A high-efficiency pickling method suitable for high-carbon high-alloy hot-rolled steel plate

Abstract

The application discloses a kind of high-efficiency pickling method suitable for high-carbon high-alloy hot-rolled steel plate, mainly solve the problem of low pickling efficiency and poor pickling quality of the pickling unit with pickling tank length of 30-60 m for pickling high-carbon high-alloy hot-rolled steel plate.The technical scheme is a kind of high-efficiency pickling method suitable for high-carbon high-alloy hot-rolled steel plate, comprising:1) pickling high-carbon high-alloy hot-rolled steel plate, the hot-rolled steel plate is pickled by pickling liquid in the pickling tank, the pickling liquid comprises hydrochloric acid, pickling accelerator and iron ions, the mass concentration of hydrochloric acid is 10%-18%, the acidity of acid solution is 120-160 g / L;The temperature of acid solution is 75-90 DEG C;2) squeeze the steel plate after pickling;3) rinse the steel plate;4) squeeze the steel plate after rinsing;5) steel plate drying.The method of the application is suitable for pickling unit with pickling tank length of 30-60 m and pickling unit without scale removing device.

Description

Technical Field

[0001] This invention relates to a pickling method for hot-rolled steel plates, and particularly to a highly efficient pickling method suitable for high-carbon, high-alloy hot-rolled steel plates, belonging to the field of hot-rolled steel plate pickling technology. Background Technology

[0002] Steel with a carbon content of 0.4%-2.0% by mass and a total alloy element content greater than 1% by mass is called high-carbon high-alloy steel. Pickling of high-carbon high-alloy steel plates is a surface treatment technology that involves repeatedly cleaning hot-rolled high-carbon high-alloy steel plates in multiple batches to remove the iron oxide scale from the surface of the steel plates and achieve a metallic luster on the finished product surface.

[0003] After hot rolling, high-carbon high-alloy steel forms a dense oxide scale of considerable thickness on the surface of the hot-rolled steel sheet, from the outside in. This oxide scale is mainly composed of FeO, Fe2O3, Fe3O4, and small amounts of eutectoid Fe, Si, and Cr oxides. This oxide scale is characterized by its dense structure and difficulty in pickling.

[0004] In industrial pickling production of high-carbon, high-alloy hot-rolled steel sheets, chemical pickling is the primary process for removing oxide scale. Plain carbon steel sheets have a porous oxide scale with microcracks, allowing acid to penetrate these cracks and reach the underlying layer, dissolving the scale and producing hydrogen gas, thus causing the scale to peel off. However, high-carbon, high-alloy steel sheets have a much denser outer oxide scale layer, making it difficult for acid to penetrate and reach the substrate surface. This hinders the reaction between the acid and the substrate, making peeling difficult. Production is particularly challenging for short pickling tank units without scale-removing devices.

[0005] In conventional pickling processes, the main approach is to increase the acid concentration and reduce the pickling speed of the steel strip. However, it is still difficult to completely remove the oxide scale from the steel strip surface, which directly affects the quality of the steel strip product. The composition, thickness, and density of the oxide scale on high-carbon high-alloy steel plates differ from those on ordinary carbon steel. Therefore, the pickling process for ordinary carbon steel is not suitable for the pickling process of high-carbon high-alloy steel plates.

[0006] Chinese patent application CN109023388A discloses a method for efficient pickling surface treatment of high-strength automotive steel strips. It is designed for automotive steels of 500-800MPa grade, and aims to improve the surface blackening, under-pickling, and over-pickling of the strips, thereby improving the quality of the strips. The pickling tank is a five-tank system with a total length of 100-150m. The long length of the pickling tank results in high equipment investment and pickling costs.

[0007] Chinese patent application CN104985018A discloses a production method for improving the pickling performance of iron oxide scale on high carbon steel wire rod. It generates easily pickled iron oxide scale by controlling the hot rolling process, but does not involve the pickling process.

[0008] Chinese patent application CN101949021A discloses a high-efficiency pickling tank, which optimizes the structure of the pickling tank but does not involve the pickling process.

