Low-cost high-corrosion-resistance nickel-plated steel strip and manufacturing method thereof

Abstract

The low-cost high-corrosion-resistance nickel-plated steel strip comprises a base plate and a Fe-Ni alloy layer covering the surface of the base plate, the base plate contains Fe and inevitable impurities and further comprises, by mass, 0.055%-0.1% of C, 0.25% < Si < = 0.45%, 0.30%-0.55% of Mn, 0 < S < = 0.01%, 0.22%-0.40% of Cu, 0.08%-0.25% of Ni, 0.30%-0.50% of Cr, 0.015% < Al < = 0.055% and the balance Fe and inevitable impurities. At least one surface of the substrate is provided with a nickel plating layer with the thickness smaller than 1 micron. Correspondingly, the invention further relates to a manufacturing method of the low-cost high-corrosion-resistance nickel-plated steel strip, the manufactured low-cost high-corrosion-resistance nickel-plated steel strip can still keep the overall corrosion resistance under the condition that the thickness of a nickel-plated layer is reduced, and the cost of raw materials for producing the nickel-plated steel strip is effectively reduced.

Description

Technical Field

[0001] The invention relates to a nickel-plated steel strip and a manufacturing method thereof, and in particular to a low-cost and high-corrosion-resistant nickel-plated steel strip and a manufacturing method thereof. Background Art

[0002] Nickel-plated steel strips are widely used in various battery housing materials, electronic components and precision instruments due to the excellent chemical stability, corrosion resistance and dissimilar metal welding performance of the surface nickel plating layer. However, as the element Ni used for surface plating, the cost is extremely high due to the limitation of international nickel ore raw material resources. In addition, the new generation of industrial product design has put forward new requirements for energy reduction, emission reduction and green environmental protection. Reducing the consumption of Ni elements for surface plating also caters to the new trend.

[0003] For example, the Chinese public application with publication number "CN111989424A" (publication date November 24, 2020) and the subject "Ni diffusion-coated steel plate and method for manufacturing Ni diffusion-coated steel plate" discloses a surface Ni diffusion-treated nickel-plated steel plate, which adopts a low-carbon aluminum-killed steel component system to produce battery shell steel, and its chemical element composition weight percentage is: C: 0.005~0.25%, Si≤0.1%, Mn: 0.05~0.9%, P≤0.025%, S≤0.025%, Al: 0.005~0.1%, N≤0.007%, B: 0~0.0052%, and the rest is Fe and unavoidable inclusions, wherein the Ni adhesion of the Fe-Ni diffusion alloy coating is 9.0~20g / m 2 The Fe concentration Cs (i.e., exposed iron ratio) of the outermost layer of the Fe-Ni diffusion alloy plating layer is 10 to 55 mass %.

[0004] The Chinese public application with the publication number of "CN107407000B" (publication date September 13, 2019) and the theme of "Manufacturing method of surface-treated steel plate for battery container and surface-treated steel plate for battery container" discloses a method for producing a surface nickel-plated steel plate for battery container, but the chemical composition of the substrate for nickel plating is not clearly defined, only indicating that low-carbon aluminum-killed steel (carbon content 0.01-0.15 wt%), ultra-low carbon steel with a carbon content of less than 0.003 wt%, or non-aging ultra-low carbon steel made by adding Ti, Nb, etc. to ultra-low carbon steel can be used. The thickness of the nickel plating layer is generally controlled at 0.5-3.5 μm, and the preferred thickness is above 2.0 μm.

[0005] However, the technical solution of CN111989424A adopts conventional low-carbon steel as the substrate, and the corrosion resistance of the steel strip mainly depends on the thickness of the surface nickel plating layer. The influence of the substrate itself on the corrosion resistance of the nickel-plated steel strip is not considered. Moreover, the technical solution of CN107407000B does not specify the composition of the substrate. Similar to patent CN111989424A, it also mainly relies on the thickness of the surface nickel plating layer to ensure the corrosion resistance of the nickel-plated steel strip.

[0006] Therefore, the nickel-plated steel strip disclosed in the prior art mainly ensures the corrosion resistance of the strip by the nickel-plated layer. The thicker the nickel-plated layer, the better the corrosion resistance of the strip. However, under the current new situation of scarce nickel resources, high raw material prices and requirements for green and environmentally friendly processes, unilaterally increasing the thickness of the nickel-plated layer not only fails to meet the requirements of green energy conservation and environmental protection, but also increases the raw material cost of the product. Therefore, there is still a lot of room for improvement in balancing the cost and corrosion resistance of nickel-plated steel strips.

