CN112251673B - Vehicle color steel plate with special coating structure and preparation method thereof - Google Patents
Vehicle color steel plate with special coating structure and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D1/00—Processes for applying liquids or other fluent materials
- B05D1/28—Processes for applying liquids or other fluent materials performed by transfer from the surfaces of elements carrying the liquid or other fluent material, e.g. brushes, pads, rollers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
- B05D3/0254—After-treatment
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
- B05D3/10—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by other chemical means
- B05D3/102—Pretreatment of metallic substrates
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
- B05D5/06—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
- C23C2/06—Zinc or cadmium or alloys based thereon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
- C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
- C23C2/36—Elongated material
- C23C2/40—Plates; Strips
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Abstract
A vehicle color steel plate with a special coating structure comprises the following components in percentage by weight: c: not more than 0.004%, not more than 0.03%, Mn: 0.7-0.8%, Cr: 0.035 to 0.055%, Nb: 0.01 to 0.02%, Ti: 0.035-0.050%, P: less than or equal to 0.020%, S: less than or equal to 0.030 percent, Als: 0.015-0.060% and N is less than or equal to 0.005%; the process comprises the following steps: pickling, cold rolling, annealing and galvanizing; finishing; a pretreatment process; and (5) color coating process. The invention solves the environmental protection problem of the existing automobile panel due to post painting, provides a 1/1 special structure coating which not only meets the requirement of special automobile manufacturers and mechanical property, but also has good anti-aging property without processing strain lines in the processing process, after the substrate is subjected to color coating, the yield strength change value AI is less than or equal to 5MPa, and the front surface and the back surface both meet the following requirements: the reverse impact is more than or equal to 9J, the T bend is less than or equal to 2T, no crack and no bright spot are generated on the surface of the T bend when the T bend is observed by a magnifying glass of 10 times, and passivation and oiling are not needed.
Description
Technical Field
The invention relates to a color-coated sheet and a preparation method thereof, and particularly belongs to a vehicle color steel plate with a special coating structure and a preparation method thereof.
Background
The color plate market of China is mainly building plates, and thin-specification and high-strength color plates dominate the market. With the development of color-coated sheet technology, the application of household appliance color sheets is very common, and with the enhancement of national environmental awareness, the application of color sheets is expanding to wider fields.
Environmental problems are the most notable worldwide problem in the development of the coil coating industry. According to the directive of the european market on the Volatile Organic Compound (VOC) content emitted by the large-scale painting of automobile bodies and by industrial metal coatings, all these sectors of the automobile industry will be forced to reconsider their existing post-painting processes. With the continuous enhancement of environmental protection consciousness of automobile enterprises in China, the application cognition of the color-coated sheet is also improved, which undoubtedly creates a very favorable opportunity for promoting the development of coil steel coatings. The color plate special for the automobile with the special coating structure is developed as the automobile stamping deformation is relatively complex.
The special car shell is produced by adopting the special car color plate with the special coating structure, the processes of degreasing, phosphorization and primary coating can be omitted, and finish paint is directly sprayed according to the requirements of the finish paint after stamping, so that the labor cost is greatly saved, and the emission is reduced.
The special color plate for the special coating structure not only needs to meet the production rhythm of the special vehicle, but also needs to ensure the required strength and excellent processing performance.
Disclosure of Invention
The invention aims to expand the application field of color-coated sheets, relieve the environmental protection pressure of the existing automobile panels due to post-painting, provide a 1/1 special structure coating which not only meets the production requirements of special automobile manufacturers, but also has good anti-aging performance without processing strain lines in the processing process, after the hot-dip galvanized substrate is subjected to the color-coating process, the yield strength change value AI is less than or equal to 5MPa, and the front surface and the back surface both meet the following requirements: the reverse impact is more than or equal to 9J, the T bend is less than or equal to 2T, and after the T bend, a magnifier of 10 times is used for observing the surface of the vehicle color steel plate with a special coating structure without cracks and bright spots and the preparation method thereof.
