Hot rolled coil manufacturing process and related steel products

Cold rolled coil production is actually a continuation of the hot rolled coil manufacturing process. In the cold rolling process and related products, the hot-rolled sheet is rolled below the recrystallization temperature, and then the rolled steel is rolled at room temperature.

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In this production process, if the silicon content of the steel plate is high, its brittleness is large and the plastic change is small, so it must be heated to 200 degrees Celsius before cold rolling. Because there is no temperature and heat rise during cold plate production, there are no defects such as holes and iron oxides that are often observed in hot rolling, and the surface and finish quality are good.

In addition to the above points, due to the high production precision of the cold plate, the performance and organization of the product can meet some special requirements, such as electromagnetic performance, deep drawing performance, etc.

Cold plates are used in a wide range of applications, such as automobile manufacturing, electrical products, rolling equipment, aviation, precision instruments, and food preserves.

The easiest way to shape metal

Early metal formers found that hammering and forging were stronger than older casting methods. But even soft metals are difficult to hammer and forge by hand, so they wanted to make machines to help make the metal forming process easier. The design of the plant created after cold plate production is very simple. It is not known who invented the first rolling machine.

Production of cold plates from the 15th to the 17th century

In the mid-15th century, small machines with gold belts and other ornaments appeared for the production of cold plates of soft metal. However, as these technologies gain more visibility in the field, the demand for rolled metal products also increases. There is evidence of the presence of lead, tin rolls and cast iron rolls in the complete rolling mills used to make cold plates in the early 17th century.

At present, the rolling mills have not yet processed the large quantities of metal we see today. And if we measure its quality by today’s exacting standards, the quality required of these early products was poor.

However, it was not developed for applications that required higher quality materials at the time. Energy will also gain more attention as the technology develops further.

At the end of the 17th century, larger steel rollers could be cast and heavier machines could be made. Horses and water wheels moved the unit.

Cold plate production in the 18th and 20th centuries

In the 18th century, four-story mill production became popular. This was because engineers at the time found that smaller diameter rolls required less stress to reduce the thickness of the metal.

Therefore, a lighter frame can be used. In the late 18th century, with the advent of steam power, rolling mills for the production of cold plates were gradually improved. During the 19th and 20th centuries, these units increased in size and power with few changes from the original design.

Steam engines are capable of producing more than 10,000 horsepower. An example of such an engine is the 12,000 hp (8.9 MW) River Don engine, designed by Davy Brothers in 1905 for making armor plates.

However, more efficient electric motor technology slowly replaced steam power in the 20th century, making the production of cold plates easier.

Production steps of today’s cold plate

If you have a good understanding of the concept of the cold plate, you will also easily understand its production process. So far it has been said that the production method of cold plate is cold rolling. If we want to create plastic deformation by passing the material between two rollers that rotate in different directions, the process is today called rolling. In terms of rolling temperature, there are two processes: cold rolling and hot rolling. As the name suggests, a cold rolling process is used to produce cold plates.

Hot-rolled semi-finished products

As mentioned at the beginning of this article, the cold plate production process is a continuation of hot plate production. Based on this, semi-finished products such as sheets or ingots must first be hot-rolled. Hot rolling is carried out in a temperature range higher than the recrystallization temperature of the target metal.

If a carbon steel plate is hot rolled, the starting temperature of this process is 1200 degrees Celsius, and the final product temperature of this hot rolling is between 800 and 900 degrees Celsius. During the hot rolling process, plates with a thickness of approx. 250 mm at the end for strips with a thickness of 2 mm.

cold rolled

The cold rolling process is carried out at a minimum of room temperature and a maximum of 200 degrees Celsius. Production is carried out using sheet or strip produced in the previous process (hot rolling). The input material for cold rolling is steel plates, heated and pickled rolled coils from continuous hot rolling mills.

The process of making cold plates from hot strips usually consists of the following units or steps:


The belt produced in the hot rolling step has an oxide crust on the surface. To remove these scales, the belt is dipped in an acid bath, usually hydrochloric acid. The conveyor belt is then washed with hot water and dried through a hot air tunnel. Finally, after lubricating the bands, they wrap around again.

cold roll

In this stage of cold plate production, the plate is pickled and rolled in an inverted cold mill to reduce its thickness. In this machine, there is an uncoiler and a coiler on both sides of the roll stand.

To reduce the thickness and reach the desired value, the sheet is repeatedly passed between the rollers. After the cold rolling, in order to reduce the stress caused by twisting and trimming of the coil, the sheet is re-rolled into a coil and sent for heat treatment again.

