Advantages of hot rolling
Hot rolling can destroy the casting structure of the steel ingot, refine the grain of the steel, and eliminate the defects of the microstructure, so that the steel structure is dense and the mechanical properties are improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent; bubbles, cracks and looseness formed during casting can also be welded under high temperature and pressure.
Disadvantages of hot rolling
① After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, and delamination (interlayer) occurs. Delamination greatly deteriorates the tensile properties of the steel in the thickness direction, and it is possible that interlayer tearing may occur when the weld shrinks. The local strain induced by weld shrinkage often reaches several times the yield point strain, which is much larger than the strain caused by the load;
②Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress without external force. Hot-rolled steel sections of various sections have such residual stresses. Generally, the larger the section size of the steel section, the larger the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of steel components under external force. For example, it may have adverse effects on deformation, stability, and fatigue resistance.
③The thickness and edge width of hot rolled steel products are not easy to control. We are familiar with thermal expansion and contraction. Since at the beginning, even if the length and thickness are up to the standard, there will be a certain negative difference after cooling. The wider the negative difference, the more obvious the thicker the thickness. Therefore, for large steel, the side width, thickness, length, angle, and sideline of the steel cannot be too accurate.