Advantages and Disadvantages of Hot Rolled Steel and Cold Rolled Steel

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esidual stress

during processing, this residual stress has a great influence on stability. Both hot rolling and cold rolling are processes of forming steel or steel sheets, which have a great influence on the microstructure and properties of steel. The rolling of steel is mainly hot rolling, and the cold rolling is only used for producing small steel and thin steel.

In general, hot rolling ( hot rolled seamless pipe ) has better mechanical properties than cold rolling. The hot rolled steel has improved tensile strength, yield strength, ductility and toughness. In addition, it is important that heat treatment eliminates residual stresses. While cold rolling refers to the processing of steel sheets or strips into various types of steel by cold drawing, cold bending, cold drawing, etc. At normal temperature, which may result from uneven deformation of the steel andduring processing, this residual stress has a great influence on stability. Both hot rolling and cold rolling are processes of forming steel or steel sheets, which have a great influence on the microstructure and properties of steel. The rolling of steel is mainly hot rolling, and the cold rolling is only used for producing small steel and thin steel.

Hot rolling

Advantages:
The cast structure of the ingot can be destroyed, the grain of the steel can be refined, and the defects of the microstructure can be eliminated, so that the steel structure is compacted and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Disadvantages:
1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (sandwich) occurs. The delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible to cause interlayer tearing when the weld is shrunk. The local strain induced by weld shrinkage often reaches several times the yield point strain and is much larger than the strain caused by the load.
2, Residual stress caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. The hot-rolled steel of various sections has such residual stress. The larger the section size of the general steel, the larger the residual stress. Although the residual stress is self-phase-balanced, it still has some influence on the performance of steel members under external force. Such as deformation, stability, fatigue and other aspects may have adverse effects.

Advantages:The cast structure of the ingot can be destroyed, the grain of the steel can be refined, and the defects of the microstructure can be eliminated, so that the steel structure is compacted and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.Disadvantages:1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (sandwich) occurs. The delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible to cause interlayer tearing when the weld is shrunk. The local strain induced by weld shrinkage often reaches several times the yield point strain and is much larger than the strain caused by the load.2, Residual stress caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. The hot-rolled steel of various sections has such residual stress. The larger the section size of the general steel, the larger the residual stress. Although the residual stress is self-phase-balanced, it still has some influence on the performance of steel members under external force. Such as deformation, stability, fatigue and other aspects may have adverse effects.

Cold rolling

Advantages:
The molding speed is fast, the output is high, and the coating is not damaged, and various cross-section forms can be formed to meet the requirements of the use conditions;
Cold rolling can cause a large plastic deformation of the steel, thereby increasing the yield point of the steel.
Disadvantages:
1. Although there is no hot plastic compression during the forming process, residual stress still exists in the section, which inevitably affects the overall and local buckling characteristics of the steel.
2. The cold-rolled steel profile is generally an open section, so that the free torsional stiffness of the section is low. It is easy to twist when being bent, and it is prone to bending and torsion buckling when pressed, and the torsion resistance is poor. + Third, the wall thickness of the cold-rolled steel is small, and there is no thickening at the corners where the plates are joined, and the ability to withstand localized concentrated loads is weak.

The main differences between hot and cold rolling are:
1. Cold-rolled steel allows partial buckling of the section, so that the bearing capacity of the bar after buckling can be fully utilized; and the hot-rolled steel does not allow local buckling of the section.

Advantages:The molding speed is fast, the output is high, and the coating is not damaged, and various cross-section forms can be formed to meet the requirements of the use conditions;Cold rolling can cause a large plastic deformation of the steel, thereby increasing the yield point of the steel.Disadvantages:1. Although there is no hot plastic compression during the forming process, residual stress still exists in the section, which inevitably affects the overall and local buckling characteristics of the steel.2. The cold-rolled steel profile is generally an open section, so that the free torsional stiffness of the section is low. It is easy to twist when being bent, and it is prone to bending and torsion buckling when pressed, and the torsion resistance is poor. + Third, the wall thickness of the cold-rolled steel is small, and there is no thickening at the corners where the plates are joined, and the ability to withstand localized concentrated loads is weak.The main differences between hot and cold rolling are:1. Cold-rolled steel allows partial buckling of the section, so that the bearing capacity of the bar after buckling can be fully utilized; and the hot-rolled steel does not allow local buckling of the section.

