Stainless steel CO2 deep treatment high-brightness surface finishing process

Abstract

The invention provides a stainless steel CO2 deep treatment high-brightness surface finishing process. The stainless steel CO2 deep treatment high-brightness surface finishing process comprises the following steps: a) adopting supercritical CO and a biological surfactant for synergistic degreasing; b) realizing transition from rough polishing to fine polishing through gradient dry ice spraying; c) performing pulse laser micro-melting repair under the protection of a CO air curtain; and d) generating the nanoscale CrO film by utilizing supercritical CO electrochemical passivation. Through the supercritical CO synergistic degreasing, gradient dry ice polishing and laser repairing processes, submicron surface finishing is achieved while the oxidation reaction is inhibited, and the method has the technical advantages that the machining efficiency is improved, the surface uniformity is enhanced, and the environmental load is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel surface treatment, and particularly to a high-brightness surface finishing process for deep treatment of stainless steel with CO2. Background Art

[0002] The core of using carbon dioxide (CO2) as a polishing medium lies in its phase change characteristics and recycling mechanism. Existing technologies propose to trigger the phase change of an aqueous solution of carbon dioxide (CO2) through frictional heat to generate gaseous CO to form a negative pressure system, and utilize the pressure difference to achieve real-time adsorption of metal debris. In this process, the recycling efficiency of CO depends on the heat conduction design of the solution chamber and the extension conduit, and this thermodynamic control can reduce medium loss. Existing technologies have verified that the CO cooling system can reduce the processing temperature, indirectly supporting its effectiveness in thermal management. However, the traditional CO polishing process has problems of low efficiency and poor consistency, and it is difficult to meet the requirements of high-precision surface treatment. Especially in the high-brightness surface treatment of stainless steel materials, it is difficult for traditional methods to achieve a uniform surface finishing effect, and oxidation and surface defects are easily generated during the treatment process. In addition, the existing technologies have limited effect on removing grease during the treatment process, and it is difficult to achieve the ideal surface cleanliness. In view of the above problems, the existing technologies urgently need to be improved. Summary of the Invention

[0003] In order to solve the above technical problems, the present application provides a high-brightness surface finishing process for deep treatment of stainless steel with CO2, which has the technical advantages of improving surface treatment efficiency, enhancing finishing uniformity, suppressing oxidation defects, and achieving environmental protection and cleaning.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present application provides a high-brightness surface finishing process for deep treatment of stainless steel with CO2, and the technical solution is as follows:

[0006] It includes the following steps: a) synergistic degreasing using supercritical CO2 and a biosurfactant; b) achieving the transition from rough polishing to fine polishing through gradient dry ice spraying; c) performing pulsed laser micro-melting repair under the protection of a CO2 gas curtain; d) generating a nanoscale CrO film by electrochemical passivation using supercritical CO2.

[0007] Further, the present application also proposes that step a) includes: immersing the workpiece in a supercritical CO2 reaction kettle, adding 0.5% - 2% of a bio-based surfactant, and circulating for 10 - 15 minutes to dissolve grease.

[0008] Further, the present application also proposes that the temperature of the reaction kettle is 35°C and the pressure is 10 MPa.

[0009] Further, the present application also proposes that the surfactant is sucrose ester.

[0010] Furthermore, the present application also proposes that step b) includes: rough polishing stage: using dry ice particles with a particle size of 2 - 3 mm, a gas pressure of 8 - 10 bar, and a spraying angle of 60° to remove macroscopic defects; fine polishing stage: switching to dry ice particles with a particle size of 0.5 - 1 mm, a gas pressure of 4 - 6 bar, and a spraying angle of 30°, so that the surface roughness Ra of the workpiece is reduced from 1.2 μm to 0.4 μm.

[0011] Furthermore, the present application also proposes that step b) further includes: supercritical CO₂ composite polishing: using supercritical CO₂ at 40°C and 15 MPa, as well as a 0.1% fluorocarbon surfactant and a 5 nm silica abrasive suspension, increasing the pressure to 20 MPa at a rate of 0.5 MPa / s and maintaining it for 5 minutes to allow the abrasive to penetrate; then reducing the pressure at a rate of 1 MPa / 2 s, and using the pressure sudden change to peel the surface layer.

[0012] Furthermore, the present application also proposes that step c) includes, after dry ice spraying, using pulsed fiber laser to scan the surface, and using a CO₂ gas curtain to inhibit oxidation, achieving micron-level remelting and eliminating subsurface cracks.

[0013] Furthermore, the present application also proposes that the pulsed fiber laser uses a pulsed fiber laser with a wavelength of 1064 nm, a power of 50 W, and a pulse width of 10 ns.

[0014] Furthermore, the present application also proposes that step d) includes using the workpiece as the anode, applying a voltage of 2 V for 5 minutes in a supercritical CO₂ electrolyte to promote the formation of a dense CrO passivation film on the surface.

