Nickel-plated steel strip with excellent processability, battery shell made of nickel-plated steel strip and manufacturing method of nickel-plated steel strip

Abstract

The present invention relates to a nickel-plated steel strip having a substrate and a ferro-nickel alloy layer on at least one surface of the substrate, the ferro-nickel alloy layer having a double-layer structure comprising a ferro-nickel alloy layer upper layer and a ferro-nickel alloy layer lower layer, the ferro-nickel alloy layer upper layer comprising a FeNi face-centered cubic solid solution, and the ferro-nickel alloy layer lower layer comprising a FeNi face-centered cubic solid solution. The lower layer of the nickel-iron alloy layer comprises a FeNi martensite body-centered tetragonal solid solution; the lower layer is located on the substrate. In addition, the invention also relates to a battery shell manufactured by the nickel-plated steel strip and a manufacturing method of the nickel-plated steel strip. The iron-nickel alloy double-layer structure in the nickel-plated steel strip can reduce stress concentration at the interface of the nickel-plated steel strip and the substrate, and the obtained nickel-plated steel strip is excellent in plating layer binding force and excellent in machining performance and mechanical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a nickel-plated steel strip and a manufacturing method thereof, in particular to a nickel-plated steel strip with excellent processability, a battery shell made of the same and a manufacturing method thereof. BACKGROUND

[0002] Under the background of global energy demand growth and rapid development of new energy technology, battery technology for electric vehicles and portable electronic devices has become the focus of research and industry. The performance of the battery is crucial to the energy conversion efficiency and the device life, among which the selection of the battery shell material is particularly important. Nickel-plated steel strip, also known as pre-plated nickel steel strip, is known for its excellent corrosion resistance, good electrical conductivity and excellent physical and chemical stability, and has become the first choice for manufacturing battery shells, electronics, automotive components and other high-end manufacturing materials.

[0003] For battery steel shell containers, after the battery shell is punched, the nickel plating by barrel plating is called post-plating. Due to the poor uniformity of the electroplating process and the problems in processability and environmental protection during production, the post-plating has been gradually eliminated. Pre-plated nickel steel strip is widely used due to its excellent electroplating uniformity, welding performance and uniform electrical conductivity. With the pursuit of safety performance and energy density of batteries, the high melting point and high strength of nickel-plated steel strip are adapting to the development trend of batteries, so the future demand for nickel-plated steel strip is growing. The coating is a decisive factor for the performance of the nickel-plated steel strip. The quality of the coating, including its uniformity, adhesion and thickness, directly affects the overall performance of the nickel-plated steel strip, including stability under extreme conditions and electrochemical performance in battery manufacturing.

[0004] Patent CN106757244A discloses a preparation method of high-flexibility nickel-plated steel strip, which first deposits a 5-10 μm thick nickel coating on the porous steel strip substrate, then performs a low-temperature stress removal treatment on the steel strip, and finally places the nickel-coated porous steel strip in a heat treatment furnace for high-temperature crystallization treatment, thereby improving the corrosion resistance and mechanical properties of the nickel-plated layer of the perforated steel strip.

[0005] Patent CN102876971A discloses a preparation method of nickel-chromium-plated steel strip for battery steel shell, which designs a double-layer plating of chromium and nickel, first plating a layer of chromium on the substrate to form a corrosion-resistant layer, and then plating a layer of nickel, thereby double increasing the corrosion resistance. However, the method is complex, high in cost and difficult to control.

[0006] Patent CN111989424A discloses a Ni diffusion plated steel plate and a manufacturing method thereof, which teaches the Ni adhesion amount and Fe concentration range of the Fe-Ni alloy coating of the Ni diffusion plated steel plate, and the ferrite grain size of the base steel plate, to obtain a nickel-plated steel plate with good stamping formability.

[0007] Patents CN102763237A, CN112239877A, CN102458701A, and CN113195795A disclose a heat treatment method for nickel-plated steel sheets. After annealing, a pure nickel layer is retained on the outermost side, and an iron-nickel alloy layer is placed between the pure nickel layer and the substrate. The method also teaches the ratio of nickel and iron elements and proposes a method to change the surface roughness of the plating layer, thereby suppressing damage to the formed can and leaving marks on the mold during battery can forming.

[0008] Patent CN114829678A discloses a Ni-plated steel sheet and a method for manufacturing the Ni-plated steel sheet. Its iron-nickel alloy layer contains a mixed phase composed of bcc phase and fcc phase, without obvious delamination. However, the mixed phase may lead to unstable performance or, due to the ratio of bcc phase to fcc phase, the desired excellent plasticity and coating adhesion cannot be achieved.

[0009] Therefore, research on the structure of nickel-iron alloy layers is limited, and existing nickel-plated steel strips cannot fully meet the requirements of battery materials. Current technologies do not address how to obtain nickel-plated steel with a specific phase structure to improve its processing performance and bonding strength, and how to use this nickel-plated steel to manufacture battery casings with superior mechanical properties. Given the increasing application of nickel-plated steel in the battery steel industry and other fields, further research is needed in this field to study the microstructure of the nickel layer and develop nickel-plated steel strips with excellent processing performance, as well as battery casings that are less prone to deformation during battery charging and discharging after stamping. Summary of the Invention

[0010] In view of the above-mentioned defects and shortcomings of the prior art, the present invention provides a nickel-plated steel strip with excellent processing performance. This nickel-plated steel strip has a double-layer nickel-iron alloy layer formed on a substrate, comprising an upper nickel-iron alloy layer and a lower nickel-iron alloy layer. The upper nickel-iron alloy layer is mainly composed of FeNi face-centered cubic (FCC) solid solution, and the lower nickel-iron alloy layer is mainly composed of martensitic body-centered tetragonal (BCT). This double-layer nickel-iron alloy layer has good adhesion to the substrate, reducing stress concentration at the interface with the substrate, and further improving the strength, toughness, and processing performance of the nickel-plated steel strip.

