Hot Rolled Steel vs. Cold Rolled Steel

When approaching a company for a quote on material costs for producing a product, you will want to know the differences between metals. One important difference to understand is hot rolled steel and cold rolled steel.

This lack of knowledge concerning the two types of steel is more common than you would think. The difference is not in their specifications or grade, but in how they are processed at a mill. When you choose metals for a job, it's important you know how the hot rolled and cold rolled steel are different.

Rolling Process

When forming metal, it has to go through a process called, rolling. This process involves passing the metal stock through one or more pairs of rolls to decrease its thickness. During the rolling, the metal will become uniform in its thickness, much like bread dough does when it's turned in the kitchen.

When the rolling is done above a certain temperature, it prevents the steel from recrystallizing. This process is called, hot rolling. Rolling performed below a specific temperature will allow for recrystallizing and is called, cold rolling. The use of roll stands which contain pairs of rolls are grouped into rolling mills and are capable of quickly processing the metal into products.

Hot Rolled Process

The milling process performed at more than 1700 degrees Fahrenheit is called hot rolling and is above steel's recrystallization temp. This process allows for the metal to be shaped and formed more easily and also create larger sizes. It is generally much less expensive to hot roll than cold rolling as it can become a finished product without delays.

Hot rolling begins with a large piece of metal which can include slabs, blooms, billets, and semi-finished casting products. When the material comes from a continuous casting operation, they are fed directly into the rolling mills at the correct temperature. Smaller companies generally begin their material at room temperature and then initiate the heating process. The larger pieces can be handled with oil or gas fired soaking pits. Smaller pieces of metal will use the induction heating method.

When the hot rolled metal cools, it will reconfigure making the finished product with a looser tolerance when compared to the cold rolled metal. This looser tolerance makes it easier to force the metal into a variety of different shapes. Hot rolling is mainly used to produce simple cross sections or sheet metal. Typical uses for this type of metal include:

1. Metal buildings

2. Railcar components

3. Water heaters

4. Agriculture equipment

5. Strappings

6. Stampings

7. Wheel rims

8. Truck frames and other such products

Cold Rolled Process

Temperatures are close to room temperature during the cold rolled process and increase the strength of the finished product by as much as 20 percent. This strength is a result of strain hardening and creates a gray finish that is smooth to the touch. The cold rolled finished product is restricted to a few limited shapes such as either flat, square, and round. If additional shapes are needed these shaping operations would be required:

1. Breakdown

2. Semi-finishing

3. Semi-roughing

4. Sizing

5. Roughing

6. Finishing

Cold rolled steel would be used best for these products:

1. Metal furniture

2. Filing cabinets

3. Tables

4. Exhaust pipes

5. Chairs

6. Home appliances

7. Water heaters

8. Shelving and other similar products

Know What You Need

Setting out to purchase high quality metal products depends on how you are planning to use the product. The end result you are looking for will determine the type of rolled steel you will need. You will need to know if it will require sizing or shaping and at what capacity they will be put to work.

Materials that are larger in size and will be put into distinct shapes will require the hot rolled process, smaller products needing to be tolerant and durable should have been created through cold rolling. If you are uncertain what your project will work best with; talk to a representative of your rolled steel supplier for suggestions or advice.

Understanding the difference between metals and how some types of steel are better suited for certain jobs, can save you money. Knowing the difference between the hot rolled and cold rolled steel will help you achieve better results and save you time. 

For more detailed information on structural steel fabrication and how it can meet the needs of your business in the United States, please contact us at Swanton Welding Company Inc. You can visit us online at SwantonWeld.com or reach us directly at 419.826.4816.