[0015] Furthermore, the present application also proposes that step d) further includes, before the electrochemical reaction, keeping the workpiece in a supercritical state for 10 minutes, using the low surface tension property of CO₂ to completely remove moisture, and avoiding oxidation caused by traditional drying.

[0016] As can be seen from the above, a high-brightness surface finishing process for deep treatment of stainless steel CO provided by the present application realizes sub-micron-level surface finishing while suppressing the oxidation reaction through supercritical CO₂ synergistic degreasing, gradient dry ice polishing, and laser repair processes, and has the technical advantages of improving processing efficiency, enhancing surface uniformity, and reducing environmental load. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a process flow chart of a high-brightness surface finishing process for deep treatment of stainless steel CO of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the accompanying drawings, where like or similar reference numerals designate like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

[0019] In the description of the present invention, it should be understood that if there are terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the accompanying drawings. This is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined.

[0020] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "mount", "connect", and "couple" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection. It may be a mechanical connection or an electrical connection. It may be directly connected or indirectly connected through an intermediate medium, and it may be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0021] As Figure 1 shown, in the prior art, carbon dioxide (CO2) as a polishing medium mainly relies on its phase change characteristics and recycling mechanism. The traditional process triggers the phase change of an aqueous carbon dioxide (CO2) solution through frictional heat, and uses the generated gaseous carbon dioxide (CO2) to form a negative pressure system to adsorb metal debris. However, the heat conduction design of this process requires maintaining a large temperature difference to ensure the recycling efficiency, resulting in a high medium loss. Although the existing cooling system can reduce the processing temperature, it cannot effectively solve the contradiction between the polishing efficiency and the surface treatment consistency. Especially when processing complex surfaces, local over-polishing or under-polishing phenomena are likely to occur.

[0022] To address the above problems, it is found that the limitations of traditional processes stem from a single phase change control mode, which cannot balance the energy requirements in different processing stages. Through analysis, it is found that the low surface treatment efficiency is directly related to pollutant residues, improper kinetic energy distribution, oxide layer formation, and the quality of the passivation film. Thus, a phased regulation concept is generated: first, establish a pollution-free pretreatment environment; second, establish a dynamic kinetic energy distribution mechanism; third, introduce oxidation inhibition means; and finally, construct controllable passivation reaction conditions. Based on this, it is proposed to combine the characteristics of supercritical fluids with gradient kinetic energy control to form a multi-stage collaborative processing scheme.

[0023] Therefore, this application proposes a high-brightness surface finishing process for deep treatment of stainless steel with carbon dioxide (CO2), including the following steps: synergistic degreasing using supercritical carbon dioxide (CO2) and a biosurfactant; achieving the transition from rough polishing to fine polishing through gradient dry ice jetting; pulsed laser micro-melting repair under the protection of a carbon dioxide (CO2) gas curtain; and electrochemically passivating with supercritical carbon dioxide (CO2) to generate a nanoscale chromium trioxide film.

[0024] Among them, the synergistic degreasing of supercritical carbon dioxide (CO2) and a biosurfactant means using the characteristics of supercritical fluids, which have both gas diffusivity and liquid solubility, and cooperating with the emulsifying effect of the biosurfactant. Specifically, it can be achieved by placing the workpiece in a high-pressure reaction kettle and adding a biodegradable surfactant. Gradient dry ice jetting means adjusting the kinetic energy parameters according to the processing stage, and specifically, it can be implemented by changing the combination of dry ice particle size and jetting pressure. Carbon dioxide (CO2) gas curtain protection means establishing an inert gas covering layer, and specifically, it can be achieved by forming a local isolation environment through a circumferential gas nozzle. Pulsed laser micro-melting repair means eliminating microscopic defects through the action of a short-time high-energy light beam, and specifically, it can be implemented using nanosecond laser pulses. Supercritical carbon dioxide (CO2) electrochemical passivation means constructing an electrochemical reaction environment in a non-aqueous medium, and specifically, the growth process of the passivation film can be controlled by adjusting the voltage parameters.

[0025] Specifically, in the pretreatment stage, the high permeability of supercritical carbon dioxide (CO2) is used to remove surface pollutants, providing a clean substrate for subsequent processing. In the polishing stage, the surface topography is gradually optimized through kinetic energy gradient adjustment. The rough polishing stage focuses on removing macroscopic defects, and the fine polishing stage focuses on reducing the surface roughness. In the repair stage, subsurface damage is eliminated through precise energy input in an inert atmosphere to avoid secondary oxidation. In the passivation stage, a uniform and dense oxide layer is formed in a non-aqueous environment to improve the surface corrosion resistance. Each stage forms a process closed-loop through the conversion of the medium state. The supercritical fluid acts both as a processing medium and as a reaction carrier, achieving the dual functions of energy utilization and surface modification.

