A method for synergistically lubricating stainless steel calender forming and stainless steel sheet

Abstract

The application provides a stainless steel calendering forming synergistic lubrication treatment method and a stainless steel plate, and belongs to the technical field of metal material plastic forming. The method comprises the following steps: performing laser micro-texturing treatment on a to-be-formed surface of a stainless steel plate to prepare a micro-pit array; coating a layer of composite nano-lubricant on the surface of the treated plate, wherein the lubricant comprises base oil, nano-solid lubricating particles, a surfactant and a polar additive; and finally performing calendering forming on the plate coated with the lubricant. The application also provides a corresponding stainless steel plate, which is provided with a micro-pit array on the surface, and the micro-pit is filled with the composite nano-lubricant. Through the synergistic effect of laser micro-texturing and the composite nano-lubricant, a stable and strong boundary lubrication film is formed at the calendering interface, the ultimate drawing ratio of the stainless steel is significantly improved, the mold wear is reduced, and the surface quality of the formed part is improved.

Description

Technical Field

[0001] This application relates to the field of metal material plastic forming technology, and in particular to a synergistic lubrication treatment method for stainless steel rolling forming. Background Technology

[0002] Stainless steel is widely used in various industrial fields due to its excellent corrosion resistance and mechanical properties. However, when performing extreme plastic forming processes such as deep drawing and long drawing, stainless steel has a high work hardening rate and a large coefficient of friction with the die. This leads to uneven material flow during the forming process, making it prone to forming defects such as cracking, wrinkling, and tearing, which seriously affects product quality and forming efficiency.

[0003] To improve the rolling and forming performance of stainless steel, existing technologies typically employ the method of coating the sheet metal surface with lubricants to reduce friction. For example, some metalworking fluid compositions improve lubrication performance by adding polar additives to the base oil. However, under the high pressure and high temperature environment of extreme rolling forming, relying solely on these traditional lubricating oil films is prone to rupture and failure, failing to provide continuous and stable lubrication. This results in poor lubrication, which not only limits the forming limits of stainless steel (such as the ultimate drawing ratio) but also exacerbates die wear, affecting the surface quality and dimensional accuracy of the final part. Therefore, there is an urgent need for a solution that can maintain efficient and stable lubrication even under extreme operating conditions to overcome the technical bottlenecks in the extreme rolling forming of stainless steel. Summary of the Invention

[0004] The purpose of this application is to provide a synergistic lubrication treatment method for stainless steel rolling forming, which aims to solve the problems in the prior art of stainless steel ultimate rolling forming, such as easy cracking, wrinkling and other forming defects, low forming limit and severe die wear caused by lubrication failure.

[0005] To achieve the above objectives, the present invention provides a synergistic lubrication treatment method for stainless steel rolling forming, comprising the following steps: performing laser microtexturing treatment on the surface of the stainless steel sheet to be formed to prepare a micro-pit array on the surface; coating a layer of composite nano-lubricant on the treated sheet surface, wherein the components of the composite nano-lubricant include: base oil, nano solid lubricating particles, surfactant and polar additive; and rolling the stainless steel sheet coated with the composite nano-lubricant.

[0006] Optionally, the calendering is hot calendering.

[0007] Furthermore, the temperature for hot rolling is 100-200℃.

[0008] Optionally, the calendering is cold calendering.

[0009] In a preferred embodiment of this application, the nano solid lubricating particles are selected from one or more of nano graphite and molybdenum disulfide.

[0010] Optionally, the polar additive is selected from one or more of stearic acid and phosphate esters.

[0011] Furthermore, the area occupancy of the micro-pit array is 5-20%.

[0012] Optionally, the micropits are circular or elliptical in shape.

[0013] Furthermore, the micro-pit is circular in shape, with a diameter of 40-60 μm and a depth of 5-15 μm.

[0014] The present invention also provides a stainless steel sheet, comprising: a stainless steel substrate having a micro-pit array formed on its surface; and a composite nano-lubricant filling the micro-pits of the micro-pit array, wherein the composite nano-lubricant comprises: base oil, nano-solid lubricating particles, surfactant, and polar additive.

