Environmentally friendly low-tin tin-plated sheet and manufacturing method thereof

Abstract

The present invention specifically relates to an environmentally friendly low-tin tin-plated plate and a manufacturing method thereof, and belongs to the technical field of alloy materials. The low-tin tin-plated plate comprises a substrate, a Fe-Sn alloy layer, a pure tin layer, a passivation film and an oil film in sequence. The tin content of the Fe-Sn alloy layer is 0.4 to 0.6 g / m 2 The alloy layer is uniform and dense, the grains are columnar, and the sum of the orientation degrees of FeSn2 (211) and FeSn2 (213) in the alloy layer is 2.5~3.0; the tin content of the pure tin layer is 0.5~0.7g / m 2 , the sum of the crystal orientation degrees of Sn(101) and Sn(200) is 2.2~2.5. The manufacturing method is based on an environmentally friendly methanesulfonic acid (MSA) electroplating tinning process and a low chromium content passivation process flow to solve the problem that low-tin tin-plated plates have poor corrosion resistance and are prone to pitting. The present invention designs the substrate composition and combines the process design of the key processes of "annealing, leveling, pickling, pre-wetting, electroplating, fluxing, soft melting, passivation, and oiling" to manufacture low-tin tin-plated plates with excellent corrosion resistance.

Description

Technical Field

[0001] The invention relates to an environmentally friendly low-tin tin-plated plate and a manufacturing method thereof, belonging to the technical field of alloy materials. Background Art

[0002] Tinplate has the characteristics of printable patterns, easy welding, corrosion resistance, safety and non-toxicity, etc. It is widely used in the packaging of food, beverages, daily necessities, and chemical reagents. The standard electrode potential of tin is -0.136V, and the standard electrode potential of iron is -0.440V. Tinplate is a cathode coating material, and its corrosion resistance mainly relies on the physical isolation effect of the tin layer on the surface of the steel substrate and the chemical inertness of the surface tin layer and the passivation film layer. Due to the high price of metallic tin, which is about 40 times the price of steel, high-tin tinplate has good corrosion resistance but high price. In order to reduce the cost of raw materials, the downstream packaging industry is increasingly using low-tin tinplate, but the tin coating amount is reduced to 1.1g / m 2 And below, the corrosion resistance of tinplate deteriorates significantly, and rust problems often occur during production, transportation and use. Therefore, how to ensure the corrosion resistance of low-tin tinplate products has become an urgent problem to be solved.

[0003] The existing technology mainly improves the corrosion resistance of low-tin tin-plated sheets through two major technical methods: the first method starts from the tin-plated layer and obtains a favorable tin layer structure by controlling the orientation of tin grains; the second method starts from the surface film layer and improves resistance to corrosive environments by changing the composition or structure of the surface film layer of the tin-plated sheet.

[0004] The first category of methods includes:

[0005] Invention patent application 202111043082.4 discloses a method for controlling the orientation of grain growth on the surface of a low-tin tin-plated plate. The technical solution is as follows: a grain orientation control agent mixed with a hydroxybenzenesulfonic acid solution and a salicylic acid solution is added to the electroplating tin solution to effectively control the grain growth orientation of the alloy layer. The resulting tin-plated plate alloy layer has dense grain arrangement, high grain orientation consistency, and excellent overall quality of the alloy layer, so that the corrosion resistance of the low-tin tin-plated plate meets the use standard.

[0006] Invention patent application 202110743567.8 discloses a method for improving the surface corrosion resistance of low-tin tin-plated sheets. The grain and crystal plane orientation of the cold-rolled substrate is controlled by changing the process system of heat treatment; on this basis, the growth direction of the tin-iron alloy layer is regulated to improve the density of the tin-iron alloy layer; before soft melting, the fluidity of the tin layer is improved by infiltration, and the porosity of the free tin layer on the surface of the tin-plated sheet is regulated, thereby improving the surface corrosion resistance of the low-tin tin-plated sheet.

[0007] The second category of methods includes:

[0008] Invention patent application 202010750406.7 discloses a composite-coated tinplate production process and tinplate. The tinplate production process includes: degreasing and pickling the steel substrate; electroplating tin on the steel substrate, with a single-sided tinning amount of 0.15 to 1.0 g / m 2 , then rinse, forming a pure tin layer with a thickness of 0.15~1.0μm on the surface of the steel substrate; melting the tinned layer to make it leveled to produce a bright surface, forming a tin-iron alloy layer with a thickness of 0.08~0.12μm between the steel substrate and the pure tin layer; electroplating chrome on the surface of the tinned steel substrate and rinsing, forming a chromium metal layer and a chromium hydrate oxide layer on the surface of the pure tin layer; finally, applying oil to the surface to form an oil film layer. On the one hand, this production process requires the transformation of related equipment for electroplating chrome, and on the other hand, it also greatly increases the use of hexavalent chromium solution and the amount of wastewater to be treated.

[0009] The disadvantages of the prior art are:

[0010] (1) Insufficient stability in industrial production: Since electroplating production is a complex chemical and electrochemical process, the composition system of the plating solution is complex. Taking the methanesulfonic acid (MSA) plating solution as an example, the plating solution used in the existing electroplating tin industry includes MSA, antioxidants, additives, etc., and the various components affect each other. The existing technology directly adds other components to the electroplating tin solution, which is easy to affect the current efficiency, coating quality, throwing power and the stability of the plating solution in long-term circulation.

[0011] (2) Difficulty in production and high cost: Since it is necessary to add special processing steps (chromium plating) and special equipment (high corrosion-resistant plates, high-current rectifiers, etc.) to the original electroplating tin production line, production control is difficult and production costs are increased.

[0012] (3) Poor environmental protection: The chrome-plating layer is obtained by using a high-concentration chromium-containing solution. On the one hand, a large amount of chromium-containing waste liquid is produced which is difficult to treat. On the other hand, the risk of residual hexavalent chromium on the surface of the tinplate is significantly increased. Summary of the invention

[0013] In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide an environmentally friendly low-tin tin-plated sheet and a manufacturing method thereof. The tin-plated sheet has excellent corrosion resistance, and the production process is environmentally friendly, simple to control, and low in cost. It is suitable for tin-plated sheets with a tin content of 1.1 g / m 2 The specific technical scheme is as follows:

[0014] A method for manufacturing an environmentally friendly low-tin tin-plated plate comprises the following steps:

[0015] Step S1, annealing: annealing the cold-rolled steel sheet in an annealing furnace, controlling the annealing temperature to 640-660°C and the annealing time to 30-45s; using a reducing protective atmosphere in the furnace, with a dew point of -50--45°C and an O2 content of 0-10ppm;

[0016] Step S2, flattening: flattening the cold-rolled steel sheet after annealing in step S1 to obtain a cold-rolled steel sheet with a flat surface.

