Hot rolling is relative to cold rolling, cold rolling is rolling below the recrystallization temperature, and hot rolling is rolling above the recrystallization temperature.
Hot-rolled 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, geological steel pipes and other steel pipes.
It can destroy the casting structure of the steel 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; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
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 delamination (interlayer) occurs. Delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible that interlayer tearing may occur 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 caused by the load.
2. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot-rolled steel sections of various cross-sections have such residual stresses. Generally, the larger the section size of the steel section, the larger 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, fatigue resistance, etc.
3. Hot-rolled steel products are not easy to control in terms of thickness and edge width. We are familiar with thermal expansion and contraction. Since at the beginning, even if the length and thickness are up to the standard, there will be a certain negative difference after the final cooling. The wider the negative difference, the thicker the thickness, the more obvious the performance. Therefore, for large-sized steel, the side width, thickness, length, angle, and sideline of the steel cannot be too precise.
Application of hot-rolled seamless steel pipe
1. Buildings include: pipeline transportation at most, underground water extraction when building buildings, boiler hot water transportation, etc.
2. Mechanical processing, bearing sleeves, processing machinery accessories, etc.
3. Electrical: gas transmission, water power generation fluid pipeline.
4. Anti-static pipes for wind power plants, etc.