The measures for realizing the aim are as follows:
a vehicle color steel plate with a special coating structure comprises the following components in percentage by weight: c: not more than 0.004%, not more than 0.03%, Mn: 0.7-0.8%, Cr: 0.035 to 0.055%, Nb: 0.01 to 0.02%, Ti: 0.035-0.050%, P: less than or equal to 0.020%, S: less than or equal to 0.030 percent, Als: 0.015-0.060%, N is less than or equal to 0.005%, and the balance is Fe and inevitable impurities.
Preferably: the content of C is not more than 0.003 percent by weight.
Preferably: the Cr content by weight percentage is as follows: 0.039-0.050%.
Preferably: the Ti content by weight percentage is as follows: 0.038-0.050%.
The method for preparing the vehicle color steel plate with the special coating structure comprises the following steps:
1) acid washing, cold rolling, annealing and galvanizing: controlling the annealing temperature to be 735-750 ℃; the temperature of the strip steel in a zinc pot is 459-472 ℃;
2) and (3) finishing: performing finishing on the premise of not passivating the surface of the steel plate and not coating oil, and controlling the finishing elongation rate to be 1.2-1.4%;
3) carrying out a pretreatment process:
A. carrying out spray type foam-free degreasing alkali washing: controlling the alkali washing temperature to be 49-58 ℃, the solution conductivity to be 10-14 ms/cm and the spraying pressure to be 3.5-4.5 MPa; controlling the running speed of the steel plate to be 120-146 m/min;
B. brushing with desalted water: controlling the temperature of the desalted water in the cleaning tank to be 43-58 ℃, and brushing until no residue is left on the surface of the steel plate;
C. rinsing with desalted water: controlling the temperature of the desalted water to be 48-53 ℃ and the conductivity to be less than or equal to 30 mu s/cm;
D. carrying out alkali film formation: controlling the conductivity of the basic film-forming solution to be 50-65 ms/cm, the film-forming temperature to be 45-55 ℃, and the alkali ratio in the basic film-forming solution to be 0.8-1.4; controlling the total content of cobalt and nickel in the film forming layer to be 7-15 mg/m2, wherein the cobalt content is 75-92%;
E. rinsing with desalted water: controlling the temperature of the desalted water to be 38-45 ℃ and the conductivity to be less than or equal to 30 mu s/cm;
F. performing chromate film forming, wherein the total acidity (chromium points) in the chromate treatment liquid is controlled to be 18-25/5 ml;
G. baking and cooling: the baking temperature is 175-200 ℃; water cooling is adopted, and coiling is carried out when the water cooling temperature is not more than 40 ℃;
4) performing a color coating process:
A. and (3) roller coating: coating by adopting a two-roller reverse coating mode, coating epoxy back paint on the front side and the back side, controlling the thickness of the front and back side coating to be 10-12 mu m, and controlling the thickness difference of the front and back side coating to be not more than 1 mu m;
B. baking and curing: adopting a five-section variable-temperature baking system: the first section baking temperature is controlled to be 225-235 ℃, the second section baking temperature is controlled to be 235-245 ℃, the third section baking temperature is controlled to be 260-270 ℃, the fourth section baking temperature is controlled to be 255-265 ℃, the fifth section baking temperature is controlled to be 230-240 ℃, and the temperature of a steel plate at the outlet of a fifth section baking furnace is controlled to be 232-238 ℃;
C. cooling and coiling: and (5) cooling the steel plate by water until the temperature of the steel plate is not more than 40 ℃ and coiling the steel plate.
It is characterized in that: the alkaline aqueous solution comprises the following raw materials in percentage by weight: sodium hydroxide: 1.2-3.0%, borate: 0.03-0.12%, no foam surfactant: 0.015-0.063%, the rest is deionized water or desalted water.
It is characterized in that: the basic film-forming solution comprises the following raw materials in percentage by weight: alkaline treatment liquid: 2.4-4.0%, nickel nitrate: 0.015-0.035%, cobalt nitrate: 0.055-0.096% and the balance deionized water or desalted water.
