A method for improving the corrosion resistance of the surface of a low-tin tinplate

Abstract

This invention relates to a technology for controlling the corrosion resistance of tin-plated sheet surfaces, particularly with low tin content (1.1 g / m²). 2 This invention relates to a method for improving the corrosion resistance of low-tin-content tin-plated sheets. The method includes the following steps: (1) controlling the grain orientation of the cold-rolled substrate through an annealing process; (2) analyzing the microstructure of the cold-rolled substrate using XRD; (3) controlling the surface characteristics of the cold-rolled substrate using conventional rolling processes and electroplating alkaline washing processes, followed by a strengthening pickling treatment; (4) depositing a tin plating layer using a Florstein-type tin plating process, followed by cleaning the tin-plated sheet in a recycling tank; and (5) finally, the tin-plated sheet undergoes conventional soft-fill and passivation processes. This invention can reduce the incidence of surface rust defects in low-tin-content tin-plated sheets for manufacturers and users, improve the pass rate of tin-plated sheet products, and is green, environmentally friendly, and effective, improving the surface corrosion resistance of low-tin-content tin-plated sheets by more than 30%.

Description

Technical Field

[0001] This invention relates to a technology for controlling the corrosion resistance of tin-plated sheet surfaces, particularly with low tin content (1.1 g / m²). 2 The corrosion resistance of tin-plated sheets is specifically a method to improve the surface corrosion resistance of tin-plated sheets with low tin content. Background Technology

[0002] Tinplate, an important component of packaging materials, combines the strength and formability of steel with the corrosion resistance, weldability, and appearance of tin. Finished products exhibit excellent corrosion resistance, sturdiness, aesthetic appeal, lightweight nature, and good formability. They are primarily used in food and beverage can manufacturing, as well as for containers, stamped products, packaging materials, and the production of toys and bottle caps.

[0003] The production process of tinplate is relatively long and complex, which can be summarized as pickling → cold rolling → degreasing and cleaning → annealing → leveling → electroplating. The electroplating process includes alkaline washing → pickling → electroplating → remelting → passivation. In terms of the development of plating solution systems, sulfuric acid, fluoroboric acid, and halogen agents were initially used in electroplating solutions, but now PSA and MSA agents are the main ones.

[0004] The benzenesulfonic acid (PSA) production process uses an electrolyte primarily composed of stannous sulfate, benzenesulfonic acid (PSA), and additives such as ENSA and EN. EN and ENSA prevent the conversion of divalent tin to tetravalent tin in the plating solution and also act as wetting agents and brighteners. This plating solution offers advantages such as good dispersing and covering power, high cathode current, solution stability, long working cycle, and a smooth and fine coating. However, its biggest drawback is its environmental impact and difficulty in recycling.

[0005] The methanesulfonic acid (MSA) production process has high conductivity and mass transfer rate, can operate at high current density, and does not contain organic additives found in general acidic plating solutions. Therefore, its wastewater treatment process is very simple, the process composition is simple, the operation is easy, and the maintenance is convenient, but the price is relatively high.

[0006] Although MSA plating solution systems are developing rapidly, PSA plating solution systems are still the most popular electroplating agents in the world, and PSA electroplating processes account for about 70% of all units currently.

[0007] Tin-plated products are often distinguished by their tin plating amount, including 1.1g / m². 2 2.2g / m 2 2.8g / m 2 5.6g / m 2 8.4g / m 2 11.2g / m 2(Equal thickness and differential thickness). Looking at both domestic and international markets, tinplate users are continuously demanding thinner plates to reduce costs. While ensuring performance, tinplate thinning is achieved in two ways: firstly, by reducing the thickness of the cold-rolled substrate, and secondly, by further reducing the tin plating amount on one side. Therefore, the proportion of double-cold-rolled products and low-tin-content tin-plated products in the total consumption of tinplate is gradually increasing. Based on this, this invention uses the PSA plating solution system as a basis, targeting tin plating amounts ≤1.1 g / m². 2 A new technology and method for improving the surface corrosion resistance of tin-plated sheets with low tin content, combined with the control of cold-rolled substrate characteristics, is proposed.

[0008] The main structure of tinplate includes a cold-rolled substrate, a tin-iron alloy layer, a free tin layer, and a passivation film. The production process of tinplate is relatively mature, and the product structure is stable. It can be said that the corrosion resistance of tinplate mainly depends on the free tin layer and the tin-iron alloy layer on the surface, whose structure is as follows: Figure 1 As shown. By Figure 1 It is known that, since the tin layer is a cathode plating layer, one of the main factors affecting the corrosion resistance of the tin-plated plate surface is the dense free tin layer and the tin-iron alloy layer, especially the tin-iron alloy layer. Only when the tin-iron alloy plating layer has relatively few pores (such as...) Figure 1 (b) is shown) in order to achieve the purpose of corrosion resistance.