[0015] Compared with existing technologies, this application has the following beneficial effects: By performing laser microtexturing treatment on the surface of stainless steel sheets and using a composite nano-lubricant containing base oil, nano-solid lubricating particles, surfactants, and polar additives, the two work synergistically to form a stable and tough boundary lubrication film at the rolling interface, which greatly reduces the coefficient of friction, makes the material flow more uniform, and effectively suppresses the generation of defects such as cracking and wrinkling, thereby significantly improving the ultimate drawing ratio of stainless steel; at the same time, the efficient lubrication and the micro-pit's ability to accommodate abrasive debris significantly reduce the direct contact between the die and the workpiece and abrasive wear, extending the die's service life; in addition, stable lubrication and uniform material flow result in higher surface quality and better dimensional consistency of the final formed parts, which can meet the needs of high-end manufacturing fields. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the process flow of the synergistic lubrication treatment method for stainless steel rolling forming according to an embodiment of this application; Figure 2 A partial cross-sectional schematic diagram of the synergistic lubrication mechanism of the calendering interface provided in the embodiments of this application; Figure 3 This is a schematic diagram showing the comparison effect of the embodiments of this application with the limiting draw ratio (LDR) under different working conditions.

[0018] Explanation of reference numerals in the attached drawings: 10 - Upper mold; 20 - Stainless steel sheet; 21 - Micro-pit; 30 - Composite nano-lubricant; 40 - Lower mold. Detailed Implementation

[0019] To better understand the technical solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the specific embodiments described herein are only for explaining this application and are not intended to limit the scope of protection of this application.

[0020] Example 1 In one embodiment of this application, a synergistic lubrication treatment method for stainless steel rolling is provided. This method involves preparing a specific microstructure on the surface of the stainless steel sheet and using a specially formulated composite nano-lubricant to achieve a synergistic effect during hot rolling, thereby significantly improving the ultimate formability of stainless steel.

[0021] Reference Figure 1 The diagram illustrates the process flow of the method provided in this embodiment. Specifically, the method mainly includes a stainless steel plate pretreatment step S100, a laser microtexturing treatment step S200, a composite nano-lubricant coating step S300, and a rolling forming step S400.

[0022] In the stainless steel plate pretreatment step S100, commercially available SUS304 austenitic stainless steel plate with a thickness of 1mm is selected as the processing object. To ensure the effectiveness of subsequent laser treatment and lubricant coating, the plate surface must be thoroughly cleaned. Specifically, the cut stainless steel plate is placed sequentially in an ultrasonic cleaning tank containing acetone and anhydrous ethanol, and ultrasonic cleaning is performed for 15 minutes in each solvent to completely remove any oil, dust, and other impurities that may be adhering to the plate surface. After cleaning, the plate surface is dried using high-pressure nitrogen and placed in a clean, dry environment for later use.

[0023] Subsequently, in the laser microtexturing process step S200, an array of micropits for storing lubricant and accommodating wear debris is precisely fabricated on the surface of the stainless steel sheet 20 to be formed. (Refer to...) Figure 2 , Figure 2The illustration schematically shows a stainless steel plate 20 with micropits 21. As a specific implementation, this embodiment uses a fiber laser with an output wavelength of 1064 nm. A high-precision galvanometer scanning system controls the focal position of the laser beam to perform ablation processing on the surface of the stainless steel plate 20. During processing, argon gas is introduced as a protective gas to prevent oxidation of the metal surface at high temperatures. The specific process parameters of the laser are set as follows: laser power 20W, pulse frequency 50kHz, and scanning speed 500mm / s. By precisely controlling the above process parameters, circular micropits arranged in a square array can be processed on the surface of the plate. The diameter of each circular micropit is set to 50μm, the depth to 10μm, and the center-to-center distance between adjacent micropits is 150μm. Based on these geometric parameters, the area occupancy of the micropit array can be calculated to be approximately 8.7%. This area occupancy is within the preferred range of 5-20%, ensuring sufficient oil storage without excessively weakening the strength of the substrate. The prepared micro-pits 21 have regular morphology and precise dimensions, which lays the structural foundation for the effective storage and synergistic effect of subsequent lubricants.

[0024] Next, in the composite nano-lubricant coating step S300, a high-performance composite nano-lubricant 30 is prepared and uniformly coated onto the surface of a textured stainless steel sheet 20 (preparing a micro-pit array). The composition of the composite nano-lubricant 30 is carefully designed to achieve a synergistic lubrication effect with the micro-pits 21. Its components, by weight percentage, include: 95.5% base oil, 2% nano-solid lubricating particles, 1% surfactant, and 1.5% polar additives.

