There are many different grades, shapes, finishes, and specifications of steel. According to the World Steel Association, there are over 3,500 grades, and they each have unique properties. Because of the different grades, there are types of steel for every application; the various styles mean that builders commonly use steel for infrastructure, wind turbines, vehicles, applicants, and many other projects.
However, optimizing the steel’s properties for different applications goes far beyond changing its chemical composition. The particular way steel gets manufactured has a significant impact on the end product and, ultimately, its uses—this is true even for steel of the same grade and specification. One crucial distinction among prefabricated steel is the difference between hot rolled vs. cold rolled. We’ll go over the differences, similarities, and benefits that each type brings to the table.
Hot Rolled vs. Cold Rolled Steel: The Differences
First off, it’s important to note that the primary difference between hot and cold rolled steel is the process of how it gets manufactured. Hot rolling is when you process the steel with heat, and cold rolling is when you process the steel at or near room temperature. While these manufacturing techniques affect the steel’s overall application and performance, you shouldn’t confuse hot and cold rolled with the metal’s grade and formal specifications, which relate more to the performance rating and metallurgical composition. Steels with different specifications and grades can be hot, or cold rolled, including basic carbon steels and other alloy steels.
While it may seem obvious to some, certain steels are better suited for specific applications, and knowing which one to use can help cut over-spending on raw materials. It can also save you time and resources on additional processing. Therefore, it’s essential to understand the main differences between hot and cold rolled steel.
Hot Rolled Steel
Hot rolled steel is when the metal is roll-pressed at extremely high temperatures. These temperatures are above 1,700˚F, which is higher than the recrystallization temperature of most steels. Hot rolling steel makes it easier to form, resulting in an end product that is easier to work with.
When processing hot rolled steel, manufacturers will first start with a billet (a large, rectangular piece of metal). They then heat the billet and send it for pre-processing, where it gets flattened into a large roll. Next, the steel gets ran through a series of rollers while maintaining a high temperature to achieve its finished dimensions. These white-hot pieces of steel then get pushed through the rollers at high speed. If manufacturing sheet metal, it’s then spun into coils and put aside to cool down. For other forms, like plates or bars, the material then gets sectioned and packaged.
Here’s the biggest drawback of hot rolled steel: the metal shrinks as it cools. Since hot rolled steel gets cooled after processing, there isn’t as much control over the final shape, which makes it less suitable for applications where precision is a requirement. Construction projects typically use hot rolled steel since minutely specific dimensions aren’t generally crucial.
You can identify hot rolled steel by its:
- Scaled surface, which is a remnant of cooling the metal from extreme temperatures
- Slightly rounded corners and edges in plate and bar products, due to the less precise finish and shrinkage
- Slight distortions from cooling—you’ll likely see trapezoidal forms rather than perfectly squared angles
Benefits of Hot Rolled Steel
Hot rolled steel usually requires much less processing than its cold rolled counterpart, making it a lot cheaper in most situations. Because it gets cooled at room temperature, it’s basically normalized, which means it’s free from stresses in the metal that can come from work-hardening or quenching processes.
Hot rolled steel is ideal for projects where material strength is more important than the surface finish and dimension tolerances. You can remove the scaling from hot rolled steel by sandblasting, grinding, or acid-bath pickling the metal. After removing the scaling, you can apply a brush or mirror finish. Descaled steel also offers a great surface for painting and other coatings.
Cold Rolled Steel
Essentially, cold rolled steel is hot rolled steel that goes through additional processing. Once the hot rolled steel cools down, it gets re-rolled near room temperature to achieve better surface qualities and more exact dimensions.
Related: Cold Welding 101
The term cold rolled steel often gets used to describe various finishing processes. Still, technically it applies only to sheets of metal that undergo compression between rollers because steel forms that get pulled (like tubes and bars) get “drawn,” not “rolled.” There are other cold finishing processes, like turning, polishing, and grinding, that modify an existing hot rolled product into a more refined one.
You can identify cold steel by its:
- Better finished surface and closer tolerances
- Smooth surfaces that often feel oily to the touch
- True, square bars with well-defined corners and edges
- Tubes with straighter, more concentric uniformity
Benefits of Cold Rolled Steel
Cold rolled steel often gets used for technically precise applications and ones where aesthetics are more important than material strength. Because it’s essentially hot rolled steel that goes through additional processing, it comes with a higher price.
Physically, cold rolled steels are usually stronger and harder than hot rolled ones. As the metal gets shaped at lower temperatures, the hardness, and resistance against deformation and tension breaking all become increased.
However, those additional treatments can create internal stress in the metal, causing unpredictable warping if you don’t relieve the stress before welding, grinding, or cutting.
Hot and Cold Rolled Steel for Manufacturing and Product Design
Depending on your project and what you want to build, different materials have their own drawbacks and benefits. For many on-off or run-of-the-mill productions, steel materials provide the building blocks for almost any structural configuration you can imagine.
Looking for the best steel for your next project? Reach out to South Austin Metals’ steel sales!
For more information about our steel sales or to get a quote for a custom project, get in touch with us here.
Related: Ferrous vs. Non-Ferrous Metals