阅读说明：本技术 一种超低铅冷轧电镀锡钢板及其制造方法 (Ultra-low-lead cold-rolled electrotinning steel plate and manufacturing method thereof ) 是由 曹美霞 陆永亮 谢志刚 许姣姣 薄炜 于 2020-04-08 设计创作，主要内容包括：本发明公开了一种超低铅冷轧电镀锡钢板及其制造方法,主要解决现有冷轧电镀锡钢板镀锡层铅含量无法稳定控制在60mg/kg以下的技术问题。本发明提供的一种超低铅冷轧电镀锡钢板的制造方法,包括以下步骤,对厚度为0.14～0.50mm的冷轧电镀锡基板进行平整、碱洗、酸洗、电镀锡、软熔、钝化、卷取得到成品的步骤,在碱洗、酸洗、电镀锡和钝化处理后分别设有清洗处理。冷轧电镀锡钢板的下屈服强度为300～465MPa,断后伸长率A-(50mm)为10～35％；硬度为54～68HR30Tm；冷轧电镀锡钢板镀锡层镀锡量为0.6～8.4g/m～(2)。本发明冷轧电镀锡钢板镀锡层铅含量≤60mg/kg,生产成本低。(The invention discloses a super-capacitorA low-lead cold-rolled electrotinning steel plate and a manufacturing method thereof mainly solve the technical problem that the lead content of a tin coating of the existing cold-rolled electrotinning steel plate can not be stably controlled below 60 mg/kg. The invention provides a manufacturing method of an ultra-low lead cold-rolled electrotinning steel plate, which comprises the following steps of leveling, alkali washing, acid washing, electrotinning, soft melting, passivating and coiling a cold-rolled electrotinning substrate with the thickness of 0.14-0.50 mm to obtain a finished product, wherein cleaning treatment is respectively carried out after the alkali washing, the acid washing, the electrotinning and the passivating treatment. The lower yield strength of the cold-rolled electroplated tin steel plate is 300-465 MPa, and the elongation percentage A after fracture 50mm 10-35%; the hardness is 54-68 HR30 Tm; the tin plating amount of the tin coating of the cold-rolled electrolytic tin-plated steel plate is 0.6-8.4g/m 2 . The lead content of the tin coating of the cold-rolled electroplated tin steel plate is less than or equal to 60mg/kg, and the production cost is low.)

1. The ultra-low lead cold-rolled electrotinning steel plate is characterized in that the cold-rolled electrotinning substrate comprises the following chemical components in percentage by weight: c: 0.04-0.15%, Si is less than or equal to 0.03%, Mn: 0.10-0.50%, P is less than or equal to 0.02%, S is less than or equal to 0.03%, Cu is less than or equal to 0.02%, Alt: 0.02-0.07%, N is less than or equal to 0.0045%, and the balance is Fe and inevitable impurity elements; lower yield strength R of cold-rolled electroplated tin steel plate with thickness of 0.14-0.50 mm_eL300 to 465MPa, tensile strength R_m320 to 500MPa, elongation after break A_50mm10-35%; the hardness is 54-68 HR30 Tm; the tin plating amount of the tin plating layer of the cold-rolled electrolytic tin-plated steel plate is 0.6-8.4g/m²The lead content of the tin coating of the cold-rolled electroplated tin steel plate is less than or equal to 60 mg/kg.

2. The manufacturing method of the ultra-low lead cold-rolled electrolytic tin plate is characterized by comprising the following steps:

carrying out flattening, alkali washing, acid washing, electrotinning, soft melting, passivation and coiling on a cold-rolled electrotinning substrate with the thickness of 0.14-0.50 mm to obtain a finished product, wherein cleaning treatment is respectively carried out after the alkali washing, the acid washing, the electrotinning and the passivation;

