How to distinguish hot and cold roll?

Hot rolling and cold rolling are two important processes in steel processing. They use different temperatures during the production process, resulting in differences in the physical properties and appearance of the final product. The following is a detailed introduction to these two processes and their differences.

Firstly, the hot rolling process is carried out at high temperatures. The steel billet is heated above the recrystallization temperature to about 1100 degrees Celsius, and then compressed multiple times through a rolling mill. Due to the good plasticity and ductility of steel at high temperatures, hot rolling can significantly change the shape and size of steel, and has higher production efficiency. Hot rolled steel usually has a rough surface and large dimensional tolerances, but due to the presence of recrystallization process, its internal grain structure is relatively good and its mechanical properties are relatively uniform.

The cold rolling process is carried out at room temperature. The hot-rolled steel is pickled to remove oxide scale, and then compressed multiple times at room temperature using a cold rolling mill. Cold rolling process can further improve the surface smoothness and dimensional accuracy of steel, and make it have higher strength and hardness. Cold rolled steel usually has a smooth surface, small dimensional tolerances, and excellent mechanical properties, but due to work hardening, its plasticity and toughness may be reduced.

In practical applications, hot-rolled and cold-rolled steel have their own advantages and disadvantages, and the selection of appropriate processes depends on specific needs. Hot rolled steel is widely used in fields such as building structures, mechanical manufacturing, and shipbuilding due to its low cost and good processability. Cold rolled steel, due to its excellent surface quality and high strength, is commonly used in the manufacturing of high-precision parts, automotive panels, and home appliance casings.

The differences between hot-rolled and cold-rolled steel can be summarized from the following aspects:

1. Production process: Hot rolling is carried out at high temperatures, and cold rolling is carried out at room temperature.
2. Surface quality: The surface of hot-rolled steel is rough, while the surface of cold-rolled steel is smooth.
3. Dimensional accuracy: Hot rolled steel has a larger dimensional tolerance, while cold rolled steel has a smaller dimensional tolerance.
4. Mechanical properties: Hot rolled steel has good plasticity and toughness, while cold-rolled steel has higher strength and hardness.
5. Application areas: Hot rolled steel is used in construction and mechanical manufacturing, while cold-rolled steel is used in high-precision and high-strength requirements.

Through the above analysis, we can clearly understand the differences and respective advantages between hot-rolled and cold-rolled steel. When selecting steel, it is important to choose the appropriate type of steel based on specific application requirements and process characteristics, in order to achieve the best usage effect.