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Production process of cold rolled sheet in galvanized sheet
In the appearance of galvanized steel sheet, cold-rolled steel sheet with cold-rolled coil slightly concealed is superior to cold-rolled steel sheet in surface quality, structure and dimensional accuracy. In terms of performance, the cold-rolled steel plate obtained directly from the hot-rolled steel plate by cold rolling process undergoes work hardening during cold rolling process, resulting in increased yield strength and partial residual internal stress. This kind of cold-rolled steel plate is called cold-rolled steel plate because its external performance is relatively "hard" cold-rolled coil (annealed state): the cold-rolled coil is obtained by bell type annealing before winding. After annealing, the work hardening and internal stress are eliminated (greatly reduced), that is to say, the yield strength is reduced to nearly before cold rolling.
In general, the default delivery status for cold rolled coils is that most of the annealed steel is now sold as coils. After purchasing coil materials, enterprises need to open the coil first, which is widely used in the automobile industry. Of course, many auto industry outsourcing uncoiler process, factory directly use uncoiler plate.
In order to ensure that the mechanical properties of various stainless steel coils such as yield strength, tensile strength, elongation and hardness meet the requirements, the stainless steel coils must undergo annealing treatment, solution treatment, aging treatment and other heat treatment before delivery. The corrosion resistance of stainless steel plate mainly depends on its alloy composition (chromium, nickel, titanium, silicon, aluminum, etc.). And stainless steel plate internal structure. Chromium plays a major role. Chromium has very high chemical stability, can form passivation film on the surface of steel, separate the metal from the outside, protect the steel plate from oxidation, and improve the corrosion resistance of steel plate. After the passive film was damaged, the corrosion resistance decreased.
Alloy elements make full use of four strengthening mechanisms, which have the most significant strengthening effect on steel under quenching and tempering. Martensite is formed during quenching and carbide is precipitated during tempering, which leads to strong second phase strengthening and greatly improves toughness. Therefore, obtaining martensite and tempering is the most economical and effective comprehensive strengthening method. When alloy elements are added to the steel, the main purpose is to improve the hardenability of the steel and to ensure that martensite can be easily obtained during quenching. Secondly, the tempering stability of the steel is improved, the martensite is kept at a higher temperature, and the carbide precipitated in the tempering process of hardened steel is finer, more uniform and more stable. In this case, alloy steel has higher strength than carbon steel under the same conditions.