the cold-rolled electrotinning substrate is obtained by annealing a cold-rolled hard steel plate through a vertical continuous annealing furnace, and the cold-rolled electrotinning substrate comprises the following chemical components in percentage by weight: c: 0.04-0.15%, Si is less than or equal to 0.03%, Mn: 0.10-0.50%, P is less than or equal to 0.02%, S is less than or equal to 0.03%, Cu is less than or equal to 0.02%, Alt: 0.02-0.07%, N is less than or equal to 0.0045%, and the balance is Fe and inevitable impurity elements; the lower yield strength R of a cold-rolled electroplated tin substrate with the thickness of 0.14-0.50 mm_eL280 to 450MPa, tensile strength R_m300 to 500MPa, elongation after break A_50mm15-40%; the hardness is 52-66 HR30 Tm;

the leveling is dual-frame wet leveling, leveling liquid is sprayed on the surface of the cold-rolled electroplated tin substrate in the leveling process, the leveling liquid is water-based organic acid ammonium salt type leveling liquid, the concentration of the leveling liquid is 1.0-2.0%, the temperature of the leveling liquid is 20-50 ℃, and the spraying flow rate of the leveling liquid is 5-10L/min; the leveling elongation is 1.0-2.0%;

the alkali washing comprises the step of immersing the cold-rolled electroplated tin substrate into alkali liquor, wherein the alkali washing mode is alkali leaching, scrubbing and electrolytic alkali washing, the alkali liquor is a mixed solution of NaOH and KOH with the mass concentration of 10-50g/L, and the mass ratio of NaOH to KOH in the alkali liquor is 1: 1, the conductivity of alkali liquor is 20-40mS/cm, the temperatures of alkali immersion cleaning and electrolytic alkali cleaning are both 70-85 ℃, and the brushing temperature is 25-50 ℃; the electrolytic alkaline washing polar plate is made of carbon steel with lead content lower than 10mg/Kg, and [ Pb ] in alkaline liquor²⁺]＜1.0mg/L；

The pickling comprises the step of immersing the cold-rolled electroplated tin substrate into acid liquor, wherein the pickling mode is chemical pickling, the acid adopted by the pickling is sulfuric acid, the mass concentration of the sulfuric acid is 50-100 g/L, the pickling temperature is 60-80 ℃, and [ Pb ] in the acid liquor²⁺]<1.0mg/L；

The electroplating is carried outTin, which comprises immersing a cold-rolled tin-electroplated substrate as a cathode in an electroplating solution, wherein the electroplating solution system is a methanesulfonic acid plating solution, the mass concentration of the methanesulfonic acid is 30-50 g/L, and [ Sn ] in the plating solution²⁺]15-30 g/L of [ Pb ] in the plating solution²⁺]Not more than 3.5mg/L, the temperature of the electroplating solution is 40-50 ℃, and the electroplating current density is 10-40A/dm²The surface tension of the plating solution is 49 to 53 dynes; controlling the tin plating amount of the tin plating layer of the cold-rolled tin-plated steel plate to be 0.6-8.4g/m²；

The reflow is combined reflow combining resistance reflow and induction reflow, the reflow temperature is 260-280 ℃, and the reflow time is 3.0-5.0 s.

The passivation comprises the step of passivating the electroplated tin steel plate after the soft melting quenching, wherein [ Pb ] is contained in a passivation solution²⁺]<1.0 mg/L; the passivation mode is one or the combination of electrolytic passivation and chemical passivation.

3. The method for manufacturing an ultra-low lead cold-rolled electrolytic tinned steel sheet according to claim 2, wherein the washing treatment is performed with desalted water as washing water and with electric conductivity<200 mu s/cm, washing water temperature of 20-70 ℃, flow rate of 0.2-8.0m³/h。

4. The method for manufacturing the ultra-low lead cold-rolled electrolytic tinned steel sheet according to claim 2, wherein the lead content of the tin coating of the cold-rolled electrolytic tinned steel sheet is less than or equal to 60 mg/kg.

Technical Field

The invention relates to a cold-rolled electrotinning steel plate and a manufacturing method thereof, in particular to an ultra-low lead cold-rolled electrotinning steel plate and a manufacturing method thereof, and specifically relates to a cold-rolled electrotinning steel plate with a tin coating lead content of less than or equal to 60mg/kg and a manufacturing method thereof, belonging to the technical field of iron-based alloys.

