Hot rolling and cold rolling are both processes for forming steel sections or steel plates. They have a great impact on the structure and properties of steel. The rolling of steel is mainly hot rolling, while cold rolling is only used to produce small section steels and thin plates. 1. Hot rolling Advantages: It can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate defects in the microstructure, thereby making the steel structure dense and improving the mechanical properties. 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 pouring can also be welded under the action of high temperature and pressure. Disadvantages: 1. After hot rolling, the non-metallic inclusions (mainly sulfides, oxides, and silicates) inside the steel are pressed into thin sheets, resulting in delamination (interlayer). Delamination greatly deteriorates the tensile properties of the steel along the thickness direction and may cause interlaminar tearing as the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain caused by load; 2. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress in the absence of external force. Hot-rolled steel sections of various sections have such residual stress. Generally, the larger the cross-section size of the section steel, the greater the residual stress. Although residual stress is self-balanced, it still has a certain impact on the performance of steel components under the action of external forces. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc. 2. Cold rolling It refers to processing steel plates or steel strips into various types of steel through cold drawing, cold bending, cold drawing and other cold processing at normal temperature. Advantages: fast forming speed, high output, and does not damage the coating. It can be made into a variety of cross-sectional forms to adapt to the needs of use conditions; cold rolling can cause large plastic deformation of steel, thereby improving the yield of the steel. point. Disadvantages: 1. Although there is no hot plastic compression during the forming process, there are still residual stresses in the section, which will inevitably affect the overall and local buckling characteristics of the steel; 2. The cold-rolled steel section is generally an open section, which makes the section free Torsional stiffness is low. It is prone to torsion when bent and torsional buckling when pressed, and its torsional resistance is poor; 3. The wall thickness of cold-rolled steel is small, and there is no thickening at the corners where the plates are connected, so it can withstand localized The ability to concentrate loads is weak. Hot rolling and cold rolling are both processes for forming steel sections or steel plates. They have a great impact on the structure and properties of steel. The rolling of steel is mainly hot rolling, while cold rolling is only used to produce small section steels and thin plates. The advantage of hot rolling is that it can destroy the casting structure of the steel ingot, refine the grains of the steel, and eliminate defects in the microstructure, thereby making the steel structure dense and improving the mechanical properties. 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 pouring can also be welded under the action of high temperature and pressure. The first disadvantage is that after hot rolling, the non-metallic inclusions (mainly sulfides, oxides, and silicates) inside the steel are pressed into thin sheets, resulting in delamination (interlayering). Delamination greatly deteriorates the tensile properties of the steel along the thickness direction and may cause interlaminar tearing as the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain caused by load. The second is the residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress in the absence of external force. Hot-rolled steel sections of various sections have such residual stress. Generally, the larger the cross-section size of the section steel, the greater the residual stress. Although residual stress is self-balanced, it still has a certain impact on the performance of steel components under the action of external forces. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc. Cold rolling refers to processing steel plates or steel strips into various types of steel through cold drawing, cold bending, cold drawing and other cold processing at normal temperature. The advantages are fast forming speed, high output, and no damage to the coating. It can be made into a variety of cross-section forms to meet the needs of use conditions; cold rolling can cause large plastic deformation of steel, thereby improving the yield of the steel. point. The first disadvantage is that although there is no hot plastic compression during the forming process, there are still residual stresses in the section, which will inevitably affect the overall and local buckling characteristics of the steel. Second, the cold-rolled steel section generally has an open section, which results in a low free torsional stiffness of the section. It is prone to torsion when subjected to bending and torsional buckling when subjected to pressure, and its torsional resistance is poor. Third, the wall thickness of cold-rolled formed steel is small, and there is no thickening at the corners where the plates are connected, so the ability to withstand localized concentrated loads is weak. The main differences between hot rolling and cold rolling are: 1. Cold-rolled shaped steel allows local buckling of the section, so that the bearing capacity of the rod after buckling can be fully utilized; while hot-rolled shaped steel does not allow local buckling of the section. 2. The causes of residual stress in hot-rolled steel and cold-rolled steel are different, so the distribution on the cross-section is also very different. The residual stress distribution on the cold-formed thin-walled steel section is curved, while the residual stress distribution on the hot-rolled steel or welded steel section is film-type. 3. The free torsional stiffness of hot-rolled steel is higher than that of cold-rolled steel, so the torsional performance of hot-rolled steel is better than that of cold-rolled steel. The difference between hot rolled stainless steel and cold rolled stainless steel Cold rolling: It is processed and rolled on the basis of hot rolled coils. Generally speaking, it is a process of hot rolling → pickling → cold rolling. Although the steel plate will heat up due to rolling during the processing, it is still called cold rolling. Since hot rolling undergoes continuous cold deformation, cold rolling has poor mechanical properties and too high hardness. It must be annealed to restore its mechanical properties. Those without annealing are called hard rolled coils. Hard rolled coils are generally used to make products that do not require bending or stretching. Its characteristics: 1. Due to a certain degree of work hardening, cold-rolled steel plates have low toughness and are more expensive; 2. There is no oxide scale on the cold rolled surface and the quality is good; 3. Products made by cold deformation have high dimensional accuracy and good surface quality; 4. Cold rolling is widely used in various industries due to its production process, such as various cold stamping parts, cold rolled and cold extruded profiles, cold rolled springs, cold drawn wire rods, cold heading bolts, etc. Hot rolling: relative to cold rolling, cold rolling is rolling below the recrystallization temperature, while hot rolling is rolling above the recrystallization temperature. Its characteristics: 1. Poor toughness and surface smoothness, low price; 2. The temperature of hot rolling is similar to that of forging; 3. The hot plate is hot-rolled and has oxide scale on the surface, and the plate thickness varies; 4. Due to its production and manufacturing technology, it is widely used in civilian applications, such as tableware, kitchen utensils, general household appliances, etc.; 5. The mechanical properties of hot-rolled steel plates are far inferior to those of cold processing and inferior to forging processing, but they have better toughness and ductility.    

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