[0025] Specifically, in this embodiment, the base oil is a polyalphaolefin synthetic oil with excellent thermal stability and low volatility. The nano-solid lubricating particles are nano-graphite particles with an average particle size of 50 nm. The surfactant is sorbitan monooleate, whose function is to utilize its lipophilic and hydrophilic groups to uniformly disperse the nano-graphite particles in the base oil, preventing aggregation and sedimentation, thereby ensuring the long-term stability of the lubricant system. The polar additive is stearic acid, whose carboxyl group at one end of its molecule has strong polarity, enabling it to preferentially adsorb onto the stainless steel surface during calendering, forming an oriented, dense physical adsorption film.

[0026] The preparation process of composite nano-lubricant 30 is as follows: First, measured amounts of sorbitan monooleate and stearic acid are added to a polyalphaolefin base oil and magnetically stirred at 300 rpm for 30 minutes in a 60°C water bath until the additives are completely dissolved, forming a transparent mixed solution. Then, measured amounts of nano-graphite powder are slowly added to the above solution, and a high-speed shear disperser is used to shear at 5000 rpm for 30 minutes to initially disperse the nanoparticles. Finally, the mixture is transferred to a high-power ultrasonic cell disruptor and ultrasonically dispersed at 400W for 1 hour to further break up any possible nanoparticle agglomerates through ultrasonic cavitation, ultimately obtaining a black, uniform, and stable suspension of composite nano-lubricant 30.

[0027] After preparation, the composite nano lubricant 30 is uniformly sprayed onto the surface of the stainless steel plate 20 that has undergone laser microtexturing treatment using a high-pressure air spray gun, ensuring that all the micro-pits are filled with the composite nano lubricant 30 and a uniform oil film with a thickness of about 5 μm is formed on the surface of the stainless steel plate 20.

[0028] Finally, the rolling forming step S400 is performed. In this embodiment, a hot rolling forming process is used. Specifically, the stainless steel sheet 20 coated with lubricant is placed in a heating furnace and preheated to 150°C. This temperature is within the preferred temperature range of 100-200°C, which helps to reduce the deformation resistance of stainless steel, improve its plasticity, and also promotes the adsorption and film formation of polar additives in the lubricant on the metal surface. After preheating, the sheet is quickly transferred to a 500-ton hydraulic press and formed using a deep drawing die including an upper die 10 and a lower die 40. During the rolling forming process, the punch speed is set to 20 mm / s.

[0029] Reference Figure 2The diagram illustrates the synergistic lubrication mechanism disclosed in this application. During the calendering process, the upper die 10 and lower die 40 apply enormous forming pressure to the stainless steel sheet 20. At the contact interface between the die and the sheet, the lubricating oil film initially covering the surface is partially squeezed out under the enormous pressure. However, the composite nano-lubricant 30 stored in numerous micro-pits 21 acts as a "secondary oil source," continuously replenishing the contact area under pressure, thus ensuring continuous lubrication. Simultaneously, the nano-graphite particles in the lubricant, due to their extremely small size and layered structure, act like microscopic ball bearings at the calendering interface, transforming the sliding friction between the die and the sheet into rolling friction and interlayer slippage, greatly reducing shear stress. Furthermore, the strong and tough adsorption film formed by stearic acid molecules on the metal surface, together with the nano-graphite particles, constructs a composite boundary lubrication film. This composite boundary lubrication film has high load-bearing capacity and low shear strength, effectively isolating the die from direct metal-to-metal contact with the sheet and preventing adhesive wear and scratches. More importantly, the micro-pit 21 structure can effectively capture and contain the tiny abrasive particles that are inevitably generated during the processing, preventing these hard particles from circulating and rolling between the interfaces, causing secondary scratches on the surface of the sheet and the mold.

[0030] Through the synergistic effect of the laser microtexturing and composite nano-lubricant described above, this embodiment achieves an exceptionally superior lubrication effect. Experimental tests show that the ultimate drawing ratio of SUS304 stainless steel sheet processed using this embodiment can be significantly increased from 1.8 under traditional oil lubrication conditions to 2.2. This increased ultimate drawing ratio means the material can withstand greater plastic deformation without cracking, resulting in a significantly improved forming limit. Simultaneously, the formed parts exhibit a high surface finish with no obvious scratches or scuffs. Weighing analysis of the mold wear revealed that, compared to traditional lubrication methods, mold wear was reduced by approximately 40%, significantly extending the mold's service life.

