High-surface-quality invar alloy cold-rolled steel strip and manufacturing method thereof

Abstract

The invention discloses a high-surface-quality invar alloy cold-rolled steel strip and a manufacturing method thereof.The manufacturing method comprises the working procedures of acid pickling, cold rolling and pre-pressing, coping, cold rolling and rolling, cleaning, annealing, leveling, shearing and packaging, the surface of an invar alloy hot-rolled steel coil is subjected to acid pickling through a mixed acid solution, cold rolling and pre-pressing are conducted through three-pass cold rolling and rolling, and the surface quality of the invar alloy hot-rolled steel coil is improved. At least three pairs of grinding heads are adopted for grinding, the grinding frequency is not less than 3 times, multi-pass cold rolling is carried out after grinding, the number n of rolling passes meets the condition that n is larger than or equal to 0.5 * m + 1, m is the thickness of the ground cold-rolled steel strip, and the unit is mm. According to the method, the technical problems that the surface quality of the invar alloy cold-rolled strip is difficult to control, the requirement is high and the like can be effectively solved, invar alloy products with high surface quality and high plate shape requirement are prepared, and the high-surface-quality use requirement of a user is met.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of invar alloy materials, and more particularly to an invar alloy cold-rolled steel strip with high surface quality and a manufacturing method thereof. BACKGROUND

[0002] With the high-quality development and industrial upgrading of China's manufacturing industry, the surface quality requirements of cold-rolled raw materials for high-end equipment in the fields of energy, petrochemical, environmental protection, etc. are becoming higher and higher. The production process of cold-rolled materials is long, and surface defects such as pits, scratches, pollution, and roughness are easily generated during the production process. During the service process of the strip processing equipment, these defects may become the breakthrough point of strong corrosive medium, resulting in local defects such as pitting corrosion and crevice corrosion, reducing the service life of the equipment, and seriously affecting the service safety of the equipment. Therefore, it is necessary to optimize the key process of cold-rolled plate production to eliminate or avoid common surface defects.

[0003] Invar alloy is a Fe-Ni alloy with a Ni content of about 36wt%, and its thermal expansion coefficient at room temperature is only about 1 / 10 of that of most metal materials, and its thermal expansion coefficient is approximately constant in the range of-200~200℃. It is widely used in practical engineering application scenarios that require high dimensional precision stability within the service temperature range, such as the construction of large LNG transport ship liquid cargo membrane tank systems. The invar alloy for LNG ships has strict requirements on the surface quality of the material, and the surface cannot have visible defects and dirt, which is almost a zero defect requirement. Therefore, how to control the surface quality of the cold-rolled strip during actual cold-rolled production is crucial.

[0004] The technologies related to the bell-type annealing furnace are as follows:

[0005] Chinese Patent Publication No. CN118417310A relates to a method for improving the surface quality of high-quality austenitic stainless steel cold-rolled plates. By optimizing the process cold plate production process, increasing the surface grinding after the first pass cold rolling and the surface coating before longitudinal cutting, and controlling the cold rolling deformation, grinding, pickling, longitudinal cutting, transverse cutting, and other key process parameters, and taking special measures, the surface defects such as pits, scratches, pollution, roughness, and micro-cracks on the surface of the cold-rolled plate are greatly reduced, and the service life and use safety are greatly improved. However, this method does not set a cleaning process after the final rolling, which results in the inability to effectively remove the oil stains and impurities generated on the surface during the rolling process of the steel coil, and there is a risk of leaving them on the surface of the finished steel coil.

[0006] Chinese patent application number CN202411417367.3 relates to a high cold formability austenitic stainless steel cold-rolled sheet and its production method. The method mainly solves the technical problem of poor cold formability of austenitic stainless steel cold-rolled sheet, optimizes the composition of austenitic stainless steel cold-rolled sheet to optimize the performance stability of the cold-rolled sheet, thereby improving the cold forming performance of the cold-rolled sheet; but the invention method does not involve surface quality control, and cannot effectively improve the surface quality of the strip.

[0007] Chinese patent publication number CN115612798A relates to a manufacturing method of high-chromium-nickel stainless steel cold-rolled thin steel strip, which significantly improves the production efficiency of hot pickling and finished product annealing, solves the problems of rough stripes, over-pickling or scale residue on the surface of high-chromium-nickel stainless steel cold-rolled sheet, and improves its corrosion resistance. The high-chromium-nickel stainless steel cold-rolled sheet produced by this process has entered the industry with high requirements for surface corrosion resistance such as electric heating pipe and automobile corrugated pipe. This method can solve the problem of rough surface, but it cannot solve the problem of dirt and foreign matter on the surface of the strip.

[0008] In summary, there are few cold-rolled strips with high surface quality requirements, and there are few cold-rolled processes related to invar alloy materials. Therefore, it is necessary to develop an invar alloy cold-rolled steel strip with high surface quality requirements and its manufacturing method to solve the problem of local defects such as point corrosion and seam corrosion caused by long production process, unstable surface quality, easy to produce pressure pit, scratches, and pollution of invar alloy cold-rolled steel strip, thereby reducing the service life of equipment and seriously affecting the safety of equipment in service. SUMMARY

[0009] In view of the defects in the prior art, the purpose of the present application is to provide an invar alloy cold-rolled steel strip with high surface quality and its manufacturing method, which can effectively solve the technical problems of difficult control and high requirements of invar alloy cold-rolled strip surface quality, prepare invar alloy products with high surface quality and high plate shape requirements, and meet the high surface quality requirements of users.

