What is the Difference Between Hot Rolled and Cold Rolled Steel?

The Difference Between Hot Rolled and Cold Rolled Steel

With such high strength capabilities, versatility, and affordability, and such a wide variety of steel products available, steel has become one of the most widely used products in manufacturing and construction. There are two different processes by which steel can be created, hot rolling and cold rolling. If you’re not familiar with the processes, here is an overview of the basic differences between these two types.

 

Rolling Temperature

Whenever a shop like WasatchSteel in Salt Lake City is working with metal, it will pass through rollers. The temperature at which the metal is rolled is what determines whether it is hot rolled or cold rolled. Hot rolling is done at a temperature above the recrystallization temperature for the metal (about 1,700-2,000 degrees Fahrenheit), which means the grains inside the metal deform and recrystallize to prevent the metal from hardening during work. It is more difficult to predict the exact finished tolerances with hot rolling because the steel will change as it cools.

 

Cold rolling is done below the recrystallization temperature, usually at room temperature. Because it does not break down the grains inside the metal, it usually increases the strength of the steel and can be done to more specific tolerances, since there is no cooling phase.

 

Steel Thickness

The hot rolling process begins with a standard steel slab, which is usually around 10 inches thick. The hot rolling process reduces the steel’s thickness to anywhere from less than 0.07 inches to about 0.35 inches, depending on what it will be used for. Once it is through the hot rolling process, it can be sent through a cold rolling process by going through more mills to make it even smaller, between 0.01 and 0.15 inches. The cold rolling process often produces a much more exact finished size, because the steel will not change as it cools.

 

Properties

With any metal, heating and cooling will change the structure of the molecules. As steel goes through the hot rolling process, it becomes softer and more easily manipulated. However, with the softer metal, it can also fracture more easily during the finishing process. Cold rolled steel has a higher tolerance before it will fracture than hot rolled steel.

 

Applications for Each Type

When you go to buy your steel from a steel supermarket such as Wasatch Steel, you should have an idea of which kind of you want. The type of steel you choose (hot or cold) depends entirely on your intended use. Hot rolling is better suited for processes where you need more ability to form the steel, such as automotive uses, pipes, water heaters, heavy agricultural equipment, metal buildings, and railroad cars.

 

Cold rolling is better suited for applications where you need better surface finish, improved thickness and flatness tolerances, and the ability to paint. It is often used for manufacturing appliances such as refrigerator doors, washer and dryer, and some automobile parts that need greater strength, such as roofs, fenders, and hoods. These are also the exposed parts of an automobile, which will often be painted. The cold rolling process also allows the steel to be painted, which makes it a popular choice for many different steel applications.