[0017] Step S3, degreasing: removing oil stains on the surface of the cold-rolled steel sheet by chemical degreasing, electrolytic degreasing, brushing, rinsing and drying to obtain a substrate with a clean surface for electroplating;

[0018] Step S4, pickling: electrolytic pickling of the substrate obtained in step S3, with a current density of 10-12 A / dm 2 The pickling solution is 70-80 g / L sulfuric acid H2SO4, the solution temperature is 30-35 °C, and the pickling time is 2-3 seconds;

[0019] Step S5, pre-wetting: immerse the pickled substrate in step S4 into a mixed solution of methanesulfonic acid and potassium hydroxybenzenesulfonate, wherein the concentration of methanesulfonic acid is 10-15 mL / L, the concentration of potassium hydroxybenzenesulfonate is 2-5 mL / L, and the solution temperature is 40-45° C.;

[0020] Step S6, electroplating tin: electroplating the substrate after the pre-wetting treatment in step S5, using a combination of current densities of "high, low, and medium" to form a total tin content of 0.9 to 1.2 g / m 2 A pure tin layer is formed to obtain a substrate having a pure tin layer plated on the surface;

[0021] Step S7, fluxing: immersing the substrate with the pure tin layer plated on the surface obtained in step S6 into a flux solution in a fluxing tank, wherein the flux solution is a salicylate aqueous solution, and the concentration of the flux solution is 0.5-1.0 g / L; adjusting the pH value of the solution to 6.5-8.0 by sodium hydroxide or potassium hydroxide; spraying the surface of the substrate with the pure tin layer plated on the surface with desalted water after it comes out of the fluxing tank to remove excess flux on the surface;

[0022] Step S8, soft melting: the substrate with the pure tin layer plated on the surface after the fluxing treatment in step S7 is quickly heated to the soft melting temperature; high-frequency inductance soft melting is adopted, the soft melting temperature is 250-255°C, and the soft melting time is 0.5-1.0s; the substrate with the pure tin layer plated on the surface after soft melting enters the water quenching tank for cooling, the water quenching water temperature is 75-85°C, and the water conductivity of the water quenching water is ≤1ms / cm; an Fe-Sn alloy layer is formed between the substrate and the pure tin layer;

[0023] Step S9, passivation: The substrate obtained in step S8 is surface treated by a two-stage passivation method of "chemical passivation + electrochemical passivation". The two-stage passivation uses a passivation solution of 20-22 g / L sodium dichromate solution, a passivation solution temperature of 40-42 ° C, a passivation solution pH of 4.2-4.4, a passivation time of 1.0-1.5 s, and a passivation charge density of 1.0-1.2 C / dm in the electrochemical passivation stage. 2 ; A passivation film is formed on the surface of the pure tin layer. The thickness of the passivation film is controlled to be 4-6 mg / m based on the Cr content. 2 ;

[0024] Step S10, oiling: Use an electrostatic oiler to oil the substrate obtained in step S9 to form an oil film on the surface of the passivation film. The oil type is DOS oil, and the oil coating amount is 3-5 mg / m 2 .

[0025] Furthermore, in the step S1, the reducing protective atmosphere in the furnace is a mixed gas of nitrogen N2 and hydrogen H2, and the volume proportion of hydrogen H2 in the mixed gas is 5% to 10%.

[0026] Furthermore, the cold-rolled steel sheet in step S1 is made of low carbon steel, and the low carbon steel comprises the following components in terms of mass percentage: C: 0.060%-0.080%, Mn: 0.10%-0.15%, Si≤0.02%, P≤0.015%, S≤0.010%, Al: 0.02%-0.04%, N: 0.0030%-0.0060%, and the remainder is Fe and other inevitable impurities.

[0027] Furthermore, in step S2, a double-frame dry leveling machine is used for leveling treatment. The working roll of the No. 1 frame adopts an electric spark texturing roll, and the surface roughness parameters of the roll are: profile arithmetic mean Ra: 1.5~1.6μm, peak number Rpc: 80~100 / cm, and the sum of the maximum profile peak height and valley depth Rz: 2.5~4.0μm; the working roll of the No. 2 frame adopts a grinding roll, and the surface roughness parameters of the roll are: profile arithmetic mean Ra: 0.4~0.5μm, peak number Rpc: 110~130 / cm, and the sum of the maximum profile peak height and valley depth Rz: 1.0~2.0μm.

[0028] Furthermore, the specific process of the step S6 electroplating tin is: using an environmentally friendly methanesulfonic acid soluble anode electroplating system, the concentration of each component in the electroplating solution is: tin ion Sn 2+ : 15-20 g / L, free acid: 30-35 mL / L, additive: 20-25 mL / L, antioxidant: 30-35 mL / L, the plating solution temperature is 40-45 ° C; open 5 plating tanks for electroplating, the current density of the plating tanks is: 15-18 A / dm2 , 10~13A / dm 2 , 10~13mA / dm 2 , 10~13A / dm 2 , 12~15A / dm 2 .

[0029] Furthermore, the salicylate aqueous solution is selected from sodium salicylate or potassium salicylate.

[0030] An environmentally friendly low-tin tin-plated plate, the environmentally friendly low-tin tin-plated plate is made by the above-mentioned environmentally friendly low-tin tin-plated plate manufacturing method, the environmentally friendly low-tin tin-plated plate is a multi-layer structure, which includes a substrate, a Fe-Sn alloy layer, a pure tin layer, a passivation film and an oil film in sequence.

[0031] Furthermore, the substrate is made of low carbon steel, and the mass percentage is: C: 0.060%~0.080%, Mn: 0.10%~0.15%, Si≤0.02%, P≤0.015%, S≤0.010%, Al: 0.02%~0.04%, N: 0.0030%~0.0060%, and the balance is Fe and other inevitable impurities; the substrate thickness is 0.12~0.50mm, and the surface roughness parameters are: profile arithmetic mean Ra: 0.3~0.4μm, peak number Rpc: 90~110 / cm, and the sum of the maximum profile peak height and valley depth Rz: 1.5~3.0μm.