[0011] Therefore, in a first aspect, the present invention provides a nickel-plated steel strip with excellent processing performance, the nickel-plated steel strip having a substrate and a nickel-iron alloy layer located on at least one side of the substrate, the nickel-iron alloy layer having a double-layer structure comprising an upper nickel-iron alloy layer and a lower nickel-iron alloy layer, wherein the upper nickel-iron alloy layer comprises a FeNi face-centered cubic solid solution, and the lower nickel-iron alloy layer comprises a FeNi martensitic body-centered tetragonal solid solution; the lower layer is located on the substrate.

[0012] In actual detection, in addition to the face-centered cubic (FCC) solid solution of FeNi, the upper layer of the nickel-iron alloy layer also contains a very small amount of the body-centered cubic (BCC) solid solution of FeNi. Therefore, "the upper layer of the nickel-iron alloy layer mainly contains the face-centered cubic (FCC) solid solution of FeNi" usually refers to the case where the volume percentage of the face-centered cubic solid solution structure of FeNi in the upper layer of the nickel-iron alloy layer is 90-99%, and the volume percentage of the body-centered cubic structure of FeNi is 1-10%. Similarly, "the lower layer of the nickel-iron alloy layer mainly contains the martensitic body-centered tetragonal (BCT) solid solution" usually refers to the case where the volume percentage of the FeNi martensitic body-centered tetragonal solid solution in the lower layer of the nickel-iron alloy layer is 88-99%, and the volume percentage of the face-centered cubic solid solution of FeNi is 1-12%.

[0013] Preferably, the upper layer of the nickel-iron alloy layer is entirely composed of the face-centered cubic solid solution of FeNi, and the lower layer of the nickel-iron alloy layer is entirely composed of the FeNi martensitic body-centered tetragonal solid solution.

[0014] In a preferred embodiment, the content of C in the substrate is 0.008-0.06% by mass percentage, preferably 0.02-0.045%.

[0015] The substrate material of the present invention selects low-carbon aluminum-killed steel. During annealing, C atoms with a content of 0.008-0.06% in the substrate will form a lower layer of FeNi martensite with Fe and Ni atoms in the nickel plating layer after diffusion.

[0016] In a preferred embodiment, in addition to containing Fe, the substrate also contains the following chemical elements by mass percentage: 0 < Si ≤ 0.04%, Mn: 0.15-0.35%, P: ≤ 0.02%, S: ≤ 0.02%, N: ≤ 0.006%, Al: 0.01-0.08%.

[0017] More preferably, the substrate has the following chemical elements by mass percentage: C: 0.008-0.06%, 0 < Si ≤ 0.04%, Mn: 0.15-0.35%, P: ≤ 0.02%, S: ≤ 0.02%, N: ≤ 0.006%, Al: 0.01-0.08%, and the balance is Fe and unavoidable impurities.

[0018] In a preferred embodiment, according to the GB / T6461 evaluation method, the average grain size of the upper nickel-iron alloy layer is 0.5-5.0 μm, preferably 1.0-4.0 μm, more preferably 2.0-3.0 μm, and the average grain size of the lower nickel-iron alloy layer is 0.1-1.0 μm, preferably 0.5-0.8 μm, more preferably 0.6-0.7 μm. Because the upper and lower nickel-iron alloy layers contain different solid solution structures, the average grain size of the upper nickel-iron alloy layer will be larger than that of the lower nickel-iron alloy layer.

[0019] In a preferred embodiment, the thickness of the nickel-iron alloy layer is 1.0-7.0 μm, preferably 2.0-6.0 μm, and more preferably 3.0-5.0 μm. The upper layer of the nickel-iron alloy layer has a thickness of 0.5-3.5 μm, preferably 1.5-2.0 μm, and the lower layer has a thickness of 0.5-3.5 μm, preferably 1.5-2.5 μm. This double-layer nickel-iron alloy structure, with the thickness of the nickel-iron alloy layer within the above-mentioned range, provides better adhesion and density, improving the stamping performance of the nickel-plated steel strip.

[0020] In a preferred embodiment, a nickel plating layer is provided above the nickel-iron alloy layer, the thickness of which is 0.1-2.0 μm, preferably 0.5-1.0 μm. Depending on the annealing conditions, the nickel in the original nickel plating layer on the substrate may diffuse completely after annealing to form a nickel-iron alloy layer; or, the nickel in the original nickel plating layer may partially diffuse, forming a three-layer structure of substrate-nickel-iron alloy layer-nickel plating layer.

[0021] In a preferred embodiment, the atomic percentage of Ni in the upper layer of the nickel-iron alloy layer, Ni / (Ni+Fe), is 20%-40%, and the atomic percentage of Ni in the lower layer of the nickel-iron alloy layer, Ni / (Ni+Fe), is 10-25%. Since diffusion is a process in which the atomic percentage of Ni decreases linearly from the surface of the nickel-plated steel sheet to the substrate, the atomic percentage of Ni in the upper layer of the nickel-iron alloy layer will be greater than the atomic percentage of Ni in the lower layer.

[0022] In a preferred embodiment, the atomic percentage of Ni, Ni / (Ni+Fe), gradually decreases to 10% from the interface between the lower layer and the upper layer toward the interface between the lower layer and the substrate. By ensuring that the Ni content in the lower layer of the nickel-iron alloy layer meets the above conditions, a structure mainly composed of the BCT phase can be formed, improving the bonding between the nickel-iron alloy layer and the substrate, thereby enhancing strength, toughness, and processing performance.

[0023] In a preferred embodiment, the interface between the upper and lower layers of the nickel-iron alloy layer is a semi-coherent interface. Generally, the interface between a conventional nickel-iron alloy layer and the substrate is an incoherent interface because their crystal structures and lattice parameters differ significantly, making it difficult to achieve a perfectly matched coherent interface. Incoherent interfaces introduce dislocations and stress concentrations due to lattice mismatch. These defects generate stress fields at the interface, leading to problems during processing and deformation, resulting in processing defects. Therefore, this invention introduces a double-layer structure into the nickel-iron alloy layer and sets the interface between the upper and lower layers as a semi-coherent interface. A semi-coherent interface refers to an interface where the crystal structures on both sides are partially matched, but a certain number of dislocations or other defects exist to adjust for lattice mismatch. This interface structure retains some of the characteristics of lattice matching while using mechanisms such as dislocations to accommodate stress and distortion caused by different lattice parameters, thereby improving the adhesion between the nickel-plated steel strip and the substrate, as well as the strength and toughness of the battery casing manufactured from it.

