Method for producing hot-dip galvanized sheet based on twin-roll thin-strip continuous casting technology

Abstract

The invention provides a method for producing a hot-dip galvanized plate based on a twin-roll thin-strip continuous casting technology. By designing the roller surface roughness distribution of the roughening roller of the fifth acid rolling rack, the roughness difference in the plate surface edge of the thin strip raw material is improved, and the edge color difference problem after the thin strip raw material is galvanized is solved; in the batch production process, the combination of a zinc layer and a thin strip substrate is effectively improved and the problem of coating falling is solved by combining the raw material components of each roll of thin strip, formulating an annealing furnace dew point adjusting scheme and performing reasonable production scheduling; the increase of the silicon content of the plating solution caused by the high-silicon-component thin strip substrate along with the increase of the working time is fully considered, and the zinc pot components are balanced in time by formulating a zinc pot component adjusting scheme, so that the generation and aggregation of zinc pot slag substances are reduced, and the surface slag defect problem is improved. And finally, stable production of the ultrathin galvanized sheet is realized. And the surface quality requirements of household appliance galvanized sheets are met.

Description

Technical Field

[0001] The invention belongs to the technical field of twin-roll casting and rolling, and particularly relates to a method for producing hot-dip galvanized sheets based on a twin-roll thin strip continuous casting technology. Background Art

[0002] With the introduction and gradual implementation of carbon fee policies in recent years, various industries have placed increasingly stringent requirements on carbon emissions during the production of products and raw materials. Taking the 3C and consumer electronics industries as an example, leading companies in the industry, such as Dell and HP, have all proposed their own carbon emission reduction plans, one of which is to use "green steel" (steelmaking raw materials with a scrap ratio of at least 50%) instead of traditional cold-rolled steel strip as the galvanized substrate for home appliances. Given the current technological level and maturity of the steel industry, the technical requirements of "green steel" basically limit its production process to an electric furnace + plate production line. Currently, Shagang is the only company in China equipped with a full-process equipment configuration of electric furnace + ultra-thin strip + cold-rolled galvanizing, meeting the production line and equipment capabilities for the full "green steel" production process.

[0003] Twin-roll thin strip casting technology, also known as ultra-thin strip technology, is a near-net ...

[0004] Patent document CN201910888761.8, "A Method for Producing Martensitic Steel Strip by Twin-Roll Thin Strip Casting," discloses a process for producing martensitic steel strip using a thin strip casting process. Using scrap steel as the raw material, the process controls key parameters such as slag alkalinity and steel inclusion types. Strip steel with a thickness of 1.5-3.0 mm is cast via twin-roll thin strip casting. The strip is then hot-rolled in an enclosed online rolling mill and coiled to obtain a coil. The composition of the martensitic steel strip is: 0.16-0.26 wt% C, 0.1-0.5 wt% Si, 0.4-1.7 wt% Mn, P ≤ 0.02 wt%, S ≤ 0.007 wt%, 0.004-0.010 wt% N, with the remainder being Fe and unavoidable impurities. Its properties include a yield strength ≥ 900 MPa, a tensile strength ≥ 1300 MPa, and an elongation ≤ 12%.

[0005] Patent document CN201710288311.6, "A Twin-Roller Casting Process for Super Austenitic Stainless Steel Strip," discloses a process for directly producing super austenitic stainless steel strip through twin-roller casting. By simplifying the hot rolling process, this method avoids the surface cracking and delamination cracking of super austenitic stainless steel during hot rolling in existing processes, enabling the production of super austenitic stainless steel with a thickness of 1.0-3.5 mm. Furthermore, the entire production process utilizes argon or a mixture of argon and hydrogen for protection, resulting in high-purity molten steel and a thin surface oxide scale. This improves product surface quality, reduces subsequent pickling costs, and increases production efficiency.

[0006] Patent document CN201810545642.8, "Method for Producing High-Strength Low-Alloy Steel by Twin-Roll Thin Strip Casting and Aging Process," discloses a method for producing high-strength low-alloy steel by twin-roll thin strip casting and aging. Compared to existing high-strength low-alloy aged steel strip, this invention combines optimized Mo and Nb microalloying with a rapid solidification process during thin strip casting. The subsequent aging treatment further improves the overall mechanical properties of the low-alloy high-strength steel. The steel composition is: 0.01-0.05wt% C, 0.5-2wt% Mn, 0.2-0.5wt% Si, 0.2-0.6wt% Mo, 0.05-0.5wt% Cr, 0.005-0.3wt% V, 0.01-0.2wt% Nb, P ≤ 0.02wt%, S ≤ 0.02wt%, with the remainder being Fe and unavoidable impurities. Its properties are: yield strength of 800-950 MPa, tensile strength of 850-1000 MPa, and elongation after fracture of 10-20%.

[0007] Patent document CN201110220789.8 "A method for manufacturing non-oriented silicon steel sheets based on twin-roll thin strip continuous casting technology" discloses a process scheme for preparing non-oriented silicon steel using twin-roll thin strip continuous casting technology. By directly performing warm rolling (200-600°C) on the cast strip coil, the cast strip structure is refined, the plasticity, plate shape and surface quality of the cast strip are improved, and convenient conditions are provided for cold rolling; in addition, by regulating the pouring temperature of the molten steel and the speed of the crystallization roller, effective control of the cast strip microstructure is achieved, and a non-oriented silicon steel cast strip with a developed columnar crystal solidification structure and texture is obtained, thereby effectively improving the magnetic induction intensity of the non-oriented silicon steel sheet.

[0008] As can be seen from the above, there is currently no technical solution for preparing galvanized sheet using cast and rolled thin strip as raw material substrate. The main reason is that the existing technology still has the following defects that have not been solved.

