A method for manufacturing a stainless steel substrate hot-dip tinned steel sheet strip

Abstract

The application discloses a manufacturing method of a stainless steel substrate hot-dip tinned plate strip, relates to the field of stainless steel tinning, and aims at solving the problems of the existing technology, such as the difficulty in controlling the thickness of a tinning interface layer, the poor adhesion of a tinning layer caused by an oxidation film on the surface of a stainless steel plate strip, and the difficulty in forming an effective metallurgical bonding interface between the tinning layer and the stainless steel substrate, and adopts the technical scheme that one side or both sides of the stainless steel plate strip are subjected to surface treatment and tinning-assisted activation pretreatment to remove an oxidation layer and impurities; the surface quality of a tin layer is controlled by temperature control in a hot-dip tinning process; the thickness of the tinning layer is controlled by a wind knife device to realize accurate control, and the yield of workpieces is greatly improved; meanwhile, degreasing, impurity removal and tinning-assisted agent addition are carried out in the hot-dip tinning process, a dense and stable Cr2O3 passivation film on the surface is damaged, the film layer defects are penetrated, the surface is activated by replacement, the passivation film is prevented from regenerating, and finally the active metal substrate is exposed, so that the liquid tin realizes effective wetting of the stainless steel and good metallurgical interface bonding.

Description

Technical Field

[0001] This invention relates to the field of stainless steel tin plating technology, specifically to a method for manufacturing hot-dip tin-plated stainless steel substrate strips. Background Technology

[0002] As an important engineering material, stainless steel is often insufficient in certain applications, such as shielding for routers, electromagnetic signal transmitters, signal receiving components, and electronic components that require welding. The appearance, color, local corrosion resistance, and weldability of ordinary stainless steel are often insufficient to meet the requirements of these specific scenarios. Therefore, it is necessary to further optimize the surface properties of stainless steel. Applying a coating to the surface of the stainless steel substrate can effectively improve the surface properties of stainless steel. At the same time, coated stainless steel can become a substitute for cupronickel, achieving the goal of reducing costs and increasing efficiency.

[0003] Currently, the mainstream technologies for obtaining tin plating on stainless steel surfaces include electroplating, electroless plating, and hot-dip plating. Among these, electroplating is a relatively mature process, allowing for the creation of plating layers of varying thicknesses and morphologies by controlling current density, electrolyte composition, and temperature. However, current electroplating processes have certain drawbacks, such as high energy consumption, severe pollution, expensive equipment, complex processes, and issues related to chemical substances and electrical safety during the process. While electroless plating can achieve uniform coating, it suffers from slow deposition rates, limited coating thickness, and stringent requirements for solution stability control, also facing the problem of chemical waste pollution.

[0004] Hot-dip tin plating is a process in which the substrate is immersed in molten metal, and an intermetallic compound layer is formed through interfacial reaction and diffusion, resulting in a coating with extremely strong adhesion. Hot-dip plating is a relatively simple process with high production efficiency, allowing for continuous production. It typically does not require complex electrolyte or chemical reagent systems, resulting in relatively low environmental pollution, and is gradually becoming the mainstream process.

[0005] During hot-dip galvanizing, the thickness of the coating and the interface layer are difficult to control. An excessively thick, brittle interface layer can cause the coating to crack easily during service, leading to material waste and even workpiece scrap. Simultaneously, the chromium (Cr) element in stainless steel forms a dense, continuous Cr2O3 passivation film on the material surface. This film severely hinders the wetting and interfacial metallurgical reaction between the molten tin and the stainless steel substrate, resulting in ineffective coating spread, poor adhesion, or even complete failure to adhere. Furthermore, tin oxidizes readily at high temperatures, generating tin oxide dross, which not only contaminates the molten tin but may also be incorporated into the coating, causing a rough, porous surface that affects both appearance and performance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the existing defects and provide a method for manufacturing hot-dip tin-plated strips on a stainless steel substrate, which can effectively solve the problems in the background art.