[0010] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0011] The first aspect of the present application provides an invar alloy cold-rolled steel strip with high surface quality and its manufacturing method, which adopts the processes of pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → flattening → shearing and packaging, specifically including the following steps:

[0012] S1, pickling, using a mixed acid solution to pickle the invar alloy hot-rolled steel coil, then using an aqueous solution to rinse, and then drying with hot air and coiling;

[0013] S2, cold rolling pre-pressing, the invar alloy hot-rolled steel coil after step S1 is treated by cold rolling pre-pressing, three passes of cold rolling are adopted, and the reduction of each pass is controlled within 0.4 mm, and the total reduction is 0.5-1.0 mm;

[0014] S3, grinding, the cold-rolled steel strip after the cold rolling pre-pressing is ground, and at least three pairs of grinding heads are used for the grinding, and the grinding times are not less than three times;

[0015] S4, cold rolling, the cold-rolled steel strip after the grinding is cold-rolled in multiple passes, and the rolling pass number n satisfies n≥0.5×m+1, and m is the thickness of the cold-rolled steel strip after the grinding, in mm;

[0016] S5, cleaning, the cold-rolled steel strip after the cold rolling is cleaned, and then annealed;

[0017] When the thickness of the invar alloy cold-rolled steel strip product is greater than 2 mm, the holding temperature of the bright annealing furnace used for annealing is greater than or equal to 1000 DEG C, and the moving speed of the invar alloy cold-rolled steel strip in the bright annealing furnace is greater than or equal to 5 m / min; otherwise, the holding temperature of the bright annealing furnace used for annealing is less than or equal to 950 DEG C, and the moving speed of the invar alloy cold-rolled steel strip in the bright annealing furnace is less than 5 m / min;

[0018] S6, the cold-rolled steel strip after the annealing is flattened, and then cut to the product size and packaged.

[0019] Preferably, in step S1:

[0020] The composition of the invar alloy hot-rolled steel coil is as follows in terms of mass percentage: C≤0.04%, Si≤0.7%, Mn≤0.8%, P≤0.040%, S≤0.08%, 30%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, and the rest is Fe and inevitable residual elements;

[0021] The thickness of the invar alloy hot-rolled steel coil strip is less than 5 mm, and preferably the thickness is 3.5-4.5 mm.

[0022] Preferably, in step S1:

[0023] The composition of the mixed acid solution is HCl, H2SO4 and water, the content of HCl is 300-400 g / L, and the content of H2SO4 is 100-200 g / L;

[0024] The aqueous solution is recycled water with an acid concentration of less than 0.15 g / L.

[0025] In step S1, the surface residual acid is rinsed clean with an aqueous solution after pickling to prevent excessive pickling corrosion of the surface of the hot-rolled coil by the residual acid solution on the surface, affecting the surface quality of the cold-rolled strip; during pickling, if the HCl concentration is less than 300 g / L, the pickling effect of the surface oxide scale is poor, the surface oxide scale of the Invar alloy hot-rolled coil cannot be effectively removed and cleaned, and the honeycomb-shaped oxides are easily left on the surface of the hot-rolled coil, resulting in surface quality defects such as "oxygen residues" on the surface of the cold-rolled coil; if the HCl concentration is greater than 400 g / L, the surface of the cold-rolled coil is easily over-corroded, and surface defects such as corrosion pits of the cold-rolled strip are formed, and the surface corrosion defects cannot be removed in the subsequent cold-rolling process. If the H2SO4 concentration is greater than 200 g / L, the surface of the cold-rolled coil is easily passivated, and the oxide scale is difficult to remove by pickling; if the H2SO4 concentration is less than 100 g / L, the HCl is easily diluted during pickling, thereby resulting in poor pickling effect of the oxide scale on the surface of the hot-rolled coil in the later stage.

[0026] Preferably, in step S2, the rolling force of the three-pass cold rolling is ≤2000N, the thickness reduction of a single pass is ≤0.4mm, and the flatness is controlled to be ≤5mm / m. For example, the rolling force of the roller is 1500-1900N, the thickness reduction of a single pass can be 0.1-0.4mm, and the flatness can be controlled to be 1-5mm / m.

[0027] In step S2, the cold rolling pre-pressing not only ensures that the thickness meets the requirements of the grinding process, but also improves the plate shape and improves the efficiency and quality of the grinding process. The grinding process can effectively improve the surface quality of the ground plate and completely remove the residual oxide scale on the surface of the Invar alloy. However, if the rolling force is greater than 2000N, the surface processing performance of the cold-rolled steel strip is poor, resulting in easy work hardening of the cold-rolled steel strip surface, affecting the subsequent grinding process effect. The thickness reduction of a single pass needs to be controlled within the range of 0.1-0.4mm, if the thickness reduction of a single pass is less than 0.1mm, the plate shape control is poor, and the subsequent grinding requirements cannot be met; if the thickness reduction of a single pass is greater than 0.4mm, the surface work hardening is large, and the strip surface is easy to slip during the subsequent grinding process, thereby affecting the grinding effect. The total reduction of the cold rolling pre-pressing is controlled within the range of 0.5-1.0mm, and it is strictly prohibited to be greater than 1.0mm, otherwise the reduction is too large and the surface of the cold-rolled strip is easy to form work hardening, and the high surface hardness easily leads to slipping of the abrasive belt on the surface of the cold-rolled steel strip during grinding, and the oxide scale on the surface of the cold-rolled steel strip cannot be ground clean.

[0028] Preferably, in step S3:

[0029] the grinding head unit used for grinding is symmetrically distributed above and below, the grinding head unit is used for grinding not less than 2 times with a 100 mesh abrasive belt, and not less than 1 time with a 150 mesh abrasive belt;

[0030] The pressure of the grinding head unit is not less than 200N, such as 250-300N. If the pressure of the grinding head is less than 200N, the metal oxides on the surface of the cold-rolled steel strip cannot be effectively removed, resulting in residual oxides. In the grinding process of step S3, the surface oxides of the invar alloy are honeycomb oxides, part of the Fe2O3 and Fe3O4 oxides are wrapped in the honeycomb Ni element structure, and it is difficult to remove the surface oxides completely by pickling. The grinding process can effectively remove the residual oxide scale on the surface of the invar alloy and improve the surface quality of the invar alloy grinding plate. In addition, at least three grinding heads are used for grinding, and the grinding frequency is not less than three times. If the number of grinding heads is too small, the cold-rolled coil will not be ground completely, resulting in some oxides remaining on the surface of the cold-rolled coil, which will form defects such as residual oxygen in the subsequent process. Because the invar alloy surface is prone to potential corrosion, after grinding with 100-mesh coarse sand belt, fine grinding is performed with 150-mesh fine sand belt, which can improve the surface roughness of the strip, reduce the depth of the grinding marks, and reduce the risk of potential corrosion. At the same time, fine grinding can further grind the residual roots of surface oxides.