[0026] Compared with existing technologies, traditional methods rely on a single phase change process to achieve debris adsorption, while this solution achieves medium function conversion through supercritical state regulation, giving full play to the physical properties of carbon dioxide (CO2) in the stages of degreasing, polishing, repair, and passivation. The thermal management of existing processes requires a complex temperature control system. This solution uses the pressure sensitivity of supercritical fluids to simplify control parameters. Traditional passivation processes are easily affected by moisture. This solution avoids hydrolysis side reactions through a non-aqueous electrochemical environment. Existing laser treatments are prone to surface oxidation. This solution maintains the intrinsic state of the metal through in-situ air curtain protection.

[0027] Through the above technical scheme, this application realizes the seamless connection of the surface treatment process and effectively controls the interface reaction conditions at each stage. The degreasing process avoids the contamination of subsequent processes by organic solvent residues, gradient polishing ensures the continuous optimization of surface morphology, the inert protection environment ensures the metallurgical quality of the repair layer, and supercritical passivation forms a uniform nano-protective layer. The controllable adjustment of process parameters adapts to the processing requirements of stainless steel of different materials, and the medium recycling rate of the overall process is significantly improved, obtaining a stainless steel surface with high finish and corrosion resistance.

[0028] The present application further proposes a technical solution of immersing the workpiece in a supercritical carbon dioxide (CO2) reactor, adding a bio-based surfactant and performing a circulation treatment.

[0029] Among them, the supercritical carbon dioxide (CO2) reactor refers to a closed container that can maintain carbon dioxide (CO2) in a supercritical state. Specifically, it can be achieved by a reaction device with a temperature and pressure joint control system. This state enables carbon dioxide (CO2) to have both gas permeability and liquid solubility. Bio-based surfactants refer to amphiphilic substances derived from natural raw materials. Specifically, they can be achieved by sucrose ester compounds, whose hydrophilic and hydrophobic structures can directionally wrap oil molecules. The cycle processing time refers to the duration of the periodic flow of the fluid in a closed system. Specifically, it can be achieved by using a variable frequency pump to drive the fluid to form turbulence, ensuring that the dissolved substances continue to detach from the surface as the fluid moves.

[0030] Specifically, the workpiece is physically wetted by a highly permeable fluid in a supercritical carbon dioxide (CO2) environment, and the grease in the surface micropores is fully contacted. The bio-based surfactant molecules spontaneously form micelle structures in the supercritical fluid, and the hydrophobic ends are embedded in the oil molecules to form inclusions. During the dynamic circulation process, the micelles encapsulating the grease migrate to the separation device with the fluid, allowing the contaminants to be separated from the workpiece surface. The processing time is set to a period in which the fluid completes more than five full cycles to ensure that the residual substances in the surface microstructure are completely removed.

[0031] Compared with the prior art, the traditional process requires multiple water washing steps after soaking in organic solvents, which easily forms a solvent residue film on the surface. This solution utilizes the complete volatility of supercritical carbon dioxide (CO2), which automatically vaporizes and detaches from the surface after decompression, without the need for additional cleaning steps. The bio-based surfactant can be recovered by phase separation by adjusting the pressure after degreasing, avoiding subsequent processing problems caused by surfactant residues in the traditional process.

[0032] Through the above technical solution, this application realizes a solvent-free degreasing process, effectively eliminating the interference of surface residues on the finishing process. After the grease is removed, there is no chemical adsorption layer on the surface, providing a clean substrate for subsequent polishing treatment and avoiding the uneven polishing phenomenon caused by incomplete degreasing in the traditional process.

[0033] This application further proposes to control the temperature of the reaction kettle at 35°C and the pressure at 10 MPa.

[0034] Among them, the temperature of 35°C refers to the lowest temperature threshold required for the formation of supercritical carbon dioxide (CO2), which can be specifically achieved by using a heating jacket with temperature feedback control. This temperature not only ensures that carbon dioxide (CO2) enters the supercritical state but also avoids the destruction of the molecular structure of the bio-surfactant due to high temperature. Among them, the pressure of 10 MPa refers to the critical pressure range for maintaining the stable flow of supercritical carbon dioxide (CO2), which can be specifically achieved by adjusting the output flow of the high-pressure pump through a proportional-integral-derivative control algorithm. This pressure reduces the load on the equipment sealing system while ensuring fluid permeability.

[0035] Specifically, during the degreasing process assisted by the bio-surfactant, the temperature is controlled at a level slightly higher than the critical temperature of carbon dioxide (CO2), enabling carbon dioxide (CO2) to maintain high diffusivity in the supercritical state, while avoiding protein denaturation and inactivation of the surfactant caused by excessive temperature. The pressure parameter is set to about twice the critical pressure value, which not only maintains the stable phase state of the supercritical fluid but also controls the fluid density in the optimal range for grease dissolution efficiency. The synergistic effect of these two parameters enables the bio-surfactant molecules to be fully dispersed in supercritical carbon dioxide (CO2), adsorbing grease molecules through polar groups, and simultaneously stripping the grease from the metal surface using the strong penetration ability of the supercritical fluid.

