Hot rolling and cold rolling

Hot rolled steel plate

By definition, steel ingots or billets are difficult to deform and process at room temperature. Generally, they are heated to 1100-1250 ℃ for rolling, and this rolling process is called hot rolling. The temperature of hot-rolled plate is high, so the deformation resistance is small, which can achieve a large amount of deformation. Taking the rolling of steel plates as an example, the thickness of continuous casting billets is generally around 230mm, but after rough rolling and finishing rolling, the final thickness is 1-20mm. At the same time, due to the small aspect ratio of steel plates and relatively low dimensional accuracy requirements, it is not easy to encounter plate shape problems, and the focus is on controlling convexity. For those with organizational requirements, it is generally achieved through controlled rolling and cooling, that is, controlling the opening temperature, final rolling temperature, and curling temperature of precision rolling to control the microstructure and mechanical properties of the strip steel.

▲ Types and uses of production processes

1. Structural steel is mainly used in the production of steel structural components, bridges, ships, and vehicles. 2. Adding special elements (P) to weather resistant steel Cu, C, etc., have good corrosion resistance and atmospheric corrosion resistance, and are used in the production of containers and special vehicles, as well as in building structures. 3. High strength steel plates with good stamping and welding properties for automotive structures, used in automotive frames Produced by SHEEL and others. 4. Hot rolled special steel is generally used for mechanical structures, including carbon steel, alloy steel, and tool steel. After undergoing heat treatment engineering, it is used in the production of various mechanical components. 5. Cold rolled raw materials are used to produce various cold rolled products, including CR, GI,  Color coated boards, etc. 6. Steel plates for steel pipes have good processing performance and compressive strength, and are used in the production of high-pressure gas pressure vessels filled with LPG, acetylene gas, and various gases with a volume of less than 500L. 7. Steel plates for high-pressure vessels have good processing performance and compressive strength, and are used in the production of high-pressure gas pressure vessels filled with LPG, acetylene gas, and various gases with a volume of less than 500L. 8. Stainless steel plates have good corrosion resistance and are mainly used in industries such as food industry, surgical equipment, aerospace, petroleum, and chemical industry.

Cold rolled steel plate

Cold rolling is the process of further rolling a steel plate to a target thickness below the recrystallization temperature at room temperature. Compared with hot-rolled steel plates, cold-rolled steel plates have a more precise thickness and a smooth and beautiful surface. Cold rolled sheets generally do not have a heating process before rolling. However, due to the small thickness of the strip steel, it is easy to encounter plate shape problems. Moreover, after cold rolling, it becomes a finished product. Therefore, in order to control the dimensional accuracy and surface quality of the strip steel, many cumbersome processes are adopted. The production line for cold rolling is long, with many equipment and complex processes. With the increasing demands of users for the accuracy of strip size, shape, and surface quality, the control model of cold rolling mills is being improved The L1 and L2 systems have more means of controlling plate shape compared to hot rolling. Moreover, the temperature of the rolling rolls and strip steel is also one of the important control indicators. By definition, steel ingots or billets are difficult to deform and process at room temperature, and most steel products are rolled using the hot rolling method. However, due to the easy formation of iron oxide scales on the surface of steel at high temperatures, the surface of hot-rolled steel is rough and the size fluctuation is large. Therefore, it is required that steel with smooth surface, precise size, and good mechanical properties be produced using hot-rolled semi-finished or finished products as raw materials and then cold rolled methods.

Application of cold-rolled steel plates in the production process

Cold rolled strip has a wide range of applications, such as automotive manufacturing, electrical products, locomotives and vehicles, aviation, precision instruments, food cans, etc. Cold rolled thin steel plate is the abbreviation for ordinary carbon structural steel cold-rolled plate, also known as cold-rolled plate, commonly known as cold plate, sometimes mistakenly written as cold rolled plate. Cold plate is a steel plate made of hot-rolled ordinary carbon structural steel strip, which is further cold-rolled into a thickness of less than 4mm. Due to the fact that rolling at room temperature does not produce oxide scale, the cold plate has good surface quality and high dimensional accuracy. Coupled with annealing treatment, its mechanical and process properties are better than hot-rolled thin steel plates. In many fields, especially in the field of home appliance manufacturing, it has gradually been used to replace hot-rolled thin steel plates.

The difference between hot rolling and cold rolling

1. Appearance and surface quality: Due to the fact that cold plates are obtained from hot plates after the cold rolling process, and cold rolling also involves some surface finishing, cold plates have better surface quality (such as surface roughness) than hot plates. Therefore, if there are high requirements for the coating quality of the product's subsequent coating, cold plates are generally chosen, and hot plates are divided into acid washed plates and non acid washed plates. The surface of acid washed plates becomes a normal metallic color due to acid washing, but the surface is still not as high as cold rolled plates. Non acid washed plates usually have an oxide layer on the surface, which is black, or there is a black layer of iron trioxide, which is like being baked by fire, and if the storage environment is not good. If it's good, it usually comes with some embroidery.

2. Performance: In general, the mechanical properties of hot and cold plates are considered to be indistinguishable in engineering. Although cold plates undergo some work hardening during the cold rolling process (although strict requirements for mechanical properties may be necessary), cold plates usually have slightly higher yield strength and surface hardness than hot plates. The specific treatment depends on the degree of annealing of the cold plate. However, no matter how annealed, the strength of the cold plate is higher than that of the hot plate. 3. Forming performance, as the performance of cold and hot plates is not significantly inferior, the influencing factors of forming performance depend on the difference in surface quality. As the surface quality is better than that of cold plates, the forming appearance effect of cold plates is generally better than that of hot plates of the same material.