Cold Rolled Sheet VS Hot Rolled SheetAuthor : Hani Time : 2022/07/01
Hot rolled plate refers to hot-rolled steel plate and strip, commonly known as hot plate, which refers to steel plate with width greater than or equal to 600mm and thickness of 0.35-200mm and steel strip with thickness of 1.2-25mm. Cold rolled sheet and hot rolled sheet are commonly used in our life. Let's see the difference between cold rolled sheet and hot rolled sheet!
1. Cold Rolled Sheet
Cold rolling is produced by processing and rolling on the basis of hot-rolled coils. Generally speaking, it is a processing process of hot rolling - pickling - cold rolling.
Cold rolling: hot rolled steel coil is used as raw material, and the cold continuous rolling is carried out after acid pickling and removing the oxide skin. The finished product is rolled hard coil. The cold work hardening caused by continuous cold deformation increases the strength and hardness of rolled hard coil and decreases the toughness and plasticity index. Therefore, the stamping performance will deteriorate and can only be used for simple deformed parts. The rolled coil can be used as the raw material of the hot galvanizing plant, because the hot galvanizing units are equipped with annealing lines. The weight of the rolled hard coil is generally 20-40 tons. The hot-rolled pickling coil is continuously rolled at room temperature. The inner diameter is 610mm.
Features: because it has not been annealed, its hardness is very high (HRB is greater than 90), and its machinability is extremely poor. It can only carry out simple directional bending less than 90 degrees (perpendicular to the coiling direction). Cold rolling is usually annealed.
2. Hot Rolled Plate
It can destroy the casting structure of ingot, refine the grain of steel, and eliminate the defects of 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 porosity formed during pouring can also be welded under high temperature and pressure.
(1) After hot rolling, the non-metallic inclusions (mainly sulfides, oxides, and silicates) in the steel are pressed into thin sheets, resulting in delamination (interlayer). Delamination greatly deteriorates the tensile properties of steel along the thickness direction, and it is possible to have interlaminar tearing when the weld shrinks. The local strain induced by weld shrinkage often reaches several times of 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 stress of internal self-equilibrium without external force. Hot rolled sections of various sections have this kind of residual stress. Generally, the larger the section size of the section steel is, the greater the residual stress is. Although the residual stress is self balanced, it still has a certain impact on the performance of steel members under external forces. For example, it may have adverse effects on deformation, stability, fatigue resistance, etc.
(3) The thickness and side width of hot-rolled steel products are not easy to control. We are familiar with thermal expansion and cold contraction. Even if the length and thickness meet the standard at the beginning of hot rolling, there will be a certain negative difference after cooling. The wider the negative difference is, the thicker the thickness is, the more obvious it is. Therefore, for large-sized steel, there is no way to require too accurate side width, thickness, length, angle, and sideline of steel.
3. Differences between Hot Rolled and Cold Rolled Plates
1. The cold plate is cold rolled, and the surface is free of oxide skin, with good quality. The hot plate is processed by hot rolling, and the surface has oxide skin, and the thickness of the plate is different.
2. Hot rolled plate has poor toughness and surface flatness, and the price is low, while cold rolled plate has good ductility and toughness, but the price is expensive.
3. Rolling is divided into cold rolling and hot rolling, with recrystallization temperature as the distinguishing point.
4. Cold rolling: cold rolling is generally used to produce strips, with a higher rolling speed. Hot rolling: the temperature of hot rolling is close to that of forging
5. The surface of the non electroplated hot rolled plate is dark brown, and the surface of the non electroplated cold rolled plate is gray. After electroplating, it can be distinguished from the smoothness of the surface, and the smoothness of cold rolled plate is higher than that of hot rolled plate.
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