[0036] Compared with the prior art, the traditional supercritical degreasing process usually uses a temperature above 40°C and a pressure above 15 MPa to accelerate the reaction rate, but this will lead to a significant increase in equipment energy consumption and attenuation of surfactant activity. By optimizing the temperature-pressure combination, while ensuring the degreasing efficiency, it not only avoids the damage to biological reagents caused by high temperature but also reduces the safety risk of high-pressure vessels.

[0037] Through the above technical solutions, the present application realizes the synergistic optimization of the preservation of biosurfactant activity and the supercritical fluid degreasing efficiency. While achieving efficient removal of grease, the operating energy consumption of the reaction system is controlled within the safe threshold range of the equipment, solving the contradiction that it is difficult to balance the degreasing effect and operating cost in the traditional process.

[0038] The present application further proposes a technical solution of using sucrose esters as surfactants in the supercritical carbon dioxide (CO2) degreasing process.

[0039] Among them, sucrose esters refer to bio-based surface active substances formed by the esterification reaction of natural sucrose and fatty acids. The range of their hydrophilic-lipophilic balance values matches the solvent characteristics of supercritical carbon dioxide (CO2), and can form a stable microemulsion system on the stainless steel surface. Among them, the hydroxyl group refers to multiple polar functional groups contained in the sucrose molecular structure, which generate directional adsorption with carbon dioxide (CO2) molecules through intermolecular forces, enhancing the ability to encapsulate grease. Among them, synthetic surfactants refer to ionic surface active substances containing sulfonic acid groups or sulfate groups prepared by chemical synthesis methods, and their molecular structures have poor compatibility with supercritical carbon dioxide (CO2).

[0040] Specifically, sucrose esters maintain a stable configuration of the molecular chain in the supercritical carbon dioxide (CO2) environment. The hydrophobic end combines with the grease on the stainless steel surface to form a micelle structure, and the hydrophilic end forms a weak hydrogen bond network with carbon dioxide (CO2) molecules through hydroxyl groups. This mechanism enables the rapid peeling of grease from the metal matrix surface, while avoiding the charge aggregation phenomenon on the metal surface caused by ionic surfactants. During the process implementation, the biodegradable characteristics of sucrose esters enable them to be harmlessly treated through pressure reduction separation after completing the degreasing function.

[0041] Compared with the prior art, traditional processes mostly use synthetic surfactants such as sodium dodecylbenzenesulfonate. The strong polar groups in their molecular structures are prone to charge adsorption with the metal surface, resulting in difficult complete removal of residues after degreasing. Moreover, the petroleum-based raw materials of synthetic surfactants are prone to molecular chain breakage in the supercritical environment, which not only affects the degreasing efficiency but also produces harmful decomposition products.

[0042] Through the above technical solutions, the present application realizes the molecular-level adaptation of the degreasing agent and the supercritical carbon dioxide (CO2) treatment process, eliminating the residue of harmful chemicals while ensuring the grease removal efficiency. This choice effectively maintains the dynamic balance of the two-phase interface during the treatment process, avoids secondary pollution on the metal surface, and the treated waste liquid can be harmlessly treated through natural degradation.

[0043] The present application further proposes to use dry ice particles with a particle size of 2 to 3 mm in the rough polishing stage, control the air pressure at 8 to 10 bar, and set the spraying angle at 60 degrees to remove macroscopic defects; in the fine polishing stage, switch to dry ice particles of 0.5 to 1 mm, adjust the air pressure to 4 to 6 bar, and adjust the spraying angle to 30 degrees, so that the surface roughness of the workpiece is reduced from Ra 1.2 μm to Ra 0.4 μm.

[0044] Among them, the particle size of the dry ice particles refers to the physical size of solid carbon dioxide (CO2), which can be specifically achieved by using different specifications of dry ice crushing equipment. The particle size difference directly affects the impact kinetic energy and the acting area. The air pressure range refers to the output pressure of the compressed air system, which can be specifically controlled in stages by a pressure regulating valve. Different pressure levels correspond to different impact intensities. The spraying angle refers to the incident angle between the dry ice particle flow and the workpiece surface, which can be specifically adjusted by a multi-degree-of-freedom robotic arm to change the nozzle direction. The angle change can change the contact trajectory between the particles and the surface.

[0045] Specifically, in the rough polishing stage, a strong impact kinetic energy is formed by larger particles and higher air pressure. Combining with the tangential force generated by the 60-degree inclined spraying, the macroscopic defects on the surface are quickly peeled off. After entering the fine polishing stage, the smaller particles produce uniform coverage at a lower air pressure. The 30-degree incident angle increases the proportion of the vertical force of the particles. Combining with the low kinetic energy characteristics of the fine particles, the surface undulation height is gradually reduced. During the parameter adjustment process of the two stages, a dynamic energy gradient is formed through the coordinated changes of the particle size, air pressure, and angle, avoiding the energy mutation caused by a single parameter in the traditional process, so as to achieve a smooth transition of the roughness while ensuring the defect removal efficiency.