[0007] To achieve the above objectives, the present invention discloses a method for manufacturing a stainless steel substrate hot-dip tin-plated strip. The technical solution adopted is to clean the surface of the stainless steel strip and remove the oxide layer, then immerse the preheated stainless steel strip in molten tin or molten tin alloy for hot-dip plating, and control the plating thickness within 1-20 μm. Hot-dip galvanizing creates a metallurgical bond between the stainless steel strip surface and the tin-containing plating layer, forming FeSn and FeSn2 phase layers. The FeSn phase layer near the stainless steel strip is a flat layer, while the FeSn2 phase layer near the tin-containing plating layer has irregular needle-like and / or block-like protrusions on the side in contact with the tin-containing plating layer. These needle-like and / or block-like protrusions are embedded in the tin-containing plating layer and are hard FeSn2 granular phases that are dispersed throughout the tin-containing plating layer, thus strengthening the tin layer.

[0008] As a preferred embodiment of the present invention, the thickness of the tin-containing plating layer ranges from 1 to 20 μm, and the thickness of the iron-tin intermetallic compound layer composed of the FeSn phase layer and the FeSn2 phase layer ranges from 1.0 to 5.0 μm.

[0009] As a preferred technical solution of the present invention, the following steps are included: Step 1: Perform surface degreasing and pickling on the stainless steel strip to remove surface stains, degrease, and remove oxidation residues, followed by drying; Step 2: The stainless steel strip obtained in Step 1 is activated and dried using a stainless steel flux. The dried stainless steel strip is then preheated at a temperature of 150-220°C. Although the oxide film has been removed by pickling in Step 1, stainless steel will quickly regenerate a very thin passivation film when exposed to air. Therefore, a flux is used for secondary removal to maintain the activated state of the stainless steel surface. Step 3: The preheated stainless steel strip is vertically immersed in molten tin or molten tin alloy for hot-dip plating. During the hot-dip plating process, an air knife is used to control the thickness of the tin-containing plating layer. After the hot-dip plating is completed, it is cooled with room temperature water for 1-3 seconds to obtain hot-dip tin-plated stainless steel strip.

[0010] As a preferred embodiment of the present invention, the method for preparing stainless steel strip in step 1 is as follows: a standard stainless steel billet is hot-rolled to form a billet, the heating temperature in the hot rolling process is selected as 1000-1100℃, followed by 5-15 passes of cold rolling processing; the thickness of the cold-rolled stainless steel strip is in the range of 0.1-1.5 mm; the rolled stainless steel strip is placed in a bell furnace for annealing treatment, the annealing temperature is in the range of 300-425℃, and the annealing time is 30-120 min, to obtain the stainless steel strip.

[0011] As a preferred embodiment of the present invention, the heating rate of the annealing treatment is 150-200℃ / h; after annealing, the heat is rapidly cooled by a fan, and N2 and H2 are used for atmosphere protection during the heat treatment process.

[0012] As a preferred technical solution of the present invention, the molten tin in step 3 is obtained by heating and melting tin ingots in a tin melting furnace, and then storing it at a temperature range of 235-290°C for later use. At this temperature, the oxidation of molten tin can be effectively slowed down.

[0013] As a preferred embodiment of the present invention, in step 1, degreasing is performed using 10-25% dilute sulfuric acid and detergent, with an acid pickling time of 15-30 minutes, followed by cleaning with detergent to remove oil, grease, and passivation film from the surface of the plated parts; surface stains are removed by cleaning with deionized water to remove residual solution, surface stains, and oxidation residues from the plated parts; finally, hot air at a temperature of 100-200℃ is used for forced-air drying.

[0014] As a preferred technical solution of the present invention, in step 2, a stainless steel flux is used for activation treatment. The activation time is 1-3 seconds and the activation temperature is 20-40℃. The flux destroys the surface oxide film through multiple actions such as acid etching, fluoride ion complexation, micro-electric displacement and interface wetting. At the same time, the flux penetrates the film defects, replaces and activates the surface, prevents the regeneration of Cr-containing passivation film, and finally exposes the active metal substrate, realizing the effective wetting and interface bonding of liquid tin to stainless steel.