[0009] Defect 1

[0010] Due to the inherent production technology characteristics of thin strip casting and rolling technology, during the casting process, the edges of the casting rolls are in a state of enclosing the molten steel to prevent edge leakage and edge rot and maintain casting continuity. This causes the thickness of the cast strip edge within 40mm to decrease sharply. The impact of this sudden thickness change is further amplified during the hot rolling process. Compared with the middle of the strip, the thinning area at the edge: (1) the roll coverage rate is low, the surface morphology is different, and the surface roughness of the edge is greater than that of the middle, and its morphology is rougher; (2) the hot rolling reduction is low, the recrystallization driving force is small, the proportion of recrystallized structure is low, and the microstructure is different. Specifically, the microstructure of the cast-rolled thin strip changes from the edge to the middle as follows: the microstructure at the very edge of the cast-rolled thin strip is similar to that of the cast strip, with high strength and low elongation; while the closer to the middle region, the greater the hot rolling reduction, the grain size of the thin strip gradually grows, and it transforms from an extremely uneven, irregular, non-equiaxed ferrite mixed crystal structure to a fully recrystallized hot-rolled microstructure. This difference in microstructure causes uneven grain deformation during the rolling process, resulting in fluctuations in the surface morphology. This grain deformation and surface morphology difference caused by microstructure differences is more obvious when producing thin twin-roll cast-rolled thin strip with a thickness of less than 1.3mm. In severe cases, orange peel texture will form on the surface of the edge area, and after subsequent galvanizing, color difference defects will form on the edge.

[0011] In response to the above-mentioned color difference problem on the edges of cast-rolled thin strip galvanized sheets, there is currently no patent for the design and innovation of relevant technical solutions.

[0012] Defect 2

[0013] Due to the inherent production technology characteristics of thin strip casting and rolling technology, silicon deoxidation must be used to control the composition of the molten steel during the composition system design process. This also means that compared with the conventional cold-rolled raw materials of galvanized steel sheets for household appliances (≤0.03wt% Si), the silicon content of the cast and rolled thin strip is not less than 0.1%. During the annealing and heating process, the silicon and manganese elements in the galvanized substrate are easily oxidized to form oxides that are enriched on the surface of the strip. At the same time, they are not easily reduced during the subsequent soaking and reduction process, which ultimately affects the wettability of the strip surface. In severe cases, it can cause zinc layer leakage and affect product quality. The commonly used technical means at present is to add a pre-oxidation section to the heating section of the annealing furnace to pre-oxidize the galvanized substrate, oxidizing the silicon and manganese elements in the substrate to the inner layer of the substrate to prevent their oxides from enriching on the substrate surface.

[0014] Taking patent document CN202210991748.7 "A method for controlling surface defects of hot-dip galvanized steel strips" as an example, the patent discloses a method for controlling surface defects of hot-dip galvanized steel strips. By adding a pre-oxidation function to the heating section of the continuous hot-dip galvanizing production line, the silicon and manganese diffused from the inside to the surface of the strip undergo internal oxidation instead of surface oxidation of the strip, thereby improving the wettability of the zinc liquid, solving the surface defects of the hot-dip galvanized steel strips, and improving the surface quality of the strips.

[0015] However, current technical documents fail to consider the impact of a uniform pre-oxidation process on galvanized substrates during large-scale production operations, when the silicon content of the substrate varies significantly. Although surface iron oxides oxidized during the pre-oxidation phase are reduced in the soaking zone, the reduced iron essentially regenerates elemental iron on the strip surface, and the microstructure, properties, and lattice structure of this iron inevitably differ from those of the substrate strip. When the silicon content of the strip is relatively low, the required degree of pre-oxidation is low; however, when the silicon content is high, the required degree of pre-oxidation increases. To ensure effective pre-oxidation in mass production, the oxidation degree standard is benchmarked against the maximum silicon and manganese content in the strip composition. This means that under these production process conditions, there is a risk of over-oxidation during the pre-oxidation process when producing galvanized sheet with relatively low silicon and manganese content. The resulting changes in the strip's microstructure further impact the stamping performance and surface quality of the finished galvanized product, failing to meet the stringent product requirements of brand customers.

[0016] Defect 3

[0017] Due to the inherent production characteristics of thin strip casting and rolling technology, after long hot-dip galvanizing operations, some elements in the high-silicon steel strip gradually diffuse into the zinc pot, increasing the silicon content in the zinc pot and affecting the zinc pot's composition. When the silicon content in the zinc pot is higher than normal during the strip's entry into the zinc pot, silicon oxide particles are easily formed and accumulate around the strip, forming slag defects and affecting the surface quality of the galvanized sheet. Summary of the Invention

[0018] To address the aforementioned shortcomings of the prior art, the present invention provides a hot-dip galvanized sheet using a short-process cast-rolled thin strip as the raw material substrate and a production method thereof. This invention manages the entire process, from pickling, annealing, and coating, to address the issues of edge color difference, zinc layer shedding, and slag-like surface defects encountered when producing hot-dip galvanized sheet using a short-process cast-rolled thin strip as the raw material substrate.

[0019] The core technical means of the present invention are summarized as follows:

[0020] (1) By designing the roughness distribution of the textured roller surface of the fifth stand of the pickling mill, the roughness difference of the edge of the thin strip raw material is improved, and the color difference problem of the edge of the thin strip raw material after galvanizing is solved;

[0021] (2) In the batch production process, the combination of the raw material composition of each roll of thin strip is combined with the formulation of the annealing furnace dew point adjustment plan and reasonable production scheduling to effectively improve the bonding between the zinc layer and the thin strip substrate and solve the problem of coating shedding;

[0022] (3) Taking into full consideration the increase in silicon content in the plating solution caused by high-silicon thin strip substrates as working hours increase, a zinc pot composition adjustment plan is formulated to timely balance the zinc pot composition, reduce the generation and aggregation of zinc pot slag, and improve the surface slag defect problem. Ultimately, stable production of ultra-thin strip galvanized sheet is achieved, meeting the surface quality requirements of home appliance galvanized sheet.