[0046] Compared with the prior art, the traditional carbon dioxide (CO2) polishing process usually uses a fixed particle size and a constant pressure, resulting in residual micro-cracks in the rough polishing stage and the need to repeatedly process the same area in the fine polishing stage. This solution forms a complementary effect between rough polishing and fine polishing through phased parameter regulation. The high impact energy in the rough polishing stage is concentrated on removing macroscopic defects, and the low impact energy in the fine polishing stage avoids secondary damage to the processed area. At the same time, the gradient parameter change eliminates the processing interruption caused by the need to stop the machine to adjust the equipment in the traditional process.

[0047] Through the above technical solutions, the present application effectively solves the problems of low surface treatment efficiency and discontinuous transition caused by a single parameter in the traditional polishing process. By adjusting the dry ice particle size, air pressure, and spraying angle in stages, after quickly removing macroscopic defects in the rough polishing stage, the fine polishing stage immediately covers the processed area with more refined parameters, avoiding repeated processing or surface damage caused by energy mismatch in the traditional process. At the same time, the parameter gradient change ensures that the surface roughness continuously decreases, making the final surface quality uniform.

[0048] The present application further proposes to add a supercritical composite polishing step in the transition stage from rough polishing to fine polishing. By using supercritical carbon dioxide (CO2) medium under specific temperature and pressure conditions, combined with a suspension formed by a fluorocarbon surfactant and nanoscale silica abrasive, abrasive penetration and surface layer stripping are achieved through staged pressure regulation.

[0049] Among them, supercritical carbon dioxide (CO3) refers to carbon dioxide (CO2) fluid above the critical point, which can be specifically achieved by adjusting the temperature above 31 °C and the pressure above 7.4 MPa. It has both the high diffusivity of a gas and the strong dissolving ability of a liquid. A fluorocarbon surfactant refers to an amphiphilic molecule containing a fluorinated chain segment, which can be specifically realized by using perfluorooctane sulfonate compounds. It has an interfacial tension characteristic lower than that of conventional surfactants. Nanoscale silica abrasive refers to silica particles with a particle size less than 100 nanometers, which can be specifically prepared by the sol-gel method. The surface hydroxyl groups thereof can form a stable dispersion system with the fluorocarbon surfactant. The gradient pressure increase process refers to increasing the system pressure at a constant rate, which can be specifically achieved by a computer-controlled hydraulic servo system. This operation mode can avoid abrasive agglomeration caused by sudden pressure changes. The rapid pressure reduction process refers to changing the pressure in a stepwise sudden drop manner, which can be specifically achieved by a solenoid valve-linked pressure relief device. The phase change expansion of the supercritical fluid generates a mechanical peeling force.

[0050] Specifically, a supercritical carbon dioxide (CO2) environment is established in a closed reaction vessel, and the medium is maintained in a highly diffusive state through a constant temperature circulation device. When the suspension formed by the fluorocarbon surfactant and the nano-abrasive is injected, the low interfacial tension characteristic of the surfactant can reduce the contact angle between the abrasive and the metal surface, promoting the spreading of the abrasive in the microscopic pores. During the gradient pressure increase process, the permeability of the supercritical fluid increases exponentially with the increase in pressure, pushing the abrasive into the subsurface defect area of the material. During the high-pressure maintenance stage, the swelling effect of supercritical carbon dioxide (CO2) on the metal matrix enables the abrasive to have molecular-level contact with the defect interface. Subsequently, the rapid pressure reduction operation triggers the instantaneous gasification of the supercritical fluid, and the shear stress generated by the volume expansion acts on the interface between the abrasive and the matrix, realizing the selective stripping of the surface residues.

[0051] Compared with the prior art, traditional carbon dioxide (CO2) polishing relies on mechanical impact under a single pressure condition and cannot achieve effective penetration of abrasives into micro-defects. The prior art uses a constant pressure maintenance method, and the abrasives only act on the surface protrusions. In contrast, the present invention establishes a complete action chain of abrasive transportation - penetration - stripping through a dynamic pressure cycle. The prior art does not introduce a surfactant-assisted dispersion mechanism, resulting in insufficient utilization rate of abrasives. The present invention utilizes the interface regulation function of fluorocarbon surfactants to form a stable dispersion system of nano-abrasives in a supercritical medium. The pressure release process of the prior art lacks controllability, while the present invention realizes directional stripping by using the mechanical energy generated by supercritical phase change through precise control of the pressure reduction rate.

[0052] Through the above technical solutions, the present application realizes the effective penetration of nano-abrasives into the sub-surface defect area of metals, eliminating the phenomena of local over-polishing or under-polishing caused by uneven abrasive distribution in traditional polishing processes. The controllable stripping force generated by the supercritical fluid phase change can synchronously remove loose abrasives and oxidation residues on the surface layer, avoiding multiple cleaning processes. This pressure cycle mechanism enables the abrasives to form a self-sharpening effect at the microscale, maintaining the stability of the polishing process. The synergistic effect of surfactants and supercritical media significantly improves the utilization efficiency of abrasives and reduces the replenishment frequency of process consumables.

