Hot-rolled seamless steel pipe :hot rolling is performed with respect to cold rolling,cold rolling is rolling below the recrystallization temperature, and hot rolling is rolling at a recrystallization temperature or higher.

Seamless Steel Pipes

Advantage of hot rolled seamless steel pipe:

The cast structure of the ingot can be destroyed, the grain of the steel can be refined, and the defects of the microstructure can be eliminated, so that the steel structure is compacted and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer an isotropic body to some extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.

Disadvantage of hot rolled seamless steel pipe:

After hot rolling, non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (sandwich) occurs. The delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible to cause interlayer tearing when the weld is shrunk. The local strain induced by weld shrinkage often reaches several times the yield point strain and is much larger than the strain caused by the load.

Residual stress caused by uneven cooling. The residual stress is the internal self-phase equilibrium stress without external force. The hot-rolled steel of various sections has such residual stress. The larger the section size of the general steel, the larger the residual stress. Although the residual stress is self-phase-balanced, it still has some influence on the performance of steel members under external force. Such as deformation, stability, fatigue and other aspects may have adverse effects.

Hot rolled steel pipes are not well controlled for thickness and side width. We are familiar with thermal expansion and contraction. Since the hot rolling is started at the beginning even if the length and thickness are up to standard, there will be a certain negative difference after cooling. The wider the width of the negative difference, the thicker the thickness is. Therefore, for large steel, the side width, thickness, length, angle, and edge of the steel cannot be too precise.