A method for cold rolling stainless steel black skin coil based on pre-conditioning by pulsed laser

Abstract

The application discloses a stainless steel black skin coil cold rolling method based on pulse laser pre-conditioning and relates to the technical field of stainless steel cold rolling strip production. On the basis of the existing short process of directly cold rolling the black skin coil, an online pulse laser surface pre-conditioning continuous production line unit is additionally arranged at the inlet of a twenty-roller cold rolling mill, so that the three modification treatments of oxide scale embrittlement pre-preparation, base material oil storage micro-nano texture formation and surface layer micro area stress annealing are simultaneously completed on the hot-rolled unannealed black skin steel strip; the modified steel strip is directly sent into the cold rolling mill for rolling, and then the welding degreasing, low-temperature annealing, three-section composite pickling and online skin pass and coiling procedures are sequentially carried out. The application converts the continuous hard oxide scale into micron-level solid lubricating particles, simultaneously constructs the oil storage texture of the steel strip and relaxes the surface layer residual stress; four core defects, i.e., the surface pitting and pit of the finished product, the excessive wear of the roller, the rolling force fluctuation and the surface micro-cracks of the difficult deformation steel grade, are completely avoided.

Description

Technical Field

[0001] This invention relates to the field of stainless steel cold-rolled strip production technology, and in particular to a method for cold rolling stainless steel black coils based on pulsed laser preconditioning. Background Technology

[0002] Stainless steel, with its excellent rust and corrosion resistance, is widely used in home appliances, kitchenware, building decoration, chemical equipment, rail transportation, and other fields. The mainstream standard production process for cold-rolled stainless steel strip in the industry is as follows: hot-rolled black strip, hot-rolled annealing and pickling, cold-rolled, cold-rolled annealing and pickling, and leveling. The complete process is equipped with dedicated hot-rolled annealing and pickling units, descaling equipment, multi-stage pickling tanks, gas-fired annealing furnaces, and other equipment, and is a mature and commonly used route for major steel mills.

[0003] Conventional processes involve multiple levels of energy and material consumption: in the hot rolling stage, oxide scale removal relies on high-temperature gas annealing, mechanical descaling, and multi-stage acid-base pickling. The annealing process continuously burns coal gas to maintain a high-temperature environment, and the pickling process generates a large amount of hazardous waste containing chromium and fluorine. The subsequent waste liquid and waste residue treatment processes are complex, resulting in high environmental protection and operation and maintenance costs. At the same time, the entire production line has a long process chain, and steel coils need to undergo two cycles of uncoiling, welding, annealing, and pickling, resulting in a long production cycle, high comprehensive production costs for labor, equipment depreciation, and electricity, and the comprehensive processing cost per ton of finished product has remained high for a long time.

[0004] To address the shortcomings of traditional processes, such as high cost, high energy consumption, and low production efficiency, the existing short-process improvement scheme eliminates the post-hot rolling annealing and pickling process. It directly feeds the hot-rolled, unannealed stainless steel coils into a 20-roll cold rolling mill for rolling, significantly reducing the number of steps and eliminating the need for gas and acid / alkali reagents in the entire hot-rolling annealing and pickling production line. This shortens the production cycle by 20%-30% and reduces the cost per ton by 500-1500 yuan, demonstrating significant economic advantages. However, this simplified process of directly cold-rolling black steel coils has three inherent technical pain points that cannot be avoided, severely restricting the surface quality of the finished product, the service life of the rolls, and production stability. The specific defects are as follows:

[0005] First, the risk of surface quality defects in finished products is high. The oxide scale formed by hot rolling is mainly composed of Cr2O3 and FeO·Cr2O3 spinel hard phases, which are much harder than the stainless steel matrix. Without pre-annealing and pickling to remove the oxide scale, the entire continuous hard oxide scale layer enters the rolling mill with the steel strip. Under the rolling pressure, it is prone to local fracture, and the hard oxide scale fragments are directly pressed into the metal matrix of the steel strip. Subsequent low-temperature annealing and pickling processes cannot completely remove the hard particles pressed into the matrix. The final finished product surface forms dense pits, indentations of varying depths, and linear scratches, with large fluctuations in surface roughness. This makes it difficult to meet the surface quality standards of high-end decorative and precision stamping stainless steel products, thus limiting the application scenarios of the products.

[0006] Secondly, the wear rate of the rolls increases significantly, leading to a substantial rise in roll consumption costs. The intact hard oxide scale on the surface of the black steel strip continuously rubs and squeezes against the first rough grinding work roll at high speed. The spinel phase of the oxide scale has extremely strong abrasive wear characteristics, continuously scraping and eroding the roll surface. In particular, the first pass of the process uses rough grinding rolls with Ra0.8-1.2μm, and the microscopic protrusion structure of the roll surface itself is more easily worn away by the hard oxide scale. The roll roughness decay rate increases by more than 40%, and the frequency of roll regrinding and replacement increases significantly. The cost of roll procurement, grinding and maintenance offsets some of the processing cost savings from the short-process technology. At the same time, frequent roll replacements cause production line downtime and reduce the effective operating rate of the unit.