[0053] The present application further proposes a technical solution that after dry ice spraying, the surface is scanned by a pulsed fiber laser, a CO gas curtain is used to inhibit oxidation, and micron-level remelting is achieved to eliminate sub-surface cracks.

[0054] Among them, scanning the surface with a pulsed fiber laser means rapidly melting the surface layer of the material through laser pulses with high energy density, which can be specifically achieved by using a laser with characteristics of short pulse width and high peak power. By controlling the laser action time and energy distribution, controllable micro-area remelting is generated on the surface layer of the material. Inhibiting oxidation with a CO gas curtain means forming a covering layer in the processing area using high-purity carbon dioxide (CO2) gas, which can be specifically achieved by forming a directional flowing gas barrier through a surrounding gas nozzle. The oxidation reaction of the metal surface is prevented by isolating oxygen from contacting the high-temperature area. Eliminating sub-surface cracks through micron-level remelting means enabling the surface layer of the material to undergo a melting and re-solidification process, which can be specifically achieved by precisely controlling the laser energy parameters and scanning path, and using the flow of liquid metal to fill micro-defects.

[0055] Specifically, this solution achieves a synergistic effect through the optimized combination of process timing. After the surface is cleaned by dry ice jetting, laser scanning is immediately carried out. The low-temperature environment remaining from the dry ice process is utilized to reduce the heat accumulation during laser processing. The instantaneous energy input of the pulsed laser enables the surface layer of the material to quickly reach the melting temperature, realizing local microzone phase transformation while keeping the matrix temperature stable. The carbon dioxide (CO2) gas protection layer continuously covers the processing area during the laser action. By the gas molecule displacement effect, the oxygen partial pressure is reduced, and at the same time, a dynamic air flow is formed on the surface of the molten pool to take away heat. During the remelting process, the microcracks existing in the subsurface of the material are self-healed under the action of surface tension in the molten state, and a dense microstructural organization is formed during the solidification and crystallization process. This technical solution, through the dynamic balance of energy input and environmental protection, eliminates defects while avoiding the expansion of the heat-affected zone and surface oxidation.

[0056] Compared with the existing technology, the traditional laser repair process does not consider the synergistic effect of the previous process and lacks an effective gas protection mechanism, resulting in an easy generation of an oxide layer and residual thermal stress cracks on the surface after processing. In the existing technology, carbon dioxide (CO2) is mainly used for cooling and debris adsorption, and its antioxidant protection function in high-temperature processing has not been developed. This solution creatively integrates three process links: dry ice pretreatment, pulsed laser remelting, and gas curtain protection. It utilizes the surface state formed by the previous process to optimize the laser energy conduction efficiency, and at the same time expands the protection function of carbon dioxide (CO2) from physical cleaning to high-temperature metallurgical process control, forming a complete surface defect repair technology chain.

[0057] Through the above technical solution, this application effectively inhibits the surface oxidation reaction during the laser processing process, eliminating the problem of surface quality deterioration caused by the formation of an oxide layer in the traditional process. At the same time, the subsurface microcracks are filled through micron-level remelting, avoiding the stress concentration phenomenon caused by defect residues. This technical solution realizes the overall improvement of the metallurgical quality of the metal surface while ensuring the repair accuracy, providing an ideal substrate condition for subsequent passivation treatment.

[0058] This application further proposes a pulsed fiber laser with a wavelength of 1064 nm, a power of 50 W, and a pulse width of 10 ns.

[0059] Among them, the pulsed fiber laser refers to a processing method that periodically releases high-energy light beams. Specifically, a laser using ytterbium-doped fiber as the gain medium can be used to achieve it, and its pulse characteristics can realize instantaneous energy input.

[0060] Among them, a wavelength of 1064 nm refers to the near-infrared band output by the laser. Specifically, an Nd:YAG crystal can be used as the active medium to achieve it. This wavelength can match the light energy absorption characteristics of the stainless steel material surface.

[0061] Among them, a power of 50W refers to the average power level output by the laser, which can be specifically achieved by adjusting the pump current and modulation frequency. This power range can ensure the formation of the molten pool while avoiding overheating of the substrate.

[0062] Among them, a pulse width of 10ns refers to the duration of a single laser pulse, which can be specifically achieved by controlling the Q value of the resonant cavity using an electro-optic modulator. The short pulse width can reduce the heat conduction time and thus narrow the heat affected zone.

