Steel strip and method for manufacturing the same

Abstract

A steel strip having excellent workability and corrosion resistance without the need for oil coating, and a method for manufacturing the same. The steel strip includes a substrate, and a phosphate layer and a stearic acid lubricant layer provided on the substrate. The upper surface of the steel strip includes a phosphate layer and a stearic acid lubricant layer, in that order from the inside to the outside, and has a surface roughness R in the range of 0.6 to 1.8 μm. a and R in the range of 6 to 16 μm z The lower surface of the strip has a stearic acid lubricant layer and a surface roughness R of 0.3 μm or less, which provides good surface lubrication during the rolling process. a and R of 2μm or less z It has good lubrication and high surface cleanliness. By using the steel strip designed with differentiated functionality of two surfaces according to the present invention, it can be directly stamped to process shell parts with high precision and large deformation, eliminating the traditional processes of coating, oiling, and post-forming cleaning required to manufacture shell parts with high precision and large deformation from traditional steel plates, and significantly improving the efficiency of part manufacturing. In addition, the steel strip has good rust and corrosion resistance, and its surface does not require oil coating treatment during storage and transportation.

Description

[Technical Field]

[0001] The present invention relates to a steel strip having excellent workability and corrosion resistance that does not require oil coating, and to a method for manufacturing the same, in the field of metal material processing. [Background technology]

[0002] In the field of metal processing, continuous and efficient processing technologies characterized by high precision, high complexity, and environmental protection requirements are widely used in the processing of automobile and machine parts. According to extensive theoretical analysis of scientific experimental studies and patent application searches, during the stamping process of shell parts with high precision and large deformation, the surface of the steel plate in contact with the female die (master die) withstands the main deformation friction force, while the surface of the steel plate in contact with the male die (punch) withstands a relatively small deformation friction force, primarily ensuring the dimensional accuracy of the inner surface. Therefore, the surface of the steel plate in contact with the female die requires sufficient lubrication during the deformation process. Rather, the surface of the steel plate in contact with the male die does not require high lubrication performance, but requires extremely high surface cleanliness. To obtain shell parts with high dimensional accuracy and high surface quality, the two surfaces must have different lubrication functions.

[0003] Material suppliers, such as JFE, Nippon Steel, and POSCO, primarily focus on developing products with superior mechanical properties. In the field of stamping material development research, as described in Patent Documents 1, 2, and 3, the main focus is on coating both sides of steel strips (e.g., coating with a lubricating layer).

[0004] Regarding the coating treatment of both sides of the steel strip surface, the main process types include the following: (1) forming a micron or submicron organic coating on the surface of the steel sheet by roll coating and baking hardening in a continuous manufacturing process, as described in Patent Documents 4, 5, and 6; and (2) forming a phosphate treatment layer / passivation layer on the surface of the steel sheet by a spray method in a continuous manufacturing process, as described in Patent Document 7.

[0005] Patent Document 5 discloses a "self-lubricating passivation solution and a hot-dip galvanized self-lubricating steel sheet coated thereby," primarily using the addition of nano MoS2 and modified nano polytetrafluoroethylene particles in the treatment agent to achieve solid lubrication of the coating. (800-1200 mg / m²) 2 A lubricating coating with a certain degree of adhesion is formed on the surface of the steel sheet by roll coating and baking hardening. The product of the invention is mainly suitable for stamping requirements of home appliances and micromotor shell materials, but does not meet the stamping requirements of high-precision components with large deformations in the automotive and machinery fields, and is not suitable for surface treatment of ordinary cold-rolled sheets.

[0006] Patent Document 7 discloses "a phosphate-pretreated electro-zinc plated automotive outer panel suitable for coating, and a method for preparing the same." In the invention, an ultra-low carbon steel sheet containing Nb is designed. After a continuous plating layer is formed on the surface of the steel sheet by gravity electroplating, 1.0~2.0 g / m 2 A phosphate pretreatment layer is formed by a double-sided spray method at a phosphate treatment temperature of 50-60°C and subjected to an oil coating treatment to obtain a product that meets the stamping lubrication and corrosion resistance requirements of automotive body materials. The resulting product can be well applied in automotive body production lines, but it cannot meet the stamping requirements for high-precision components with large deformations in the automotive and machinery sectors, nor can it achieve the manufacturing requirements for differential double-sided lubrication functions.

[0007] Patent Document 8 discloses a "phosphate treatment-saponification production process" involving a drum-type continuous phosphate treatment / saponification process for processing small parts. The process mainly comprises the following steps: entering the drum → degreasing → first rinse → phosphate treatment → second rinse → surface preparation → saponification → exiting the drum. Here, the phosphate treatment temperature is 60-85°C with a dipping time of 3-10 minutes, and the saponification temperature is 55-80°C with a dipping time of 0.5-5 minutes. This process implements surface lubrication functionality in the finished parts through high-temperature phosphate treatment and saponification, but this is not suitable for the continuous production of steel strips.