[0032] Furthermore, the amount of tin in the Fe-Sn alloy layer is 0.4 to 0.6 g / m 2 The alloy layer is uniform and dense, the grains are columnar, and the sum of the orientation degrees of FeSn2 (211) and FeSn2 (213) in the alloy layer is 2.5~3.0;

[0033] Furthermore, the amount of tin in the pure tin layer is 0.5 to 0.7 g / m 2 , the sum of the Sn(101) and Sn(200) crystal plane orientation degrees is 2.2~2.5.

[0034] The beneficial effects of the present invention are:

[0035] (1) Excellent corrosion resistance: The present invention achieves excellent corrosion resistance through substrate composition design combined with a comprehensive process scheme covering "annealing, leveling, pickling, pre-wetting, electroplating, fluxing, soft melting, passivation, and oiling". The existing technology simply relies on the control of tin grain orientation and alloy layer, or increases the thickness of the passivation film or changes the composition of the film to improve corrosion resistance. The technical means are single, and the formation process of the substrate, tin layer, and passivation layer and the integrity of the previous and subsequent processes are not considered, and the comprehensive effect of the multi-layer structure on the corrosion resistance of the tinplate surface is ignored. The present invention starts from the substrate composition and surface structure of the tinplate, controls the key factors that affect the uniformity, density, coverage, and favorable orientation of the tin layer one by one, and combines the enhanced protection of the passivation layer to ultimately achieve excellent corrosion resistance. Specifically, the following steps are taken: ① Before electroplating, by selecting a substrate with low content of alloying elements such as Si, Mn, and Al and adding N elements, the generation of surface oxides is effectively reduced; at the same time, a lower annealing temperature is matched, and annealing is performed in a reducing atmosphere with high hydrogen content, low oxygen content, and low dew point, so as to further reduce surface oxidation. Furthermore, an enhanced pickling treatment is used to remove the surface oxide film formed finally before electroplating, so as to obtain a fresh and clean surface without obvious oxides; at the same time, the substrate is given a specific surface profile (moderate Ra, high Rpc, and low Rz) through the double-frame leveling of "electric spark texturing roller + grinding roller", so as to provide a suitable electrodeposition base for subsequent electroplating of tin; further, through the pre-wetting treatment of "methanesulfonic acid + potassium hydroxybenzenesulfonate" with specific components, the substrate surface is activated before electroplating to promote the generation of favorable oriented tin grains. ② In electroplating, an MSA electroplating solution with suitable components and concentrations is used, and a "high + low + medium" combination of electroplating current density control is further used to promote efficient, orderly and uniform deposition of tin ions on the substrate surface, obtain tin grains with suitable grain size and favorable orientation, and reduce microcracks and pores caused by stress and uneven distribution of the tin layer. ③ After electroplating, a salicylate aqueous solution with a pH close to neutral is used for fluxing to avoid the pitting rust problem caused by the residue of the strong acid flux, and a rapid heating, low reflow temperature and short residence time reflow treatment, a "chemical passivation + electrochemical passivation" combination of passivation and electrostatic oiling are used to further obtain a uniform and dense alloy layer, and the resulting FeSn2 grain orientation is beneficial to corrosion resistance, while retaining a sufficient amount of pure tin layer, and obtaining a stable passivation film layer and a uniformly covered oil film, and finally forming a composite film structure on the surface of the tinplate that effectively resists corrosion, so that the manufactured tinplate has excellent corrosion resistance.

[0036] (2) The method is simple and easy to operate, and the production cost is low: the manufacturing method of the tinplate of the present invention does not require the addition of special process flow or equipment. Compared with the prior art which requires the addition of high-current rectifiers, high-corrosion-resistant plates and other equipment, the production cost is lower; at the same time, the pre-wetting and fluxing reagent components added by the present invention are simple and easy to obtain, and will not affect the original solution system; the process control methods such as the electroplating current density and the passivation power provided by the present invention are all within the controllable range of the existing production line and are easy to operate on the original tin-plating production line. The method is simple and easy to operate.

[0037] (3) Environmental friendliness of the process: The present invention is based on an environmentally friendly methanesulfonic acid (MSA) electroplating tinning process and a low chromium content passivation process. Compared with the prior art that uses a benzenesulfonic acid system plating solution and increases the concentration of the hexavalent chromium solution, the production process of the present invention is significantly environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a schematic diagram of the process flow of the tinplate manufacturing method of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0040] Combined with Figure 1 It can be seen that the method for manufacturing the environmentally friendly low-tin tin-plated plate comprises the following steps:

[0041] S1. Annealing: The cold-rolled steel sheet is annealed in an annealing furnace, the annealing temperature is controlled at 640-660°C, and the annealing time is 30-45s; a reducing protective atmosphere is used in the furnace, the H2 content is 5%-10%, the dew point in the furnace is -50--45°C, and the O2 content is 0-10ppm. The cold-rolled steel sheet is low-carbon steel, and the mass percentage is C: 0.060%-0.080%, Mn: 0.10%-0.15%, Si≤0.02%, P≤0.015%, S≤0.010%, Al: 0.02%-0.04%, N: 0.0030%-0.0060%, and the balance is Fe and other inevitable impurities.

[0042] S2, leveling: the cold-rolled steel sheet after annealing in step S1 is leveled by a double-stand dry leveling machine; the working roll of the No. 1 stand adopts an electric spark texturing roll, and the roller surface roughness parameters are, Ra (profile arithmetic mean): 1.5~1.6μm, Rpc (peak number): 80~100 / cm, Rz (sum of maximum profile peak height and valley depth): 2.5~4.0μm; the working roll of the No. 2 stand adopts a grinding roll, and the roller surface roughness parameters are, Ra: 0.4~0.5μm, Rpc: 110~130 / cm, Rz: 1.0~2.0μm.

[0043] S3. Degreasing: Use chemical degreasing, electrolytic degreasing, brushing, rinsing and drying to remove oil stains on the surface of the cold-rolled steel plate to obtain a substrate with a clean surface.

[0044] S4, pickling: electrolytic pickling of the substrate in step S3, with a current density of 10-12 A / dm 2 The pickling solution is 70-80 g / L sulfuric acid H2SO4, the solution temperature is 30-35°C, and the pickling time is 2-3s.