[0009] Existing technologies lack effective pickling methods for high-carbon, high-alloy hot-rolled steel plates, resulting in poor pickling quality and high pickling costs. Summary of the Invention

[0010] The purpose of this invention is to provide a highly efficient pickling method for high-carbon, high-alloy hot-rolled steel plates, primarily addressing the problems of low pickling efficiency and poor pickling quality in existing pickling units with pickling tanks of 30-60m in length when pickling high-carbon, high-alloy hot-rolled steel plates. This method achieves low-cost, high-efficiency pickling of high-carbon, high-alloy hot-rolled steel plates, resulting in a surface free of iron oxide scale residue and exhibiting high surface quality.

[0011] The technical idea of ​​this invention is to achieve efficient pickling by optimizing the pickling process, such as controlling the concentration of iron ions in the acid solution, acid additives, acidity, and acid temperature.

[0012] The technical solution adopted in this invention is a highly efficient pickling method suitable for high-carbon, high-alloy hot-rolled steel plates, the method comprising:

[0013] 1) High-carbon, high-alloy hot-rolled steel plates are pickled using a pickling solution in a pickling tank. The pickling solution comprises hydrochloric acid, a pickling accelerator, and iron ions. The hydrochloric acid concentration is 10%–18%, the acidity is 120–160 g / L, and the temperature is 75–90℃. The pickling accelerator comprises 0.1%–1.0% of the hydrochloric acid volume. The accelerator consists of: 20%–25% carboxylates, 15%–20% urea, 5%–10% phosphates, and water as the remaining component. The iron ion concentration is 10–100 mg / L. The high-carbon, high-alloy hot-rolled steel plate contains 0.4%–2.0% carbon and the sum of the alloying elements is greater than 1%. The pickling tank length is 30–60 m.

[0014] 2) After pickling, the steel plate is squeezed dry. The pickling and squeezing roller is used to squeeze the steel plate dry, and the pressure of the pickling and squeezing roller is controlled at 0.3-0.5MPa.

[0015] 3) The steel plate is rinsed by rinsing it with rinsing water in a rinsing tank after squeezing it dry. The rinsing water includes industrial desalinated water and rinsing inhibitor. The conductivity of the rinsing water is ≤100μs / cm, the pH value of the rinsing water is 6-9, and the temperature of the rinsing water is 30-70℃. The rinsing inhibitor consists of: 35%-40% carboxylates, 1%-5% aliphatic carboxylic acids, <1% ammonium hydroxide, and the remaining component is water.

[0016] 4) After rinsing, squeeze the steel plate dry. Use rinsing and squeezing rollers to squeeze the steel plate dry, and control the pressure of the rinsing and squeezing rollers to be 0.3-0.5MPa.

[0017] 5) Drying the steel plate: Dry the rinsed and squeezed steel plate with hot air at a temperature of 120-170℃ and a pressure of 0.03-0.05MPa.

[0018] Furthermore, in step 1), when the length of the pickling tank is 30-40m, adding a pickling accelerator to the last pickling tank has a good effect, which reduces the risk of intergranular corrosion of high-carbon high-alloy steel plates while increasing the pickling speed.

[0019] When the pickling tank is 50-60m long, adding a pickling accelerator at 1 / 2 to 3 / 4 of the total length of the pickling tank will have a good effect, reducing the risk of intergranular corrosion of high-carbon high-alloy steel plates while increasing the pickling speed.

[0020] When multiple pickling tanks are connected in series, the volume concentration of the pickling accelerator in the pickling solution is distributed in a positive gradient from low to high concentration, which increases the pickling speed of steel plates or strips while saving costs.

[0021] The method of the present invention is applicable to pickling units with pickling tanks of 30 to 60 m in length and pickling units without scale breaking devices.

[0022] The method of this invention is based on the following research findings:

[0023] The applicant's research revealed that the process of removing oxide scale by hydrochloric acid pickling can be summarized into three aspects: the dissolution effect of the iron oxide scale reacting with the acid, the redox reaction, and the stripping effect of hydrogen. The principle is illustrated by the following chemical reaction:

[0024] Fe₂O₃ + 6HCl = 2FeCl₃ + 3H₂O (1)

[0025] Fe3O4+8HCl=2FeCI3+FeCl2+4H2O (2)

[0026] FeO + 2HCl = FeCl2 + H2O (3)

[0027] Fe + 2HCl = FeCl₂ + 2[H] (4)