Mechanism and action of each element and main process in the invention
The C content of the invention is selected to be less than or equal to 0.004%, and preferably the C content is not more than 0.003%. Since cementite is the cathode relative to carbon steel (the matrix is ferrite). Therefore, when the carbon content is increased, the number and area of the cathodes are increased, and accordingly, the corrosion current thereof is increased, thereby causing the corrosion resistance thereof to be lowered. Carbon is known to be the most effective solid solution strengthening element, and therefore, carbon steel gradually hardens with an increase in carbon content, while its cold working (stamping, drawing) and welding properties deteriorate. In addition, the higher the carbon content in steel is, the more the iron-zinc reaction is, the greater the loss of iron, and the thicker the iron-zinc alloy layer becomes, which deteriorates the adhesiveness of the zinc coating. On the other hand, the C content is as low as possible in order to ensure good anti-aging properties of the product. By combining the factors, the C content needs to be strictly controlled on the premise of ensuring the mechanical property of the color-coated sheet, and the carbon content is less than or equal to 0.004 percent.
The Si content of the invention is less than or equal to 0.03 percent, and the Si content is preferably not more than 0.002 percent. Silicon is a strong solid solution strengthening element, and the strength of steel can be improved by adding a certain amount of silicon, but the high silicon content in steel matrix has adverse effect on hot galvanizing. As the silicon content in the steel base increases, the SiO2 content generated by oxidation of silicon increases, which affects the effect of the subsequent pickling process, and when SiO2 remains on the surface of the steel sheet after pickling, the ζ phase of the iron-zinc alloy layer in the plated layer after galvanizing becomes drastically thick, a gray plated layer is formed, and the adhesion of the plated layer deteriorates. Therefore, the silicon content must be controlled within a suitable range. Therefore, the Si content is less than or equal to 0.03%.
The Mn content of the invention is 0.7-0.8%. Mn strengthens ferrite and also increases the strength of the precoat base material by solid solution. In addition, the addition of manganese to steel prevents embrittlement of steel due to sulfur during hot working, but as the Mn content of the color-coated sheet is higher, the workability thereof is gradually decreased. Therefore, the Mn content is 0.7 to 0.8%.
The Cr content of the invention is selected to be 0.035-0.055%, preferably the Cr content is: 0.039-0.055%. The addition of Cr to steel can improve the strength and hardness, and the reduction of area and the elongation are also slightly improved, on the other hand, the addition of Cr can improve the corrosion resistance of steel and the corrosion resistance of a matrix. Therefore, the Cr content is 0.035 to 0.055.
The Nb content is selected to be 0.01-0.02%. Nb is a typical microalloying element. Nb in steel is characterized by increasing the recrystallization temperature of austenite, thereby achieving the purposes of refining austenite grains and improving the yield strength of the steel. However, when the Nb content is more than 0.03%, the strengthening effect begins to decrease, so that the Nb content is 0.01 to 0.02%.
The Ti content of the invention is 0.035-0.050%. Ti is also a typical microalloying element. Both it and N, O, C have very strong affinity. In addition, the affinity of Ti and S is greater than that of Fe and S, so that titanium sulfide is preferentially generated in the steel containing Ti, the probability of producing iron sulfide is reduced, and the hot brittleness of the steel can be reduced. The carbide formed by Ti and C has strong binding force, is extremely stable and is not easy to decompose, the carbide begins to be slowly dissolved in the solid solution only when the heating temperature is higher than 1000 ℃, and the TiC particles have the function of preventing the steel grains from growing and coarsening before the TiC particles are not dissolved. Ti can also produce insoluble carbide particles with Fe and C, is enriched at the grain boundary of steel to prevent the coarsening of the steel grains, and can also be dissolved in gamma and alpha phases to form solid solution to strengthen the steel. Therefore, the addition amount of Ti should be controlled to be 0.035-0.050%.
The content of P in the invention is less than or equal to 0.020%. In general, for precoat base materials that are required to have good corrosion resistance, the phosphorus content is preferably as low as possible, since phosphorus is easily segregated, causing embrittlement of steel, deterioration in weldability, and the like, and therefore, the P content is 0.020% or less.