[0045] S5, pre-wetting: immerse the pickled substrate in step S4 into a mixed solution of methanesulfonic acid and potassium hydroxybenzenesulfonate, wherein the concentration of methanesulfonic acid is 10-15 mL / L, the concentration of potassium hydroxybenzenesulfonate is 2-5 mL / L, and the solution temperature is 40-45°C.

[0046] S6, electroplating tin: electroplating the substrate after the pre-wetting treatment in step S5 to obtain a tin-plated plate. An environmentally friendly methanesulfonic acid soluble anode electroplating system is used, and the concentration of each component in the electroplating solution is: tin ion (Sn 2+ ) 15-20 g / L, free acid 30-35 mL / L, additive 20-25 mL / L, antioxidant 30-35 mL / L, plating solution temperature 40-45 °C. Open 5 plating tanks for electroplating, the current density of the plating tanks is: 15-18 A / dm 2 , 10~13A / dm 2 , 10~13mA / dm 2 , 10~13A / dm 2 , 12~15A / dm 2 .

[0047] S7, fluxing: immerse the tinplate in step S6 into a fluxing solution, wherein the flux is a salicylate aqueous solution (including sodium salicylate or potassium salicylate) with a flux concentration of 0.5-1.0 g / L; adjust the solution pH to 6.5-8.0 by using sodium hydroxide or potassium hydroxide; and spray the surface of the tinplate with desalted water to remove excess flux.

[0048] S8, soft melting: quickly heat the tinplate after the fluxing treatment in step S7 to the soft melting temperature; adopt high-frequency inductance soft melting, the soft melting temperature is 250~255℃, and the soft melting time is 0.5~1.0s; after soft melting, the substrate enters the water quenching tank for cooling, the water quenching water temperature is 75~85℃, and the water quenching water conductivity is ≤1ms / cm.

[0049] S9, passivation: The substrate is surface treated by a two-stage passivation method of "chemical passivation + electrochemical passivation". The passivation solution is a sodium dichromate solution with a concentration of 20-22 g / L, a passivation solution temperature of 40-42 °C, a passivation solution pH of 4.2-4.4, a passivation time of 1.0-1.5 s, and a passivation charge density of 1.0-1.2 C / dm in the electrochemical passivation stage. 2 , control the passivation film thickness to 4~6mg / m 2 (measured in Cr content).

[0050] S10, Oiling: Use electrostatic oiling machine, the oiling type is DOS oil, the oiling amount is 3-5mg / m 2 .

[0051] The invention provides an environmentally friendly low-tin tin-plated plate, which is manufactured by the method and consists of a substrate, a Fe-Sn alloy layer, a pure tin layer, a passivation film and an oil film from the inside to the outside. The substrate is low carbon steel, and the mass percentage is calculated as follows: C: 0.060%~0.080%, Mn: 0.10%~0.15%, Si≤0.02%, P≤0.015%, S≤0.010%, Al: 0.02%~0.04%, N: 0.0030%~0.0060%, and the remainder is Fe and other inevitable impurities; the substrate thickness is 0.12~0.50mm, and the surface roughness parameters are, Ra (profile arithmetic mean): 0.3~0.4μm, Rpc (peak number): 90~110 / cm, Rz (sum of maximum profile peak height and valley depth): 1.5~3.0μm; the tin content of the Fe-Sn alloy layer is 0.4~0.6g / m 2 The alloy layer is uniform and dense, the grains are columnar, and the sum of the orientation degrees of FeSn2 (211) and FeSn2 (213) in the alloy layer is 2.5-3.0; the tin content of the pure tin layer is 0.5-0.7 g / m 2 The sum of the Sn(101) and Sn(200) crystal orientation degrees is 2.2~2.5; the total tin content is 0.9~1.2g / m 2 The weight of the passivation film is 4 to 6 mg / m 2 (calculated based on Cr content); the weight of the oil film is 3-5 mg / m 2 .

[0052] The principles involved in the technical solution of the present invention are as follows:

[0053] The present invention improves the corrosion resistance of low-tin tin-plated plates through three technical measures, which are as follows:

[0054] First, before electroplating, a substrate with a specific composition is selected, and through annealing, leveling, pickling and pre-impregnation treatment, a uniform, clean, activated substrate surface with specific surface structure characteristics is obtained, which provides a basis for obtaining a high-quality tin plating layer.

[0055] Secondly, during electroplating, the tin ions are efficiently and orderly deposited on the substrate surface by controlling the composition of the electroplating solution and the electroplating current density, thereby obtaining tin grains with suitable size and favorable orientation, while reducing microcracks and pores caused by stress and uneven distribution of the tin layer.

[0056] Third, after electroplating, through fluxing, soft melting, passivation and oiling control, a uniform and dense alloy layer is further obtained on the basis of the high-quality tin-plated layer in the previous process, and the FeSn2 grain orientation is beneficial to the corrosion resistance. At the same time, a sufficient amount of pure tin layer is retained, and a stable passivation film layer and a uniformly covering oil film are obtained on the surface of the tin layer, finally forming a tinplate surface film structure that effectively resists corrosion.

[0057] The reasons for selecting the key process parameters of the present invention are described in detail below:

[0058] (1) Substrate composition: in terms of mass percentage, C: 0.060%~0.080%, Mn: 0.10%~0.15%, Si≤0.02%, P≤0.015%, S≤0.010%, Al: 0.02%~0.04%, N: 0.0030%~0.0060%.

[0059] C: Controlling the right amount of C is beneficial to obtaining the strength and hardness required by the tinplate. At the same time, the corrosion resistance of the steel decreases with the increase of the C content. Too high a C content will also cause the plasticity of the steel to deteriorate, which is not conducive to the processing and use of the tinplate. Therefore, the present invention selects a C content of 0.06% to 0.08%.

[0060] Mn: Mn, as a solid solution strengthening element, can improve the strength of the steel plate without significantly reducing the plasticity. At the same time, Mn combines with S to form MnS to reduce the hot brittleness of the steel. However, if the Mn content is too high, Mn oxides are easily formed during high-temperature heating, thereby affecting the quality of the coating. Therefore, the present invention selects a Mn content of 0.10% to 0.15%.