[0009] Therefore, improving the corrosion resistance of tinplate involves two aspects: increasing the tin content and improving the density of the tin-iron alloy layer on the tinplate surface. According to user requirements, the product specifications of tinplate fix the required tin content on the surface, making it impossible to improve corrosion resistance solely by adjusting the tin content. Summary of the Invention

[0010] Based on the above, this invention provides a method for improving the surface corrosion resistance of low-tin-content tin-plated sheets. By changing the heat treatment process, the grain orientation of the cold-rolled substrate is controlled. Furthermore, the growth direction of the tin-iron alloy layer is adjusted to increase its density. Before soft melting, the fluidity of the tin layer is improved by wetting, and the porosity of the free tin layer on the surface of the tin-plated sheet is controlled, thereby enhancing the surface corrosion resistance of the low-tin-content tin-plated sheet.

[0011] The technical solution of this invention is as follows:

[0012] A method for improving the corrosion resistance of a low-tin-content tin-plated board surface includes the following steps:

[0013] (1) Controlling the grain orientation of cold-rolled substrates through annealing process;

[0014] The annealing process is as follows:

[0015] Rapid heating; furnace temperature: 700℃~780℃; heating time: 190~210s.

[0016] Further heating is required, with furnace temperature ranging from 780℃ to 920℃ and heating time from 90 to 120 seconds.

[0017] Cool to 120–140°C for 70–90 seconds in a non-oxidizing atmosphere of 10–12% H2 and 88–90% N2.

[0018] Using water as the medium, the mixture was cooled to room temperature in 10–15 seconds.

[0019] (2) The microstructure of the cold-rolled substrate was analyzed using the XRD method, see [link to XRD analysis]. Figure 2 This is the XRD pattern of a cold-rolled steel sheet;

[0020] Based on the following formula:

[0021]

[0022] Where: n is the number of peaks

[0023] I HKL The required diffraction angle and intensity of the crystal plane diffraction peaks for the sample

[0024] Let i be the diffraction intensity of each peak, i = 1, 2, 3.

[0025] I 标HKL To determine the standard crystal plane diffraction intensity at the required diffraction angle

[0026] The standard crystal plane diffraction intensity corresponding to each peak

[0027] Calculate the grain orientation degree of different cold-rolled sheets and control the cold-rolled sheets in the range of crystal planes (110), (200) and (211);

[0028] The ranges of the crystal planes (110), (200), and (211) are shown in the table below:

[0029] Table 1 Grain orientation control range for different cold-rolled sheets

[0030]

[0031] (3) The surface characteristics of the cold-rolled substrate are controlled by conventional (secondary cold) rolling process and electroplating alkaline washing process (refer to patent CN201610179709.1 or CN201710295976.X). After that, the cold-rolled substrate is subjected to enhanced pickling treatment.

[0032] (4) The tin plating layer is deposited by using the Froststein-type tin plating process (refer to patent CN201510956732.2), and the tin-plated plate is cleaned by the recycling tank;

[0033] (5) Finally, the tin-plated board undergoes conventional soft-fill and conventional passivation processes, which can improve the surface corrosion resistance of the low-tin-content tin-plated board.

[0034] Furthermore, in step (1), deionized water is used as the medium to cool to room temperature.

[0035] Furthermore, the pickling treatment is intensified in step (3), and the solution composition and conditions are as follows: sulfuric acid: 30-75 g / L, nitric acid: 10-20 g / L, phenolsulfonic acid: 5-10 g / L, solution temperature: 30-40℃, current density: 20-30 A / dm³ 2 .

[0036] Furthermore, after pickling in step (3), the surface characteristics of the cold-rolled sheet are controlled as follows:

[0037] When the average roughness is 0.4 μm ≤ Ra ≤ 0.5 μm, Rpc ≤ 60 and Rvk ≤ 0.5 μm;

[0038] When the roughness Ra≦0.4μm, Rpc≦50 and Rvk≦0.4μm;

[0039] When the average roughness Ra≧0.5, Rpc≦70 and Rvk≦0.6μm.

[0040] Furthermore, in step (4), the recycling tank includes a first recycling tank and a second recycling tank.