[0008] Patent Document 9 discloses a "phosphate treatment-saponification process for 27SiMn steel," providing a surface lubrication treatment method suitable for high-precision cold-drawn steel pipes, including: pickling → high-temperature phosphate treatment (70°C) → saponification treatment for 27SiMn steel parts. Similarly, this application employs a non-differentiated treatment on both sides and is not suitable for continuous production of steel strips.

[0009] From the above, it is clear that shell parts with high precision and large deformation require two surfaces of the material to have different lubrication functions. Conventional processes achieve differential lubrication of steel sheets by applying a film (plastic lubricating film) or lubricant to the surface in contact with the male die during stamping. However, this approach does not meet the requirements of high efficiency and environmental protection. Current technology mainly focuses on lubrication equipment for the stamping process, methods for applying lubricants, and precision stamping lubricant compositions. With the increasing demand for high-precision, large-deformation shell parts, simplifying processing and production processes to produce more cost-effective and competitive products will become an industrial requirement. Therefore, it is necessary to provide steel strips with excellent performance (e.g., machinability and corrosion resistance), high efficiency, and environmental compatibility (e.g., no oil coating), as well as methods for producing them. [Prior art documents] [Patent Documents]

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Patent Document 9

Summary of the Invention

[0011] An object of the present invention is to provide a steel strip that does not use an oil coating and has excellent workability and corrosion resistance, and a method for manufacturing the same. The two surfaces of the steel strip have functions differentiated in the thickness direction. The upper surface (i.e., the surface having a phosphate treatment layer and a stearic acid lubricant layer) has a surface roughness R of 0.6 to 1.8 μm a and a surface roughness R of 6 to 16 μm z to provide good surface lubricity during the rolling process. The lower surface (i.e., the surface having only a stearic acid lubricant layer) has a surface roughness R of 0.3 μm or less a and a surface roughness R of 2 μm or less zIt has good lubricity and high surface cleanliness. Therefore, the steel strip provided by the present invention meets the requirements of a continuous high-efficiency stamping process for shell parts with large deformations of high precision, and can eliminate the need for coating, oiling, and post-forming cleaning during the stamping process of manufacturing shell parts with high precision and large deformations using conventional steel plates. The obtained parts can be directly packed and delivered, and as a result, the efficiency of part manufacturing can be greatly improved. Moreover, the steel strip has good rust resistance and corrosion resistance, and the obtained parts do not require a rust prevention oil coating during storage and transportation.

[0012] In one aspect, the present invention provides a steel strip, which includes a substrate, a phosphate treatment layer and a stearic acid lubricant layer disposed on the substrate. In the thickness direction of the substrate, the phosphate treatment layer and the stearic acid lubricant layer are sequentially arranged from the inside to the outside on the upper surface of the substrate, the stearic acid lubricant layer is disposed on the lower surface of the substrate, and the upper surface of the steel strip has a surface roughness R of 0.6 to 1.8 μm a and a surface roughness R of 6 to 16 μm z The lower surface of the steel strip has a surface roughness R of 0.3 μm or less a and a surface roughness R of 2 μm or less <000001 / >has.

[0013] Preferably, in addition to Fe and inevitable impurities, the substrate contains the following chemical elements in wt%: C: 0.1 to 0.7%, 0.2% ≤ Si ≤ 2%, 0.2% ≤ Mn ≤ 2%, Cr: 0.2 to 1.4%, 0.01% ≤ Al ≤ 0.06%, and Mo: 0.05 to 0.2%. Here, the inevitable impurities include P ≤ 0.04% and S ≤ 0.05%.

[0014] To more clearly describe the present invention, it should be noted that the terms “top” and “bottom” (or “upper side” and “lower side”) are used to distinguish two surfaces (or sides) of a substrate or steel strip in the thickness direction. Specifically, in this specification, a surface or side having a phosphate treatment layer and a stearic acid lubricant layer is referred to as the “top” or “upper side,” and a surface or side having only the stearic acid lubricant layer is referred to as the “bottom” or “lower side.” However, since those skilled in the art will understand that the terms “top” and “bottom” are relative descriptions that change depending on the orientation of the product, such descriptions are not intended to unduly limit the present invention.

[0015] In this specification, when describing the relative positions of the phosphate treatment layer and the stearic acid lubricant layer on the upper surface of the substrate, "inside to outside" refers to the direction from the side closer to the substrate to the side further away from the substrate. For example, in Figure 1, "inside to outside" refers to the direction from the bottom to the top.

[0016] Preferably, the substrate contains the following chemical elements in wt%: C: 0.1~0.7%, 0.2%≦Si≦2%, 0.2%≦Mn≦2%, Cr: 0.2~1.4%, 0.01%≦Al≦0.06%, Mo: 0.05~0.2%, with the remainder being Fe and unavoidable impurities, where the unavoidable impurities include P≦0.04% and S≦0.05%.

[0017] In the steel strip substrate according to the present invention, the design principle for the content of each element is as follows:

[0018] If the elemental carbon content is less than 0.1%, the strength will be insufficient. If the elemental carbon content exceeds 0.7%, the chemical reactivity of the material surface will be reduced, which will affect the phosphate treatment and passivation film formation on the surface. The molding stability of the material may also be insufficient. Therefore, the elemental carbon content should be controlled to be within the range of 0.1% to 0.7%.

