Rolling is a metal forming process that employs the use of a series of rollers to alter the shape, improve the uniformity, and/or enhance the mechanical properties of materials. Rolled steel can be categorized into two types—hot rolled steel and cold rolled steel—which demonstrate distinct characteristics that make them suitable for different applications. When choosing a rolled steel material for a project, it is important to be aware of the differences between the two types and how they affect their performance.

Hot rolled steel is steel that has undergone the rolling process at a temperature above its recrystallization temperature (usually 1700° F or greater). Compared to unprocessed steel, the processed material exhibits greater formability and workability, making it easier to work with in subsequent processing operations.

The hot rolling process starts with a large, rectangular slab of metal referred to as a billet. First, the billet is heated and compressed into a large roll. While still hot, it passes through a series of rotating rollers to achieve the desired dimensions. In sheet metal production operations, the rolled steel is then wound into coiled rolls and left to cool. In production operations involving other forms, the processed material is cut into the specified units and packaged.

Benefits of Hot Rolled Steel
Hot rolled steel offers several manufacturing advantages, such as:

Lower cost: Hot rolled steel tends to be less expensive than cold rolled steel since it involves less processing.
Better workability: As the hot rolling process occurs at elevated temperatures, the processed material is easy to form and shape.
Little to no internal stress: The hot rolling process involves cooling the steel gradually, which allows the material to essentially normalize its structure and become free of internal stresses.

Cold rolled steel is hot rolled steel that has undergone additional processing to improve its dimensional and mechanical properties. During the cold rolling process, cooled hot rolled steel passes through another series of rollers at room temperature. Since the material is no longer hot and malleable, a significantly higher amount of pressure is required to compress it into the desired shape. While this process can be more labor-intensive and expensive than the hot rolling process, it can achieve tighter dimensional tolerances and better surface qualities.

Benefits of Cold Rolled Steel
Compared to hot rolled steel, cold rolled steel offers a variety of advantages, such as:

Greater strength: Cold rolled steel can exhibit strength up to 20% greater than that of hot rolled steel, which makes it more suitable for use in high-stress applications.
Better surface finishes: Parts and products made from cold rolled steel generally have a smooth and shiny surface that is free of rust and scale.
Higher precision: Unlike hot rolled steel, cold rolled steel does not shrink after the forming process. This quality allows for the creation of highly precise components that require little to no secondary processing.

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