The S content of the invention is less than or equal to 0.030 percent. In general, S is a harmful impurity element in steel, and the smaller the content of S, the better the corrosion resistance. Therefore, the S content is less than or equal to 0.020%.
The content of Als is 0.015-0.06%. The addition of Al in the steel can form acid-soluble aluminum (Als) and acid-insoluble aluminum, the Als comprises solid-solution aluminum and AlN, and dispersed AlN particles can prevent austenite grains from growing and refine the grains. However, in the case of low carbon aluminum killed steel, the amount of inclusions in the steel increases with the increase of Als, and the size of inclusions also increases, which results in deterioration of the coating adhesion, corrosion resistance and press workability of the color-coated sheet. But in order to ensure that N and Al in steel are fully combined to generate AlN, reduce the aging of a finished product of a color-coated plate, completely deoxidize molten steel and the surface quality of a continuous casting billet, Als is ensured to be more than or equal to 0.01 percent. Therefore, the content of the solAl is selected to be 0.015 to 0.06 percent.
The content of N in the invention is less than or equal to 0.005 percent. Like C, N is a solid solution element. As the content of N in the steel increases, the punching workability of the steel is deteriorated (for example, the values of N and r are reduced), and meanwhile, the solid solution of N is a main cause of aging of the precoat raw sheet finished product, and particularly, the influence of nitrogen is large for the strain aging effect after flattening, so that N is required to be as low as possible. Therefore, the N content in the steel should be less than or equal to 0.005%.
The annealing temperature is controlled to be 735-750 ℃, and a low-temperature recrystallization annealing mode is adopted, so that compared with the high-temperature annealing (above 800 ℃) of the conventional IF steel, the method can reduce the gas consumption in the furnace, and achieve the aim of low-cost green manufacturing.
The invention adopts a two-roller reverse coating mode to carry out one-time coating (1/1), the front and the back surfaces are coated with high-performance epoxy back paint, the thickness of the film layer is controlled to be 10-12 mu m by optimizing the coating process, and the thickness difference of the front and the back surface film layers is required to be not more than 1 mu m. Is due to the following: 1) the front side and the back side are coated with epoxy back paint, so that the subsequent stamping processing of a user is facilitated, and the time and the cost for distinguishing the front side and the back side are saved; 2) compared with an 2/1 or 2/2 coating structure (one coating is adopted when the back film thickness is 5 microns, two coatings are generally adopted when the back film thickness is more than 8 microns), the cost can be saved by adopting a 1/1 one-step coating mode.
The five-section variable-temperature baking is adopted, so that the 1/1-structured coating has good coating performance, wherein the temperature of the 1 section and the 2 section in the five-section variable-temperature process is slightly lower, so that the solvent in the paint film can be fully volatilized before the paint film is cured; the temperature of the 3 section and the 4 section is slightly higher to ensure the complete curing of the coating; the temperature of the steel plate at the outlet of the baking furnace is controlled to be 232-238 ℃ in the 5-section temperature setting, so that the curing quality of the organic coating is ensured.
Description of the drawings: in each embodiment of the invention, the raw material composition and the weight percentage content of the alkaline aqueous solution are all in the following limited ranges: sodium hydroxide: 1.2-3.0%, borate: 0.03-0.12%, no foam surfactant: 0.015-0.063%, the rest is deionized water or desalted water, and the components are uniformly mixed for use.
Similarly, the basic film-forming solution in each example of the present invention has the following raw material composition and weight percentage content: alkaline treatment liquid: 2.4-4.0%, nickel nitrate: 0.015-0.035%, cobalt nitrate: 0.055-0.096%, the rest is deionized water or desalted water, and the components are uniformly mixed for use.
Compared with the prior art, the invention solves the environmental protection problem of the prior automobile panel due to post painting, provides 1/1 special structure coating which meets the production requirement of special automobile manufacturers and mechanical property, has no processing strain line in the processing process, namely has good anti-aging property, the yield strength change value AI is less than or equal to 5MPa after the hot galvanizing substrate is subjected to the color coating process, and both the front side and the back side meet the following requirements: the reverse impact is more than or equal to 9J, the T bend is less than or equal to 2T, and no crack and no bright spot exist on the surface of the glass observed by a magnifying glass of 10 times after the T bend.