[0019] Si: Elemental silicon (Si) can effectively improve the formability (moldability) of materials under high-strength conditions. However, if the Si content is too high (>2%), it will be selectively oxidized and precipitated during heat treatment, and the precipitate will concentrate on the surface, thereby affecting the performance of subsequent phosphate treatment and passivation film formation reactions. Therefore, the elemental Si content should be controlled to be in the range of 0.2% to 2%.

[0020] Mn: Elemental manganese (Mn) can play a role in guaranteeing the strength and hardness of the material. However, if the Mn content is too high (>2%), it will also be selectively oxidized and precipitated during the heat treatment process, and the precipitate will concentrate on the surface, thereby affecting the performance of subsequent phosphate treatment and passivation film formation reactions. Therefore, the elemental Mn content should be controlled to be in the range of 0.2% to 2%.

[0021] Cr, Al, and Mo: These elements primarily function to refine the crystalline structure. If their content is too low, the above effect cannot be fully realized. Excessive addition is not economical for product manufacturing. Therefore, the content of elements Cr, Al, and Mo is controlled to be within the ranges of 0.2% to 1.4%, 0.01% to 0.06%, and 0.05% to 0.2%, respectively.

[0022] Inevitable impurities include the elements P and S. If the content of P and S is too high, it will affect the toughness of the material and prevent it from meeting the moldability requirements under large deformations. Therefore, the content of impurity elements P and S is controlled so as not to exceed 0.04% and 0.05%, respectively.

[0023] Preferably, the substrate has a thickness of 1.0 to 6.0 mm. In this specification, “substrate thickness” does not include the thickness of the one phosphate treatment layer and the two stearic acid lubricant layers on the upper and lower surfaces of the substrate. If the substrate thickness is less than 1 mm, the shell walls of the parts are likely to be too thin to meet the requirements for large deformation and load-bearing performance after deep drawing. If the substrate thickness is greater than 6 mm, the production line for manufacturing cold-rolled products cannot achieve effective manufacturing. With a substrate thickness of 1.0 to 6.0 mm, the steel strip according to the present invention is suitable for processing shell parts with high precision and large deformation.

[0024] Preferably, the phosphate-treated layer has a grain size (i.e., maximum grain length) of 8 to 20 μm. In the phosphate-treated layer, the crystal grains become elongated, and their grain size is measured according to standard GB / T38933-2020.

[0025] Preferably, the phosphate-treated layer (i.e., phosphate-treated film) is 1-3 g / m². 2 It has a weight and is measured according to standard GB / T38933-2020.

[0026] Grain size of the phosphate-treated layer, 8-20 μm, and / or 1-3 g / m² 2 The weight of the phosphate-treated layer, on the one hand, provides better three-dimensional space for subsequent stearic acid film formation, thereby effectively increasing the retention capacity of stearic acid lubricant on the product surface. On the other hand, it ensures better uniform distribution of lubricant during the deformation process and can provide further lubrication by utilizing its good frictional lubrication properties. The phosphate-treated layer according to the present invention is a non-high-density phosphate-treated film having coarse crystals, which effectively reduces the amount of wear particles during the stamping process, thereby extending the life of the die.

[0027] The upper surface of the steel strip according to the present invention comprises a phosphate treatment layer and a stearic acid lubricant layer, in that order, from the inside out. That is, the upper surface is designed to have a structure consisting of a phosphate treatment layer and a stearic acid coating. Both the phosphate treatment film and the stearic acid saponified film have lubricating functions, and their combination can effectively improve lubrication stability during the stretch deformation process. The upper surface has a surface roughness R of 0.6 to 1.8 μm. a and surface roughness R of 6-16 μm z This ensures that the surface of the steel strip has good surface lubrication during the stretching process.

[0028] The underside of the steel strip according to this invention is a stearic acid lubrication layer. Stearic acid is a processing lubricant that provides both internal and external lubrication. It has good thermal stability and excellent release properties (preventing adhesion and accumulation on the mold surface) during high-speed continuous stamping processes, avoiding abnormal abrasive particle contamination on the inner surface of the formed part. It ensures surface lubrication and high surface cleanliness. The underside has a surface roughness R of 0.3 μm or less. a and surface roughness R of 2 μm or less z It holds.

[0029] The upper and lower surfaces of the steel strip according to the present invention have a structural design with differentiated functions, which can provide individualized functional requirements between forming and stamping processes that demand high efficiency and high precision.