[0031] Example 2 As an optional implementation, this embodiment aims to illustrate that the components of the composite nano-lubricant in the synergistic lubrication treatment method provided in this application have a certain degree of selectivity. By replacing different types of functional components, excellent lubrication effects can also be achieved. The overall process flow of this embodiment is the same as that of Embodiment 1, with the main difference being the lubricant formulation used in the composite nano-lubricant coating step S300.

[0032] In this embodiment, the pretreatment step S100 and the laser microtexturing treatment step S200 of the stainless steel plate are exactly the same as those in Example 1, that is, a circular micro-pit array with a diameter of 50μm, a depth of 10μm and a spacing of 150μm is prepared on the surface of a 1mm thick SUS304 stainless steel plate 20.

[0033] In the composite nano-lubricant coating step S300, this embodiment uses a composite nano-lubricant 30 with a different formulation. The components of this lubricant, by weight percentage, include: 94.5% base oil, 2.5% nano-solid lubricating particles, 1% surfactant, and 2% polar additives. The content of each component can be adjusted as needed to achieve a synergistic lubrication effect; for example, 90-98% base oil and 1-5% nanoparticles.

[0034] Specifically, the base oil is an ester-based synthetic oil, which possesses excellent high-temperature performance and good solubility for additives. The nano-solid lubricating particles are molybdenum disulfide nanoparticles with an average particle size of 80 nm. Molybdenum disulfide is a classic layered solid lubricant, with its layers bound by weak van der Waals forces, making it highly slip-prone and exhibiting an extremely low coefficient of friction under high temperature and pressure. Oleamide is used as the surfactant to ensure uniform dispersion of the molybdenum disulfide nanoparticles in the ester oil. The polar additive is a sulfur-phosphorus phosphate ester, a high-performance extreme pressure additive. Under the high temperature and pressure of the calendering process, the phosphate ester reacts chemically with the stainless steel surface, forming a chemical reaction film composed of iron phosphate, iron sulfide, etc. This chemical reaction film is denser, more wear-resistant, and has a stronger load-bearing capacity compared to a physically adsorbed film.

[0035] The preparation and coating methods of the lubricant are similar to those in Example 1. Oleamide and phosphate ester are dissolved in ester synthetic oil, and then molybdenum disulfide nanoparticles are added. After high-speed shearing and ultrasonic dispersion treatment, a uniform and stable composite nano lubricant 30 is obtained, which is then coated on the surface of the textured plate.

[0036] In the subsequent calendering step S400, the process parameters are the same as in Example 1, i.e., hot calendering is performed at a temperature of 150°C. During the forming process, the micro-pits 21 also serve the functions of oil storage and replenishment. Correspondingly, the lubrication mechanism at the interface becomes a combination of the physical lubrication effect of molybdenum disulfide nanoparticles and the chemical lubrication effect of the chemical reaction film formed by the phosphate ester. These two, together with the ester base oil and the surface microtexture, also construct an efficient and tough lubrication system at the calendering interface.

[0037] Experimental results show that the stainless steel sheet processed using the method of this embodiment can achieve an ultimate drawing ratio of 2.15. Although this value is slightly lower than that of Example 1, it is still a significant improvement compared to the 1.8 of the traditional lubrication method. This result demonstrates the universality of the method of this application, namely, that the nano-solid lubricating particles can be selected from one or more of nano-graphite and molybdenum disulfide, and the polar additives can also be selected from one or more of stearic acid and phosphate esters. Through different combinations of effective components, the beneficial effect of improving the ultimate formability of stainless steel can be achieved.

[0038] Example 3 This embodiment aims to illustrate that the morphology, size, and arrangement of the micro-pit array prepared by the laser microtexturing process step S200 in the method of this application can be optimized to adapt to different stress states and lubrication requirements, thereby further improving the synergistic lubrication effect. The pretreatment, lubricant formulation and coating, and hot calendering steps in this embodiment are the same as those in Embodiment 1. The core difference lies in the parameter setting of the laser microtexturing process step S200.