Drawings
FIG. 1 is a metallographic structure diagram of the present invention.
Detailed Description
The present invention is described in detail below:
table 1 is a list of chemical compositions of each example and comparative example of the present invention;
table 2 shows the main process parameters of each example and comparative example of the present invention;
table 3 shows the performance results of the examples of the present invention and the comparative examples.
The preparation method comprises the following steps:
1) acid washing, cold rolling, annealing and galvanizing: controlling the annealing temperature to be 735-750 ℃; the temperature of the strip steel in a zinc pot is 459-472 ℃;
2) and (3) finishing: performing finishing on the premise of not passivating the surface of the steel plate and not coating oil, and controlling the finishing elongation rate to be 1.2-1.4%;
3) carrying out a pretreatment process:
A. carrying out spray type foamless degreasing and alkali washing: controlling the alkali washing temperature to be 49-58 ℃, the solution conductivity to be 10-14 ms/cm and the spraying pressure to be 3.5-4.5 MPa; controlling the running speed of the steel plate to be 120-146 m/min;
B. brushing with desalted water: controlling the temperature of the desalted water in the cleaning tank to be 43-58 ℃, and brushing until no residue is left on the surface of the steel plate;
C. rinsing with desalted water: controlling the temperature of the desalted water to be 48-53 ℃ and the conductivity to be less than or equal to 30 mu s/cm;
D. carrying out alkali film formation: controlling the conductivity of the basic film-forming solution to be 50-65 ms/cm, the film-forming temperature to be 45-55 ℃, and the alkali ratio in the basic film-forming solution to be 0.8-1.4; controlling the total content of cobalt and nickel in the film forming layer to be 7-15 mg/m2, wherein the cobalt content is 75-92%;
E. rinsing with desalted water: controlling the temperature of the desalted water to be 38-45 ℃ and the conductivity to be less than or equal to 30 mu s/cm;
F. performing chromate film forming, wherein the total acidity (chromium points) in the chromate treatment liquid is controlled to be 18-25/5 ml;
G. conventional baking and cooling: the baking temperature is 175-200 ℃; water cooling is adopted, and coiling is carried out when the water cooling temperature is not more than 40 ℃;
4) performing a color coating process:
A. and (3) roller coating: coating by adopting a two-roller reverse coating mode, coating epoxy back paint on the front side and the back side, controlling the thickness of the front and back side coating to be 10-12 mu m, and controlling the thickness difference of the front and back side coating to be not more than 1 mu m;
B. baking and curing: adopting a five-section variable-temperature baking system: the first section baking temperature is controlled to be 225-235 ℃, the second section baking temperature is controlled to be 235-245 ℃, the third section baking temperature is controlled to be 260-270 ℃, the fourth section baking temperature is controlled to be 255-265 ℃, the fifth section baking temperature is controlled to be 230-240 ℃, and the temperature of a steel plate at the outlet of a fifth section baking furnace is controlled to be 232-238 ℃;
C. cooling and coiling: and (5) cooling the steel plate by water until the temperature of the steel plate is not more than 40 ℃ and coiling the steel plate.
TABLE 1 tabulated (wt%) chemical compositions for inventive and comparative examples
TABLE 2 Main Process parameters of the examples of the invention and comparative examples
TABLE 2-1
Tables 2-2
Table 3 performance results for inventive and comparative examples
As can be seen from the above table 3, the yield strength of the automotive color plate is controlled to be 270-310 MPa, the elongation is more than or equal to 32%, the yield strength change after color coating baking aging is less than 5MPa, and the automotive color plate has good anti-aging performance; this colored steel is 1/1 coating structure, and two-sided being epoxy back paint, the thick control of membrane is at 10~12 um, and positive and negative two sides all satisfy: the reverse impact is more than or equal to 9J, the T bend is less than or equal to 2T, and no crack and bright spot (exposed zinc spot) exist on the surface of the glass when the glass is observed by a magnifying glass of 10 times after the T bend.
