Environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel

Abstract

The present invention belongs to the technical field of surface treatment of metal materials, and particularly relates to an environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel. The aqueous treatment agent is prepared by dissolving or dispersing a composition in an aqueous medium. The specific composition of the aqueous treatment agent is: A. A compound selected from compounds containing fluoride ions; B. A compound selected from metal ion compounds containing Cu, Zn, Mn, Ni, and Fe; C. A compound selected from organic acids; D. A compound selected from surfactants. The aqueous treatment agent may be diluted by adding 0 to 20 parts of water to 1 part of the treatment agent before use. The treatment agent can impart excellent phosphatability to the surface of high-strength steel sheets and is mainly applied to the surface modification treatment of high-strength steel.

Description

Technical Field

[0001] The present invention relates to the technical field of surface treatment of metal materials, and in particular, to an environmentally friendly aqueous treatment agent for high-strength coil steel surfaces that can impart excellent phosphatability to the surface of high-strength steel plates and is mainly applied to surface modification treatment of high-strength steel.

Background Art

[0002] The phosphate treatment process born in the early 20th century is currently widely used in the pre-painting treatment process of automobiles / household appliances. After a century of technological development, a very mature technical system has already been formed in terms of the formulation of phosphate treatment solutions, film-forming mechanisms, and action mechanisms. Phosphate treatment mainly involves bringing a phosphate treatment solution into contact with the surface of a steel plate, and through acid erosion and the oxidation action of an accelerator, rapidly reducing the hydrogen ion content in the interface region, gradually dissociating phosphate ions, and forming metal ions and phosphate precipitates. A phosphate layer that uniformly, finely, and completely covers the metal surface can effectively improve the adhesion of the coating and the corrosion performance under the coating film. Conventional automobile bodies are usually applied with normal cold rolling, and when combined with zinc plating materials and phosphate treatment, good and stable effects can be obtained. Currently, the problem of phosphate treatment application for automotive materials with novel surface characteristics is relatively prominent and is also a research hot spot in the industry.

[0003] In recent years, with the progress of steel material technology, the application of ultra-high-strength steel has become increasingly widespread. Especially in high-strength steel for automobiles, due to its remarkable effects from the perspectives of safety, environmental protection, and weight reduction, the ultra-high-strength steel material technology has entered a stage of rapid development and generalization. On the other hand, ultra-high-strength steel requires the addition and use of more alloying elements, which directly changes the surface properties of the material. According to research, the compositions formed by elements such as Mn, Si, and Cr through selective oxidation are unevenly distributed on the surface of the steel plate, often causing problems such as coarsening of crystals and poor coating during the phosphate treatment process, significantly reducing its phosphate treatability and unable to meet the requirements of coating applications. In response, major domestic and foreign steel manufacturers have conducted a lot of technical research to optimize the phosphate treatability of the high-strength steel surface. Most of them focus on the control of selective oxidation of elements such as Mn, Si, and Cr on the extreme surface of the steel plate (for example, CN102834531, CN102482728, CN102534359, CN108368590). This type of patented technology needs to ensure the control of surface selective oxidation precipitates while effectively balancing the degree of internal oxidation and the oxidation state of the extreme surface. The process window is narrow, the difficulty is high, and it is not compatible with materials of different composition systems, and it is necessary to design the process according to the material.

[0004] Patents related to the phosphate modification treatment technology for the surface of high-strength steel mainly include two technologies: surface electrolytic pickling to remove the oxidation enrichment layer and surface flash plating treatment to cover the oxidation enrichment layer. In publication numbers CN104136644, CN103124799, CN104508155, and CN103305749, methods for removing the oxidation enrichment layer on the surface of high-strength steel that affects phosphate treatability by the surface electrolytic pickling process of cold-rolled sheets are proposed. This type of technology has good workability and compatibility with materials of different composition systems, but it also has problems such as high energy consumption and being not environmentally friendly. It is necessary to add a pickling process and cannot be applied to the conventional high-strength steel manufacturing line.

[0005] In Publication No. CN104471115, in order to optimize the surface phosphating property and the mold release adhesion resistance, it was proposed to perform zinc plating treatment on the surface of a steel sheet by flash plating with a coating rate of 60% or more. At the same time, in the published literature, technologies for manufacturing high-strength steel with good phosphating properties by flash nickel plating, flash iron plating, etc. were also reported. This type of technology can endow the surface of the high-strength steel material with new stable properties by the plating layer, but the energy consumption is too large, it is not environmentally friendly, and it is necessary to add a plating process, which cannot be applied to the conventional high-strength steel production line.