[0041] Furthermore, in step (4), a solution is prepared in the second recovery tank, the composition of which is: tin ion concentration 3-5 g / L, hydroquinone 1-3 g / L, and decyl glucoside 1-5 ml / L.

[0042] The beneficial effects of this invention are:

[0043] 1. Based on the orientation degree control of cold-rolled substrate, a method for improving the surface corrosion resistance of low-tin-content tin-plated sheets is proposed. This method can effectively improve the surface corrosion resistance of tin-plated sheets and provides a basis for improving the production of tin-plated sheet surface quality.

[0044] 2. This method for improving the corrosion resistance of tinplate surfaces can reduce the incidence of rust defects on low-tin-content tinplate surfaces for manufacturers and users, thereby improving the pass rate of tinplate products.

[0045] 3. This method for improving the corrosion resistance of tin-plated sheets is green, environmentally friendly, and effective, and can improve the corrosion resistance of low-tin-content tin-plated sheets by more than 30%. Attached Figure Description

[0046] Figure 1 The surface structure of the tinplate is: (a) cross-sectional structure; (b) a tin-iron alloy layer with excellent corrosion resistance; and (c) a tin-iron alloy layer with poor corrosion resistance.

[0047] Figure 2 This is the XRD pattern of a cold-rolled steel sheet.

[0048] Figure 3 These are the XRD patterns of different cold-rolled sheets. Figure 3 (a) is the XRD pattern of Example 1. Figure 3 (b) is the XRD pattern of Example 2. Figure 3 (c) is the XRD pattern of Example 3.

[0049] Figure 4 It refers to the surface morphology of different tin-plated plates and their tin-iron alloy layers. Figure 4 (a) shows the surface morphology of the free tin layer and tin-iron alloy layer of the tin-plated plate in Example 1. Figure 4 (b) shows the surface morphology of the free tin layer and tin-iron alloy layer of the tin-plated plate in Example 2. Figure 4 (c) shows the surface morphology of the free tin layer and tin-iron alloy layer of the tin-plated plate in Example 3. Detailed Implementation

[0050] To better understand the present invention, the following embodiments and accompanying drawings further illustrate the content of the present invention, but the content of the invention is not limited to the following embodiments.

[0051] Example 1

[0052] 1) Select a low-carbon cold-rolled substrate for tin plating of DR material. Its chemical composition is as follows: C: 0.025%, Si: 0.004%, Mn: 0.41%, Al: 0.08%, P≤0.011%, S≤0.005%, with the balance being Fe and unavoidable impurities.

[0053] 2) The annealing process is controlled as follows:

[0054] Rapid heating; furnace temperature: 720℃±10℃; heating time: 200s.

[0055] Further heating, furnace temperature: 890℃±10℃, heating time: 100s;

[0056] Cool to 130±5℃ for 80s in a non-oxidizing atmosphere of 12% H2 and 88% N2;

[0057] Using deionized water as the medium, the temperature was cooled to room temperature in 12 seconds.

[0058] 3) The microstructure of the cold-rolled substrate was analyzed using the XRD method, such as... Figure 3 As shown in (a).

[0059] Based on the following formula:

[0060]

[0061] Where: n is the number of peaks

[0062] I HKL The required diffraction angle and intensity of the crystal plane diffraction peaks for the sample

[0063] Let i be the diffraction intensity of each peak, i = 1, 2, 3.

[0064] I 标HKL To determine the standard crystal plane diffraction intensity at the required diffraction angle

[0065] The standard crystal plane diffraction intensity corresponding to each peak

[0066] The grain orientation degrees of the cold-rolled substrate were calculated to be 0.09 for (110), 0.75 for (200), and 0.55 for (211).

[0067] 4) The surface characteristics of the cold-rolled substrate are controlled by a conventional secondary cold rolling process and an electroplating alkaline washing process. The cold-rolled substrate undergoes a strengthening pickling process with a solution composition of 65 g / L sulfuric acid, 15 g / L nitric acid, and 7 g / L phenolsulfonic acid. The solution temperature is 35℃, and the current density is 27 A / dm³. 2 .

[0068] 5) Surface characteristics of the secondary cold-rolled sheet after pickling: average roughness Ra 0.35μm, Rpc 49 and Rvk 0.35μm.

[0069] 6) Tin plating is achieved by using PSA plating solution to deposit tin plating layer; the tin-plated plate is cleaned in the recovery tank, and the solution in the second recovery tank is composed of tin ion concentration of 4g / L, hydroquinone 1.5g / L, and decyl glucoside 3ml / L.