The above examples are merely preferred examples and are not intended to limit the embodiments of the present invention.
Claims (3)
1. A preparation method of a vehicle color steel plate with a special coating structure comprises the following steps:
1) acid washing, cold rolling, annealing and galvanizing: controlling the annealing temperature to be 735-750 ℃; the temperature of the strip steel in a zinc pot is 459-472 ℃;
2) and (3) finishing: performing finishing on the premise of not passivating the surface of the steel plate and not coating oil, and controlling the finishing elongation to be 1.2-1.4%;
3) carrying out a pretreatment process:
A. carrying out spray type foam-free degreasing alkali washing: controlling the alkali washing temperature to be 49-58 ℃, the solution conductivity to be 10-14 ms/cm and the spraying pressure to be 3.5-4.5 MPa; controlling the running speed of the steel plate to be 120-146 m/min;
B. brushing with desalted water: controlling the temperature of the desalted water in the cleaning tank to be 43-58 ℃, and brushing until no residue is left on the surface of the steel plate;
C. rinsing with desalted water: controlling the temperature of the desalted water at 48-53 ℃ and the conductivity of the desalted water is less than or equal to 30 mus/cm;
D. carrying out alkali film formation: controlling the conductivity of the basic film-forming solution to be 50-65 ms/cm, the film-forming temperature to be 45-55 ℃, and the alkali ratio in the basic film-forming solution to be 0.8-1.4; controlling the total content of cobalt and nickel in the film formation layer to be 7-15 mg/m2Wherein the cobalt content is 75-92%;
E. rinsing with desalted water: controlling the temperature of desalted water to be 38-45 ℃ and the conductivity to be less than or equal to 30 mus/cm;
F. performing chromate film forming, and controlling the total acidity in the chromate treatment liquid to be 18-25 per 5 ml;
G. conventional baking and cooling: the baking temperature is 175-200 ℃; water cooling is adopted, and coiling is carried out when the water cooling temperature is not more than 40 ℃;
4) performing a color coating process:
A. and (3) roller coating: coating by adopting a two-roller reverse coating mode, coating epoxy back paint on the front side and the back side, controlling the thickness of the front and back side coating to be 10-12 mu m, and controlling the thickness difference of the front and back side coating to be not more than 1 mu m;
B. baking and curing: adopting a five-section variable-temperature baking system: the first section baking temperature is controlled to be 225-235 ℃, the second section baking temperature is controlled to be 235-245 ℃, the third section baking temperature is controlled to be 260-270 ℃, the fourth section baking temperature is controlled to be 255-265 ℃, the fifth section baking temperature is controlled to be 230-240 ℃, and the temperature of a steel plate at the outlet of a fifth section baking furnace is controlled to be 232-238 ℃;
C. cooling and coiling: water cooling is carried out until the temperature of the steel plate does not exceed 40 ℃, and then coiling is carried out;
the automobile color steel plate with the special coating structure comprises the following components in percentage by weight: c: not more than 0.004%, not more than 0.03%, Mn: 0.7-0.8%, Cr: 0.035 to 0.055%, Nb: 0.01-0.03%, Ti: 0.035-0.050%, P: less than or equal to 0.020%, S: less than or equal to 0.030 percent, Als: 0.015-0.060%, N is less than or equal to 0.005%, and the balance is Fe and inevitable impurities.
2. The method for preparing the vehicle color steel plate with the special coating structure according to claim 1, wherein the method comprises the following steps: the water solution adopted by the spray type foamless degreasing alkali washing comprises the following raw materials in percentage by weight: sodium hydroxide: 1.2-3.0%, borate: 0.03-0.12%, no foam surfactant: 0.015-0.063%, the rest is deionized water or desalted water.
3. The method for preparing the vehicle color steel plate with the special coating structure according to claim 1, wherein the method comprises the following steps: the basic film-forming solution comprises the following raw materials in percentage by weight: alkaline treatment liquid: 2.4-4.0%, nickel nitrate: 0.015-0.035%, cobalt nitrate: 0.055-0.096% and the balance deionized water or desalted water.
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