A scratch-resistant galvanized steel strip and its preparation method

Abstract

This invention relates to the field of galvanized steel technology, and proposes a scratch-resistant galvanized steel strip and its preparation method. The scratch-resistant galvanized steel strip comprises, from bottom to top, a steel strip, a hot-dip galvanized layer, and a passivation layer. During the preparation of the passivation layer, each 1L of passivation solution includes the following components: 5-10g sodium molybdate, 1-2g sodium nitrate, 0.1-0.3g sodium metavanadate, 0.5-0.8g titanylfluoride, and 0.2-0.5g bis(1,6-hexanetriamine)pentamethylenephosphonic acid. This technical solution solves the problems of poor scratch resistance and low surface hardness of existing galvanized steel strips.

Description

Technical Field

[0001] This invention relates to the field of galvanized steel technology, specifically to a scratch-resistant galvanized strip steel and its preparation method. Background Technology

[0002] With the rapid development of the national economy, the demand for steel is increasing. To improve the surface properties of strip steel, surface coating treatments are often applied. Among these, galvanized strip steel has become the main choice for protection due to the low standard electrode potential of zinc. In the galvanizing process, chromate passivation is widely used for the passivation treatment of the zinc coating. However, this passivation solution contains hexavalent chromium ions, which pose carcinogenic and toxic risks. Therefore, chromium-free passivation processes are increasingly becoming a research direction and hot topic. Furthermore, existing galvanized strip steel passivation methods still suffer from low surface quality, resulting in low surface hardness, insufficient coating adhesion, and poor scratch resistance. Summary of the Invention

[0003] This invention proposes a scratch-resistant galvanized steel strip and its preparation method, which solves the problems of poor scratch resistance and low surface hardness of galvanized steel strip in related technologies.

[0004] The technical solution of the present invention is as follows:

[0005] This invention proposes a scratch-resistant galvanized steel strip, which, from bottom to top, comprises a steel strip, a hot-dip galvanized layer, and a passivation layer;

[0006] When the passivation layer is prepared, each 1L of passivation solution contains the following components: 5-10g sodium molybdate, 1-2g sodium nitrate, 0.1-0.3g sodium metavanadate, 0.5-0.8g fluorotitanic acid, and 0.2-0.5g bis(1,6-hexanetriamine)pentamethylenephosphonic acid.

[0007] As a further technical solution, the passivation solution also includes the following components: 5-8g of organosilicon passivating agent.

[0008] As a further technical solution, the passivation solution also includes the following components: 5-8g of modified organosilicon passivating agent; the modified organosilicon passivating agent is obtained by mixing organosilicon passivating agent and nano-cerium oxide in a mass ratio of 3:2-4:1.

[0009] As a further technical solution, the organosilicon passivating agent is one of hexadecyltrimethoxysilane, tetraethoxysilane, and hexamethyldisiloxane.

[0010] In this invention, a mixture of organosilicon passivating agent and nano-cerium oxide is added to the passivation solution. By combining organic passivation and non-polar passivation, the scratch resistance of the galvanized steel strip coating and the surface hardness of the galvanized steel strip are further improved.

[0011] As a further technical solution, the nano-cerium oxide is polysilicic acid modified nano-cerium oxide.

[0012] As a further technical solution, the raw materials for the polysilicic acid modified nano-cerium oxide include sodium silicate and nano-cerium oxide, wherein the mass ratio of sodium silicate to nano-cerium oxide is 1:12~14.

[0013] As a further technical solution, the preparation method of the polysilicic acid modified nano-cerium oxide includes the following steps: adjusting the pH of the aqueous solution of sodium silicate to 1~2, adding nano-cerium oxide, mixing, aging, crushing, and obtaining polysilicic acid modified nano-cerium oxide.

[0014] In this invention, by using polysilicic acid to modify nano-cerium oxide, the adhesion and bonding force of nano-cerium oxide are improved, thereby further enhancing the scratch resistance of the coating and the surface hardness of the galvanized steel strip.

[0015] As a further technical solution, the thickness of the hot-dip galvanized layer is 50~60μm.

[0016] As a further technical solution, the thickness of the passivation layer is 3~5μm.

[0017] The present invention also proposes a method for preparing the aforementioned scratch-resistant galvanized steel strip, comprising the following steps:

[0018] S1. Degrease, pickle, and wash the strip steel to obtain pretreated strip steel;

[0019] S2. After the pretreated strip steel is coated with flux, it is immersed in zinc, cooled, and then galvanized strip steel is obtained.

[0020] S3. Mix the components of the passivation solution to obtain the passivation solution;

[0021] S4. The galvanized steel strip is immersed in the passivation solution and then cured to obtain scratch-resistant galvanized steel strip.

[0022] As a further technical solution, the zinc bath composition during zinc immersion includes 0.1wt%~0.5wt% Al in addition to Zn and other unavoidable impurities.

