irstly, after hot rolling, non-metallic inclusions (mainly sulfides and oxides, and silicates) in steel are pressed into thin sheets and stratified (interlayer). Layering of steel in the thickness direction of tensile properties is significantly degraded, and interlaminar tearing may occur during welding shrinkage. The local strain caused by weld shrinkage reaches the yield point strain, which is usually several times larger than the load caused by strain.


The second is the residual stress caused by uneven cooling. Under the internal self-balanced stress without external force, there are various kinds of residual stresses in the section of hot rolled steel. The larger the section size, the larger the residual stress. Although the residual stress comes from equilibrium, it still has some influence on the performance of steel members under load. Such as deformation, stability, fatigue and so on may have adverse effects.