[0023] More specifically, the technical solution of the present invention uses twin-roll cast thin strip with a thickness specification of 0.9 to 1.3 mm as raw material, and carries out acid continuous rolling, continuous annealing, hot-dip galvanizing, leveling, post-treatment passivation, and coiling to obtain hot-dip galvanized sheet with short-process cast thin strip as raw material substrate.

[0024] The key process steps of acid continuous rolling, continuous annealing and coating of the present invention are described as follows.

[0025] 1. Acid continuous rolling

[0026] (1) The raw material for acid continuous rolling is twin-roll cast thin strip. The width of the thin strip raw material in the same batch is l (unit: mm), the thickness is T (unit: mm), and the roughness value of the middle part of the thin strip raw material is r 中 , the surface roughness of the strip steel at 10mm away from the edge of the strip steel is r 10 .

[0027] The pickling continuous rolling adopts five-stand continuous rolling. The length of the texture roller of the 5# stand is L (in mm), and the distance from the edge of the texture roller (Ll) / 2 is the outermost edge of the strip.

[0028] The roughness of the middle area of the textured roller of the 5# stand is R 中 The roller surface roughness in the area from the edge to the edge of the roller [(Ll) / 2+10] mm is R 边10 The roller surface roughness in the area from [(Ll) / 2+10]mm to [(Ll) / 2+25]mm from the roller edge is R 边25 The roller surface roughness in the area from [(Ll) / 2+25]mm to [(Ll) / 2+40]mm from the roller edge is R 边40 The roller surface roughness in the area from [(Ll) / 2+40]mm to [(Ll) / 2+60]mm from the roller edge is R 边60 .

[0029] The cast and rolled thin strip is rolled through five stands to obtain the target thickness of t (unit: mm) of galvanized raw material hardened strip. The surface morphology of the cast and rolled thin strip changes after acid rolling. After acid rolling, the roughness of the middle part of the thin strip hardened coil is Г 中 , the surface roughness of the strip steel at 10mm away from the edge of the strip steel is Г 边10 .

[0030] Among them, the surface roughness Г of the hard plate after pickling is approximately the product of the surface roughness of the 5# texturing roller in the pickling continuous rolling and the overprint coefficient K, that is, Г≈R×K.

[0031] The overprint coefficient, K, reflects the extent to which the roughness of the No. 5 texture roller transfers to the strip surface topography during the pickling continuous rolling process. Its value is related to the steel grade, rolling force, and overprinting method. The smaller |K-1|, the greater the degree of overprinting of the texture roller surface roughness. In actual production, the effects of steel grade and rolling force on the degree of overprinting of the strip surface topography are negligible.

[0032] Among them, the degree of roller surface roughness overprinting varies with the overprinting method. That is, when the surface roughness R of the 5# texturing roller is less than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the small roughness overprints the large roughness, the |K-1| value is large, and the greater the difference between the two, the larger the |K-1| value, K≥1; when the surface roughness R of the 5# texturing roller is greater than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the large roughness overprints the small roughness, the |K-1| value is large, and the greater the difference between the two, the smaller the |K-1| value, 0<K≤1. The specific scheme is as follows:

[0033] When a small roughness overlays a large roughness, that is, R < r, and R / r ≤ 50%, the K value is 1.4;

[0034] When a small roughness overlays a large roughness, that is, R<r, and 50%<R / r≤75%, the K value is 1.2;

[0035] When a small roughness overlays a large roughness, that is, R < r, and 75% < R / r ≤ 90%, the K value is 1.05;

[0036] When a small roughness overlays a large roughness, that is, R < r, and R / r > 90%, the K value is 1;

[0037] When a large roughness overlays a small roughness, that is, R>r, and r / R≤50%, the K value is 0.9;

[0038] When a large roughness overlays a small roughness, that is, R>r, and 50%<r / R≤80%, the K value is 0.95;

[0039] When a large roughness overlays a small roughness, that is, R>r, and r / R>80%, the K value is 1.

[0040] According to the formula Г≈R×K, when the surface roughness of the edge of the cast-rolled thin strip material is greater than that of the middle area, in order to ensure the surface quality of the galvanized finished product, it is necessary to ensure that the surface roughness of the galvanized raw material rolled hard plate after pickling is consistent. Therefore, it is necessary to adjust the surface roughness distribution of the pickling rolling No. 5 texturing roller, that is, to reduce the roller surface roughness of the edge area of the texturing roller and gradually increase it as it approaches the middle of the strip, and finally keep it consistent with the roller surface roughness in the middle area. The specific solution is as follows:

[0041] R 边10 ≈(R 中 ×K 中 ) / K 边10 ≈(K 中 / K 边10 )×R 中 ;

[0042] R 边25 =R 边10 +(R 中 -R 边10 )×70%≈(0.7+0.3K 中 / K 边10 )×R 中 ;

[0043] R 边40 =R 边10 +(R 中 -R 边10 )×90%≈(0.9+0.1K 中 / K 边10 )×R 中 ;

[0044] R 边60 =R 中 .