[0030] The surface of the steel strip according to the present invention, which is in contact with the female die during the forming process, is a phosphate-treated layer and a stearic acid-lubricated layer. The surface has good surface lubrication performance during the rolling process. The surface has a surface roughness R a : 0.6~1.8 μm and surface roughness R z : Has a thickness of 6-16 μm. The surface roughness of the steel strip surface in contact with the female mold is too low, i.e., R a <0.6μm or R z When the surface roughness is <6μm, the surface lubrication components are rapidly lost during the deformation and spreading process, leading to insufficient lubrication and abrasion of the material surface, and therefore damaging the die. If the surface roughness is too high, i.e., Ra >1.8μm or R z When the thickness is >16μm, lubrication is sufficient during the deformation and spreading process, but excessive wear particles will be generated during continuous stamping, which will affect the die's lifespan.

[0031] The surface of the steel strip according to the present invention, which is in contact with the male die during the forming process, is a stearic acid lubricating layer. The surface has good lubrication and high surface cleanliness. The surface has a surface roughness R a ≤0.3 μm and surface roughness R z It has a surface roughness of ≤2μm. The surface of the steel strip in contact with the male die is the inner surface of the formed part. A smoother surface design can meet the high dimensional accuracy requirements of the formed part. At the same time, the surface is in close contact with the die during the forming process. A suitable surface lubrication component will provide sufficient lubrication during the forming process. If the surface roughness of the steel strip surface in contact with the male die is too high, i.e., R a >0.3μm or R z When the thickness is >2μm, the risk of poor dimensional accuracy and smoothness on the inner surface of the molded part will increase.

[0032] The upper and lower surfaces of the steel strip according to the present invention employ a differentiated functional design, where the surface of the steel strip in contact with the male die has good lubrication and high surface cleanliness, and the surface of the steel strip in contact with the female die has good surface lubrication performance during stretching. According to the present invention, the requirements for a continuous and efficient stamping process during the processing of shell parts with high precision and large deformation can be met, and processes such as coating or oil coating during the stamping process to manufacture shell parts with high precision and large deformation using conventional steel plates can be eliminated. The resulting product can be packaged and shipped as is, eliminating the need for post-forming cleaning and significantly improving manufacturing efficiency.

[0033] Simultaneously, both the upper and lower surfaces of the steel strip are coated with stearic acid. After the stearic acid forms a film, it has an excellent corrosion barrier function at room temperature, which can effectively improve the rust and corrosion resistance of the steel strip surface. Parts produced from the steel strip do not require additional rust-preventive oil coatings.

[0034] In another embodiment, the present invention provides a method for manufacturing a steel strip (for example, the steel strip described above), 1) Degreasing: A step in which rolled steel material is fed into a degreasing tank containing an alkaline degreasing agent by a tension roller, and the steel material is degreased at a degreasing temperature of 30 to 60°C, wherein oil stains on the surface of the steel material can be cleaned by using the alkaline degreasing agent. 2) First rinse: A step of rinsing the surface of the degreased steel material with rinse water, wherein the rinse water is industrial pure water having an conductivity of ≤10 μS / cm, or the rinse water is a mixture of tap water with 0.2 to 1.1 wt% corrosion inhibitor. 3) Activation and passivation: A surface conditioning agent is sprayed onto the rinsed upper surface of the steel material at a spray pressure of 0.4 to 1.2 bar, in a spray direction that forms a clamping angle of 90 to 135° with the direction of movement of the steel material, thereby activating it, and phosphate is applied to the lower surface of the steel material. Chemical A step of coating with a passivation agent having rear function and passivating it, 4) Phosphate treatment: The step of subjecting the activated steel material's upper surface to a phosphate treatment treatment using a high-pressure spray of a phosphate treatment agent, wherein the phosphate treatment treatment is carried out for 6 to 12 seconds at a spray pressure of 5 to 8 bar, in a spray direction that forms an angle of 90 to 135° with respect to the direction of movement of the steel material. 5) Second rinse: The process involves rinsing the surface of the steel material with industrial pure water having an conductivity of ≤10 μS / cm, and then applying the surface of the steel material to the surface that has been rinsed and then subjected to a draw-drying treatment. 6) Saponification: The process includes the steps of applying a stearic acid treatment agent to the top and bottom surfaces of a steel material at a temperature of 70-90°C, and then treating the surface of the steel material with compressed air purging and a wiping roller.

[0035] Preferably, in step 2), the surface of the steel material is rinsed by a spray method, with a spray pressure of 2 to 4 bar.

[0036] Preferably, in step 2), the corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate, and sodium silicate.

[0037] Preferably, in step 3), the surface modifier is selected from a colloidal titanium salt-based surface modifier, such as a commercially available PL-Z from parkerizing.

[0038] Preferably, in step 3), phosphate Chemical Passivation agents with rear function are passivation agents based on zirconate or chromic acid.

[0039] Preferably, in step 4), the phosphate treatment agent is selected from a zinc-manganese-nickel triparticle phosphate treatment solution, such as parkerizing or commercially available PB-181.

[0040] Preferably, in step 4), the spray angle is 100 to 120° with respect to the direction of movement of the steel material.

[0041] Preferably, in step 5), the surface of the steel material is rinsed by a spray method, with a spray pressure of 1 to 4 bar and a spray angle of 90 to 120° with respect to the direction of movement of the steel material.

[0042] Preferably, in step 6), the stearic acid treatment agent is applied by spraying.