[0007] In summary, the present invention aims to solve the defects of existing thick nickel-plated steel strips, such as high cost and poor corrosion resistance of thin nickel-plated layers, and hopes to obtain a low-cost and highly corrosion-resistant nickel-plated steel strip product. Summary of the invention

[0008] One of the purposes of the present invention is to provide a low-cost, high-corrosion-resistant nickel-plated steel strip, which overcomes the defect of poor corrosion resistance of traditional nickel-plated steel strips in a thin coating state. The yield strength of the low-cost, high-corrosion-resistant nickel-plated steel strip is ≥340MPa, the tensile strength is ≥425MPa, and the elongation after fracture is ≥30%, which can meet the stringent corrosion resistance requirements in a relatively thin coating state. Its corrosion resistance determined according to GB / T 6461-2002 is above level 8. In the present invention, the low-cost, high-corrosion-resistant nickel-plated steel strip described in the present invention is rationally designed with respect to the chemical composition of the steel strip substrate and is combined with an optimized manufacturing process, which can ensure that the nickel-plated steel strip still has excellent corrosion resistance under the condition of a small amount of nickel coating, effectively reduce the cost of raw materials, and has good promotion prospects and application value.

[0009] To achieve the above object, the present invention provides a nickel-plated steel strip, comprising a substrate and a Fe-Ni alloy layer located on at least one surface of the substrate, wherein the substrate contains, in addition to more than 95% by mass of Fe and unavoidable impurities, the following chemical elements in terms of mass percentage:

[0010] C: 0.055~0.1%, 0.25<Si≤0.45%, Mn: 0.30~0.55%, Cu: 0.218~0.40%, Ni: 0.08%~0.25%, Cr: 0.30~0.50%, 0.015≤Al≤0.055%,

[0011] The thickness of the Fe-Ni alloy layer is within 1 μm, preferably 0.2-1 μm, and more preferably 0.2-0.5 μm.

[0012] In the substrate of the nickel-plated steel strip according to the present invention, the design principles of the chemical elements are as follows:

[0013] C: In the substrate of the nickel-plated steel strip of the present invention, the addition of C can make C dissolve into the steel plate matrix, play a role of solid solution strengthening, and C can form fine carbide precipitation ions, play a role of precipitation strengthening. However, if the C content is too high, it will have an adverse effect on the machinability of the strip. Therefore, in the substrate of the nickel-plated steel strip of the present invention, the mass percentage of the C element is controlled to be 0.055-0.1%.

[0014] Si: In the substrate of the nickel-plated steel strip described in the present invention, the Si element can increase the strength of the steel plate in the form of solid solution strengthening, thereby appropriately improving the strength of the battery shell punched from the steel plate and improving the pressure resistance of the steel shell. In addition, when Si and Cu elements coexist, it is also beneficial to improve the corrosion resistance of the steel. However, it should be noted that when the Si element content is too high, the hot working performance and welding performance of the steel plate will deteriorate. Therefore, it is necessary to control the mass percentage of the Si element within a reasonable range to improve the corrosion resistance of the material while ensuring the processing performance of the material. Therefore, in the substrate of the low-cost and highly corrosion-resistant nickel-plated steel strip described in the present invention, the mass percentage of the Si element is controlled to be 0.25<Si≤0.45%.

[0015] Mn: In the substrate of the nickel-plated steel strip described in the present invention, the Mn element exists mainly in the form of solid solution in the steel, and can play a composite role with the C element to improve the strength of the steel plate. However, it should be noted that when the Mn element content is too high, it will cause the plastic strain ratio of the steel plate after annealing to decrease, damage the isotropy of the steel plate, and be unfavorable to the formability of the steel plate. Therefore, in the substrate of the low-cost and high-corrosion-resistant nickel-plated steel strip described in the present invention, the mass percentage of the Mn element is controlled to be 0.30-0.55%.

[0016] Cu: In the substrate of the nickel-plated steel strip described in the present invention, Cu is an important element for improving the corrosion resistance of steel and can act as an active cathode during the corrosion process of the steel plate substrate. Under certain conditions, Cu can promote the anodic passivation of the steel plate substrate, thereby reducing the corrosion rate of the steel. In addition, in the substrate with surface nickel plating, adding Cu element to the steel can effectively reduce the coupling current between the nickel and the steel substrate in the pinholes formed in the nickel plating layer, greatly improving the corrosion resistance of the nickel-plated steel. However, it should be noted that excessive Cu will deteriorate the hot working properties of the material. Therefore, in the substrate of the low-cost and highly corrosion-resistant nickel-plated steel strip described in the present invention, the mass percentage of the Cu element is controlled to be between 0.218 and 0.40%.