[0031] Preferably, in step S4:

[0032] The cold rolling process uses a twenty-roll cold rolling mill;

[0033] The number of rolling passes satisfies the following requirements: when the invar cold-rolled steel strip product thickness is less than 2mm, the number of rolling passes n is greater than or equal to 4, otherwise, the number of rolling passes n is less than 4;

[0034] In the cold rolling process of step S4, the pass reduction amount of multi-pass cold rolling is set from large to small. In the preferred scheme, the first pass reduction amount can be controlled in the range of 0.3-0.5mm, the second pass reduction amount can be controlled in the range of 0.2-0.3mm, the third pass reduction amount is controlled in the range of 0.1-0.2mm, and if a fourth rolling pass is needed, the fourth pass reduction amount is controlled in the range of 0.1-0.15mm.

[0035] In the cold rolling process of step S4, the cold-rolled coil after grinding is rolled to the target thickness, and the rolling passes are adjusted according to the requirements of different target thicknesses. If the invar cold-rolled steel strip product thickness is less than 2mm, the number of rolling passes n is greater than or equal to 4; if the product thickness is greater than or equal to 2mm, the number of rolling passes n is less than 4, so that the rolling thickness of each pass is controlled within a reasonable range, preventing the rolling reduction of a single pass from being too large, thereby causing texture in the internal structure of the invar material, affecting the anisotropy of the strip, and causing differences in the welding performance of the material in different directions.

[0036] Preferably, in step S5:

[0037] In the cleaning process, a Na2SO4 alkaline solution with a concentration of ≥0.5% is used, and after cleaning, the surface of the cold-rolled steel coil is cleaned with a brush, and then hot air with a temperature of ≥60°C is used for blowing and drying; for example, the concentration of the alkaline solution can be 0.6-1.0%, and the temperature of the hot air can be 60-80°C.

[0038] In the annealing process, when the thickness of the Invar cold-rolled steel strip product is >2 mm and ≤4 mm, the holding temperature is 1000-1050°C, and the moving speed is 5-8 m / min; otherwise, when the thickness of the Invar cold-rolled steel strip product is ≥0.5 mm and ≤2 mm, the holding temperature is 900-950°C, and the moving speed is 2-4 m / min. In the cleaning process of step S5, a Na2SO4 alkaline solution is used, and hot air is used to dry the surface water marks, so as to prevent rolling emulsion and water marks from remaining on the surface of the steel coil and forming oxides; through the cleaning process, the rolling oil and residual dirt and foreign matters on the surface of the cold-rolled strip can be effectively removed, the hot air blowing can effectively dry the water vapor on the surface of the strip, and rusting of the surface of the strip can be prevented, so as to improve the surface quality.

[0039] In the annealing process of step S5, when the thickness of the product is >2 mm (for example, 2-4 mm, not including 2 mm), the holding temperature of the bright annealing furnace is ≥1000°C (for example, 1000-1050°C), and the moving speed is ≥5 m / min (for example, 5-8 m / min); if the holding temperature is less than 1000°C, the microstructure of the strip cannot be fully recrystallized, so that the residual stress in the material cannot be released. When the thickness of the product is ≤2 mm (for example, 0.5-2 mm, including 2 mm), the holding temperature of the bright annealing furnace is ≤950°C (for example, 900-950°C), and the moving speed of the Invar cold-rolled steel strip in the bright annealing furnace is <5 m / min (for example, 2-4 m / min); if the temperature is greater than 950°C and the moving speed of the steel strip is too fast, the cold-rolled strip cannot be fully recrystallized, and the residual stress in the cold-rolled strip cannot be effectively removed.

[0040] Preferably, in step S6, in the skin pass process, the skin pass force of the skin pass roll is >200 N, and the flatness requirement is ≤5 mm / m. For example, the skin pass force can be controlled to be 210-250 N, and the flatness is ≤3 mm / m.

[0041] The second aspect of the present application provides a high-surface-quality Invar cold-rolled steel strip obtained by the manufacturing method of the high-surface-quality Invar cold-rolled steel strip according to the first aspect of the present application, wherein the yield strength of the Invar cold-rolled steel strip is ≥250 MPa, the surface flatness is ≤3 mm / m, the plate shape wave height is ≤3.5 mm, the oxygen residual density is ≤5 / m 2 (for example, ≤2 / m 2 ), the dirt defect density is ≤5 / m 2 (for example, ≤2 / m2 ).

[0042] Preferably, the yield strength of the Invar alloy cold-rolled steel strip is ≥285MPa (e.g., 285-300MPa).

[0043] The high surface quality Invar alloy cold-rolled steel strip and its manufacturing method provided by this invention have the following beneficial effects:

[0044] This invention removes honeycomb-like iron oxide scale and microcracks from the surface of Invar alloy through pickling and grinding processes, improving the surface quality of cold-rolled strip raw materials. Pre-cold rolling before grinding ensures the strip thickness meets the grinding requirements while improving the strip shape and increasing the efficiency and quality of the grinding process. The grinding process effectively improves the surface quality of the ground strip, completely removing residual oxide scale from the Invar alloy surface. After cold rolling, a cleaning process further removes dirt and foreign matter from the surface of the cold-rolled steel strip, improving surface quality. This invention controls the surface quality of cold-rolled strip through multiple processes, rationally setting the relationship between finished product thickness and annealing temperature and moving speed process parameters to ensure sufficient removal of rolling stress while avoiding excessively long high-temperature annealing time, which could lead to grain growth and deterioration of the strip's mechanical properties. It effectively solves the technical challenges of difficult oxide scale removal, difficult surface quality control, and high requirements for Invar alloy cold-rolled strip, producing Invar alloy products with high surface quality and high strip shape requirements, meeting users' demands for high-surface-quality products. Attached Figure Description