[0061] Si: Si is easily enriched and oxidized on the steel surface. The oxide of Si is chemically inert and tightly combined with the steel matrix, making it difficult to remove by pickling. The oxide of Si covering the surface of the tin-plated substrate will cause problems such as missed plating, loose coating, and poor bonding, which seriously affects the product quality. Therefore, the lower the Si content, the better. The present invention selects Si≤0.02%.

[0062] P: P is an impurity element and is easily segregated, resulting in decreased plasticity and corrosion resistance of steel. In the present invention, P is selected to be ≤ 0.015%.

[0063] S: For tinplate, S is a harmful impurity element and is easy to form sulfide inclusions, which is not conducive to the forming of steel plates. In the present invention, S is selected to be ≤0.010%.

[0064] N: N in steel belongs to interstitial solid solution atoms, and can combine with Al to form AlN precipitation phase, which plays a role in solid solution strengthening and precipitation strengthening. For tinplate, increasing the N content can effectively improve the strength and hardness of the tinplate, but when the N content is too high, the hardness of the tinplate is too high and the plasticity deteriorates, which is not conducive to the processing and forming of the tinplate. At the same time, as the nitrogen content increases, the recrystallization temperature of the tinplate increases, and a higher annealing temperature will cause the oxide film on the surface of the substrate to increase, which is not conducive to the quality of the coating. Therefore, the present invention selects an N content of 0.0030% to 0.0060%.

[0065] Al: Al is added as a deoxidizer during the steelmaking process. At the same time, Al can combine with N to form AlN, which plays a role in precipitation strengthening. However, too high an Al content will increase steelmaking inclusions, deteriorate continuous casting castability, and cause surface defects. Al-containing oxides are enriched on the substrate surface, affecting the bonding strength of the coating and being detrimental to corrosion resistance. Therefore, the Al content range selected in the present invention is 0.02%-0.04%.

[0066] (2) Annealing: Cold-rolled steel sheets are prone to forming oxide films on the surface during annealing, especially Si and Mn elements are enriched on the surface to form oxides that are difficult to remove, which is not conducive to subsequent electroplating. Therefore, a lower annealing temperature and a shorter annealing time are used to reduce the content of oxides generated at high temperatures. However, the annealing temperature cannot be lower than the recrystallization temperature of the steel sheet. The annealing temperature is selected to be 640~660℃, and the annealing time cannot be less than 30s to avoid the problem of incomplete recrystallization of the steel sheet structure, resulting in excessive strength and deterioration of processing performance. Furthermore, a reducing protective atmosphere is used in the furnace, with a H2 content of 5%~10%, a furnace dew point of -50~-45℃, and an O2 content of 0~10ppm. By lowering the dew point and oxygen content, the formation of oxides of elements such as Si and Mn is suppressed, and sufficient H2 reduces the surface iron oxide to iron, thereby obtaining a substrate surface with good plating properties.

[0067] (3) Leveling: The leveling treatment gives the substrate a specific surface structure to ensure that the structure of the tin-plated layer deposited on the surface is uniform and dense, and the bonding strength and corrosion resistance of the coating are improved. Using two sets of working rollers with different surface structures for leveling can more accurately control the surface structure of the tin-plated substrate; at the same time, dry leveling can effectively avoid surface defects and rust problems caused by residual leveling liquid. The surface roughness control principle of the working roller is as follows: 1) The working roller of the No. 1 frame adopts an electric spark texturing roller. The high-roughness texturing roller is used to copy uniform and dense concave and convex points on the cold-rolled steel plate to improve the surface bonding strength, avoid poor coating bonding caused by too small roughness and insufficient tin layer coverage caused by too large roughness; according to the corresponding relationship between the roller surface roughness and the substrate surface roughness, the roller surface roughness Ra of the working roller is selected to be 1.5~1.6μm and Rpc is 80~100 / cm ; 2) The working rolls of the No. 2 stand are ground rolls, and the roll surface roughness Ra is selected to be 0.4~0.5μm and Rpc is 110~130 pieces / cm; the grinding rolls with small roughness are used to create longitudinal lines on the surface of the substrate, and the peaks with large surface protrusions are ground off, thereby improving the coverage of the tin plating layer; 3) Furthermore, the roll surface roughness parameter Rz of the working rolls of the No. 1 and No. 2 stands is controlled within an appropriate range. On the one hand, due to the limitations of solution ion diffusion and soft molten tin layer leveling during the electroplating process, the coating quality is poor at the peaks that are too high and the valleys that are too low on the surface of the substrate, indicating that a large Rz value is not conducive to corrosion resistance; on the other hand, when the Rz value is too low, the Ra value is bound to be low, resulting in poor bonding and adhesion of the coating; therefore, Rz is selected as 2.5~4.0μm (No. 1 stand) and 1.0~2.0μm (No. 2 stand), respectively.

[0068] (4) Pickling: Through enhanced pickling, the oxide film on the surface of the substrate can be effectively removed, exposing the fresh iron matrix and providing a good surface foundation for electroplating. The pickling solution is 70-80g / L sulfuric acid (H2SO4), the solution temperature is 30-35°C, and the pickling time is 2-3s, which can effectively remove the oxide layer. If the concentration is low, the pickling time is short, and the oxide layer is not completely removed; if the concentration is too high, local corrosion is severe after over-pickling, and surface pores are formed, which is not conducive to the subsequent electroplating of tin to form a smooth coating; if the pickling time is increased, the production line speed needs to be reduced, and the production efficiency decreases; by adopting electrolytic pickling and maintaining a high current density, the unit can achieve enhanced pickling effect under the condition of cold-rolled steel plate speed (350-400m / min). Therefore, the current density of 10-12A / dm is selected. 2 .

[0069] (5) Pre-wetting: Pre-wetting is to immerse the pickled substrate in a mixed solution of methanesulfonic acid and potassium hydroxybenzenesulfonate before electroplating. The organic groups of the wetting agent will be adsorbed on the substrate, increasing the cathode polarization effect, thereby effectively adjusting the electrochemical state of the substrate surface, changing the deposition rate and structure of tin ions on the substrate surface, and promoting the formation of a dense tin layer during the electroplating process. At the same time, pre-wetting is also conducive to the growth of tin grains along the preferred orientation of Sn (101) and Sn (200). Since the

[101] and

[200] orientations of Sn have lower planar energy, the tin-plated layer with this structural feature has better coating stability and corrosion resistance. Since methanesulfonic acid and potassium hydroxybenzenesulfonate are both components of the electroplating solution, even if a small amount of pre-wetting solution is brought into the electroplating tin process, it will not affect the entire plating solution system. Therefore, methanesulfonic acid and potassium hydroxybenzenesulfonate are selected as pre-wetting agents. The concentration of methanesulfonic acid is 10-15 mL / L, the concentration of potassium hydroxybenzenesulfonate is 2-5 mL / L, and the solution temperature is maintained at 40-45° C., which can ensure that the pre-wetting reaction is sufficient.