[0045] 2. Continuous annealing

[0046] The annealing raw material is cast-rolled thin strip hard coil produced after the aforementioned acid continuous rolling process. Annealing is performed in a horizontal continuous annealing furnace, which consists of a preheating section, a heating section, a soaking section, and a cooling section. At the end of the heating section, the furnace atmosphere is adjusted to increase the dew point and oxygen content to achieve pre-oxidation of the strip. This section is called the pre-oxidation section. After pre-oxidation, the strip enters the soaking reduction section, where the dew point is maintained at -50°C to ensure sufficient reduction of iron oxide on the strip surface.

[0047] Among them, the same batch of cast and rolled thin strip raw materials are arranged from low to high silicon content m, with the lowest silicon content being a (unit: wt%) and the highest being b (unit: wt%). 0.1≤a≤m≤b≤1.0wt%. At the beginning of production, the silicon content of the strip is the lowest and the required pre-oxidation degree is the smallest. The dew point of the pre-oxidation stage is recorded as T daAs the production process progresses, the silicon content of the strip increases and the required degree of pre-oxidation increases. The dew point of the pre-oxidation section at this stage is recorded as T dm At the end of production, the silicon content of the strip reaches the maximum value b, the required pre-oxidation degree is the maximum, and the dew point in the pre-oxidation furnace is recorded as T db The specific plan is:

[0048] When the silicon content gradually increases in the range of 0.1wt%≤m<0.3wt%, the dew point of the pre-oxidation section is -25℃≤T dm Increase slowly within -22℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 1.5℃;

[0049] When the silicon content gradually increases in the range of 0.3wt%≤m<0.6wt%, the dew point of the pre-oxidation section is -22℃≤T dm Increase slowly within -16℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 2℃;

[0050] When the silicon content gradually increases in the range of 0.6wt%≤m<1.0wt%, the dew point of the pre-oxidation section is -16℃≤T dm Increase slowly within -6℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 2.5℃.

[0051] 3. Coating process

[0052] After continuous annealing, the strip is cooled to the zinc bath temperature and then enters the zinc bath through the furnace nose to complete the hot-dip galvanizing. As the production of cast and rolled thin strip hot-dip galvanizing continues, the zinc bath composition needs to be sampled and measured every 4 hours to facilitate the adjustment of the bath composition. The specific plan is as follows:

[0053] When the silicon content of the plating solution exceeds 0.01wt%, pure zinc ingot (Zn99.99) is added to adjust the composition;

[0054] When the silicon content of the plating solution exceeds 0.03wt%, it is necessary to switch to transition coil or other galvanized varieties;

[0055] When the silicon content drops below 0.01wt%, the cast and rolled thin strip galvanized sheet is cut back for production.

[0056] Principle Description

[0057] Further theoretical explanation of some technical solutions:

[0058] Among them, the degree of roller surface roughness overprinting varies with the overprinting method. That is, when the surface roughness R of the 5# texturing roller is less than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the small roughness overprints the large roughness, the |K-1| value is large, and the greater the difference between the two, the larger the |K-1| value, K≥1; when the surface roughness R of the 5# texturing roller is greater than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the large roughness overprints the small roughness, the |K-1| value is small, and the greater the difference between the two, the larger the |K-1| value, 0<K≤1. The specific scheme is as follows:

[0059] When a small roughness overlays a large roughness, that is, R < r, and R / r ≤ 50%, the K value is 1.4;

[0060] When a small roughness overlays a large roughness, that is, R<r, and 50%<R / r≤75%, the K value is 1.2;

[0061] When a small roughness overlays a large roughness, that is, R < r, and 75% < R / r ≤ 90%, the K value is 1.05;

[0062] When a small roughness overlays a large roughness, that is, R < r, and R / r > 90%, the K value is 1;

[0063] When a large roughness overlays a small roughness, that is, R>r, and r / R≤50%, the K value is 0.9;

[0064] When a large roughness overlays a small roughness, that is, R>r, and 50%<r / R≤80%, the K value is 0.95;

[0065] When a large roughness overlays a small roughness, that is, R>r, and r / R>80%, the K value is 1.

[0066] After machining, the surface of a material is left with many uneven peaks and valleys. These microscopic geometric features, formed by valleys spaced at small distances, are called surface roughness. The greater the difference between these peaks and valleys on the material's surface, the greater the surface roughness. Therefore, when a small roughness is overlaid on a large roughness, a roller with a smaller difference between peaks and valleys cannot completely overlay a steel plate with a larger difference between peaks and valleys, and the overlay is difficult and inefficient. Conversely, when a large roughness is overlaid on a small roughness, a roller with a larger difference between peaks and valleys can more easily overlay a steel plate with a smaller difference between peaks and valleys, resulting in high overlay efficiency.

[0067] The |K-1| value represents the difference between the degree of overprinting and complete overprinting (i.e., 100% overprinting rate). The greater the overprinting difficulty, the lower the overprinting efficiency, and the larger the |K-1| value. Conversely, the easier the overprinting difficulty, the higher the overprinting efficiency, and the smaller the |K-1| value.

[0068] Beneficial technical effects

[0069] Compared with the prior art, the technical concept and corresponding technical solutions of the present invention can at least achieve the following beneficial technical effects:

[0070] (1) The present invention takes into account the production technology characteristics of thin strip casting and rolling technology, namely, the large differences in organizational structure, strength performance and surface quality in the edge and middle areas of the cast and rolled thin strip raw materials. By designing the roughness distribution of the textured roller surface of the fifth pickling rolling stand, the problem of roughness difference in the edge and middle areas of the thin strip raw material plate surface is significantly improved, and a rolled hard plate surface with a uniform morphology is obtained, thereby avoiding the color difference problem caused by the surface morphology difference of the finished product edge after subsequent hot-dip galvanizing, and improving the surface quality of the ultra-thin strip galvanized plate;

[0071] (2) The present invention takes into account the production technology characteristics of the thin strip casting technology, that is, the silicon content of the cast and rolled thin strip caused by silicon deoxidation is not less than 0.1%. Compared with the conventional method of adding a pre-oxidation section in the annealing furnace to oxidize the silicon and manganese elements to the inner layer of the substrate, the present invention further combines the raw material composition of each roll of thin strip, formulates the dew point adjustment plan of the annealing furnace and performs reasonable production scheduling, avoids the risk of excessive oxidation when the silicon content of the raw materials varies greatly in large-scale production, and effectively improves the bonding between the zinc layer and the thin strip substrate, solving the problem of coating shedding.