[0039] In this embodiment, the laser microtexturing process S200 is performed using a femtosecond laser. It is understood that femtosecond lasers have extremely short pulse widths, falling under the category of "cold processing," which can yield microstructures with steeper edges and smaller heat-affected zones.

[0040] In this embodiment, a laser processes an array of densely arranged hexagonal elliptical micropits on the surface of a stainless steel plate 20. Each elliptical micropit has a major axis of 60 μm, a minor axis of 30 μm, and a depth of 12 μm. Compared to a square arrangement, the dense hexagonal arrangement achieves higher coverage at the same pit spacing. In this embodiment, by adjusting the arrangement parameters, the area occupancy of the micropit array is increased to 15%, which remains within the preferred range of 5-20%, thus providing a larger oil storage space.

[0041] In one embodiment, the orientation of the elliptical micro-pits is intentionally controlled during processing so that their major axis is perpendicular to the main direction of material flow during subsequent calendering. For example, when deep drawing a rectangular box-shaped part, the material mainly flows along the length and width directions; in this case, the major axis of the elliptical micro-pits can be arranged perpendicular to these flow directions.

[0042] Its working principle lies in the fact that, compared to isotropic circular micropits, directional elliptical micropits exhibit enhanced hydrodynamic effects in a specific direction. When its major axis is perpendicular to the material flow direction, it can more effectively guide the composite nano-lubricant 30 stored within the pit to the contact area between the mold and the sheet metal that requires the most lubrication, thereby helping to form a thicker hydrodynamic oil film. At the same time, the higher area occupancy also means a more abundant supply of lubricant throughout the calendering process.

[0043] This embodiment uses the exact same composite nano-lubricant formulation and hot calendering process parameters as Example 1. Experimental test results show that, for drawing conditions in a specific direction, the sheet material treated with the process in this embodiment can further increase its ultimate drawing ratio to 2.25, which is slightly better than Example 1. This indicates that by specifically optimizing the morphology, arrangement, and orientation of the microtexture, the synergistic lubrication effect can be further enhanced, thereby achieving a higher forming limit.

[0044] Example 4 This embodiment aims to verify the applicability of the synergistic lubrication treatment method provided in this application under different process conditions, especially its effect under non-hot calendering, i.e., cold calendering forming conditions. The pretreatment step S100, laser microtexturing treatment step S200, lubricant formulation and coating step S300 of this embodiment are exactly the same as those in Example 1. The core difference lies in the process conditions of the calendering forming step S400.

[0045] In this embodiment, the calendering step S400 employs a cold calendering process. Specifically, a stainless steel sheet 20 coated with the composite nano-lubricant 30 described in Example 1 and having a circular micro-pit array on its surface is directly deep-drawn at room temperature (approximately 25°C). Other parameters, such as the hydraulic press, die, and punch speed (20 mm / s), are consistent with those in Example 1.

[0046] Understandably, during cold rolling, the lack of thermal assistance to soften the material makes the deformation resistance and work hardening effect of stainless steel more pronounced, and the requirements for lubrication conditions more stringent. In traditional cold rolling processes, lubrication failure is one of the main causes of forming failure.

[0047] However, even without thermal assistance, the robust boundary lubrication film constructed in this application still plays a crucial role. The lubrication system, synergistically constructed by the oil storage and replenishment functions of the micro-pits 21, the micro-ball effect of the nano-graphite particles, and the strong adsorption film formed by stearic acid, can still effectively reduce friction during cold work hardening, improve the tribological state of the mold-sheet interface, and promote more uniform material flow within the mold, thereby effectively suppressing cracking caused by local stress concentration or wrinkling caused by poor material flow.

[0048] Experimental results show that under cold rolling conditions, the ultimate drawing ratio of SUS304 stainless steel sheet lubricated with conventional machine oil is only 1.6. However, after adopting the synergistic lubrication treatment method of this embodiment, the ultimate drawing ratio can be increased to 1.9. Although the absolute value and improvement of the ultimate drawing ratio are not as significant as those under hot rolling conditions, a significant performance improvement is still achieved compared to existing cold rolling technologies. This result fully demonstrates that the method of this application has broad process applicability, not only showing remarkable effects in the field of hot rolling but also bringing significant technological progress in the field of cold rolling.