[0017] Ni: In the substrate of the nickel-plated steel strip described in the present invention, adding an appropriate amount of Ni element can not only improve the corrosion resistance of the material, but also improve the hot processing performance of the material. Since an appropriate amount of Cu element needs to be added to the steel of the present invention to improve the corrosion resistance of the steel, but the addition of Cu element is more likely to cause liquid precipitation on the surface of the steel during the hot rolling process, resulting in crack defects on the surface of the steel. The formation of crack defects on the surface of the hot-rolled strip is very easy to cause tissue inheritance during the subsequent cold rolling annealing process, and finally deteriorate the deep drawing performance of the steel. Therefore, adding an appropriate amount of Ni element to the steel can effectively reduce the liquid precipitation phenomenon of Cu element on the surface of the steel during hot rolling and improve the hot-rolled surface quality of the steel. In addition, adding an appropriate amount of Ni element to the steel can also improve the thermal strength of the steel and maintain the structural stability of the battery shell punched by the steel under the heated state. Therefore, in the substrate of the low-cost and high-corrosion-resistant nickel-plated steel strip described in the present invention, the mass percentage of the Ni element is controlled to be between 0.08% and 0.25%.

[0018] Cr: In the substrate of the nickel-plated steel strip described in the present invention, the Cr element can not only be dissolved in ferrite, but also can increase the self-corrosion potential of the steel, inhibit the occurrence of corrosion, and improve the corrosion resistance of the material. However, it should be noted that when the content of the Cr element in the steel is too high, the hot working performance of the steel plate will deteriorate. Therefore, in the substrate of the low-cost and highly corrosion-resistant nickel-plated steel strip described in the present invention, the mass percentage of the Cr element is controlled to be 0.30-0.50%.

[0019] Al: In the substrate of the nickel-plated steel strip of the present invention, Al is one of the effective deoxidizing elements in steel, which can reduce the number of N atoms dissolved in the substrate, thereby improving the toughness and dynamic strain aging of the strip, and can form AlN refined grains. However, too high an Al content will form large-sized Al 2 O 3 and AlN, will damage the mechanical properties and welding properties of the strip. Therefore, in the present invention, the mass percentage of the Al element is controlled to be 0.015-0.055%.

[0020] P: In the substrate of the nickel-plated steel strip described in the present invention, P is an inevitable inclusion element. Too high a content of P element will cause central segregation of the ingot and affect the hot working performance of the substrate. In addition, since the battery shell is a deep thinning and stretching part, the P element will weaken the grain boundary bonding force and aggravate the secondary processing brittleness of the cold-rolled strip. The secondary processing brittleness of the steel will seriously affect the thinning and stretching ability of the strip and deteriorate the forming performance of the steel. However, considering the manufacturing cost of the substrate, in the substrate of the low-cost and high-corrosion-resistant nickel-plated steel strip described in the present invention, the mass percentage of the impurity element P is controlled to be 0.06 <P≤0.10%。

[0021] S: In the substrate of the nickel-plated steel strip described in the present invention, an appropriate amount of S element can be added to inhibit the electrochemical reaction of the anode reaction and the cathode reaction, which is beneficial to improve the corrosion resistance of the steel plate. However, when the S element content in the steel is too high, it is easy to cause central segregation of the ingot, resulting in hot brittleness, which is not conducive to the forming performance of the steel. Based on this, in the substrate of the low-cost and high-corrosion-resistant nickel-plated steel strip described in the present invention, the mass percentage of the S element is controlled to be 0<S≤0.01%, preferably 0.002~0.01%.

[0022] Furthermore, in order to reduce the amount of Ni used, the thickness of the nickel-plated layer of the nickel-plated steel strip is controlled within a range of 1 μm or less, preferably 0.2 to 1 μm, and more preferably 0.2 to 0.5 μm.

[0023] The Fe content on the surface of the Fe-Ni alloy coating of the nickel-plated steel strip is 2 to 70% by weight, preferably 5 to 60%, and more preferably 14 to 57% by weight.

[0024] In the manufacturing method described in the present invention, the formation of the Fe-Ni alloy layer is marked by the weight percentage of the Fe element on the surface of the nickel-plated steel strip of the present invention (iron exposure rate). When the surface iron exposure rate of the steel strip after continuous annealing heat treatment is too high, it means that the Fe-Ni diffusion is too sufficient. Too high an iron exposure rate easily leads to more Fe being exposed on the surface of the steel strip, deteriorating the corrosion resistance of the steel; however, when the surface iron exposure rate of the steel after continuous annealing heat treatment is too low, it means that the Fe-Ni diffusion is not sufficient, and the nickel plating layer is prone to pinhole defects, affecting the corrosion resistance of the steel strip. Therefore, the iron exposure rate of the Fe-Ni alloy coating is preferably 2-70%, preferably 5-60%, and more preferably 14-57%.

[0025] Preferably, the Fe—Ni alloy layer of the nickel-plated steel strip is formed by diffusion annealing of a dull Ni plating layer or a semi-bright Ni plating layer.