[0070] (6) Electroplating tin: The electroplating tin process is the key link to determine the performance of the tin-plated layer. Environmentally friendly methanesulfonic acid plating solution and soluble anode plating system are used. After process tests, process parameters that are beneficial to the quality of the tin-plated layer are summarized. Among them, the concentration of each component in the electroplating solution is: tin ion (Sn 2+ ) 15~20g / L, free acid 30~35mL / L, additive 20~25mL / L, antioxidant 30~35mL / L, plating solution temperature 40~45℃. On this basis, the grain size and density of the tin plating layer can be controlled by controlling the current density distribution of different plating tanks. The first plating tank uses a high current density (15~18A / dm 2 ) to start electroplating, which is conducive to rapid activation of the surface and obtaining fine tin grains, providing sufficient electrochemical deposition sites for subsequent tin deposition; the current density of the 2nd to 4th electroplating tanks is appropriately reduced (10-13A / dm 2 ) and remain stable, which can ensure that tin ions are deposited efficiently and evenly on the surface, reducing the stress and microscopic pores caused by excessively high deposition rates; the fifth electroplating tank appropriately increases the current density to 12-15A / dm 2 , which is beneficial to enhance the deep plating ability and coating coverage, thereby improving the uniformity and density of the overall tin plating layer.

[0071] (7) Fluxing: The flux of the present invention adopts salicylate aqueous solution (including sodium or potassium salicylate), the flux concentration is 0.5-1.0 g / L, and the pH value of the solution is adjusted to 6.5-8.0 by sodium hydroxide or potassium hydroxide. Through the fluxing treatment, a layer of flux molecules can be adsorbed on the surface of the tin-plated layer generated by electroplating, which promotes the fluidity of liquid tin on the surface of the tin-plated plate and improves the leveling effect. At the same time, the flux provides crystal nuclei for the generation of the tin-iron alloy layer during the soft melting process, improves the quality of the alloy layer (FeSn2), and promotes the formation of a uniform and dense dendritic tin-iron alloy layer. The dendrites of the alloy layer are uniformly dense, the growth direction is relatively regular, and the dendrites are columnar. Compared with the process without using flux, the alloy layer of the tin-plated plate has a larger dendrite size and a good fluxing effect; at the same time, the flux improves the (211) and (213) crystal plane orientation ratio of the FeSn2 grains in the alloy layer, further improving the corrosion resistance of the alloy layer. Furthermore, the flux of the present invention is nearly neutral, which avoids excessive corrosion of the tin layer by conventional acidic fluxes (such as salicylic acid flux, potassium dihydroxybenzene sulfonate and sulfuric acid mixture flux), thereby avoiding the problem of pitting rust on low-tin tin-plated plates caused by flux residues.

[0072] (8) Soft melting: High-frequency inductor soft melting can quickly heat the tin plate to the soft melting temperature to avoid oxidation of the tin layer caused by too long heating time. The melting point of tin is 231.9℃. The soft melting temperature is 250-255℃ and the soft melting time is 0.5~1.0s. This can ensure that the tin layer is completely soft melted and Fe and Sn react to form a uniform and dense alloy layer FeSn2 (alloy tin content is 0.4~0.6g / m 2 ), and can avoid the problem of insufficient tin layer coverage caused by too high reflow temperature and too long reflow time, which leads to too thick alloy layer and too thin pure tin layer. After reflow, the substrate enters the water quenching tank for cooling. The water quenching water temperature is 75~85℃, which can ensure that the molten tin is cooled and solidified quickly, avoiding the water quenching spot defects on the surface. At the same time, the water conductivity of the water quenching water is selected to be ≤1ms / cm, which reduces the impurity elements in the water remaining in the tin layer, improves the purity of the surface tin, and is beneficial to corrosion resistance.

[0073] (9) Passivation: A two-stage passivation process of "chemical passivation + electrochemical passivation" is adopted, in which the passivation solution is a sodium dichromate solution with a concentration of 20-22 g / L, the passivation solution temperature is 40-42 °C, the passivation solution pH is 4.2-4.4, and the passivation time is 1.0-1.5 s. The first stage of chemical passivation is conducive to the formation of a uniform passivation film layer and improves the covering effect of the passivation film. On this basis, the second stage adopts electrochemical passivation to further increase the thickness of the passivation film layer and the Cr content of the film layer. If the charge density is too low, the passivation film thickness is too thin; if the charge density is too large, the passivation film generation rate is large and the film layer is uneven; therefore, the passivation charge density of 1.0-1.2 C / dm is selected in the electrochemical passivation stage. 2 The final passivation film thickness is controlled to be 4-6 mg / m2 (measured in Cr content) and the film layer is uniform and dense, achieving the effect of enhancing the corrosion resistance of tinplate.

[0074] (10) Oiling: Use an electrostatic oiler, the oil type is DOS oil, and the oiling amount is 3-5 mg / m 2 Electrostatic oiling can coat the tinplate surface with a uniform oil film. DOS oil has a single component and good compatibility with paint. If the amount of oil applied is too low, it cannot completely cover the surface of the substrate and is prone to rust. If the amount of oil applied is too high, the tinplate is prone to leaking paint during painting, affecting the corrosion resistance of the final product. Therefore, the oil application amount is selected to be 3-5 mg / m 2 .

[0075] A specific embodiment of the present invention (Example 1) is given below:

[0076] The specific steps are as follows: select a cold-rolled steel sheet with a low carbon steel composition as the substrate, and its chemical composition is calculated by mass percentage, C: 0.065%, Mn: 0.12%, Si: 0.01%, P: 0.012%, S: 0.005%, Al: 0.033%, N: 0.0045%, and the balance is Fe and other inevitable impurities, and then perform the following steps in sequence:

[0077] S1. Annealing: A continuous annealing furnace is used to anneal the cold-rolled steel sheet. The annealing temperature is controlled at 650°C and the annealing time is 40s. A reducing protective atmosphere is used in the furnace, with a H2 content of 10%, a furnace dew point of -48°C, and an O2 content of 5ppm.