[0007] Third, the rolling lubrication conditions deteriorate, resulting in large fluctuations in rolling force and increased difficulty in strip shape control. The surface of untreated black-skinned steel strip is uneven, and the continuous hard oxide layer blocks the direct contact between the rolling oil and the metal matrix, making it difficult for the rolling oil to form a continuous and uniform oil film on the contact surface between the rolls and the steel strip. The friction coefficient increases sharply in local dry friction areas, causing periodic fluctuations in the overall rolling force. The steel strip's lateral extension is unevenly distributed, easily leading to strip shape defects such as edge waviness, center waviness, and warping. To improve the oiling effect, the existing process can only continuously increase the roughness of the first roll, further aggravating roll wear and forming a vicious cycle of "poor lubrication, increased roll surface roughness, and accelerated roll wear." The rolling process window is narrow, and the requirements for unit operation and raw material stability are stringent.

[0008] In addition, the surface of hot-rolled steel strip has a significant work-hardened layer, and a large amount of residual rolling stress accumulates at the interface between the oxide scale and the matrix. During direct cold rolling, the surface hardened layer does not match the plastic deformation capacity of the steel strip core, and the rolling stress easily induces microcracks on the surface of the steel strip. This defect is more prominent for difficult-to-deform steels such as martensitic stainless steels like 410 and Cr13, and ferritic stainless steels like 430. This results in increased dispersion of the mechanical properties of the finished product and a decrease in the product qualification rate.

[0009] Existing improvement methods can only alleviate the above problems by adjusting downstream process parameters such as rolling deformation rate, annealing temperature, pickling agent concentration, and leveling pressure. They cannot fundamentally eliminate the complete and continuous structure of hard oxide scale, improve the oil storage and lubrication capacity of the steel strip surface, or relax surface residual stress. The core contradictions of surface defects, roll wear, and poor rolling stability remain unresolved. Therefore, the industry urgently needs a new pretreatment process that can adapt to the direct cold rolling short-process route for black strip coils, control the oxide scale structure from the source, optimize rolling lubrication, and relax surface stress. This new process should retain the low-cost advantages of eliminating hot rolling annealing and pickling while completely solving the inherent defects of the existing short-process route. Summary of the Invention

[0010] The main objective of this invention is to provide a cold rolling method for stainless steel black strip based on pulsed laser preconditioning. Addressing existing technical problems in the process of eliminating hot rolling annealing and pickling and directly cold rolling black strip steel coils, such as surface pitting defects, severe roll wear, poor rolling lubrication, and the tendency for surface micro-cracks in difficult-to-deform steel grades, this invention embeds semiconductor laser annealing and metal laser cleaning texturing cross-disciplinary laser manufacturing technologies into the pre-cold rolling process. An online pulsed laser surface preconditioning continuous production line unit is set up at the cold rolling mill inlet to perform a streamlined composite modification treatment on hot-rolled black strip steel. This transforms the hard oxide scale from a source of rolling defects into a controllable process aid medium, simultaneously constructing an oil-retaining micro-texture on the steel strip surface and relaxing residual surface stress. While retaining the advantages of short-process, low-cost, and low-energy consumption, this method comprehensively improves the surface quality of the finished product, reduces roll wear, stabilizes the rolling process, and broadens the range of steel grades adaptable to the short-process technology.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A cold rolling method for stainless steel black coils based on pulsed laser preconditioning includes the following steps:

[0013] S1. Preparation of hot-rolled black steel coil uncoiling and conveying;

[0014] Hot-rolled unannealed stainless steel black-skinned coils of grades 201, 304, 316, 410, 430, 409, 443, and Cr13 are selected. The thickness of the hot-rolled base material is 3.0-8.0 mm. The finished product thickness can be rolled to 0.3-6.0 mm and the steel strip width is 900-2000 mm. The surface of the steel strip is originally formed with a continuous and complete Cr2O3 and FeO·Cr2O3 spinel hard oxide layer without any pre-annealing, descaling, or pickling pretreatment.

[0015] The steel coil is hoisted to the uncoiler unit, and the matching correction device realizes the transverse centering of the steel strip. The steel strip conveying speed is linked and synchronized with the rolling speed of the 20-roll cold rolling mill at the rear end. Dust removal blowing rollers are set in front of the steel strip extending to the uncoiler unit to remove loose floating dust and large pieces of oxide scale debris from the surface, so as to avoid impurities blocking the laser beam and affecting the modification effect.

[0016] This step is the basis of the short process, which eliminates the need for the entire production line of traditional hot rolling annealing and pickling, thus reducing costs and cycle time. However, the original complete hard oxide scale will bring three major problems: surface defects, roll wear, and lubrication failure. The source modification and control are completed by the continuous laser pretreatment unit in step S2.

