Detection and analysis of the performance of high-strength color coating plates

0 Introduction
coated steel plate (color plate) is organic coated steel plate, also known as pre-coated steel plate. It is a metal strip steel as a substrate (e.g. cold-rolled steel plate, hot galvanized plate, electro-galvanized plate, etc.) through strict process control, on its surface coated with a variety of polymer coatings (e.g. polyester, silicone polyester, polyfluoroethylene resin, etc.) or pasted with a variety of plastic films (e.g. polyethylene film, etc.) made of products. It has excellent corrosion resistance, durability, cold bending molding, decoration and good economic and environmental protection effects, available for direct use by users, widely used in construction, home appliances
, transportation and other industries
. At present, China's color coated plate is mainly used in the field of construction, such as residential steel structure, high-rise steel structure, light steel structure, etc. , the amount of the total domestic color plate production accounted for more than 85%. In order to increase the strength, weight and cost reduction of building components, more and more color plate users have adopted high strength (e.g. yield strength of 350 MPa), thin specifications (plate thickness less than 0.8 mm) color plate. At present, some automotive exterior plates have also begun to try to use high-intensity color coating plate, such as a COSCO Group export to North America van exterior plate on the thickness of between 0.4 to 0.5 mm, yield strength of 350 MPa color coated steel plate. In this paper, the properties of the high-strength TS350 GD-Z color plate developed by Wugang are studied, including the gold phase tissue of the substrate, the composition of the substrate clamps, the mechanical properties, the physical properties of the coating, the corrosion resistance of salt spray, etc., and the test results are analyzed.
1 Test materials and methods
1.1 test materials
test materials for Wugang developed TS350 GD-Z color plate steel plate, using 250 t furnace smelting, chemical composition see Table 1, paint used in color coatings see Table 2.
TS350 GD-Z color plate with steel plate chemical composition
color coating used in the paint
TS350 GD-Z color plate performance test samples are randomly selected at the scene of Wugang two cold-rolled color plate production unit, product size 0.45 mm ×1,253 mm×L mm, galvanized layer mass of 275 g/m2 (double-sided).
1.2 The test method
The main manufacturing process of TS350 GD-Z color plate is as follows: First, by iron water desulfurization, converter smelting, steel water will be continuously cast into billets, and then cast blank hot roll into steel strips, and then hot-rolled steel belt for acid washing, cold rolling, and then cold-rolled steel belt for hot galvanizing, color coating.
tests used in this test are carried out in accordance with relevant national standards or process requirements.
the gold phase tissue, grain size, etc. of the color plate substrate tested with ALYMPUS G×71, the plagiarism and galvanizing layer composition of the color plate substrate were analyzed with Quanta400 scanning electron microscope (SEM), the coating composition of the color plate was analyzed with GD PROFILERHR Glow Spectrometer (GDS), and the coating composition of the color plate was detected with ST-ISO-3 salt mist tank Performance, salt spray test temperature is (35±2) degrees C, the concentration of sodium chloride solution is 5%, before the test in the sample surface cross-line, sample placement angle and vertical direction of 15 degrees, the dash according to GB / T 13448-2006, unlined area bubbles and rust rating according to GB / T 1766-1995. The detection method of coating physical properties (e.g. film thickness, pencil hardness, gloss, cup protrusion value, T bend value, impact value, etc.) shall be carried out according to GB/T 13448-2006.
2 Test board performance test results and analysis
2.1 gold phase analysis
of the trial TS350 GD-Z substrate for tissue, grain size, free carbon seeer level, clamping level analysis, the results can be seen in Table 3, Figure 1.
from Table 3, Figure 1 can be drawn: TS350 GD-Z tissue for ferring body and pearlesome body and a small amount of free carbon seepage body, grain size of 12, indicating that TS350 GD-Z steel grain is fine, in order to ensure the high strength of TS350 GD-Z color plate laid a good foundation. The clamping level is D1, which indicates that the steel is pure, which is beneficial to improve the processing and molding performance of the TS350 GD-Z color plate.
2.2 Scanning electroscope analysis
the test of the TS350 GD-Z color plate substrate debris, coating composition of the electro-mirror (electronic needle, energy spectrum) analysis, the test results are shown in Table 4, Table 5, Figure 2.