[0043] Preferably, in step 6), the stearic acid contained in the stearic acid treatment agent is C18 or C16 stearic acid.

[0044] Preferably, in step 6), the stearic acid treatment agent comprises one or more of sodium stearate, magnesium stearate, and zinc stearate.

[0045] Preferably, in step 3) and / or step 4), the movable baffles are provided in the width direction of the steel material at a distance of 2 to 6 cm, preferably 3 to 5 cm, from each of the edges on both sides of the steel material. In other words, the movable baffles are in approximately the same plane as the steel material and perpendicular to the length direction (i.e., direction of movement) of the steel material, and the gap between the movable baffles and the edges of the steel material is 2 to 6 cm, preferably 3 to 5 cm.

[0046] Preferably, in step 3) and / or step 4), the steel material moves at a speed of 40 to 80 m / min.

[0047] In the manufacturing method according to the present invention, The main purpose of degreasing is to effectively clean the surface of the steel material. The temperature of the degreasing agent is controlled within 30-60°C. If the temperature is too low (<30°C), the cleaning capacity will be significantly reduced, making it difficult to guarantee surface cleanliness or requiring a large amount of cleaning additives, which is bad for the environment. If the temperature is too high (>60°C), the energy consumption will be too high and will not meet the requirements for low-carbon production.

[0048] Residual degreasing agents on the surface of the steel material are washed and removed by the first rinse, and the cleaning effect is confirmed by the continuous state of the surface water film. Rust problems can easily occur during the first rinse process. This can be effectively avoided mainly by the quality of the rinse water and corrosion suppression techniques. The corrosion process of metal materials in water is mainly an electrochemical reaction, and the conductivity of water directly affects the difficulty of the rust reaction. The conductivity of water is influenced by the number of ionic impurities, which is mainly characterized by conductivity. Newly degreased metal surfaces are susceptible to rust. The rinsing process uses industrial pure water with a conductivity of ≤10 μS / cm, which can effectively control the rust problem.

[0049] Tap water containing 0.2–1.1 wt% of a corrosion inhibitor can effectively reduce the risk of surface rust during the cleaning process while thoroughly cleaning the surface. If the amount of corrosion inhibitor added is too low (i.e., <0.2 wt%), the corrosion inhibitory effect cannot be achieved. If the amount is too high (i.e., >1.1 wt%), it is not economically or environmentally advantageous. The added corrosion inhibitor is selected from one or more of the following: sodium phosphate, sodium nitrite, sodium benzoate, and sodium silicate.

[0050] Activation and passivation: On the one hand, a surface modifier is sprayed onto the upper surface of the steel to form a surface modifier activated layer that promotes homogeneous nucleation for phosphate treatment. On the other hand, phosphate Chemical A passivation agent with rear function is applied to the lower surface of the steel material, and phosphate ChemicalA rust-resistant passivation layer with rear functionality is formed. In the activation and passivation processes, it is necessary to effectively control the mutual interference between the upper and lower surface treatment processes. Preferably, during the process of spraying the surface modifier, the spray pressure is controlled to within 0.4 to 1.2 bar. If the pressure is too low (less than 0.4 bar), the amount of surface modifier sprayed will be insufficient, resulting in insufficient activation. If the spray pressure is too high (greater than 1.2 bar), this will also affect the amount of surface modifier adsorbed, resulting in insufficient phosphate treatment of the product. If the spray angle is 90 to 135°, preferably 100 to 120°, with respect to the direction of movement of the steel material, the influence of the surface modifier on the lower surface can be better avoided.

[0051] Phosphates on the surface of steel materials Chemical Methods for applying passivation agents with rear-side functionality may include spraying, roller coating, and brush coating. When spraying is used, the spray angle relative to the direction of movement of the steel material should be controlled to reduce mutual interference between the treatment agent on the upper and lower surfaces caused by spray splashing.

[0052] To avoid interference between the two surfaces during the spraying process, it is preferable that the movable baffles are provided at a distance of 2–6 cm from each side edge of the steel material. The main objective is to avoid cross-contamination of surface treatment agents during the spraying process. If the gap between the steel material and the movable baffles is too large (>6 cm), the different treatment agents on the upper and lower surfaces will significantly affect each other during the spraying process. If the gap between the steel material and the movable baffles is too small (<2 cm), there is a greater risk that the edges of the steel material will collide with each other during normal production. The gap between the steel material and the movable baffles is preferably 3–5 cm.

[0053] The main purpose of phosphate treatment is to rapidly form uniformly distributed phosphate-treated crystalline particles on one side of the steel material, resulting in a fast, uniform, and low-density coating (see Figure 1). By spraying the phosphate treatment agent at high pressure, the phosphate-treated coating is formed within 6 to 12 seconds. This is a low-density phosphate-treated coating with a particle length in the range of 8 to 20 μm and a density of 1 to 3 g / m². 2 It consists of long, plate-like phosphate-treated crystalline particles having a phosphate-treated film weight (i.e., the weight of the phosphate-treated layer). On the one hand, the phosphate-treated film layer can improve the spatial capacity for the subsequent formation of the stearic acid film, thereby increasing the amount of stearic acid lubricant retained on the product surface. On the other hand, the phosphate-treated film layer can better ensure a uniform distribution of lubricant during the deformation process, and can provide further lubrication function using its inherent good friction and lubrication properties. The design of a non-high-density phosphate-treated film with coarse crystals can effectively reduce the amount of wear debris during the stamping process, thereby extending die life.