[0026] Dull Ni coating or semi-bright Ni coating is generally obtained by a plating solution without S element additives to avoid cracking of the Fe-Ni alloy layer formed after annealing. If a plating solution containing S element additives is used, the Ni coating is easily brittle after alloying heat treatment of diffusion annealing, resulting in severe cracking of the Fe-Ni alloy layer during the punching process of manufacturing the battery shell, which deteriorates the corrosion resistance of the surface treated steel sheet.

[0027] Preferably, the microstructure of the substrate of the nickel-plated steel strip is ferrite and cementite.

[0028] Preferably, in the substrate of the nickel-plated steel strip, the proportion of ferrite in volume percentage is 92% or more.

[0029] Preferably, the grain size of the substrate of the nickel-plated steel strip is level 9-11.

[0030] The low-cost and high-corrosion-resistant nickel-plated steel strip according to the present invention has a yield strength of ≥340 MPa, a tensile strength of ≥425 MPa, and an elongation after fracture of ≥30%, and has a corrosion resistance of 8 or above as determined according to GB / T 6461-2002.

[0031] The present invention also proposes a method for manufacturing the above-mentioned nickel-plated steel strip, comprising the following steps:

[0032] 1) Smelting and casting according to the chemical composition designed in the present invention;

[0033] 2) Hot rolling, coiling and pickling;

[0034] 3) cold rolling to obtain a steel substrate;

[0035] 4) The steel substrate is subjected to quenching and annealing at a temperature of 750 to 820° C. and a soaking time of 50 to 190 seconds;

[0036] 5) plating nickel on at least one surface of the steel substrate;

[0037] 6) Diffusion annealing;

[0038] 7) Optional flattening to obtain a nickel-plated steel strip.

[0039] The following is a detailed description of this method:

[0040] <Hot rolling and coiling>

[0041] Since the carbonitride second phase particles will dissolve during the heating process of the continuous casting slab, these particles will re-precipitate during the hot rolling coiling process, but the particle size is finer and the distribution is more dispersed than that in the continuous casting slab, so it is beneficial to improve the corrosion resistance of the steel plate. When the hot rolling heating temperature is too low, the degree of dissolution of the second phase particles is reduced, which will affect the precipitation in the subsequent processing process and is not conducive to the corrosion resistance of the steel; when the heating temperature is too high, it will cause grain coarsening and produce thicker oxide scales, which are difficult to remove in subsequent processes. Therefore, in step 2) of the manufacturing method described in the present invention, the hot rolling heating temperature is controlled to be 1180~1290℃.

[0042] Accordingly, when the final rolling temperature is too low, the steel cannot be rolled in the austenite single phase region, resulting in mixed crystals in the steel, affecting the stability of the structure and performance, while when the final rolling temperature is too high, the grains are easily coarsened. Therefore, in step 2), the hot rolling final rolling temperature is controlled to be 830-920°C, preferably 850-900°C.

[0043] Furthermore, in step 2), the coiling temperature is controlled to be 620-720° C., preferably 650-690° C. Finally, the steel plate is pickled and dephosphorized before cold rolling.

[0044] <Cold Rolling>

[0045] After hot rolling and coiling, the steel plate is cold rolled, and the cold rolling reduction rate is preferably controlled to be 60% to 85%. This is because the plastic strain ratio r value of the cold-rolled steel plate generally increases with the increase of the cold rolling reduction rate. Increasing the cold rolling reduction rate increases the deformation energy in the steel and the recrystallization driving force, thereby reducing the recrystallization temperature and facilitating the formation of {111} texture after annealing. However, it should be noted that due to the high alloy content in the substrate, when the cold rolling reduction rate exceeds 80%, the mill load increases significantly, which not only reduces the production efficiency of the cold rolling unit, but also increases the manufacturing cost. More preferably, the cold rolling reduction rate is controlled to be 70 to 80%.

[0046] <Quenching and annealing>

[0047] In the above technical scheme, in order to ensure the overall corrosion resistance of the steel strip under the premise of reducing the thickness of the nickel plating layer on the surface of the steel strip, the corrosion resistance of the steel substrate is mainly improved by adding an appropriate amount of alloy elements such as Cu / Ni / Cr in the substrate. However, in order to ensure the processing and forming performance of the steel strip, the increase in the content of alloy elements in the substrate will inevitably increase the annealing and recrystallization temperature of the steel strip. Therefore, the present invention controls the substrate tempering annealing temperature to 750℃~820℃, and the soaking time is 50~190s. Preferably, the tempering annealing temperature of the substrate is controlled to be 770~800℃, and the soaking time is 60~180s.

