Hot-rolled seamless pipes are relative to cold drawn seamless tubing. Cold rolling is rolling below the crystallization temperature, and hot rolling is rolling above the recrystallization temperature.
Advantages of hot rolled seamless pipe
It can destroy the casting structure of the steel ingot, refine the grains 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 along 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 of hot rolled seamless pipe
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and stratification (interlayer) occurs. Delamination greatly deteriorates the properties of the steel in tension through the thickness, and there is a possibility of interlaminar tearing as the weld shrinks. The local strain induced by the shrinkage of the weld often reaches several times the strain at the yield point, which is much larger than the strain caused by the load;
2. Residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress without external force. Hot-rolled steel sections of various sections have this kind of residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although the residual stress is self-equilibrium, 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, fatigue resistance, etc.
3. For hot-rolled steel products, it is difficult to control the thickness and side width. We are familiar with thermal expansion and cold contraction. Even if the length and thickness of the hot-rolled products meet the standard at the beginning, there will still be a certain negative difference after cooling. The wider the side width and the thicker the thickness of this negative difference, the more obvious. Therefore, for large-sized steel, the side width, thickness, length, angle, and edge of the steel cannot be too precise.
Tips: There are two types of seamless pipes: hot-rolled and cold-rolled (drawn) seamless steel pipes.
1. Hot-rolled steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes.
2. Cold-rolled (dial) seamless steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high-pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, and other steel pipes. It also includes carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless steel thin-walled steel pipes, and special-shaped steel pipes.
3. Steel pipe dimension: The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-75mm. The outer diameter of cold-rolled seamless steel pipe can reach 6mm, and the wall thickness can reach 0.25mm. The outer diameter of thin-walled pipe can reach 5mm, and the wall thickness can be less than 0.25mm. The dimensional accuracy of cold rolling is higher than that of hot rolling.
Advantages of hot rolled seamless pipe
It can destroy the casting structure of the steel ingot, refine the grains 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 along 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 of hot rolled seamless pipe
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and stratification (interlayer) occurs. Delamination greatly deteriorates the properties of the steel in tension through the thickness, and there is a possibility of interlaminar tearing as the weld shrinks. The local strain induced by the shrinkage of the weld often reaches several times the strain at the yield point, which is much larger than the strain caused by the load;
2. Residual stress caused by uneven cooling. Residual stress is the internal self-equilibrium stress without external force. Hot-rolled steel sections of various sections have this kind of residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although the residual stress is self-equilibrium, 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, fatigue resistance, etc.
3. For hot-rolled steel products, it is difficult to control the thickness and side width. We are familiar with thermal expansion and cold contraction. Even if the length and thickness of the hot-rolled products meet the standard at the beginning, there will still be a certain negative difference after cooling. The wider the side width and the thicker the thickness of this negative difference, the more obvious. Therefore, for large-sized steel, the side width, thickness, length, angle, and edge of the steel cannot be too precise.
Tips: There are two types of seamless pipes: hot-rolled and cold-rolled (drawn) seamless steel pipes.
1. Hot-rolled steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, geological steel pipes and other steel pipes.
2. Cold-rolled (dial) seamless steel pipes are divided into general steel pipes, low and medium pressure boiler steel pipes, high-pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, and other steel pipes. It also includes carbon thin-walled steel pipes, alloy thin-walled steel pipes, stainless steel thin-walled steel pipes, and special-shaped steel pipes.
3. Steel pipe dimension: The outer diameter of hot-rolled seamless pipe is generally greater than 32mm, and the wall thickness is 2.5-75mm. The outer diameter of cold-rolled seamless steel pipe can reach 6mm, and the wall thickness can reach 0.25mm. The outer diameter of thin-walled pipe can reach 5mm, and the wall thickness can be less than 0.25mm. The dimensional accuracy of cold rolling is higher than that of hot rolling.
