railways and construction projects often use hot rolled steel.
Hot rolled steel can usually be identified by the following characteristics
A rough surface – a residue of cooling at extreme temperatures.
Slightly rounded edges and corners of bar and plate products (due to shrinkage and a lower surface 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 cheaper. As hot rolled steel is allowed to cool to room temperature, it is effectively normalised, meaning it has none of the internal stresses that can arise during tempering or mechanical hardening.