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hot rolled coil steel
There are some key differences between the hot plate and cold rolled coil:
1 production process
Hot-rolled sheets are produced in a metal melting process, the product of which is extracted in the form of coils. It is formed at temperatures above 1000 degrees Celsius and is used in large steel products.
The cold rolled sheet is one of the metal processes that is carried out using rolls at near normal (room temperature) temperatures. It reduces the thickness of steel sheets and steel plates. The hardness of cold-rolled steel is higher than that of hot-rolled steel.
2- The price of the hot plate and cold plate
Cold plates cost twice as much as hot plates. To produce a cold plate, there is a salting and oiling step to prepare the plate for cold rolling, and these factors themselves increase the cost of a cold plate.
In addition, polishing, drawing, and grinding are steps that increase the price of cold-rolled sheets.
3D for cold and hot plates
Black sheets are produced and sold mainly in fabric sizes. The thickness of the board is between 15 and 100 mm. Common sizes and factory fabrics for boards are: (1000x2000)-(1250x2500)-(1000x6000)-(1500x6000)-(2000x6000).
Oil plates are cold-rolled plates in thicknesses of 1000, 1250, 1500, and 2000 mm.
4- Use of hot and cold plates
Hot-rolled sheets are used to manufacture larger products. Hot-rolled sheets are made into coils and used to produce cold-rolled sheets. The hot-rolled sheet is more flexible than a cold-rolled sheet due to its lower carbon content.
5- Hot and cold plate alloys
White hot-rolled sheets use ST37 alloy. Cold-rolled or oil-rolled plates are divided into three categories according to their alloys:
- ST12 alloy standard plate
- ST13 alloy half tension plate
- ST14 alloy super tensile plate
Hot rolling process
Hot rolling refers to the process of coil formation above the recrystallization temperature of the metal. Recrystallization is a phenomenon that occurs in the microstructure of the steel and changes its morphology.
In general, the microstructure of the steel begins to change when it is subjected to severe deformation after exposure to high temperatures.
Above the recrystallization temperature, new seeds germinate and grow. Improving the ductility of steel is one of the most important results of recrystallization.
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The recrystallization temperature of steel depends on its chemical composition and is determined by the phase diagram of iron and carbon.
warm up
In general, the recrystallization temperature of ordinary carbon steel is between 400 and 700 degrees Celsius.
However, raising the temperature of the workpiece beyond the above range makes the manufacture of the hot plate easier. Of course, the temperature can be increased to such an extent that the oxidation of the steel surface does not increase.
Oxidation therefore has an inhibitory effect, so that the hot rolling process is usually carried out at temperatures around 1000 degrees Celsius.
rolling phase
In order to achieve a temperature suitable for the production of hot plates, a preheating step is required. The main material for the manufacture of different types of heating plates is steel pieces.
Sheets with a predetermined chemical composition are transferred to the sheet rolling line. The plates are produced by continuous casting and are very thick.
Plate preheating is carried out in furnaces, usually with gaseous fuel. After the plate has reached the desired temperature, the furnace valve is opened and the plate is placed on the roll line. Typically there are 3 sets of roller shutters in front of the slab.
Re-rolling: The first step in the re-rolling phase, where the main deformation of the plate occurs. The thickness of the plate decreases and the length increases.
Intermediate rolling: In the second stage, the intermediate rolling, the thickness of the hot plate approaches the final thickness.
Light rolling: In the final stage of light rolling, the thickness of the plate is adjusted and the dimensional accuracy is high.
Since hot rolling is carried out at high temperature, the final surface of the plate has an oxide layer. The main difference between a hot plate and a cold plate is that the dark oxide layer darkens the surface of the hot plate.
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There are several ways to remove the oxide layer. Methods such as:
- water pressure
- Pickling
- stoning
- sandblasting
After reaching the desired thickness, the heating plate is usually wound into a coil. Of course, this problem depends on the thickness of the sheet, for high thickness sheets spiral coils are not possible, they arrive in the final state in the form of cut sheets.
At this stage the sheet has lost a lot of temperature but has not yet cooled down completely.
To allow the hotplates to cool down completely, they are usually brought to room temperature. Due to this cooling operation, known as normalization, the chemical structure and granulation become uniform.
Cold rolling process
The cold rolling process refers to a form of rolling performed at low temperature, the purpose of which is to reduce the thickness of the hot plate and transform it into a cold plate. At this stage another difference is formed between hot and cold plates.
Typically, hot plate types with a thickness of 1.5 to 5 mm are used, and by performing this process, their thickness is in the range of 0.12 to 2.5 mm.
Thinning in this area is impossible during hot rolling and the dimensional accuracy is low. In general, the cold rolling process has the following results on the steel plate:
- Provides low thickness with appropriate precision
- Improve the surface quality of the plate
- Changes in physical and mechanical properties
- Preparation of cold plate surface coating
hot rolled coil Malaysia and other countries
Countries like Malaysia are experts in producing and manufacturing hot rolled coil in comparison with other countries. Both these hot and cold rolled coils are manufactured in many different ways.
The difference between hot and cold plates is also related to the raw materials. Steel ingots are the raw material for the production of heating plates.