[0070] 7) After conventional soft capacitor and passivation processes, the tin content is low (1.1g / m). 2 The surface porosity of the tin-plated sheet was improved from 13.9 to 6.5 mg / dm³. 2 The corrosion resistance is improved by 53.2%, and the surface morphology of its free tin layer and tin-iron alloy layer is as follows: Figure 4 As shown in (a).

[0071] Example 2

[0072] 1) Select a low-carbon cold-rolled substrate for tin plating of CA material. Its chemical composition is as follows: C: 0.03%, Si: 0.005%, Mn: 0.37%, Al: 0.07%, P≤0.012%, S≤0.005%, with the balance being Fe and unavoidable impurities.

[0073] 2) The annealing process is controlled as follows:

[0074] Rapid heating; furnace temperature: 720℃±10℃; heating time: 200s.

[0075] Further heating, furnace temperature: 890℃±10℃, heating time: 100s;

[0076] Cool to 130±5℃ for 80s in a non-oxidizing atmosphere of 12% H2 and 88% N2;

[0077] Using deionized water as the medium, the temperature was cooled to room temperature in 12 seconds.

[0078] 3) The microstructure of the cold-rolled substrate was analyzed using the XRD method, such as... Figure 3 As shown in (b).

[0079] Based on the following formula:

[0080]

[0081] Where: n is the number of peaks

[0082] I HKL The required diffraction angle and intensity of the crystal plane diffraction peaks for the sample

[0083] Let i be the diffraction intensity of each peak, i = 1, 2, 3.

[0084] I 标HKL To determine the standard crystal plane diffraction intensity at the required diffraction angle

[0085] The standard crystal plane diffraction intensity corresponding to each peak

[0086] The grain orientation degrees of the cold-rolled substrate were calculated to be 0.36 for (110), 0.15 for (200), and 0.73 for (211).

[0087] 4) The surface characteristics of the cold-rolled substrate are controlled by conventional cold rolling process and electroplating alkaline washing process. The cold-rolled substrate undergoes a strengthening pickling process with a solution composition of 60 g / L sulfuric acid, 17 g / L nitric acid, and 5 g / L phenolsulfonic acid. The solution temperature is 32℃, and the current density is 30 A / dm³. 2 .

[0088] 5) Surface characteristics of cold-rolled sheet after pickling: average roughness Ra 0.47 μm, Rpc 57 and Rvk 0.46 μm.

[0089] 6) Tin plating is achieved by using PSA plating solution to deposit tin plating layer; the tin-plated plate is cleaned in the recovery tank, and the solution in the second recovery tank is composed of tin ion concentration of 3g / L, hydroquinone 1g / L, and decyl glucoside 5ml / L.

[0090] 7) After conventional soft capacitor and passivation processes, the tin content is low (1.1g / m). 2 The surface porosity of the tin-plated sheet was improved from 12.7 mg / dm³ to 5.3 mg / dm³. 2 The corrosion resistance is improved by 58.3%, and the surface morphology of its free tin layer and tin-iron alloy layer is as follows: Figure 4 As shown in (b).

[0091] Example 3

[0092] 1) Select a low-carbon cold-rolled substrate for tin plating of CA material. Its chemical composition is as follows: C: 0.01%, Si: 0.006%, Mn: 0.42%, Al: 0.06%, P≤0.009%, S≤0.003%, with the balance being Fe and unavoidable impurities.

[0093] 2) The annealing process is controlled as follows:

[0094] Rapid heating, furnace temperature: 770℃±10℃, heating time: 195s;

[0095] Further heating, furnace temperature: 910℃±10℃, heating time: 115s;

[0096] Cool to 135±5℃ for 70s in a non-oxidizing atmosphere of 11% H2 and 89% N2;

[0097] Using deionized water as the medium, the water was cooled to room temperature in 15 seconds.

[0098] 3) The microstructure of the cold-rolled substrate was analyzed using the XRD method, such as... Figure 3 As shown in (c).

[0099] Based on the following formula:

[0100]

[0101] Where: n is the number of peaks

[0102] I HKL The required diffraction angle and intensity of the crystal plane diffraction peaks for the sample

[0103] Let i be the diffraction intensity of each peak, i = 1, 2, 3.

[0104] I 标HKL To determine the standard crystal plane diffraction intensity at the required diffraction angle

[0105] The standard crystal plane diffraction intensity corresponding to each peak

[0106] The grain orientation degrees of the cold-rolled substrate were calculated to be 0.37 for (110), 0.14 for (200), and 0.75 for (211).