[0017] S2. Online pulsed laser surface preconditioning continuous pipeline unit processing;

[0018] This step is set as a laser-sealed station, installed between the 20-roll cold rolling mill and the uncoiler unit. It is a closed, integrated, continuous processing production line, synchronized with the steel strip conveyor speed throughout. It is equipped with an adjustable pulse width fiber laser, a follow-type silicon carbide high-pressure blowing knife, and a speed closed-loop linkage control system. The process includes the following steps according to the steel strip's direction of travel:

[0019] S2.1, Feed guide section;

[0020] The steel strip is conveyed into the laser sealing station by step S1. The laser sealing station is equipped with a laser emitter and upper and lower paired limit guide rollers to ensure that the steel strip maintains a constant irradiation distance between both sides of the laser emitter and the steel strip, and that the steel strip is centered laterally without deviation. The surface of the guide rollers is covered with a wear-resistant ceramic layer to avoid scratching the surface of the untreated black steel strip. A speed detection sensor is reserved in the feeding guide section to collect the steel strip's travel speed in real time and synchronously feed it back to the laser to adjust the scanning frequency, ensuring that the laser scanning overlap rate is stably controlled between 10% and 30%, achieving full coverage and uniform irradiation of the upper and lower surfaces of the steel strip, and eliminating local missed treatment areas.

[0021] S2.2, Pulsed laser irradiation modification section;

[0022] The steel strip passes through the pulsed laser irradiation modification section at a uniform speed. The pulsed fiber laser scans back and forth along the width of the steel strip. Relying on the instantaneous energy input of nanosecond / femtosecond pulses, three types of physical and metallurgical modification behaviors occur simultaneously on the surface of the steel strip. The three modifications are completed in parallel, eliminating the need for multiple strip passes and multiple equipment treatments. The laser energy density is uniformly controlled below the threshold for complete ablation and peeling of the oxide scale, without completely removing the oxide scale from the surface of the steel strip. Relying on the laser thermo-mechanical coupling effect, the three-stage modification of oxide scale embrittlement pre-fabrication, substrate oil-retaining texture formation, and surface micro-area stress annealing are completed sequentially within a single production line.

[0023] The technical principle of this invention is as follows:

[0024] Utilizing the laser-thermal-mechanical coupling effect, the three-stage modification process—mortise and tenet prefabrication of oxide scale, oil-retaining texture formation of substrate, and micro-area stress annealing of the surface layer—is completed sequentially within a single production line.

[0025] 1) Controllable crushing modification of oxide scale embrittlement;

[0026] The laser energy density is lower than the complete ablation threshold of Cr2O3 and FeO·Cr2O3 spinel oxide scale. The instantaneous high temperature and rapid cooling of the pulsed laser create huge interfacial thermal stress, which induces uniform, fine and penetrating network microcracks in the entire continuous hard oxide scale and at the interface between the oxide scale and the stainless steel substrate. The originally complete and hard oxide shell is transformed into a modified film with a pre-crack network.

[0027] During subsequent cold rolling under pressure, the modified oxide scale is uniformly broken into 1-10μm micron-sized fine particles along the pre-made microcracks, without large pieces breaking off and embedding into the metal matrix. The fine oxide debris is uniformly dispersed inside the rolling oil. Its mechanism is that the hard particles act as micro-rolling bodies between the rolls and the steel strip, reducing the direct contact area. At the same time, the particles are embedded in the textured pits to avoid scratching the matrix. Moreover, the small size allows them to be completely dissolved and removed in the subsequent three-stage composite pickling process, eliminating pits, indentations, and point-like surface defects from the source.

[0028] 2) In-situ oil-storing micro / nano-woven structure modification of substrate;

[0029] Laser pulse irradiation of the steel strip surface instantly generates a plasma expansion effect, forming a directional micro-impact stress wave. Combined with micron-level ultra-fast thermal cycling, a periodically arranged pit-type micro-nano texture with a depth of 1-5μm is generated on the surface of the stainless steel substrate. This micro-texture is a natural oil storage cavity, which can continuously store rolling oil during the cold rolling process. It forms a continuous, highly adhesive lubricating oil film at the contact interface between the roll and the steel strip, which significantly reduces the interfacial friction coefficient and solves the problem of lubrication failure caused by the original black oxide scale of the steel strip blocking the oil film.

[0030] Relying on the self-lubricating ability of the oil-storage texture, the roughness of the first roll is reduced from Ra0.8-1.2μm in the original short process to Ra0.5-0.8μm, resulting in fewer roll protrusions and improved wear resistance. The finer oxide scale reduces the abrasive wear intensity, and the dual effect reduces roll wear, breaking the vicious cycle of "oil on the rough roll and increased roll wear".

[0031] 3) Selective surface micro-region stress annealing modification;

[0032] The laser heat-affected zone is strictly confined to within 5μm of the steel strip surface, and the overall temperature rise of the steel strip substrate is ≤50℃ with no additional gas energy consumption. The instantaneous peak temperature of the laser exceeds the recrystallization temperature of the stainless steel surface. It is used for localized instantaneous heat treatment only on the hot-rolled hardened surface and oxide scale stress concentration areas to relax the residual rolling stress on the steel strip surface, soften the work-hardened thin layer, and reduce the difference in plastic deformation between the surface and the core.