[0023] As a further technical solution, the zinc liquid composition, in addition to Zn and other unavoidable impurities, also includes 0.3wt%~0.4wt% Al.

[0024] The working principle and beneficial effects of this invention are as follows:

[0025] 1. In this invention, by adding fluorotitanic acid and bis(1,6-hexyltriamine)pentamethylenephosphonic acid to the sodium molybdate passivation solution system of galvanized strip steel, the adhesion, density and surface quality of the passivation film of galvanized strip steel are improved, and the scratch resistance and surface hardness of the coating of galvanized strip steel are significantly improved. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] In the following examples and comparative examples, the strip steel is Q215 strip steel with a thickness of 3mm.

[0028] Example 1

[0029] The scratch-resistant galvanized steel strip consists of, from bottom to top, a steel strip, a 50μm thick hot-dip galvanized layer, and a 3μm thick passivation layer.

[0030] The method for preparing scratch-resistant galvanized steel strip includes the following steps:

[0031] S1. Degrease, pickle, and wash the strip steel to obtain pretreated strip steel;

[0032] S2. After the pretreated strip steel is coated with flux, it is immersed in a zinc pot at 450°C for hot-dip galvanizing for 3 seconds, then removed and cooled to obtain galvanized strip steel; wherein, the zinc liquid in the zinc pot contains 0.3wt% Al, and the balance is Zn and other unavoidable impurities;

[0033] S3. Take 5g of sodium molybdate, 1g of sodium nitrate, 0.1g of sodium metavanadate, 0.5g of fluorotitanic acid, and 0.2g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, mix them, and add deionized water to make up to 1L to obtain a passivation solution.

[0034] S4. Immerse the galvanized steel strip in the passivation solution, remove it and cure it to obtain scratch-resistant galvanized steel strip.

[0035] Example 2

[0036] The scratch-resistant galvanized steel strip consists of, from bottom to top, a steel strip, a 50μm thick hot-dip galvanized layer, and a 3μm thick passivation layer.

[0037] The method for preparing scratch-resistant galvanized steel strip includes the following steps:

[0038] S1. Degrease, pickle, and wash the strip steel to obtain pretreated strip steel;

[0039] S2. After the pretreated strip steel is coated with flux, it is immersed in a zinc pot at 480°C for hot-dip galvanizing for 4 seconds, then removed and cooled to obtain galvanized strip steel; wherein, the zinc liquid in the zinc pot contains 0.4wt% Al, and the balance is Zn and other unavoidable impurities;

[0040] S3. Take 8g of sodium molybdate, 1.5g of sodium nitrate, 0.2g of sodium metavanadate, 0.6g of fluorotitanic acid, and 0.35g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, mix them, and add deionized water to make up to 1L to obtain a passivation solution.

[0041] S4. Immerse the galvanized steel strip in the passivation solution, remove it and cure it to obtain scratch-resistant galvanized steel strip.

[0042] Example 3

[0043] The scratch-resistant galvanized steel strip consists of, from bottom to top, a steel strip, a hot-dip galvanized layer with a thickness of 60 μm, and a passivation layer with a thickness of 5 μm.

[0044] The method for preparing scratch-resistant galvanized steel strip includes the following steps:

[0045] S1. Degrease, pickle, and wash the strip steel to obtain pretreated strip steel;

[0046] S2. After the pretreated strip steel is coated with flux, it is immersed in a zinc pot at 460°C for hot-dip galvanizing for 4 seconds, then removed and cooled to obtain galvanized strip steel; wherein, the zinc liquid in the zinc pot contains 0.3wt% Al, and the balance is Zn and other unavoidable impurities;

[0047] S3. Take 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, 0.8g of fluorotitanic acid, and 0.5g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, mix them, and add deionized water to make up to 1L to obtain a passivation solution.

[0048] S4. Immerse the galvanized steel strip in the passivation solution, remove it and cure it to obtain scratch-resistant galvanized steel strip.

[0049] Example 4

[0050] The difference between this embodiment and Embodiment 3 lies only in step S3 of the method for preparing scratch-resistant galvanized strip steel: 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, 0.8g of fluorotitanic acid, 0.5g of bis(1,6-hexanetriamine)pentamethylenephosphonic acid, and 5g of organosilicon passivating agent are mixed and then deionized water is added to make up to 1L to obtain a passivation solution; wherein, the organosilicon passivating agent is hexadecyltrimethoxysilane.

[0051] Example 5

[0052] The difference between this embodiment and Embodiment 3 lies only in step S3 of the method for preparing scratch-resistant galvanized strip steel: 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, 0.8g of fluorotitanic acid, 0.5g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, and 8g of organosilicon passivating agent are mixed and then deionized water is added to make up to 1L to obtain a passivation solution; wherein, the organosilicon passivating agent is hexadecyltrimethoxysilane.

