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Advantages and disadvantages of hot rolled steel
By definition, steel ingots or billets are difficult to deform at room temperature and difficult to process. Generally, they are heated to 1100-1250 °C for rolling. This rolling process is called hot rolling.
The termination temperature of hot rolling is generally 800 to 900 ° C, and then it is generally cooled in air, so the hot rolling state is equivalent to normalizing treatment.
Most steels are rolled by the hot rolling method. Due to the high temperature, the steel delivered in the hot-rolled state has a layer of iron oxide scale on the surface, so it has certain corrosion resistance and can be stored in the open air.
However, this layer of iron oxide scale also makes the surface of hot-rolled steel rough and the size fluctuates greatly. Therefore, steel with smooth surface, accurate size and good mechanical properties is required, and hot-rolled semi-finished products or finished products are used as raw materials for cold rolling production.
advantage:
The forming speed is fast, the output is high, and the coating is not damaged, and it can be made into a variety of cross-sectional forms to meet the needs of use conditions; cold rolling can cause a large plastic deformation of the steel, thereby increasing the yield point of the steel.
shortcoming:
1. After hot rolling, the non-metallic inclusions (mainly sulfides and oxides, as well as silicates) inside the steel are pressed into thin sheets, resulting in delamination. Delamination greatly deteriorates the tensile properties of the steel through the thickness, and there is the potential for interlaminar tearing as the weld shrinks. The local strain induced by the shrinkage of the weld often reaches several times the yield point strain, which is much larger than the strain induced by the load;
2. Residual stress caused by uneven cooling. Residual stress is the stress of internal self-phase equilibrium without external force. Hot-rolled section steel of various sections has such residual stress. Generally, the larger the section size of the section steel, the greater the residual stress. Although the residual stress is self-balanced, it still has a certain influence on the performance of the steel member under the action of external force. For example, it may have adverse effects on deformation, stability, and fatigue resistance.
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