[0063] Specifically, when a laser beam with a wavelength of 1064nm acts on the stainless steel surface, its energy is selectively absorbed by the metal surface layer to form a local micro-melting area. The setting of a power of 50W enables the control of the molten pool depth and avoids substrate deformation caused by excessive energy. The short pulse mode with a pulse width of 10ns realizes rapid melting and solidification of the material through instantaneous high-energy impact, effectively suppressing heat diffusion. Under the protection of the CO gas curtain, the contact with oxygen is blocked during the dynamic solidification process of the molten pool, and the oxidation reaction is inhibited. At the same time, the transient heat input of the short pulse fills and repairs the subsurface micro-cracks during the remelting process, and the surface grains are refined due to rapid cooling, ultimately achieving an improvement in surface integrity.

[0064] Compared with the prior art, the traditional laser repair process uses continuous laser or long pulses in the millisecond level, resulting in an increase in the thickness of the oxide layer and an expansion of the heat affected zone due to high heat input. However, in this solution, through the synergistic effect of nanosecond-level short pulses, specific wavelength, and power, combined with gas curtain protection, a balance between heat input and oxidation inhibition is achieved. The prior art relies on a single cooling system for temperature control and cannot solve the problems of oxidation and subsurface defects simultaneously. This solution, through the optimization of laser parameters and the combined use of protective gas, maintains the surface cleanliness while repairing defects.

[0065] Through the above technical solution, this application solves the problems of insufficient control of the oxidation reaction and excessive heat affected zone during the laser micro-melting process, realizes the elimination of subsurface cracks and the optimization of the surface grain structure, and finally obtains a stainless steel surface with high integrity.

[0066] This application further proposes using the workpiece as the anode, applying a voltage in a supercritical carbon dioxide (CO2) electrolyte to promote the formation of a dense chromium oxide passivation film on the surface. Before the electrochemical reaction, the workpiece is maintained in the supercritical state for a certain period of time, and the low surface tension characteristic of carbon dioxide (CO2) is used to remove moisture.

[0067] Among them, the supercritical carbon dioxide (CO2) electrolyte refers to an ionic conduction medium formed by dissolving an electrolyte in a carbon dioxide (CO2) fluid system where the temperature and pressure exceed the critical point. Specifically, it can be achieved by dissolving a solution containing sodium nitrate in supercritical carbon dioxide (CO2), and this medium enters the metal micro-porous structure through osmosis. Maintaining the supercritical state means maintaining carbon dioxide (CO2) above the critical temperature and critical pressure in the reaction kettle, which can be specifically achieved through the coordinated control of a pressure pump and a heating device. Carbon dioxide (CO2) under this state has the dual characteristics of a gas and a liquid. The low surface tension characteristic of carbon dioxide (CO2) means that the surface tension value of supercritical carbon dioxide (CO2) is significantly lower than that of liquid water, specifically manifested as a surface tension lower than 5 mN / m, and this characteristic enables it to effectively displace the water molecules adsorbed on the metal surface.

[0068] Specifically, after the workpiece is placed in a closed reaction vessel, carbon dioxide (CO2) is pressurized to the supercritical state and maintained for a certain period of time. At this time, the low surface tension of carbon dioxide (CO2) enables it to penetrate into the micro-pores on the metal surface and completely displace and discharge the residual moisture. Subsequently, in the electrolyte environment maintaining the supercritical state, by applying a voltage, the chromium element in the stainless steel substrate undergoes an anodic oxidation reaction. Carbon dioxide (CO2) as the reaction medium not only provides an ion transport channel but also ensures the uniform growth of the chromium oxide film layer by suppressing side reactions. The supercritical state treatment in the pretreatment stage replaces the traditional drying process, eliminating both the pre-oxidation risk caused by high-temperature treatment and the surface damage caused by mechanical water removal.

[0069] In some specific embodiments, the time in the pre-treatment stage of the electrochemical reaction can be from 10 minutes to 15 minutes, and the voltage parameter can be in the range of 1.5 V to 3 V. The electrolyte composition can be a solution containing nitrate, and the critical parameters of carbon dioxide (CO2) can be controlled in the range of a temperature of 31 °C to 40 °C and a pressure of 7.39 MPa to 20 MPa.

[0070] Compared with the prior art, when the traditional process uses hot air drying or vacuum dehydration to treat the metal surface, the high-temperature environment is likely to cause premature oxidation of chromium elements, resulting in a loose structure of the passivation film. However, in this solution, through the physical displacement effect of supercritical carbon dioxide (CO2), complete removal of moisture can be achieved at room temperature, avoiding the negative impact of thermal oxidation on the quality of the passivation film. At the same time, supercritical carbon dioxide (CO2) as the reaction medium can effectively block the contact with oxygen and provide an oxygen-free environment for the anodic oxidation reaction.

[0071] Through the above technical solution, this application realizes the passivation treatment of the metal surface in a water-free environment, overcoming the pore defects of the film layer caused by residual moisture in the traditional process. The formed chromium oxide passivation film has a continuous and dense structural feature, significantly improving the corrosion resistance of the stainless steel workpiece.

[0072] The present application further proposes to place the workpiece in a supercritical state for a certain period of time before the electrochemical reaction, and utilize the low surface tension property of carbon dioxide (CO₂) to completely remove moisture.

