Hot rolled seamless tube
Hot rolling is relative to cold rolling. Cold rolling is rolling performed below the recrystallization temperature, and hot rolling is rolling performed above the recrystallization temperature.
Advantages
It can destroy the casting structure of steel ingots, refine the grains of steel, and eliminate the defects of micro-structure, 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, the non-metallic inclusions (mainly sulfides and oxides, and silicates) in the steel are pressed into thin slices, 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.
1. Hot rolled steel products are difficult to control in terms of thickness and edge width. We are familiar with thermal expansion and contraction. Since hot rolling at the beginning, even if the length and thickness are up to standard, there will still be a certain negative difference after cooling. The wider the negative difference, the thicker the thickness, the more obvious the performance. Therefore, for large steel, the width, thickness, length, angle, and edge of the steel cannot be required to be too precise.
Advantages
It can destroy the casting structure of steel ingots, refine the grains of steel, and eliminate the defects of micro-structure, 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, the non-metallic inclusions (mainly sulfides and oxides, and silicates) in the steel are pressed into thin slices, 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.
1. Hot rolled steel products are difficult to control in terms of thickness and edge width. We are familiar with thermal expansion and contraction. Since hot rolling at the beginning, even if the length and thickness are up to standard, there will still be a certain negative difference after cooling. The wider the negative difference, the thicker the thickness, the more obvious the performance. Therefore, for large steel, the width, thickness, length, angle, and edge of the steel cannot be required to be too precise.
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