An easy-to-clean cold-rolled annealed sheet and its manufacturing method

Abstract

This invention discloses an easy-to-clean cold-rolled annealed steel sheet and its manufacturing method. The manufacturing method of the cold-rolled annealed steel sheet is as follows: Cold rolling: the surface roughness of the final rolling roll Ra ≥ 2.0 μm; Annealing: the hydrogen content in the furnace is 3~5%, the oxygen content in the furnace is 10~30 ppm, and the dew point in the furnace is -30~-50℃; Leveling: the surface roughness of the leveling work roll Ra ≥ 2.7 μm, RPc ≥ 100 pieces / cm; Oiling; Barrel making; Cleaning; Painting. This invention optimizes the cold rolling, annealing, and leveling processes, controls the surface tension of the strip steel, and ensures that the surface of the strip steel is clean while meeting the requirements for surface quality and rust prevention of the cold-rolled steel sheet and reducing the degreasing temperature, thus saving cleaning costs for downstream customers. Finally, combined with batch experiments, a regression equation surface tension control model is established, which can guide the production line to be adjusted in a timely manner according to the customer's production conditions to avoid affecting the cleaning quality of downstream customers.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to an easy-to-clean cold-rolled annealed sheet and its manufacturing method. Background Technology

[0002] Cold-rolled annealed steel sheets have high surface activity and are prone to corrosion. To prevent corrosion during storage and transportation that could affect downstream use, rust-preventive oil is typically applied to the steel sheet surface. Downstream customers using cold-rolled annealed steel sheets need to perform multiple processes, including forming (such as stamping into barrels), cleaning and degreasing, phosphating / silane treatment, drying, and painting. If the oil film on the steel sheet surface cannot be completely removed during the cleaning and degreasing process, water droplets will form on the steel sheet surface due to the incompatibility of oil and water. After silane or phosphating, watermarks and phosphating spots will appear, which cannot be covered by water-based paint.

[0003] The prevailing view is that the thicker the anti-rust oil film on the surface of the steel plate, the better the anti-rust performance, but it is not conducive to cleaning. Processing users often ask steel mills to reduce the amount of oil applied to the steel plate to meet the cleaning quality requirements. However, in order to prevent cold-rolled annealed plates from rusting, steel mills tend to increase the amount of oil applied to prevent rust.

[0004] To prevent rust from cold-rolled annealed steel sheets, steel mills currently apply a high amount of rust-preventive oil, typically 500-1000 mg / m² per side. 2 Downstream molding customers requested that the oil coating amount be 200~500mg / m² per side. 2 In between, use a low-viscosity rust-preventive oil so that it can be cleaned off after processing and molding. Summary of the Invention

[0005] Technical problem solved: To address the above-mentioned technical problems, the present invention provides an easy-to-clean cold-rolled annealed sheet and its manufacturing method, which can take into account the surface quality, rust prevention performance and cleaning quality of the cold-rolled annealed sheet.

[0006] Technical solution: A cold-rolled annealed sheet that is easy to clean, with a surface tension greater than or equal to 37 mN / m.

[0007] Preferably, the peak density RPc, surface roughness Ra, and oxide film thickness of the cold-rolled annealed sheet satisfy the following:

[0008]

[0009] Where Y represents surface tension, X1 represents peak density RPc, X2 represents surface roughness Ra, and X3 represents oxide film thickness, with oxide film thickness ≤ 60 nm.

[0010] A method for manufacturing an easy-to-clean cold-rolled annealed sheet includes the following steps:

[0011] S1. Cold rolling: The surface roughness of the rolls in the last rolling pass Ra≥2.0μm;

[0012] S2. Annealing: The hydrogen content in the furnace is 3~5%, the oxygen content in the furnace is 10~30ppm, and the dew point in the furnace is -30~-50℃;

[0013] S3. Leveling: The surface roughness of the leveling work roller Ra≥2.7μm, and the peak density RPc≥100 particles / cm;

[0014] S4. Drying;

[0015] S5. Apply oil;

[0016] S6. Molding and processing;

[0017] S7. Cleaning: Perform pre-degreasing, degreasing, cleaning, phosphating / silane treatment and drying in sequence;

[0018] S8. Spray painting.

[0019] Preferably, the concentration of the emulsion used in S1 is 0.5~1.0%.

[0020] Preferably, the annealing temperature in S2 is above the recrystallization temperature.

[0021] Preferably, the rolling force of the wet leveling mill in S3 is 3500~9000KN, and the thickness of the chromium plating layer on the rolls is ≥5μm.

[0022] Preferably, the drying temperature in step S4 is greater than 100°C.

