Difference Between Hot Rolled and Cold Rolled Steel

Main Difference – Hot Rolled vs Cold Rolled Steel

Steel is a metal alloy made from iron along with other elements. Steel is widely used all over the world due to its high strength and low cost when compared to other types of metals and metal alloys. Steel can be found in different forms and names according to the elements included in it according to the method of production, application, etc. Hot rolled steel and cold rolled steel are two types of steel that are named according to the method of production. Rolling is a type of processing method used in mills where steel is produced. Rolling is done to reduce the thickness of steel and to make this thickness uniform. The key difference between hot rolled and cold rolled steel is that hot rolled steel is produced at high temperatures whereas cold rolled steel is produced at room temperature.

Key Areas Covered

1. What is Hot Rolled Steel
     – Definition, Production, and Benefits
2. What is Cold Rolled Steel
     – Definition, Production, and Benefits
3. What is the Difference Between Hot Rolled and Cold Rolled Steel
     – Comparison of Key Differences

Key Terms: Cold Rolled Steel, Hot Rolled Steel, Metal Alloy, Mills, Rolling, Steel

What is Hot Rolled Steel

Hot rolled steel is a type of steel that is made by rolling steel at very high temperatures. The production of this steel involves passing the steel through rollers at temperatures above 1700^oF. This temperature is the recrystallization temperature of most steels. Recrystallization of steel is the replacement of deformed steel grains with defects free grains.

At temperatures higher than the recrystallization temperature of steel, the steel can be made easily; the products made from this steel is also easy to work with. Hot rolled steel is typically cheap. This is because hot rolled steel requires less processing and it is manufactured without any delays in the process. But when the steel cools down, it shrinks slightly. Then the size of the final product cannot be easily controlled. Therefore, hot rolled steel is used where slight differences of shape and size are not that much considered.

Figure 1: Production of Hot Rolled Steel

In the production process of hot rolled steel, the starting material is a large metal cube called a billet. This billet is first heated and sent through a roller to obtain a large steel roll. Then, this large steel roll is passed through several rollers while keeping its temperature above the recrystallization temperature. Here, different forms of hot rolled steel can be also made by slightly changing the process. For example, in order to obtain the steel as white-hot strands, steel is pushed through the rollers at a high speed.

What is Cold Rolled Steel

Cold rolled steel is a type of steel that is made by rolling steel at low temperatures such as the room temperature. The production of cold rolled steel is done at temperatures below the recrystallization temperature of steel.

Most of the times, cold rolled steel is made from the further processing of hot rolled steel. Here, the steel is further processed in cold reduction mills. When hot rolled steel is cooled to the room temperature, these steel rolls are compressed between rollers.

Cold rolling processing forms steel with more accurate sizes and shapes. In the production of steel bars, it is drawn instead of passing steel through rollers and may include other processing steps such as turning, grinding or polishing.

Figure 2: Cold Rolled Carbon Containing Steel

Therefore, cold rolled steel gives a perfectly finished surface with correct dimensions. But cold rolled steel products are more costly compared to other steel products due to complicated processing methods. However, cold rolled steel products are more preferred due to several reasons. For example, bars made from this process are square and have well-defined corners and edges, and the products are smooth and feel oily when touched.

Difference Between Hot Rolled and Cold Rolled Steel         

Definition

Hot Rolled Steel: Hot rolled steel is a type of steel that is made by rolling steel at very high temperatures.

Cold Rolled Steel: Cold rolled steel is a type of steel that is made by rolling steel at low temperatures such as room temperature.

Temperature

Hot Rolled Steel: Hot rolled steel is produced at temperatures above 1700^oF.

Cold Rolled Steel: Cold rolled steel is produced at temperatures such as room temperature or below.

Cost

Hot Rolled Steel: Hot rolled steel is comparatively cheap.

Cold Rolled Steel: Cold rolled steel is costly when compared to hot rolled steel.

Benefits

Hot Rolled Steel: Hot rolled steel is used where exact dimensions of the final product are not necessary.

Cold Rolled Steel: Cold rolled steel gives the exact dimensions and well-defined edges.

Drawbacks

Hot Rolled Steel: Hot rolled steel gives products with slightly different sizes than the required dimensions.

Cold Rolled Steel: Production cost is high due to advanced processing methods.

Conclusion           

Hot rolled steel and cold rolled steel have different applications according to their properties. Both of them are types of steel but are different from each other when the production process is considered. The key difference between hot rolled and cold rolled steel can be given as hot rolled steel is produced at high temperatures whereas cold rolled steel is produced at room temperature. 

References:

1. Done, Brad. “Hot Rolled vs Cold Rolled Steel.” Bollards by Reliance Foundry, Reliance Foundry Co. Ltd, 26 July 2017, Available here. Accessed 25 Sept. 2017.
2. “Rolling (Metalworking).” Wikipedia, Wikimedia Foundation, 11 Sept. 2017, Available here. Accessed 25 Sept. 2017.

Image Courtesy:

1. “1568604” (Public Domain) via Pixabay
2. “Carbon Steel Cold Rolled Sheet Coil” By Jatinsanghvi – Own work (CC BY-SA 3.0) via Commons Wikimedia