Both hot rolling and cold rolling are the forming processes of section steel or steel plate, which have great influence on the microstructure and properties of steel. Hot rolling is the main rolling process of steel, while cold rolling is only used to produce small section steel and thin plate.

 

 

 

1、 Hot rolling

 

 

 

Advantages: it can destroy the casting structure of the ingot, refine the grain 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 porosity 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, as well as silicates) inside the steel are pressed into thin sheets, resulting in delamination (sandwich) phenomenon. Delamination can deteriorate the tensile properties of the steel along the thickness direction, and interlaminar tearing may occur when the weld shrinks. The local strain induced by weld shrinkage is often several times of that at yield point, which is much larger than that caused by load.

 

 

 

2. Residual stress caused by uneven cooling. The residual stress is the internal self balance stress without external force. All kinds of hot-rolled section steel have this kind of residual stress. The larger the section size of general section steel is, the larger the residual stress is. Although the residual stress is self balanced, it has a certain influence on the performance of steel members under external force. Such as deformation, stability, anti fatigue and other aspects may have adverse effects.

 

 

 

2、 Cold rolling

 

 

 

It refers to the processing of steel plate or strip into various types of steel after cold drawing, cold bending, cold drawing and other cold working at room temperature.

 

 

 

Advantages: fast forming speed, high output, and no damage to the coating, can be made into a variety of cross-section forms to meet the needs of service conditions; cold rolling can make the steel produce great plastic deformation, so as to improve the yield point of the steel.

 

 

 

Disadvantages: 1. Although there is no hot plastic compression in the forming process, there is still residual stress in the section, which inevitably affects the overall and local buckling characteristics of steel.

 

 

 

2. Cold rolled section steel is generally open section, which makes the free torsion stiffness of section low. It is easy to appear torsion in bending, and it is easy to appear flexural torsional buckling in compression;

 

 

 

3. The wall thickness of cold-rolled steel is small, and there is no thickening at the corner of plate connection, so the ability to bear local concentrated load is weak

 

 

 

3、 The main differences between hot rolling and cold rolling are as follows:

 

 

 

1. Local buckling is allowed in cold-rolled section, which can make full use of the post buckling bearing capacity of the bar, while local buckling is not allowed in hot-rolled section.

 

 

 

2. The reason of producing residual stress is different between hot rolled section and cold rolled section, so the distribution of residual stress on section is also different. The distribution of residual stress on cold-formed thin-walled steel section is bending type, while that on hot-rolled or welded steel section is film type.

 

 

 

3. The free torsion stiffness of hot-rolled section steel is higher than that of cold-rolled section steel, so the torsion resistance of hot-rolled section steel is better than that of cold-rolled section steel.