[0033] During cold rolling, the deformation of the steel strip surface and core is synchronous and uniform, which effectively suppresses micro-cracks on the surface of 410, Cr13 martensitic and 430 ferritic stainless steel, reduces the dispersion of mechanical properties of finished products, broadens the range of steel grades that can be adapted to short processes, and increases the process tolerance window.

[0034] S2.3, High-pressure purging and cleaning section;

[0035] After passing through the pulsed laser irradiation modification section, the steel strip enters the high-pressure purging and cleaning section. The high-pressure purging and cleaning section is equipped with symmetrically arranged vertically and vertically following silicon carbide high-pressure air knives. The high-speed airflow blows away a small amount of completely loose oxide debris from the surface of the steel strip in real time, preventing the debris from re-adhering to the surface of the steel strip and preventing it from being carried into the cold rolling mill and forming pressure defects. The oxide dust generated by purging is equipped with a closed dust collection and recovery device, and the dust is collected centrally and does not overflow, meeting the environmental protection production requirements of the workshop.

[0036] S2.4, Discharge transition section;

[0037] The discharge transition section is located at the entrance of the 20-roll cold rolling mill. A buffer transition roller is installed in the discharge transition section. After the modified steel strip is purged, it is sent out of the laser pretreatment closed station through the buffer transition roller. The steel strip is smoothly transported to the entrance of the 20-roll cold rolling mill, realizing seamless and continuous connection between the two processes.

[0038] S3, direct cold rolling using a 20-roll cold rolling mill;

[0039] The black steel strip, after being modified by the S2 pulsed laser continuous production line with triple composite, is directly fed into the Senkimir 20-roll cold rolling mill for rolling; the total thickness deformation rate is controlled at 50%-80%, the number of rolling passes is 5-15, the deformation rate per pass is 5%-25%, and the rolling process is lubricated by spraying rolling oil.

[0040] The roll configuration is optimized based on the S2 lubrication optimization effect: the first pass work roll uses a medium-low roughness roll with Ra0.5-0.8μm, and all other passes use a uniform Ra0.3-0.5μm flat roll; the hot-rolled black steel coil has a "fish head" shaped structure at the beginning and end, and after the strip is threaded, a special coiling machine is used to complete the coiling of the steel strip. After rolling, a continuous cold-rolled steel coil is obtained.

[0041] Thanks to the triple modification effect of the S2 laser preconditioning line, the rolling force fluctuation range in this step is greatly reduced, the strip shape defects such as edge waviness, middle waviness, and flaring are significantly reduced, and the roll wear rate is significantly decreased.

[0042] S4. Steel strip welding and degreasing treatment;

[0043] The S3 rolled steel coils are fed into an uncoiler for secondary uncoiling. Shearing equipment removes the beginning and end rolling defects. Two online continuous welding processes are used depending on the target thickness of the steel strip. Before welding, high-pressure gas purging ensures the weld area is clean. After welding, the strips are uniformly degreased to remove rolling oil and micron-sized oxide scale debris from the surface.

[0044] Steel strip with a finished thickness of 0.3-2.5mm: roller resistance lap welding, weld lap amount 1-3mm, welding speed 5-11m / min, welding current 3000-25000A;

[0045] Finished steel strip with a thickness of 2.5-8.0mm: MIG butt welding, 1.2mm diameter ER309L stainless steel welding wire, steel strip butt gap ≤2mm, welding speed 0.8-1.5m / min, welding voltage 27-31V, wire feeding speed 8-14m / min.

[0046] After welding, the steel strip continuously passes through the alkaline washing and high-pressure water rinsing degreasing section to thoroughly remove the surface rolling oil and fine oxide particles. The clean steel strip is then conveyed to the annealing furnace inlet.

[0047] S5. Low-temperature annealing treatment;

[0048] After degreasing, the steel strip is fed into a continuous annealing furnace for annealing. The specific annealing temperature in this process is adjusted according to the steel grade and thickness to suppress the secondary formation of oxide scale on the steel strip surface at high temperatures. The holding time in the furnace is uniformly controlled at 1.0-3.0 min / mm, with different steel grades matched with specific temperature control ranges.

[0049] 410 and 430 ferritic stainless steel, 800-860℃;

[0050] 304 austenitic stainless steel, 1030-1130℃;

[0051] 409 stainless steel, 870-935℃;

[0052] 443 stainless steel, 910-980℃.

[0053] After the steel strip is heat-insulated, it is rapidly cooled by a combination of mist cooling and air cooling to a temperature below 120°C before being sent out of the annealing furnace. Low-temperature exit from the furnace reduces secondary oxidation of the steel strip by air and lowers the consumption of reagents in the subsequent S6 pickling process.