Background

Tin plate is the main packaging material in the food industry. With the development of the modern modernization process of China, the living standard of people is improved day by day, the application range of the tin plate is expanded, and the using amount of the tin plate is increased day by day. At the same time, there is an increasing demand for tin plate properties, especially for safety issues in direct contact food packaging, such as BS EN 10333: 2005Steel for packaging-Flat Steel Products Integrated for Use in contact with Foodstiffs, Products or Beverages for Human and Animal Condition-Tin Coated Steel (Tinplate) specifies: the tin ingot for tin-plated products contains more than 99.85% of total tin, less than 0.01% of lead, less than 0.01% of cadmium, less than 0.03% of arsenic and less than 0.01% of lead.

The Chinese national standard GB/T2520-.

In the direct contact type food application, because the surface of the tin plate is free from paint, the food is directly filled after processing and forming, the food is directly contacted with the tin plate, and Pb elements in a plating layer can partially migrate into contents such as the food under a sealing condition, therefore, higher requirements are put forward for the plating layer Pb of the tin plate for the direct contact type food.

Chinese patent application publication No. CN106282980A discloses a lead removing device and process, which mainly uses lead removing agent to co-deposit lead in the plating solution, thereby achieving the purpose of reducing the lead content in the plating solution.

The application publication No. CN104213183A discloses a method for treating lead ions in acid-washing electrotinning liquid, which mainly adopts Ba2+, Pb2+ and SO 42-to generate barium sulfate and lead sulfate, SO that the lead sulfate and the barium sulfate are co-precipitated to further achieve the purpose of removing lead in the plating liquid.

The lead in the tin plate coating is mainly derived from acid pickling and electrolytic tin plating. The acid cleaning is mainly from babbitt metal polar plate adopted by electrolytic acid cleaning, the lead content of the polar plate is above 90%, and the polar plate is soaked in acid liquor to be dissolved to produce Pb²⁺Active metal Fe and non-active Pb on strip steel²⁺A displacement reaction occurs, the generated lead is attached to the tin-plated substrate, and the reaction always exists no matter the polarity of the substrate; meanwhile, when the strip steel is electrified as a cathode, Pb in the pickling solution²⁺And is attached to the substrate through the plating process, a plating reaction occurs.

In the process of electroplating tin, because tin and lead are homologous elements and have close chemical properties, the tin and the lead often form paragenic ores and are reduced simultaneously in the smelting process to form a lead-tin alloy. The lead-tin alloy is dissolved in the methanesulfonic acid solution by blowing oxygen and is converted into tin ions and lead ions, and because the concentration difference between the tin ions and the lead ions is large, the deposition of lead is inhibited in the electroplating process, so that the lead is enriched in the solution along with the addition of tin particles, and when the lead is enriched to a certain concentration, the lead begins to be separated out.

In conclusion, in the production process of the electrolytic tinning product, lead replacement and electroplating deposition can occur in the electrolytic pickling process of the electrolytic tinning product. The in-vitro lead reduction of the plating solution can reduce the lead adhesion on the surface of the strip steel in the electrotinning process, but needs to increase equipment investment and introduce a lead reduction medium, thereby increasing the production cost and increasing the unstable elements of the plating solution system.

Disclosure of Invention

The invention aims to provide an ultra-low lead cold-rolled electrotinning steel plate and a manufacturing method thereof, and mainly solves the technical problem that the lead content of a tin coating of the existing cold-rolled electrotinning steel plate cannot be stably controlled below 60 mg/kg.

The technical idea of the invention is that the components and the performance of the electrotinning substrate are controlled; the alkaline washing, acid washing and electrotinning production processes related to the production of the cold-rolled electrotinning steel plate are improved, and the lead content of a tinned layer of the cold-rolled electrotinning steel plate is less than or equal to 60 mg/kg.

The cold-rolled electrotinning steel plate is used for direct contact type food packaging materials, and the packaging (food, medicine) can made of the cold-rolled electrotinning steel plate has the advantages that the inner surface of the can body is not printed and coated, and the can body can directly contact the contents such as food, medicine and the like.