[0006] The development of an environmentally friendly aqueous treatment agent that can optimally control the phosphating property of the high-strength steel surface is of great significance for the efficient practical application and generalization of high-strength steel technology for automobiles.

Summary of the Invention

Problems to be Solved by the Invention

[0007] The object of the present invention is to provide an environmentally friendly aqueous treatment agent for optimally modifying the phosphating property of the high-strength steel surface.

Means for Solving the Problems

[0008] Through theoretical analysis, a large number of laboratory scientific researches, and practical verifications, the technical route of the environmentally friendly aqueous treatment agent for nano-modification of a good phosphate-treated surface has been finally determined. According to the surface characteristics of typical high-strength steel, an aqueous treatment agent containing one or more components among fluorine-containing compounds, metal ion compounds, organic acid compounds, and surfactants is formed. The treatment agent can meet the requirements for application in the high-speed continuous production process of high-strength coil steel and the manufacturing process of processed parts. As a specific treatment method, a wet film can be formed on the surface of the steel plate by impregnation, spraying, roll coating, etc., and a surface modification layer with a thickness of several nanometers can be rapidly formed from the treatment agent on the surface of the steel plate by spraying or baking. The modified treatment layer can form epitaxial active nucleation sites having the same crystal orientation as the phosphate crystal on the surface of the steel plate, thereby significantly improving the phosphatability of the surface of high-strength steel plates containing high alloying elements (such as Mn, Si, Cr, Mo, etc.) without affecting the processing performance such as forming and joining.

[0009] The technical solution of the present invention is: An environmentally friendly surface modification aqueous treatment agent for phosphate treatment of high-strength steel products, wherein the surface treatment agent (aqueous treatment agent) is prepared by dissolving or dispersing a composition in an aqueous medium, and the specific composition of the surface treatment agent is: A. A compound selected from compounds containing fluoride ions; B. A compound selected from metal ion compounds containing Cu, Zn, Mn, Ni, Fe; C. A compound selected from organic acids; and D. A compound selected from surfactants; That's it.

[0010] As the use process of the surface treatment agent according to the present invention, 0 to 20 parts of water can be added to 1 part of the treatment agent for dilution and then used, or it can be used directly without adding water.

[0011] The metal ions according to the present invention are not limited to those in a specific valence state. The compound containing fluoride ions in the aqueous treatment agent according to the present invention includes one or more of ammonium fluorotitanate, ammonium fluorozirconate, potassium fluorotitanate, potassium fluorozirconate, etc. The content of F element in the solution is 0.3 - 1.8 mol / L in molar concentration, preferably 0.3 - 1.7 mol / L, and more preferably 0.6 - 1.1 mol / L. On the one hand, the additive can play a role in surface etching homogenization, and on the other hand, it can deposit titanium or zirconium in a spot-like manner on the material surface to form nucleation active sites contributing to the phosphate treatment. When the content of F element is less than 0.3 mol / L, the film-forming property of the surface treatment agent is poor, affecting the modification treatment effect. However, when the content of F element exceeds 1.8 mol / L, the stability of the surface treatment agent tends to decrease significantly.

[0012] One or more metal ion compounds containing Cu, Zn, Mn, Ni, and Fe in the aqueous treatment agent according to the present invention include sulfates, carbonates, nitrates containing copper ions, sulfates, phosphates, formates, acetates containing Zn ions, phosphates, carbonates, nitrates containing Mn ions, nitrates, oxalates containing Fe ions, sulfates, nitrates, carbonates containing Ni ions. The content of the metal ion compound in the solution is 0.05 - 0.6 mol / L in molar concentration, preferably 0.07 - 0.6 mol / L, and more preferably 0.1 - 0.25 mol / L. The main function of the additive is to further add isomorphous nucleation sites of phosphate crystals. When the content is less than 0.05 mol / L, the effect of effectively adding nucleation sites for phosphate treatment cannot be achieved. However, when the content exceeds 0.6 mol / L, the thickness of the modified film layer is too large, forming a uniform passivation effect, which directly affects the paintability of the treated surface.

