Last Update: February 4, 2015.
As noted in an earlier post, different types of steel undergo a wide range of processes to achieve the proper physical properties. Many people have heard that there’s a difference between hot and cold rolled steel, but don’t understand what how each product is made, what industries they serve, and what type is the best for their own needs. Like the name suggests, all rolled steel types are passed through either two or four rolls, which squeeze the steel and apply pressure to flatten or shape it into the desired shape, which changes the physical properties of the steel. The steel almost always goes through rolls more than once until the shape or approximate shape of the steel is achieved.
Hot Rolled Steel
The process of hot rolling involves rolling steel at a temperature above the steel’s recrystallization temperature, which takes place over 1700 degrees Fahrenheit. Steel that is above the recrystallization temperature can be shaped and formed much more easily than colder steel, and the steel can start in much larger sizes. It is also typically cheaper to manufacture than cold rolled steel, and is often manufactured without pauses or delays in the process so the steel doesn’t need to be reheated. During the cooling process, hot rolled steel will shrink and the size and shape of the steel will be less predictable than cold rolled steel.
Hot rolled products often will have a scaly finish and more rounded and less precise corners than cold rolled steel will.
What It’s Used For
You’ll find hot rolled products like hot rolled steel bars in the welding and construction trades such as making railroad tracks, I-beams, and other steel construction materials that don’t require super precise shapes.
Cold Rolled Steel
Cold rolled steel is manufactured at temperatures below its recrystallization temperature, typically at around room temperature. Because the steel is manufactured at a much lower temperature, there’s no need to worry about the steel shrinking or changing form or appearance.
The cold rolled steel end products like cold finished steel bar has a much smoother appearance and may have square corners more accurate in dimension and finish
What It’s Used For
Cold rolled steel is much more preferred in the machining world where the quality of the steel is an important factor of the quality of the final product, and the appearance of the steel is also an important factor.