[0028] 2[H]=H2↑ (5)

[0029] FeCl3 + [H] = FeCl2 + HCl (6)

[0030] 2FeCl3 + Fe = 3FeCl2 (7)

[0031] Reaction (4) and (5) involve hydrochloric acid penetrating into the gaps of the iron oxide scale, reacting with elemental iron to generate hydrogen gas. The expansion force of the hydrogen gas can peel some of the iron oxide scale off the steel plate surface. Reaction (1), (2), and (3) involve the chemical dissolution of the iron oxide scale, mainly through a chemical reaction with hydrochloric acid to generate corresponding ions that dissolve in the acid solution. Reaction (6) and (7) are mainly redox reactions, reducing ferric iron to ferrous iron. Among them, reaction (3) and (4) are the fastest reactions, while reaction (8) is the slowest. To accelerate the reaction rate, it is necessary to speed up the reaction and increase the rate of each chemical reaction.

[0032] The increase in iron ions, especially the increase in the content of ferric ions, increases the self-corrosion current of the steel plate, indicating an increase in the corrosion rate, which in turn increases the pickling speed.

[0033] The rationale for the production process adopted in this invention is as follows:

[0034] 1. Setting the pickling acid composition and acid temperature

[0035] The process of removing oxide scale by hydrochloric acid pickling can be summarized in three aspects: the dissolution effect of the iron oxide scale by reacting with the acid, the redox effect, and the stripping effect of hydrogen. Hydrochloric acid penetrates into the gaps in the iron oxide scale and reacts with elemental iron to generate hydrogen gas. The expansion force of the hydrogen gas can peel some of the iron oxide scale off the steel plate surface. This process is influenced by several factors. On the other hand, the pickling chemical reaction process is affected by the acid concentration and temperature. Higher acid concentrations and temperatures result in a faster chemical reaction, allowing for quicker removal of iron oxide scale from the steel plate or strip surface. Considering production costs and the actual capacity of the equipment, this section sets the acid concentration in the pickling tank to 10%–18% hydrochloric acid, and the acid temperature to 75℃–90℃.

[0036] 2. Setting of pickling accelerator in pickling acid solution

[0037] The components of the pickling accelerator function as follows: Carboxylate, being an anionic surfactant, acts as a surfactant, accelerating the penetration of acid into the iron oxide scale. Urea acts as a reducing agent, activating the outer layer of the iron oxide scale and reacting the high-valence metal oxides on the outer layer, which are difficult to react with acid, to generate low-valence metal oxides that are easily soluble in acid, thus accelerating the dissolution of the iron oxide scale. Phosphate acts as an emulsifier and dispersant, ensuring that the carboxylate and urea are evenly distributed in the solution, preventing deposition and aggregation.

[0038] Pickling accelerators in acid solutions can enhance the activation of iron oxide scale, reducing the high-valence iron in the scale to low-valence iron, making it easier for the scale to react with the acid, increasing the wettability of the acid, and allowing the acid to quickly penetrate the scale and accelerate the reaction. Based on calculations of the unit's production speed, the volume fraction concentration of the pickling accelerator at 0.1% to 1.0% of the acid solution can meet the production needs of steel plates or strips at different speeds.

[0039] 3. Setting the iron ion content in the pickling acid solution

[0040] The increase in iron ions in the acid solution, especially the increase in the content of ferric ions, increases the chemical reaction of the solution according to reaction formula (7), as ferric ions have strong oxidizing properties. According to the inventor's electrochemical experiments, it was found that the self-corrosion current of the steel plate increased with the increase of iron ions, indicating that the corrosion rate increased, thereby increasing the pickling speed. However, according to the solution diffusion theory, an excessively high iron ion content will reduce the chemical reaction rate of reactions (1), (2), (3), and (4), so the iron ion content, iron ion concentration, and iron ion mass concentration should be 10-100 mg / L.

[0041] Compared with existing technologies, this invention has the following advantages: 1. The method of this invention effectively combines existing pickling processes. By using pickling accelerators, acid temperature, acidity, and iron ion concentration, and in conjunction with the unit process, it achieves efficient pickling of high-carbon, high-alloy hot-rolled steel plates while ensuring product surface quality. 2. This invention is applicable to pickling units with pickling tanks of 30-60m in length and pickling units without descaling devices, achieving efficient pickling of high-carbon, high-alloy hot-rolled steel plates. Detailed Implementation

[0042] The present invention will be further described below with reference to Examples 1 to 5.