[0078] S2. Leveling: The cold-rolled steel sheet after annealing in step S1 is leveled by a double-stand dry leveling machine; the working roll of the No. 1 stand adopts an electric spark texturing roll, and the roller surface roughness parameters are, Ra (profile arithmetic mean): 1.5μm, Rpc (number of peaks): 91 / cm, Rz (sum of maximum profile peak height and valley depth): 3.2μm; the working roll of the No. 2 stand adopts a grinding roll, and the roller surface roughness parameters are, Ra: 0.43μm, Rpc: 116 / cm, Rz: 1.3μm.

[0079] S3. Degreasing: Use chemical degreasing, electrolytic degreasing, brushing, rinsing and drying to remove oil stains on the surface of the cold-rolled steel plate to obtain a substrate with a clean surface.

[0080] S4, pickling: electrolytic pickling of the substrate in step S3, with a current density of 11A / dm 2 The pickling solution is 76g / L sulfuric acid H2SO4, the solution temperature is 32℃, and the pickling time is 2s.

[0081] S5, pre-wetting: immerse the pickled substrate in step S4 into a mixed solution of methanesulfonic acid and potassium hydroxybenzenesulfonate, wherein the concentration of methanesulfonic acid is 12 mL / L, the concentration of potassium hydroxybenzenesulfonate is 3 mL / L, and the solution temperature is 44°C.

[0082] S6, electroplating tin: electroplating the substrate after the pre-wetting treatment in step S5 to obtain a tin-plated plate. An environmentally friendly methanesulfonic acid soluble anode electroplating system is used, and the concentration of each component in the electroplating solution is: tin ion (Sn 2+ ) 18mL / L, free acid 31mL / L, additive 23mL / L, antioxidant 32mL / L, plating solution temperature 44°C. Open 5 plating tanks for electroplating, the current density of the plating tanks is: 16A / dm 2 , 11A / dm 2 , 11mA / dm 2 , 11A / dm 2 , 14A / dm 2 .

[0083] S7, fluxing: immerse the tinplate in step S6 into a fluxing solution, wherein the flux is a sodium salicylate aqueous solution with a flux concentration of 0.6 g / L, and the pH value of the solution is adjusted to 7.4 by sodium hydroxide. After the substrate comes out of the fluxing tank, the surface of the substrate is sprayed with desalted water to remove excess flux.

[0084] S8, soft melting: the tinplate after the fluxing treatment in step S7 is quickly heated to the soft melting temperature, high-frequency inductance soft melting is adopted, the soft melting temperature is 252°C, the soft melting time is 0.7s, and after soft melting, the substrate enters the water quenching tank for cooling, the water quenching water temperature is 75°C, and the water quenching water conductivity is 0.1ms / cm.

[0085] S9, passivation: The substrate is treated with "chemical passivation + electrochemical passivation". The passivation solution is a sodium dichromate solution with a concentration of 22g / L, the passivation solution temperature is 42°C, the passivation solution pH is 4.4, the passivation time is 1.2s, and the passivation charge density in the electrochemical passivation stage is 1.2C / dm 2 , control the passivation film thickness to 4~6mg / m 2 (measured in Cr content);

[0086] S10, Oiling: Use electrostatic oiling machine, the oiling type is DOS oil, the oiling amount is 3mg / m 2 .

[0087] The surface roughness Ra of the tin-plated plate prepared by the above method is 0.37μm, Rpc is 95 pieces / cm, Rz is 2.1μm, and the total tin content is 1.12g / m 2 The tin content of the pure tin layer is 0.63g / m 2 The tin content of the alloy layer is 0.49g / m 2The weight of the surface passivation film is 5.5 mg / m 2 (calculated based on Cr content), the weight of the oil film is 3 mg / m 2 The structure of the tin layer and alloy layer of the tinplate was analyzed by XRD. The sum of the crystal orientation degrees of Sn(101) and Sn(200) was 2.3, and the sum of the crystal orientation degrees of FeSn2(211) and FeSn2(213) in the alloy layer was 2.7.

[0088] The following are examples 2 to 11 of the present invention, the overall process of the manufacturing method thereof is the same as that of example 1, as shown in the attached Figure 1 As shown, there are differences in the specific process parameters in the manufacturing method compared with Example 1, as shown in Table 1.

[0089] Table 1

[0090]

[0091] The characteristics of the tinplates obtained in Examples 2 to 11 are shown in Table 2.

[0092] Table 2

[0093]

[0094] The tinplates of Examples 1 to 11 of the present invention were subjected to corrosion resistance tests, including porosity and neutral salt spray tests (5% NaCl, 2 hours), and paint adhesion tests were conducted in accordance with the industry standard QB / T 2763-2006 "Coated Tin (or Chromium) Thin Steel Sheets", and the results are shown in Table 3. It can be seen that the tinplates of Examples 1 to 11 of the present invention have a porosity of 7 to 10 mgFe / dm2, a salt spray grade of 1 to 2, and an adhesion of 1. In comparison, the tinplates (tin coating amount of 1.1 g / m2) manufactured by the prior art have a porosity of 12 to 15 mgFe / dm2, a salt spray grade of 3, and an adhesion of 2, indicating that the environmentally friendly low-tin tinplate of the present invention has excellent corrosion resistance and adhesion.

[0095] Table 3

[0096]

