Oil-free steel strip with excellent processability and corrosion resistance and manufacturing method thereof

Abstract

An oil-free steel strip with excellent processability and corrosion resistance and a manufacturing method thereof, wherein one surface of the steel strip is a stearate lubricating layer, and its surface roughness Ra≤0.3μm, Rz≤2μm, and has good lubricity and high surface cleanliness; the other surface of the steel strip includes a phosphating layer and a stearate lubricating layer from the inside to the outside, and the surface roughness Ra is 0.6-1.8μm, and Rz is 6-16μm, and the surface has good surface lubricity during the extension process. The steel strip with the differentiated functional design of the two surfaces of the present invention can be directly stamped to process high-precision and large-deformation shell parts, eliminating the laminating, oiling, and post-molding cleaning operations in the stamping process of high-precision and large-deformation shell parts made of traditional steel plates, greatly improving the parts manufacturing efficiency; and the steel strip has good rust and corrosion resistance, and the surface does not need to be oiled during storage and transportation.

Description

Technical Field

[0001] The invention relates to the technical field of metal surface treatment and manufacturing, and in particular to an oil-free strip steel with excellent processability and corrosion resistance and a manufacturing method thereof. Background Art

[0002] In the field of metal material processing, continuous and efficient processing technology characterized by high precision, high complexity and environmental protection requirements is widely used in the fields of automobile and mechanical parts processing. After theoretical analysis, a large number of laboratory scientific research and application practice surveys, it is shown that during the stamping process of high-precision large deformation shell parts, the steel plate surface in contact with the die bears the main deformation friction; the steel plate surface in contact with the convex film has relatively small deformation friction, which mainly guarantees the dimensional accuracy of the inner surface. Therefore, the steel plate surface in contact with the die needs to provide sufficient lubrication during the deformation process, while the steel plate surface in contact with the punch does not need too high lubrication performance, but requires ultra-high surface finish. In order to ensure the acquisition of shell parts with high dimensional accuracy / high surface quality, different lubrication functions are required on both sides of the material.

[0003] Material suppliers such as JFE, Nissin, and POSCO mainly focus on the development of products with excellent mechanical properties. In the field of stamping material development and research, they mainly focus on double-sided coating treatment of strip steel for lubrication functional coatings on the surface of strip steel, such as Japanese patent JP05076347B2, Japanese patent JP8295985A, and Korean patent KR376927B1.

[0004] In the double-sided coating treatment of the strip surface, the main process types are: (1) forming a micron or submicron organic coating on the steel plate surface by roller coating + baking curing during the continuous manufacturing process, specifically referring to Chinese patents CN104451638, CN103289569, and CN105463436; (2) forming a phosphating layer / passivation layer on the steel plate surface by spraying during the continuous manufacturing process, specifically referring to Chinese patent CN111349867A.

[0005] Chinese patent CN103289569 discloses "a self-lubricating passivation liquid and a hot-dip galvanized self-lubricating steel plate coated with it", which mainly plays the role of solid lubrication of the coating by adding nano-MoS2 and modified nano-PTFE particles in the treatment agent. The coating is coated with 800-1200 mg / m2 of adhesive on the surface of the steel plate by roller coating + baking curing. 2 The invented product is mainly applicable to the stamping needs of household appliances and micro-motor housing materials, but cannot meet the large deformation stamping of high-precision parts in the automotive and mechanical fields, and cannot be used as a surface treatment for ordinary cold-rolled plates.

[0006] Chinese patent CN111349867 discloses "a coating-friendly pre-phosphating electro-galvanized automobile outer panel and its preparation method", which designs a Nb-containing ultra-low carbon steel plate to form a continuous coating on the steel plate surface by gravity electroplating process, and then forms a 1.0-2.0g / m2 coating by double-sided spraying at a phosphating temperature of 50-60°C. 2 The pre-phosphating layer is treated with oil to form a product that meets the stamping lubrication and corrosion resistance requirements of automobile body materials. It can be well applied in the body production line, but it cannot meet the large deformation stamping requirements of high-precision parts in the automotive and mechanical fields, and it cannot achieve the manufacturing requirements of double-sided differentiated lubrication functions.