[0024] In a preferred embodiment, the nickel-plated steel strip has a yield strength of 290-360 MPa, a tensile strength of 320-380 MPa, and an elongation of ≥40%.

[0025] In a preferred embodiment, the interfacial bonding strength between the nickel-iron alloy layer and the substrate is 15-25 MPa.

[0026] The present invention also relates to a battery casing made from the aforementioned nickel-plated steel strip.

[0027] On the other hand, the present invention provides a method for manufacturing the above-mentioned nickel-plated steel strip, which includes the following steps performed in sequence:

[0028] (1) After heating the billet, rough rolling and finish rolling are performed to obtain a hot-rolled substrate;

[0029] (2) The hot-rolled substrate is cold-rolled to obtain a cold-rolled steel strip;

[0030] (3) Electroplating is performed on the cold-rolled steel strip to form an original nickel plating layer on the cold-rolled steel strip, thereby obtaining a nickel-plated cold-rolled steel strip;

[0031] (4) Anneal the nickel-plated cold-rolled steel strip to obtain nickel-plated steel strip.

[0032] In a preferred embodiment, in step (1), the roughing temperature is 1000-1200℃ and the finishing temperature is 850-1050℃.

[0033] In a preferred embodiment, in step (2), the cold rolling reduction rate is 50-90%.

[0034] In a preferred embodiment, in step (3), the electroplating is performed using an electroplating solution comprising: 220-320 g / L nickel sulfate, 30-50 g / L nickel chloride, and 30-50 g / L boric acid. Preferably, the electroplating solution has a pH of 3-5, a temperature of 45-65°C, and a current density of 20-100 A / dm³. 2 Preferably 30-60 A / dm 2 .

[0035] In a preferred embodiment, in step (3), additives are added during the electroplating process, including brighteners, leveling agents, and wetting agents.

[0036] In a preferred embodiment, in step (4), the annealing is performed by continuous annealing or shroud annealing.

[0037] In a preferred embodiment, the method further includes an alkaline washing and / or acid washing step between steps (2) and (3).

[0038] In a preferred embodiment, when continuous annealing is used, the soaking temperature is 700-850°C, preferably 750-790°C, the soaking time is 40-120 seconds, preferably 60-80 seconds, and then the temperature is lowered to a temperature point 1 of 650-690°C at a rate greater than 50°C / s, the holding time is 5-60 seconds, and then the temperature is lowered to room temperature at a rate of 100-150°C / s.

[0039] In a preferred embodiment, when using a bell-type annealing, the heat spread temperature is 580-780°C, preferably 650-750°C, and the heat spread time is 15-30 hours, preferably 15-20 hours. After heating, air cooling is performed for 10-20 minutes, followed by air cooling to a temperature point 2 of 300-380°C, and then water cooling to room temperature.

[0040] In a preferred embodiment, the alkaline washing solution comprises: 75-85 g / L sodium hydroxide, 15-25 g / L anhydrous sodium carbonate, and 15-25 g / L sodium phosphate; preferably, the alkaline washing temperature is 55-65°C, and the current density is 10-20 A / dm³. 2 The alkaline washing time is 1-3 minutes.

[0041] In a preferred embodiment, the pickling solution is a 5% hydrochloric acid solution; preferably, the pickling time is 1-3 minutes and the pickling temperature is 25-30°C.

[0042] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, in step 3), the thickness of the initial nickel plating layer is 0.3-6.0 μm. The present invention, by coating a nickel layer with a thickness within the above-mentioned range onto the steel strip and then annealing it, facilitates the formation of a double-layer nickel-iron alloy layer with a thickness in the range of 1.0-7.0 μm on the substrate, thereby improving the mechanical properties of the nickel-plated steel strip, extending the service life of the material, and improving the bonding strength at the interface between the plating layer and the substrate.

[0043] Invention effects:

[0044] The nickel-plated steel strip of this invention has a double-layer nickel-iron alloy layer comprising an upper layer and a lower layer. The upper layer is mainly composed of a γ-FeNi face-centered cubic (FCC) solid solution structure, and the lower layer is mainly composed of a Fe-Ni martensitic body-centered tetragonal (BCT) structure. Through the nickel-iron alloy layer with the above-mentioned structure, the nickel-plated steel strip of this invention can improve the bonding strength at the interface between the plating layer and the substrate, reduce stress concentration at the interface, and improve toughness and processing performance. Battery cases made from this nickel-plated steel strip have superior mechanical properties and are less prone to deformation during battery charging and discharging. Attached Figure Description

[0045] Figure 1 Electron backscatter diffraction (EBSD) Kikuchi pattern quality (IQ) map of a nickel-plated steel strip according to an embodiment of the present invention (EDAX Team Hikari Plus system, magnification of 2000X, step size set to 50nm);

[0046] Figure 2(a) is a transmission Kikuchi diffraction (TKD) (IQ) pattern of a nickel-plated steel strip according to an embodiment of the present invention (Bruker OPTIMUS coaxial TKD system, magnification of 10000x, step size set to 10nm).

[0047] Figure 2(b) is a TKD PH diagram of a nickel-plated steel strip according to an embodiment of the present invention;

[0048] Figure 3 EBSD diffraction pattern quality (PH) map of a nickel-plated steel strip according to an embodiment of the present invention (TSL OIM Analysis 8 and Oxford Crystal);

[0049] Figure 4(a) shows the morphology of position 1 in the nickel-iron alloy layer and its

[001] region axis SAED pattern according to an embodiment of the present invention;

[0050] Figure 4(b) shows the morphology of position 2 in the nickel-iron alloy layer according to an embodiment of the present invention and its

[111] region axis SAED pattern;

[0051] Figure 4(c) shows a high-resolution superlattice SAED pattern of region 2

[111] in a nickel-iron alloy layer according to an embodiment of the present invention.

