Is one a better choice for your project?
What type of rolled steel would make the better choice for your project? It’s important to understand the fundamental differences between hot and cold rolled steel in order to select the best one for your needs.
Rolling is a metalworking process where the metal is passed through one or more pairs of rolls, which reduces thickness and makes the material uniform throughout the roll. Imagine the steel as if rolling dough through a pasta-maker, flattening and thinning it out until you have an even, smooth product. The two types of rolling are hot and cold, which is determined by the metal’s temperature during processing. Hot rolling occurs when the metal is heated above its recrystallization temperature. Cold rolling is when the metal is processed while below the recrystallization point.
Hot Rolled Steel
Hot rolling involves rolling the steel at a temperature point above its recrystallization temperature, typically around or above 1700 degrees F. This means the steel can be shaped and formed easily, including producing much larger sizes. Since the manufacturing can be done without pauses or delays in the process, this means hot rolled steel is typically cheaper than cold rolled steel.
Because of the high processing temperature, the hot rolled steel will have a rougher, scaly finish and will also shrink slightly as it cools. This means the finished product can vary in its size and shape dimensions, and at a lower price point than the same item produced through cold rolling. Hot rolled steel is best suited for uses like welding, railroad tracks or construction, where precise shapes and tolerances may not be required.
Cold Rolled Steel
Cold rolled steel is manufactured below its recrystallization temperature. Essentially, it’s hot rolled steel with additional processing in cold reduction mills. Because it is typically produced around room temperature, the process allows for closer dimensional tolerances and a wider range of surface finishes for the steel.
‘Cold rolled’ is often mistakenly used to describe all steel products, but it refers specifically to the rolling of flat rolled sheet and coil products. For other steel shapes produced below the recrystallization temperature, the accurate terminology is “cold finishing”. For instance, a cold finished steel bar is produced by cold drawing (pulling) the metal, then turning, grinding and polishing. This produces a much more precise end product with four advantages:
- Increased yield and tensile strength
- Fewer surface imperfections due to the turning process
- Grinding gives closer size accuracy and precise shapes
- Polishing improves the surface finish
The exception is cold rolled sheet versus hot rolled sheet. For this particular product, the cold rolled steel has a low carbon content and is typically annealed (heat treatment to increase ductility). This means cold rolled sheet will be softer than hot rolled sheet.
Overall, cold rolled and cold finished steel is superior to hot rolled steel in finish, straightness and tolerance, and comes at a higher price point. It would be the recommended choice when visual appeal is a priority for your project. Typical uses include building materials for sheds and garages, metal furniture, and home appliances.
Buy Hot Rolled or Cold Rolled Steel
Here at FastMetals we offer a range of Hot Rolled and Cold Rolled steel products – we offer great quality product, reasonable pricing and fast shipping – shop online at FastMetals.com or call us toll free at (833) 327-8685.