[0007] Chinese patent CN105018920A discloses "a phosphating saponification production process", which involves a drum-type continuous phosphating / saponification process for processing small parts, mainly including: entering the drum → degreasing → primary cleaning → phosphating → secondary cleaning → surface adjustment → saponification → exiting the drum 8 process flows, wherein the phosphating temperature is 60-85°C, the immersion time is 3-10 minutes, and the saponification temperature is 55-80°C, the immersion time is 0.5-5 minutes. This process mainly realizes the surface lubrication function of the finished parts by high-temperature phosphating + saponification treatment, and cannot be applied to realize continuous strip manufacturing.

[0008] Chinese patent CN105296997A discloses "a phosphating-saponification treatment process for 27SiMn steel", which is mainly applied to a surface lubrication treatment method for high-precision cold-drawn steel pipes. The 27SiMn steel parts are pickled → high-temperature phosphating (70°C) → saponification treatment, which is also a double-sided non-differential treatment and cannot be applied to achieve continuous strip manufacturing.

[0009] Therefore, the processing of high-precision and large-deformation shell parts puts forward different lubrication function requirements on both sides of the material. The traditional method of achieving double-sided differentiation of steel plates is to coat the steel plate punch contact surface with a film (plastic lubrication film) or apply lubricant oil during the stamping process. This method cannot meet the requirements of efficient / environmentally friendly manufacturing. The research on coating in the stamping process mainly focuses on lubrication devices, lubricant application methods, and lubricant compositions for fine stamping. With the increasing demand for high-precision and large-deformation shell parts, it is the requirement of the entire industry to simplify the processing and production process of parts and produce products with higher cost-effectiveness and market competitiveness. Summary of the invention

[0010] The object of the present invention is to provide an oil-free steel strip with excellent processability and corrosion resistance and a manufacturing method thereof, wherein the two surfaces of the steel strip have differentiated functions, wherein the surface roughness of one surface is Ra≤0.3μm, Rz≤2μm, and it has good lubricity and high surface cleanliness; the surface roughness of the other surface is Ra of 0.6-1.8μm, and Rz of 6-16μm, and it has good surface lubrication performance during the extension process, meeting the continuous and efficient stamping process requirements during the processing of high-precision and large-deformation shell parts, eliminating the coating, oiling and cleaning operations of conventional steel plates during the stamping process of high-precision and large-deformation shell parts, and the produced parts can be directly packaged and shipped, greatly improving the parts manufacturing efficiency; and the steel strip has good anti-rust and anti-corrosion properties, and the produced parts do not need to be coated with anti-rust oil during storage and transportation.

[0011] To achieve the above purpose, the technical solution of the present invention is as follows:

[0012] An oil-free steel strip with excellent processability and corrosion resistance, the oil-free steel strip comprising a substrate, one surface of the substrate being a stearate lubricating layer, the surface roughness of which Ra≤0.3μm, Rz≤2μm; the other surface of the substrate comprising a phosphating layer and a stearate lubricating layer from inside to outside, the surface roughness of which Ra is 0.6-1.8μm, and Rz is 6-16μm.

[0013] Preferably, the chemical composition mass percentage of the substrate is: C: 0.1-0.7%, Si≤2%, P≤0.04%, S≤0.05%; Mn≤2%, Cr: 0.2-1.4%, Al≤0.06%, Mo: 0.05-0.2%, and the remainder is Fe and other inevitable impurities.

[0014] Preferably, the substrate has a thickness of 1.0 to 6.0 mm.

[0015] In the oil-free steel strip with excellent processability and corrosion resistance described in the present invention:

[0016] In the composition design of the strip steel substrate of the present invention: if the C element content is too high (>0.7%), the surface chemical reactivity of the material will be reduced, thereby affecting the surface phosphating and passivation film-forming properties, and the material molding stability is likely to be insufficient.

[0017] The Si element can effectively improve the forming properties of the material under high-strength conditions. If the content is too high (>2%), it will be selectively oxidized and precipitated during the heat treatment process. The precipitates will be enriched on the surface, affecting the subsequent phosphating and passivation film-forming reaction performance.