[0054] The processing time for conventional continuous phosphate treatment of steel materials is generally 15 seconds or more. In this invention, effective surface phosphate treatment can be performed in 6 to 12 seconds by using a high-pressure spray and controlling the spray pressure to be within 4 to 10 bar. Therefore, the phosphate treatment efficiency can be greatly improved. When the spray pressure is too low (<4 bar), the phosphate treatment efficiency of the continuous manufacturing process does not meet the requirement of rapid phosphate treatment (6 to 12 seconds), and the size of the resulting phosphate crystals is small (particle length <8 μm), failing to meet the surface requirements of the continuously produced steel products. When the spray pressure is too high (>10 bar), excessive splashing occurs, easily affecting the underside and adversely affecting the stability of the phosphate treatment effect and the uniform distribution of phosphate crystals. The spray direction is at an angle of 90 to 135°, preferably 100 to 120°, with respect to the direction of movement of the steel material.

[0055] Second rinse: The main purpose of this is to effectively clean any residual phosphate treatment agents from the surface. The risk of rust in this process is significantly reduced due to the effects of the phosphate and passivation coatings on the steel surface, eliminating the need for special rust prevention control. Both sides of the steel are rinsed with industrial pure water having an conductivity of ≤10 μS / cm. The rinse water temperature is room temperature, and the spray pressure is 1-4 bar. The spray direction forms an angle of 90-120° with the direction of movement of the steel. If tap water with high conductivity is used as is, electrolyte residues will remain on the surface. These will be directly covered by a stearic acid lubricant film in subsequent processes, and therefore will affect the rust resistance of the product during storage and transportation. After rinsing, the surface can be squeezed dry (e.g., by using a squeezing roll or squeezing machine) to effectively reduce the amount of water on the surface.

[0056] Stearic acid treatment (saponification): Liquid stearic acid is applied to the surface of the steel material by spraying at 70-90°C, and the surface coating layer is treated to be uniform by using a wiping roller. Preferably, the stearic acid is C18 or C16 stearic acid. Preferably, the stearic acid treatment agent is formulated from one or more of sodium stearate, magnesium stearate, and zinc stearate. After the liquid stearic acid is sprayed onto the surface of the steel material, it is blown with compressed air, and a wiping roller is used to ensure uniform treatment of the surface coating.

[0057] After the steps described above are completed, the steel material is wound up by a winding machine and then packaged for delivery. The steel strip produced by the method described above exhibits excellent rust and corrosion resistance, and as a result it does not require additional rust-preventive oil coating during storage and transportation.

[0058] The beneficial effects of this invention are as follows: 1. According to the present invention, a steel strip can be obtained in which two surfaces have differentiated functions, where the surface having only the stearic acid lubricant layer has good lubricity and high surface cleanliness, and the surface having both the phosphate treatment layer and the stearic acid lubricant layer has good surface lubricity during the rolling process. This satisfies the requirements of a continuous and efficient stamping process during the process of manufacturing shell parts with high precision and large deformation. However, when using conventional steel sheets, it is necessary to perform film coating and oil coating during the stamping process to manufacture shell parts with high precision and large deformation, and the parts need to be cleaned after they have been processed into parts. Rather, when using a steel strip according to the present invention, shell parts with high precision and large deformation can be stamped and processed directly. Compared with conventional steel sheets, processes such as film coating, oil coating, or post-forming cleaning can be omitted, and the resulting parts can be directly packaged and delivered. As a result, the efficiency of parts manufacturing can be greatly improved. Moreover, stearic acid is applied to both sides of the steel strip. After forming a stearic acid film, the rust resistance and corrosion resistance of the steel strip surface can be effectively improved, eliminating the need to coat the steel strip with rust-preventive oil during storage and transportation. 2. In the manufacturing method provided by the present invention, after the substrate is degreased and rinsed, the two surfaces of the substrate are activated and passivated respectively, the process parameters are controlled to prevent interference between the treatment of the two surfaces, and a one-sided phosphate treatment spray process combined with a two-sided saponification process is used to achieve continuous production of steel strips having differentiated functions on the two surfaces. 3. The high-pressure spray phosphate treatment process of the present invention significantly reduces the effective treatment time under appropriate machine length conditions. The overall feed rate of the steel strip can be controlled within 40-80 m / min, satisfying the requirements for the highly efficient manufacturing of conventional steel strips. As a result, the method can be directly connected to existing continuous annealing and leveling processes for cold-rolled steel strips and can also be used as an independent surface treatment method to realize the continuous manufacturing of steel strips with differentiated functions on two surfaces. [Brief explanation of the drawing]

[0059] [Figure 1] Figure 1 is a schematic diagram of a steel strip according to the present invention. [Modes for carrying out the invention]

[0060] The present invention will be described in detail below with reference to figures, examples, and comparative examples. However, the present invention is not limited to the following examples.