[0054] S6, Three-stage composite pickling treatment;

[0055] After low-temperature annealing, the steel strip is continuously passed through a three-stage composite pickling process: an electrolytic sodium sulfate tank, an electrolytic nitric acid tank, and a nitric acid-hydrofluoric acid mixed acid tank. Each pickling tank outlet is equipped with a silicon carbide brush roller that simultaneously brushes the steel strip on both sides, thoroughly dissolving and removing micron-sized oxide scale debris generated during rolling, ensuring that the steel strip is free of iron scale residue.

[0056] Sodium sulfate electrolytic cell: sodium sulfate concentration 112-120g / L, electrolysis current 4000-6000A, cell temperature 65-85℃;

[0057] Electrolytic nitric acid tank: Nitric acid concentration of 90-150g / L for 410 and 430 steel, 120-180g / L for 304 steel, electrolysis current of 4000-6000A, tank temperature of 30-60℃;

[0058] Nitric acid and hydrofluoric acid mixed acid tank: 410 and 430 steel grade nitric acid 120-180g / L, hydrofluoric acid 15-25g / L; 304 steel grade nitric acid 120-220g / L, hydrofluoric acid 15-30g / L; tank temperature 30-55℃.

[0059] After pickling, the steel strip undergoes multi-stage countercurrent rinsing with clean water to completely remove residual acidic solution from the surface and prevent pitting defects in the finished product.

[0060] S7. Online leveling and finished product roll packaging;

[0061] After pickling and rinsing, the clean steel strip is fed into a double-roll leveler for high-pressure online leveling, which optimizes the strip shape and further reduces the surface roughness of the finished product. The leveling roller roughness Ra is 0.04-0.2μm, the leveling pressure is 150-900 tons, and the steel strip elongation is 0.2-2.0%. After leveling, the unevenness of the steel strip can be controlled within 6mm / m. The surface roughness Ra of the finished product after a single leveling is stable at 0.2-0.7μm, and the roughness can be reduced to below Ra 0.2μm after multiple levelings.

[0062] The leveled steel strip is fed into the slitting unit to remove the welded and rolled defective sections at the beginning and end. After being coiled, bundled, and packaged, the finished stainless steel cold-rolled steel strip is obtained. The finished product has a thickness of 0.3-6.0mm and a width of 900-2000mm. Its mechanical properties meet the general stainless steel standards GB / T3280, JISG4305, and EN10088.

[0063] The advantages of the technical solution of the present invention compared with the prior art are as follows:

[0064] 1. This invention adds a closed-loop segmented pulsed laser preconditioning line at the entrance of a 20-roll cold rolling mill. Utilizing adjustable pulse width pulsed lasers, it simultaneously completes three stages of modification: oxide scale embrittlement pretreatment, substrate oil-retaining micro / nano texturing, and surface micro-area stress annealing. This achieves integrated multi-stage pretreatment processes, eliminates the need for multiple offline processing steps, and allows for direct modification of existing stainless steel cold rolling production lines. Simultaneously, by integrating pulsed laser texturing and micro-area instantaneous laser annealing technologies, a novel short-process route is established, involving hot-rolled black sheet material, laser preconditioning, and direct cold rolling. This eliminates the hot-rolling annealing and pickling process, resulting in significant savings in fuel gas and acid / alkali reagent consumption, a 20%-30% reduction in production cycle time, and a 500-1500 RMB reduction in processing cost per ton. This fully preserves the core advantages of the short-process cost reduction and efficiency improvement while controlling defects from the rolling source.

[0065] 2. This invention achieves the technical effect of transforming a complete hard oxide scale into a 1-10μm micron-level controllable solid lubricating medium by controlling the laser energy density below the threshold for complete ablation of the oxide scale and inducing the generation of uniform, interconnected network microcracks within the continuous hard oxide scale. This prevents the oxide scale from breaking off in large pieces and being pressed into the steel strip matrix during the rolling process, eliminating defects such as pitting, indentation, and dotted scratches on the finished product surface from the root. Fine oxide debris can be completely dissolved and removed in the subsequent three-stage composite pickling process with silicon carbide brush rollers. The surface roughness of the finished product is stable at Ra0.2-0.6μm, and the smoothness is superior to that of traditional two-stage annealing and pickling 2B stainless steel, making it suitable for high surface requirements.

[0066] 3. This invention utilizes the laser pulse plasma expansion impact effect to in-situ prepare a 1-5μm periodic pit oil-retaining micro-nano texture on the surface of the steel strip substrate. This achieves the technical effect of forming a continuous, highly adherent lubricating oil film on the contact surface between the roll and the steel strip, significantly reducing the interfacial friction coefficient. As a result, the roughness of the first roll can be reduced from the original short-process Ra0.8-1.2μm to Ra0.5-0.8μm, breaking the vicious cycle of "relying on the rough grinding roll to carry oil and aggravating roll wear". The abrasive wear intensity of oxide scale is significantly reduced, the roll regrinding cycle is extended by more than 35%, the cost of roll procurement and grinding maintenance is reduced, the frequency of roll replacement downtime is reduced, and the effective operating rate of the unit is significantly improved.

