Difference between Hot and Cold Rolled Steel

Rolling is a process of metal forming that uses a series of rollers to modify the shape, enhance the uniformity, and/or improve the mechanical properties of materials. rolled steel has two sub-categories: hot rolled steel and cold rolled steel. Both exhibit distinct characteristics that make them suitable for diverse applications. While zeroing in on a rolled steel material for a specific project, it is essential to be aware of the primary differences between these two types and how effective their performance is.  

Hot rolled steel

Hot Rolled steel is basically steel that has successfully undergone the process of rolling at a temperature that is above its recrystallisation temperature (up to or exceeding 1700° F). In comparison with unprocessed steel, the processed material demonstrates enhanced workability and formability, making it much easier to work within processing operations. 

The process of hot rolling begins with a large and rectangular slab of metal known as a billet. Initially, the billet is heated and subsequently compressed into a large roll. While still hot, it eventually passes through a series of rotating rollers to attain the desired dimensions. When it comes to operations of sheet metal production, the rolled steel is further wound into coiled rollers and then left to cool. Regarding product operations that involve other forms, the processed material is efficiently cut into specified units and then packaged.

Benefits Of Hot Rolled steel

• Lower Costs

• Enhanced Workability

• Minimal to No Internal Stress

Applications of Hot Rolled steel

• Construction Materials (such as I-beams)

• Railroad Equipment (tracks and components of railcars)

• Automobile parts (such as wheel rims and frames)

• Agricultural Equipment

Cold Rolled Steel

Cold Rolled steel is basically hot rolled steel that has undergone further processing to enhance its mechanical and dimensional properties. During the process of cold rolling, hot rolled steel that has been cooled passes through an additional series of rollers at room temperature. Because the material is no longer malleable and hot, a higher amount of pressure is needed to successfully compress it into the desired shape. This process reduces the ductility of the cold rolled steel making it tough for framing operations. So, to recover the ductility, this steel undergoes the annealing process. The is a heat treatment the relieves the stress on the metal during the cold rolling procedure and increase ductility. 

While this specific process is much more labour intensive and costly in comparison with the hot rolling process, it can ultimately achieve tighter dimensional tolerances and enhanced surface qualities.

When it comes to Hot Rolled vs Cold Rolled steel, the benefits of the latter include:

• Superior Strength

• Enhanced Surface Finishes

• Greater Precision

Applications Of Cold Rolled steel

• Mechanical Components

• Metal Furniture

• Rods, Strips, Sheets, and Bars

• Home Appliances

• Aerospace structures

Key differences between Hot Rolled steel And Cold Rolled steel

As indicated earlier, the primary difference between Hot Rolled and Cold Rolled steel is the temperature at which they need to be processed. Hot Rolled steel is rolled above the recrystallisation temperature of the material, whereas cold rolled steel is rolled below the recrystallisation temperature of the material. Besides this quality, there are some other distinctions between the two materials, which are mentioned below:

• Surface Quality

Hot rolled steel has the tendency to have rough surfaces and edges, which need decarburisation or other specific treatments to eventually prepare it for use in production operations. In contrast, Cold Rolled steel tends to have a smooth and shiny surface that permits it to be used as-is in diverse product operations.

• Material Hardness

The process of cold rolling produces steel with much-enhanced hardness and strength in comparison with steel produced by the process of hot rolling.

• Internal Stress

The enhanced hardness and material strength produced by the process of cold rolling come with greater internal stresses. These stresses need to be relieved prior to processing of the material, failing which the final product or part may experience warping.

These two primary types of steel must not be confused with the grades or technical specifications that are used for the classification of steel based on physical characteristics and composition. Steel can be hot or cold rolled irrespective of its grade or metallurgical specifications.

The Final Word:

While considering steel options for a specific project, it is crucial to remember that some materials will work in a much better way in comparison with others for certain purposes. Knowing which type of steel offers the most ideal properties for a given application can successfully prevent overspending on raw materials and save precious time in the long run.