[0013] The organic acid compounds in the aqueous treatment agent according to the present invention include organic acid compounds having a complex formation or chelate formation function, such as citric acid, oxalic acid, tannic acid, lactic acid, tartaric acid, and salicylic acid. In some embodiments, the organic acid compound is citric acid, oxalic acid, tartaric acid, or tannic acid. The content of the organic acid compound in the solution is 0.03 to 0.4 mol / L in molar concentration, preferably 0.05 to 0.2 mol / L. The compound has a certain cleaning effect on the surface of the steel sheet, and a part of the formed reaction product adheres to the surface of the steel sheet, thereby promoting the rapid nucleation and growth of the phosphate film. When the content is less than 0.03 mol / L, the surface cleaning effect is significantly reduced, but when the content exceeds 0.4 mol / L, it significantly affects the stability of the treatment agent system.

[0014] The compounds selected from the surfactants in the surface treatment agent according to the present invention mainly include sodium dodecyl sulfate, sodium dodecyl sulfonate, calcium dodecyl sulfonate, octadecylamine, triethanolamine, etc. The content of the surface treatment agent compound in the solution is 0.002 to 0.015 mol / L in molar concentration, preferably 0.003 to 0.01 mol / L. The main function of the additive is to improve the film-forming property of the treatment agent, reduce the surface tension after film formation, optimize the rapid wetting effect between the surface of the steel sheet and the phosphate treatment agent in the pre-painting treatment process, and achieve the purpose of improving the phosphate treatment property. When the content is less than 0.002 mol / L, the optimization of the film-forming property of the treatment agent becomes less significant, but when the content exceeds 0.015 mol / L, the film-forming quality of the treatment agent is significantly affected, and the effect of optimizing the phosphate treatment property after film formation is reduced.

[0015] The environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to the present invention can be applied to the continuous production lines of pickled high-strength steel and cold-rolled high-strength steel, and can form a wet film on the surface of the steel sheet by impregnation, spraying, roll coating, etc., and can rapidly form a nano-scale surface modification layer from the treatment agent on the surface of the steel sheet by spraying, baking, etc. The effect of significantly optimizing the phosphatability of the high-strength steel surface has been realized.

[0016] In some embodiments, the present invention provides a method for improving the phosphatability of high-strength steel, which includes treating the high-strength steel with the environmentally friendly aqueous treatment agent described in the present text by impregnation, spraying, roll coating, etc. In some embodiments, the method further includes treating the high-strength steel with a degreasing agent to remove dirt and oil adhered to its surface, then washing with pure water to remove the alkaline components remaining on the surface, spraying and drying, and then surface-treating the high-strength steel with the environmentally friendly aqueous treatment agent. In some embodiments, the high-strength steel is pickled high-strength steel or high-strength steel obtained by cold rolling.

[0017] In some embodiments, the present invention provides a method for phosphatizing high-strength steel, which includes treating the surface of high-strength steel using the method described in the present text, and then sequentially performing degreasing, water washing, surface conditioning, phosphatizing, water washing, and drying on the surface-treated high-strength steel.

[0018] In some embodiments, the present text further provides high-strength steel having a nano-scale surface modification layer formed by drying the surface treatment agent described in the present text on its surface. After being phosphatized, the high-strength steel has a phosphatized crystal coverage rate of ≧80%, preferably 100%, a phosphatized crystal size of ≦6 μm, preferably ≦4 μm, and a weight of the phosphate film of ≧2 g / m 2 and preferably ≧2.3 g / m 2Thus, in some embodiments, the present invention further provides a phosphate-treated steel sheet obtained by phosphate treating the high strength steel described herein, wherein the phosphate crystal coverage is ≥ 80%, preferably 100%, the phosphate crystal size is ≤ 6 μm, and the weight of the phosphate film is ≥ 2 g / m 2 The phosphate treatment described herein can be carried out using a conventional treatment agent (for example, PB-L3065 type phosphating solution). [Effects of the Invention]

[0019] Beneficial technical effects of the present invention: The present invention provides an environmentally friendly aqueous treatment agent for improving the phosphate treatability of high-strength steel so that the surface of high-strength steel plate has excellent phosphate treatability. The aqueous treatment agent of the present invention is an environmentally friendly aqueous treatment agent that can meet the requirements for application to high-speed continuous production processes of high-strength coil steel and manufacturing processes for processed parts without affecting processing performance such as forming and joining. DETAILED DESCRIPTION OF THE INVENTION

[0020] To facilitate a better understanding of the present invention, the present invention will be described in detail with reference to examples and comparative examples, but the scope of the present invention is not limited to these examples. The surface treatment agent compositions used and the types of treated steel sheets will be described below: (1) Test sample plate: The material used in the examples is a typical 80 kg class ultra-high strength steel with a standard of 1.2 mm, and the composition of the components is shown in Table 1.

