A low-tin tin-plated steel sheet and a method for manufacturing the same

Abstract

The present invention relates to a tinplate steel sheet with an extremely low tin content (0.30-0.85 g / m 2 ) and a method for manufacturing the same, and a passivation method for the tinplate steel sheet. The tinplate steel sheet of the present invention has excellent finishing properties (paint film adhesion) and corrosion resistance, while having an extremely low tin content. The passivation method of the present invention can effectively compensate for the insufficient corrosion resistance caused by the low tin content, improve the service life of the steel sheet, and optimize the production cost and process flow.

Description

Technical Field

[0001] This invention relates to a tin-plated steel sheet and its preparation method, particularly a tin-plated steel sheet with low tin content and its preparation method. Background Technology

[0002] Tinplate is made by plating a layer of pure tin onto both sides of cold-rolled low-carbon thin steel sheets. It is a product with a complex production process, long manufacturing time, strict quality requirements, and high technical difficulty. Because tin is non-toxic, and steel itself possesses advantages such as high strength, excellent formability, superior corrosion resistance, good weldability, a bright appearance, and excellent printability, it has irreplaceable advantages in the food and beverage packaging field, where high-temperature sterilization is required, and has been widely used for a long time. However, as tin is a scarce resource, its cost has always been high, and with the continuous expansion of its application areas, the demand for tin continues to increase, further driving up its cost.

[0003] Tinplate used for manufacturing metal food or beverage cans undergoes a process involving pretreatment, electroplating, and remelting of the steel strip. The resulting tin-plated layer comprises an alloy tin layer (tin-iron alloy layer) and a free tin layer (pure tin layer). Because tin is easily oxidized in air, passivation treatment is typically required to ensure the tinplate exhibits excellent performance, forming a functional protective layer. Traditional passivation methods typically use sodium dichromate (Na₂Cr₂O₇) at a concentration of 25±5 g / L.

[0004] Traditional tin-plated steel sheets typically require a high tin content to ensure sufficient corrosion resistance and other mechanical properties. The tin content of traditional tin-plated steel sheets is generally between 1.1 and 15.1 g / m². 2 This leads to higher production costs, as well as environmental and resource utilization inefficiencies. Therefore, with increasing demands for environmental protection and energy conservation, developing tin-plated products with lower tin content is particularly important. However, when the tin content of the tin plating layer decreases (the tin layer becomes thinner), the corrosion resistance of the steel plate significantly declines. Traditional passivation processes cannot effectively compensate for the insufficient corrosion resistance caused by the thinning of the tin layer. Therefore, to solve the corrosion resistance problem caused by the thinning of the tin layer, a new passivation process is urgently needed. Summary of the Invention

[0005] To address the aforementioned problems in this field, the inventors have discovered that by employing a specific passivation method (especially a combination of a specific cathode electrolysis current density and a specific processing time), the insufficient corrosion resistance caused by low tin content can be effectively compensated for, thereby improving the service life of the steel plate and optimizing production costs and processes. This innovative process can ensure good corrosion resistance in low-tin-content tin-plated steel plates while reducing resource waste and enhancing environmental friendliness.

[0006] Therefore, in a first aspect, this disclosure provides a tin-plated steel sheet, comprising: a carbon steel substrate, a tin-plated layer formed on at least one surface of the carbon steel substrate, and a surface passivation layer formed on the tin-plated layer, wherein the tin-plated layer comprises a tin-iron alloy layer on the carbon steel substrate and a pure tin layer on the tin-iron alloy layer, and the tin plating weight on one side of the tin-plated layer is 0.30-0.85 g / m². 2 The tin content of the tin-iron alloy layer is less than 65% by mass of the total tin content, and the surface passivation layer contains 1.0-15.0 mg / m³. 2 Metallic chromium and 2.5-30.0 mg / m³ 2 Chromium oxide.

[0007] In a preferred embodiment, the tin plating amount on one side of the tin-plated layer is 0.30-0.75 g / m. 2 More preferably 0.30-0.55 g / m 2 .

[0008] In a preferred embodiment, the tin content of the tin-iron alloy layer is less than 60% by mass of the total tin content, preferably less than 55% by mass.

[0009] In a preferred embodiment, the tin-plated steel sheet is a steel sheet tin-plated on one side only.

[0010] In one embodiment, the tin content of the tin-iron alloy layer is 25% by mass or more of the total tin content, preferably 35% by mass or more.

[0011] In one embodiment, the tin-plated steel sheet further includes an oil layer formed on the surface passivation layer.

[0012] In one embodiment, the paint film adhesion of the tin-plated steel sheet is grade 3 or below, preferably grade 2 or below, and more preferably grade 1.

