Hot rolling is relative to cold rolling, cold rolling is rolling below the recrystallization temperature, while hot rolling is rolling above the recrystallization temperature.

Advantages of hot-rolled steel pipes

Hot rolling can destroy the as-cast microstructure of the ingot, refine the grain of steel, eliminate microstructural defects, make the steel organization tight and improve the mechanical properties. This improvement is reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; the formation of bubbles, cracks and ossification during casting, and can be welded up under high temperature and pressure.

Disadvantages of hot-rolled steel pipe

1. After hot rolling, the non-metallic inclusions inside the steel (mainly sulfides and oxides, and silicates) are pressed into sheets, and the phenomenon of delamination (lamination) occurs. The layered tensile properties of the steel in the thickness direction deteriorate significantly and may show interlaminar tearing during welding shrinkage. The local strain caused by weld shrinkage often reaches several times the yield point strain, which is much greater than the load induced.

2 Residual stresses caused by uneven cooling. Residual stress is the internal self-phase equilibrium stress in the absence of external forces, a variety of cross-sectional hot-rolled steel has residual stress, so that usually the larger the cross-sectional size of the steel, the greater the residual stress. Residual stresses are self-balancing, but still have some influence on steel members in the performance of external forces. Such as deformation, stability, fatigue resistance, etc. may have a negative impact.

3. The thickness and edge width of hot rolled steel products are not well controlled. We are familiar with the thermal expansion and contraction, even if at the beginning of the hot rolling out are standard length, thickness, and finally after cooling there will still be some negative difference, the greater the side width of this negative difference, the more obvious the increase in the performance of the thickness. So for large steel, the side width, thickness, length, angle and edge line of steel are not regular and require too much precision. Hot rolled normal steel, low and medium pressure boiler tube, high pressure boiler tube, steel pipe, stainless steel pipe, petroleum cracking pipe, geological steel pipe and other kinds of steel pipe.

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