[0053] Example 6

[0054] The difference between this embodiment and Embodiment 3 lies only in step S3 of the method for preparing scratch-resistant galvanized strip steel: 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, 0.8g of fluorotitanic acid, 0.5g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, and 8g of organosilicon passivating agent are mixed and then deionized water is added to make up to 1L to obtain a passivation solution; wherein, the organosilicon passivating agent is a mixture of hexadecyltrimethoxysilane and nano-cerium oxide in a mass ratio of 1:1.

[0055] Example 7

[0056] The only difference between this embodiment and Embodiment 3 is that step S3 of the method for preparing scratch-resistant galvanized strip steel is as follows: Take 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, 0.8g of fluorotitanic acid, 0.5g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, and 8g of organosilicon passivating agent, mix them, and add deionized water to make up to 1L to obtain a passivation solution; wherein, the organosilicon passivating agent is a mixture of hexadecyltrimethoxysilane and nano-cerium oxide in a mass ratio of 4.5:0.5.

[0057] Example 8

[0058] The only difference between this embodiment and Embodiment 3 is that step S3 of the method for preparing scratch-resistant galvanized strip steel is as follows: Take 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, 0.8g of fluorotitanic acid, 0.5g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, and 8g of organosilicon passivating agent, mix them, and add deionized water to make up to 1L to obtain a passivation solution; wherein, the organosilicon passivating agent is a mixture of hexadecyltrimethoxysilane and nano-cerium oxide in a mass ratio of 3:2.

[0059] Example 9

[0060] The only difference between this embodiment and Embodiment 3 is that step S3 of the method for preparing scratch-resistant galvanized strip steel is as follows: Take 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, 0.8g of fluorotitanic acid, 0.5g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, and 8g of organosilicon passivating agent, mix them, and add deionized water to make up to 1L to obtain a passivation solution; wherein, the organosilicon passivating agent is a mixture of hexadecyltrimethoxysilane and nano-cerium oxide in a mass ratio of 4:1.

[0061] Example 10

[0062] The only difference between this embodiment and Embodiment 9 is that the nano-cerium oxide is polysilicic acid modified nano-cerium oxide. The preparation method of polysilicic acid modified nano-cerium oxide includes the following steps: adjusting the pH of a 10% sodium silicate aqueous solution to 2, adding nano-cerium oxide, mixing, aging, and crushing to obtain polysilicic acid modified nano-cerium oxide; wherein, the mass ratio of sodium silicate to nano-cerium oxide is 1:10.

[0063] Example 11

[0064] The only difference between this embodiment and Embodiment 9 is that the nano-cerium oxide is polysilicic acid modified nano-cerium oxide. The preparation method of polysilicic acid modified nano-cerium oxide includes the following steps: adjusting the pH of a 10% sodium silicate aqueous solution to 2, adding nano-cerium oxide, mixing, aging, and crushing to obtain polysilicic acid modified nano-cerium oxide; wherein, the mass ratio of sodium silicate to nano-cerium oxide is 1:16.

[0065] Example 12

[0066] The only difference between this embodiment and Embodiment 9 is that the nano-cerium oxide is polysilicic acid modified nano-cerium oxide. The preparation method of polysilicic acid modified nano-cerium oxide includes the following steps: after adjusting the pH of an aqueous solution of sodium silicate with a mass fraction of 10% to 2, nano-cerium oxide is added, mixed, matured, and crushed to obtain polysilicic acid modified nano-cerium oxide; wherein, the mass ratio of sodium silicate to nano-cerium oxide is 1:12.

[0067] Example 13

[0068] The only difference between this embodiment and Embodiment 9 is that the nano-cerium oxide is polysilicic acid modified nano-cerium oxide. The preparation method of polysilicic acid modified nano-cerium oxide includes the following steps: adjusting the pH of a 10% sodium silicate aqueous solution to 2, adding nano-cerium oxide, mixing, aging, and crushing to obtain polysilicic acid modified nano-cerium oxide; wherein, the mass ratio of sodium silicate to nano-cerium oxide is 1:14.

[0069] Comparative Example 1

[0070] The only difference between this comparative example and Example 3 is that step S3 of the method for preparing scratch-resistant galvanized strip steel is as follows: take 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, and 1.3g of fluorotitanic acid, mix them, and add deionized water to make up to 1L to obtain a passivation solution.

[0071] Comparative Example 2

[0072] The only difference between this comparative example and Example 3 is that step S3 of the method for preparing scratch-resistant galvanized strip steel is as follows: Take 10g of sodium molybdate, 2g of sodium nitrate, 0.3g of sodium metavanadate, and 1.3g of bis(1,6-hexyltriamine)pentamethylenephosphonic acid, mix them, and add deionized water to make up to 1L to obtain a passivation solution.

