In short, hot rolled steel is processed on a rolling mill at high temperatures, and that’s it. Cold rolled steel, on the other hand, is processed the same way as hot rolled steel, but once it cools to room temperature, it undergoes additional processing to achieve different benefits. Generally speaking, hot rolled steel has a rougher surface, wider tolerances, and is less expensive. It is most often used in construction, welding, and other projects that don’t require tight tolerances and an excellent finish. In contrast, cold rolled steel has a smoother surface finish, is stronger, and has tighter tolerances. If tight tolerances, a smooth surface finish, or consistency are critical, then cold rolled steel is a better choice.
Hot Rolled Steel
Hot rolling is the rolling process that almost all steel goes through. First, the steel is heated to over 1700 F (926 C), which is above the metal’s recrystallization temperature. Because of this, the steel is easy to manipulate, shape, and form. After the material is formed, it is cooled to room temperature. During this process, the metal contracts as it cools, which can cause slight warping. This is why hot rolled steel has looser tolerances than cold rolled steel.
Hot rolled steel also tends to be cheaper than cold rolled steel due to tighter tolerances and slightly lower strength.
You can visually identify hot rolled steel by the following characteristics:
ď‚· Rough and flaky surface
ď‚· Dry or oil-free finish
ď‚· Any edges on the material are rounded
For projects that require low cost, high strength, or high production, use hot rolled steel. Construction, welding, railroads, and I-beams all commonly use hot rolled steel. If you need precise shapes or tight tolerances, use cold rolled steel.
Cold rolled steel
Cold rolling starts out as hot rolled material. But once it cools, it undergoes further processing. At room temperature, cold rolled steel is either annealed or drawn through rollers, depending on what the manufacturer needs the metal for. These processes tighten the tolerances on the material, actually making the material stronger. The surface finish, tolerances, straightness, and consistency of cold rolled steel are always better than hot rolled steel. Therefore, it is usually a bit more expensive.
If a cold rolled product has been annealed, it will be easier to process than hot rolled material. After it has been processed into the desired shape, it should also be heat treated to further harden it. If it has just been run through rollers, then it will be harder and harder to process.
You can visually identify cold rolled steel by the following characteristics:
ď‚· Smooth surface
ď‚· Greasy or oily feel
ď‚· Any edges are sharp
Cold rolled steel is used when tolerances, higher strength, or surface finish are the most important qualities.