[0015] In a preferred embodiment of the present invention, in step 3, the hot-dip galvanizing temperature is 235-290℃, the immersion and leaching rates are 20-200 m / min, and the immersion time is 1-5 s. The thickness of the coating and the intermetallic compound layer are controlled by adjusting various process parameters such as temperature, time, and strip winding / unwinding speed during the hot-dip galvanizing process. Specifically, the higher the hot-dip galvanizing temperature, the thinner the coating and the thicker the intermetallic compound layer; the lower the temperature, the opposite occurs. The longer the immersion time, the thicker the intermetallic compound layer; the shorter the time, the opposite occurs. Within a given range, the immersion time has no significant effect on the coating thickness. The faster the strip winding / unwinding speed, the thicker the coating, but the worse the uniformity; the slower the speed, the opposite occurs, and the intermetallic compound layer has no significant effect.

[0016] As a preferred embodiment of the present invention, the above-mentioned method for manufacturing stainless steel substrate hot-dip tin-plated strip is carried out on one or both sides of the stainless steel strip.

[0017] Compared with existing technologies, the advantages of this invention are as follows: By using tin and tin alloys as the coating material for hot-dip tin-plated stainless steel, and employing an air knife device to precisely control the coating thickness during the hot-dip plating process, the yield of workpieces is greatly improved. Simultaneously, degreasing, impurity removal, and the addition of fluxing agents during the hot-dip plating process, through the synergistic effects of acid dissolution, complexation reaction, ion replacement, and interface activation, the dense and stable Cr2O3 passivation film on the surface is destroyed. This process penetrates film defects, replaces and activates the surface, prevents passivation film regeneration, and ultimately exposes the active metal substrate. This achieves effective wetting and interfacial bonding of liquid tin to stainless steel, promoting the reaction between Fe and Sn. The hot-dip plating process can effectively control the Fe-Sn interface layer thickness, meeting the service requirements of hot-dip tin-plated stainless steel strip. Furthermore, this technology enables continuous production with high efficiency. Attached Figure Description

[0018] Figure 1 The images shown are SEM images and EDS results of the interface of the hot-dip tin-plated stainless steel sheet and strip with pure tin plating in Embodiment 1 of the present invention. Figure 2 The images shown are SEM images and EDS results of the Sn-Sb-Ag coated hot-dip tin-plated stainless steel strip interface in Example 2 of this invention. Figure 3 The SEM image and EDS results of the Sn-Ag1.0 coating hot-dip tin-plated stainless steel strip in Example 3 of the present invention are shown. Figure 4 These are detailed SEM observation and test results of the iron-tin interface layer in various embodiments of the present invention; Figure 5 This is a schematic diagram of the interface of the tin-plated layer on the hot-dip tin-plated stainless steel material of the present invention. Figure 6 The figures show the performance test results of various embodiments of the present invention; Figure 6 (a) is a stress-strain curve diagram of various embodiments of the present invention; Figure 6 (b) is a comparison diagram of the tensile strength of various embodiments of the present invention; Figure 6 (c) is a comparison chart of the conductivity of various embodiments of the present invention; Figure 6 (d) is a comparison diagram of the microhardness of various embodiments of the present invention; Figure 7 The graph shows the results of the 100-grid test in various embodiments of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 This embodiment discloses a first implementation of the present invention, which employs the following technical solution: The material used is 304 stainless steel sheet and strip, with the following elemental composition: Step 1: Hot rolling of 200 mm thick stainless steel billets. The heating temperature in the hot rolling process is selected as 1100℃, the heating rate is 150℃ / h in the range of room temperature to 400℃, and the heating rate is 200℃ / h above 400℃, with a holding time of 3h; a total of 14 hot rolling passes are made, with a total reduction rate of 97.75%; hot-rolled stainless steel sheet and strip are obtained. Step 2: The hot-rolled stainless steel strip is cold-rolled using a multi-roll mill with 10 cold rolling passes and a total reduction of 95.56% to obtain the cold-rolled stainless steel strip. Step 3: The annealing heat treatment process of cold-rolled stainless steel sheet and strip is carried out at a temperature of 350℃, a heating rate of 150℃ / h, and a holding time of 30 min, using N2+H2 as the protective atmosphere; thus obtaining stainless steel substrate strip. Step 4: The stainless steel substrate strip is subjected to surface degreasing and pickling treatment. Degreasing is performed using 15% dilute sulfuric acid and detergent (including sodium carbonate as an alkali additive and sodium alkylbenzene sulfonate as an anionic surfactant). The pickling time is 20 minutes. Then, it is cleaned with detergent and deionized water to remove surface stains, degrease, and remove oxidation residues. It is then dried with hot air at 150°C. The stainless steel strip is obtained with a thickness of 0.2 mm and a width of 500 mm. Step 5: The stainless steel strip is activated using a zinc ammonium stainless steel flux composed of ammonium chloride and zinc chloride. The activation time is 3 seconds and the activation temperature is 25°C. After activation, it is dried by blowing hot air at 150°C. Step 6: After preheating the stainless steel strip to 200℃, vertically immerse it in pure tin molten metal for hot-dip plating. The immersion and leaching rates are 80 m / min, the hot-dip plating temperature is 285℃, and the plating time is 5s. During the hot-dip plating process, the tin layer thickness is controlled by an air knife. The pure tin molten metal is obtained by heating and melting commercial pure tin in a tin melting furnace. After melting, the temperature is continuously maintained within the range of 235-290℃ to prevent tin oxidation. Step 7: After hot-dip galvanizing, the stainless steel strip is cooled with room temperature water for 3 seconds at room temperature to obtain a hot-dip tin-plated stainless steel strip with a pure tin coating. The thickness of the coating is 5 μm and the thickness of the intermetallic compound layer is 3 μm.