The invention adopts the technical scheme that the ultra-low lead cold-rolled electrolytic tin plate comprises the following chemical components in percentage by weight: c: 0.04-0.15%, Si is less than or equal to 0.03%, Mn: 0.10-0.50%, P is less than or equal to 0.02%, S is less than or equal to 0.03%, Cu is less than or equal to 0.02%, Alt: 0.02-0.07%, N is less than or equal to 0.0045%, and the balance is Fe and inevitable impurity elements; lower yield strength R of cold-rolled electroplated tin steel plate with thickness of 0.14-0.50 mm_eL300 to 465MPa, tensile strength R_m320 to 500MPa, elongation after break A_50mm10-35%; the hardness is 54-68 HR30 Tm; the tin plating amount of the tin plating layer of the cold-rolled electrolytic tin-plated steel plate is 0.6-8.4g/m²The lead content of the tin coating of the cold-rolled electroplated tin steel plate is less than or equal to 60 mg/kg.

The manufacturing method of the ultra-low lead cold-rolled electrolytic tin plate comprises the following steps:

carrying out flattening, alkali washing, acid washing, electrotinning, soft melting, passivation and coiling on a cold-rolled electrotinning substrate with the thickness of 0.14-0.50 mm to obtain a finished product, wherein cleaning treatment is respectively carried out after the alkali washing, the acid washing, the electrotinning and the passivation;

the cold-rolled electrotinning substrate is a cold-rolled hard steel plate which is vertically connectedThe cold-rolled electroplated tin substrate is obtained after annealing of a annealing furnace, and comprises the following chemical components in percentage by weight: c: 0.04-0.15%, Si is less than or equal to 0.03%, Mn: 0.10-0.50%, P is less than or equal to 0.02%, S is less than or equal to 0.03%, Cu is less than or equal to 0.02%, Alt: 0.02-0.07%, N is less than or equal to 0.0045%, and the balance is Fe and inevitable impurity elements; the lower yield strength R of a cold-rolled electroplated tin substrate with the thickness of 0.14-0.50 mm_eL280 to 450MPa, tensile strength R_m300 to 500MPa, elongation after break A_50mm15-40%; the hardness is 52-66 HR30 Tm;

the leveling is dual-frame wet leveling, leveling liquid is sprayed on the surface of the cold-rolled electroplated tin substrate in the leveling process, the leveling liquid is water-based organic acid ammonium salt type leveling liquid, the concentration of the leveling liquid is 1.0-2.0%, the temperature of the leveling liquid is 20-50 ℃, and the spraying flow rate of the leveling liquid is 5-10L/min; the leveling elongation is 1.0-2.0%;

the alkali washing comprises the step of immersing the cold-rolled electroplated tin substrate into alkali liquor, wherein the alkali washing mode is alkali leaching, scrubbing and electrolytic alkali washing, the alkali liquor is a mixed solution of NaOH and KOH with the mass concentration of 10-50g/L, and the mass ratio of NaOH to KOH in the alkali liquor is 1: 1, the conductivity of alkali liquor is 20-40mS/cm, the temperatures of alkali immersion cleaning and electrolytic alkali cleaning are both 70-85 ℃, and the brushing temperature is 25-50 ℃; the electrolytic alkaline washing polar plate is made of carbon steel with lead content lower than 10mg/Kg, and [ Pb ] in alkaline liquor²⁺]＜1.0mg/L；

The pickling comprises the step of immersing the cold-rolled electroplated tin substrate into acid liquor, wherein the pickling mode is chemical pickling, the acid adopted by the pickling is sulfuric acid, the mass concentration of the sulfuric acid is 50-100 g/L, the pickling temperature is 60-80 ℃, and [ Pb ] in the acid liquor²⁺]<1.0mg/L；

The electrolytic tinning comprises the step of immersing a cold-rolled electrolytic tinning substrate serving as a cathode into an electroplating solution, wherein the electroplating solution system is a methanesulfonic acid electroplating solution, the mass concentration of the methanesulfonic acid is 30-50 g/L, and [ Sn ] in the electroplating solution²⁺]15-30 g/L of [ Pb ] in the plating solution²⁺]Not more than 3.5mg/L, the temperature of the electroplating solution is 40-50 ℃, and the electroplating current density is 10-40A/dm²The surface tension of the plating solution is 49 to 53 dynes; controlling the tin plating amount of the tin plating layer of the cold-rolled tin-plated steel plate to be 0.6-8.4g/m²；

The reflow is combined reflow combining resistance reflow and induction reflow, the reflow temperature is 260-280 ℃, and the reflow time is 3-5 s.

