To process hot rolled steel, manufacturers first start with a large, rectangular length of metal, called a billet. The billet is heated and then sent for pre-processing, where it is flattened into a large roll. From there, it is kept at a high temperature and run through a series of rollers to achieve its finished dimensions. The white-hot strands of steel are pushed through the rollers at high speeds. For steel sheet, rolled steel is spun into coils and left to cool. For other forms, such as bars or alloy steel plates, materials are sectioned and packaged.
Steel shrinks slightly as it cools. Since hot rolled steel is cooled after processing, there is less control over its final shape, making it less suitable for precision applications. Hot rolled steel is often used in applications where minutely specific dimensions aren’t crucial. Railroad tracks and construction projects often use hot rolled steel.
Hot rolled steel can often be identified by the following characteristics:
A scaled surface—a remnant of cooling from extreme temperatures
Slightly rounded edges and corners for bar and weathering steal plate products (due to shrinkage and less precise finishing)
Slight distortions, where cooling may result in slightly trapezoidal forms, as opposed to perfectly squared angles
What are the benefits of hot rolled steel?
Hot rolled steel typically requires much less processing than cold rolled steel sheet, which makes it a lot cheaper. Because hot rolled steel is allowed to cool at room temperature, it’s essentially normalized—meaning it’s free from internal stresses that can arise from quenching or work-hardening processes.
Hot rolled steel is ideal where dimensional tolerances aren’t as important as overall material strength, and where surface finish isn’t a key concern. Where surface finish is a concern, scaling can be removed by grinding, sand blasting, or acid-bath pickling. Once scaling has been removed, various brush or mirror finishes can also be applied. Descaled steel also offers a better surface for painting and other surface coatings.