[0052] Figure 4(d) shows the morphology of position 3 in the nickel-iron alloy layer and its

[001] region axis SAED pattern according to an embodiment of the present invention;

[0053] Figure 4(e) shows the band morphology at position 3 and a typical twin (112) in a nickel-iron alloy layer according to an embodiment of the present invention.

[0054] Figure 5 A bright-field transmission electron microscope (TEM) image (JEOL F200) of a nickel-iron alloy layer according to an embodiment of the present invention;

[0055] Figure 6(a) is a bright-field TEM image of Ni and Fe elements in a nickel-iron alloy layer according to an embodiment of the present invention;

[0056] Figure 6(b) is a TEM EDS L1 line scan image of a nickel-iron alloy layer according to an embodiment of the present invention;

[0057] Figure 6(c) is a TEM EDS L2 line scan image of a nickel-iron alloy layer according to an embodiment of the present invention. Detailed Implementation

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0059] As used herein, the term “and / or” refers to and covers any and all possible combinations of more than one of the listed items.

[0060] In this paper, the EBSD experiments on nickel-plated steel strips were conducted using the EDAX Team Hikari Plus system with a magnification of 2000X and a step size of 50nm.

[0061] In this paper, the TKD experiment of nickel-plated steel strip was conducted using the Bruker OPTIMUS coaxial TKD system with a magnification of 10000x and a step size of 10nm.

[0062] In this paper, the EBSD and TKD analyses of nickel-plated steel strips were performed using TSL OIM Analysis 8 and Oxford Crystal analysis software.

[0063] In this paper, the ratio of the upper and lower layers of the nickel-iron alloy layer in the nickel-plated steel strip was obtained using EBSD combined with Image-Pro Plus image analysis software.

[0064] In this paper, the TEM analysis of nickel-plated steel strips was performed using a JEOL F200 instrument.

[0065] In this paper, yield strength is the yield limit of a metallic material when it yields, that is, the stress that resists a small amount of plastic deformation.

[0066] In this paper, tensile strength (Rm) is the critical value for the transition of a metal from uniform plastic deformation to localized concentrated plastic deformation, and it is also the maximum load-bearing capacity of a metal under static tensile conditions. Tensile strength is the resistance to the maximum uniform plastic deformation of a material.

[0067] In this paper, elongation, which is the percentage of the total deformation ΔL of the gauge length segment after tensile fracture to the original gauge length L: δ=ΔL / L×100%, is an indicator describing the plastic properties of the material.

[0068] In this article, bonding strength refers to the measure of the degree of bonding between the nickel plating layer and the substrate after annealing.

[0069] In this article, cold rolling reduction rate refers to the percentage of the amount of reduction of the workpiece after cold rolling to the height of the workpiece before rolling.

[0070] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The microstructural features of the nickel-plated steel strip involved in this embodiment are as follows: Figure 1 As shown in -6.

[0071] This embodiment relates to a nickel-plated steel strip with excellent processing performance, which has a substrate and a nickel-iron alloy layer located on at least one side of the substrate. The nickel-iron alloy layer has a double-layer structure including an upper nickel-iron alloy layer and a lower nickel-iron alloy layer. The upper nickel-iron alloy layer is mainly composed of FeNi face-centered cubic solid solution, and the lower nickel-iron alloy layer is mainly composed of FeNi martensite body-centered tetragonal solid solution. The lower layer is located on the substrate.

[0072] Figure 1 The Kikuchi pattern quality (IQ) graph of EBSD is shown, as follows. Figure 1 As shown, in the nickel-plated steel strip of the present invention, the nickel-iron alloy layer on the substrate layer 3 exhibits a double-layer structure. The average grain size of the upper nickel-iron alloy layer 1 is about 1.47 μm, and a twin-like structure is observed inside; the lower nickel-iron alloy layer 2 is identified as a fine-grained region with an average grain size of about 0.49 μm, indicating the formation of a martensitic structure; the grain size in the substrate layer 3 exceeds 10 μm.

[0073] Figure 2(a) and 2(b)The image quality and phase diagram of the nickel-iron alloy layer analyzed using coaxial TKD are shown. Figure 2(a) further confirms that the nickel-iron alloy layer on substrate layer 3 is a bilayer structure, consisting of an upper nickel-iron alloy layer 1 and a lower nickel-iron alloy layer 2. Figure 2(b) shows the presence of a small number of body-centered cubic (BCC) structures ranging from tens to hundreds of nanometers in the upper nickel-iron alloy layer, which is mainly composed of face-centered cubic (FCC) solid solution structures. Similarly, a small number of face-centered cubic (FCC) structures were also found in the lower layer, which is mainly composed of body-centered tetragonal (BCT) structures.

[0074] Figure 3 The results of the EBSD phase distribution analysis are shown, combined with Figure 3 As shown in Figure 2(b), the upper layer 1 of the nickel-iron alloy layer is mainly composed of a face-centered cubic (FCC) structure, while the lower layer 2 is mainly composed of a body-centered tetragonal (BCT) structure. Figure 4 shows the morphology and diffraction pattern of different positions within the upper layer 1 and the lower layer 2 of the nickel-iron alloy layer, which further confirms the phase structure of the upper and lower layers. Figure 4(a) shows the morphology and diffraction pattern of the zone axis at position ①

[001] within the upper layer 1 of the nickel-iron alloy layer. This position is confirmed to be a face-centered cubic (FCC) structure phase, which is identified as a γ (FeNi) solid solution phase. A twin of approximately 625 nm × 87.5 nm was also found in this region, with a twin angle of 60°. <111> This pattern was also observed and verified in transmission Kikuchi diffraction (TKD) analysis. Figure 4(b) and 4(c) Figure 4(d) shows the morphology and diffraction pattern of position ② along the

[111] zone axis within the upper layer 1 of the nickel-iron alloy layer. This position confirms that the matrix structure is also FCC. Figure 4(d) shows the morphology and diffraction pattern of position ③

[001] zone axis within the lower layer 2 of the nickel-iron alloy layer. This position is confirmed to be a body-centered tetragonal (BCT) structure phase (diffraction patterns confirm BCC / BCT, the two structures are similar, and Figure 4(e) and TKD results confirm that it is a BCT martensite phase). No obvious superstructure was observed. As can be seen from Figure 4(e), significant layered features are observed in the morphology of the lower layer 2 of the nickel-iron alloy layer along the

[113] zone axis, which is a phenomenon at the twin boundaries of martensitic steel.