[0021] Take a small amount of sample and use a scanning electron microscope to obtain SEM images and EDS results, such as Figure 1 As shown, the line scan results indicate that the thickness of the iron-tin intermetallic compound layer in Example 1 is about 3 μm. The particulate matter in Example 1 is located in the intermetallic compound layer, and the main element is Fe.

[0022] Example 2 The difference between this embodiment and Embodiment 1 is that the stainless steel billet thickness is 200 mm, the final tin-plating strip thickness is 0.3 mm, the width is 500 mm, and Sn-Sb-Ag alloy is used as the raw material for the tin plating layer.

[0023] Step 1: The heating temperature in the hot rolling process is selected as 1090℃; Step 2, 8 cold rolling passes, total reduction rate 88.9%; Step 3: The annealing heat treatment process is held at a temperature of 35 min, and a protective atmosphere of N2+H2 is used. Step 4: Degreasing is performed using 10% dilute sulfuric acid for 25 minutes; drying is then carried out using hot air at 180℃. Step 5: After activation, dry with hot air at 180℃; Step 6: The preheated stainless steel strip is vertically immersed into the Sn-Sb-Ag metal liquid for hot-dip galvanizing, wherein the immersion and leaching rates are 100 m / min, the hot-dip galvanizing temperature is 285℃, and the immersion time is 3s. Step 7: After hot-dip galvanizing, the stainless steel strip is cooled with room temperature water for 1 second at room temperature to obtain a hot-dip tin-plated stainless steel strip with Sn-Sb-Ag coating. The thickness of the coating is 8-10 μm and the thickness of the intermetallic compound layer is 2 μm.

[0024] Take a small amount of sample and use a scanning electron microscope to obtain SEM images and EDS results, such as Figure 2 As shown in the line scan results, the thickness of the iron-tin intermetallic compound layer in Example 2 is about 2 μm, no obvious particles were observed, and the interface bonding is clear.

[0025] Example 3 The difference between this embodiment and Embodiment 1 is that the final tin-plating strip has a thickness of 1 mm and a width of 1000 mm; and Sn-Ag1.0 alloy is used as the raw material for the tin plating layer.