[0072] (3) The present invention takes into account the production technology characteristics of thin strip casting and rolling technology, that is, the strip steel in a high silicon composition system undergoes a long-term hot dip plating operation, which causes the composition of the plating solution to change. By formulating a zinc pot composition adjustment plan, the zinc pot composition is balanced in time, the generation and aggregation of zinc pot slag is reduced, and the surface slag defect problem is improved. DETAILED DESCRIPTION

[0073] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0074] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0075] The following are embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments that can be obtained by ordinary technicians in this field without making any creative work are within the scope of protection of the present invention.

[0076] As described in the summary of the invention, the key process steps of acid continuous rolling, continuous annealing and coating of the present invention are introduced as follows.

[0077] 1. Acid continuous rolling

[0078] (1) The raw material for acid continuous rolling is twin-roll cast thin strip. The width of the thin strip raw material in the same batch is l (unit: mm), the thickness is T (unit: mm), and the roughness value of the middle part of the thin strip raw material is r 中 , the surface roughness of the strip steel at 10mm away from the edge of the strip steel is r 10 .

[0079] The pickling continuous rolling adopts five-stand continuous rolling. The length of the texture roller of the 5# stand is L (in mm), and the distance from the edge of the texture roller (Ll) / 2 is the outermost edge of the strip.

[0080] The roughness of the middle area of the textured roller of the 5# stand is R 中 The roller surface roughness in the area from the edge to the edge of the roller [(Ll) / 2+10] mm is R 边10 The roller surface roughness in the area from [(Ll) / 2+10]mm to [(Ll) / 2+25]mm from the roller edge is R 边25 The roller surface roughness in the area from [(Ll) / 2+25]mm to [(Ll) / 2+40]mm from the roller edge is R 边40 The roller surface roughness in the area from [(Ll) / 2+40]mm to [(Ll) / 2+60]mm from the roller edge is R 边60 .

[0081] The cast and rolled thin strip is rolled through five stands to obtain the target thickness of t (unit: mm) of galvanized raw material hardened strip. The surface morphology of the cast and rolled thin strip changes after acid rolling. After acid rolling, the roughness of the middle part of the thin strip hardened coil is Г 中 , the surface roughness of the strip steel at 10mm away from the edge of the strip steel is Г 边10 .

[0082] Among them, the surface roughness Г of the hard plate after pickling is approximately the product of the surface roughness of the 5# texturing roller in the pickling continuous rolling and the overprint coefficient K, that is, Г≈R×K.

[0083] The overprint coefficient, K, reflects the extent to which the roughness of the No. 5 texture roller transfers to the strip surface topography during the pickling continuous rolling process. Its value is related to the steel grade, rolling force, and overprinting method. The smaller |K-1|, the greater the degree of overprinting of the texture roller surface roughness. In actual production, the effects of steel grade and rolling force on the degree of overprinting of the strip surface topography are negligible.

[0084] Among them, the degree of roller surface roughness overprinting varies with the overprinting method. That is, when the surface roughness R of the 5# texturing roller is less than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the small roughness overprints the large roughness, the |K-1| value is large, and the greater the difference between the two, the larger the |K-1| value, K≥1; when the surface roughness R of the 5# texturing roller is greater than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the large roughness overprints the small roughness, the |K-1| value is large, and the greater the difference between the two, the smaller the |K-1| value, 0<K≤1. The specific scheme is as follows:

[0085] When a small roughness overlays a large roughness, that is, R<r, and R / r≤50%, the K value is 1.4;

[0086] When a small roughness overlays a large roughness, that is, R < r, and 50% < R / r ≤ 75%, the K value is 1.2;

[0087] When a small roughness overlays a large roughness, that is, R < r, and 75% < R / r ≤ 90%, the K value is 1.05;

[0088] When a small roughness overlays a large roughness, that is, R < r, and R / r > 90%, the K value is 1;

[0089] When a large roughness overlays a small roughness, that is, R>r, and r / R≤50%, the K value is 0.9;

[0090] When a large roughness overlays a small roughness, that is, R>r, and 50%<r / R≤80%, the K value is 0.95;

[0091] When a large roughness overlays a small roughness, that is, R>r, and r / R>80%, the K value is 1.

[0092] According to the formula Г≈R×K, when the surface roughness of the edge of the cast-rolled thin strip material is greater than that of the middle area, in order to ensure the surface quality of the galvanized finished product, it is necessary to ensure that the surface roughness of the galvanized raw material rolled hard plate after pickling is consistent. Therefore, it is necessary to adjust the surface roughness distribution of the pickling rolling No. 5 texturing roller, that is, to reduce the roller surface roughness of the edge area of the texturing roller and gradually increase it as it approaches the middle of the strip, and finally keep it consistent with the roller surface roughness in the middle area. The specific solution is as follows:

[0093] R 边10 ≈(R 中 ×K 中 ) / K 边10 ≈(K 中 / K 边10 )×R 中 ;

[0094] R 边25 =R 边10 +(R 中 -R 边10)×70%≈(0.7+0.3K 中 / K 边10 )×R 中 ;

[0095] R 边40 =R 边10 +(R 中 -R 边10 )×90%≈(0.9+0.1K 中 / K 边10 )×R 中 ;

[0096] R 边60 =R 中 .