[0045] Figure 1 This is a schematic flowchart of the high surface quality Invar alloy cold-rolled steel strip and its manufacturing method according to the present invention;

[0046] Figure 2 This is a microscopic morphology diagram of the oxide layer on the surface of Invar alloy hot-rolled steel coil;

[0047] Figure 3 This is a microscopic morphology image of the high surface quality Invar alloy cold-rolled steel strip prepared in Example 1 of the present invention;

[0048] Figure 4 This is a photograph of the high surface quality Invar alloy cold-rolled steel strip of Embodiment 1 of the present invention. Detailed Implementation

[0049] To better understand the above-mentioned technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0050] Example 1

[0051] like Figure 1As shown, the manufacturing process of the high surface quality Invar alloy cold-rolled steel strip in this embodiment is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging.

[0052] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution, dried with hot air, and then coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 310g / L, H2SO4 content of 190g / L, and the remainder being an aqueous solution. The surface of the hot-rolled steel coil was then cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three passes of cold rolling pre-pressing, with a rolling force of 1900N. The first pass resulted in a thickness reduction of 0.15mm, with flatness controlled to ≤5mm / m. The subsequent two passes gradually increased the reduction (0.35mm and 0.40mm respectively), ensuring a total reduction of 0.90mm in the cold rolling pre-pressing process. Finally, the cold-rolled steel strip was ground, with three pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. The grinding head applied a reduction force of 250N each time. The cold rolling process was performed using a 20-roll cold rolling mill, with four passes (n≥0.5×3.1+1=2.55, resulting in a cold-rolled steel strip thickness of 3.1mm). The reduction amounts per pass were 0.5mm, 0.3mm, 0.2mm, and 0.1mm, respectively, with the final rolled thickness controlled at 2.0mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 0.9% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it was dried using 60℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 930℃. The cold-rolled steel strip moves at a speed of 4m / min in the continuous annealing furnace. After annealing, the cold-rolled coil needs to be leveled. The leveling roller force is controlled at 250N, and the straightness must meet ≤3mm / m. Then, it is cut according to the user's size requirements.

[0053] Example 2

[0054] like Figure 1 As shown, the manufacturing process of the high surface quality Invar alloy cold-rolled steel strip in this embodiment is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging.

[0055] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution, dried with hot air, and then coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 380g / L, H2SO4 content of 180g / L, and the remainder being an aqueous solution. The surface of the hot-rolled steel coil was then cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three passes of cold rolling pre-pressing, with a rolling force of 1950N. The first pass resulted in a thickness reduction of 0.25mm, with flatness controlled to ≤4mm / m. The subsequent two passes gradually increased the reduction (0.30mm and 0.35mm respectively), ensuring a total reduction of 0.9mm in the cold rolling pre-pressing process. Finally, the cold-rolled coil was ground, with five pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. Each grinding operation involved a grinding head reduction force of 300N. The cold rolling process was performed using a 20-roll cold rolling mill, with three passes (n≥0.5×3.1+1=2.55, resulting in a cold-rolled steel strip thickness of 3.1mm). The reduction amounts per pass were 0.3mm, 0.2mm, and 0.1mm, respectively, with the final rolled thickness controlled at 2.5mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 1.0% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it was dried using 80℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 1050℃. The cold-rolled steel strip moves at a speed of 5m / min in the continuous annealing furnace. After annealing, the cold-rolled coil needs to be leveled. The leveling roller force is controlled at 300N, and the straightness must meet ≤2mm / m. Then, it is cut according to the user's size requirements.

[0056] Example 3

[0057] like Figure 1 As shown, the manufacturing process of the high surface quality Invar alloy cold-rolled steel strip in this embodiment is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging.

[0058] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution and dried with hot air before being coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 390g / L, H2SO4 content of 150g / L, and the remainder being an aqueous solution. The surface of the hot-rolled steel coil was then cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three passes of cold rolling pre-pressing, with a rolling force of 1800N. The first pass resulted in a thickness reduction of 0.20mm, with flatness controlled to ≤4mm / m. The subsequent two passes had reductions of 0.30mm and 0.30mm respectively, ensuring a total reduction of 0.8mm in the cold rolling pre-pressing process. Finally, the cold-rolled coil was ground, with six pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. Each grinding operation involved a grinding head reduction force of 350N. The cold rolling process was performed using a 20-roll cold rolling mill, with three passes (n≥0.5×3.2+1=2.6, resulting in a cold-rolled steel strip thickness of 3.2mm). The reduction amounts for each pass were 0.5mm, 0.3mm, and 0.2mm, respectively, with the final rolled thickness controlled at 2.2mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 1.5% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it was dried using 75℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 920℃. The cold-rolled steel strip moves at a speed of 4m / min in the continuous annealing furnace. After annealing, the cold-rolled coil needs to be leveled. The leveling roller force is controlled at 280N, and the straightness must meet ≤2mm / m. Then, it is cut according to the user's size requirements.

[0059] Example 4

[0060] like Figure 1 As shown, the manufacturing process of the high surface quality Invar alloy cold-rolled steel strip in this embodiment is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging.

