The types of steel plates are generally divided into three types according to their thickness: thick plate (more than 6mm), medium plate (3-6mm) and thin plate (less than 3mm). In terms of plate making process, low-carbon steel plate can be divided into cold rolling and hot rolling. Hot rolling alone can produce about 1.2 mm low carbon steel plate and about 2 mm stainless steel plate, and thinner plate can be produced by cold rolling, annealing and quenching and tempering rolling.
Cold rolled steel plate
When cold rolled steel sheet is used for parts forming, the plastic deformation of the material is required to be large, and the surface shall be free of wrinkles, cracks and other parts. Use different grades of steel plates for different parts. For example, there are three types of steel plates for automobile in Japan. The first type (SPCC) is ordinary cold-rolled steel plate, usually rolled by boiling steel, the second type (SPCD) is rolling steel plate, and the third type (SPCE or SPCEN) is cold-rolled steel plate for deep drawing.
In the past, boiling steel was limited to unimportant stamping parts due to its large component segregation, unstable performance and sensitive aging. If aluminum killed steel without aging is used, the cost is 10-20% higher than that of general rimmed steel. In the past, finishing and cold rolling was used to inhibit the aging effect of boiling steel plate, but in fact, it only delayed the occurrence of aging. All countries are studying new ways to improve. The uncoiled annealed steel plate (O.C. A) developed by the United States is a special annealing of boiling steel plate in an atmosphere containing water vapor and hydrogen. Because this atmosphere can remove the dissolved carbon in the steel and the combined carbon in the carbide, the aging sensitivity is suppressed, and the steel plate is further softened. At the same time, due to the growth of recrystallized grains, the {111} aggregate crystal arranged parallel to the steel plate surface increased. According to the research of American Armco Steel Company, this is related to improving the plastic deformation anisotropy of the steel plate, which improves the stamping formability of the steel plate by 84. In recent years, on the basis of uncoiled annealing steel plate, the united annealing method steel plate (U.A.D) has been developed. This is to weld several coils of steel plate into a coil, and put them in a special annealing furnace for decarburization treatment, which has the advantages of lower cost than uncoiled annealing, The steel plate treated in this way has been widely used in cold rolled steel plate for drawing.
Hot-rolled steel plate
Compared with cold-rolled steel plate, the manufacturing process is simpler and the cost is lower, but foreign experience believes that the hot-rolling method is only applicable to the manufacturing of steel plates with a thickness of more than 1.6 mm, and it is uneconomical for thinner steel plates. The surface quality and dimensional accuracy of hot-rolled steel plates are not as good as cold-rolled steel plates. In addition to the frame longitudinal beams, cross beams and various supports, hot-rolled steel plates on automobiles also need to be stamped with wheel rims and discs with certain strength, and the stress is small Shell cover plate with low surface requirements. The former is 3-5 mm thick steel plate, while the latter is used for both medium and thin plates. The use of hot rolled plates on automobiles is mainly thick plates. In the standard of hot SLSN plates for automobiles formulated by the Japan Automobile Association, SAPH is used as car beams and wheels, and SPH is hot-rolled mild steel plate, which is used to manufacture non-stressed shells.
Recently, more and more hot rolled steel plates abroad are rolled by continuous casting billet, and the surface quality of steel plates has also been improved and stabilized. Coiled hot-rolled steel plates are also widely used.