[0097] 2. Continuous annealing

[0098] The annealing raw material is cast-rolled thin strip hard coil produced after the aforementioned acid continuous rolling process. Annealing is performed in a horizontal continuous annealing furnace, which consists of a preheating section, a heating section, a soaking section, and a cooling section. At the end of the heating section, the furnace atmosphere is adjusted to increase the dew point and oxygen content to achieve pre-oxidation of the strip. This section is called the pre-oxidation section. After pre-oxidation, the strip enters the soaking reduction section, where the dew point is maintained at -50°C to ensure sufficient reduction of iron oxide on the strip surface.

[0099] Among them, the same batch of cast and rolled thin strip raw materials are arranged from low to high silicon content m, with the lowest silicon content being a (unit: wt%) and the highest being b (unit: wt%). 0.1≤a≤m≤b≤1.0wt%. At the beginning of production, the silicon content of the strip is the lowest and the required pre-oxidation degree is the smallest. The dew point of the pre-oxidation stage is recorded as T da As the production process progresses, the silicon content of the strip increases and the required degree of pre-oxidation increases. The dew point of the pre-oxidation section at this stage is recorded as T dm At the end of production, the silicon content of the strip reaches the maximum value b, the required pre-oxidation degree is the maximum, and the dew point in the pre-oxidation furnace is recorded as T db The specific plan is:

[0100] When the silicon content gradually increases in the range of 0.1wt%≤m<0.3wt%, the dew point of the pre-oxidation section is -25℃≤T dm Increase slowly within -22℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 1.5℃;

[0101] When the silicon content gradually increases in the range of 0.3wt%≤m<0.6wt%, the dew point of the pre-oxidation section is -22℃≤T dm Increase slowly within -16℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dmIncrease by 2℃;

[0102] When the silicon content gradually increases in the range of 0.6wt%≤m<1.0wt%, the dew point of the pre-oxidation section is -16℃≤T dm Increase slowly within -6℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 2.5℃.

[0103] 3. Coating process

[0104] After continuous annealing, the strip is cooled to the zinc bath temperature and then enters the zinc bath through the furnace nose to complete the hot-dip galvanizing. As the production of cast and rolled thin strip hot-dip galvanizing continues, the zinc bath composition needs to be sampled and measured every 4 hours to facilitate the adjustment of the bath composition. The specific plan is as follows:

[0105] When the silicon content of the plating solution exceeds 0.01wt%, pure zinc ingot (Zn99.99) is added to adjust the composition;

[0106] When the silicon content of the plating solution exceeds 0.03wt%, it is necessary to switch to transition coil or other galvanized varieties;

[0107] When the silicon content drops below 0.01wt%, the cast and rolled thin strip galvanized sheet is cut back for production.

[0108] The specific embodiments are described as follows (the roughness units in the table below are all μm):

[0109] Table 1 Surface roughness control of cast thin strip and hard coil

[0110]

[0111] Table 2 Dew point control in pre-oxidation section of cast and rolled thin strip galvanized sheet

[0112]

[0113]

[0114] In summary, the present invention protects a hot-dip galvanized sheet with a short-process cast-rolled thin strip as a raw material substrate and a production method thereof. By designing the roughness distribution of the textured roller surface of the fifth pickling rolling stand, the roughness difference in the edge of the thin strip raw material plate is improved, and the color difference problem of the edge of the thin strip raw material after galvanizing is solved; in the batch production process, combined with the composition of each roll of thin strip raw material, by formulating the annealing furnace dew point adjustment plan and carrying out reasonable production scheduling, the combination of the zinc layer and the thin strip substrate is effectively improved, and the problem of coating shedding is solved; taking into full consideration the increase in the silicon content of the plating solution caused by the high-silicon thin strip substrate as the working time increases, by formulating the zinc pot composition adjustment plan to balance the zinc pot composition in time, reduce the generation and aggregation of zinc pot slag, and improve the surface slag defect problem. Finally, a stable production of ultra-thin strip galvanized sheet is achieved. The surface quality requirements of household appliance galvanized sheet are met.

[0115] The key process steps are as follows:

[0116] 1. Acid continuous rolling

[0117] (1) The raw material for acid continuous rolling is twin-roll cast thin strip. The width of the thin strip raw material in the same batch is l (unit: mm), the thickness is T (unit: mm), and the roughness value of the middle part of the thin strip raw material is r 中 , the surface roughness of the strip steel at 10mm away from the edge of the strip steel is r 10 .

[0118] The pickling continuous rolling adopts five-stand continuous rolling. The length of the texture roller of the 5# stand is L (in mm), and the distance from the edge of the texture roller (Ll) / 2 is the outermost edge of the strip.

[0119] The roughness of the middle area of the textured roller of the 5# stand is R 中 The roller surface roughness in the area from the edge to the edge of the roller [(Ll) / 2+10] mm is R 边10 The roller surface roughness in the area from [(Ll) / 2+10]mm to [(Ll) / 2+25]mm from the roller edge is R 边25 The roller surface roughness in the area from [(Ll) / 2+25]mm to [(Ll) / 2+40]mm from the roller edge is R 边40 The roller surface roughness in the area from [(Ll) / 2+40]mm to [(Ll) / 2+60]mm from the roller edge is R 边60 .

[0120] The cast and rolled thin strip is rolled through five stands to obtain the target thickness of t (unit: mm) of galvanized raw material hardened strip. The surface morphology of the cast and rolled thin strip changes after acid rolling. After acid rolling, the roughness of the middle part of the thin strip hardened coil is Г 中 , the surface roughness of the strip steel at 10mm away from the edge of the strip steel is Г 边10 .