[0107] 4) The surface characteristics of the cold-rolled substrate are controlled by a conventional secondary cold rolling process and an electroplating alkaline washing process. The cold-rolled substrate undergoes a strengthening pickling process with a solution composition of 60 g / L sulfuric acid, 17 g / L nitric acid, and 5 g / L phenolsulfonic acid. The solution temperature is 32℃, and the current density is 30 A / dm³. 2 .

[0108] 5) Surface characteristics of cold-rolled sheet after pickling: average roughness Ra 0.56 μm, Rpc 68 and Rvk 0.51 μm.

[0109] 6) Tin plating is achieved by using PSA plating solution to deposit tin plating layer; the tin-plated plate is cleaned in the recovery tank, and the solution in the second recovery tank is composed of tin ion concentration of 5g / L, hydroquinone of 45g / L, and decyl glucoside of 4ml / L.

[0110] 7) After conventional soft capacitor and passivation processes, the tin content is low (1.1g / m). 2 The surface porosity of the tin-plated sheet was improved from 11.6 to 4.1 mg / dm³. 2 The corrosion resistance is improved by 64.7%, and the surface morphology of its free tin layer and tin-iron alloy layer is as follows: Figure 4 As shown in (c).

[0111] Of course, those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Any modifications or variations of the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for improving the corrosion resistance of a low-tin-content tin-plated board surface, characterized in that, Includes the following steps: (1) Controlling the grain orientation of cold-rolled substrates through annealing process; The annealing process is as follows: Rapid heating; furnace temperature: 700℃~780℃; heating time: 190~210s. Further heating is required, with furnace temperature ranging from 780℃ to 920℃ and heating time from 90 to 120 seconds. Cool to 120-140°C for 70-90 seconds in a non-oxidizing atmosphere of 10-12% H2 and 88-90% N2. Using water as the medium, the mixture is cooled to room temperature in 10-15 seconds. (2) The microstructure of the cold-rolled substrate was analyzed using the XRD method, based on the following formula: , Where: n is the number of peaks The required diffraction angle and intensity of the crystal plane diffraction peaks for the sample Let i be the diffraction intensity of each peak, i = 1, 2, 3. To determine the standard crystal plane diffraction intensity at the required diffraction angle The standard crystal plane diffraction intensity corresponding to each peak Calculate the grain orientation degree of different cold-rolled sheets and control the cold-rolled sheets within the range of crystal planes (110), (200) and (211); The ranges of the crystal planes (110), (200), and (211) are shown in the table below: , (3) The surface characteristics of the cold-rolled substrate are controlled by conventional rolling process and electroplating alkaline washing process. Then, the cold-rolled substrate is subjected to enhanced pickling treatment. (4) The tin plating layer is deposited by the Froststein-type tin plating process, and the tin-plated plate is cleaned by the recycling tank; The recovery tank includes a first recovery tank and a second recovery tank; a solution is prepared in the second recovery tank, the composition of which is: tin ion concentration 3~5g / L, hydroquinone 1~3g / L, decyl glucoside 1~5ml / L; (5) Finally, the tin-plated board undergoes conventional soft melting and passivation processes; The low tin content refers to a tin plating weight of ≤1.1g / m². 2 .

2. The method for improving the corrosion resistance of a low-tin-content tin-plated sheet surface according to claim 1, characterized in that, In step (1), deionized water is used as the medium and the mixture is cooled to room temperature.

3. The method for improving the corrosion resistance of a low-tin-content tin-plated sheet surface according to claim 1, characterized in that, In step (3), the pickling process is enhanced. The solution composition is: sulfuric acid: 30~75g / L, nitric acid: 10~20g / L, phenol sulfonic acid: 5~10g / L.

4. The method for improving the corrosion resistance of a low-tin-content tin-plated sheet surface according to claim 1, characterized in that, In step (3), the pickling conditions are enhanced as follows: solution temperature 30~40℃, current density 20~30A / dm³. 2 .

5. The method for improving the corrosion resistance of a low-tin-content tin-plated sheet surface according to claim 1, characterized in that, After pickling in step (3), the surface characteristics of the cold-rolled sheet are controlled as follows: When the average roughness is 0.4 μm ≤ Ra < 0.5 μm, Rpc ≤ 60 and Rvk ≤ 0.5 μm; When the roughness Ra < 0.4 μm, Rpc ≦ 50 and Rvk ≦ 0.4 μm; When the average roughness Ra≧0.5, Rpc≦70 and Rvk≦0.6μm.

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