[0026] Step 1: The heating temperature in the hot rolling process is selected as 1070℃; Step 2, 6 cold rolling passes, total reduction rate 77.8%; Step 3, the annealing heat treatment process temperature is 400℃; Step 6: After the stainless steel strip is fully preheated at 200℃, it is vertically immersed in Sn-Ag1.0 metal liquid for hot-dip galvanizing. The immersion and leaching rates are 80 m / min, the hot-dip galvanizing temperature is 285℃, and the immersion time is 3s. Step 7: After hot-dip galvanizing, the stainless steel strip is cooled with room temperature water for 2 seconds to obtain a hot-dip tin-plated stainless steel strip with Sn-Ag1.0 coating. The thickness of the coating is 2-4 μm and the thickness of the intermetallic compound layer is 1 μm.

[0027] Take a small amount of sample and use a scanning electron microscope to obtain SEM images and EDS results, such as Figure 3 As shown in the line scan results, the thickness of the iron-tin intermetallic compound layer in Example 3 is about 2 μm, and the particles in the interface layer are located in the tin layer, with Ag as the main element.

[0028] pass Figures 1-3 As shown in the line scan results of Examples 1-3, during the hot-dip tin plating process, Fe atoms in the stainless steel substrate diffuse into the liquid Sn, undergoing an interfacial metallurgical reaction to generate intermetallic compounds FeSn2 and FeSn layers. The main reactions are as follows: Fe + 2Sn = FeSn2 Fe + FeSn2 = 2FeSn Detailed interface SEM observations were performed on the iron-tin interface layers of the three sets of sample examples. The results are as follows: Figure 4 As shown. Figure 4 a represents the iron-tin interface layer of Example 1. As can be observed from the figure, the thicknesses of both the FeSn2 phase and the FeSn phase are approximately 1.5 μm. Figure 4 b represents the iron-tin interface layer of Example 2. As can be observed from the figure, the thicknesses of both the FeSn2 phase and the FeSn phase are approximately 1.0 μm. Figure 4 c represents the iron-tin interface layer of Example 3. As can be observed from the figure, the thicknesses of both the FeSn2 phase and the FeSn phase are approximately 1.0 μm.

[0029] In all three embodiments, the interface layer is continuous, dense, and free of obvious pores. This effectively avoids the decrease in material shielding effectiveness and unstable signal transmission caused by discontinuous interface layers or numerous pores, ensuring the shielding effect of electric and magnetic fields and preventing shielding failure and signal interference. At the same time, the complete interface layer can meet the strength required for welding components, ensuring the reliability of workpiece assembly and long-term use.

[0030] A schematic diagram of the interface structure of hot-dip tin-plated stainless steel strip products can be drawn by combining the three sets of embodiments, such as... Figure 5 As shown, the overall interface structure of this product can be divided into four layers: the first layer is a tin-containing plating layer (i.e., a tin plating layer); the second layer is an FeSn2 phase layer; the third layer is an FeSn phase layer; and the fourth layer is a stainless steel substrate layer. The FeSn phase layer is relatively flat, while the FeSn2 phase layer exhibits needle-like or blocky protrusions. The intermetallic compound layer achieves a good metallurgical bond between the tin layer and the stainless steel substrate, resulting in better adhesion of the plating.

[0031] Performance testing Vickers Hardness: The surface hardness of the coating was measured using a fully automatic Vickers hardness tester, model VH500-3A, under a load of 100g; Tensile Strength: A universal tensile testing machine, model UTM-4304, was used, with the tensile rate set to 1.0 mm / min; Conductivity: The conductivity of each embodiment was tested using a conductivity meter, employing the eddy current method. The performance test results were obtained at room temperature. Figure 6 As shown in the figure and the table below: Meanwhile, to test the adhesion between the tin plating and the stainless steel strip, a cross-cut adhesion test was conducted. According to GB / T 9286-2021 standard, given that the plating thickness of this patent is less than 20 μm, a cross-cut spacing of 1 mm was selected. The results are as follows... Figure 7 As shown.

