Optimizing steel’s properties for each application goes beyond changing the chemical composition, however. The manufacturing processing of steel can also have a significant impact on steel products—even when the grades and specifications are the same. One key distinction among pre-fabricated steel products is the difference between hot rolled and cold rolled steel.
Hot rolled steel is steel that has been roll-pressed at very high temperatures—over 1,700˚F, which is above the re-crystallization temperature for most steels. This makes the steel easier to form, and resulting in products that are easier to work with.
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.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.
Cold “rolled” steel is often used to describe a range of finishing processes, though technically “cold rolled” applies only to galvanized sheets that undergo compression between rollers. Steel forms that are pulled, such as bars or tubes, are “drawn,” not rolled. Other cold finishing processes include turning, grinding, and polishing—each of which is used to modify existing hot rolled stock into more refined products.