The color coated steel plate is made by cold-rolled steel plate, electro-galvanized steel plate, hot-dip galvanized steel plate or galvanized steel plate as substrate after surface degreasing, phosphating, chromate treatment, and coated with organic coating. .
The common coatings for color coated steel sheets are polyester (BHP XRW coating system, Baosteel JZ, Korea PGS, Taiwan PE), followed by silicon resin (PSS), fluororesin (PVDF), etc. After coating and baking, the thickness of the coating is generally 20-25μ on the surface and 8-10μ on the back. Color coated steel sheets are generally quoted as ASTM A527 (galvanized), ASTM AT92 (aluminum galvanized), JIS G3302 in Japan, EN/0142 in Europe, KS D3506 in Korea, Q/BQB420 in Baosteel
Common steel grades for color steel plates
In China, for the selection of color coated steel sheets, users are concerned about steel grades. Because most of the domestic color coated steel production plants have fewer types of steel, most of them are DC51 (because they buy hot rolled sheets or rolled hard rolls is basically a steel type), some color coated steel sheets with hot-dip galvanizing lines It is difficult to produce all-hard steel (S550) or high-strength steel (S350, etc.) by hot-dip galvanizing, because they are uncontrollable on the quality and chemical composition of the substrate. Therefore, the quality stability is poor, resulting in large fluctuations in performance, resulting in deterioration of the profiled sheet.
For buildings, the weight of the load (wind load, snow load, construction workers and machinery), the span of the building, the design of the span, etc. all depend on the strength of the steel plate, and the color and galvanized sheet for the building maintenance structure. In terms of foreign countries, there are corresponding standards. Such as ASTM653, ASTM792 in the United States, JISG3302, JISG3321 in Japan, EN10215, EN10147 in Europe, and the like. Divided into CQ (common commercial grade), DQ (general stamping), HSS (high-strength structural steel), and FH (fully hard steel) according to the major types of steel.
(1) CQ common commercial grade
Non-ferrous metal smelters (copper, zinc, aluminum, lead, etc.) are the most challenging years for color coated steel sheets. However, reasonable selection of materials, design, and environmental protection can ensure or improve the service life of color coated steel. It should be possible to replace or maintain it for 10 years.
(2) DQ general stamping
Since the general color plates for construction are roll-formed or composite sandwiches, the punching performance of the materials is not high, so it is rarely used in the construction field (except for some door and window color plates).
(3) HSS high strength structural steel
According to the European standard HSS, it can be divided into 4-5 steel grades of different strengths. However, since ordinary CQ grade materials can replace low-strength HSS steels, the steel grades with yield strengths of 280Mpa and 345Mpa are used more on the market. The TSTE28 and TS350GD produced by Baosteel are the two steel grades.
Compared with ordinary CQ, HSS steel has several advantages:
(a) The steel has good fire resistance and shock resistance due to relatively low yield.
(b) For thicker steel plates, it can be used to make long span arched panels.
(c) For general exterior and roof panel types, it can be appropriately thinned compared to CQ materials, thereby saving material consumption.
(4) FH full hard steel
It is a kind of steel grade that improves the yield strength of steel plate by controlling the annealing temperature. According to the international common standard, the yield strength is ≥550Mpa and the tensile strength is ≥570Mpa. These materials have high strength and low elongation, and are suitable for forming steel plates with shallow plate shape, which can greatly save materials when used. Therefore, countries are eager to research and develop such steel grades. In foreign standards, materials with high strength and good elongation are also described. For example, HSLA (low alloy high strength) is used to add strengthening alloying elements during steel making. However, due to the high strength, there is a limit to increasing the rolling reduction rate during rolling in steel mills. Therefore, it is a thin color coated board for maintenance structure. HSLA steel grades are rarely used (another disadvantage is the high cost).
According to the experience of Baosteel’s many years of steel use, the guarantee of the final product form of color coated steel plate is closely related to the strength grade of the steel plate, the shape of the profiled steel plate and the processing machine.
In general, the more processing passes, the better the plate shape, the slower the processing speed and the better the plate shape. For the profiled steel plate type, the plate shape of the shallow wave plate is superior to the high wave plate. For the strength of the steel sheet, the tendency of the plate shape after strength processing is more pronounced.
Another reason for the relatively poor shape of high-strength steel is that a very colorful coating factory only reduces the annealing temperature of hot-dip galvanizing to increase the yield strength of the material, which leads to an imbalance of mechanical properties in the width direction of the steel sheet. This imbalance is caused by the uneven temperature of the strip in the entire width direction, and the temperature drop may cause the temperature of the part to be lower than the annealing temperature of the recrystallization of the steel sheet.
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