[0061] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution, dried with hot air, and then coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 320g / L, H2SO4 content of 195g / L, and the remainder being an aqueous solution. The surface of the hot-rolled steel coil was then cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three passes of cold rolling pre-pressing, with a rolling force of 1700N. The first pass resulted in a thickness reduction of 0.20mm, with flatness controlled to ≤5mm / m. The subsequent two passes had reductions of 0.20mm and 0.30mm respectively, ensuring a total reduction of 0.7mm in the cold rolling pre-pressing process. Finally, the cold-rolled coil was ground, with six pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. Each grinding operation involved a grinding head reduction force of 350N. The cold rolling process was performed using a 20-roll cold rolling mill, with three passes (n≥0.5×3.3+1=2.65, resulting in a cold-rolled steel strip thickness of 3.3mm). The reductions per pass were 0.40mm, 0.30mm, and 0.10mm, respectively, with the final rolled thickness controlled at 2.5mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 1.5% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it was dried using 75℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 950℃. The cold-rolled steel strip moves at a speed of 4m / min in the continuous annealing furnace. After annealing, the cold-rolled coil needs to be leveled. The leveling roller force is controlled at 280N, and the flatness meets the requirement of ≤2mm / m. Then, it is cut according to the user's size requirements.

[0062] Example 5

[0063] like Figure 1 As shown, the manufacturing process of the high surface quality Invar alloy cold-rolled steel strip in this embodiment is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging.

[0064] A 4.0 mm thick Invar alloy hot-rolled steel coil (composition shown in Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution and dried with hot air before being coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 380 g / L, H2SO4 content of 115 g / L, and the remainder being an aqueous solution. After pickling, the surface of the hot-rolled steel coil was cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10 g / L. The pickled hot-rolled coil underwent three-pass cold rolling pre-pressing, with a rolling force of 1600 N. The thickness reduction in the first pass was 0.20 mm, and the flatness was controlled to be ≤3.5 mm / m. The reductions in the subsequent two passes were 0.30 mm and 0.30 mm, respectively, ensuring a total cold rolling pre-pressing reduction of 0.80 mm. The cold-rolled coil was then ground, with six pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. Each grinding operation involved a grinding head reduction force of 350N. The cold rolling process was performed using a 20-roll cold rolling mill, with three passes (n≥0.5×3.2+1=2.6, resulting in a cold-rolled steel strip thickness of 3.2mm). The reductions per pass were 0.4mm, 0.2mm, and 0.1mm, respectively, with the final rolled thickness controlled at 2.5mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 1.5% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the steel coil. Finally, the strip was dried using 75℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 940℃. The cold-rolled steel strip moves at a speed of 4m / min in the continuous annealing furnace. After annealing, the cold-rolled coil needs to be leveled. The leveling roller force is controlled at 280N, and the straightness must meet ≤2mm / m. Then, it is cut according to the user's size requirements.

[0065] Comparative Example 1

[0066] Most parameters of this comparative example are the same as those of Example 4, the difference being in the cold rolling pre-pressing and cold rolling processes. The specific process flow is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging.

[0067] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Example 4 of Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution, dried with hot air, and then coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 320g / L, H2SO4 content of 195g / L, and the remainder being an aqueous solution. After pickling, the surface of the hot-rolled steel coil was cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three-pass cold rolling pre-pressing, with a rolling force of 1900N. The thickness reduction in the first pass was 0.50mm, and the flatness was controlled to be ≤4mm / m. The reductions in the subsequent two passes were 0.25mm and 0.30mm, respectively, ensuring a total reduction of 1.05mm in the cold rolling pre-pressing process. Finally, the cold-rolled coil was ground, with six pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. Each grinding operation involved a grinding head reduction force of 350N. The cold rolling process was performed using a 20-roll cold rolling mill, with three passes (n≥0.5×2.95+1=2.475mm, resulting in a cold-rolled steel strip thickness of 2.95mm). The reduction amounts per pass were 0.60mm, 0.40mm, and 0.15mm, respectively, with the final rolled thickness controlled at 1.80mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 1.5% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it was dried using 75℃ hot air. After drying, the cold-rolled coil needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 950℃. The cold-rolled steel strip moves at a speed of 4m / min in the continuous annealing furnace. After annealing, the cold-rolled coil needs to be leveled. The leveling roller force is controlled at 280N, and the flatness meets the requirement of ≤2mm / m. Then, it is cut according to the user's size requirements.

[0068] Comparative Example 2

[0069] This comparative example is largely the same as Example 1, except for the pickling process. The specific process flow is pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging, as detailed below:

[0070] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Example 1 of Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution, dried with hot air, and then coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 500g / L, H2SO4 content of 300g / L, and the remainder being an aqueous solution. After pickling, the surface of the hot-rolled steel coil was cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three-pass cold rolling pre-pressing, with a rolling force of 1900N. The thickness reduction in the first pass was 0.15mm, and the flatness was controlled to be ≤5mm / m. The reduction was gradually increased in the subsequent two passes (0.35mm and 0.40mm, respectively), ensuring that the total reduction in cold rolling pre-pressing was 0.90mm. The cold-rolled coil is then ground, with three pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations use 100-mesh abrasive belts, and the third uses 150-mesh abrasive belts. Each grinding operation involves a grinding head reduction force of 250N. The cold rolling process is performed using a 20-roll cold rolling mill, with four passes (n≥0.5×3.1+1=2.55, resulting in a cold-rolled steel strip thickness of 3.1mm). The reductions per pass are 0.5mm, 0.3mm, 0.2mm, and 0.1mm, respectively, with the final rolled thickness controlled at 2.0mm to ensure the cold-rolled steel strip shape fully meets the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip is cleaned and annealed. Cleaning uses a 0.9% Na2SO4 alkaline solution. After cleaning, brushes are installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it is dried using 60℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 930℃. The cold-rolled steel strip moves at a speed of 4m / min in the continuous annealing furnace. After annealing, the cold-rolled coil needs to be leveled. The leveling roller force is controlled at 250N, and the straightness must meet ≤3mm / m. Then, it is cut according to the user's size requirements.