[0097] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for manufacturing an environmentally friendly low-tin tin-plated sheet, characterized in that: The following steps are involved: Step S1, annealing: annealing the cold-rolled steel sheet in an annealing furnace, controlling the annealing temperature to 640-660°C and the annealing time to 30-45s; using a reducing protective atmosphere in the furnace, with a dew point of -50--45°C and an O2 content of 0-10ppm; Step S2, flattening: flattening the cold-rolled steel sheet after annealing in step S1 to obtain a cold-rolled steel sheet with a flat surface; A double-stand dry leveling machine is used for leveling. The No. 1 stand working roll adopts an electrospark texturing roll, and the roll surface roughness parameters are: profile arithmetic mean Ra: 1.5~1.6μm, peak number Rpc: 80~100 / cm, maximum profile peak height and valley depth sum Rz: 2.5~4.0μm; the No. 2 stand working roll adopts a grinding roll, and the roll surface roughness parameters are: profile arithmetic mean Ra: 0.4~0.5μm, peak number Rpc: 110~130 / cm, maximum profile peak height and valley depth sum Rz: 1.0~2.0μm; Step S3, degreasing: removing oil stains on the surface of the cold-rolled steel sheet by chemical degreasing, electrolytic degreasing, brushing, rinsing and drying to obtain a substrate with a clean surface for electroplating; Step S4, pickling: electrolytic pickling of the substrate obtained in step S3, with a current density of 10-12 A / dm 2 The pickling solution is 70-80 g / L sulfuric acid H2SO4, the solution temperature is 30-35 °C, and the pickling time is 2-3 seconds; Step S5, pre-wetting: immerse the pickled substrate in step S4 into a mixed solution of methanesulfonic acid and potassium hydroxybenzenesulfonate, wherein the concentration of methanesulfonic acid is 10-15 mL / L, the concentration of potassium hydroxybenzenesulfonate is 2-5 mL / L, and the solution temperature is 40-45° C.; Step S6, electroplating tin: electroplating the substrate after the pre-wetting treatment in step S5, using a combination of current densities of "high, low, and medium" to form a total tin content of 0.9 to 1.2 g / m 2 A pure tin layer is formed to obtain a substrate having a pure tin layer plated on the surface; The specific process of electroplating tin is: using an environmentally friendly methanesulfonic acid soluble anode electroplating system, the concentration of each component in the electroplating solution is: tin ion Sn 2+ : 15-20 g / L, free acid: 30-35 mL / L, additive: 20-25 mL / L, antioxidant: 30-35 mL / L, the plating solution temperature is 40-45 ° C; open 5 plating tanks for electroplating, the current density of the plating tanks is: 15-18 A / dm 2 , 10~13A / dm 2 , 10~13mA / dm 2 , 10~13A / dm 2 , 12~15A / dm 2 ; Step S7, fluxing: immersing the substrate with the pure tin layer plated on the surface obtained in step S6 into a flux solution in a fluxing tank, wherein the flux solution is a salicylate aqueous solution, and the concentration of the flux solution is 0.5-1.0 g / L; adjusting the pH value of the solution to 6.5-8.0 by sodium hydroxide or potassium hydroxide; spraying the surface of the substrate with the pure tin layer plated on the surface with desalted water after it comes out of the fluxing tank to remove excess flux on the surface; Step S8, soft melting: the substrate with the pure tin layer plated on the surface after the fluxing treatment in step S7 is quickly heated to the soft melting temperature; high-frequency inductance soft melting is adopted, the soft melting temperature is 250-255°C, and the soft melting time is 0.5-1.0s; the substrate with the pure tin layer plated on the surface after soft melting enters the water quenching tank for cooling, the water quenching water temperature is 75-85°C, and the water conductivity of the water quenching water is ≤1ms / cm; an Fe-Sn alloy layer is formed between the substrate and the pure tin layer; Step S9, passivation: The substrate obtained in step S8 is subjected to surface treatment by a two-stage passivation method of "chemical passivation + electrochemical passivation". The two-stage passivation uses a passivation solution of 20-22 g / L sodium dichromate solution, a passivation solution temperature of 40-42 ° C, a passivation solution pH of 4.2-4.4, a passivation time of 1.0-1.5 s, and a passivation charge density of 1.0-1.2 C / dm in the electrochemical passivation stage. 2 ; A passivation film is formed on the surface of the pure tin layer. The thickness of the passivation film is controlled to be 4-6 mg / m based on the Cr content. 2 ; Step S10, oiling: Use an electrostatic oiler to oil the substrate obtained in step S9 to form an oil film on the surface of the passivation film. The oil type is DOS oil, and the oil coating amount is 3-5 mg / m 2 .

2. The method for manufacturing an environmentally friendly low-tin tin-plated sheet according to claim 1, characterized in that: In the step S1, the reducing protective atmosphere in the furnace is a mixed gas of nitrogen N2 and hydrogen H2, and the volume proportion of hydrogen H2 in the mixed gas is 5% to 10%.

3. The method for manufacturing an environmentally friendly low-tin tin-plated sheet according to claim 1, characterized in that: The cold-rolled steel sheet in step S1 is low-carbon steel, and the low-carbon steel comprises the following components in terms of mass percentage: C: 0.060%-0.080%, Mn: 0.10%-0.15%, Si≤0.02%, P≤0.015%, S≤0.010%, Al: 0.02%-0.04%, N: 0.0030%-0.0060%, and the remainder is Fe and other inevitable impurities.

4. The method for manufacturing an environmentally friendly low-tin tin-plated sheet according to claim 1, characterized in that: The salicylate aqueous solution is selected from sodium salicylate or potassium salicylate.

5. An environmentally friendly low-tin tin-plated sheet, characterized in that: The environmentally friendly low-tin tin-plated sheet is made by the manufacturing method of the environmentally friendly low-tin tin-plated sheet described in any one of claims 1-4. The environmentally friendly low-tin tin-plated sheet is a multi-layer structure, which includes a substrate, a Fe-Sn alloy layer, a pure tin layer, a passivation film and an oil film in sequence.

6. The environmentally friendly low-tin tin-plated sheet according to claim 5, characterized in that: The substrate is made of low carbon steel, and the mass percentage is: C: 0.060%~0.080%, Mn: 0.10%~0.15%, Si≤0.02%, P≤0.015%, S≤0.010%, Al: 0.02%~0.04%, N: 0.0030%~0.0060%, and the balance is Fe and other inevitable impurities; the substrate thickness is 0.12~0.50mm, and the surface roughness parameters are: profile arithmetic mean Ra: 0.3~0.4μm, peak number Rpc: 90~110 / cm, and the sum of the maximum profile peak height and valley depth Rz: 1.5~3.0μm.

7. The environmentally friendly low-tin tin-plated sheet according to claim 5, characterized in that: The tin content of the Fe-Sn alloy layer is 0.4 to 0.6 g / m 2 The alloy layer is uniform and dense, the grains are columnar, and the sum of the orientation degrees of FeSn2 (211) and FeSn2 (213) planes in the alloy layer is 2.5~3.

0.

8. The environmentally friendly low-tin tin-plated sheet according to claim 5, characterized in that: The tin content of the pure tin layer is 0.5 to 0.7 g / m 2 , the sum of the Sn(101) and Sn(200) crystal plane orientation degrees is 2.2~2.5.

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