What is the difference between hot-rolled and cold-rolled steel sheets?

As you know, steel sheets are one of the most widely used raw materials in various industries. From construction and bridge building to the manufacture of all kinds of household appliances, car bodies, ships, industrial machinery, and all kinds of civil and industrial projects, the mark of these sheets can be seen in all corners of modern and contemporary life. However, among the vast array of steel products, two types of cold and hot rolled sheets hold a special place and are widely used in various industries.

In this latest article from the SAFA website, we intend to provide a comprehensive and scientific review of cold and hot rolled sheets. In this way, you will be able to choose the right one for your projects by fully understanding the differences, advantages, and applications of each.

Full Introduction to Cold Rolled Sheet

Cold rolled sheet, also known as Cold Sheet, is one of the most important and widely used types of steel sheet that is re-rolled at a temperature lower than the recrystallization temperature of steel after going through hot rolling stages. This process, known as cold rolling, increases the strength and hardness of the sheet and gives it a smooth and uniform surface. The low temperature in the cold rolling process and the production and manufacturing method of the sheets under special pressure are the main characteristics of cold rolled sheet production. These types of sheets have a smooth and polished surface and have excellent resistance, good cutting properties, and high paintability.

The fact that it is said that cold rolling is done at a low temperature actually means that the process temperature is around 300 to 400 degrees Celsius, and unlike the hot rolling process, which will be explained later, the shaping of the ingots and their conversion into sheets is done at a lower temperature. As a result of not using high heat, the manufacturing method and forming of cold rolled sheets are more complex and difficult, but the result is a smoother sheet with higher strength and resistance.

Advantages of Cold Rolled Sheet

If we want to mention the advantages of sheet production using the cold rolling method, we should refer to the most important features and capabilities that this sheet has, which are as follows:

• Good paintability and color variety of cold rolled sheets
• High variety in offering sheets with different and completely custom sizes
• Strength, resistance, and high tolerance of cold rolled sheets to shocks and stresses
• Uniform and smooth surface of cold rolled sheets
• High cutting and forming ability
• A more beautiful appearance and more delicacy and ideal for use in the construction of practical equipment

Applications of Cold Rolled Sheet

Today, cold rolled sheets have many applications in various manufacturing and construction industries and all kinds of civil and industrial projects. The main applications of cold rolled sheets include:

• Use in the construction of many industrial structures such as various steel halls, garages, and warehouses
• Manufacture of various metal panels and commonly used building parts
• Use and application of cold rolled sheets for the manufacture of household appliances such as refrigerators, freezers, washing machines, dishwashers, etc.
• Use of galvanized and painted cold rolled sheets for use in conditions that require rust resistance, such as roofs of halls and warehouses, etc.

Stages of Cold Rolled Sheet Production

Depending on the type of application, the type of customer orders, and other factors and parameters, the cold rolled sheet production process usually includes the following steps:

• Preparation:  In this step, hot rolled sheets with high thickness are cut to the desired thickness for cold rolling.
• Pickling: To remove any impurities and dirt from the surface of the sheet, pickling is used.
• Cold rolling: The sheets are rolled between cold rollers and their thickness is gradually reduced.
• Annealing: In order to de-stress and increase the ductility of the sheet, it is placed at a high temperature.
• Oiling: To protect the sheet from corrosion and rust, its surface is covered with a thin layer of oil.
• Packaging: Cold rolled sheets are packaged in appropriate packaging for transportation after inspection and quality control.

Full Introduction to Hot Rolled Sheet

Hot rolled sheet, also known as black sheet or Hot Sheet, is another of the most famous and widely used steel sheets that is produced by a process called hot rolling. In fact, hot rolled sheet is a type of steel sheet that is rolled directly from hot-heated steel ingots at high temperatures (above the recrystallization temperature). This method has many differences with the method of sheet production using the cold rolling process. The most important difference, as can be found from the name of the process, is in the temperature of the different stages of sheet production.

In the hot rolled sheet production process, these sheets are passed through ovens with very high temperatures and are produced with a lot of heat. The production process of this type of sheet is such that the steel ingots enter the hot rolling production line and with an increase in temperature up to 1100 degrees Celsius, these ingots become significantly soft and flexible; then they pass through various rollers to reach the desired thickness. This process allows the hot rolled sheet to have high flexibility and ductility.

It should be noted that hot rolled sheets, in the hot rolling production process, due to the sudden heating and cooling of the ingots, which is one of the most basic operations in the hot rolling process, have a matte appearance and a rough texture. For this reason, hot rolled sheets are also known as "black sheets".

Advantages of Hot Rolled Sheet

If we want to mention the advantages of sheet production using the hot rolling method, we should refer to the most important features and capabilities that this sheet has, which are as follows:

• Hot rolled sheet has more ductility and flexibility and is easier to work with in the next stages of processing.

• Hot rolled sheet requires less processing and therefore has a lower price.

• For uses that do not require special finishing, it is very efficient and cost-effective.

• Hot rolled sheet has more ease in the welding process.

Applications of Hot Rolled Sheet

Today, hot rolled sheets have many applications in various manufacturing and construction industries and all kinds of different projects. The main applications of hot rolled sheets include:

• For the construction of various tanks and tankers, the manufacture of the body of machinery and special parts of cars and ships**
• For the construction of other steel sections, such as various types of building and industrial profiles**
• Manufacture of thick pipes for transporting oil and gas, water, sewage, etc.**
• Body of steam boilers and heat exchangers**

Stages of Hot Rolled Sheet Production

1. Melting: First, the extracted iron ore is melted in blast furnaces and converted into molten steel.

2. Casting: In the next step, the molten steel is poured into ingot molds and after they have cooled, they are turned into steel ingots.

3. Hot rolling: In the third step, the prepared steel ingots from the previous step process are heated in the furnace and slowly heated. Then they are placed between the strips of hot rolling rollers. This process, which is also known as the sizing process, continues until the final rolling and the hot rolled sheets reach the desired thickness and dimensions.

4. Cutting: After the completion of these steps, the hot rolled sheets are cut to the desired thickness and dimensions.

5. Packaging: Finally, the hot rolled sheets, after various inspections and approval by the quality control team, are packaged in appropriate packaging for transportation.

Comparison Table of Hot Rolled Sheet and Cold Rolled Sheet

SAFA, the Best Supplier of Steel Products

SAFA Steel Products Manufacturing Company, by offering a variety of steel products in different thicknesses and dimensions, can meet all your needs and requirements. SAFA, with its high-quality and extremely durable products, makes the dream of realizing every one of your industrial and construction projects come true. To receive free consultation and more information about our products, you can contact the experienced experts of SAFA Steel Industries.