[0071] Comparative Example 3

[0072] This comparative example is largely the same as Example 1, except for the pickling process. The specific process flow is pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging, as detailed below:

[0073] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Example 1 of Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution and dried with hot air before being coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 200g / L, H2SO4 content of 90g / L, and the remainder being an aqueous solution. After pickling, the surface of the hot-rolled steel coil was cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three-pass cold rolling pre-pressing, with a rolling force of 1900N. The thickness reduction in the first pass was 0.15mm, and the flatness was controlled to be ≤5mm / m. The reduction in the subsequent two passes gradually increased (0.35mm and 0.40mm, respectively), ensuring that the total reduction in cold rolling pre-pressing was 0.90mm. The cold-rolled coil was then ground, with three pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. Each grinding operation involved a grinding head reduction force of 250N. The cold rolling process was performed using a 20-roll cold rolling mill, with four passes (n≥0.5×3.1+1=2.55, resulting in a cold-rolled steel strip thickness of 3.1mm). The reduction amounts per pass were 0.5mm, 0.3mm, 0.2mm, and 0.1mm, respectively, with the final rolled thickness controlled at 2.0mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 0.9% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it was dried using 60℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 930℃. The cold-rolled steel strip moves at a speed of 4m / min within the furnace. After annealing, the cold-rolled steel strip needs to be leveled. The leveling roller force is controlled at 250N, and the straightness must meet the requirement of ≤3mm / m. Finally, it is cut according to the user's size requirements.

[0074] Comparative Example 4

[0075] This comparative example is largely the same as Example 2, except for the cold rolling process. The specific process flow is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging.

[0076] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Example 2 of Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution and dried with hot air before being coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 380g / L, H2SO4 content of 180g / L, and the remainder being an aqueous solution. After pickling, the surface of the hot-rolled steel coil was cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three-pass cold rolling pre-pressing, with a rolling force of 1950N. The thickness reduction in the first pass was 0.25mm, and the flatness was controlled to be ≤4mm / m. The reduction in the subsequent two passes gradually increased (0.30mm and 0.35mm, respectively), ensuring a total cold rolling pre-pressing reduction of 0.9mm. The cold-rolled coil was then ground, with five pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-mesh abrasive belts, while the third grinding operation used 150-mesh abrasive belts. Each grinding operation involved a grinding head reduction force of 300N. The cold rolling process was performed using a 20-roll cold rolling mill, with three passes (n≥0.5×3.1+1=2.35, resulting in a cold-rolled steel strip thickness of 3.1mm). The reduction amounts per pass were 0.2mm, 0.4mm, and 0.2mm, respectively, with the final rolled thickness controlled at 2.3mm to ensure the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After the cold rolling process, the strip was cleaned and annealed. Cleaning was performed using a 1.0% Na2SO4 alkaline solution. After cleaning, brushes were installed inside the equipment to clean the surface of the cold-rolled steel strip, and finally, it was dried using 80℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 1050℃. The cold-rolled steel strip moves at a speed of 5m / min within the furnace. After annealing, the cold-rolled steel strip needs to be leveled using a leveling roller with a flatness control of 300N and a straightness requirement of ≤5mm / m. Finally, it is cut according to the user's size requirements.

[0077] Comparative Example 5

[0078] This comparative example is largely the same as Example 5, except for the annealing process. The specific process flow is pickling → cold rolling pre-pressing → grinding → cold rolling → cleaning → annealing → leveling → shearing and packaging, as detailed below:

[0079] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Example 5 of Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution, dried with hot air, and then coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 380g / L, H2SO4 content of 115g / L, and the remainder being an aqueous solution. After pickling, the surface of the hot-rolled steel coil was cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three-pass cold rolling pre-pressing, with a rolling force of 1600N. The thickness reduction in the first pass was 0.20mm, and the flatness was controlled to be ≤3.5mm / m. The reductions in the subsequent two passes were 0.30mm and 0.30mm respectively, ensuring a total cold rolling pre-pressing reduction of 0.80mm. The cold-rolled coil is then ground, with six pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations use 100-mesh abrasive belts, while the third uses 150-mesh belts. Each grinding operation involves a grinding head reduction of 350N. The cold rolling process is performed on a 20-roll cold rolling mill, with three passes (n≥0.5×3.2+1=2.6, resulting in a cold-rolled strip thickness of 3.2mm). The reductions per pass are 0.4mm, 0.2mm, and 0.1mm, respectively, with the final rolled thickness controlled at 2.5mm to ensure the strip shape fully meets the requirements of subsequent leveling and shearing processes. After cold rolling, the strip is cleaned and annealed. Cleaning uses a 1.5% Na2SO4 alkaline solution. After cleaning, brushes are installed inside the equipment to clean the surface of the cold-rolled strip, and finally, it is dried using 75℃ hot air. After drying, the cold-rolled steel strip needs to be further annealed in a continuous bright annealing furnace at a holding temperature of 1050℃. The cold-rolled steel strip moves at a speed of 6m / min within the furnace. After annealing, the cold-rolled steel strip needs to be leveled using a leveling roller controlled at 280N, with a flatness requirement of ≤5mm / m. Finally, it is cut according to the user's size requirements.

[0080] Comparative Example 6

[0081] This comparative example is largely the same as Example 3, except that it undergoes annealing directly without a cleaning process after cold rolling. The specific process flow is as follows: pickling → cold rolling pre-pressing → grinding → cold rolling → annealing → leveling → shearing and packaging.