[0048] In addition, in the prior art, the nickel-plated steel strip substrate tempering and the diffusion alloying heat treatment of the nickel-plated layer are usually completed by a single annealing (i.e., only subsequent diffusion annealing is performed). However, in the present technical solution, under the premise of reducing the thickness of the nickel-plated layer on the surface of the steel strip, increasing the annealing temperature of the steel strip has the risk of increasing the surface iron exposure rate of the nickel-plated layer, which will reduce the corrosion resistance of the nickel-plated steel strip. Therefore, in the present technical solution, two annealings are performed successively, i.e., firstly, the substrate tempering annealing is performed, and then the subsequent alloying continuous annealing of the nickel-plated layer is performed. While ensuring the forming performance of the steel substrate, the surface iron exposure rate of the nickel-plated diffusion layer can be controlled, thereby improving the corrosion resistance of the steel strip.

[0049] <Nickel plating>

[0050] In the technical solution, after the above-mentioned substrate quenching and annealing, the obtained steel substrate needs to be subjected to continuous surface nickel plating treatment, so as to form a nickel plating layer on at least one surface of the steel substrate. Conventional nickel plating methods can be used, preferably continuous electroplating method, wherein the process steps of continuous nickel plating treatment include but are not limited to: degreasing, electrolytic degreasing, water washing, acid activation, cleaning, continuous nickel plating, cleaning and drying.

[0051] Among them, degreasing, electrolytic degreasing and acid activation are all pre-treatment steps for continuous nickel electroplating, which can remove oil and activate the steel substrate to keep the steel substrate in an active state before starting nickel electroplating.

[0052] After the acid activation is completed, the steel substrate can be cleaned and then added to a plating bath for nickel plating. The plating bath can be a plating bath commonly used in nickel plating processes, such as a Watt bath, an aminosulfonic acid bath, a borofluoride bath, and a chloride bath.

[0053] For example, when a Watt bath is used as a plating bath, the Watt bath solution formula can be controlled as follows: nickel sulfate: 250-380 g / L, nickel chloride: 30-60 g / L, boric acid 20-60 g / L, pH 3.0-5.0, bath temperature 40-65°C; the current density in the electroplating process can be controlled to 2-20 A / dm 2 (Preferably 5 to 10 A / dm 2 ), and then a nickel plating layer can be formed on the surface of the steel substrate.

[0054] In addition, it should be noted that, as mentioned above, the bright nickel plating layer containing S is easy to form hot brittleness after alloying heat treatment, which will cause serious cracking of the plating layer of the battery shell made of steel strip after punching and deteriorate the corrosion resistance, so it is not selected. Therefore, the present invention uses a semi-bright nickel plating layer or a non-bright nickel plating layer that does not contain S. In the electroplating plating solution for forming the semi-bright nickel plating layer, it is sufficient to add a semi-bright additive that does not contain S to the above plating solution.

[0055] Preferably, the thickness of the nickel plating layer is 1 μm or less.

[0056] <Diffusion Annealing>

[0057] According to the manufacturing method of the present invention, in step 6), the steel plate after nickel plating is subjected to continuous annealing heat treatment to promote the recrystallization process and the Fe-Ni element mutual diffusion process (also known as nickel plating layer alloying diffusion annealing) of the steel plate substrate and the nickel plating layer on its surface during the heat treatment process, which can effectively reduce the pinhole defects in the nickel plating layer and enhance the bonding strength between the nickel plating layer and the substrate, thereby improving the corrosion resistance of the material.

[0058] In the present technical solution, the alloying diffusion annealing treatment of the nickel plating layer can be carried out by continuous annealing or hood annealing. Moreover, since the substrate itself has been tempered annealed, the temperature of continuous annealing can be appropriately lowered compared with the prior art. Specifically, for the continuous furnace diffusion annealing method, the annealing soaking temperature is controlled to be 600-710°C, and the soaking time is 20-90s. For the hood furnace diffusion annealing method, the annealing soaking temperature is controlled to be 400-500°C, and the insulation time is 1-4h. Since the substrate has completed sufficient recrystallization annealing before the nickel plating layer diffusion annealing, the nickel plating layer diffusion annealing heat treatment will not have a significant effect on the mechanical properties of the steel strip.

[0059] <Leveling>

[0060] After continuous annealing to form an alloyed nickel-plated layer, a flattening process can be used to optimize the surface roughness, surface morphology, plate shape and mechanical properties of the product. Considering the flattening effect, the flattening rate is controlled to be 0.5-2.0%, preferably 1-1.5%.

