Advantage
(1) Hot rolling can significantly reduce energy consumption and cost. During hot rolling, the metal has high plasticity and low deformation resistance, which greatly reduces the energy consumption of metal deformation.
(2) Hot rolling can improve the processing performance of metals and alloys, that is, break the coarse grains in the casting state, significantly heal cracks, reduce or eliminate casting defects, transform the as-cast structure into a deformed structure, and improve the processing performance of the alloy.
(3) Hot rolling usually uses large ingots and large rolling reductions, which not only improves production efficiency but also creates conditions for increasing the rolling speed and realizing the continuity and automation of the rolling process.
Shortcoming
(1) After hot rolling, the non-metallic inclusions (mainly sulfides, oxides, and silicates) inside the steel are pressed into thin sheets, causing delamination (sandwiching). Delamination greatly deteriorates the tensile properties of the steel along the thickness direction and may cause interlaminar tearing as 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 load.
(2) Residual stress caused by uneven cooling. Residual stress is the internal self-balanced stress in the absence of external force. Hot-rolled steel sections of various sections have such residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although residual stress is self-balanced, it still has a certain impact on the performance of steel components under the action of external forces. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc.
(3) Hot rolling cannot control the required mechanical properties of the product very accurately, and the structure and properties of hot-rolled products cannot be uniform. Its strength index is lower than cold work hardened products, but higher than fully annealed products, and its plasticity index is higher than cold work hardened products, but lower than fully annealed products.
(4) The thickness and size of hot-rolled products are difficult to control, and the control accuracy is relatively poor; the surface of hot-rolled products is rougher than that of cold-rolled products, with the Ra value generally ranging from 0.5 to 1.5 μm. Therefore, hot rolled products are generally used as blanks for cold rolling processing.

Answers

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