[0023] Preferably, in step S5, an electrostatic oiling machine is used for oiling, with a single-sided oiling amount of 200~500 mg / m². 2 The kinematic viscosity of the rust-preventive oil at 40℃ is 7~35 mm. 2 / s.

[0024] Preferably, in step S7, the pre-degreasing and degreasing temperature is 35~45℃, and the pH of the cleaning solution used for cleaning is 13±0.5.

[0025] Beneficial Effects: This invention optimizes the cold rolling, annealing, and leveling processes to control the surface tension of the strip steel. While meeting the requirements for surface quality and rust prevention in cold-rolled sheets, and reducing degreasing temperature, it still ensures a clean strip surface, saving cleaning costs for downstream customers. Finally, combined with batch testing, a regression equation surface tension control model is established, which can guide timely adjustments to the production line based on customer production conditions, avoiding any impact on the cleaning quality for downstream customers. Attached Figure Description

[0026] Figure 1 This is a diagram illustrating the good cleaning effect;

[0027] Figure 2 This is a diagram illustrating poor cleaning performance. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] To achieve the objectives of this invention, the production method for cold-rolled annealed steel sheets mainly includes the following process flow: cold rolling, annealing, leveling, drying, oiling, forming, cleaning, and painting. The main process control points are as follows:

[0030] S1. Cold rolling: Hot coils are cold rolled on a single stand or multiple stands, with the final rolling pass using rolls with a surface roughness Ra≥2.0μm and an emulsion concentration of 0.5%~1.0%;

[0031] S2. Annealing: Annealing above the recrystallization temperature, with a hydrogen content of 3-5% in the furnace, an oxygen content of 10-30 ppm in the furnace, and a dew point of -30 to -50℃ in the furnace;

[0032] S3. Leveling: The rolling force of the wet leveling machine is 3500~9000KN, the surface roughness of the work roll Ra≥2.7μm, the peak density RPc≥100 pieces / cm, and the thickness of the chrome plating layer on the roll is ≥5μm.

[0033] S4. Drying: Drying temperature > 100℃;

[0034] S5. Oiling: Apply oil using an electrostatic oiling machine, with an oiling amount of 200~1000 mg / m² per side. 2 Rust-preventive oil kinematic viscosity at 40℃ is 7~35 mm. 2 / s.

[0035] S6. Molding and processing;

[0036] S7. Cleaning: Pre-degreasing → Degreasing → Cleaning → Phosphating / Silane treatment → Drying; Pre-degreasing and degreasing temperature 35~45℃, cleaning solution pH maintained at 13±0.5; This can clean the oil film on the strip surface, so that the silane and phosphating processes will not produce watermarks, phosphating spots and other problems.

[0037] S8. Spray painting: Spraying various colors of water-based paint.

[0038] The cleaning performance test will be conducted below:

[0039] The ease of cleaning of cold-rolled annealed steel sheets is assessed using the surface water film coverage rate after cleaning as an indicator. When the anti-rust oil on the steel sheet surface is thoroughly cleaned, the water film is continuous and uniform, with a coverage rate of 99% or higher. Good and poor cleaning results are respectively categorized as follows: Figure 1 and Figure 2As shown. Using the water film coverage after cleaning as an indicator of ease of cleaning performance, different combinations of factors that may affect the ease of cleaning performance of cold-rolled annealed sheets were tested while maintaining a stable pH value of 13±0.5 for the cleaning solution in the downstream customer's cleaning process. The results are as follows:

[0040]

[0041] As shown in the table above, when the cleaning temperature is 90℃ and the kinematic viscosity of the rust-preventive oil is 40℃, the kinematic viscosity is 7~35 mm. 2 / s, oil application rate: 200~1000 mg / m² per side 2 When the surface tension of cold-rolled annealed steel sheets is above 30 mN / m, the water film coverage after cleaning can reach 99% or higher. When the cleaning temperature drops to 60℃, the kinematic viscosity of the rust-preventive oil at 40℃ is 7~35 mm. 2 / s, oil application rate 200~1000 mg / m 2 The surface tension of the cold-rolled annealed sheet needs to reach 34 mN / m or higher, and the water film coverage rate after cleaning should reach 99%. When the cleaning temperature is reduced to 35℃, the surface tension of the cold-rolled annealed sheet needs to reach 37 mN / m or higher.

[0042] Through multiple cleaning practices, it was determined that the amount of rust-preventive oil applied, the kinematic viscosity, and the ease of cleaning of cold-rolled annealed steel sheets are generally correlated and do not significantly affect the ease of cleaning performance of cold-rolled annealed steel sheets. The cleaning temperature and the surface tension of the steel sheet before oiling significantly affect the cleaning quality.