[0061] In the above technical solution, compared with the prior art, the low-cost, high-corrosion-resistant nickel-plated steel strip and the manufacturing method thereof according to the present invention include but are not limited to the advantages and beneficial effects described below:

[0062] The low-cost and high-corrosion-resistant nickel-plated steel strip of the present invention adopts a reasonable chemical element composition design for the steel substrate, adds appropriate amounts of alloy elements such as Cu / Ni / Cr, and optimizes the annealing process of the nickel-plated steel strip. While ensuring the excellent forming performance of the steel, the overall corrosion resistance of the nickel-plated steel strip can be ensured under the condition of a thinner Fe-Ni alloy layer, further reducing the cost of raw materials and having great promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 The schematic diagram of the hierarchical structure of the low-cost and highly corrosion-resistant nickel-plated steel strip according to the present invention is shown as an example.

[0064] Figure 2 This is the surface morphology of the nickel-plated steel strip in Example 2.

[0065] Figure 3 This is a microstructure photograph of the nickel-plated steel strip of Example 1.

[0066] Figure 4 This is a microstructure photograph of the nickel-plated steel strip of Comparative Example 2. DETAILED DESCRIPTION

[0067] The present invention is further described below in conjunction with the following examples and comparative examples to make the content of the present invention clearer and easier to understand. However, it should be noted that the present invention is not limited to the following disclosed examples.

[0068] Examples 1-6 and Comparative Examples 1-5

[0069] The nickel-plated steel strips of Examples 1-6 were prepared by the following steps:

[0070] (1) Smelting and casting are performed according to the chemical element composition design described in Table 1 below to obtain a substrate, i.e., a steel substrate;

[0071] (2) Hot rolling, coiling and pickling: The substrate is hot rolled and coiled, the hot rolling heating temperature is controlled to be 1180-1290° C., the hot rolling final rolling temperature is controlled to be 830-920° C., and the coiling temperature is controlled to be 620-720° C.; then, the substrate obtained after hot rolling and coiling is pickled and dephosphorized by conventional methods in the art;

[0072] (4) Cold rolling: The pickled substrate is cold rolled, and the cold rolling reduction rate is controlled to be 60% to 85%;

[0073] (5) Substrate annealing: The cold-rolled steel substrate is annealed at a temperature of 750°C to 820°C and a soaking time of 50 to 190 seconds.

[0074] (6) plating nickel on at least one surface of the substrate: sequentially degreasing, electrolytic degreasing, water washing, acid activation, cleaning, continuous nickel electroplating, cleaning and drying the cold-rolled substrate, wherein the thickness of the nickel plating layer is controlled to be about 0.5 μm;

[0075] (7) Diffusion heat treatment of nickel plating: alloying diffusion annealing treatment of nickel plating is carried out by continuous annealing or bell annealing. For continuous furnace diffusion annealing, the annealing temperature is controlled to be 600-710°C, and the soaking time is 20-90s. For bell furnace diffusion annealing, the annealing temperature is controlled to be 400-520°C, and the temperature is kept for 1-4h.

[0076] (8) Flattening: The nickel-plated steel strip is flattened, and the flattening rate is controlled to be 0.5-2.0%.

[0077] The comparative steel strips of Comparative Examples 1 to 5 were prepared by similar steps as described above, but their element composition ranges and / or process conditions did not meet the requirements of the present invention.

[0078] Table 1 lists the mass percentage designs of various chemical elements of the high corrosion-resistant and heat-resistant nickel-plated steel strips of Examples 1-6 and the comparative steel strips of Comparative Examples 1-5.

[0079] Table 1 (wt.%, the balance is Fe and other inevitable impurities)

[0080] serial number C Si Mn P S Cu Ni Cr Al Example 1 0.056 0.44 0.440 0.084 0.002 0.343 0.157 0.346 0.055 Example 2 0.062 0.32 0.530 0.062 0.004 0.397 0.082 0.464 0.036 Example 3 0.073 0.35 0.480 0.068 0.005 0.368 0.196 0.303 0.051 Example 4 0.097 0.26 0.390 0.092 0.006 0.262 0.213 0.432 0.046 Example 5 0.080 0.41 0.500 0.098 0.009 0.302 0.249 0.387 0.015 Example 6 0.091 0.38 0.320 0.072 0.007 0.218 0.112 0.498 0.023 Comparative Example 1 0.048 0.44 0.50 0.084 0.002 0.320 0.110 0.350 0.055 Comparative Example 2 0.067 0.27 0.32 0.010 0.007 0.24 0.18 0.46 0.085 Comparative Example 3 <![CDATA[ 0.003 ]]> 0.03 0.235 0.014 0.004 <![CDATA[ 0.17 ]]> 0.083 <![CDATA[ 0.028 ]]> 0.043 Comparative Example 4 0.057 0.04 <![CDATA[ 0.140 ]]> 0.009 0.004 0.23 <![CDATA[ 0.009 ]]> <![CDATA[ 0.018 ]]> 0.038 Comparative Example 5 0.067 0.35 0.35 0.092 0.007 <![CDATA[ 0 ]]> <![CDATA[ 0 ]]> <![CDATA[ 0 ]]> 0.035

[0081]

[0082] The obtained nickel-plated steel strips of Examples 1-6 and the comparative steel strips of Comparative Examples 1-5 were sampled respectively, and the surface of each example and comparative example sample was observed and analyzed to detect the structure, mechanical properties and corrosion resistance of each steel strip.