[0067] 4. This invention achieves the technical effects of relaxing residual stress during surface rolling, softening the work-hardened thin layer, and reducing the difference in plastic deformation between the surface and interior of the steel strip by limiting the laser heat-affected zone to only 5μm of the steel strip surface and applying instantaneous local heat treatment only to the hot-rolled hardened layer and oxide scale stress concentration area, while keeping the steel strip matrix at room temperature throughout the process. This results in a 60% reduction in the periodic fluctuation amplitude of rolling force, uniform transverse extension of the steel strip, and a significant reduction in plate shape defects such as edge waviness, center waviness, and warping. At the same time, it effectively suppresses microcracks on the surface of difficult-to-deform stainless steels such as 410, Cr13 martensitic, and 430 ferritic, reducing the dispersion of finished product mechanical properties, widening the process tolerance window, and enabling stable mass production of the entire series of stainless steels including 201, 304, 316, 410, 430, 409, 443, and Cr13. Detailed Implementation

[0068] To make the technical means, creative features, objectives and effects of this invention easier to understand, the following detailed description is provided in conjunction with specific embodiments. Operations in the embodiments of this invention that do not specify process conditions adopt the conventional process of stainless steel cold rolling in this field.

[0069] Example 1:

[0070] The raw material used is unannealed 06Cr13 martensitic stainless steel hot-rolled black strip with a thickness of 4.0 mm and a width of 1258 mm. The surface of the steel strip is covered with a Cr2O3 and FeO·Cr2O3 composite oxide layer. The chemical composition of the steel coil by mass fraction is: C: 0.0334%, Cr: 13.3306%, Si: 0.7168%, Mn: 0.3544%, Ni: 0.1109%, P: 0.0317%, S: 0.001%, N: 0.0151%, with the balance being Fe and unavoidable impurities.

[0071] Implement in sequence according to S1-S7:

[0072] S1. Hot-rolled black steel coil uncoiling and material preparation: The black steel coil is fed and uncoiled. The steel strip conveyor speed is 8m / min, which is synchronized with the speed of the twenty-roll mill. The front dust removal roller removes surface slag.

[0073] S2. The online pulsed laser surface preconditioning continuous production line unit is set as a laser closed station and installed between the twenty-roll cold rolling mill and the uncoiler unit. It is equipped with an adjustable pulse width pulsed fiber laser, a follower silicon carbide high-pressure blowing air knife, and a speed closed-loop linkage control system.

[0074] S2.1 Feeding guide section: The steel strip is centered and limited, and the speed sensor is linked to the laser in real time; a laser emitter is set in the laser closed station, and the laser emitter is controlled to make the laser scanning overlap rate stably controlled at 18%, so as to achieve uniform irradiation of the upper and lower surfaces of the steel strip.

[0075] S2.2 Pulsed Laser Irradiation Modification Section: A 10ns pulsed fiber laser is used, and the laser energy density is controlled at 85% of the Cr2O3 oxide scale ablation threshold, corresponding to a measured energy density of approximately 2.8J / cm², with a laser scanning overlap rate of 20%. Simultaneously, the oxide scale network microcrack prefabrication, 1-3μm oil-storing microtexture preparation, and surface micro-region stress relaxation triple modification are completed.

[0076] S2.3 High-pressure purging cleaning section: Silicon carbide air knife purges loose oxide debris, and dust is recovered in a closed system;

[0077] S2.4, Discharge transition section: The strip is smoothly fed to the cold rolling mill through the buffer transition roller.

[0078] S3, Direct cold rolling on a 20-roll cold rolling mill: The modified steel strip is fed into a Senkimir 20-roll mill for rolling, with a total deformation rate of 50% and a thickness of 2.0 mm after rolling. It is rolled in 7 passes with a single-pass deformation rate of 8%-18%. The roughness of the first work roll is Ra0.6μm, and the roughness of the remaining passes is Ra0.3-0.5μm. A matching coiler completes the coil winding.

[0079] S4. Steel strip welding and degreasing: Uncoil and cut off the defective sections at the beginning and end, use roller resistance lap welding, with a weld overlap of 2mm, welding speed of 7.8m / min, and welding current of 16000A; after the weld is blown off, it enters the degreasing section to remove the rolling oil.

[0080] S5. Low-temperature annealing treatment: Annealing furnace temperature 815℃, holding time 1.8min / mm; after holding, rapid cooling to 110℃ by mist cooling and air cooling before unloading.

[0081] S6. Three-stage composite pickling treatment: Electrolytic sodium sulfate tank concentration 112g / L, current 5000A, temperature 70℃; Electrolytic nitric acid tank nitric acid concentration 170g / L, current 5000A, temperature 50℃; Mixed acid tank nitric acid 170g / L, hydrofluoric acid 18g / L, temperature 35℃; Silicon carbide brush roller washing at the outlet of each tank, multi-stage clean water rinsing.

[0082] S7. Online leveling and finished product slitting and packaging: Double roller leveling machine, leveling roller Ra0.05μm, leveling pressure 650 tons, elongation 0.8%; longitudinal cutting, slitting and packaging to obtain finished products.