The passivation comprises the step of passivating the electroplated tin steel plate after the soft melting quenching, wherein [ Pb ] is contained in a passivation solution²⁺]<1 mg/L; the passivation mode is one or the combination of electrolytic passivation and chemical passivation.

Further, in the washing treatment, the washing water is desalted water and the conductivity is high<200 mu s/cm, the temperature of the cleaning water is 20-70 ℃, and the flow is 0.2-8.0m³/h。

The production process adopted by the invention has the following reasons:

1. leveling parameter setting

The wet leveling process has the main function of covering the surface of the substrate with one very thin leveling liquid film to prevent active Fe element and O in air₂Oxidation reaction occurs to generate iron oxide, which is not beneficial to subsequent acid washing. The wet leveling process is characterized in that: and spraying a leveling solution with a certain concentration in the leveling process of the tin-plated annealed substrate to form a uniform film between the strip steel and the leveling roller.

After the rolling of the traditional dry flattening process, if reasonable package is not available in the process of storage and transportation, Fe on the surface of the substrate is easy to react with O in the air due to high air humidity in the south of Yangtze river₂Oxidation reaction takes place to produce Fe₂O₃Before tinning, the tin can be effectively removed by means of high strength such as electrolytic pickling and the like. On-site and laboratory researches show that Pb can be increased to deposit 30-50 mg/kg on the surface of the substrate in the electrolytic pickling process. The invention is therefore based on wet-levelling. The concentration of the leveling solution is 1.0-2.0%, the temperature of the leveling solution is 20-50 ℃, the spraying flow is 5-10L/min, the leveling process is sufficiently lubricated, the roller consumption is low, the roller surface structure cannot cause uneven residue of the leveling solution on the surface of the substrate when being copied, and the alkaline cleaning before tinning is facilitated.

2. Alkaline cleaning parameter setting

The method has the main effects of removing residual emulsion rolled on the surface of the strip steel and a leveling liquid film covered on the surface of the strip steel in a wet leveling manner, and improving the adhesion efficiency of metal tin in the post-process. The method is characterized in that a leveled tin-plated substrate is fully soaked in alkali liquor, the strip steel is subjected to alkali immersion cleaning by adopting the modes of alkali immersion cleaning, brushing and electrolytic alkali cleaning, a surface residual leveling liquid film and residual iron are removed, then brushing is carried out, the surface of a steel plate is brushed by a brush roll in demineralized water at the temperature of 25-50 ℃, strong physical cleaning is applied to the strip steel, residues adhered to the surface of the strip steel are removed, and finally, electrolytic alkali cleaning is carried out, so that hydrogen bubbles and oxygen bubbles generated by electrochemical reaction deeply clean the residues at the low-lying part of the strip steel, and the effect of thoroughly cleaning the surface and the low-lying part of the strip steel is achieved.

