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1. Cold-formed steels allow local buckling of the cross-section so that the post-buckling bearing capacity can be fully utilized; hot-rolled steels do not allow local buckling of the cross-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-wall section steel is curved, while the residual stress distribution on the hot-section or welded section is thin-film type.
3. The 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.
Cold-rolled seamless pipe refers to a steel plate or strip processed into various types of steel by cold drawing, cold bending, cold drawing and the like at room temperature.
Advantages and Disadvantages Different advantages: high forming speed, high yield, and no damage to the coating, can be made into a variety of cross-sectional forms to meet the needs of the use of conditions; cold rolling can make steel produce a large plastic deformation, thus improving the The yield point of the steel.
Disadvantages: 1. Although there is no thermal plastic compression in the forming process, there are still residual stresses in the cross-section, which will inevitably affect the properties of the steel as a whole and local buckling; 2. Cold-rolled steel profiles are generally open cross-section, making the cross-section free Low torsional stiffness. It tends to twist during bending, bending and torsion buckling tends to occur during compression, and the torsion resistance is poor. 3. The wall thickness of cold-rolled formed steel is relatively small, and it is not thickened at the corners where the plates join, and it can withstand locality. The ability to concentrate loads is weak.
The hot-rolled seamless pipe is relative to a cold-rolled seamless pipe, the cold-rolled seamless pipe is a rolling performed at a temperature lower than the recrystallization temperature, and the hot-rolled seamless pipe is a rolling performed at a temperature higher than the recrystallization temperature.
Advantages: It can destroy the ingot casting structure, 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 looseness 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, and silicates) inside the steel are pressed into thin sheets and a layering (sandwich) phenomenon occurs. Stratification greatly degrades the properties of the steel in the thickness direction, and it is possible that interlayer tearing occurs when the weld seam shrinks. The local strain induced by weld shrinkage often reaches several times the strain at yield point, much larger than the strain caused by load; 2. Residual stress caused by uneven cooling. Residual stress is the stress of the internal self-phase equilibrium under the action of no external force. Hot rolled steel of various sections has such residual stress. The larger the section size of general steel, the greater the residual stress. Although the residual stress is self-balanced, it still has some influence on the performance of steel components under external forces. Such as deformation, stability, anti-fatigue and other aspects may have an adverse effect. 3. Hot-rolled steel products have poor control over thickness and side width. We are familiar with thermal expansion and contraction, because the beginning of hot rolling even if the length and thickness are up to standard, and finally there will be a certain negative difference after cooling, the wider the width of the negative difference, the thicker the more obvious the performance. So for large steels, there is no way to be too precise about the width, thickness, length, angle, and edges of the steel.
Process difference