[0083] Detection Methods

[0084] Nickel plating thickness detection: The nickel plating thickness on the strip surface is detected by energy dispersive X-ray fluorescence spectrometer THICK 800A. During the detection process, 5 points are randomly selected on the strip surface for detection. The thickness of the nickel plating on the strip surface is the average of the 5 detection values:

[0085] Determination of exposed iron rate of Fe-Ni alloy coating: In the present invention, the surface of each embodiment and comparative example sample is scanned by a scanning electron microscope energy spectrum analyzer (OXFORD Instruments X-Max) to further observe and detect the Fe-Ni alloy layer, and the scanning area needs to be ≥500*200μm to obtain the mass percentage content (exposed iron rate) of Fe element on the surface of nickel-plated steel strip.

[0086] Grain size rating: Take the finished product samples of the embodiments and comparative examples, grind and polish the sample cross sections, and then use 4% nitric acid alcohol solution to erode to expose the substrate structure morphology of the nickel-plated steel strip. Then, according to GB / T 6394-2017 "Method for Determination of Average Grain Size of Metals", the intercept method is used to grade the grain size of the finished product substrate structure.

[0087] Microstructure inspection: The microstructure and distribution of the substrate steel material of the nickel-plated steel strip of the present invention are inspected according to GB / T 13298-1991 "Methods for the inspection of metal microstructures".

[0088] Corrosion resistance evaluation: According to GB / T 6461-2002 "Rating of samples and test pieces of metal and other inorganic coatings on metal substrates after corrosion tests" and GB / T10125-2012 "Artificial atmosphere corrosion test salt spray test", neutral salt spray corrosion tests were carried out on various embodiments and comparative steels produced with different substrates and the same nickel plating layer thickness. The salt spray corrosion conditions were controlled as follows: 35°C, 5% NaCl solution, and the steel was allowed to stand for 24 hours after the edge wrapping. After the salt spray test, the steel was allowed to stand for 1 hour before cleaning and drying. Subsequently, the surface corrosion state of the steel in each embodiment and comparative example was rated, which was divided into 1 to 9 grades, with 9 being the best and 1 being the worst.

[0089] Mechanical properties testing: At room temperature of 25°C, according to GB / T 228.1-2010 "Tensile test of metallic materials Part 1: Room temperature test method", the tensile strength, yield strength and elongation after fracture of the steel materials of each embodiment and comparative example were tested.

[0090] Table 3 lists the grain size grades and various performance test results of the high corrosion-resistant and heat-resistant nickel-plated steel strips of Examples 1-6 and the comparative steel strips of Comparative Examples 1-5.

[0091] Table 3 Grain size grade and performance test results of nickel-plated steel strip

[0092]

[0093] It can be seen from Table 3 above that, compared with Comparative Examples 1-5, the nickel-plated steel strips of Examples 1-6 of the present invention have significantly improved comprehensive properties, with a yield strength between 343 and 385 MPa, a tensile strength between 427 and 501 MPa, an elongation after fracture between 31.2 and 35.3%, a grain size of 9 to 11, and a corrosion resistance of 8 to 9.

[0094] In addition, the microstructures of the comparative steel strips of Comparative Examples 2 and 5 consist of ferrite+cementite+bainite, which is due to the structural phase transformation under the condition of higher tempering annealing temperature, which results in their yield strength being lower than that of Examples 1-6.

[0095] In terms of steel surface corrosion resistance rating, Examples 1-6 have better corrosion resistance than Comparative Examples 1-5.

[0096] It can be seen from the accompanying drawings in the specification that Figure 1 The cross-sectional structure diagram of a low-cost, highly corrosion-resistant nickel-plated steel strip product is shown, which includes a substrate (10), on which is an Fe-Ni alloy layer (20) formed by surface nickel plating and then heat treatment. Figure 2 This is a SEM image of the surface of the nickel-plated steel strip of Example 2, and the detected contents (mass percentage) of the elements in the frame of the image are shown in the following table.

[0097]

[0098] like Figure 3 The microstructure photo of the nickel-plated steel strip of Example 1 shows that the low-cost, high-corrosion-resistant nickel-plated steel strip substrate structure is mainly ferrite, which contains a small amount of cementite, and the grain size is 10.5. Figure 4 In the nickel-plated steel strip of Comparative Example 2, it can be observed that bainite is formed, and the grain size is only level 8.

