Hot-rolled (HR) steel and cold-rolled (CR) steel mainly have the following differences.
- In terms of process
We roll hot-rolled steel at high temperatures, while we roll cold-rolled steel at normal temperatures.
- Performance
The mechanical properties of hot-rolled steel are relatively low and the elongation is better.
We have work hardened cold-rolled steel to make it have high strength but relatively poor elongation.
The surface quality of cold-rolled steel is usually better than that of hot-rolled steel, and is more smooth and flat.
- Dimensional accuracy
Cold rolled steel has higher dimensional accuracy and less dimensional fluctuation.
- Application
We often use hot rolled steel in structural parts, large mechanical parts and other situations where surface requirements are not high, but we need larger size specifications.
Cold-rolled steel is more used for products that require high precision and high surface quality, such as automotive panels and electrical housings.
Definition and principle of hot rolling
- Definition of hot rolling: Hot rolling refers to the process of rolling deformation of metal materials above the recrystallization temperature.
- The principle of hot rolling: We heat the metal billet to a higher temperature to make it achieve austenitic state, and it has good plasticity and low deformation resistance.
- Then, through the rotation and extrusion of the roll, we make the metal billet be plastic deformed, so as to change its shape, size and structure.
- During the hot rolling process, the metal undergoes a series of metallurgical changes such as dynamic recrystallization, and finally obtains a hot-rolled product with specific properties and shapes.
- Through hot rolling, we can achieve large deformation processing to produce various specifications of sheet metal, profiles, pipes and other metal products.
Hot rolling process
First, to prepare the metal blank, usually steel ingot or continuous casting billet.
- The billet is heated in the heating furnace to make it reach the appropriate hot rolling temperature.
- The heated billet is then fed to the rolling mill, where it is gradually rolled thinner and longer under the action of multiple rolls to achieve changes in shape and size.
- During the rolling process, multiple passes may be carried out, each of which further deforms and refines the billet.
- At the same time, there will be corresponding cooling and lubrication measures to control temperature and reduce friction.
- After the completion of rolling, the hot rolled product is processed as needed, such as cutting, straightening, etc., to meet the final requirements of use.
- The entire process requires precise temperature control, roll adjustment and process parameter setting to ensure the quality and performance of the hot rolled product.
Characteristics of hot rolling
- High production efficiency.
- We can machine it to thick specifications.
- Good product plasticity.
- The cost is relatively low.
- The surface is rough.
Advantages of hot rolling
- Hot rolling has many advantages. It has high production efficiency and can realize mass production quickly.
- Low cost, compared with some other processing methods in terms of cost has obvious advantages.
- It can also improve material properties, such as promoting the grain refinement of the metal, thereby improving the comprehensive mechanical properties.
- At the same time can process thick specification products, very suitable for the production of thick metal products.
- And we have a wide range of applications, and we can use it for a variety of metal materials and a variety of product types of production.
Application of hot rolled steel
- One of the many differences between hot-rolled and cold-rolled steel is the price.
- We find that hot-rolled steel tends to be cheaper than cold-rolled steel because we don’t have any delays in its manufacturing process and it doesn’t need to be reheated like cold-rolled steel.
- We can use it in applications where precise shapes and we do not require tolerances.
Definition of cold rolling:
Cold rolling refers to the process of rolling deformation of metal materials below the recrystallization temperature.
The principle of cold rolling
- The metal billet at room temperature or close to room temperature through the extrusion and tensile action of the roll, plastic deformation, thereby changing its shape, size and organizational structure.
- In the cold rolling process, the strain hardening phenomenon of the material is more obvious, which increases its strength and hardness.
- At the same time, by controlling the rolling process parameters, the requirements of high precision and good surface quality of the product can be realized.
- Cold rolling is usually used to produce metal products with high precision and surface quality requirements such as sheet and strip.
Characteristics of cold rolling
- High dimensional accuracy: it can produce products with very small dimensional tolerances.
- Good surface quality: smooth, flat and bright surface can be obtained.
- Excellent mechanical properties: high strength after work hardening.
- Various thickness specifications: can meet different thickness requirements, especially thinner specifications.
- The process is more complex: compared with hot rolling, its process and control requirements are more stringent.
- The production speed is relatively slow: due to normal temperature processing, the efficiency will be lower than hot rolling.
Cold rolled steel is used for applications of factors such as tolerance, surface condition, concentricity and straightness. It also provides a more aesthetically pleasing and visually appealing surface.