In the production process of steel, hot rolling and cold rolling are two crucial forming processes. They have a significant impact on the organization and properties of steel. The purpose of this article is to discuss the differences between these two processes in depth and help readers better understand their applications and properties.
First, the hot rolling process
Hot rolling, as the name suggests, is the rolling process in the steel heated to a high temperature state. Usually, the ingot or billet will be heated to 1100 ℃ ~ 1250 ℃ temperature range, followed by rolling in the mill. The termination temperature of hot rolling is usually controlled at 800°C to 900°C, after which the steel is cooled naturally in air.
The surface of hot rolled steel will form a layer of iron oxide, which not only gives the steel a certain corrosion resistance, so that it can be stored in the open air, but also leads to a rougher surface and larger dimensional fluctuations. Therefore, for steel with high requirements for surface finish and dimensional accuracy, cold rolling is usually carried out on the basis of hot rolled semi-finished or finished products.
The advantages of hot rolling include fast forming speeds, high yields, and the ability to produce a wide range of cross-sectional forms of steel without damaging the coating. In addition, hot rolling can significantly increase the yield point of steel and improve its mechanical properties.
Second, cold rolling process
Unlike hot rolling, cold rolling is a steel rolling process at room temperature. Although the steel plate will be warmed up during processing, but the overall temperature is still in the lower range. Cold rolling is usually hot rolled steel coil as raw material, after pickling to remove the oxide skin, in the rolling mill for pressure processing, and finally get rolled hard coil.
Cold rolled steel has a high surface finish and a smooth feel, which is mainly due to the pickling process. At the same time, the strength and hardness of cold rolled steel is also relatively high, with good plasticity and elongation, so it is widely used in automotive, home appliance and hardware industries.
The main advantage of cold rolling is that it can destroy the casting organization of the ingot, refine the grain of the steel, and eliminate the defects of the microstructure, thus improving the mechanical properties of the steel. In addition, cold rolling can also to a certain extent eliminate defects such as bubbles, cracks and looseness formed during casting.
Third, the difference between hot rolling and cold rolling
1. temperature differences: hot rolling at high temperatures, while cold rolling is completed at room temperature. This is the most significant difference between the two processes.
2. surface quality: cold rolled steel surface finish is high, while the hot rolled steel is relatively rough.
3. Performance characteristics: the yield point of hot rolled steel is higher, but the strength and hardness of cold rolled steel is higher. In addition, the forming properties of cold rolled steel are superior to those of hot rolled steel.
Overall, hot rolling and cold rolling have their own characteristics and advantages, the choice of which process depends on the specific needs of the application and the performance requirements of the steel. By understanding the differences and characteristics of these two processes, we can better select the right steel for the project.
