Steel is roll-pressed at temperatures exceeding 1,700˚F, at which the 3-dimensional arrangement of atoms in the crystalline metal are permanently reoriented to increase ductility while lowering excess hardness. In this process, molten hot steel slabs are passed through a series of rotating rollers, which render the metal defect-free and the stock is compressed into desired shapes and dimensions. The metal is then left to cool. The resulting material is “hot rolled” steel. This steel has a myriad of applications across industries.
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There are many steel products and parts that require steel with precise dimensions and higher surface quality than hot rolled steel. With this in mind, existing hot-rolled steel is further compressed, squeezed, turned, precision ground, and polished into desired shapes and sizes. All of this happens at room temperature and only mechanical strength, no heat, is employed. The end product is a more refined material- cold rolled steel (or CR steel).
More strength
Unlike hot rolled steel, CR steel doesn’t undergo structural changes during its generation since its shape change is achieved without the use of any heat. At the same time, large rollers compress and roll the material, bringing intense pressure on it, hardening it in process. The result is that CR steel is able to withstand a significant amount of stress. Strength-wise, it outshines hot-rolled steel of the same grade by a margin of nearly 20%.
Improved surface finish
The cold rolling process also refines the inner structure of the metal and smoothens its surface, leaving it with an oily or greasy finish, depending again on the type of cold-rolling process applied. Compared to hot rolled steel, cold rolled steel presents buyers with a wider range of surface finishes and mechanical properties. Take, for instance, bright annealed (BA) finish.
BA finish is first cold rolled, then heated to a range between ˚F to ˚F, before being cooled. BA derives its smooth, bright, and reflective “mirror finish” from this annealing process. Typically, cold rolled sheets have fewer surface blemishes than hot rolled ones, and, consequently, products shaped from cold rolled steel exhibit a clean and polished surface free of rust or oxide deposits. Moreover, this steel lends itself well to being painted and has increased corrosion resistance.
Tighter tolerance
Among other things, CR steel sheets come with tighter tolerance, an industry term indicative of the thickness of the material. The cold rolling process generates steel that is generally thinner, with closer dimensional tolerances, than the ones produced by hot rollers. With very high tight tolerance, steel tempered through the “full-hard cold rolling process” leads the way.
Full-hard cold rolling is capable of trimming the metal thickness by nearly half, which is remarkably high tolerance. Therefore, it is significant as an input material for products that require higher metal tolerances. That’s not all, cold rolled steel can be easily slit with very high precision to the desired length, its thickness suitably adjusted, and bends/curves fixed.
Common applications
Cold-rolled steel is used in applications where factors, such as medium-to-high tensile strengths, fine surface quality, flatness (straightness) and formability are paramount:
Automotive
Aerospace structural components
Civil engineering (e.g., steel sheds, industrial buildings, garages)
Home appliances
Metal furniture
Pipes and tubes, refrigeration tubes
Bear seals
Oil filters
Fire extinguishers
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Since cold rolling involves more processing and consumes more resources, it carries a higher price than HR steel of the same grade. Besides, compared to hot rolled steel, it takes far more effort to deform CR steel and draw it into new shapes without breaking. However, some loss of ductility might be a small price to pay for increased hardness in scenarios where the latter is a more compelling need.
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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.
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Hot rolled steel is steel that has undergone the rolling process at a temperature above its recrystallization temperature (usually ° 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.
Hot rolled steel offers several manufacturing advantages, such as:
Since hot rolled steel shrinks slightly during the cooling stage, there is a lesser degree of control over its final shape. For this reason, it is typically used in applications that do not require extremely tight tolerances, such as:
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.
Compared to hot rolled steel, cold rolled steel offers a variety of advantages, such as:
Cold rolled steel is often used for applications that require tighter tolerances and better surface finishes. Typical parts and products include:
As indicated above, the main difference between hot rolled steel and cold rolled steel is the temperature at which they are processed. Hot rolled steel is rolled above the material’s recrystallization temperature, whereas cold rolled steel is rolled below the material’s recrystallization temperature. Beyond this quality, there are a few other distinctions between the two materials, including in regard to the following:
These two steel types should not be confused with the technical specifications or grades used to classify steel by composition or physical characteristics. Steel can be hot rolled or cold rolled regardless of its metallurgical specifications or grade.
When evaluating steel options for a project, it is important to keep in mind that some materials will work better than others for certain purposes. Understanding which type of steel offers the right properties for a given application can prevent overspending on raw materials and save time in the long run.
Cold forming is an umbrella term that encompasses several forming processes that occur at or near room temperature, such as bending, drawing, and rolling. At Grob Inc, we specialize in cold rolling specialized profiles onto bar stock.
Our team manufactures cold rolled parts and products from a variety of metals, such as aluminum, naval brass, stainless steel, and other steel alloys. The finished components demonstrate higher tensile strength, greater material hardness, tighter dimensional tolerances, and a better surface finish than ones produced through high-heat forming methods. Additionally, since the cold rolling process involves the displacement of material—rather than the removal of material—our production operations occur with a better material usage to waste ratio.
Some of the parts and products we regularly produce in these operations include:
For additional information about our cold forming capabilities, check out our cold forming process page.
When considering the use of steel for a project, it is essential to be aware of the differences between hot and cold rolled steel. Both materials exhibit characteristics that make them suitable for different use cases, but cold rolled steel offer numerous advantages over hot rolled steel, including, but not limited to, better strength, dimensional tolerance, and surface finish. For customers looking for a cold rolling partner, the Grob team is here to help.
By partnering with us for their cold rolled metal needs, our customers benefit from our:
To find out more about our standard and custom cold rolling capabilities or discuss your next project with one of our experts, contact us today.
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