[0061] Refer to Figure 1, which shows the structure of a steel strip provided by an embodiment of the present invention. Surface A of the substrate includes, in order from the inside out, a phosphate treatment layer 1 and a stearic acid lubricant layer 2, and surface B of the substrate is the stearic acid lubricant layer 2. [Examples]

[0062] The substrate compositions of the examples and comparative examples of the present invention are shown in Table 1. Here, the remainder consists of Fe and unavoidable impurities other than P and S. The manufacturing process parameters of the examples and comparative examples of the present invention are shown in Table 2. The evaluation results of the process implementation effect in the examples and comparative examples of the present invention are shown in Table 3.

[0063] The two surface roughness parameters of the steel strip, Ra ("arithmetic mean deviation") and Rz ("ten-point mean of minute irregularities"), are measured using a Mahr MARSURF-PS10 portable roughness measuring instrument from Mahr, Germany (measurements are performed in accordance with standard GB / T1031).

[0064] The implementation effects of the process according to the present invention were evaluated according to the following evaluation criteria.

[0065] (1) Process -- Evaluation of degreasing effect The degreasing and cleaning effects on the surface of the steel strip were evaluated by the continuity of the water film on the surface during the water washing process after degreasing. The state of the water film on the washed surface after degreasing was visually observed: ◎: The water film on the surface is uniform and continuous, with 100% coverage. ×: The water film on the surface was clearly discontinuous and had a coverage rate of less than 100%.

[0066] (2) Process -- Rust phenomenon after rinsing 1 The rust condition on the surface of the steel strip after the first rinse, before activation and passivation, was visually observed: ◎: The surface was rust-free, and the rust / area percentage was 0%. ×: There were rust spots on the surface, and the rusted area was greater than 0%.

[0067] (3) Process -- Phosphate treatment effect Samples were taken after phosphate treatment. The size of the phosphate crystals on the upper surface of the phosphate-treated steel strip was observed by SEM: ◎: The size of the phosphate-treated crystals on the top surface was 8-20 μm, and the crystals were uniformly distributed. 1 g / m 2 ≤Weight of phosphate-treated coating ≤3g / m 2 . ○: The size of the phosphate-treated crystals on the top surface was 8-20 μm. However, the crystals were partially unevenly distributed. 1 g / m 2 ≤Weight of phosphate-treated coating ≤3g / m 2 . △: The size of the phosphate-treated crystals on the top surface is <8 μm or >20 μm, and the weight of the phosphate-treated film is <1 g / m². 2 or >3g / m 2 That was the case. ×: No significant phosphate-treated crystals on the top surface.

[0068] (4) Process -- Cleansing effect Samples were taken after phosphate treatment. The underside of the untreated steel strip was observed by SEM: ◎: No phosphate-treated crystals were observed. ○: Mild phosphorylation was observed in localized areas, but no significant phosphate-treated crystals were observed. △: Slight phosphate-treated crystals were observed on the surface. ×: Significant phosphate-treated crystals were observed on the surface.

[0069] As shown in Table 3, Examples 1 to 6 were processed according to the process described in the present invention, and all process effects of the resulting steel strips were excellent. The lower surface of the steel strip was a stearic acid lubricant layer with a surface roughness R of 0.3 μm or less. a and surface roughness R of 2 μm or less z The lower surface had good lubricity and high surface cleanliness. The upper surface of the steel strip contained, in order from the inside out, a phosphate treatment layer and a stearic acid lubricant layer, and its upper surface had a surface roughness R in the range of 0.6 to 1.8 μm. a and surface roughness R in the range of 6 to 16 μm z It possessed this property, and therefore the upper surface had good surface lubricity during the spreading process.

[0070] In Comparative Example 1, phosphate Chemical The lack of rear treatment resulted in significant phosphate crystal formation on the underside due to a partial phosphate treatment effect. In Comparative Example 2, a degreasing temperature close to room temperature failed to achieve effective surface cleaning, and a short phosphate treatment time combined with low spray pressure did not result in significant phosphate crystal formation on the top surface. In Comparative Example 3, the use of highly conductive tap water as rinse water 1 caused significant rust during the post-degreasing water washing process, negatively impacting the subsequent phosphate treatment.

[0071] Regarding the steel strip obtained in the example of the present invention, the surface of the steel strip was subjected to a neutral salt spray test in accordance with standard ASTM-B117. No rust was observed on the surface of the steel strip after 24 hours. The corrosion resistance of the steel strip was clearly better than that of conventional oil-coated steel sheets (which show rust after approximately 12 hours in the neutral salt spray test). This indicates that the steel strip obtained by the present invention has good rust and corrosion resistance and meets the corrosion resistance requirements for 4 months of storage and transport without surface rust.