Different from a dry type flat substrate with the surface mainly containing residual Fe powder, a wet type flat substrate with the surface uniformly covered with a flat liquid film can be completely removed only by adopting a mode of scrubbing and electrolytic alkali washing after being soaked in alkali liquor for 3-5 s. Alkali liquor used for alkali immersion cleaning and scrubbing cleaning is prepared from the following main components in parts by mass: 1 NaOH: KOH, KOH and NaOH are strong electrolytes in water, improve the conductivity of the aqueous solution and promote electrolysis. The mass ratio of the components is 1: 1 NaOH: KOH solution, NaOH is much more hydroscopic than KOH, NaOH is easily associated with CO in air under the catalysis of water₂Reaction to produce Na₂CO₃The conductivity of the alkaline solution is greatly influenced, meanwhile, the viscosity of the aqueous solution of NaOH is high, the aqueous solution of NaOH is easily adhered to the surface of the strip steel after degreasing and can be removed only by high-temperature or large-flow rinsing, KOH has excellent conductivity, the viscosity of the aqueous solution is low, the radius of potassium ions is large, the aqueous solution is easier to deform, the strong instant dipole moment exists, and the cleaning effect is excellent. But KOH is high in price, and the mass ratio of KOH to KOH is 1: 1 NaOH: the KOH solution can realize the degreasing efficiency of more than 90 percent within 30 days under certain conditions, and the cost is 1 time lower than that of the pure KOH solution, therefore, the invention sets the mass ratio as 1: 1 NaOH: KOH main solution, wherein the mass concentration of alkali liquor is 10-50g/L, the conductivity is 20-40mS/cm, the temperature of alkali immersion cleaning and electrolytic alkali cleaning is 70-85 ℃, and the brushing temperature is 25-50 ℃. The electrolytic alkaline washing polar plate is made of carbon steel with lead content lower than 10mg/Kg, the carbon steel is slightly dissolved in alkaline liquor, and [ Pb ] is contained in alkaline liquor²⁺]＜1.0mg/L。

3. Pickling parameter setting

The method mainly has the functions of removing iron oxides on the surface of the tinned substrate, activating the surface of strip steel, improving nucleation points of first-time tin sedimentation of electrolytic tinning, and simultaneously, replacing a babbitt alloy electrolytic pickling method with a pure chemical pickling method to avoid Pb dissolved in a pickling solution²⁺The replacement and electroplating reactions occur in the electrolytic pickling process, so that a layer of metal lead is electroplated and attached to the surface of the strip steel, and in the subsequent electrotinning process, the metal lead attached in the electrolytic pickling process and a tin layer form a lead-tin-iron alloy layer in the subsequent reflow process, which brings great trouble to the control of the lead content of the finished tinned plate.

Experimental research shows that when the pickling time is 1s, the traditional babbitt metal electrolytic pickling method is adopted for pickling and lead increasing amount is 30-50 mg/kg. The acid cleaning of the invention adopts pure chemical acid cleaning, and is firstly based on wet-type flattening, and because the surface of the wet-type flattened tinned substrate is uniformly covered with a flattening liquid film, O in the air is isolated₂The Fe on the surface of the substrate is effectively inhibited by oxidation reaction with the Fe on the substrate₂O₃Can be completely removed at a lower pickling efficiency. Secondly, a pure chemical pickling method is adopted to replace a babbit alloy electrolytic pickling method, so that Pb in a pickling polar plate is prevented from being dissolved in a pickling solution to form Pb²⁺The replacement reaction and the electroplating reaction are generated in the electrolytic pickling process and attached to the surface of the strip steel, and in the subsequent electrolytic tinning process, the metal lead attached in the electrolytic pickling process and the tin layer form a lead-tin-iron alloy layer in the subsequent reflow process, which brings great trouble to the control of the lead content of the finished tinned plate. According to practical experience, the wet-type flat substrate is subjected to pure chemical pickling by a sulfuric acid solution with the sulfuric acid concentration of 50-100 g/L and the temperature of 60-80 ℃ for 4 times, so that iron oxides on the surface of the tin-plated substrate can be fully removed, the surface of the strip steel is activated, and [ Pb ] in the pickling solution is fully removed²⁺]The concentration is less than or equal to 1mg/L, and the acid liquor and the acid washing residues remained on the surface of the strip steel after acid washing can be fully removed by adopting 2-pass vertical desalted water for washing after acid washing.

4. Setting of parameters of electrotinning

The main function is Sn²⁺In an acid solution, through electrolytic reaction, electron deposition is obtained on the surface of the strip steel as a cathodeThe deposition is changed into metal Sn, and a metal tin layer with the target thickness is uniformly attached to the surface of the strip steel by controlling the electroplating current. The process of the electrolytic tinning is characterized in that the tinning substrate after chemical pickling is vertically placed into an electroplating solution.

