ASTM A283 Grade C Mild Carbon Steel Sheet/6mm Thick Galvanized Carbon Steel Sheet Metal

Hot and cold rolled steel

Steel comes in many grades, sizes, shapes and finishes - worldsteel lists more than 3,500 different grades, each with unique properties. Variety of types means steel can be used in a wide range of applications in infrastructure, appliances, vehicles, wind turbines and more

However, optimizing the properties of a steel for each application goes beyond just changing the chemical composition. The manufacturing and processing of steel can also have a significant impact on steel products - even if 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 steel and cold rolled steel?

It is important to note that the main difference between hot rolled steel and cold rolled steel lies in one of the processes. "Hot rolling" refers to working with heat. "Cold rolling" refers to a process performed at or near room temperature. Although these techniques affect overall performance and application, they should not be confused with the formal specifications and grades of steel, which relate to metallurgical composition and performance grades. Different grades and sizes of steel can be hot rolled or cold rolled - including base carbon steel and other alloy steels

Hot rolled steel is steel that is rolled at very high temperatures (over 1,700°F), above the recrystallization temperature of most steels. This makes the steel easier to form and results in an easier-to-use product

To process hot-rolled steel, manufacturers first start with a large rectangular piece of metal, called a billet. The billet is heated and sent for pretreatment, where it is flattened into a large coil. From there, it is held at high temperature and passed through a series of rollers to reach its final size. The white-hot strand is pushed through the rollers at high speed. For sheet metal, rolled steel is spun into coils and cooled. For other forms, such as bars or sheets, the material is divided and packaged

What are the benefits of hot rolled steel?

Hot rolled steel generally requires less machining than cold rolled steel, which makes it much cheaper. Because hot rolled steel can be cooled at room temperature, it is essentially normalized - meaning it has no internal stresses due to the quenching or work hardening process

Hot rolled steel is ideal where dimensional tolerances are less important than overall material strength and surface finish is not a critical issue. Where surface finish is a concern, scaling can be removed by grinding, sandblasting, or acid bath pickling. A variety of brushes or mirror finishes can also be used after scaling has been removed. Rust-removed steel also provides a better finish for paint and other surface coatings

cold rolled steel

Cold-worked steel is generally harder and stronger than standard hot-rolled steel

Cold rolled steel is essentially hot rolled steel that has been further processed. Once the hot rolled steel has cooled, it is then re-rolled at room temperature for more precise dimensions and better surface quality

Cold 'rolled' steel is often used to describe a range of finishing processes, but technically 'cold rolled' only applies to sheet that is subjected to compression between rolls. A drawn steel form, such as bar or tube, is "drawn", not rolled. Other cold-finishing processes include turning, grinding and polishing - each of which is used to transform existing hot-rolled billets into more refined products

Cold rolled steel can usually be identified by the following characteristics:

Better, more finished surfaces with tighter tolerances

Smooth surfaces are often greasy to the touch

The bars are true and square, and usually have well-defined edges and corners

Tubes have better concentricity and straightness

What are the benefits of cold rolled steel?

Cold rolled steel has better surface properties than hot rolled steel, so it is not surprising that cold rolled steel is often used for technically more precise applications or where aesthetics are important. But they are more expensive due to the extra processing of cold finished products

In terms of physical properties, cold rolled steel is generally harder and stronger than standard hot rolled steel. As the metal is formed at lower temperatures, the hardness, tensile fracture and deformation resistance of the steel are all increased by work hardening

However, these additional treatments also create internal stresses within the material. This can lead to unpredictable warpage if the steel is not stress relieved before cutting, grinding or welding

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