Hot rolling and cold rolling are both profile or steel forming processes, they have a great impact on the organization and properties of steel, steel rolling is mainly hot rolling, cold rolling is only used to produce small size sections and thin plates. I. Hot rolling Advantages: it can destroy the casting organization of the ingot, refine the grain of steel, and eliminate microstructural defects, so that the steel organization is dense and 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 together under the action of high temperature and pressure. Disadvantages:1. After hot rolling, the non-metallic inclusions inside the steel (mainly sulfides and oxides, and silicates) are pressed into thin sheets, and delamination (interlayer) occurs. Delamination greatly deteriorates the properties of the steel in tension along the thickness direction, and there is a risk of interlaminar tearing during weld shrinkage. Local strains induced by weld shrinkage often reach several times the yield point strain, much larger than the load-induced strain; 2. Residual stresses caused by uneven cooling. Residual stress is the internal self-equilibrium stress in the absence of external forces, a variety of cross-sectional hot-rolled steel sections have such residual stress, generally the larger the section size of the steel, the greater the residual stress. Although the residual stress is self-balancing, but the performance of steel members under the action of external forces still has a certain impact. Such as deformation, stability, fatigue resistance and other aspects may have a negative effect. II. Cold rolling It refers to the cold processing of steel plate or strip into various types of steel at room temperature after cold drawing, cold bending, cold drawing, etc. Advantages: forming speed, high yield, and do not damage the coating, can be made into a variety of cross-sectional forms to meet the needs of the conditions of use; cold rolling can make a large plastic deformation of steel, thereby increasing the yield point of steel. Disadvantages: 1. Although the forming process does not undergo thermal plastic compression, there is still residual stress in the cross-section, which must have an impact on the overall and local buckling characteristics of the steel; 2. Cold-rolled section style is generally open section, making the free torsional stiffness of the cross-section is low. In the bending prone to torsion, bending and torsional buckling when pressed, poor torsional performance; 3. Cold rolled formed steel wall thickness is smaller, and not thickened at the corner of the plate articulation, the ability to withstand localized concentrated load is weak. Hot rolling and cold rolling are profiles or steel forming process, they have a great impact on the organization and performance of steel, steel rolling is mainly hot rolling, cold rolling is only used for the production of small sections and thin plates. The advantage of hot rolling is that it can destroy the casting organization of the ingot, refine the grain of steel, and eliminate microstructural defects, so that the steel organization is dense and the mechanical properties are improved. This improvement is mainly reflected in the direction along the rolling, so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded together under the action of high temperature and pressure. Disadvantage one is that after hot rolling, the non-metallic inclusions inside the steel (mainly sulfides and oxides, and silicates) are pressed into thin sheets and delamination (intercalation) occurs. Delamination greatly deteriorates the properties of the steel in tension along the thickness direction, and there is a risk of interlayer tearing during weld shrinkage. The local strain induced by weld shrinkage often reaches several times the yield point strain, much larger than the load-induced strain. The second is the residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress in the absence of external forces, a variety of cross-sectional hot-rolled steel sections have such residual stresses, generally the larger the section size of the steel, the greater the residual stress. Although the residual stress is self-balancing, but the performance of steel members under the action of external forces still has a certain impact. Such as deformation, stability, fatigue resistance and other aspects may have a negative effect. Cold rolling refers to the cold processing of steel plates or strips into various types of steel at room temperature, after cold drawing, cold bending, cold drawing, etc.. The advantages are fast forming, high yield, and no damage to the coating, can be made into a variety of cross-sectional forms to adapt to the needs of the conditions of use; cold rolling can make a large plastic deformation of steel, thereby increasing the yield point of steel. The disadvantage is that although the forming process does not go through the thermal plastic compression, but there is still residual stress in the cross-section, the overall and local yielding characteristics of the steel is bound to have an impact. The second is that the cold-rolled steel style is generally open section, making the free torsional stiffness of the cross-section is low. In the bending prone to torsion, bending and torsional buckling when pressed, poor torsional performance. Third, the cold rolled formed steel wall thickness is small, and not thickened at the corners of the plate articulation, the ability to withstand localized concentrated load is weak.

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