Advantages of Cold Rolled Steel
Product19 May 2022
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.
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 1700˚F to 2100˚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
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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