[0075] Figure 5 Bright-field TEM images of the nickel-iron alloy layers are shown. It can be observed that the thickness of the upper nickel-iron alloy layer 1 ranges from 1.58 to 2.35 μm, the thickness of the lower nickel-iron alloy layer 2 ranges from 1.65 to 2.66 μm, and the remainder is the substrate layer 3. It is evident that the thickness of the upper and lower nickel-iron alloy layers significantly exceeds the thickness of the original nickel plating layer. This phenomenon clearly indicates that during the annealing process, Ni elements diffused into the substrate material, leading to a transformation in the microstructure and phase structure of the substrate material, resulting in the formation of the specific upper and lower nickel-iron alloy layers.

[0076] Figure 6 shows TEM EDS line scan images of Ni and Fe elements in the nickel-iron alloy layer. As shown in Figure 6(a), the nickel-iron alloy layer on the substrate is a double-layer structure consisting of a top nickel-iron alloy layer 1 and a bottom nickel-iron alloy layer 2. The L1 line scan spans the top nickel-iron alloy layer 1, the bottom nickel-iron alloy layer 2, and the substrate layer 3, while the L2 line scan is transverse to the bottom nickel-iron alloy layer 2. Figure 6(b) is the TEM EDS L1 line scan image of the nickel-iron alloy layer. Figure 6(c) is the TEM EDS L2 line scan image of the nickel-iron alloy layer.

[0077] As shown in Figure 6(b), from the outer surface of the upper nickel-iron alloy layer 1 towards the interface between the lower nickel-iron alloy layer 2 and the upper nickel-iron alloy layer 1, the atomic percentage of Ni (Ni / (Ni+Fe)) is 20-40%, with the Fe content gradually increasing and the Ni content gradually decreasing. From the outer surface of the lower nickel-iron alloy layer 2 (at the interface with the upper layer 1, corresponding to position S2 in Figure 6(a)) towards the substrate layer 3, the atomic percentage of Ni (Ni / (Ni+Fe)) is 10-25%, with the Fe content gradually increasing and the Ni content gradually decreasing. As shown in Figure 6(c), the Ni and Fe content in the lower nickel-iron alloy layer 2 is relatively consistent across all transverse positions, with no significant fluctuations observed, indicating that the lower nickel-iron alloy layer 2 is unlikely to be a compound phase precipitated from the upper nickel-iron alloy layer 1 during cooling.

[0078] At the interface between the nickel-iron alloy layer 2 and the substrate layer 3 (corresponding to position S3 in Figure 6(a)), the Fe and Ni content fluctuates significantly, with Ni content decreasing significantly and Fe content increasing significantly. The fluctuation in element content at S3 may be due to Ni, as an austenitic stabilizing element with an FCC structure, having a higher solubility in the nickel-iron alloy layer 2 during annealing than the BCC phase in the substrate. After cooling, the compositional gradient is preserved due to the absence of diffusion-induced phase transformation and the short transformation time. Based on this information, it can be concluded that the nickel-iron alloy layer 2 is actually a martensitic layer.

[0079] The nickel-plated steel strip of the present invention can be manufactured by a method comprising the following steps performed sequentially:

[0080] (1) After heating the billet, rough rolling and finish rolling are performed to obtain a hot-rolled substrate;

[0081] (2) The hot-rolled substrate is cold-rolled to obtain a cold-rolled steel strip;

[0082] (3) Electroplating is performed on the cold-rolled steel strip to form an original nickel plating layer on the cold-rolled steel strip, thereby obtaining a nickel-plated cold-rolled steel strip;

[0083] (4) Anneal the nickel-plated cold-rolled steel strip to obtain nickel-plated steel strip.

[0084] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, in step (1), the roughing temperature is 1000-1200°C and the finishing temperature is 850-1050°C.

[0085] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, in step (2), the cold rolling reduction rate is 50-90%.

[0086] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, in step (3), electroplating is carried out using an electroplating solution comprising the following components: 220-320 g / L nickel sulfate, 30-50 g / L nickel chloride, 30-50 g / L boric acid, a pH value of 3-5, a temperature of 45-65°C, and a current density of 20-100 A / dm³. 2 Preferably 30-60 A / dm 2 .

[0087] The primary nickel plating solution chosen is Watt's nickel plating solution, with nickel sulfate, nickel chloride, and boric acid as its main components. Ni in the plating solution... 2+ The main culprit is nickel sulfate, which affects the crystallization and polarization of the electroplated layer. High concentrations and proportions of nickel sulfate result in coarser grains and poor surface gloss. Conversely, low concentrations and proportions hinder charge transfer, leading to poor conductivity and unsuitability for high-current-density electroplating processes. Therefore, to achieve good grain size and surface gloss, the concentration and proportion of nickel sulfate in the electroplating solution must be carefully controlled. Industrially, the concentration of nickel sulfate is typically controlled at 220-320 g / L, resulting in a uniform coating thickness and good corrosion resistance. Nickel chloride in the electroplating solution acts as an anodic depolarizer, accelerating the dissolution and retention of Ni in the electrolyte. 2+ Ion balance. Furthermore, nickel chloride also improves the conductivity and dispersibility of the electroplating solution, and makes the electroplating solution more uniformly distributed on the electrode surface. When the nickel chloride concentration is high, it accelerates the dissolution of the anode, generating a large amount of Cl in the process. - This roughens the coating surface, leading to numerous defects such as burrs and cracks. To achieve a bright and smooth coating surface, the concentration of sodium chloride needs to be controlled within the range of 30-50 g / L. As a weakly acidic buffer, boric acid releases H₂ in the electroplating solution. + This can reduce the generation of OH. - The amount of boric acid is important. However, when the boric acid content is high, it will precipitate through crystallization, eventually leading to defects such as burrs and pinholes on the coating surface; when the content is low, it will cause the pH value of the plating solution to fluctuate within a large range. Therefore, in order to make the coating denser and more uniform, the concentration of boric acid is generally controlled at around 30-50 g / L.