[0018] The Mn element plays a role in ensuring the strength and hardness of the material. If the Mn content is too high (>2%), it will also be selectively oxidized and precipitated during the heat treatment process. The precipitates will be enriched on the surface, affecting the subsequent phosphating and passivation film-forming reaction performance.

[0019] As impurity elements, P and S elements should be controlled in a lower range as much as possible. When their content is too high, it will affect the toughness of the material and cannot meet the requirements of large deformation forming performance.

[0020] Cr, Al, and Mo elements mainly play the role of refining crystals, and excessive addition is not conducive to the economic efficiency of product manufacturing.

[0021] The material thickness of high-precision, large deformation shell parts is generally 1 to 6 mm. If the substrate thickness is too thin, when the substrate thickness is less than 1 mm, after large deformation and deep drawing, the shell wall of the component is prone to be too thin to meet the requirements of load-bearing performance. If the substrate thickness is too thick, when the substrate thickness is greater than 6 mm, the cold-rolled product manufacturing production line cannot achieve effective manufacturing.

[0022] The surface of the steel strip described in the present invention is a stearate lubricating layer. Stearate is a material processing lubricant that takes into account both internal lubrication and external lubrication functions. It has good thermal stability and excellent demolding performance (avoiding adhesion and accumulation on the mold surface) during continuous and rapid stamping, avoiding the influence of abnormal grinding particle contamination on the inner surface of the molded parts, and achieving lubricity and high surface cleanliness of the surface. Its surface roughness Ra≤0.3μm, Rz≤2μm.

[0023] The other surface of the strip steel includes a phosphating layer and a stearate lubricating layer from the inside to the outside, that is, the surface adopts a phosphating + stearate coating structure design, and both the phosphating film and the saponifying film have lubrication functions. The combination of the two can effectively improve the lubrication stability during the tensile deformation process, and its surface roughness Ra is 0.6-1.8μm, and Rz is 6-16μm, ensuring that the surface of the strip steel has good surface lubrication performance during the extension process. The structural design with differentiated functions on the two surfaces of the strip steel can provide personalized functional requirements in the high-speed and high-precision forming and stamping process.

[0024] The surface of the strip steel in contact with the die during the forming process of the strip steel of the present invention is a phosphating layer and a stearate lubricating layer, and the surface has good surface lubrication performance during the extension process, and the surface roughness is Ra: 0.6-1.8μm, Rz: 6-16μm. When the surface roughness of the strip steel in contact with the die is low, that is, Ra<0.6 or Rz<6, the surface lubricating component is lost quickly during the deformation and extension process, and the lubrication performance is insufficient, resulting in roughening of the material surface and damage to the die; when the roughness is too high, that is, Ra>1.8 or Rz>16, the lubrication performance during the deformation and extension process is sufficient, and excessive wear debris is likely to occur during the continuous stamping process, affecting the life of the die.

[0025] The surface of the strip steel in contact with the punch during the strip steel forming process of the present invention is a stearate lubricating layer, which has good lubricity and high surface cleanliness, with a surface roughness of Ra≤0.3μm and Rz≤2μm. The surface of the strip steel in contact with the punch is the inner surface of the formed part, and the 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 mold throughout the forming process, and the appropriate surface lubricating component will fully play the lubricating role in the forming process. When the roughness of the surface in contact with the punch is too high, that is, Ra>0.3 or Rz>2, the risk of poor dimensional accuracy and smoothness of the inner surface of the formed part increases.

[0026] The two surfaces of the steel strip described in the present invention adopt differentiated functional designs, wherein the surface of the steel strip in contact with the punch has good lubricity and high surface cleanliness, and the surface of the steel strip in contact with the die has good surface lubrication performance during the extension process, which meets the continuous and efficient stamping process requirements during the processing of high-precision and large-deformation shell parts, and eliminates the lamination and oiling operations of conventional steel plates during the stamping process of high-precision and large-deformation shell parts. The products produced can be directly packaged and shipped, eliminating the cleaning process after forming at the user end, thereby greatly improving product manufacturing efficiency.