[0082] A 4mm thick Invar alloy hot-rolled steel coil (composition shown in Example 3 of Table 1) was pickled using a mixed acid solution. After pickling, it was rinsed with an aqueous solution and dried with hot air before being coiled up. The mixed acid solution consisted of HCl and H2SO4, with HCl content of 390g / L, H2SO4 content of 150g / L, and the remainder being an aqueous solution. After pickling, the surface of the hot-rolled steel coil was cleaned with an aqueous solution, which was circulating water, and the acid concentration was controlled below 0.10g / L. The pickled hot-rolled coil underwent three-pass cold rolling pre-pressing, with a rolling force of 1800N. The thickness reduction in the first pass was 0.20mm, and the flatness was controlled to be ≤4mm / m. The reductions in the subsequent two passes were 0.30mm and 0.30mm respectively, ensuring a total cold rolling pre-pressing reduction of 0.8mm. The cold-rolled coil was then ground, with six pairs of grinding heads symmetrically distributed vertically. The first and second grinding operations used 100-grit abrasive belts, while the third grinding operation used 150-grit abrasive belts. Each grinding operation involved a grinding head reduction force of 350N. The cold rolling process for the ground coil was performed using a 20-roll cold rolling mill, with three passes (n≥0.5×3.2+1=2.6, resulting in a cold-rolled steel strip thickness of 3.2mm). The reduction amounts per pass were 0.5mm, 0.3mm, and 0.2mm, respectively, with the final rolled thickness controlled at 2.2mm. This ensured the cold-rolled steel strip shape fully met the requirements of subsequent leveling and shearing processes. After cold rolling, the strip was annealed in a continuous bright annealing furnace at a holding temperature of 920℃. The cold-rolled steel strip moved at a speed of 4m / min within the furnace. The annealed cold-rolled coil underwent leveling, with the leveling rolls applying a straightness force of 280N and maintaining a straightness of ≤2mm / m. Finally, it was sheared according to the user's size requirements.

[0083] Figure 2 The figure shows the microstructure of the oxide layer on the surface of the hot-rolled steel coil used in Embodiment 1 of the present invention. As can be seen from the figure, the surface of the hot-rolled Invar alloy has a large number of defects such as honeycomb-shaped iron oxide scale and microcracks, which need to be further processed. Figure 3 The image shows the microstructure of the Invar alloy cold-rolled steel strip after treatment by the method in Example 1. As can be seen from the image, its surface is smooth and free of defects such as oxide scale and cracks. Figure 4 The figure shows the finished product after the entire process of Example 1 is completed. As can be seen from the figure, the cold-rolled finished product prepared in Example 1 has a smooth surface and no obvious oxygen residue or dirt defects.

[0084] Table 1. Composition (wt%) of hot-rolled steel coils in the examples

[0085]

[0086] Table 2. Process parameters for the examples and comparative examples

[0087]

[0088] Performance tests were conducted on the Invar alloy cold-rolled steel strips manufactured in Examples 1-5 and Comparative Examples 1-6. The oxygen residue defect density and contamination defect density were detected using a high-speed defect acquisition camera system, which effectively classified the defect types and calculated the average density (number of defects per m³). 2 The wavy height was measured using an L-shaped ruler, and the test results are shown in Table 3.

[0089] Table 3. Properties of Invar alloy cold-rolled steel strips prepared in the examples and comparative examples.

[0090]

[0091] As shown in Tables 2 and 3, the Invar alloy cold-rolled steel strip manufactured in the embodiments of the present invention has a surface oxygen residual density of ≤2 atoms / m. 2 The wavy height is 2.5–3.3 mm, and the dirt density is ≤2 particles / m³. 2 Its yield strength is 287–295 MPa.

[0092] Based on Examples 1, 2, and 3, it can be seen that when HCl and H2 are present in the mixed acid solution... S When the O4 concentration is outside the range required by this invention, the oxide scale on the surface of the hot-rolled steel coil cannot be cleaned by pickling, resulting in a large amount of oxide scale defects remaining on the surface of the subsequently obtained Invar alloy cold-rolled steel strip.

[0093] Based on Example 2 and Comparative Example 4, it can be seen that the reduction amount of each cold rolling pass was not set in descending order. Furthermore, when the finished thickness of the Invar alloy cold-rolled steel strip is ≤2mm, the number of cold rolling passes should be greater than 4. However, the number of cold rolling passes in Comparative Example 4 is only 3. This will result in a larger deformation amount per pass, leading to a poor strip shape that cannot meet the user's standard requirements.

[0094] As can be seen from Example 3 and Comparative Example 6, if annealing is performed directly without cleaning after cold rolling, a large number of dirt defects will appear on the surface of the strip, which cannot meet the user's requirements.

[0095] As can be seen from Example 4 and Comparative Example 1, when the single-pass reduction in the cold rolling pre-pressing process exceeds 0.4 mm, the strip surface undergoes severe work hardening, making it impossible to completely remove the oxide scale in subsequent processes. This ultimately results in a large amount of residual oxide scale defects on the surface of the Invar alloy cold-rolled steel strip. Furthermore, the first pass reduction in the cold rolling process is 0.60 mm, and the second pass reduction is 0.40 mm, both exceeding the set requirements. This causes texture to form within the Invar alloy material, affecting the anisotropy of the strip and consequently leading to differences in the material's weldability in different directions.

[0096] As can be seen from Example 5 and Comparative Example 5, the annealing process of Comparative Example 5 does not meet the annealing process of the present invention, resulting in a yield strength of only 200 MPa, which does not meet the user's requirements, namely, the yield strength of the material after annealing is required to be greater than 250 MPa. Therefore, it can be seen that the Invar alloy cold-rolled steel strip manufactured by the process of Comparative Example 5 cannot meet the user's requirements.

[0097] In summary, the high surface quality Invar alloy cold-rolled steel strip and its manufacturing method of the present invention improve the surface quality of cold-rolled strip raw materials by removing honeycomb-like iron oxide scale and microcrack defects on the surface of Invar alloy through pickling and grinding. The pre-grinding cold rolling process before grinding ensures that the thickness meets the requirements of the grinding process, while also improving the strip shape and increasing the efficiency and quality of the grinding process. Furthermore, this grinding process effectively improves the surface quality of the ground strip, completely removing residual oxide scale from the Invar alloy surface. After grinding with coarse abrasive belt, fine grinding with 150-mesh fine abrasive belt improves the surface roughness of the strip, reduces the depth of grinding marks, reduces the risk of potential corrosion, and further cleans the root residue of surface oxides. The secondary cold rolling process is designed with rolling passes according to the rolling thickness system, ensuring that the rolling thickness of each pass is controlled within a reasonable range, preventing excessive reduction in a single pass, which could create texture and affect the weldability of the strip. The surface of the cold-rolled steel strip is further cleaned with a Na2SO4 alkaline solution to remove dirt and foreign matter, improving surface quality. This invention controls the surface quality of the cold-rolled strip through multiple processes. By rationally setting the relationship between the finished product thickness, holding temperature, and moving speed, the rolling stress of the cold-rolled strip is fully removed, while avoiding excessively long high-temperature annealing time, which could lead to grain growth and deterioration of the strip's mechanical properties. The above-mentioned process parameters effectively solve the technical challenges of controlling the high surface quality of Invar alloy cold-rolled strip, producing products with high surface quality and high profile requirements, meeting user demands for high-quality products.