[0073] Among them, the supercritical state refers to the physical state in which carbon dioxide (CO₂) is above the critical temperature and critical pressure. Specifically, it can be achieved by adjusting the temperature of the reaction kettle to above 31 °C and the pressure to above 7.38 MPa. This state enables carbon dioxide (CO₂) to have both gas diffusivity and liquid solubility.

[0074] Among them, the low surface tension property means that the surface tension value of supercritical carbon dioxide (CO₂) is significantly lower than that of conventional liquids. Specifically, by maintaining supercritical conditions, its surface tension can be reduced to about 0.1 mN / m magnitude. This property enables it to penetrate the microscopic pore structure on the surface of the workpiece.

[0075] Specifically, before electrochemical passivation, the workpiece is placed in a supercritical carbon dioxide (CO₂) environment, and the temperature and pressure of the reaction kettle are controlled to make carbon dioxide (CO₂) enter the supercritical phase state. In this state, the low surface tension of carbon dioxide (CO₃) enables it to fully wet the microscopic structure on the surface of the workpiece, and displace and carry the residual moisture through capillary action. Due to the molecular motion characteristics of supercritical carbon dioxide (CO₃), the moisture is transported to the fluid phase and discharged with the circulation system. The entire process realizes water removal through physical phase changes without introducing external heat sources, thus avoiding the metal surface oxidation reaction caused by high-temperature environment.

[0076] Compared with the prior art, the traditional process uses hot air drying or vacuum dehydration, and its high-temperature treatment will cause the preferential oxidation of chromium elements on the surface of stainless steel, resulting in the formation of an oxide layer on the substrate before passivation. However, in this solution, through the physical water removal mechanism of supercritical carbon dioxide (CO₂), water removal is completed at room temperature, which not only eliminates the influence of moisture on the passivation reaction but also maintains the intrinsic chemical state of the metal surface.

[0077] Through the above technical solution, the present application effectively avoids the metal surface oxidation problem caused by high temperature in the traditional drying process, ensures the cleanliness and chemical stability of the substrate before the passivation reaction, and provides an ideal surface condition for the subsequent formation of a uniform and dense chromium oxide passivation film.

[0078] It should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. However, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A high-brightness surface finishing process for deep treatment of stainless steel C02, characterized in that, It includes the following steps: a) Using supercritical CO and biosurfactant for synergistic degreasing; b) Achieving the transition from rough polishing to fine polishing by gradient dry ice spraying; c) Conducting pulsed laser micro-melting repair under the protection of a CO gas curtain; d) Generating a nano-scale Cr₂O₃ film by supercritical CO electrochemical passivation.

2. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 1, characterized in that, The step a) includes: Immersing the workpiece in a supercritical CO reactor, adding 0.5% - 2% bio-based surfactant, and circulating for 10 - 15 minutes to dissolve the grease.

3. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 2, characterized in that, The temperature of the reactor is 35°C and the pressure is 10 MPa.

4. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 2, characterized in that, The surfactant is sucrose ester.

5. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 1, characterized in that, The step b) includes, Rough polishing stage: Using dry ice particles with a particle size of 2 - 3 mm, air pressure of 8 - 10 bar, and spraying angle of 60° to remove macroscopic defects; Fine polishing stage: Switching to dry ice particles with a particle size of 0.5 - 1 mm, air pressure of 4 - 6 bar, and spraying angle of 30° to reduce the surface roughness Ra of the workpiece from 1.2 μm to 0.4 μm.

6. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 2, wherein, The step b) also includes: Supercritical CO composite polishing: Using supercritical CO at 40°C and 15 MPa, 0.1% fluorocarbon surfactant, and 5 nm silica abrasive suspension, increasing the pressure to 20 MPa at a rate of 0.5 MPa / s and maintaining for 5 minutes to allow the abrasive to penetrate; then decreasing the pressure at a rate of 1 MPa / 2 s and using the pressure change to peel off the surface layer.

7. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 1, characterized in that, The step c) includes, after dry ice spraying, using pulsed fiber laser to scan the surface, and the CO gas curtain inhibits oxidation to achieve micron-level remelting and eliminate subsurface cracks.

8. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 7, characterized in that, The pulsed fiber laser uses a pulsed fiber laser with a wavelength of 1064 nm, a power of 50 W, and a pulse width of 10 ns.

9. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 1, characterized in that, The step d) includes, Using the workpiece as the anode, applying a voltage of 2 V for 5 minutes in a supercritical CO electrolyte to promote the formation of a dense Cr₂O₃ passivation film on the surface.

10. The stainless steel C02 deep treatment high-brightness surface finishing process according to claim 9, characterized in that, The step d) also includes, before the electrochemical reaction, the workpiece is maintained in the supercritical state for 10 minutes, and the low surface tension property of CO is used to completely remove moisture to avoid oxidation caused by traditional drying.

Images