[0027] At the same time, stearate is coated on both surfaces of the strip. After stearate forms a film, it has excellent corrosive medium barrier function at room temperature, which can effectively improve the anti-rust and anti-corrosion properties of the strip surface. Parts produced with this strip do not need to be coated with anti-rust oil.

[0028] The method for manufacturing the oil-free steel strip with excellent processability and corrosion resistance of the present invention comprises the following steps:

[0029] 1) Degreasing

[0030] The strip enters the degreasing tank through the tension roller, and the oil stains on the surface of the strip are cleaned by alkaline degreasing agent, and the temperature of the alkaline degreasing agent is 30-60℃;

[0031] 2) First rinse

[0032] The surface of the degreased steel strip is cleaned with rinsing water, wherein the rinsing water is industrial pure water with a conductivity of ≤10us / cm, or the rinsing water is tap water + a corrosion inhibitor with a mass fraction of 0.2 to 1.1%;

[0033] 3) Activation and passivation

[0034] Spraying a phosphating surface conditioning agent onto one surface of the rinsed steel strip, with a spraying pressure of 0.4 to 1.2 bar, and a spraying direction that forms an angle of 90 to 135 degrees with the running direction of the steel strip; applying a passivation treatment agent with a phosphating barrier function onto the other surface of the steel strip;

[0035] 4) Phosphating

[0036] The strip surface sprayed with the phosphating surface conditioning agent is phosphated by high-pressure spraying, the phosphating treatment time is 6 to 12 seconds, the spraying pressure is 5 to 8 bar, and the spraying direction is at an angle of 90 to 135 degrees to the running direction of the strip;

[0037] 5) Second rinse

[0038] Use industrial pure water with conductivity ≤10us / cm to rinse the strip surface, and squeeze the surface dry after rinsing;

[0039] 6) Saponification

[0040] A stearate treatment agent is applied to the surface of the steel strip, and then the surface of the steel strip is purged and wiped with a roller using compressed air, wherein the coating temperature is 70 to 90°C.

[0041] Preferably, in step 2), the surface of the steel strip is rinsed by spraying, and the spraying pressure is 2 to 4 bar.

[0042] Preferably, in step 2), the corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate and sodium silicate.

[0043] Preferably, in step 3), the passivation treatment agent having phosphating barrier function is a Zr acid salt passivation treatment agent or a Cr acid salt passivation treatment agent.

[0044] Preferably, in step 4), the spraying direction forms an angle of 100 to 120° with the running direction of the strip.

[0045] Preferably, in step 5), the surface of the steel strip is rinsed by spraying, the spraying pressure is 1 to 4 bar, and the spraying direction forms an angle of 90 to 120° with the running direction of the steel strip.

[0046] Preferably, in step 6), the stearate treating agent is applied by spraying.

[0047] Preferably, in step 6), the stearate in the stearate treating agent is C18 or C16 stearate.

[0048] Preferably, in step 6), the stearate treatment agent is prepared by mixing any one or more of sodium stearate, magnesium stearate, and zinc stearate.

[0049] Preferably, in step 3) and / or step 4), movable baffles are arranged on both sides of the steel strip at a distance of 2 to 6 cm from the edge of the steel strip, preferably 3 to 5 cm.

[0050] Preferably, in step 3) and / or step 4), the running speed of the strip steel is 40 to 80 m / min.

[0051] In the manufacturing method of the present invention:

[0052] The main purpose of degreasing is to effectively clean the surface dirt of the strip. The temperature of the degreasing agent is controlled at 30-60℃. If the temperature is too low (<30℃), the cleaning ability will be significantly reduced and the surface cleaning effect will be difficult to guarantee, or a large amount of cleaning additives will be required, which is not environmentally friendly; if the temperature is too high (>60℃), the energy consumption will be too high and will not meet the requirements of low-carbon production.

