After the steel is rolled, the non-metallic impurities in the special-shaped steel will be pressed into thin sheets to form layered interlayer. Delamination will deteriorate the tensile properties of steel, and interlayer tear may occur when the weld shrinks.

Uneven cooling of hot-rolled profile steel will cause residual stress. Although the residual stress is self-equilibrium, it still has a certain impact on the performance of steel members under external forces, such as deformation, stability and fatigue resistance. Moreover, the thickness and edge width of hot rolled steel products are not easy to control. 

　We all know the truth of thermal expansion and cold contraction, because when hot rolling comes out, even if the length and thickness meet the standard, there will still be a certain negative difference after cooling, and the wider the negative difference edge width is, the thicker the thickness will be.