[0043] In Examples 1 to 5, there are 3 pickling tanks, and the total length of the pickling tanks is 40m.

[0044] Example 1: A highly efficient pickling method for high-carbon, high-alloy hot-rolled steel plates, comprising the following steps:

[0045] 1) High-carbon, high-alloy hot-rolled steel plates were pickled. The 2.5mm thick hot-rolled steel plates were pickled using a pickling solution in a pickling tank. The pickling solution included hydrochloric acid, a pickling accelerator, and iron ions. The hydrochloric acid concentration was 18%, and the acid solution temperature was 80℃. The pickling accelerator had a volume content of 0.1% (carboxylates), a urea content of 20%, a phosphate content of 10%, and the remaining component was water. The iron ion concentration was 10 mg / L, and the acidity was 150 g / L.

[0046] 2) After pickling, the steel plate is squeezed dry. The pickling and squeezing roller is used to squeeze the pickled steel plate dry to remove the acid from the surface of the steel plate. The pressure of the pickling and squeezing roller is controlled to be set to 0.3MPa.

[0047] 3) Rinse the steel plate by rinsing it with rinsing water in the rinsing tank. The rinsing water has a conductivity of ≤100μs / cm, a pH value of 6~9, a rinsing inhibitor of type BH2 with a content of 0.1%, and a rinsing water temperature of 70℃.

[0048] 4) After rinsing, squeeze the steel plate dry. Use rinsing and squeezing rollers to squeeze the steel plate dry, and remove the rinsing water from the surface of the steel plate by squeezing. Control the pressure of the rinsing and squeezing rollers to 0.35MPa.

[0049] 5) Drying: The steel plate after rinsing and squeezing is dried with hot air to remove residual moisture from the surface of the steel plate. The hot air temperature is 150℃ and the hot air pressure is 0.05MPa.

[0050] The pickling speed of 60Si2Mn steel pickled according to Example 1 was increased from 8 m / min to 15 m / min in the existing conventional process.

[0051] Example 2: A highly efficient pickling surface treatment technology for high-carbon high-alloy steel plates, comprising the following steps:

[0052] 1) High-carbon, high-alloy hot-rolled steel plates were pickled. The 5.99mm thick hot-rolled steel plates were pickled in the pickling solution in the pickling tank. The pickling solution included hydrochloric acid, pickling accelerator, and iron ions. The hydrochloric acid mass concentration was 16%, and the acid solution temperature was 85℃. The volume content of the pickling accelerator in the pickling solution was 0.3%. The mass fraction of the pickling accelerator carboxylate was 25%. The mass fraction of urea was 15%. The mass fraction of phosphate was 10%. The remaining component was water. The iron ion concentration was 30mg / L, and the acidity of the acid solution was 180g / L.

[0053] 2) After pickling, the steel plate is squeezed dry. The pickling and squeezing roller is used to squeeze the pickled steel plate dry to remove the acid from the surface of the steel plate. The pressure of the pickling and squeezing roller is controlled to be set to 0.5MPa.

[0054] 3) Rinse the steel plate by rinsing it with rinsing water in the rinsing tank. The rinsing water has a conductivity of ≤100μs / cm, a pH value of 6~9, a rinsing inhibitor of type BH2 with a content of 0.15%, and a rinsing water temperature of 70℃.

[0055] 4) After rinsing, squeeze the steel plate dry. Use rinsing and squeezing rollers to squeeze the steel plate dry, and remove the rinsing water from the surface of the steel plate by squeezing. Control the pressure of the rinsing and squeezing rollers to 0.4MPa.

[0056] 5) Drying: The steel plate after rinsing and squeezing is dried with hot air to remove residual moisture from the surface of the steel plate. The hot air temperature is 150℃ and the hot air pressure is 0.05MPa.

[0057] According to Example 2, the pickling speed of 60Si2Mn steel was increased from 8 m / min in the existing conventional process to 20 m / min.