[0053] The first rinse will wash away the residual degreasing agent on the surface of the strip, and the cleaning effect of the surface oil will be confirmed by the continuous state of the surface water film. Rust problems are prone to occur during the first rinse, which can be effectively avoided mainly by the quality of the rinse water and corrosion inhibition technology. The corrosion process of metal materials in water is mainly an electrochemical reaction, and the conductivity of water directly affects the difficulty of the corrosion reaction. The conductivity of water is affected by the number of anions and cations in the impurities, and is mainly characterized by conductivity. The surface of fresh metal materials after degreasing is prone to rust. The use of industrial pure water with a conductivity of ≤10us / cm in the rinsing process can effectively control the occurrence of rust problems.

[0054] The rinsing water uses tap water + 0.2-1.1% by mass of corrosion inhibitor, which can effectively reduce the risk of surface corrosion during the water washing process while fully cleaning the surface. When the amount of corrosion inhibitor added is too low (less than 0.2%), it cannot have an effective corrosion inhibition effect. When the additive is excessive (greater than 1.1%), it does not meet the requirements of economic and environmental protection. The added corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate, and sodium silicate.

[0055] Activation & passivation: On the one hand, a phosphating surface regulator is sprayed on one surface of the strip to form a surface activation layer that promotes uniform nucleation of phosphating. On the other hand, a passivation treatment agent with a phosphating barrier function is applied to the other surface of the strip to form an anti-rust passivation layer with a phosphating barrier function. During the activation & passivation treatment process, it is necessary to effectively control the mutual interference between the upper and lower surface treatment processes. During the spraying of the phosphating surface regulator, the spraying pressure is controlled at 0.4-1.2 bar. When the pressure is too low, less than 0.4 bar, the spraying amount of the phosphating surface regulator is insufficient and the activation is insufficient. When the spraying pressure is too high, greater than 1.2 bar, it will also affect the adsorption amount of the phosphating surface regulator, resulting in insufficient phosphating treatment of the product. The spraying direction is at an angle of 90-135° to the running direction of the strip, and the angle between the spraying direction and the running direction of the strip is preferably 100-120°, which can effectively avoid the influence of the phosphating surface regulator on the other surface.

[0056] The passivation treatment agent with phosphating barrier function on the strip surface can be applied by spraying, roller coating, brushing, etc. When spraying, it is necessary to control the angle range between the spraying direction and the running direction of the strip to reduce the mutual influence of the upper and lower surface treatment agents caused by the spray splash.

[0057] In order to avoid interference between the two surfaces during the spraying process, movable baffles can be set on both sides of the strip at a distance of 2 to 6 cm from the edge of the strip. The main purpose is to avoid the problem of mutual contamination of the two surface treatment agents during the spraying process. When the gap between the strip and the movable baffle is too large (> 6 cm), the different treatment agents on the upper and lower surfaces will significantly affect each other during the spraying process; when the gap between the strip and the movable baffle is too small (< 2 cm), there is a greater risk of strip edge collision during normal production. The gap between the strip and the movable baffle is preferably 3 to 5 cm.

[0058] The main purpose of phosphating is to quickly form uniformly distributed phosphating crystal particles on one side of the strip, which is characterized by rapid, uniform, and non-dense film formation. Through high-pressure spraying, a phosphating film is formed within 6 to 12 seconds. It is a non-dense phosphating film composed of long, flake-shaped phosphating crystal particles. The crystal particle size is 8 to 20 μm in length and the film weight is 1 to 3 g / m 2 On the one hand, the phosphate film layer can provide a three-dimensional space for the subsequent stearate film formation, effectively increasing the storage capacity of stearate lubricant on the product surface; on the other hand, it ensures the uniform distribution of lubricant during the deformation process, and provides further lubrication function by using its own good friction and lubrication properties. The design of coarse crystallized non-dense phosphate film can effectively reduce the amount of wear debris in the stamping process, thereby increasing the life of the mold.

[0059] Conventional continuous strip steel phosphating treatment time generally takes more than 15 seconds. The present invention uses high-pressure spraying and controls the spray pressure at 4 to 10 bar, which can control the effective surface phosphating treatment within 6 to 12 seconds, greatly improving the phosphating efficiency. When the spray pressure is low (<4 bar), the phosphating efficiency of the continuous manufacturing process does not meet the requirements of fast 6 to 12 seconds phosphating treatment, and the size of the phosphating crystals produced is small (particle size length <8 μm), which cannot meet the surface requirements of continuous strip steel production products. When the spray pressure is too high (>10 bar), excessive splashing will occur, which is easy to affect the other surface, and has an adverse effect on the stability of the phosphating effect and the uniform distribution of the phosphating crystals. The spray direction is at an angle of 90 to 135° to the running direction of the strip steel, and the angle between the spray direction and the running direction of the strip steel is preferably 100 to 120°.