[0049] To more intuitively demonstrate the synergistic effects and beneficial benefits of the technical solution in this application, please refer to [link / reference needed]. Figure 3 . Figure 3 It is a bar chart with the horizontal axis representing four different lubrication conditions and the vertical axis representing the limiting drawing ratio measured under hot rolling conditions.

[0050] Operating condition A represents the conventional lubrication condition, which is hot rolling of a smooth stainless steel plate coated with ordinary machine oil without texturing treatment, with a limit drawing ratio of 1.8, serving as a benchmark.

[0051] Condition B represents the laser-textured condition only, where the stainless steel plate undergoes the same laser microtexturing treatment as in Example 1, but without any lubricant applied during rolling (dry friction), and its limiting draw ratio is 1.9. This indicates that the micro-pit structure itself can play a certain role in reducing friction by reducing the contact area and capturing wear debris, but the effect is limited.

[0052] Condition C represents the condition with only composite nano-lubricant, i.e., coating the surface of a smooth stainless steel plate without texture treatment with the same composite nano-lubricant as in Example 1, with a limiting draw ratio of 2.0. This indicates that the lubricant itself has excellent performance, but because the smooth surface cannot effectively maintain the lubricating film, the lubricant is easily extruded under high pressure, resulting in its performance not being fully realized.

[0053] Operating condition D represents the synergistic lubrication condition of this application, which combines laser microtexturing and composite nano-lubricant (as in Example 1), achieving a maximum drawing ratio of 2.2. It is evident that operating condition D significantly outperforms operating conditions A, B, and C. More importantly, its performance improvement (2.2 - 1.8 = 0.4) is greater than the sum of the improvement values ​​of operating condition B (1.9 - 1.8 = 0.1) and operating condition C (2.0 - 1.8 = 0.2) (0.1 + 0.2 = 0.3). This "1+1>2" effect strongly demonstrates the significant synergistic effect between laser microtexturing and composite nano-lubricant. In other words, it is this synergistic effect, rather than a simple superposition of the two technologies, that achieves the breakthrough improvement in the forming limit of stainless steel.

[0054] Accordingly, this application also provides a stainless steel sheet 20 that has undergone synergistic lubrication treatment. The sheet comprises a stainless steel substrate with a pre-defined array of micro-pits 21, such as circular or elliptical micro-pits, formed on its surface. A composite nano-lubricant 30 fills the micro-pits 21 of the micro-pit array and optionally covers the surface of the sheet. As previously mentioned, the components of the composite nano-lubricant 30 may include base oil, nano-solid lubricating particles, surfactants, and polar additives. It is understood that this pre-treated sheet can serve as an intermediate product, directly used in subsequent rolling forming processes, thereby providing convenience to users and helping to ensure the final forming effect.

[0055] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for synergistic lubrication treatment in stainless steel rolling forming, characterized in that, Includes the following steps: Laser microtexturing is performed on the surface of the stainless steel sheet to be formed in order to prepare a micro-pit array on the surface; A composite nano-lubricant is coated on the surface of the treated sheet material. The components of the composite nano-lubricant include: base oil, nano solid lubricating particles, surfactant, and polar additives. The stainless steel sheet coated with the composite nano lubricant is rolled into shape.

2. The method according to claim 1, characterized in that, The calendering process is hot calendering.

3. The method according to claim 2, characterized in that, The temperature for hot rolling is 100-200℃.

4. The method according to claim 1, characterized in that, The calendering process is a cold calendering process.

5. The method according to claim 1, characterized in that, The nano-solid lubricating particles are selected from one or more of nano-graphite and molybdenum disulfide.

6. The method according to claim 1, characterized in that, The polar additive is selected from one or more of stearic acid and phosphate esters.

7. The method according to claim 1, characterized in that, The area occupancy of the micro-pit array is 5-20%.

8. The method according to claim 1, characterized in that, The micro-pits are circular or elliptical in shape.

9. The method according to claim 1, characterized in that, The micro-pits are circular in shape, with a diameter of 40-60 μm and a depth of 5-15 μm.

10. A stainless steel sheet, characterized in that, include: A stainless steel substrate, wherein a micro-pit array is formed on the surface of the stainless steel substrate; as well as A composite nano lubricant is filled in the micro-pits of the micro-pit array, and the components of the composite nano lubricant include: base oil, nano solid lubricating particles, surfactant and polar additive.

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