[0058] Example 3: A highly efficient pickling surface treatment technology for high-carbon high-alloy steel plates, comprising the following steps:

[0059] 1) High-carbon, high-alloy hot-rolled steel plates were pickled. The 3.5mm thick hot-rolled steel plates were pickled in the pickling solution in the pickling tank. The pickling solution included hydrochloric acid, pickling accelerator, and iron ions. The mass concentration of hydrochloric acid was 18%, and the acid solution temperature was 85℃. The volume content of pickling accelerator in the pickling solution was 0.7%. The mass fraction of carboxylate in the pickling accelerator was 20%, the mass fraction of urea was 18%, the mass fraction of phosphate was 10%, and the remaining component was water. The iron ion concentration was 20mg / L, and the acidity of the acid solution was 195g / L.

[0060] 2) After pickling, the steel plate is squeezed dry. The pickling and squeezing roller is used to squeeze the pickled steel plate dry to remove the acid from the surface of the steel plate. The pressure of the pickling and squeezing roller is controlled to be set to 0.5MPa.

[0061] 3) Rinse the steel plate by rinsing it with rinsing water in the rinsing tank. The rinsing water has a conductivity of ≤100μs / cm, a pH value of 6~9, a rinsing inhibitor of type BH4 with a content of 0.3%, and a rinsing water temperature of 60℃.

[0062] 4) After rinsing, squeeze the steel plate dry. Use rinsing and squeezing rollers to squeeze the steel plate dry, and remove the rinsing water from the surface of the steel plate by squeezing. Control the pressure of the rinsing and squeezing rollers to 0.5MPa.

[0063] 5) Drying: The steel plate after rinsing and squeezing is dried with hot air to remove residual moisture from the surface of the steel plate. The hot air temperature is 150℃ and the hot air pressure is 0.05MPa.

[0064] According to Example 3, the pickling speed of 60Si2Mn steel was increased from 8 m / min in the existing conventional process to 30 m / min.

[0065] Example 4: A highly efficient pickling surface treatment technology for high-carbon high-alloy steel plates, comprising the following steps:

[0066] 1) High-carbon, high-alloy hot-rolled steel plates were pickled. The 3.0mm thick hot-rolled steel plates were pickled using a pickling solution in a pickling tank. The pickling solution included hydrochloric acid, a pickling accelerator, and iron ions. The hydrochloric acid concentration was 18%, and the acid solution temperature was 83℃. The pickling accelerator had a volume content of 0.5%; the pickling accelerator carboxylate mass fraction was 22%; the urea mass fraction was 15%; the phosphate mass fraction was 8%; the remaining component was water; the iron ion concentration was 100mg / L, and the acidity was 150g / L.

[0067] 2) After pickling, the steel plate is squeezed dry. The pickling and squeezing roller is used to squeeze the pickled steel plate dry to remove the acid from the surface of the steel plate. The pressure of the pickling and squeezing roller is controlled to be set to 0.5MPa.

[0068] 3) Rinse the steel plate by rinsing it with rinsing water in the rinsing tank. The rinsing water has a conductivity of ≤100μs / cm, a pH value of 6~9, a rinsing inhibitor of type BH2 with a content of 0.2%, and a rinsing water temperature of 70℃.

[0069] 4) After rinsing, squeeze the steel plate dry. Use rinsing and squeezing rollers to squeeze the steel plate dry, and remove the rinsing water from the surface of the steel plate by squeezing. Control the pressure of the rinsing and squeezing rollers to 0.5MPa.

[0070] 5) Drying: The steel plate after rinsing and squeezing is dried with hot air to remove residual moisture from the surface of the steel plate. The hot air temperature is 150℃ and the hot air pressure is 0.05MPa.

[0071] According to Example 4, the pickling speed of steel grade SK85 was increased from 40 m / min in the existing conventional process to 60 m / min.

[0072] Example 5: A highly efficient pickling surface treatment technology for high-carbon high-alloy steel plates, comprising the following steps:

[0073] 1) High-carbon, high-alloy hot-rolled steel plates were pickled. The 2.75mm thick hot-rolled steel plates were pickled in the pickling solution in the pickling tank. The pickling solution included hydrochloric acid, pickling accelerator, and iron ions. The mass concentration of hydrochloric acid was 13%, and the acid solution temperature was 85℃. The volume content of pickling accelerator in the pickling solution was 0.7%. The mass fraction of pickling accelerator carboxylate was 25%. The mass fraction of urea was 20%. The mass fraction of phosphate was 5%. The remaining component was water. The iron ion concentration was 80mg / L, and the acidity of the acid solution was 160g / L.

