Hot rolling, the process used to make hot rolled steel, involves rolling steel at high temperatures (typically over 1700˚F). These high temperatures are above steel’s recrystallization temperature, allowing the steel to be easily shaped, formed, and made in larger sizes. As it cools, hot rolled steel tends to shrink non-uniformly, giving less control on the size and shape of the finished product when compared to cold rolled steel.
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Hot rolled steel tends to have a scaly finish which can be removed by pickling, grinding, or sand-blasting. This steel is essentially normalized, meaning free from internal stresses that can arise from quenching or work-hardening processes, because it is allowed to cool at room temperature. Other properties may include:
Hot rolled steel tends to be cheaper than cold rolled steel because it is manufactured without any delays in the process and does not require reheating like cold rolled steel. It is also essentially normalized as it is allowed to cool at room temperature; this means it’s free from internal stresses that can arise from quenching or work-hardening processes.
One of the many differences between hot and cold rolled steel is price. Hot rolled steel tends to be cheaper than cold rolled steel because it is manufactured without any delays in the process and does not require reheating like cold rolled steel. It can be used in applications where precise shapes and tolerances are not required, such as:
Customers often ask us about the differences between hot rolled steel and cold rolled steel. There are some fundamental differences between these two types of metal. The differences between hot rolled steel and cold rolled steel relate to how these metals are processed at the mill, not the product specification or grade. Hot rolled steel involves rolling the steel at high temperatures, whereas cold rolled steel is processed further in cold reduction mills where the material is cooled, followed by annealing and/or tempers rolling.
Hot rolling is a mill process that involves rolling the steel at a high temperature (typically at a temperature over 1700° F), which is above the steel’s recrystallization temperature. This process begins with heating large steel slabs, billets, or blooms and then rolling them at high temperatures. The rolling process involves passing the heated steel through a series of rollers to achieve the desired shape and thickness. When steel is above the recrystallization temperature, it can be shaped and formed easily, and the steel can be made in much larger sizes.
Hot rolled steel typically has a rougher, more scaled surface than cold rolled steel. The scaling, formed as the steel cools at room temperature, is often removed later via a process called pickling, which involves the use of acid baths. However, the slightly irregular surface finish and less precise dimensional tolerances of hot rolled steel make it less suitable for applications requiring a smooth, refined surface or tight dimensional tolerances.
Hot rolled steel is typically cheaper than cold rolled steel because it is often manufactured without any delays in the process, and therefore the reheating of the steel is not required (as it is with cold rolled). When the steel cools off, it shrinks slightly, thus giving less control over the size and shape of the finished product when compared to cold rolled.
Uses: Hot rolled products like hot rolled steel bars are used in the welding and construction trades to make railroad tracks and I-beams, for example. Hot rolled steel is used in situations where precise shapes and tolerances are not required.
Cold rolled steel is essentially hot rolled steel that has had further processing. The steel is processed further in cold reduction mills, where the material is cooled (at room temperature), followed by annealing and/or tempers rolling. This process will produce steel with closer dimensional tolerances and a wider range of surface finishes. The term “cold rolled” is mistakenly used on all products when the product name actually refers to the rolling of flat rolled sheet and coil products.
When referring to bar products, the term used is “cold finishing,” which usually consists of cold drawing and/or turning, grinding, and polishing. This process results in higher yield points and has four main advantages:
All cold products provide a superior surface finish and are superior in tolerance, concentricity, and straightness compared to hot rolled.
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Cold finished bars are typically more challenging to work with than hot rolled due to the increased carbon content. However, this cannot be said about cold rolled sheet and hot rolled sheet. With these two products, the cold rolled product has low carbon content, and it is typically annealed, making it softer than hot rolled sheet.
The advantages of cold rolled steel include its superior surface finish, higher strength, and tighter dimensional tolerances compared to hot rolled steel. However, the increased strength and reduced ductility of cold rolled steel can make it more challenging to work with in certain fabrication processes than hot rolled steel.
Uses: Any project where tolerances, surface condition, concentricity, and straightness are the major factors. Due to its improved surface finish and tighter tolerances, cold rolled steel is suitable for applications where aesthetics and precise dimensions are important. It is commonly used in applications requiring high precision and a high-quality finish, such as in manufacturing appliances, automotive parts, furniture, and metal containers. It is also frequently employed in the construction of consumer electronics and in metalworking projects where a smooth, polished appearance is desired.
Understanding HR and CR sheet differences helps ensure that you choose the most appropriate material for your project’s requirements. Here are some key points to consider when deciding between hot rolled and cold rolled steel:
Application Requirements – If the project requires high precision, tight tolerances, or a smooth surface finish, cold rolled steel is typically the better choice. Hot rolled steel is often sufficient for projects where its structural integrity is more important than its appearance. Its ease of fabrication also makes it suitable for welding and bending processes.
Cost Considerations – Hot rolled steel is generally less expensive than cold rolled steel because of its simpler production process and lower finishing requirements. If cost is a primary concern and the application permits, opting for hot rolled steel can be more economical. Cold rolled steel, while more expensive, offers higher strength and a better surface finish and may be worth the investment for some projects.
Desired Material Properties – Cold rolled steel typically offers higher strength and hardness due to the cold working process. Hot rolled steel has better ductility, which is beneficial in applications that involve forming or shaping the steel.
Aesthetic Preferences – If the appearance of the steel is important, cold rolled steel’s smooth, polished surface may be preferable. It’s ideal for projects where the steel will be visible and aesthetics are a consideration. In applications where the steel will be coated, painted, or hidden, the rougher surface of hot rolled steel may not be an issue.
Lead Time – Availability of the specific type and grade of steel required for your project can also influence the decision. Some steel grades are more readily available in either hot rolled or cold rolled form.
You can check out our video below to find out the difference between hot rolled steel and cold rolled steel:
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