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 sections of 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 defects in the microstructure, thereby making the steel structure dense and improving its 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, non-metallic inclusions (mainly sulfides, oxides, and silicates) inside the steel are pressed into thin sheets, resulting in delamination (sandwiching). 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 the 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 temperatures.
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.
②Cold-rolled steel sections generally have open sections, which results in lower 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;
③The 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.
3. 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.
③The 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.
Post time: Jan-11-2024