[0013] The tin-plated steel sheet disclosed herein possesses excellent coating properties (coating adhesion) and corrosion resistance while having a low tin content. Compared with existing conventional tin-plated steel sheet products, the tin-plated steel sheet disclosed herein can effectively save tin resources, reduce usage costs, and simultaneously offer superior performance.

[0014] In a second aspect, this disclosure provides a passivation method for tin-plated steel sheets, comprising the following steps:

[0015] The tin-plated steel sheet is passivated in a passivation solution.

[0016] The passivation treatment is a cathode electrolysis treatment, with a treatment time of 0.05-0.8 seconds and a current density of 30 A / dm³. 2 -100 A / dm 2The passivation solution contains 20-180 g / L of CrO3 and 0.2-1.8 g / L of H2SO4.

[0017] In a preferred embodiment, the passivation solution is prepared using industrial pure water.

[0018] In a preferred embodiment, the tin plating amount on one side of the tin-plated steel sheet is 0.30-0.85 g / m². 2 .

[0019] In a preferred embodiment, the temperature of the passivation solution is 32°C-65°C.

[0020] In a preferred embodiment, the passivation treatment further includes a chemical impregnation treatment performed before and / or after the cathodic electrolysis treatment.

[0021] In a preferred embodiment, the chemical impregnation treatment time prior to the cathodic electrolysis treatment is 1-5 times the cathodic electrolysis treatment time.

[0022] In a preferred embodiment, the chemical impregnation treatment time following the cathodic electrolysis is 2-9 times the cathodic electrolysis treatment time.

[0023] In one implementation, the anode used in the cathodic electrolysis process is plain carbon steel or an inert material, such as lead-tin alloy, platinum, iridium oxide, etc.

[0024] The passivation method disclosed herein, through the combined application of specific passivation solutions, electrolytic treatment time, and current density, can significantly improve the coating adhesion and corrosion resistance of tin-plated steel sheets, effectively compensating for the insufficient corrosion resistance caused by the thinning of the tin layer. Therefore, it is particularly suitable for the passivation treatment of tin-plated steel sheets with low tin content.

[0025] In a third aspect, this disclosure provides a method for preparing a tin-plated steel sheet, comprising sequentially performing tin electroplating, reflow treatment, and passivation treatment on a carbon steel substrate, wherein the passivation treatment is a cathodic electrolysis treatment, the cathodic electrolysis treatment time is 0.05-0.8 seconds, and the current density is 30 A / dm³. 2 -100A / dm 2 The passivation solution contains 20-180 g / L of CrO3 and 0.2-1.8 g / L of H2SO4.

[0026] In one embodiment, the substrate of the tin-plated steel sheet is a cold-rolled carbon steel sheet or strip. The substrate of the tin-plated steel sheet is subjected to cold rolling and annealing, or it can be subjected to secondary cold rolling after annealing.

[0027] In one embodiment, the preparation method of this disclosure further includes alkaline washing and / or acid washing steps prior to tin plating.

[0028] In one embodiment, the main salt of the electroplating solution used in the tin electroplating process is tin methanesulfonate or tin phenolsulfonate, and the electroplating solution may also contain electroplating additives.

[0029] In a preferred embodiment, the remelting process is a resistance remelting process, an induction remelting process, or a combination thereof, and the remelting temperature is 250-270°C.

[0030] In a preferred embodiment, the preparation method of this disclosure further includes an oiling treatment after passivation. In one embodiment, the oiling amount is 1.5 mg / m³. 2 -9.5mg / m 2 .

[0031] The preparation method disclosed herein has a short process flow, is simple, and has low application cost. This method can yield low-tin-content tin-plated steel sheets with good coating properties (coating adhesion) and corrosion resistance. Attached Figure Description

[0032] Figure 1 A schematic cross-sectional view of an exemplary tin-plated steel sheet according to one embodiment of the present invention is shown. Detailed Implementation

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0034] In this paper, the tin content was determined according to GB / T 1838-2008. The content of components in the surface passivation layer (such as the content of metallic chromium and chromium oxide) was determined by X-ray fluorescence spectrometry.

[0035] In this paper, the rating criteria for paint film adhesion are as follows: 0% of the peeling area is grade 1, 0% < peeling area ≤ 10% is grade 2, 10% < peeling area ≤ 25% is grade 3, 25% < peeling area ≤ 50% is grade 4, and peeling area > 50% is grade 5.

[0036] like Figure 1 As shown, an exemplary tin-plated steel sheet according to one embodiment of the present invention includes: a carbon steel substrate (1), a tin-iron alloy layer (2), a pure tin layer (3), a surface passivation layer (4), and an oil layer (5).