[0098] In addition, the high surface quality Invar alloy cold-rolled steel strip prepared by this invention can be widely used in aerospace, energy transportation and other fields; improving the surface quality of Invar alloy cold-rolled steel strip and reducing process costs is conducive to further promoting the application of Invar alloy.

[0099] Those skilled in the art should recognize that the above embodiments are merely illustrative of the present invention and are not intended to limit the present invention. Any variations or modifications to the above embodiments that are within the spirit and essence of the present invention will fall within the scope of the claims of the present invention.

Claims

1. A method for manufacturing a high surface quality Invar alloy cold-rolled steel strip, characterized in that: The process involves pickling, cold rolling pre-pressing, grinding, cold rolling, cleaning, annealing, leveling, shearing, and packaging, specifically including the following steps: S1, pickling: Invar alloy hot-rolled steel coils are pickled using a mixed acid solution, then rinsed with an aqueous solution, dried with hot air, and then coiled up. S2, cold rolling pre-pressing: The Invar alloy hot-rolled steel coil processed in step S1 is subjected to cold rolling pre-pressing. Three-pass cold rolling is used, with the reduction per pass controlled within 0.4 mm and the total reduction being 0.5 to 1.0 mm. S3, grinding, grinding the cold-rolled steel strip after cold rolling and pre-pressing. The grinding head unit used for grinding shall use at least 3 pairs of grinding heads and the grinding shall be performed no less than 3 times. S4, cold rolling, involves subjecting the ground cold-rolled steel strip to multiple cold rolling passes. The number of rolling passes n satisfies n≥0.5×m+1, where m is the thickness of the ground cold-rolled steel strip in mm. S5, Cleaning, involves cleaning the cold-rolled steel strip after it has been cold-rolled, followed by annealing; When the finished thickness of the Invar alloy cold-rolled steel strip is >2mm, the holding temperature of the bright annealing furnace used for annealing is ≥1000℃, and the moving speed of the Invar alloy cold-rolled steel strip in the bright annealing furnace is ≥5m / min; conversely, when the thickness is less than 2mm, the holding temperature of the bright annealing furnace used for annealing is ≤950℃, and the moving speed of the Invar alloy cold-rolled steel strip in the bright annealing furnace is <5m / min. S6 involves flattening the annealed cold-rolled steel strip, then cutting it to the finished size and packaging it.

2. The method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to claim 1, characterized in that: In step S1: The composition of the Invar alloy hot-rolled steel coil, by mass percentage, is as follows: C≤0.04%, Si≤0.7%, Mn≤0.8%, P≤0.040%, S≤0.08%, 30%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, with the remainder being Fe and unavoidable residual elements; The thickness of the Invar alloy hot-rolled steel coil and strip is less than 5 mm.

3. The method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to claim 1, characterized in that: In step S1: The mixed acid solution consists of HCl, H2SO4 and water, with the HCl content satisfying: 300 g / L < HCl < 400 g / L, and the H2SO4 content satisfying: 100 g / L < H2SO4 < 200 g / L. The aqueous solution is circulating water with an acid concentration of less than 0.15 g / L.

4. The method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to claim 1, characterized in that: In step S2, the rolling force of the three-pass cold rolling rolls is ≤2000N, and the flatness is controlled to be ≤5mm / m.

5. The method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to claim 1, characterized in that: In step S3: The grinding head unit used for grinding is symmetrically distributed vertically. The grinding head unit is first ground with 100-mesh abrasive belt at least twice, and then ground with 150-mesh abrasive belt at least once. The pressing force of the grinding head unit shall not be less than 200N.

6. The method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to claim 1, characterized in that: In step S4: The cold rolling process uses a 20-roll cold rolling mill. The number of rolling passes must meet the following requirements: when the finished thickness of the Invar alloy cold-rolled steel strip is <2mm, the number of rolling passes n≥4; otherwise, the number of rolling passes n<4. In the cold rolling process, the reduction amount of each pass in the multi-pass cold rolling is set from large to small.

7. The method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to claim 1, characterized in that... In step S5: During the cleaning process, an alkaline solution of Na2SO4 with an alkali concentration of ≥0.5% is used. After cleaning, the surface of the cold-rolled steel strip is brushed with a brush, and then hot air at a temperature of 60°C or higher is used for blowing and drying. During the annealing process, when the thickness of the finished Invar alloy cold-rolled steel strip is >2mm and ≤4mm, the holding temperature is 1000~1050℃ and the moving speed is 5~8m / min; conversely, when the thickness of the finished Invar alloy cold-rolled steel strip is ≥0.5mm and ≤2mm, the holding temperature is 900~950℃ and the moving speed is 2~4m / min.

8. The method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to claim 1, characterized in that: In step S6, during the leveling process, the leveling force of the leveling roller is >200N, and the flatness requirement is ≤5mm / m.

9. A high surface quality Invar alloy cold-rolled steel strip obtained by a method for manufacturing high surface quality Invar alloy cold-rolled steel strip according to any one of claims 1 to 8, characterized in that: The Invar alloy cold-rolled steel strip has a yield strength ≥250MPa, surface flatness ≤3mm / m, surface waviness ≤3.5mm, and oxygen residual density ≤5 particles / m³. 2 Dirt defect density ≤ 5 / m 2 .

10. The high surface quality Invar alloy cold-rolled steel strip according to claim 9, characterized in that: The yield strength of the Invar alloy cold-rolled steel strip is ≥285MPa.

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