2. The causes of residual stresses in hot-rolled and cold-rolled steels are different, so the distribution on the cross-section is also very different. The residual stress distribution on the section of the cold-formed thin-walled steel is curved, while the residual stress distribution on the section of the hot-striped steel or welded steel is a film type.

Tips: ASTM A53 Gr.B is the grade in ERW high frequency welded pipe, divided into A and B grades. ASTM is only a set of specifications. ASTM steel pipe A53 A corresponds to the Chinese standard GB raw material is 10# steel, and A53 B corresponds to the Chinese standard GB raw material 20#.
For example: ASTM (standard) A53 (grade) gr is grade (abbreviation of grade) b (grade B)

Rolling is a key process in metalworking, one which can lead to the improved strength and grain orientation needed to accomplish different fabrication techniques and applications. The basic metal rolling procedure involves passing the metal through a pair of heavy rolls that give the metal the desired shape and thickness, but from there the process can be adapted based upon the metal&#;s application. There are two main types of steel rolling; hot rolling and cold rolling. As implied by the name, difference between the two depends on the rolled metal&#;s temperature at the time of rolling. Hot rolling works on metals heated beyond their recrystallization temperature while cold rolling works on metals whose temperature is below its recrystallization temperatures. Both of these methods lead to decidedly different outcomes, each of which will be better suited to a certain type of application.

Hot Rolled Steel

Steel&#;s recrystallization temperature stands at degrees Fahrenheit. As such, during the hot rolling process the temperature must exceed that level. It&#;s much easier to shape and form steel at such temperatures, hence most complex and bulky designs form better under high temperatures. Hot rolling steel has its advantages and disadvantages.

Some of the advantages of this process include:

• High rate of production.

• Suitable for large reduction.

• Production of a wide range of shapes like blooms, billets, sheets, slabs, tubes, bars, structural section, and others.

Some of the main disadvantages are:

• High cost of equipment.

• Poor finish and poor dimensional accuracy.

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• Suitable for large sections&#; production.

Cold Rolled Steel

 

Cold rolling is performed at room temperature, meaning that the steel is below its recrystallization temperature. Since the steel won&#;t be so malleable this technique might require stronger mills but will definitely be more accurate as the steel doesn&#;t will not change its shape and orientation upon cooling. Examples of cold rolled steel products include; bars, strips, rods and sheets. These products are normally smaller than hot-rolled ones.

Some advantages of this process include:

• High rate of production.

• Good finish and good dimensional accuracy.

• Suitable for among others, the production of foils, plates and sheets.

Disadvantages include:

• Deformation limited to small reductions

• It is limited to only a few shapes and their variations such like square, round, and flat.

• High cost of equipment

Hot rolled steel is usually cheaper to produce than cold rolled steel. This is mainly because the hot rolled steel is more malleable, hence you don&#;t need heavier rollers or more production cycles to form a product. However, because its shape can shift after the process is over hot rolled steel can lead to additional reshaping expenditures down the line.

Rollers in Rolling Mills

Rolls come in various sizes and geometries. In the course of their application they are made to endure strong forces, wear, thermal stresses, and bending moments along with other such conditions. The material used to make the roll is an important factor as far as their strength, wear resistance, and rigidity is concerned. Ductile Iron, cast iron, forged steel, and cast steel are among the most common.

Metal Rolling Defects

There is the possibility of a number of defects with metal rolling. They include;

• Surface defects arising from scale, dirt, rust, and other impurities in the material.

• Internal defects due to improper distribution of the material in final product

• Wavy edges, center cracks, and edge cracks

A good fabricator should leave you at liberty of choosing between hot rolling and cold rolling. Moreover, the steel fabrication shop should have the right tools and skill needed to give you the best quality product for each procedure. Choosing a company with the right equipment, personnel, and experience is essential. At Swanton Welding, we have the top quality rolling and forming equipment necessary to guarantee precision and high accuracy. We take pride in our ability to meet high-end contracts with finesse. Our highly skilled team and fully equipped production floor will be all you need to get the job done in record time, so contact us today.

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