[0121] Among them, the surface roughness Г of the hard plate after pickling is approximately the product of the surface roughness of the 5# texturing roller in the pickling continuous rolling and the overprint coefficient K, that is, Г≈R×K.

[0122] The overprint coefficient, K, reflects the extent to which the roughness of the No. 5 texture roller transfers to the strip surface topography during the pickling continuous rolling process. Its value is related to the steel grade, rolling force, and overprinting method. The smaller |K-1|, the greater the degree of overprinting of the texture roller surface roughness. In actual production, the effects of steel grade and rolling force on the degree of overprinting of the strip surface topography are negligible.

[0123] Among them, the degree of roller surface roughness overprinting varies with the overprinting method. That is, when the surface roughness R of the 5# texturing roller is less than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the small roughness overprints the large roughness, the |K-1| value is large, and the greater the difference between the two, the larger the |K-1| value, K≥1; when the surface roughness R of the 5# texturing roller is greater than the surface roughness r of the raw material plate of the cast and rolled thin strip, that is, when the large roughness overprints the small roughness, the |K-1| value is large, and the greater the difference between the two, the smaller the |K-1| value, 0<K≤1. The specific scheme is as follows:

[0124] When a small roughness overlays a large roughness, that is, R<r, and R / r≤50%, the K value is 1.4;

[0125] When a small roughness overlays a large roughness, that is, R < r, and 50% < R / r ≤ 75%, the K value is 1.2;

[0126] When a small roughness overlays a large roughness, that is, R < r, and 75% < R / r ≤ 90%, the K value is 1.05;

[0127] When a small roughness overlays a large roughness, that is, R < r, and R / r > 90%, the K value is 1;

[0128] When a large roughness overlays a small roughness, that is, R>r, and r / R≤50%, the K value is 0.9;

[0129] When a large roughness overlays a small roughness, that is, R>r, and 50%<r / R≤80%, the K value is 0.95;

[0130] When a large roughness overlays a small roughness, that is, R>r, and r / R>80%, the K value is 1.

[0131] According to the formula Г≈R×K, when the surface roughness of the edge of the cast-rolled thin strip material is greater than that of the middle area, in order to ensure the surface quality of the galvanized finished product, it is necessary to ensure that the surface roughness of the galvanized raw material rolled hard plate after pickling is consistent. Therefore, it is necessary to adjust the surface roughness distribution of the pickling rolling No. 5 texturing roller, that is, to reduce the roller surface roughness of the edge area of the texturing roller and gradually increase it as it approaches the middle of the strip, and finally keep it consistent with the roller surface roughness in the middle area. The specific solution is as follows:

[0132] R 边10 ≈(R 中 ×K 中 ) / K 边10 ≈(K 中 / K 边10 )×R 中 ;

[0133] R 边25 =R 边10 +(R 中 -R 边10 )×70%≈(0.7+0.3K 中 / K 边10 )×R 中 ;

[0134] R 边40 =R 边10 +(R 中 -R 边10 )×90%≈(0.9+0.1K 中 / K 边10 )×R 中 ;

[0135] R 边60 =R 中 .

[0136] 2. Continuous annealing

[0137] The annealing raw material is cast-rolled thin strip hard coil produced after the aforementioned acid continuous rolling process. Annealing is performed in a horizontal continuous annealing furnace, which consists of a preheating section, a heating section, a soaking section, and a cooling section. At the end of the heating section, the furnace atmosphere is adjusted to increase the dew point and oxygen content to achieve pre-oxidation of the strip. This section is called the pre-oxidation section. After pre-oxidation, the strip enters the soaking reduction section, where the dew point is maintained at -50°C to ensure sufficient reduction of iron oxide on the strip surface.

[0138] Among them, the same batch of cast and rolled thin strip raw materials are arranged from low to high silicon content m, with the lowest silicon content being a (unit: wt%) and the highest being b (unit: wt%). 0.1≤a≤m≤b≤1.0wt%. At the beginning of production, the silicon content of the strip is the lowest and the required pre-oxidation degree is the smallest. The dew point of the pre-oxidation stage is recorded as T daAs the production process progresses, the silicon content of the strip increases and the required degree of pre-oxidation increases. The dew point of the pre-oxidation section at this stage is recorded as T dm At the end of production, the silicon content of the strip reaches the maximum value b, the required pre-oxidation degree is the maximum, and the dew point in the pre-oxidation furnace is recorded as T db The specific plan is:

[0139] When the silicon content gradually increases in the range of 0.1wt%≤m<0.3wt%, the dew point of the pre-oxidation section is -25℃≤T dm Increase slowly within -22℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 1.5℃;

[0140] When the silicon content gradually increases in the range of 0.3wt%≤m<0.6wt%, the dew point of the pre-oxidation section is -22℃≤T dm Increase slowly within -16℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 2℃;

[0141] When the silicon content gradually increases in the range of 0.6wt%≤m<1.0wt%, the dew point of the pre-oxidation section is -16℃≤T dm Increase slowly within -6℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 2.5℃.

[0142] 3. Coating process

[0143] After continuous annealing, the strip is cooled to the zinc bath temperature and then enters the zinc bath through the furnace nose to complete the hot-dip galvanizing. As the production of cast and rolled thin strip hot-dip galvanizing continues, the zinc bath composition needs to be sampled and measured every 4 hours to facilitate the adjustment of the bath composition. The specific plan is as follows:

[0144] When the silicon content of the plating solution exceeds 0.01wt%, pure zinc ingot (Zn99.99) is added to adjust the composition;

[0145] When the silicon content of the plating solution exceeds 0.03wt%, it is necessary to switch to transition coil or other galvanized varieties;

[0146] When the silicon content drops below 0.01wt%, the cast and rolled thin strip galvanized sheet is cut back for production.