[0021] [Table 1]

[0022] (2) Sample plate processing and cleaning method: The above materials were processed into sample pieces of 30*70 mm by shearing, spray-washed with an alkaline degreaser (pH = 11 - 12) to remove the dirt and oil adhering to the surface, then washed with pure water to remove the alkaline components remaining on the surface, blown dry with cold air, and then prepared for use.

[0023] (3) Composition of the aqueous surface treatment agent The composition formulation and treatment method of the environmentally friendly aqueous treatment agent used in the examples are shown in Table 2. However, Comparative Example 4 is the original surface material that is not surface-treated with the said treatment agent.

[0024]

Table 2

[0025] After the above-mentioned surface treatment sample plates obtained in the examples and comparative examples were subjected to a rust preventive oil coating treatment of 1000 mg / m 2 and left for one week, the phosphatability of the pretreatment before painting was evaluated. Referring to the pretreatment process before painting in an automobile factory mainly including the processes of degreasing, surface conditioning, and phosphate treatment, a simulation was carried out in the laboratory. Commercially available products from Parkerizing were used as the related treatment agents, and the specific process parameters are shown in Table 3.

[0026]

Table 3

[0027] After the sample plates were treated in the above-mentioned manner, the phosphate crystal coverage rate and crystal size were microscopically observed using a scanning electron microscope, and the weight of the phosphate film was measured by the chemical dissolution film method. The specific method was as follows.

[0028] (1) Evaluation of the phosphate crystal coverage rate Using a scanning electron microscope (equipment: Zeiss scanning electron microscope SIGMA 500), the phosphate-treated surface of the sample piece was observed at a magnification of 1000 times and evaluated by the coverage area ratio of the phosphate film.

[0029] ◎: Phosphate film coverage rate = 100% ○: 80% ≤ Phosphate film coverage rate < 100% △: 60% ≤ Phosphate film coverage rate < 80% ×: Phosphate film coverage rate < 60% [[ID=⑨]](2) Measurement of phosphate crystal size Using a scanning electron microscope (equipment: Zeiss scanning electron microscope SIGMA 500), the phosphate-treated surface of the sample piece was observed at a magnification of 2000 times. The length dimensions of 5 random phosphate crystals were measured using a ruler, and the average value was taken.

[0030] (3) Measurement of the weight of the phosphate film First, a 30*70 mm phosphate-treated sample plate was weighed (Mettler MS-TS analytical balance), and W0 was recorded. Next, the sample piece was immersed in a phosphate film stripping solution (solution: 50 g / L of anhydrous chromic acid, temperature: 75 °C), held for 15 min, then taken out, washed with deionized water for 40 s, blown dry with cold air, and then weighed for the second time, and W1 was recorded. The weight W of the phosphate film was obtained by calculation:

[0031]

Number

[0032] As can be seen from the implementation effects (shown in Table 4), Examples 1 to 6 all showed good phosphate treatability in all evaluation items. In particular, Examples 1, 2, 3, 4, and 6 had excellent comprehensive performance. As can be seen from the comparison between the examples and Comparative Example 4, the materials surface-treated with the treatment agent all showed a remarkable improvement in phosphate treatability. As can be seen from the comparison between Example 6 and Comparative Example 1, if the component content of the treatment agent is insufficient, it will be impossible to achieve an effective improvement in the phosphate treatability of the surface of the treated sample plate. As can be seen from Examples 1, 2 and Comparative Example 2, the phosphate treatability of the surface of the sample plate can be optimized by an appropriate amount of F-containing compound and metal salt addition amount. However, if added excessively, due to the increase in the film thickness, it is disadvantageous to the rapid growth of the phosphate film, and thus a phenomenon of reduced phosphate treatability appears. As can be seen from Example 4 and Comparative Example 3, the excessive addition of the surfactant affects the film-forming effect of the treatment agent, thereby significantly reducing the optimization effect of the phosphate treatability of the surface of the treated sample plate. As can be seen from Examples 3, 4, and 5, the treatment agent can be applied to typical coating treatment methods such as spraying, impregnation, and roll coating, and has better process compatibility.

