For hot-rolled seamless steel tubes, cold-rolled seamless steel tubes are rolled at temperatures lower than recrystallization rolling, but hot-rolled seamless steel tubes are rolled at recrystallization temperatures or higher.


Advantages: The ingot can destroy the structure, refine the grain size of the steel, eliminate the defect microstructure, and improve the compact structure and mechanical properties of the steel. This improvement is mainly embodied in the rolling direction, which makes the steel no longer have a certain degree of isotropy; bubbles, cracks and looseness are formed during pouring, and can also be welded together under high temperature and high pressure.


Disadvantages:
1. Non-metallic inclusions (mainly sulphides and oxides, as well as silicates) in hot-rolled seamless steel tubes are extruded into sheets and laminated (interlayer) by hot-rolled steel tube manufacturers. Layering along the thickness direction makes the tension properties of steel deteriorate significantly, and there may be interlayer tear weld shrinkage. The local strain caused by weld shrinkage reaches the yield point strain, which is often several times larger than the load caused by strain.


2. Residual stress caused by uneven cooling. Residual stress is self-balanced in the absence of external force. Hot-rolled steel has many cross-sections such as residual stress. The larger the cross-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 members under load. Such as deformation, stability, fatigue and so on may have adverse effects.


3. The edge control of thickness and width of hot rolled steel products is not good in this respect. We are familiar with thermal expansion and shrinkage, because the beginning and length of hot rolling are standard, and the final cooling may have some negative differences. The wider the edge width of this negative difference, the more obvious the thickness performance. Therefore, for large steel, the width, thickness, length and angle of steel edge, there is no rule requiring too precise edge.