Both hot rolling and cold rolling are processes for forming steel or steel plates. They have a great impact on the structure and properties of steel. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small steel 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 the defects of the microstructure, so that the steel structure is dense 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; the bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure. Disadvantages: 1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, and silicates) inside the steel are pressed into thin sheets, and delamination (interlayer) occurs. Delamination greatly deteriorates the properties of the steel in tension through the thickness, and there is a possibility of 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 the load; 2. Residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress without external force. Hot-rolled steel sections of various sections have this kind of residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although the residual stress is self-equilibrium, it still has a certain influence on the performance of the steel member under the action of external force. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc. 2. Cold rolling It refers to the steel plate or steel strip processed into various types of steel through cold drawing, cold bending, cold drawing and other cold processing at room temperature. Advantages: fast forming speed, high output, and no damage to the coating, can be made into a variety of cross-sectional forms to meet the needs of the use conditions; cold rolling can cause a large plastic deformation of the steel, thereby improving the yield of the steel point. Disadvantages: 1. Although there is no thermal 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 style of cold-rolled steel is generally an open section, which makes the section free Lower torsional rigidity. It is prone to torsion when it is bent, and it is prone to bending and torsional buckling when it is compressed, and its torsional performance is poor; 3. The wall thickness of cold-rolled formed steel is small, and there is no thickening at the corner of the plate connection, which can withstand local stress The ability to concentrate loads is weak. Both hot rolling and cold rolling are processes for forming steel or steel plates. They have a great impact on the structure and properties of steel. The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small steel 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 the defects of the microstructure, so that the steel structure is dense 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; the bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure. The first disadvantage is that after hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, resulting in delamination (interlayer). Delamination greatly deteriorates the properties of the steel in tension through the thickness, and there is a possibility of 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 the load. The second is the residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress without external force. Hot-rolled steel sections of various sections have this kind of residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although the residual stress is self-equilibrium, it still has a certain influence on the performance of the steel member under the action of external force. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc. Cold rolling refers to the processing of steel plates or strips into various types of steel products at room temperature through cold processing such as cold drawing, cold bending, and cold drawing. The advantage is that the forming speed is fast, the output is high, and the coating is not damaged. It can be made into a variety of cross-sectional forms to meet the needs of the use conditions; cold rolling can cause a large plastic deformation of the steel, thereby improving the yield of the steel. point. The first disadvantage is that although there is no thermal 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. The second is that the style of cold-rolled steel is generally an open section, which makes the free torsional stiffness of the section low. It is prone to torsion when it is bent, and it is easy to buckle when it is compressed, and its torsional performance is poor. The third is that the wall thickness of the cold-rolled formed steel is small, and there is no thickening at the corners where the plates are connected, and the ability to withstand local concentrated loads is weak. The main differences between hot rolling and cold rolling are: 1. The cold-rolled formed steel allows local buckling of the section, so that the bearing capacity of the bar after buckling can be fully utilized; while the hot-rolled section does not allow local buckling of the section. 2. The reasons for the residual stress of 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 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 be heated up due to rolling during processing, it is still called cold rolling. Due to the continuous cold deformation of hot rolling, the mechanical properties are relatively poor and the hardness is too high. It must be annealed to restore its mechanical properties, and it is called hard rolled coil without annealing. 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 sheets have low toughness and are more expensive; 2. The cold-rolled surface has no scale and is of good quality; 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 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, and 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 processed by hot rolling, and the surface has oxide skin, and the thickness of the plate has a difference; 4. Due to its production process, it is widely used in civilian applications, such as kitchen utensils, general household appliances, etc.; 5. The mechanical properties of hot-rolled steel sheets are far inferior to those of cold processing and inferior to forging processing, but they have better toughness and ductility.  

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