[0072] [Table 1]

[0073] [Table 2]

[0074] [Table 3] [Explanation of Symbols]

[0075] 1. Phosphate-treated layer 2. Stearic acid lubricant layer

Claims

1. A steel strip comprising a substrate and a phosphate treatment layer and a stearic acid lubricant layer disposed on the substrate, In the thickness direction of the substrate, the phosphate treatment layer and the stearic acid lubricant layer are arranged sequentially from the inside out on the upper surface of the substrate that comes into contact with the male mold during the molding process, and the stearic acid lubricant layer is arranged on the lower surface of the substrate that comes into contact with the female mold during the molding process. The upper surface of the steel strip has a surface roughness R of 0.6 to 1.8 μm. ａ and surface roughness R of 6 to 16 μm ｚ It has, The lower surface of the steel strip has a surface roughness R of 0.3 μm or less. ａ and surface roughness R of 2 μm or less ｚ Having, Steel strip.

2. In addition to Fe and unavoidable impurities, the substrate further contains the following chemical elements in wt%: C: 0.1-0.7%, 0.2% ≤ Si ≤ 2%, 0.2% ≤ Mn ≤ 2%, Cr: 0.2-1.4%, 0.01% ≤ Al ≤ 0.06%, and Mo: 0.05-0.2%, where the unavoidable impurities include P ≤ 0.04% and S ≤ 0.05%, as described in claim 1.

3. The steel strip according to claim 1, wherein the substrate contains the following chemical elements in wt%: C: 0.1-0.7%, 0.2% ≤ Si ≤ 2%, 0.2% ≤ Mn ≤ 2%, Cr: 0.2-1.4%, 0.01% ≤ Al ≤ 0.06%, Mo: 0.05-0.2%, and the remainder is Fe and unavoidable impurities, where the unavoidable impurities include P ≤ 0.04% and S ≤ 0.05%.

4. The substrate has a thickness of 1.0 to 6.0 mm, the phosphate-treated layer has a grain size of 8 to 20 μm, and / or the phosphate-treated layer has a grain size of 1 to 3 g / m². ２ A steel strip according to claim 1, having the weight of [amount].

5. A method for manufacturing a steel strip as described in claim 1, 1) Degreasing: The process involves feeding rolled steel material into a degreasing tank containing an alkaline degreasing agent using a tension roller, and degreasing the steel material at a degreasing temperature of 30 to 60°C. 2) First rinse: The step of rinsing the surface of the degreased steel material with rinsing water which is industrial pure water having an conductivity of ≤10 μS / cm, or a mixture of tap water with 0.2 to 1.1 wt% of a corrosion inhibitor, 3) Activation and passivation: The process involves spraying a surface conditioning agent onto the upper surface of the rinsed steel material at a spray pressure of 0.4 to 1.2 bar, in a spray direction that forms a bounding angle of 90 to 135° with the direction of movement of the steel material, thereby activating it, and then coating the lower surface of the steel material with a passivation treatment agent having a phosphate chloride barrier function, thereby passivating it. 4) Phosphate treatment: The activated steel material's upper surface is subjected to a phosphate treatment using a high-pressure spray of a phosphate treatment agent, wherein the phosphate treatment is carried out for 6 to 12 seconds at a spray pressure of 5 to 8 bar, in a spray direction that forms an angle of 90 to 135° with respect to the direction of movement of the steel material. 5) Second rinse: The process involves rinsing the surface of the steel material with industrial pure water having an conductivity of ≤10 μS / cm, and then subjecting the surface of the steel material to a wringing and drying treatment after rinsing. 6) Saponification: A method comprising the steps of applying a stearic acid treatment agent to the upper and lower surfaces of the steel material at a temperature of 70 to 90°C, and then treating the surface of the steel material with compressed air purging and wiping rollers.

6. The method according to claim 5, wherein in step 2), the surface of the steel material is rinsed by spraying at a spray pressure of 2 to 4 bar.

7. The method according to claim 5, wherein in step 2), the corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate, and sodium silicate.

8. The method according to claim 5, wherein in step 3), the passivation agent is a passivation agent based on zirconic acid or a passivation agent based on chromic acid and / or the passivation agent is applied by one or more of the following: spray, roller coating, and brush coating.

9. The method according to claim 5), wherein in step 5), the surface of the steel material is rinsed by spraying at a spray pressure of 1 to 4 bar at a spray angle of 90 to 120° with respect to the direction of movement of the steel material.

10. The method according to claim 5, wherein in step 6), the stearic acid treatment agent is applied by spraying.

11. The method according to claim 5, wherein in step 6), the stearic acid contained in the stearic acid treatment agent is C18 or C16 stearic acid, and / or the stearic acid treatment agent comprises one or more of sodium stearate, magnesium stearate, and zinc stearate.

12. The method according to claim 5, wherein in step 3) and / or step 4), the movable baffles are provided at a distance of 2 to 6 cm from both sides of the steel material in the width direction.

13. The method according to claim 5, wherein in step 3) and / or step 4), the steel material moves at a speed of 40 to 80 m / min.

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