Cold rolling is a processing and rolling process that is based on hot-rolled coils. Generally speaking, it is a process of hot rolling, acid washing, and cold rolling. Hot rolled plates have low hardness, easy processing, and good ductility. Cold rolled plates have high hardness and are relatively difficult to process, but they are not easily deformed and have high strength. Hot rolled plates have relatively low strength and surface quality (with oxidation and low smoothness), but good plasticity, generally medium thick plates. Cold rolled plates have high strength, hardness, and surface smoothness, generally thin plates, and can be used as stamping plates

　　Hot rolled steel plates have mechanical properties far inferior to cold processing and second only to forging processing, but they have good toughness and ductility

　　Cold rolled steel plates have a certain degree of work hardening and low toughness, but can achieve a good yield to strength ratio. They are used for cold bending spring plates and other parts. At the same time, due to the yield point being close to the tensile strength, there is no predictability of danger during use, and accidents are prone to occur when the load exceeds the allowable load.  

　　The difference between hot-rolled plate and cold-rolled plate can be attributed to the following points:

　　1. The cold plate is processed by cold stamping to produce an oxygen free surface, ensuring good quality. The hot plate is processed by hot stamping and has oxide skin on the surface, with a thickness difference.  

　　2. Rolling is divided into cold rolling and hot rolling, with recrystallization temperature as the distinguishing point.  

　　3. Hot rolled plates have poor toughness and surface smoothness, and are cheaper, while cold-rolled plates have good ductility and toughness, but are more expensive. 4. The surface of non electroplated hot-rolled plates is black brown, while the surface of non electroplated cold-rolled plates is gray. After electroplating, it can be distinguished by the smoothness of the surface, and the smoothness of cold-rolled plates is higher than that of hot-rolled plates.  

　　5. Cold rolling: Cold rolling is generally used for producing strip, and its rolling speed is relatively high. Hot rolling: The temperature of hot rolling is similar to that of forging. Product characteristics of hot rolling and cold rolling:

　　Cold rolling: Using hot-rolled steel coils as raw materials, after acid washing to remove oxide skin, cold rolling is carried out, and the finished product is rolled hard coil. Due to continuous cold deformation, the cold work hardening caused by cold deformation increases the strength and hardness of the rolled hard coil, and reduces the toughness and plasticity index. Therefore, the stamping performance will deteriorate, and it can only be used for parts with simple deformation. Rolled hard coils can be used as raw materials for hot-dip galvanizing plants, as hot-dip galvanizing units are equipped with annealing wires. The weight of the rolled hard coil is generally between 20-40 tons, and the steel coil is continuously rolled on the hot-rolled acid washed coil at room temperature. The inner diameter is 610mm. Product features: Due to the lack of annealing treatment, its hardness is very high (HRB greater than 90), and its mechanical processing performance is extremely poor. It can only perform simple directional bending less than 90 degrees (perpendicular to the winding direction). Cold rolling usually undergoes annealing treatment.  

　　Advantages of hot rolling: It can destroy the casting structure of steel ingots, refine the grain size of steel, and eliminate defects in the microstructure, thereby making the steel structure dense and improving its mechanical properties. 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 pouring can also be welded under high temperature and pressure. Disadvantages of hot rolling:

　　1. Hot rolled steel products are difficult to control in terms of thickness and edge width. We are familiar with thermal expansion and contraction, because even if the length and thickness meet the standards during hot rolling at the beginning, there will still be a certain negative difference after cooling. The wider the edge width and the thicker the thickness, the more obvious this negative difference is. So for large-sized steel, it is not possible to require too precise specifications for the width, thickness, length, angle, and edge lines of the steel.  

　　2. After hot rolling, non-metallic inclusions (mainly sulfides, oxides, and silicates) inside the steel are compressed into thin sheets, resulting in delamination (interlayer) phenomenon. Layering greatly deteriorates the tensile properties of steel along the thickness direction, and there is a possibility of interlayer tearing during weld shrinkage. The local strain induced by weld shrinkage often reaches several times the yield point strain, much larger than the strain caused by load;  

　　3. Residual stress caused by uneven cooling. Residual stress is the stress that self balances internally in the absence of external forces, and various hot-rolled steel sections have such residual stresses. Generally, the larger the cross-sectional size of the steel section, the greater the residual stress. Although residual stress is self balanced, it still has a certain impact on the performance of steel components under external forces. It may have adverse effects on deformation, stability, fatigue resistance, and other aspects.