[0088] During the electroplating process, either a soluble or insoluble anode can be used. When using a soluble anode, nickel blocks or nickel balls are added to the titanium blue. When using an insoluble anode, the formation of sulfate ions must be controlled.

[0089] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, in step (3), additives are added during the electroplating process, including brighteners, leveling agents and wetting agents.

[0090] Adding certain additives during the electroplating process can improve the surface quality of the plating layer. Brighteners primarily increase the gloss of the plating layer and make the surface denser and smoother. Leveling agents mainly increase the smoothness of the plating surface and reduce its roughness. Wetting agents effectively improve the wettability of the electroplating solution on the substrate surface, making the electroplating process more uniform, promoting the removal of hydrogen bubbles from the substrate surface, and ultimately effectively reducing the porosity of the plating surface.

[0091] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, in step (4), the annealing is performed by continuous annealing or shroud annealing.

[0092] In a preferred embodiment, the method for manufacturing nickel-plated steel strip of the present invention further includes an alkaline washing and / or acid washing step between steps (2) and (3).

[0093] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, when continuous annealing is used, the soaking temperature is 700-850°C, preferably 750-790°C, and the soaking time is 40-120 seconds, preferably 60-80 seconds. Then, the temperature is lowered to a temperature point 1 of 650-690°C at a rate greater than 50°C / s, held for 5-60 seconds, and then lowered to room temperature at a rate of 100-150°C / s. As the annealing temperature increases, the cooling rate decreases, the grain size increases, and the alloy layer thickness increases.

[0094] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, when using a bell-type annealing process, the soaking temperature is 580-780°C, preferably 650-750°C, and the soaking time is 15-30 hours, preferably 15-20 hours. After heating, air cooling is performed for 10-20 minutes, followed by air cooling to a temperature point 2 of 300-380°C, and then water cooling to room temperature. As the annealing temperature increases and the holding time increases, the grain size increases, and the alloy layer thickness increases.

[0095] Nickel-plated steel strip is commonly used in stamped battery containers. To improve the adhesion of the nickel layer, the nickel-plated steel coil generally needs to undergo annealing. After heat treatment, a nickel-iron alloy layer of a certain thickness is formed, thereby improving the adhesion and density of the material. Controlling the thickness of the nickel-iron alloy layer is crucial, because if the thickness is too small, the above-mentioned objectives cannot be achieved. An appropriately thick nickel-iron alloy layer, due to its increased hardness, also improves the stamping performance of the material, making it easier for the nickel-plated steel strip to form a nickel-plated steel shell. However, if the thickness of the nickel-iron alloy layer is too large, the stamping effect may be unsatisfactory due to the excessive hardness of the nickel-iron layer on the substrate. This invention, through controlled annealing, can control the thickness of the nickel-iron alloy layer within a suitable range and form the aforementioned specific double-layer structure, thereby obtaining a nickel-plated steel strip with excellent performance.

[0096] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, the alkaline washing solution comprises 75-85 g / L sodium hydroxide, 15-25 g / L anhydrous sodium carbonate, and 15-25 g / L sodium phosphate; preferably, the alkaline washing temperature is 55-65°C, and the current density is 10-20 A / dm³. 2 The alkaline washing time is 1-3 minutes.

[0097] Alkaline washing can remove residual oil, iron powder, oxides, and other contaminants from the surface of steel plates before electroplating, improving the quality and adhesion of the coating. Sodium hydroxide, due to its strong saponification ability, is often used to decompose grease in alkaline washing and is therefore a major component of the solution. In addition, sodium phosphate and sodium carbonate are also commonly used chemicals in alkaline washing solutions. Sodium carbonate, being weakly alkaline, readily reacts with metal salts and is thus a commonly used chemical in alkaline washing. Sodium phosphate effectively improves water solubility and is also a commonly used chemical in alkaline washing solutions.

[0098] In a preferred embodiment, in the method for manufacturing nickel-plated steel strip of the present invention, the pickling solution is a 5% hydrochloric acid solution; preferably, the pickling time is 1-3 minutes and the pickling temperature is 25-30°C.

[0099] The main purpose of pickling is to remove impurities such as oxides and rust remaining on the surface of the steel plate, further improving the cleanliness and surface activity of the steel plate. Pretreatment before electroplating generally uses hydrochloric acid, sulfuric acid, and phosphoric acid. The pickling raw materials are generally selected based on the material of the substrate before electroplating. To avoid corrosion of the substrate, the steel plate surface should be rinsed immediately with deionized water after pickling. During the rinsing process, it is important to prevent hydrogen ions from the hydrochloric acid solution from being carried into the plating bath.