[0060] Second rinse: The main function is to effectively clean the phosphating agent remaining on the surface. Due to the effect of the phosphating film and the surface passivation film on the strip surface, the rust risk of this process is significantly reduced, and no special anti-rust control is required. The strip surface is rinsed with industrial pure water with a conductivity of ≤10us / cm. The rinsing water temperature is room temperature, the spray pressure is 1-4bar, and the spray direction is 90-120° with the running direction of the strip. If high-conductivity tap water is used directly, electrolyte residue will form on the surface, which will be directly coated under the stearic acid lubricating film in the subsequent process, affecting the anti-rust performance of the product during storage and transportation. After rinsing, the surface is squeezed dry to effectively reduce the amount of water on the surface.

[0061] Stearate treatment (saponification treatment): Spray stearate liquid at 70-90°C onto the strip surface, and use a wiping roller to evenly treat the surface film. Stearate uses C18 or C16 stearate, which is mixed with any one or more of sodium stearate, magnesium stearate, and zinc stearate. After the liquid stearate is sprayed onto the strip surface, it is purged with compressed air and then treated evenly with a wiping roller.

[0062] After completing the above process, the strip steel is curled by a coiling machine and then packaged for shipment. Since the steel coil has excellent anti-rust and anti-corrosion properties, it does not need to be coated with anti-rust oil during storage and transportation.

[0063] Beneficial effects of the present invention:

[0064] 1. The present invention obtains a steel strip with differentiated functions on both sides, one of which has good lubricity and high surface cleanliness, and the other surface has good surface lubricity during the extension process, which meets the requirements of continuous and efficient stamping process during the processing of high-precision and large-deformation shell parts; while traditional steel plates need to be coated and oiled during the stamping process of processing high-precision and large-deformation shell parts, and the parts need to be cleaned after being processed into parts. The steel strip described in the present invention can be used to directly stamp high-precision and large-deformation shell parts. Compared with conventional steel plates, it eliminates the operations of coating, oiling and cleaning after forming, and can be directly packaged and shipped, greatly improving the efficiency of parts manufacturing; and both surfaces of the steel strip are coated with stearate, which effectively improves the rust and corrosion resistance of the steel strip surface after film formation, and the steel strip does not need to be coated with anti-rust oil during storage and transportation.

[0065] 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, and the parameters in the process are controlled to prevent interference in the treatment process of the two surfaces. Subsequently, a single-sided phosphating spray process + a double-sided saponification process are adopted to realize the continuous manufacturing of strip steel with differentiated functions on both surfaces.

[0066] 3. The present invention adopts a high-pressure spray phosphating process, which greatly reduces the effective processing time under the condition of appropriate equipment length. The overall running speed of the strip can be controlled at 40-80m / min, meeting the needs of efficient manufacturing of conventional strip steel, so that this method can be directly connected to the existing cold-rolled strip continuous annealing and leveling process, and can also be used as a separate strip surface treatment method to achieve continuous manufacturing of strip steel with differentiated functions on both surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 It is a schematic structural diagram of the strip steel according to an embodiment of the present invention. DETAILED DESCRIPTION

[0068] The present invention will be described in detail below by referring to the accompanying drawings, examples and comparative examples, but the scope of the present invention is not limited by these examples.

[0069] See also Figure 1 , which shows the structure of the strip steel according to an embodiment of the present invention. The oil-free strip steel includes a substrate, and the A surface of the substrate includes a phosphating layer 1 and a stearate lubricating layer 2 from the inside to the outside, and the B surface of the substrate is the stearate lubricating layer 2.