The results of the electronic probe analysis of the substrate clamps, the results of the analysis of the composition of the galvanized layer of the color plate, and the micromorphism of the galvanized layer of the SEM analysis of the color plate of the color plate
can be seen from Table 4: the substrate of the TS350 GD-Z is mainly grainy Al2O3, while the column-shaped Al2O3 is less, which is conducive to improving the processing performance of TS350 GD-Z. From Figure 2, it can be seen that the galvanizing layer is continuous and uniform, which lays a good foundation for ensuring the adhesion and corrosion resistance of the galvanized layer.
2.3 Glow Spectroscopy analysis
the two TS350 GD-Z color plate galvanized layers and coating components were tested for glow spectral analysis, the results of which are shown in Figures 3 and 4.
Graphite gray plate coating structure and composition analysis, ink black color plate coating structure and composition analysis
from Figure 3, Figure 4 can be seen: the trial TS350 GD-Z product zinc layer thickness of 20 to 35 m;
2.4 Technical properties and zinc layer adhesion
According to the chemical composition and finished product specifications of TS350 GD-Z steel, the main process parameters for the design of hot galvanizing are as follows: unit speed≥120 m/min The aeration temperature is ≥750 degrees C, the zinc liquid temperature is (450 to 470 degrees C), the extension rate of light is ≥0.4%, and the elongation rate of pull is ≥0.5%. The statistical results of the detection of the properties of the metal and the adhesion of the zinc layer can be found in Table 6.
TS350 GD-Z thermal galvanizing plate performance and zinc layer adhesion statistics
as can be seen from Table 6: The trial TS350 GD-Z has a force performance of GB/T 1 2754-2006 "R P0.2 (or R eH) ≥350 MPa; R m≥420 MPa; A 80mm ≥14%" requirement. Yield strength range is controlled in (350-425) MPa, pull strength range is controlled at (445-515) MPa, mechanical performance fluctuations are small, indicating that the TS350 GD-Z production of the process control is more stable. Zinc layer adhesion is level 1, indicating that the galvanized layer adhesion is good.
factors that determine the mechanical properties of high-strength color plates are the chemical composition of the substrate and the thermal galvanizing defying process. In general, in order to increase the strength of color plate, more alloy elements such as Mn, Si, A1, Cr, P, Ti, Nb, Mo have been added to the high-strength color plate steel. Some of these elements are prone to surface abundance, such as Mn, Si, A1, Ti, Nb, etc., which are more affinity with oxygen than Fe and may be oxidizing. In the process of continuous hot galvanizing production, alloy elements continue to spread from the inside of the steel plate to the surface, and constantly oxidize, so that the alloy elements on the surface of the steel plate more and more, resulting in the alloy elements in the form of oxides on the surface of the rich, resulting in a thin film of oxidation, this thin oxide film will have an adverse effect on the adhesion of the coating and corrosion resistance of the color plate. Therefore, the selection of alloy elements is not only beneficial to the performance of the color plate substrate, but also consider the effect on the plating of the steel plate, considering the role of individual elements, but also considering the effect of interaction between elements.
In short, for high-strength color plate products, should be guaranteed strength at the same time, as far as possible in the steel less alloy elements, more use of hot-rolled, cold-rolled and hot galvanized production process parameters to improve the high-strength color plate coating adhesion and corrosion resistance, reduce production costs.
2.5 coating physical performance
color coating production unit speed ≥80 m/min, lye concentration ≥1.5%, lye temperature of 50 to 80 degrees C, coating curing temperature (PMT) of 220 to 245 degrees C, finish curing time ≤1 min, coating surface type of 2/2, color plate front coating physical performance test results are 7. As can be seen from Table 7, the physical properties of the trial TS350 GD-Z color plate products meet the quality requirements of GB/T 12754-2006.
TS350 GD-Z thermal galvanizing plate performance and zinc layer adhesion statistics
2.6 salt spray corrosion test
the test time is 500 h, the fog reduction is 1.3 mL/ (80 cm2.h), salt spray test evaluation results are seen in Table 8.
3 kinds of TS350 GD-Z color plate salt spray test results
From Table 8, it can be seen that the trial production of 3 kinds of TS350 GD-Z color plate products resistant to salt spray corrosion performance has reached GB /T 12754-2006 quality requirements.
3 Conclusion
(1) For high-strength color plate, the selection of alloy elements in steel should not only be conducive to the mechanical properties of the color plate substrate, but also consider the impact on the plating of steel plate, should be guaranteed strength at the same time, as little alloy elements as possible in the steel, more methods to change the parameters of the production process to improve the strength and corrosion resistance of color plate, reduce production costs.
(2) the trial production of TS350 GD-Z color plate products have reached GB / T12754-2006 indicators.