[0043] Therefore, the most critical indicator affecting the easy-to-clean performance of cold-rolled annealed steel sheets is the surface tension (Y) of the steel sheet before oiling. It is correlated with the peak density RPc (X1), surface roughness Ra (X2), and oxide film thickness (X3) of the strip, and conforms to the following relationship:

[0044]

[0045] In the above formula, Y represents the surface tension of the cold-rolled annealed sheet before oiling, in mN / m; X1 represents the peak density RPc, in cells / cm; X2 represents the surface roughness Ra, in μm; and X3 represents the oxide film thickness on the sheet surface. It can be seen from the formula that there is a significant positive correlation between the surface tension of the strip and RPc, Ra, and oxide film thickness. This formula can guide steel mills to adjust their processes during production to produce steel sheets that meet cleaning requirements.

[0046] Further testing on the factors affecting surface tension is as follows:

[0047] The main factors affecting the surface roughness of cold-rolled steel sheets are: the roughness of the cold-rolling work rolls, the roughness of the leveling work rolls, and the leveling rolling mileage.

[0048] The main factors affecting the oxide film on the surface of cold-rolled annealed steel sheets are: the roughness of the cold-rolled work rolls, the dew point inside the furnace, the hydrogen content inside the furnace, and the oxygen content inside the furnace.

[0049]

[0050] Test Example 3, based on Test Example 2, modified the surface roughness of the cold-rolled work rolls, increasing it from 0.5 μm to 2 μm. This resulted in an increase in both the surface roughness and oxide film thickness of the finished cold-rolled annealed sheet, leading to a 5 mN / m increase in surface tension before oiling. Test Example 4, based on Test Example 3, adjusted the furnace atmosphere, increasing the oxide film thickness by 10 nm, resulting in a surface tension increase to 37 mN / m, which meets cleaning quality requirements. Test Example 5 further increased the surface roughness of the cold-rolled work rolls to 3.0 μm, achieving a surface tension of 37 mN / m for cold-rolled annealing within 150 km without adjusting the furnace atmosphere. Test Example 6, adjusting the furnace atmosphere, increased the oxide film thickness to 50 nm, but resulted in noticeable oxide color defects on the sheet surface, which was unacceptable to the customer. Therefore, the optimal oxide film thickness is ≤30 nm.

Claims

1. A method for manufacturing an easy-to-clean cold-rolled annealed sheet, characterized in that, The steps include the following: S1. Cold rolling: The surface roughness of the rolls in the last rolling pass Ra≥2.0μm; S2. Annealing: The hydrogen content in the furnace is 3~5%, the oxygen content in the furnace is 10~30ppm, and the dew point in the furnace is -30~-50℃; S3. Leveling: The surface roughness of the leveling work roller Ra≥2.7μm, and the peak density RPc≥100 particles / cm; S4. Drying; S5. Apply oil; S6. Molding and processing; S7. Cleaning: Perform pre-degreasing, degreasing, cleaning, phosphating / silane treatment and drying in sequence; S8. Spray painting; A cold-rolled annealed sheet that is easy to clean is obtained, with a surface tension greater than or equal to 37 mN / m, and the peak density RPc, surface roughness Ra, and oxide film thickness meet the following requirements: ， Where Y represents surface tension, X1 represents peak density RPc, X2 represents surface roughness Ra, and X3 represents oxide film thickness, with oxide film thickness ≤ 60 nm.

2. The method for manufacturing the easy-to-clean cold-rolled annealed sheet according to claim 1, characterized in that, The concentration of the emulsion used in S1 is 0.5~1.0%.

3. The method for manufacturing the easy-to-clean cold-rolled annealed sheet according to claim 1, characterized in that, The annealing temperature in S2 is above the recrystallization temperature.

4. The method for manufacturing the easy-to-clean cold-rolled annealed sheet according to claim 1, characterized in that, The rolling force of the wet leveling mill in S3 is 3500~9000KN, and the thickness of the chromium plating layer on the rolls is ≥5μm.

5. The method for manufacturing the easy-to-clean cold-rolled annealed sheet according to claim 1, characterized in that, The drying temperature in S4 is greater than 100℃.

6. The method for manufacturing the easy-to-clean cold-rolled annealed sheet according to claim 1, characterized in that, In step S5, an electrostatic oiling machine is used for oiling, with a single-sided oiling amount of 200~500 mg / m². 2 The kinematic viscosity of the rust-preventive oil at 40℃ is 7~35 mm. 2 / s.

7. The method for manufacturing the easy-to-clean cold-rolled annealed sheet according to claim 1, characterized in that, In S7, the pre-degreasing and degreasing temperature is 35~45℃, and the pH of the cleaning solution used for cleaning is 13±0.5.

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