[0083] Finished product inspection results: No pitting or dents on the surface; surface roughness Ra 0.50-0.58μm; mechanical properties Rp0.2=272MPa, Rm=505MPa, A50=33%; rolling force fluctuation during rolling process ≤8%; roughness decay of only 0.06μm after continuous rolling of 350 tons on the first roll, roll consumption significantly reduced; no surface microcracks in the steel strip, flatness ≤5mm / m, meeting the requirements of GB / T3280 standard.

[0084] Example 2:

[0085] Raw materials used: 3.0mm thick, 1262mm wide unannealed SUS430 ferritic stainless steel hot-rolled black steel coil; chemical composition by mass fraction: C: 0.0316%, Cr: 16.2731%, Si: 0.3189%, Mn: 0.2783%, Ni: 0.0940%, P: 0.0285%, S: 0.0035%, N: 0.0394%, balance Fe and impurities.

[0086] Implement in sequence according to S1-S7:

[0087] S1. Hot-rolled black steel coil uncoiling and material preparation: Black steel coil is fed and uncoiled, steel belt conveyor speed is 7.5m / min, the speed of the whole line is synchronized, and the front dust removal roller cleans the surface floating skin.

[0088] S2. The online pulsed laser surface preconditioning continuous production line unit is set as a laser closed station and installed between the twenty-roll cold rolling mill and the uncoiler unit. It is equipped with an adjustable pulse width pulsed fiber laser, a follower silicon carbide high-pressure blowing air knife, and a speed closed-loop linkage control system.

[0089] S2.1 Feeding guide section: The steel strip is centered and limited, and the speed sensor is linked to the laser in real time; a laser emitter is set in the laser closed station, and the laser emitter is controlled to make the laser scanning overlap rate stably controlled at 18%, so as to achieve uniform irradiation of the upper and lower surfaces of the steel strip.

[0090] S2.2 Pulsed Laser Irradiation Modification Section: A femtosecond pulsed laser with a pulse width of 150 fs and an energy density of 82% of the oxide scale ablation threshold, corresponding to approximately 1.5 J / cm² in actual measurement, and a scanning overlap rate of 25% are used; a 2-4 μm periodic oil-storing microtexture is generated on the surface of the steel strip, a uniform network of microcracks is formed inside the oxide scale, and the surface stress is simultaneously relaxed, resulting in triple modification.

[0091] S2.3 High-pressure purging cleaning section: Silicon carbide air knife purges loose oxide debris, and dust is recovered in a closed system;

[0092] S2.4, Discharge transition section: The strip is smoothly fed to the cold rolling mill through the buffer transition roller.

[0093] S3, Direct cold rolling on a 20-roll cold rolling mill: The modified steel strip is fed into a Senkimir 20-roll mill for rolling, with a total deformation rate of 60% and a thickness of 1.2mm after rolling. It is rolled in 7 passes with a single-pass deformation rate of 10%-22%. The first pass has a Ra of 0.55μm, and the remaining passes have Ra of 0.3-0.5μm flat rolls. A coiling aid is used to complete the coiling of the steel coil.

[0094] S4. Steel strip welding and degreasing: Uncoil and cut off the defective sections at the beginning and end, use roller resistance lap welding with an overlap of 2mm, welding speed of 7.8m / min, current of 15000A, and after the weld is blown off, enter the degreasing section to remove the rolling oil.

[0095] S5. Low-temperature annealing treatment: furnace temperature 825℃, holding temperature for 1.3min / mm, after holding temperature, rapid cooling to 115℃ by mist cooling and air cooling before unloading from the furnace.

[0096] S6. Three-stage composite pickling treatment: Sodium sulfate electrolytic tank: sodium sulfate concentration 112g / L, current 5000A, temperature 70℃; Nitric acid electrolytic tank: nitric acid concentration 180g / L, current 5000A, temperature 50℃; Mixed acid: nitric acid 180g / L, hydrofluoric acid 18g / L, temperature 35℃; Silicon carbide brush rollers at the outlet of each tank are used for full-process brushing and multi-stage rinsing with clean water.

[0097] S7. Online leveling and finished product rewinding and packaging: Double roller leveling machine, leveling roller Ra0.05μm, pressure 650 tons, elongation 0.8%, after leveling, rewinding and packaging.

[0098] Finished product inspection: The surface is smooth and free of point defects, with a roughness Ra of 0.42-0.50 μm; Rp0.2=332MPa, Rm=488MPa, A50=32%; the rolling force is stable without significant fluctuations, the roll wear rate is reduced by 40%, there are no surface microcracks, and the plate shape and mechanical properties are superior to those of conventional short-process products without laser pretreatment.

[0099] Comparative Example

[0100] The raw materials, steps S1 and S3-S7 process parameters are the same as in Example 1. The pulsed laser surface preconditioning production line unit in S2 is cancelled. The black steel strip directly enters the twenty-roll mill for rolling. The first roll in S3 is a Ra1.0μm rough grinding roll.

