热轧钢Hot 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 sheet metal, rolled steel is spun into coils and left to cool. For other forms, such as bars or 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 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
Hot rolled steel typically requires much less processing than cold rolled steel, 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.