[0070] The composition of the substrate of the embodiment of the present invention and the comparative example is shown in Table 1, and the remainder of the composition is Fe and other inevitable impurities. Table 2 shows the manufacturing process parameters of the embodiment and the comparative example. The evaluation results of the process implementation effect of the embodiment of the present invention and the comparative example are shown in Table 3. The roughness Ra and Rz of the two surfaces of the strip steel were measured by using the Mahr MARSURF PS 10 mobile roughness measuring instrument of Germany (measurement refers to the standard GB / T 1031).

[0071] Evaluation criteria for the implementation effect of the process of the present invention:

[0072] (1) Process - Degreasing Effect Evaluation

[0073] The degreasing and cleaning effect of the strip surface is evaluated by the continuous state of the surface water film during the water washing process after degreasing. Visual observation of the surface water film state after degreasing and water washing:

[0074] ◎: The surface water film is uniform and continuous, with a coverage rate of 100%;

[0075] ×: The surface water film is obviously discontinuous and the coverage is less than 100%.

[0076] (2) Process - Rust phenomenon after rinsing 1

[0077] Visual observation of the rust on the strip surface after the first rinse and before activation and passivation:

[0078] ◎: No rust on the surface, rust area 0%;

[0079] ×: There are rust spots on the surface, and the rust area is greater than 0%.

[0080] (3) Process - Phosphating Effect

[0081] After phosphating, samples were taken and the size of phosphating crystals on the surface of the phosphating strip was observed by SEM:

[0082] ◎: The size of the phosphating crystals on the upper surface is 8 to 20 μm, and the crystals are evenly distributed;

[0083] 0: The size of the phosphating crystals on the upper surface is 8 to 20 μm, but the crystals are unevenly distributed locally;

[0084] △: The size of the phosphating crystals on the upper surface is less than 8μm or greater than 20μm;

[0085] ×: No significant phosphating crystals on the upper surface.

[0086] (4) Process - Cleaning effect

[0087] After phosphating, the surface of the strip steel that has not been phosphated was observed by SEM:

[0088] ◎: No phosphate crystals;

[0089] 0: Slight phosphating in some areas, without obvious phosphating crystals;

[0090] △: Slight phosphating crystallization on the surface;

[0091] ×: Phosphate crystals are obvious on the surface.

[0092] As shown in Table 3, Examples 1-6 are processed according to the process of the present invention, and the obtained steel strips all have excellent process effects. The surface is a stearate lubricating layer with a surface roughness of Ra≤0.3μm and Rz≤2μm, and has good lubricity and high surface cleanliness. The other side includes a phosphating layer and a stearate lubricating layer from the inside to the outside, with a surface roughness Ra of 0.6-1.8μm and Rz of 6-16μm. The surface has good surface lubricity during the extension process, realizing the differentiated functional design of the two surfaces of the steel strip, and meeting the continuous and efficient stamping process requirements in the processing of high-precision and large-deformation shell parts.

[0093] In Comparative Example 1, the phosphating barrier treatment process was not considered during phosphating, and the lower surface was partially affected by phosphating to form obvious phosphating crystals. In Comparative Example 2, the degreasing temperature was close to room temperature and could not meet the requirements for effective surface cleaning. At the same time, due to the short phosphating time and too low spraying pressure, no significant phosphating crystals were formed on the upper surface. In Comparative Example 3, due to the use of tap water with high conductivity in the rinse water 1, obvious rust occurred during the water washing process after degreasing, which had an adverse effect on the subsequent phosphating.

[0094] The steel strip obtained in the embodiment of the present invention is subjected to a neutral salt spray test on the surface of the steel strip in accordance with the ASTM B117 standard. No rust is produced on the surface of the steel strip for 24 hours, and its corrosion resistance is significantly better than that of conventional oiled steel plates (the time for rust to appear on the surface in the neutral salt spray test is about 12 hours). This indicates that the steel strip obtained in the present invention has good anti-rust and anti-corrosion properties, and can meet the corrosion resistance requirement of no rust on the surface of the steel strip during storage and transportation for 4 months.