Through production verification, in a system that the electroplating solution is methanesulfonic acid, the mass concentration of the methanesulfonic acid is 30-50 g/L, the temperature of the electroplating solution is 40-50 ℃, the electroplating current per pass is 2000-4000A, and the electroplating current density is 10-40A/dm²It was found that [ Pb ] was present at the same level in the plating bath²⁺]The surface tension of the plating solution is changed through the addition of additives and the like, the Pb sedimentation in the tin electroplating process can be changed, and the surface tension of the plating solution is counted to be 49-53 dyne, so that the electroplating precipitation of Pb on the surface of strip steel can be inhibited.

Through inspection, plating solution is [ Sn²⁺]15 to 30g/L, [ Pb ]²⁺]Less than or equal to 3.5mg/L, and Pb synchronously settled in the electrotinning process is less than or equal to 40 mg/kg; when [ Pb ]²⁺]When the concentration is more than 3.5mg/L, the production requirement of the invention cannot be met.

Compared with the prior art, the invention has the following positive effects: 1. the method adopts the combination of wet leveling and pure chemical pickling processes, thereby not only ensuring that the oxide film on the surface of the substrate is fully removed before electrotinning, but also eliminating the phenomenon that the Pb is increased to deposit 30-50 mg/kg on the surface of the substrate in the traditional electrolytic pickling process. 2. According to the [ Pb ] in the plating solution²⁺]≤3.5mg/L，[Sn²⁺]15-30 g/L, and Pb settled synchronously in the electrotinning process is less than or equal to 40mg/kg, so that the mass fraction of Pb in a plating layer in the electrotinning process can be less than or equal to 60 mg/kg. 3. The method does not need to adopt raw material tin particles with higher-level purity, does not need to consume a large amount of funds to additionally increase lead removal equipment, ensures that the lead content of the tin coating of the cold-rolled electroplated tin steel plate is less than or equal to 60mg/kg, improves the safety of the cold-rolled electroplated tin steel plate for direct contact type food, reduces the equipment investment, and reduces the cost of raw and auxiliary materials.

Detailed Description

The present invention is further described below with reference to examples 1 to 4, which are shown in tables 1 to 7.

A manufacturing method of an ultra-low lead cold-rolled electrolytic tin plate comprises the following steps:

carrying out flattening, alkali washing, acid washing, electrotinning, soft melting, passivation and coiling on a cold-rolled electrotinning substrate with the thickness of 0.14-0.50 mm to obtain a finished product, wherein cleaning treatment is respectively carried out after the alkali washing, the acid washing, the electrotinning and the passivation;

the cold-rolled electrotinning substrate is obtained by annealing a cold-rolled hard steel plate through a vertical continuous annealing furnace, and the cold-rolled electrotinning substrate comprises the following chemical components in percentage by weight: c: 0.04-0.15%, Si is less than or equal to 0.03%, Mn: 0.10-0.50%, P is less than or equal to 0.02%, S is less than or equal to 0.03%, Cu is less than or equal to 0.02%, Alt: 0.02-0.07%, N is less than or equal to 0.0045%, and the balance is Fe and inevitable impurity elements; the lower yield strength R of a cold-rolled electroplated tin substrate with the thickness of 0.14-0.50 mm_eL280 to 450MPa, tensile strength R_m300 to 500MPa, elongation after break A_50mm15-40%; the hardness is 52-66 HR30 Tm;

the leveling is dual-frame wet leveling, leveling liquid is sprayed on the surface of the cold-rolled electroplated tin substrate in the leveling process, the leveling liquid is water-based organic acid ammonium salt type leveling liquid, the concentration of the leveling liquid is 1.0-2.0%, the temperature of the leveling liquid is 20-50 ℃, and the spraying flow rate of the leveling liquid is 5-10L/min; the leveling elongation is 1.0-2.0%;

the alkali washing comprises the step of immersing the cold-rolled electroplated tin substrate into alkali liquor, wherein the alkali washing mode is alkali leaching, scrubbing and electrolytic alkali washing, the alkali liquor is a mixed solution of NaOH and KOH with the mass concentration of 10-50g/L, and the mass ratio of NaOH to KOH in the alkali liquor is 1: 1, the conductivity of alkali liquor is 20-40mS/cm, the temperatures of alkali immersion cleaning and electrolytic alkali cleaning are both 70-85 ℃, and the brushing temperature is 25-50 ℃; the electrolytic alkaline washing polar plate is made of carbon steel with lead content lower than 10mg/Kg, and [ Pb ] in alkaline liquor²⁺]＜1.0mg/L；