Electrolytic washing

Electrolytic cleaning is used to remove impurities and surface grease, iron powder and solid non-ferrous metal particles formed during cold rolling of sheets. This process step may not be performed in some cold plate production cells.


Up to this stage, the produced cold plates have a non-uniform structure in terms of the distribution of alloying elements. In order to homogenize the metallographic structure of the rolled plate and achieve the expected mechanical properties, it must be subjected to a series of heat treatments such as annealing or annealing.

the skin pass rolling

After annealing, hardening and other heat treatment of the product, according to the requirements of most customers, reduce the corrugation on the surface of the sheet, make it smooth and produce appropriate hardness and roughness on it to improve the mechanical properties from the operation. Use shell rolling.

In this operation, four rolls are placed on one or two shelves. Often we also see a reduction in plate thickness during rolling shell operations.

Tension leveling

At this stage, the last stage of the production of cold-rolled sheets, the final operations are carried out to remove the surface waves and edges of the cold-rolled sheet and to flatten the surface of the cold-rolled sheet to the desired degree. Finally, to prevent the plate from rusting, it is lubricated. That is why cold plates are also called oil plates on the market.

Hot rolled coil and related products

We know that steel sheets and related products are produced by hot rolling and cold rolling, and many products have been originate from them.

The factory began to produce steel plates from the production of pig iron and continued until the production of steel plates as follows:

  • Processing of primary mined iron ore
  • Production of sponge iron
  • Ingot production
  • Conversion of billets to soft coils by hot rolling process
  • Production of soft coils by cold rolling
  • Additional operations for the production of steel and end coil products
  • The final process is carried out and the steel sheets as galvanized and colored are painted.

Processing of primary mined iron ore

In the first step, known as the most basic and the beginning of the steel plate production process, during special operations metal impurities are separated from the crushed iron ore in a process called palletization and roasting of said iron ore. it is ready for use.

Production of sponge iron

In the second step, the pellets produced during the reduction process react directly with elemental carbon to form pure iron.

Because at this stage the pellets lose oxygen and are in a porous, sponge-like state, hence the name sponge iron. This sponge iron is gradually used as raw material for steel production in other stages of steel sheet production.

Ingot production

In the third stage of steel sheet production, molten steel is filled into empty bulk bottles for further processing. The molten steel with a temperature close to 1650 degrees Celsius should enter the casting stage after finishing the operation.

Hot rolled coil and related products

After this step, the molten steel produced enters the casting machine and becomes a steel billet or ingot, and the molten crucible is placed on a casting tower that can hold two crucibles.

Finally, after other peripheral processes such as drumming and sorting, the molten material is discharged into the mold and cooled by the water flow around the mold along a semi-arc path to form a long strip with a rectangular cross-section, which is taken out by the casting machine and the steel ingot They form steel.

Conversion of billets to soft coils by hot rolling process

In the fourth step, the steel is subjected to a hot rolling process. At this stage of the steel sheet production process, the ingot is heated to a temperature of 1200 degrees Celsius in special furnaces until it becomes red and ductile. Pass the fried slabs between the rollers to reduce their thickness.

Finally, after cooling, it is removed from the machine as a hot coil. The sheet metal obtained in this step can be used directly and can be used in subsequent processes such as cold rolling or finish rolling.

Production of soft coils by cold rolling

In the fifth step, a cold rolling process is formed on the steel plate. In this process, the hot coil first goes through a pickling process until the surface of the plate is completely smooth and clean, which is why this product is also called pickling coil. After pickling, the desired roll will enter the cold rolling process.

During this process, the pickled, almost cold coils are passed through the rollers, making the thickness of the coils thinner than before under the pressure of the rollers.

The remaining product from this process is the original coil. This raw coil can be used directly and can go into the next process. During the rolling process, the green coil is ready for use after annealing, shell rolling and steel plate modification. Cold-rolled sheets are commonly used in the manufacture of household appliances, filters, bodywork and car interiors, and much more.

Coating of galvanized and colored steel sheets

In the sixth phase of steel plate production, also called the last phase, steel plate coating is carried out. Coated steel sheets are mostly colored, galvanized or tinned and are of the highest quality and most resistant to any rust and impact for special purposes.

For example, a plated tin plate has a surface covered with elemental tin, which covers the surface of the plate in a thin layer. Coated iron sheets are generally used in the manufacture of cans, food packaging and tin cans.

Hot rolled coil and related products

During the galvanizing process, the surface of the plate is covered with a thin layer of zinc, which is often used in the construction of tanks.

Normally, galvanized sheets can also be used as semi-finished products in processes that require color coating. But what does the color coating process mean? In the process, they used steel sheets covered with paint as the visible layer. This sheet is used to make tools for sheds, household appliances, etc.

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