[0073] Comparative Example 3

[0074] The only difference between this comparative example and Example 3 is that step S3 of the method for preparing scratch-resistant galvanized strip steel is as follows: take 10g of sodium molybdate, 2g of sodium nitrate, and 0.3g of sodium metavanadate, mix them, and add deionized water to make up to 1L to obtain a passivation solution.

[0075] The scratch-resistant galvanized steel strips obtained in Examples 1-13 and Comparative Examples 1-3 were subjected to performance tests respectively:

[0076] Wear resistance was tested at room temperature using a wear testing machine. During the test, the sample was processed into upper and lower samples as a friction pair. The load was 200 N, the rotation speed was 50 r / min, the wear time was 3 h, and the wear amount was recorded after wear.

[0077] The Vickers hardness of the passivation layer of galvanized steel strip was tested using a microhardness tester with a test load of 1.96 N and a holding time of 15 s.

[0078] The test results are shown in the table below:

[0079]

[0080] Comparing the data from Examples 1-13 and Comparative Examples 1-3, it can be seen that the galvanized steel strips prepared in Examples 1-13 have higher Vickers hardness and lower wear compared to Comparative Examples 1-3. This indicates that adding fluorotitanic acid and bis(1,6-hexyltriamine)pentamethylenephosphonic acid to the sodium molybdate passivation solution system for galvanized steel strips can significantly improve the scratch resistance of the coating and the surface hardness of the galvanized steel strips.

[0081] Comparing the data from Examples 3-9, it can be seen that the galvanized steel strips prepared in Examples 6-9 have higher Vickers hardness and lower wear compared to Examples 3-5. This indicates that the addition of a mixture of hexadecyltrimethoxysilane and nano-cerium oxide to the passivation solution can further improve the scratch resistance of the coating and the surface hardness of the galvanized steel strip.

[0082] Comparing the data from Examples 9 to 13, it can be seen that, compared with Example 9, the galvanized steel strips prepared in Examples 10 to 13 have higher Vickers hardness and lower wear, indicating that by using polysilicic acid-modified nano-cerium oxide, the scratch resistance of the coating and the surface hardness of the galvanized steel strip can be further improved.

[0083] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A scratch-resistant galvanized steel strip, characterized in that, From bottom to top, it includes strip steel, hot-dip galvanized layer, and passivation layer; When the passivation layer is prepared, each 1L of passivation solution contains the following components: 5-10g sodium molybdate, 1-2g sodium nitrate, 0.1-0.3g sodium metavanadate, 0.5-0.8g fluorotitanic acid, and 0.2-0.5g bis(1,6-hexanetriamine)pentamethylenephosphonic acid.

2. The scratch-resistant galvanized steel strip according to claim 1, characterized in that, The passivation solution also includes the following components: 5-8g of organosilicon passivating agent.

3. The scratch-resistant galvanized steel strip according to claim 1, characterized in that, The passivation solution also includes the following components: 5-8g of modified organosilicon passivating agent; the modified organosilicon passivating agent is obtained by mixing organosilicon passivating agent and nano-cerium oxide in a mass ratio of 3:2-4:

1.

4. The scratch-resistant galvanized steel strip according to claim 2 or 3, characterized in that, The organosilicon passivating agent is one of hexadecyltrimethoxysilane, tetraethoxysilane, and hexamethyldisiloxane.

5. The scratch-resistant galvanized steel strip according to claim 3, characterized in that, The nano-cerium oxide is polysilicic acid modified nano-cerium oxide.

6. The scratch-resistant galvanized steel strip according to claim 5, characterized in that, The raw materials for the polysilicic acid modified nano-cerium oxide include sodium silicate and nano-cerium oxide, and the mass ratio of sodium silicate to nano-cerium oxide is 1:12~14.

7. The scratch-resistant galvanized steel strip according to claim 6, characterized in that, The preparation method of the polysilicic acid modified nano-cerium oxide includes the following steps: adjusting the pH of the sodium silicate aqueous solution to 1-2, adding nano-cerium oxide, mixing, aging, and crushing to obtain polysilicic acid modified nano-cerium oxide.

8. The scratch-resistant galvanized steel strip according to claim 1, characterized in that, The thickness of the hot-dip galvanized layer is 50~60μm.

9. The scratch-resistant galvanized steel strip according to claim 1, characterized in that, The passivation layer has a thickness of 3~5μm.

10. A method for preparing scratch-resistant galvanized steel strip according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Degrease, pickle, and wash the strip steel to obtain pretreated strip steel; S2. After the pretreated strip steel is coated with flux, it is immersed in zinc, cooled, and then galvanized strip steel is obtained. S3. Mix the components of the passivation solution to obtain the passivation solution; S4. The galvanized steel strip is immersed in the passivation solution and then cured to obtain scratch-resistant galvanized steel strip.

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