[0147] The above description is only a specific embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, they can make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing hot-dip galvanized sheet based on twin-roll thin strip casting technology, characterized in that: The method comprises the following steps: (1) Using a thin strip with a thickness of 0.9 to 1.3 mm obtained by twin-roller thin strip casting as raw material, the hardened strip is obtained by acid continuous rolling; (2) Continuously annealing the hardened strip steel, dynamically adjusting the dew point temperature of the pre-oxidation section according to the silicon content of the strip steel during the annealing process; (3) Immerse the annealed strip into a zinc pot for hot-dip galvanizing, and regularly test the silicon content of the zinc liquid to adjust the composition of the zinc pot.

2. The method according to claim 1, wherein: The acid continuous rolling adopts five-stand continuous rolling to reduce the roughness of the roller surface in the edge area of the texturing roller and gradually increase it near the middle of the strip until it is consistent with the roughness of the roller surface in the middle area. R 边10 ≈(R 中 ×K 中 ) / K 边10 ≈(K 中 / K 边10 )×R 中 ; in: R 边10 R is the roller surface roughness in the area from the edge to the roller edge [(Ll) / 2+10] mm, 中 K is the roughness of the middle area of the texturing roller of the 5# stand, 中 is the middle overprint coefficient, K 边10 It is the overprint coefficient of the 10mm edge area.

3. The method according to claim 2, characterized in that The roller surface roughness is further controlled as follows: R 边25 =R 边10 +(R 中 -R 边10 )×70%≈(0.7+0.3K 中 / K 边10 )×R 中 ; in: R 边25 It is the roller surface roughness in the area from [(Ll) / 2+10]mm to [(Ll) / 2+25]mm from the roller edge.

4. The method according to claim 3, characterized in that The roller surface roughness is further controlled as follows: R 边40 =R 边10 +(R 中 -R 边10 )×90%≈(0.9+0.1K 中 / K 边10 )×R 中 ; in: The roller surface roughness in the area from [(Ll) / 2+25]mm to [(Ll) / 2+40]mm from the roller edge is R 边40 .

5. The method according to claim 4, characterized in that The roller surface roughness is further controlled as follows: R 边60 =R 中 , in: R 边60 It is the roller surface roughness in the area from [(Ll) / 2+40]mm to [(Ll) / 2+60]mm from the roller edge.

6. The method according to any one of claims 1 to 5, characterized in that The annealing raw material is the cast-rolled thin strip hard coil produced after the acid continuous rolling process. The annealing adopts a horizontal continuous annealing furnace. The annealing process is divided into preheating section, heating section, soaking section and cooling section.

7. The method according to claim 6, characterized in that At the end of the heating section, the furnace atmosphere is adjusted to increase the dew point and oxygen content to achieve pre-oxidation of the strip. This furnace section is defined as the pre-oxidation section.

8. The method according to claim 7, characterized in that After pre-oxidation, the strip enters the soaking reduction section. The dew point temperature of the atmosphere in this furnace section is -50℃, which ensures the full reduction of the iron oxide on the strip surface.

9. The method according to any one of claims 1 to 5, characterized in that The hard coils of the same batch of cast and rolled thin strip raw materials are arranged from low to high according to the silicon content m, with the lowest silicon content being a (unit: wt%) and the highest being b (unit: wt%), 0.1≤a≤m≤b≤1.0wt%: At the beginning of production, the silicon content of the strip is the lowest and the required pre-oxidation degree is the smallest. The dew point of the pre-oxidation section is recorded as T da ; As the production process progresses, the silicon content of the strip increases and the required pre-oxidation degree increases. The dew point of the pre-oxidation section at this stage is recorded as T dm ; At the end of production, the silicon content of the strip reaches the maximum value b, the required pre-oxidation degree is the highest, and the dew point in the pre-oxidation furnace is recorded as T db .

10. The method according to any one of claims 1 to 5, characterized in that When the silicon content gradually increases in the range of 0.1wt%≤m<0.3wt%, the dew point of the pre-oxidation section is -25℃≤T dm Increase slowly within -22℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 1.5℃.

11. The method according to any one of claims 1 to 5, characterized in that When the silicon content gradually increases in the range of 0.3wt%≤m<0.6wt%, the dew point of the pre-oxidation section is -22℃≤T dm Increase slowly within -16℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 2℃.

12. The method according to any one of claims 1 to 5, characterized in that When the silicon content gradually increases in the range of 0.6wt%≤m<1.0wt%, the dew point of the pre-oxidation section is -16℃≤T dm Increase slowly within -6℃, where the dew point temperature T increases with every 0.1wt% increase in silicon content m. dm Increase by 2.5℃.

13. The method according to any one of claims 1 to 5, characterized in that As the production of cast and rolled thin strip hot-dip galvanizing continues, the zinc pot composition is sampled and measured every 4 hours to facilitate adjustment of the plating solution composition.

14. The method according to any one of claims 1 to 5, characterized in that: When the silicon content of the plating solution exceeds 0.01wt%, pure zinc ingot (Zn99.99) is added to adjust the composition; When the silicon content of the plating solution exceeds 0.03wt%, it is necessary to switch to transition coil or other galvanized varieties; When the silicon content drops below 0.01wt%, the cast and rolled thin strip galvanized sheet is cut back for production.

15. A method for improving the color difference of the edge of a twin-roll cast galvanized thin strip, characterized by: By adjusting the roughness gradient from the edge to the middle of the textured roller of the fifth stand of pickling mill, the surface roughness difference between the edge and the middle of the hardened strip steel is made ≤10%.

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