Compared with cold rolling, cold rolling is lower than the recrystallization temperature of rolling, and hot rolling is carried out at higher recrystallization temperature than rolling.


Benefits:
Hot-rolled seamless steel pipes can damage the casting structure of ingots, refine the grain size of steel, eliminate the defects of micro-structure, densify the structure of steel and improve the mechanical properties. This improvement is reflected in the rolling direction, so that the steel no longer has a certain degree of isotropy; pouring to form bubbles, cracks and osteoporosis, can also be welded together under 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 sheets, and the phenomenon of stratification (lamination) occurs. By means of tensile properties, the steel layers in the thickness direction are significantly deteriorated, and may occur in the shrinkage interlayer tearing of weld seam. The local strain caused by weld shrinkage is often several times that of yield point strain, and the strain is much larger than that caused by load.


2. Hot rolled steel products have poor thickness and edge width control. We are familiar with thermal expansion and shrinkage, even if the beginning of hot rolling is the standard length, thickness, or there will be some negative end after cooling, the wider the edge width of this negative difference, the more obvious the thickness increase. Therefore, there is no legal requirement to be too precise for large steel with steel edge width, thickness, length, angle and edge line.




3. Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot rolled steel with various sections has residual stress. Usually, the larger the section size of steel, the larger the residual stress. Residual stress is self-balanced, but the external force of steel members may have some influence on the performance. If deformation, stability, anti-fatigue may have adverse effects.