[0100] The present invention will be further described in detail below with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0101] Example

[0102] Examples 1-16 and Comparative Examples 1-8

[0103] The nickel-plated steel strips in Examples 1-16 were prepared using the following steps:

[0104] (1) After heating and roughing and finishing rolling according to the chemical composition shown in Table 1, hot-rolled substrate is obtained: the C content is controlled to be 0.008-0.06%, the Si content is 0.015%-0.04%, the Mn content is 0.15%-0.35%, the Al content is 0.01-0.08%, P≤0.02%, S≤0.02%, and N≤0.006%;

[0105] (2) The hot-rolled substrate is cold-rolled to obtain a cold-rolled steel strip; optionally, the cold-rolled steel strip is alkali-washed and / or pickled;

[0106] (3) Electroplating is performed on the cold-rolled steel strip to form an initial nickel plating layer, resulting in nickel-plated cold-rolled steel strip: the current density is controlled at 30-80 A / dm. 2

[0107] (4) Annealing the nickel-plated cold-rolled steel strip to form a nickel-iron alloy layer on the cold-rolled steel strip to obtain nickel-plated steel strip. In Examples 1-8, continuous annealing is used, with a soaking temperature of 750-790℃ and a soaking time of 60-80 seconds. Then, the temperature is reduced to temperature point 1 of 650-690℃ at a rate of 65-110℃ / s, and the holding time is 10-60 seconds. Then, the temperature is reduced to room temperature at a rate of 100-150℃ / s. In Examples 9-16, bell-type annealing is used, with a soaking temperature of 650-720℃ and a soaking time of 15-20 hours. After heating, air cooling is performed for 10-20 minutes. Then, air cooling is performed to temperature point 2 of 300-380℃. Then, water cooling is performed to room temperature.

[0108] Comparative Examples 1-8 were manufactured using essentially the same method as the embodiments of this application, but one or more of their substrate composition and process parameters do not meet the requirements of this application.

[0109] The chemical composition of the substrates in Examples 1-16 and Comparative Examples 1-8, and the specific process parameters of the nickel-plated steel strips are shown in Tables 1 and 2. Table 1 lists the chemical composition of the substrates in the nickel-plated steel sheets of Examples 1-16 and Comparative Examples 1-8. Table 2 lists the specific process parameters of the nickel-plated steel strips in Examples 1-16 and Comparative Examples 1-8.

[0110]

[0111]

[0112]

[0113] Then, the nickel-plated steel strips obtained in Examples 1-16 and Comparative Examples 1-8 were cut into square samples with a side length of 10 mm using a grinding wheel to facilitate subsequent microscopic observation. Sample preparation was performed using a Scoos2 HiVac DualBeam scanning electron microscope. A 50 μm × 20 μm cross-sectional area was prepared by ion beam cutting for EBSD analysis, and thin sections of 6 μm × 8 μm × 60 nm were cut out for coaxial TKD analysis and TEM studies.

[0114] Microstructural analysis was performed on the samples after sampling. The results are listed in Table 3.

[0115] The microstructure analysis methods for the samples in each embodiment and comparative example are as follows:

[0116] EBSD experiments on nickel-plated steel strips were conducted using the EDAX Team Hikari Plus system with a magnification of 2000X and a step size of 50nm.

[0117] The TKD experiment of nickel-plated steel strip was conducted using the Bruker OPTIMUS coaxial TKD system with a magnification of 10000x and a step size of 10nm.

[0118] The EBSD and TKD analyses of the nickel-plated steel strip were performed using TSL OIM Analysis 8 and Oxford Crystal analysis software.

[0119] TEM analysis of the nickel-plated steel strip was performed using a JEOL F200 instrument.

[0120] The ratio of the upper and lower layers of the nickel-iron alloy layer in the nickel-plated steel strip was obtained using EBSD combined with Image-Pro Plus image analysis software.

[0121] The interfacial bonding strength between the nickel-iron alloy layer of the nickel-plated steel strip and the substrate was characterized by the following method:

[0122] The bonding strength of the plating layers was evaluated using the interfacial strength of the nickel plating layer, employing a micron-sized scratch tester (Hysitron TI 950 model) with a load increase rate of 10 N / min, a scratch length of 8 mm, a triangular pyramidal indenter with a 60° cone angle, made of diamond, and a tip curvature radius of 6 μm. The interfacial bonding strength was determined by the data corresponding to the abrupt change in transverse stress. Each sample was measured three times, and the average value was used for data analysis.

[0123] Table 3 lists the microstructure and properties of the nickel-plated steel strips of Examples 1-16 and Comparative Examples 1-8.

[0124]

[0125]

[0126] As shown in Table 3, the nickel-iron alloy layer in the nickel-plated steel strips of Examples 1-16 has a double-layer structure consisting of an upper layer and a lower layer. The microstructure of the upper layer is mainly FeNi(FCC) solid solution (volume percentage above 90%), while the lower layer is mainly FeNi martensitic BCT solid solution (volume percentage above 88%). The thickness of the nickel-iron alloy layer is 1.0-7.0 μm, with the upper layer having a thickness of 0.5-3.5 μm and the lower layer having a thickness of 0.5-3.5 μm. Furthermore, the interface between the upper and lower layers in Examples 1-16 is a semi-coherent interface, with the average grain size of the upper layer of the nickel-iron alloy layer being 0.5-5.0 μm and the average grain size of the lower layer being 0.1-1.0 μm. In the nickel-iron alloy layer, the atomic percentage of Ni (Ni / (Ni+Fe)) in the upper layer is 20-40%, and in the lower layer it is 10-25%. From the interface between the lower and upper layers towards the interface between the lower layer and the substrate layer, the atomic percentage of Ni gradually decreases to 10%. In contrast, the nickel-iron alloy layer in the nickel-plated steel strips in Comparative Examples 1-8 is a single-layer structure, which is a FeNi(FCC) solid solution structure.

[0127] Furthermore, as shown in Table 3, the mechanical properties of the nickel-plated steel strips in Examples 1-16 all meet the requirements of yield strength ≥290MPa, tensile strength ≥320MPa, elongation ≥40%, and interfacial bonding strength between the nickel-iron alloy layer and the substrate of 15-25MPa. In contrast, the yield strength, tensile strength, elongation, and bonding strength of Comparative Examples 1-8 are all poor.

[0128] All publications, patent applications, patents and other references mentioned in this invention are incorporated herein by reference in their entirety.