[0032] Combined with performance test results Figure 4 It can be seen that the FeSn phase layer and FeSn2 in Example 1 are relatively thick, and the overall performance is lower than that in Example 2 and Example 3; in terms of electrical conductivity, since the coatings in Example 2 and Example 3 are doped with alloying elements, the electrical conductivity is lower than that in Example 1.

[0033] The cross-cut adhesion test results showed that the coating adhesion of all three sets of examples reached GB / T 9286-2021 Grade 0, with completely smooth edges and no coating peeling.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for manufacturing a hot-dip tin-plated stainless steel substrate strip, characterized in that: After cleaning the surface of the stainless steel strip, removing the oxide layer and activating it with flux, the preheated stainless steel strip is immersed in molten tin or molten tin alloy for hot-dip plating, and the plating thickness is controlled within 1-20μm. Hot-dip galvanizing creates a metallurgical bond between the stainless steel strip surface and the tin-containing plating layer, forming FeSn phase layer and FeSn2 phase layer. The FeSn phase layer near the stainless steel strip is a flat layer, while the FeSn2 phase layer near the tin-containing plating layer has irregular needle-like and / or block-like protrusions on the side in contact with the tin-containing plating layer. These needle-like and / or block-like protrusions are embedded in the tin-containing plating layer.

2. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 1, characterized in that: The thickness of the tin-containing plating layer ranges from 1 to 20 μm, and the thickness of the iron-tin intermetallic compound layer composed of the FeSn phase layer and the FeSn2 phase layer ranges from 1.0 to 5.0 μm.

3. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 1 or 2, characterized in that, Includes the following steps: Step 1: Perform surface degreasing and pickling on the stainless steel strip to remove surface stains, degrease, and remove oxidation residues, followed by drying; Step 2: The stainless steel sheet and strip obtained in Step 1 are activated using a stainless steel plating flux and then dried; subsequently, the dried stainless steel sheet and strip are preheated; the preheating temperature is controlled at 150-220 ℃. Step 3: The preheated stainless steel strip is vertically immersed in molten tin or molten tin alloy for hot-dip plating. During the hot-dip plating process, an air knife is used to control the thickness of the tin-containing plating layer. After the hot-dip plating is completed, it is cooled with room temperature water for 1-3 seconds to obtain hot-dip tin-plated stainless steel strip.

4. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 3, characterized in that, The method for preparing stainless steel sheet and strip in step 1 is as follows: a standard stainless steel billet is hot-rolled into a billet, and the heating temperature in the hot rolling process is selected as 1000-1100℃, followed by 5-15 passes of cold rolling processing; the thickness of the cold-rolled stainless steel strip is in the range of 0.1-1.5 mm; the rolled stainless steel sheet and strip are placed in a bell furnace for annealing treatment, and the annealing temperature is in the range of 300-425℃, and the annealing time is 30-120 min, to obtain the stainless steel sheet and strip.

5. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 4, characterized in that: The annealing process involves a heating rate of 150-200℃ / h; after annealing, the mixture is rapidly cooled by a fan, and N2 and H2 are used for atmosphere protection during the heat treatment process.

6. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 3, characterized in that: The molten tin in step 3 is obtained by heating and melting tin ingots in a tin melting furnace. After melting, it is kept warm and stored for later use. The holding temperature range is 235-290℃.

7. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 3, characterized in that: In step 1, degreasing is performed using 10-25% dilute sulfuric acid and detergent, with an acid washing time of 15-30 minutes, followed by cleaning with detergent; surface stains are removed by cleaning with deionized water; and finally, hot air at a temperature of 100-200℃ is used for forced-air drying.

8. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 3, characterized in that: In step 3, the hot-dip plating temperature is 235-290℃, the immersion and leaching rate is 20-200m / min, and the plating time is 1-5s.

9. The method for manufacturing stainless steel substrate hot-dip tin-plated strip according to claim 3, characterized in that: The operation objects of steps 1 to 3 are one or both sides of the stainless steel strip.

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