[0037] The low-tin-content tin-plated steel sheet disclosed herein has a stable surface, good coating performance and corrosion resistance, and does not contain heavy metals and organic components that are potentially toxic to the human body. It is non-toxic for food contact, environmentally friendly, and particularly suitable for food cans, beverage cans, chemical cans, and electronic components.

[0038] In one embodiment, the method for preparing the tin-plated steel sheet disclosed herein includes the following steps performed sequentially: alkaline washing and / or acid washing of a carbon steel substrate, tin plating, reflow treatment, passivation treatment, rinsing treatment, and oiling treatment.

[0039] Alkaline washing and / or acid washing are common surface pretreatment processes in the production of tin-plated steel sheets. They aim to remove oxides, oil, rust, and other impurities from the carbon steel substrate surface, providing a good base for subsequent tin plating. Alkaline washing can use sodium hydroxide (NaOH) solution. Acid washing can use dilute sulfuric acid (H₂SO₄) or hydrogen chloride (HCl) solution.

[0040] Tin plating can be performed using commonly used plating solutions in this field, including tin sulfate solution and tin chloride solution. The plating solution may also contain plating additives, such as brighteners, dispersants, catalysts, complexing agents, buffers, leveling agents, inhibitors, and adhesives.

[0041] The remelting process typically takes 30 seconds to 2 minutes, and can be adjusted depending on the tin layer thickness and the desired flatness. After remelting, a tin-iron alloy layer (Sn-Fe alloy layer) is formed between the carbon steel substrate and the pure tin layer.

[0042] After passivation, the steel plate can be rinsed, either by immersion rinsing or by spray rinsing. After rinsing, it can be dried with hot air or steam.

[0043] Oiling can be done using electrostatic oiling. Common oiling solutions include mineral oil, synthetic oil, vegetable oil, and silicone oil.

[0044] Example

[0045] The tin-plated steel sheet and its manufacturing method disclosed herein will be further explained and described below with reference to specific embodiments. However, such explanation and description do not constitute an undue limitation on the technical solution of this disclosure.

[0046] Examples 1-5 and Comparative Examples 1-10

[0047] The chemical compositions of the carbon steel substrates of Examples 1-5 and Comparative Examples 1-10 are as follows (by weight percentage): C: 0.086, Si: 0.019, Mn: 0.41, P: 0.017, S: 0.008, Al: 0.045, Cu: 0.009, Ni: 0.010, Cr: 0.022, Mo: 0.02, with the balance being Fe and unavoidable impurities.

[0048] The tin-plated steel sheets of Examples 1-5 and Comparative Examples 1-10 were prepared using the following steps:

[0049] 1) Alkali washing and / or pickling: The carbon steel substrate that has been cold rolled and annealed and tempered is subjected to alkali washing and pickling treatment.

[0050] 2) Tin plating treatment: Tin plating treatment is carried out in a tin plating solution with tin methanesulfonate as the main salt.

[0051] 3) Softening treatment: Full induction softening is used for softening treatment, and the softening temperature is 265℃.

[0052] 4) Passivation treatment: The passivation treatment was carried out using cathodic electrolysis, with the passivation solution, current density, and treatment time shown in Table 1. The temperature of the passivation solution was 40℃.

[0053] 5) Rinsing treatment: After passivation treatment, the product is cleaned and dried.

[0054] 6) Oiling treatment: Apply DOS oil by electrostatic spraying, with an oiling amount of 3.5 mg / m². 2 .

[0055] The composition of the tin-plated steel sheets obtained in Examples 1-5 and Comparative Examples 1-10 is shown in Table 2. The tin content was determined according to GB / T 1838-2008. The composition of the passivation film was determined by X-ray fluorescence method.

[0056] Table 1.

[0057]

[0058]

[0059] Note: The passivation solution used in Examples 1-5 and Comparative Examples 1-8 was CrO3+H2SO4; the passivation solution used in Comparative Examples 9-10 was sodium dichromate (Na2Cr2O7).

[0060] Table 2.

[0061]

[0062]

[0063] Samples of the tin-plated steel sheets from Examples 1-5 and Comparative Examples 1-10 were taken and their paint film adhesion and corrosion resistance were evaluated. The evaluation results are listed in Table 3.

[0064] Paint film adhesion evaluation method: On a scratch tester with a pitch of 1.5mm, set the scratching speed to 90-100r / min and scratch a thread line with a length of 60mm-80mm and a diameter of 10mm. The scratching depth should be adjusted until it just penetrates the coating. Gently brush away the scratched coating debris with a brush, then apply 3M 610 adhesive tape to the scratch line, ensuring that the tape adheres completely to the coating and pressing the tape firmly. Next, fix the coating sample and quickly peel off the adhesive tape at an upward angle. Finally, observe and record the area of ​​coating that has been peeled off. The peeling area is 0% for Grade 1, 0% < peeling area ≤ 10% for Grade 2, 10% < peeling area ≤ 25% for Grade 3, 25% < peeling area ≤ 50% for Grade 4, and peeling area > 50% for Grade 5.

