Hot rolling is relative to cold rolling, which is lower than the recrystallization temperature of rolling, and hot rolling is performed at a recrystallization temperature higher than rolling.


Advantage:
The hot-rolled seamless steel pipe can damage the foundry structure of the steel ingot, refine the grain of the steel, eliminate the structural defects, make the steel structure dense, and improve the mechanical properties. This improvement is reflected in the rolling direction, so that the steel is no longer of certain isotropy; bubbles, cracks and osteoporosis formed during casting can be welded together under high temperature and high pressure.


Disadvantages:
1. After hot rolling, non-metallic inclusions (mainly sulfides and oxides, and silicates) inside the steel are pressed into a thin plate, and delamination (lamination) occurs. The delamination tensile properties of the steel in the thickness direction are significantly deteriorated and may occur between the weld shrinkage layers. The local strain caused by welding shrinkage often reaches several times the yield point strain, and the strain is much larger than the induced load;


2. Hot rolled steel, poor thickness and edge width control. We are familiar with thermal expansion and contraction. Even if the length and thickness of the hot rolling are standard, there will be some negative after the final cooling. The wider the width of the negative difference, the greater the thickness and the more obvious the performance. Therefore, there is no legal requirement for the steel of width, thickness, length, angle and edge of the steel edge to be too precise.




three. Residual stress caused by uneven cooling. Residual stress refers to the internal self-phase-balanced stress without external force. The hot-rolled steel of various cross-sections has a residual stress. Generally, the larger the cross-sectional dimension of steel, the greater the residual stress. The residual stress is self-phase balanced, but it has a certain influence on the external force of the steel member. Deformation, stability, fatigue resistance, etc. may have adverse effects.