And the hot plate type is the input to the cold plate line. As previously mentioned, the surface of the heating plate contains an oxide layer.
In order to carry out a cold rolling process with suitable surface quality, these layers must first be removed by pickling before rolling.
In addition to the poor surface quality of the plate at the end of the production process, the mechanical properties of the plate can also be affected if there are oxides on the surface.
Pickling is usually done with sulfuric or hydrochloric acid. Pickling takes place in a private bath and depends on acid concentration, temperature and treatment time.
cold rolled
Unlike hot rolling, the process is carried out at a temperature level below the recrystallization temperature. In fact, no preheating is required to make this product. This question is the difference between a hot plate and a cold plate.
The high friction at this stage leads to a temperature rise which must be controlled so that it does not exceed the recrystallization temperature.
At temperatures below recrystallization, the deformation of the steel can make it difficult to machine. This means that the steel grains are very fine and its strength is 20% higher than that of the heating plates.
Therefore, cold plates have better mechanical properties than hot plates. In cold rolling, lubricants or oil lubricants are used to reduce the temperature at which friction occurs. Therefore, the name of oiled paper is very common in this type of sheet.
annealing
Due to the extreme cold working of the previous step, the strength of the cold plate is significantly reduced, thereby reducing the ductility and ductility of the plate.
To improve the ductility of the cold plate, they reduced its strength using an annealing operation. Annealing is performed continuously and discontinuously on cold plate production lines. It is generally heated to a certain temperature and cooled slowly, softening the material.
skin during annealing
To improve the surface properties of the cold plate, a shell rolling or tempering rolling process is performed. In the process, the surface roughness is also improved, and the cold plate becomes opaque.
Comparison of hot and cold plates
There are many varieties of steel plates produced by different factories. If you are looking for the most suitable sheet, you must therefore be aware of the difference between hot and cold sheets. For example, in cases where high-strength steel is required, you should use a hot plate.
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If the appearance and aesthetics of the final product are important, you should choose cold plates, such as colored a plate, galvanized a plate, or roof plate. Each of these cold plates comes in a different type. For example, each grade of the oiled board is used for a specific application.
Sometimes when comparing hot and cold plates, price is more attractive to customers than features, pros and cons.
For those responsible for the raw material supply for the project, it is necessary and necessary to provide online daily steel plate price lists as well as comparisons between different brands.
Thickness has a great influence on the flexibility of the steel sheet. For this reason, hot plates are usually cut into slabs, while cold plates are produced in rolls. At the time of consumption, cutting and bending of cold plates is easier than other groups.
What are the benefits of using a cold plate?
Cold plates have better surface properties than hot plates and are often used for more precise technical applications or where aesthetics are important. But since more processes are made, they are more expensive.
In terms of physical properties, cold plates are generally harder and stronger than hot plates.
Since the cold plate is formed at a lower temperature, the steel's hardness, fracture resistance, tensile strength and deformation resistance increase. However, additional processes carried out on the plate can cause internal stresses in the material.
If the steel is not reduced in internal stresses before cutting, grinding or welding, it can cause warping of the plate.
Application of cold plate:
- aerospace structure
- household appliances
- metal furniture
- belt type
- Metal rods and tubes
- some car parts (mudguards, fuel tanks, axles and seats)
- Tank housing, tank top, tank bottom, etc.
As one of the most widely used steels in the country, hot plates are produced by hot rolling. The plates are supplied by different factories in different sizes and thicknesses.
hot rolled coil images
Each type of hot plate has different properties and uses depending on the type of construction and the alloys used in it.
Before buying and using a hot plate, it is necessary to be familiar with its features and have a sufficient understanding of its specifications, different types, uses, advantages and disadvantages.
How are hot-rolled plates produced?
The manufacturing process for the heating plate is as follows:
Step 1: Preheating oven (hot rolling)
At this stage, the clock or plate goes into a preheating furnace with a temperature of 1300 degrees Celsius. Through this work, all structural defects in the Takthal caused by casting operations were repaired.
The second stage: rough rolling (rough rolling)
After preheating the furnace, the billet enters the rough rolling rack and its thick oxide layer is separated by hydraulic pressure, that is, the billet is descaled.
The sheet was then pressed with a press and passed through a roller to reduce its thickness by 75%. This reduction in thickness results in an increase in width, which is controlled by vertical rollers.
Step 3: Coil box
At this stage, the thin sheet is wound by itself after entering the coil box. After a while, the sheet is removed from the spool box, ready for final rolling again during the deoxidation process.
The coil box is located between the first rolling and the final rolling, the purpose is to break the shell, make the temperature of the plate uniform, increase the production capacity and increase the production speed.
Step 4: Final rolling (rolling shelves)
In the last rolling step, the steel sheet passes through the rolling stand at a speed of 10-20 meters per second. It is worth mentioning that the mechanical properties of the sheet are improved at this stage.
Step 5: Cooling operation (cooling step)
After leaving the rolling stand, the steel sheet enters a cooling station to reduce its temperature.
Step 6: Tighten
Finally, the sheet enters the coiling stage, after twisting and packaging, it is ready for sale on the market.
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