[0065] Corrosion Resistance Assessment Method: Based on the usage characteristics in the food packaging industry, corrosion resistance is assessed under sulfur-containing environments. The solution formulation used is as follows: 0.50g L-cysteine ​​hydrochloride (C3H8NO2SCl) or 0.56g L-cysteine ​​hydrochloride (C3H8NO2SCl·H2O), 3.60g potassium dihydrogen phosphate (KH2PO4), and 18g disodium hydrogen phosphate (Na2HPO4·12H2O). The above components are dissolved separately in water, mixed, and diluted to 1000mL. The assessment method is as follows: The coated sample is placed in the above sulfur resistance test solution, sealed, and then placed in an autoclave. It is boiled at 121℃ for 60 minutes. After cooling, the sample is removed and rinsed clean, and the surface is observed for sulfide corrosion. ○○ indicates no sulfide corrosion, good corrosion resistance; ○ indicates slight sulfide corrosion, acceptable corrosion resistance; △ indicates significant sulfide corrosion, poor corrosion resistance.

[0066] Table 3.

[0067]

[0068]

[0069] All publications, patent applications, patents, and other references mentioned in this disclosure are incorporated herein by reference in their entirety.

[0070] While this disclosure has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the disclosure in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of this disclosure to these descriptions. Various changes in form and detail, including some simple deductions or substitutions, can be made by those skilled in the art without departing from the spirit and scope of this disclosure.

Claims

1. A tin-plated steel sheet, comprising: The invention comprises a carbon steel substrate, a tin-plated layer formed on at least one surface of the carbon steel substrate, and a surface passivation layer formed on the tin-plated layer, wherein the tin-plated layer includes a tin-iron alloy layer on the carbon steel substrate and a pure tin layer on the tin-iron alloy layer, and the single-sided tin plating weight of the tin-plated layer is 0.30-0.85 g / m². 2 The tin content of the tin-iron alloy layer is less than 65% by mass of the total tin content, preferably 25% to 60% by mass, and the surface passivation layer contains 1.0-15.0 mg / m³. 2 Metallic chromium and 2.5-30.0 mg / m³ 2 Chromium oxide.

2. The tin-plated steel sheet according to claim 1, wherein, The tin-plated steel sheet also includes an oil layer formed on the surface passivation layer.

3. The tin-plated steel sheet according to claim 1 or 2, wherein, The paint adhesion of the tin-plated steel sheet is below level 3.

4. A passivation method for tin-plated steel sheet, comprising the following steps: The tin-plated steel sheet is passivated in a passivation solution. The passivation treatment is a cathode electrolysis treatment, with a treatment time of 0.05-0.8 seconds and a current density of 30 A / dm³. 2 -100 A / dm 2 The passivation solution contains 20-180 g / L of CrO3 and 0.2-1.8 g / L of H2SO4.

5. The passivation method according to claim 4, wherein, The tin plating amount on one side of the tin-plated steel sheet is 0.30-0.85 g / m². 2 .

6. The passivation method according to claim 4 or 5, wherein, The temperature of the passivation solution is 32℃-65℃.

7. The passivation method according to claim 4 or 5, wherein, The passivation treatment further includes a chemical impregnation treatment performed before and / or after the cathodic electrolysis treatment. Preferably, the chemical impregnation treatment time before the cathodic electrolysis treatment is 1-5 times the cathodic electrolysis treatment time, and the chemical impregnation treatment time after the cathodic electrolysis treatment is 2-9 times the cathodic electrolysis treatment time.

8. The method for preparing tin-plated steel sheet according to any one of claims 1 to 3, comprising sequentially performing electroplating tin treatment, reflow treatment, and passivation treatment on a carbon steel substrate, wherein, The passivation treatment is a cathodic electrolysis treatment, with a treatment time of 0.05-0.8 seconds and a current density of 30 A / dm³. 2 -100A / dm 2 The passivation solution contains 20-180 g / L of CrO3 and 0.2-1.8 g / L of H2SO4.

9. The preparation method according to claim 8, wherein, The softening process is a resistance softening process, an induction softening process, or a combination thereof, and the softening temperature is 250-270℃.

10. The preparation method according to claim 8 or 9, wherein, The preparation method further includes an oiling treatment after passivation, with an oiling amount of 1.5 mg / m³. 2 -9.5mg / m 2 .

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