Hot Rolled Steel Plate and Cold Rolled Steel Plate

Hot Rolled Steel Plate

By definition, ingots or billets are difficult to deform and process at room temperature. Generally, they are heated to 1100~1250 ℃ for rolling. This rolling process is called hot rolling. The temperature of the hot rolled plate is high, so the deformation resistance is small, and large deformation can be achieved. Take the rolling of steel plates as an example. Generally, the thickness of the continuous casting slab is about 230 mm, and after rough rolling and finishing rolling, the final thickness is 1~20 mm. At the same time, due to the small width-thickness ratio of the steel plate and the relatively low requirements for dimensional accuracy, the shape problem is not easy to occur, and the convexity is mainly controlled. If the structure is required, it is generally realized by controlling rolling and cooling, that is, controlling the starting temperature, finishing temperature, and crimping temperature of finish rolling to control the microstructure and mechanical properties of strip steel.

Type and Purpose

1. Structural Steel

It is mainly used for the production of steel structures, bridges, ships, and vehicles.

2. Weathering Steel

Add special elements (P, Cu, C, etc.) with good corrosion resistance and atmospheric corrosion resistance, which are used in the production of containers and special vehicles, as well as building structures.

3. Steel for Automobile Structure

High-strength steel plates with good stamping and welding properties are used in the production of automobile FRAME, wheels, etc.

4. Hot-rolled Special Steel

Carbon steel, alloy steel and tool steel for general mechanical structures are used for the production of various mechanical parts after heat treatment.

5. Cold Rolled Raw Plate

It is used to produce various cold rolling products, including CR, GI, color-coated plates, etc.

6. Steel Plate for Steel Pipe

With good processing performance and compressive strength, it is used as a high-pressure gas pressure vessel for filling LPG, acetylene gas, and various gases with volumes below 500L.

7. Stainless Steel Plate

Stainless steel has good corrosion resistance and is mainly used in the food industry, surgical equipment, aerospace, petroleum, chemical industry, and other industries.

Cold Rolled Steel Sheet

Cold rolling is to further thin the steel plate to the target thickness below the recrystallization temperature at room temperature. Compared with a hot-rolled steel plate, the thickness of a cold-rolled steel plate is more accurate, and the surface is smooth and beautiful. Generally, there is no heating process for cold rolled sheets before rolling. However, due to the small thickness of the strip steel, the flatness problem is easy to occur. In addition, cold-rolled products are finished products. Therefore, in order to control the dimensional accuracy and surface quality of the strip steel, many cumbersome processes are used. The cold rolling production line is long, the equipment is many, and the process is complex.

With the improvement of users’ requirements for strip size accuracy, shape, and surface quality, there are more control models, l1 and l2 systems, and shape control methods for cold rolling mills than for hot rolling mills. Moreover, the temperature of roll and strip steel is also an important control index. By definition, ingots or billets are difficult to deform and process at room temperature, and most steels are rolled by hot rolling. However, because the steel surface is easy to generate scale under high temperatures, making the hot rolled steel surface rough and the size fluctuates greatly, steel with a smooth surface, accurate size, and good mechanical properties are required to be produced by cold rolling using hot rolled semi-finished products or finished products as raw materials.

Application of Cold Rolled Steel Sheet

Cold-rolled sheets and strips are widely used, such as automobile manufacturing, electrical products, rolling stock, aviation, precision instruments, food cans, etc. Cold rolled steel sheet is the abbreviation of ordinary carbon structural steel cold rolled sheet, also known as a cold rolled sheet, commonly known as cold rolled sheet, which is sometimes mistakenly written as cold rolled sheet. Cold plates are hot-rolled steel strips of ordinary carbon structural steel, which are further cold-rolled into steel plates with a thickness of less than 4mm. The cold plate has the good surface quality and high dimensional accuracy because it does not produce scale when rolled at room temperature. In addition to annealing, its mechanical and technological properties are better than hot-rolled steel sheets. In many fields, especially in the field of home appliance manufacturing, it has gradually replaced hot rolled steel sheets.

Difference between Hot Rolling and Cold Rolling

1. Appearance and Surface quality

since the cold plate is obtained from the hot plate after the cold rolling process, and some surface finishing is also carried out during the cold rolling process, the cold plate is better than the hot plate in terms of surface quality (such as surface roughness). Therefore, if there is a high requirement for the coating quality of the product such as painting, the cold plate is generally selected, and the hot plate is divided into acid-washed plate and non-acid-washed plate. The surface of the acid-washed plate becomes normal metal color because of the acid washing, However, the surface is not as high as that of the cold plate because it has not been cold rolled. The surface of the plate that has not been pickled usually has an oxide layer with black hair, or there is an iron oxide black layer. Generally speaking, it looks like it has been baked by fire. In addition, if the storage environment is not good, it usually has some embroidery.

2. Performance

In general, the mechanical properties of hot plates and cold plates are considered to be indistinguishable in engineering. Although there is some work hardening of the cold plate during cold rolling, (although it does not rule out the strict requirements for mechanical properties, it needs to be treated differently), the yield strength of the cold plate is generally slightly higher than that of the hot plate, and the surface hardness is also higher, depending on the degree of annealing of the cold plate. However, the strength of annealed cold plate is higher than that of the hot plate.

3. Formability
Since the performance of the hot and cold plates is basically not too different, the influencing factors of the forming performance depend on the difference in the surface quality. Since the surface quality is better from the cold plate, generally speaking, the steel plate of the same material, the cold plate is better than the cold plate. The forming appearance of the hot plate is better.