[0095]

[0096]

[0097]

Claims

1. An oil-free steel strip with excellent processability and corrosion resistance, characterized in that: The oil-free steel strip comprises a substrate, one surface of which is a stearate lubricating layer, and the surface roughness Ra≤0.3μm, Rz≤2μm; The other surface of the substrate includes a phosphating layer and a stearate lubricating layer from the inside to the outside, and its surface roughness Ra is 0.6-1.8 μm, and Rz is 6-16 μm; the phosphating layer is a non-dense phosphating film composed of long strip-shaped flaky phosphating crystal particles, the crystal particle size length is 8-20 μm, and the film weight is 1-3 g / m 2 .

2. The oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 1, characterized in that: The chemical composition mass percentage of the substrate is: C: 0.1-0.7%, Si≤2%, P≤0.04%, S≤0.05%; Mn≤2%, Cr: 0.2-1.4%, Al≤0.06%, Mo: 0.05-0.2%, and the balance is Fe and other inevitable impurities.

3. The oil-free steel strip with excellent processability and corrosion resistance according to claim 1 or 2, characterized in that: The substrate has a thickness of 1.0 to 6.0 mm.

4. The method for manufacturing oil-free steel strip having excellent processability and corrosion resistance according to any one of claims 1 to 3, characterized in that: The steps include: 1) Degreasing The strip enters the degreasing tank through the tension roller, and the oil stains on the surface of the strip are cleaned with alkaline degreasing agent. The degreasing temperature is 30-60℃; 2) First rinse The surface of the degreased steel strip is cleaned with rinsing water, wherein the rinsing water is industrial pure water with a conductivity of ≤10 μs / cm, or the rinsing water is tap water + a corrosion inhibitor with a mass fraction of 0.2 to 1.1%; 3) Activation and passivation Spraying a phosphating surface conditioning agent onto one surface of the rinsed steel strip, with a spraying pressure of 0.4 to 1.2 bar, and a spraying direction that forms an angle of 90 to 135 degrees with the running direction of the steel strip; applying a passivation treatment agent with a phosphating barrier function onto the other surface of the steel strip; 4) Phosphating The strip surface sprayed with the phosphating surface conditioning agent is phosphated by high-pressure spraying, the phosphating treatment time is 6 to 12 seconds, the spraying pressure is 5 to 8 bar, and the spraying direction is at an angle of 90 to 135 degrees to the running direction of the strip; 5) Second rinse The strip surface is rinsed with industrial pure water with a conductivity of ≤10μs / cm, and then the surface is squeezed dry after rinsing; 6) Saponification A stearate treatment agent is applied to the surface of the steel strip, and then the surface of the steel strip is purged and wiped with a roller using compressed air, wherein the coating temperature is 70 to 90°C.

5. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 2), the surface of the strip is rinsed by spraying at a pressure of 2 to 4 bar.

6. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 2), the corrosion inhibitor is selected from one or more of sodium phosphate, sodium nitrite, sodium benzoate and sodium silicate.

7. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 3), the passivation treatment agent having the phosphating barrier function is a Zr acid salt passivation treatment agent or a Cr acid salt passivation treatment agent.

8. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 4), the spraying direction is at an angle of 100 to 120° to the running direction of the strip.

9. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 5), the surface of the strip is rinsed by spraying, the spraying pressure is 1 to 4 bar, and the spraying direction is at an angle of 90 to 120 degrees to the running direction of the strip.

10. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 6), the stearate treatment agent is applied by spraying.

11. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance according to claim 4 or 10, characterized in that: In step 6), the stearate in the stearate treating agent is C18 or C16 stearate.

12. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance according to claim 4 or 10, characterized in that: In step 6), the stearate treatment agent is prepared by mixing any one or more of sodium stearate, magnesium stearate, and zinc stearate.

13. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance according to claim 11, characterized in that: In step 6), the stearate treatment agent is prepared by mixing any one or more of sodium stearate, magnesium stearate, and zinc stearate.

14. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 3) and / or step 4), movable baffles are arranged on both sides of the steel strip at a distance of 2 to 6 cm from the edge of the steel strip.

15. The method for manufacturing oil-free steel strip with excellent processability and corrosion resistance as claimed in claim 4, characterized in that: In step 3) and / or step 4), the running speed of the strip steel is 40 to 80 m / min.

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