[0101] Finished product inspection comparison: The finished product surface has dense dot-like indentations and local pitting defects, with a roughness Ra of 0.65-0.85μm; the rolling force fluctuation range is up to 32%; after rolling the same tonnage of steel coil, the roughness of the first roll decreases by 0.22μm, and the roll consumption increases significantly; microcracks exist on the surface of the local steel strip, the elongation A50 is only 29%, and the product qualification rate decreases; the comprehensive energy consumption per ton is 18% higher.

[0102] Through comparison with examples and comparative examples, it can be confirmed that after adding a segmented pulsed laser preconditioning continuous production line unit, the present invention fully retains the low-cost advantage of eliminating hot rolling annealing and pickling, while solving the four major defects from the source: oxide scale intrusion, poor lubrication, roll wear, and surface stress cracks. The surface quality of the finished product, rolling stability, roll service life, and mechanical properties are all significantly improved. It is compatible with all series of martensitic, ferritic, and austenitic stainless steels and has extremely high industrial promotion value.

Claims

1. A cold rolling method for stainless steel black coils based on pulsed laser preconditioning, characterized in that, Includes the following steps: S1. Preparation of hot-rolled black steel coil uncoiling and conveying; S2. Online pulsed laser surface preconditioning continuous pipeline unit processing; S3, direct cold rolling using a 20-roll cold rolling mill; S4. Steel strip welding and degreasing treatment; S5. Low-temperature annealing treatment; S6, Three-stage composite pickling treatment; S7. Online leveling and finished product roll packaging; The step S2 is set in the front section of the twenty-roll cold rolling mill, which is a closed integrated continuous processing production line. It is divided into a feeding guide section, a pulsed laser irradiation modification section, a high-pressure purging cleaning section, and a discharge transition section along the steel strip travel direction. The single-pass belt simultaneously completes the three-fold modification of oxide scale embrittlement prefabrication, substrate oil storage micro-nano weaving, and surface micro-zone stress annealing.

2. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 1, characterized in that, In step S1, the steel coil is hoisted to the uncoiler unit, and a matching correction device is used to achieve transverse centering of the steel strip. The steel strip conveying speed is controlled to be synchronized with the rolling speed of the 20-roll cold rolling mill at the rear end in real time. A dust removal blowing roller is provided at the front end of the feed to remove loose floating dust and oxide scale debris from the surface.

3. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 2, characterized in that, Step S2 is set as a laser sealing station, installed between the 20-roll cold rolling mill and the uncoiler unit, equipped with an adjustable pulse width fiber laser, a follower silicon carbide high-pressure blowing air knife, and a speed closed-loop linkage control system.

4. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 3, characterized in that, The steps involved in determining the direction of the steel strip's travel are as follows: S2.1, Feed guide section; S2.2, Pulsed laser irradiation modification section; S2.3, High-pressure purging and cleaning section; S2.4, Discharge transition section.

5. The cold rolling method for stainless steel black coils based on pulsed laser preconditioning according to claim 4, characterized in that, In step S2.1, a laser emitting head is installed in the laser enclosed station. The laser emitting head is controlled so that the laser scanning overlap rate is stably controlled at 10%-30%, so as to achieve uniform irradiation covering the upper and lower surfaces of the steel strip.

6. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 5, characterized in that, In step S2.2, the steel strip passes through the pulsed laser irradiation modification section at a uniform speed, and the laser energy density of the laser emitting head is controlled to be uniformly controlled below the threshold for complete ablation and peeling of the oxide scale. The three-stage modification of oxide scale embrittlement prefabrication, substrate oil storage weaving, and surface micro-area stress annealing is completed sequentially in a single production line.

7. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 6, characterized in that, The process parameters for the triple modification in the pulsed laser irradiation modification section include: 1) Controllable fracture modification of oxide scale: Pulsed laser induces the generation of uniform network microcracks inside the oxide scale, and the oxide scale breaks into fine particles of 1-10μm after rolling and pressure. 2) In-situ oil storage texture modification of substrate: Periodic pit-type micro-nano oil storage texture with a depth of 1-5μm is generated on the surface of the steel strip substrate; 3) Selective surface micro-zone stress annealing modification: The laser heat-affected zone is confined within 5μm of the steel strip surface. Only the surface hardened layer and oxide scale interface stress zone are subjected to instantaneous local heat treatment, and the overall temperature rise of the steel strip substrate is ≤50℃.

8. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 4, characterized in that, In step S2.3, a symmetrically arranged, following silicon carbide high-pressure air knife is installed in the high-pressure purging cleaning section, and the oxide dust generated by purging is equipped with a closed dust collection and recovery device.

9. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 1, characterized in that, In step S6, the three-stage composite pickling process consists of an electrolytic sodium sulfate tank, an electrolytic nitric acid tank, and a nitric acid-hydrofluoric acid mixed acid tank, with each pickling tank outlet equipped with a silicon carbide brush roller for double-sided brushing.

10. The method for cold rolling stainless steel black coils based on pulsed laser preconditioning according to claim 1, characterized in that, A two-roller leveling machine is provided in step S7.