At present, ASTM A500 square pipes are all rolled from billets, and the main rolling methods are cold rolling and hot rolling, which will affect the structure and properties of ASTM A500 square pipes to varying degrees.
1. Hot rolled ASTM A500 square tube
Advantages:
It can destroy the casting structure of Gangdian, refine the grains of the square tube, and eliminate the defects of the microstructure, so as to make the structure of the ASTM A500 square tube compact and improve the mechanical properties of the steel tube. This improvement is mainly reflected in the rolling direction, so that the ASTM A500 square tube is no longer an isotropic body to a certain extent; the bubbles, cracks and porosity formed during casting can also be welded under the action of high temperature and pressure .
Disadvantages:
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, and silicates) inside the ASTM A500 square tube are pressed into thin sheets and delaminated. Delamination greatly deteriorates the tensile properties of the square tube in the thickness direction, and there is a possibility of interlaminar tearing when 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 induced by the load;
2. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase equilibrium without external force. Hot-rolled section steel of various sections has such residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although the residual stress is self-balanced, 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, and fatigue resistance.
2. Cold rolled ASTM A500 square tube
It refers to the processing of steel plates or steel strips into various types of square tubes through cold working such as cold drawing, cold bending, and cold drawing 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 use conditions; cold rolling can make ASTM A500 square tube produce a lot of plastic deformation, thereby improving the Yield point of ASTM A500 square tube.
Disadvantages: 1. Although there is no thermal plastic compression during the forming process, there is still residual stress in the section, which will inevitably affect the overall and local buckling characteristics of the ASTM A500 square tube;
2. The style of cold-rolled section steel is generally a mountain section, which makes the free machine rotational stiffness of the section low. When bending, it is easy to rotate, and it is easy to bend torsional buckling when it is compressed, and the torsional performance is poor;
3. The wall thickness of cold-rolled forming steel is small, and it is not thickened at the corners where the plates are connected, and the ability to withstand local concentrated loads is weak.
The main differences between hot rolled ASTM A500 square pipe and cold rolled ASTM A500 square pipe are:
1. Cold-rolled section steel allows local buckling of the section, so that the bearing capacity of the member after buckling can be fully utilized; while hot-rolled section steel 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 section of cold-formed thin-walled steel is curved, while the residual stress distribution on the cross-section of hot-rolled or welded steel is thin-film.
3. The free machine rotational 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.
1. Hot rolled ASTM A500 square tube
Advantages:
It can destroy the casting structure of Gangdian, refine the grains of the square tube, and eliminate the defects of the microstructure, so as to make the structure of the ASTM A500 square tube compact and improve the mechanical properties of the steel tube. This improvement is mainly reflected in the rolling direction, so that the ASTM A500 square tube is no longer an isotropic body to a certain extent; the bubbles, cracks and porosity formed during casting can also be welded under the action of high temperature and pressure .
Disadvantages:
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, and silicates) inside the ASTM A500 square tube are pressed into thin sheets and delaminated. Delamination greatly deteriorates the tensile properties of the square tube in the thickness direction, and there is a possibility of interlaminar tearing when 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 induced by the load;
2. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase equilibrium without external force. Hot-rolled section steel of various sections has such residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although the residual stress is self-balanced, 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, and fatigue resistance.
2. Cold rolled ASTM A500 square tube
It refers to the processing of steel plates or steel strips into various types of square tubes through cold working such as cold drawing, cold bending, and cold drawing 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 use conditions; cold rolling can make ASTM A500 square tube produce a lot of plastic deformation, thereby improving the Yield point of ASTM A500 square tube.
Disadvantages: 1. Although there is no thermal plastic compression during the forming process, there is still residual stress in the section, which will inevitably affect the overall and local buckling characteristics of the ASTM A500 square tube;
2. The style of cold-rolled section steel is generally a mountain section, which makes the free machine rotational stiffness of the section low. When bending, it is easy to rotate, and it is easy to bend torsional buckling when it is compressed, and the torsional performance is poor;
3. The wall thickness of cold-rolled forming steel is small, and it is not thickened at the corners where the plates are connected, and the ability to withstand local concentrated loads is weak.
The main differences between hot rolled ASTM A500 square pipe and cold rolled ASTM A500 square pipe are:
1. Cold-rolled section steel allows local buckling of the section, so that the bearing capacity of the member after buckling can be fully utilized; while hot-rolled section steel 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 section of cold-formed thin-walled steel is curved, while the residual stress distribution on the cross-section of hot-rolled or welded steel is thin-film.
3. The free machine rotational 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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