Difference between hot rolling and cold rolling
Hot rolling and cold rolling are both forming processes of section steel or steel plate, and they have a great influence on the structure and properties of steel. Do you know what is the difference between them? As a professional supplier engaged in the steel industry for many years, let’s introduce them.
The rolling of steel is mainly hot rolling, and cold rolling is only used to produce small section steel and sheet.
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 an isotropic body to a certain extent; bubbles, cracks and looseness formed during casting can also be welded under the action of 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 flakes, and delamination (interlayer) occurs. Delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and interlayer tearing may occur when the weld seam shrinks. The local strain induced by the shrinkage of the weld 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-phase equilibrium stress without external force. Hot-rolled sections of various sections have this type of residual stress. Generally, the larger the section size of the section, the larger the residual stress. Although the residual stress is self-balanced, it still has a certain effect on the performance of steel members under external forces. For example, it may have adverse effects on deformation, stability, and fatigue resistance.
2. Cold rolling
Advantages: It refers to cold-drawn, cold-formed, cold-drawn and other cold processing of steel plates or steel strips into various types of steel 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 in the forming process, there is still residual stress in the cross 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 cross section, making the cross section free Low torsional stiffness. It is prone to torsion when bending, bending and torsion buckling is easy to occur under compression, and the torsional resistance is poor; 3. The thickness of the cold-rolled steel is small, and there is no thickening at the corner where the plate joins. The ability to concentrate loads is weak.
The main differences between hot rolling and cold rolling are:
- The cold-rolled formed steel allows local buckling of the cross-section, so that the bearing capacity of the member after buckling can be fully used; while the hot-rolled steel does not allow local buckling of the cross-section.
- 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 cross section of cold-formed thin-walled steel is curved, while the residual stress distribution on the section of hot-rolled or welded steel is thin film.
- The free torsional stiffness of hot-rolled steel is higher than that of cold-rolled steel, so the torsion resistance of hot-rolled steel is better than that of cold-rolled steel.
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