The pickling comprises the step of immersing the cold-rolled electroplated tin substrate into acid liquor, wherein the pickling mode is chemical pickling, the acid adopted by the pickling is sulfuric acid, the mass concentration of the sulfuric acid is 50-100 g/L, the pickling temperature is 60-80 ℃, and [ Pb ] in the acid liquor²⁺]<1.0mg/L；

The electrolytic tinning comprises immersing a cold-rolled electrolytic tinning substrate as a cathode in an electroplating solution, wherein the electroplating solution system is a methanesulfonic acid electroplating solution, and the quality of the methanesulfonic acid isThe concentration is 30-50 g/L, [ Sn ] in the plating solution²⁺]15-30 g/L of [ Pb ] in the plating solution²⁺]Not more than 3.5mg/L, the temperature of the electroplating solution is 40-50 ℃, and the electroplating current density is 10-40A/dm²The surface tension of the plating solution is 49 to 53 dynes; controlling the tin plating amount of the tin plating layer of the cold-rolled tin-plated steel plate to be 0.6-8.4g/m²；

The reflow is combined reflow combining resistance reflow and induction reflow, the reflow temperature is 260-280 ℃, and the reflow time is 3-5 s.

The passivation comprises the step of passivating the electroplated tin steel plate after the soft melting quenching, wherein [ Pb ] is contained in a passivation solution²⁺]<1 mg/L; the passivation mode is one or the combination of electrolytic passivation and chemical passivation.

Further, in the washing treatment, the washing water is desalted water and the conductivity is high<200 mu s/cm, the temperature of the cleaning water is 20-70 ℃, and the flow is 0.2-8 m³/h。

Table 1 shows the chemical composition (in weight percent) of the cold-rolled electrotinning substrate of the examples of the invention, with the balance being Fe and unavoidable impurities.

Table 1 chemical composition of cold-rolled electrolytic tin plating substrates of examples of the present invention, unit: and (4) weight percentage.

Element(s)	C	Si	Mn	P	S	Cu	Alt	N
									The invention	0.04-0.20	≤0.03	0.10-0.50	≤0.02	≤0.02	≤0.01	0.02-0.07	≤0.0045
Example 1	0.145	0.030	0.21	0.010	0.020	0.0026	0.05	0.0045
									Example 2	0.065	0.017	0.45	0.020	0.008	0.0014	0.04	0.0018
Example 3	0.061	0.021	0.28	0.015	0.015	0.0028	0.07	0.0026
									Example 4	0.053	0.020	0.31	0.018	0.018	0.0100	0.02	0.0033

TABLE 2 mechanical properties of cold-rolled electroplated tin substrates according to the examples of the present invention

Table 3 parameters of the wet planarization process of the examples of the present invention, the planarization liquid is water-based organic acid ammonium salt.

TABLE 4 alkali washing process control parameters of the examples of the present invention

TABLE 5 Pickling Process control parameters of the examples of the invention

Acid pickling parameters	Pickling temperature/. degree.C.)	Sulfuric acid concentration/g/L	In pickling solution [ Pb ]2+]/mg/L
				The invention	60～80	50～100	＜1.0
Example 1	65.3	80	0.61
				Example 2	74.5	63	0.75
Example 3	68.2	74	0.32
				Example 4	71.6	92	0.44

TABLE 6 control parameters of the electrotinning process of the examples of the present invention

TABLE 7 Cold-rolled tin-electroplated steel sheet Performance parameters of the inventive examples

In addition to the above embodiments, the present invention may have other embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.