[0033]

Table 4

[0034] Of course, as those skilled in the art can understand, the above examples are only for explaining the present invention and not for limiting the present invention. As long as it is within the scope of the substantial spirit of the present invention, any changes or modifications to the above examples are all included in the scope of the claims of the present invention.

Claims

1. An aqueous treatment agent prepared by dissolving or dispersing a composition in an aqueous medium, and the specific composition of the aqueous treatment agent is as follows: A. A compound selected from compounds containing fluoride ions; B. A compound selected from metal ion compounds containing Cu, Zn, Mn, Ni, and Fe; C. A compound selected from organic acids; D. A compound selected from surfactants An environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel, characterized by the above.

2. The compound containing fluoride ions is one or more selected from the group consisting of ammonium fluorotitanate, ammonium fluorozirconate, potassium fluorotitanate, and potassium fluorozirconate. The environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to Claim 1.

3. The content of element F in the aqueous treatment agent solution is 0.3 to 1.8 mol / L in molar concentration, preferably 0.3 to 1.7 mol / L, and more preferably 0.6 to 1.1 mol / L. The environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to Claim 1 or 2.

4. The metal ion compound containing Cu is selected from the group consisting of sulfates, carbonates, and nitrates containing copper ions; The metal ion compound containing Zn is selected from the group consisting of sulfates, phosphates, formates, and acetates containing Zn ions; [[ID= ​ ​ ​ ​ ​ ​ The organic acid compound is an organic acid compound having a complex formation or chelate formation function, and is preferably at least one selected from the group consisting of citric acid, oxalic acid, tannic acid, lactic acid, tartaric acid, and salicylic acid. An environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to claim 1.

7. The content of the organic acid compound in the aqueous treatment agent solution is 0.03 to 0.4 mol / L in molar concentration, preferably 0.05 to 0.2 mol / L. An environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to claim 1 or 6.

8. The compound selected from the surfactant is at least one selected from the group consisting of sodium dodecyl sulfate, sodium dodecyl sulfonate, calcium dodecyl sulfonate, octadecylamine, and triethanolamine. An environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to claim 1.

9. The content of the surfactant in the aqueous treatment agent solution is 0.002 to 0.015 mol / L in molar concentration, preferably 0.003 to 0.01 mol / L. An environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to claim 1 or 8.

10. An environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to claim 1, further characterized by containing 0 to 20 parts by weight of water.

11. Use of an environmentally friendly aqueous treatment agent for improving the phosphatability of high-strength steel according to any one of claims 1 to 10 in a continuous production line of pickled high-strength steel and cold-rolled high-strength steel.

12. A method for improving the phosphatability of high-strength steel, including treating high-strength steel with an environmentally friendly aqueous treatment agent according to any one of claims 1 to 10 by impregnation, spraying, or roll coating, and preferably, the high-strength steel is pickled high-strength steel or high-strength steel obtained by cold rolling.

13. The method according to claim 12, further comprising treating high-strength steel with a degreasing agent to remove dirt and oil adhering to the surface thereof, then washing with pure water to remove alkaline components remaining on the surface, spraying and drying, and then surface-treating the high-strength steel with the environmentally friendly aqueous treatment agent.

14. A high-strength steel having a nano-scale surface modification layer formed by drying the environmentally friendly aqueous treatment agent according to any one of claims 1 to 10 on its surface, or a phosphate-treated steel sheet obtained by phosphate-treating the high-strength steel, preferably having a phosphate crystal coverage rate of ≧ 80%, preferably 100%, a phosphate crystal size of ≦ 6 μm, and a phosphate film weight of ≧ 2 g / m ２ A phosphate-treated steel sheet characterized by the above.

15. A method for phosphatizing high-strength steel, comprising treating the surface of the high-strength steel using the method according to claim 12 or 13, and sequentially performing degreasing, water washing, surface conditioning, phosphatizing, water washing, and drying on the surface-treated high-strength steel.

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