[0074] 2) After pickling, the steel plate is squeezed dry. The pickling and squeezing roller is used to squeeze the pickled steel plate dry to remove the acid from the surface of the steel plate. The pressure of the pickling and squeezing roller is controlled to be set to 0.5MPa.

[0075] 3) Rinse the steel plate by rinsing it with rinsing water in the rinsing tank. The rinsing water has a conductivity of ≤100μs / cm, a pH of 6~9, a rinsing inhibitor of type BH4 with a content of 0.2%, and a rinsing water temperature of 70℃.

[0076] 4) After rinsing, squeeze the steel plate dry. Use rinsing and squeezing rollers to squeeze the steel plate dry, and remove the rinsing water from the surface of the steel plate by squeezing. Control the pressure of the rinsing and squeezing rollers to 0.5MPa.

[0077] 5) Drying: The steel plate after rinsing and squeezing is dried with hot air to remove residual moisture from the surface of the steel plate. The hot air temperature is 150℃ and the hot air pressure is 0.05MPa.

[0078] According to Example 5, the pickling speed of steel grade SK85 was increased from 40 m / min in the existing conventional process to 55 m / min.

[0079] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A highly efficient pickling method suitable for high-carbon high-alloy hot-rolled steel sheets, characterized by, The method comprises the following steps: 1) pickling high-carbon high-alloy hot-rolled steel plate, pickling 2.0-12.7 mm thick hot-rolled steel plate through pickling liquid in a pickling tank, the pickling liquid comprising hydrochloric acid, pickling accelerator and iron ions, mass concentration of hydrochloric acid being 10%-18%, acidity of the pickling liquid being 120-160 g / L, temperature of the pickling liquid being 75-90 ℃, volume content of the pickling accelerator being 0.1%-1.0% of the volume of hydrochloric acid, the pickling accelerator comprising carboxylate with a mass fraction of 20%-25%, urea with a mass fraction of 15%-20%, phosphate with a mass fraction of 5%-10%, and the rest being water, mass concentration of iron ions being 10-100 mg / L, the high-carbon high-alloy hot-rolled steel plate having a carbon content of 0.4%-2.0% and a total content of alloying elements greater than 1%, and the pickling tank having a length of 30-60 m; 2) squeezing the pickled steel plate, squeezing the pickled steel plate with pickling squeezing rollers, and controlling the pressure of the pickling squeezing rollers to be 0.3-0.5 MPa; 3) rinsing the steel plate, rinsing the squeezed steel plate with rinsing water in a rinsing tank, the rinsing water comprising industrial desalted water and rinsing inhibitor, the rinsing water having an electrical conductivity of ≤100 μs / cm, a pH value of 6-9, and a temperature of 30-70 ℃, and the rinsing inhibitor comprising carboxylate with a mass fraction of 35%-40%, fatty carboxylic acid with a mass fraction of 1%-5%, ammonium hydroxide with a mass fraction of <1%, and the rest being water; 4) squeezing the rinsed steel plate, squeezing the rinsed steel plate with rinsing squeezing rollers, and controlling the pressure of the rinsing squeezing rollers to be 0.3-0.5 MPa; 5) drying the steel plate, drying the squeezed steel plate with hot air, the hot air having a temperature of 120-170 ℃ and an air pressure of 0.03-0.05 MPa.

2. The efficient pickling method for high carbon high alloy hot-rolled steel sheet according to Claim 1, characterized by, When the length of the pickling tank is 30-40 m, the pickling accelerator is added in the last pickling tank.

3. The efficient pickling method for high carbon high alloy hot-rolled steel sheet according to Claim 1, characterized by, When the length of the pickling tank is 50-60 m, the pickling accelerator is added at a position 1 / 2-3 / 4 of the total length of the pickling tank.

4. The efficient pickling method for high carbon high alloy hot-rolled steel sheet according to Claim 1, characterized by, When the pickling tank comprises multiple tanks connected in series, the pickling accelerator is distributed in the pickling liquid in a positive gradient from low concentration to high concentration.