[0099] From the above, it can be seen that the low-cost, high-corrosion-resistant nickel-plated steel strip described in the present invention adopts a reasonable chemical element composition design, such as adding appropriate amounts of alloy elements such as Cu / Ni / Cr, and optimizing the design of hot rolling coiling, cold rolling, substrate tempering annealing, continuous electroplating nickel, nickel-plated layer diffusion heat treatment and flattening processes, while ensuring the excellent stamping forming performance of the steel, the corrosion resistance and heat resistance of the steel after punching can be improved. Compared with battery shell steel with conventional composition systems, the low-cost, high-corrosion-resistant nickel-plated steel strip described in the present invention is more suitable for the harsh service environment requirements of new energy power batteries with high corrosion resistance.

[0100] The low-cost high-corrosion-resistant nickel-plated steel strip has excellent performance, with a yield strength of ≥340MPa, a tensile strength of ≥425MPa, an elongation after fracture of ≥30%, and a corrosion resistance greater than grade 8 as determined according to GB / T 6461-2002.

[0101] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0102] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A nickel-plated steel strip, characterized in that: The nickel-plated steel strip comprises a substrate and a Fe-Ni alloy layer located on at least one surface of the substrate. The substrate contains, in addition to more than 95% by mass of Fe and inevitable impurities, the following chemical elements in terms of mass percentage: C: 0.055-0.1%, 0.25<Si≤0.45%, Mn: 0.30-0.55%, Cu: 0.218-0.40%, Ni: 0.08%-0.25%, Cr: 0.30-0.50%, 0.015≤Al≤0.055%; and The thickness of the Fe-Ni alloy layer is within 1 μm, preferably 0.2-1 μm, and more preferably 0.2-0.5 μm.

2. The nickel-plated steel strip according to claim 1, characterized in that The substrate has the following chemical elements in mass percentage: C: 0.055~0.1%, 0.25<Si≤0.45%, Mn: 0.30~0.55%, Cu: 0.218~0.40%, Ni: 0.08%~0.25%, Cr: 0.30~0.50%, 0.015≤Al≤0.055%, and the balance is Fe and unavoidable impurities.

3. The nickel-plated steel strip according to claim 1 or 2, characterized in that: The Fe content on the surface of the Fe-Ni alloy layer is 2-70% by weight, preferably 5-60%, and more preferably 14-57%.

4. The nickel-plated steel strip according to claim 1 or 2, characterized in that: The Fe-Ni alloy layer is formed by diffusion annealing of a dull Ni plating layer or a semi-bright Ni plating layer.

5. The nickel-plated steel strip according to claim 1 or 2, characterized in that: The microstructure of the substrate is ferrite and cementite.

6. The nickel-plated steel strip according to claim 1 or 2, characterized in that: In the substrate, the proportion of ferrite by volume percentage is 92% or more.

7. The nickel-plated steel strip according to claim 1 or 2, characterized in that: The grain size of the substrate is 9-11.

8. The nickel-plated steel strip according to claim 1 or 2, characterized in that: The yield strength of the nickel-plated steel strip is ≥340MPa, the tensile strength is ≥425MPa, the elongation after fracture is ≥30%, and the corrosion resistance determined according to GB / T 6461-2002 is above level 8.

9. The method for producing a nickel-plated steel strip according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: 1) Smelting and casting according to the chemical composition of claim 1 or 2; 2) Hot rolling, coiling and pickling; 3) cold rolling to obtain a steel substrate; 4) The steel substrate is subjected to quenching and annealing at a temperature of 750 to 820° C. and a soaking time of 50 to 200 seconds; 5) plating nickel on at least one surface of the steel substrate; 6) Diffusion annealing to form a Fe-Ni alloy layer on the steel substrate; 7) Flattening to obtain nickel-plated steel strip.

10. The method according to claim 9, characterized in that The method satisfies one or more of the following conditions: In step 2), the hot rolling heating temperature is controlled to be 1180-1290°C, the hot rolling finishing temperature is controlled to be 830-920°C, and the coiling temperature is controlled to be 620-720°C; In step 3), the cold rolling reduction rate is controlled to be 60-85%; In step 5), the thickness of the nickel plating layer is 0.2-1 μm; In step 6), the diffusion annealing is continuous annealing or bell annealing. When continuous annealing is used, the continuous annealing temperature is controlled to be 600-710° C., and the holding time is 20-90 seconds; when bell annealing is used, the bell furnace annealing temperature is controlled to be 400-520° C., and the holding time is 1-4 hours; In step 7), the smoothing rate is controlled to be 0.5-2.0%.

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