[0129] While the present invention has been illustrated and described with reference to certain preferred embodiments, those skilled in the art should understand that the above description is a further detailed explanation of the invention in conjunction with specific embodiments, and should not be construed as limiting the specific implementation of the invention to these descriptions. Various changes in form and detail can be made by those skilled in the art, including several simple deductions or substitutions, without departing from the spirit and scope of the invention.

Claims

1. A nickel-plated steel strip, characterized in that, The nickel-plated steel strip has a substrate and a nickel-iron alloy layer on at least one side of the substrate, The nickel-iron alloy layer is a double-layer structure including a nickel-iron alloy layer upper layer and a nickel-iron alloy layer lower layer, wherein the nickel-iron alloy layer upper layer contains FeNi face-centered cubic solid solution and the nickel-iron alloy layer lower layer contains FeNi martensitic body-centered tetragonal solid solution; The lower layer is on the substrate.

2. The nickel-plated steel strip defined in claim 1 wherein, The content of C in the substrate is 0.008-0.06% by mass, preferably 0.02-0.045% by mass.

3. The nickel-plated steel strip defined in claim 2, characterized in that, The substrate contains Fe and the following chemical elements by mass: 0 4. The nickel-plated steel strip defined in claim 1, wherein The average grain size of the nickel-iron alloy layer upper layer is 0.5-5.0 μm and the average grain size of the nickel-iron alloy layer lower layer is 0.1-1.0 μm.

5. The nickel-plated steel strip defined in claim 1, wherein The thickness of the nickel-iron alloy layer is 1.0-7.0 μm, wherein the thickness of the nickel-iron alloy layer upper layer is 0.5-3.5 μm and the thickness of the nickel-iron alloy layer lower layer is 0.5-3.5 μm.

6. The nickel-plated steel strip defined in claim 1, wherein The nickel-iron alloy layer upper layer has a nickel-plated layer thereon, and the thickness of the nickel-plated layer is 0.1-2.0 μm.

7. The nickel-plated steel strip defined in claim 1 wherein, The atomic percentage of Ni / (Ni+Fe) in the nickel-iron alloy layer upper layer is 20-40% and the atomic percentage of Ni / (Ni+Fe) in the nickel-iron alloy layer lower layer is 10-25%.

8. The nickel-plated steel strip defined in claim 1, wherein From the interface between the nickel-iron alloy layer lower layer and the nickel-iron alloy layer upper layer towards the interface between the nickel-iron alloy layer lower layer and the substrate, the atomic percentage of Ni / (Ni+Fe) gradually decreases to 10%.

9. The nickel-plated steel strip defined in claim 1 wherein, The interface between the nickel-iron alloy layer upper layer and the lower layer is a semi-coherent interface.

10. The nickel-plated steel strip defined in claim 1, wherein The yield strength of the nickel-plated steel strip is 290-360 MPa, the tensile strength is 320-380 MPa, and the elongation is ≥40%.

11. The nickel-plated steel strip defined in claim 1 wherein, The interfacial bonding strength between the nickel-iron alloy layer and the substrate is 15-25 MPa.

12. A battery shell manufactured from the nickel-plated steel strip according to any one of claims 1 to 11.

13. A method of manufacturing the nickel-plated steel strip according to any one of claims 1 to 11, characterized in that, The method comprises the following steps performed in sequence: (1) heating a cast slab, rough rolling and finish rolling to obtain a hot-rolled substrate; (2) cold rolling the hot-rolled substrate to obtain a cold-rolled steel strip; (3) electroplating the cold-rolled steel strip to form an original nickel-plated layer on the cold-rolled steel strip and obtain a nickel-plated cold-rolled steel strip; (4) annealing the nickel-plated cold-rolled steel strip to obtain a nickel-plated steel strip.

14. The method of claim 13, wherein, The method satisfies one or more of the following features: In step (1), the rough rolling temperature is 1000-1200 °C and the finish rolling temperature is 850-1050 °C; In step (2), the cold rolling reduction is 50-90%; In step (3), the electroplating is performed using an electroplating solution comprising: nickel sulfate 220-320 g / L, nickel chloride 30-50 g / L, boric acid 30-50 g / L, preferably, the pH value of the electroplating solution is 3-5, the temperature is 45-65 °C, the current density is 20-100 A / dm 2 , preferably 30-60 A / dm 2 ; In step (3), an additive is added in the electroplating process, and the additive includes brightener, leveling agent, wetting agent; In step (4), the annealing is continuous annealing or batch annealing; The method further comprises a step of alkaline cleaning and / or acid cleaning between steps (2) and (3).

15. The method of claim 13, wherein, When using continuous annealing, the soaking temperature is 700-850℃, the soaking time is 40-120 seconds, then the temperature is decreased to a temperature point 1 of 650-690℃ at a rate of greater than 50℃ / s, the holding time is 5-60 seconds, and then the temperature is decreased to room temperature at a rate of 100-150℃ / s.

16. The method of claim 13, wherein, When using bell annealing, the soaking temperature is 580-780℃, the soaking time is 15-30 hours, after the heating is completed, air cooling is performed, the air cooling time is 10-20 minutes, then the temperature is decreased to a temperature point 2 of 300-380℃ by air cooling, and then the temperature is decreased to room temperature by water cooling.

17. The method of claim 13, wherein, The composition of the alkaline solution in the alkaline cleaning includes: sodium hydroxide 75-85 g / L, anhydrous sodium carbonate 15-25 g / L, sodium phosphate 15-25 g / L; preferably, in the alkaline cleaning, the alkaline cleaning temperature is 55-65 ℃, the current density is 10-20 A / dm 2 , and the alkaline cleaning time is 1-3 minutes.

18. The method of claim 13, wherein, The composition of the acid cleaning solution in the acid cleaning is a 5% hydrochloric acid solution; preferably, the acid cleaning time is 1-3 minutes, and the acid cleaning temperature is 25-30℃.

19. The method of claim 13, wherein, In step 3), the thickness of the original nickel plating layer is 0.3-6.0μm.

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