Hot-rolled pickled steel sheet for vehicle coil spring and method for manufacturing the same

Abstract

The application discloses a hot-rolled pickling steel plate for vehicle coil spring and a manufacturing method thereof, and mainly solves the technical problems of the low yield and high manufacturing cost of the existing hot-rolled pickling steel plate for vehicle coil spring which cannot be produced by using a continuous casting slab and a hot continuous rolling mode. The technical scheme is as follows: a hot-rolled pickling steel plate for vehicle coil spring, the chemical components of the hot-rolled pickling steel plate are as follows: C: 0.56% to 0.63%, Si: 1.6% to 2.0%, Mn: 0.7% to 1.0%, P: less than or equal to 0.020%, S: less than or equal to 0.005%, Al: less than or equal to 0.01%, N: less than or equal to 0.004%, Cr: 0.1% to 0.2%, and the balance is Fe and inevitable impurity elements; the elongation after fracture of the hot-rolled pickling steel plate with a thickness of 2.5 to 5.0 mm and a width of 1000 to 1300 mm is 16% to 25%; and the hot-rolled pickling steel plate is used for manufacturing vehicle coil springs.

Description

Technical Field

[0001] This invention relates to a spring steel, and more particularly to a hot-rolled pickled steel sheet for vehicle coil springs and its manufacturing method. Specifically, the hot-rolled pickled steel sheet for vehicle coil springs with a thickness of 2.5-5.0 mm and a width of 1000-1300 mm is produced by continuous casting slab and hot continuous rolling, belonging to the field of iron-based alloy technology. Background Technology

[0002] Silicon-manganese spring steel is one of the most widely used spring steel varieties in my country. It has advantages such as low alloy element content, good tempering stability, good resistance to spring reduction, and excellent performance after heat treatment. According to its final application, it is generally divided into bars, flat bars, wires, and plates. Different types of springs generally require quenching and tempering after manufacturing to improve strength, elasticity, or eliminate internal stress. Different applications of springs have different requirements for hardenability and fatigue resistance. Among them, steel plates are mostly used in railway vehicles, automobiles, and tractors to manufacture flat springs that bear heavy loads or large, important coiled springs that bear alternating loads and operate under high stress.

[0003] Due to its high carbon and high alloy content, spring steel is prone to various types of microstructure segregation. Generally, the tendency for microstructure inhomogeneity increases with the increase of slab width. Furthermore, the high Si content makes it susceptible to edge cracking after shearing. For springs subjected to alternating stress over long periods, both of these factors directly affect their fatigue performance. Therefore, spring steel is mostly produced as hot-rolled narrow strip steel with a width of less than 600mm using small square billets. This reduces microstructure inhomogeneity and avoids edge quality problems caused by slitting. Simultaneously, the smaller slab size of hot-rolled narrow strip steel also lowers the heating temperature of the preheating furnace, which is beneficial for controlling the decarburization layer depth. However, the production efficiency, yield, and production flexibility of hot-rolled narrow strip steel are inevitably affected and constrained.

[0004] The Chinese patent application CN104233098A, entitled "A Low-Cost 60Si2Mn Spring Steel and Its Production Process", adopts continuous casting of small square billets, secondary heating and cooling to produce billets in length, requiring a heating temperature of 1120±20℃ and a total heating time of ≥ 260min.

[0005] Chinese patent application publication number CN111961981A, entitled "A 60Si2Mn spring steel for railway fasteners and its preparation method", requires that small square billets be cooled in a pit and then reheated and rolled into bars. The requirements are: pit entry temperature of 500-600℃, pit cooling time of 48-50h, pit exit temperature ≤200℃, secondary heating temperature of 950-1150℃, total heating time of 240-300min, and final rolling temperature of 900-1000℃.

[0006] The Chinese patent application publication number CN112760570A, entitled "A Novel 60Si2Mn Spring Flat Steel and Its Preparation Method", describes the production of narrow strip steel by continuous casting of billets and rolling of flat steel. It requires an initial rolling temperature of 1020-1050℃, a final rolling temperature of 850-900℃, and slow cooling of the rolled stock for more than 24 hours.

[0007] Most of the steel used for coil springs is in the form of bars, wires, and hot-rolled narrow strips, and the existing rolling processes are mainly designed to meet the specific size and specifications of each type of spring. Summary of the Invention

[0008] The purpose of this invention is to provide a hot-rolled pickled steel sheet for vehicle coil springs and its manufacturing method, mainly to solve the technical problems of existing hot-rolled pickled steel sheets for vehicle coil springs that cannot be produced by continuous casting slabs or hot continuous rolling, resulting in low yield and high manufacturing cost.

[0009] The method of this invention enables the direct slitting of hot-rolled pickled steel sheets to produce vehicle coil springs without annealing, solving the problem that existing hot-rolled pickled steel sheets for vehicle coil springs must be annealed before slitting and coiling, thus reducing the production cost of vehicle coil springs.

[0010] The technical concept of this invention is to adopt a high-Si + ultra-low-aluminum composition design to improve the purity of the steel and meet the requirements of high elasticity and high fatigue of spring steel; to achieve the uniformity of microstructure, strength and plasticity requirements of wide plate spring steel through the design of hot rolling heating process, rolling process and slow cooling process, and improve the edge cutting quality; in terms of pickling process, the efficient removal of iron oxide scale of high-Si steel is achieved through the reasonable setting of pickling process.

[0011] The technical solution adopted in this invention is a hot-rolled pickled steel sheet for vehicle coil springs, the chemical composition by weight percentage of which is: C: 0.56%~0.63%, Si: 1.6%~2.0%, Mn: 0.7%~1.0%, P≤0.020%, S≤0.005%, Al≤0.01%, N≤0.004%, Cr: 0.1%~0.2%, with the balance being Fe and unavoidable impurity elements.

[0012] The microstructure of the hot-rolled pickled steel sheet of this invention consists of a small amount of ferrite and pearlite; according to the American Society for Testing and Materials (ASTM)...

[0013] ASTM E45-13, "Standard Test Method for Determination of Inclusion Content in Steel," uses Method A to examine inclusions in steel plates. Inclusions of categories A, B, C, and D are all below grade 2.0; inclusions of categories A, B, C, and D have a grade ≤ 2.0; the yield strength R of hot-rolled pickled steel plates with a thickness of 2.5–5.0 mm and a width of 1000–1300 mm is... p0.2 The tensile strength is 600-750 MPa, and the tensile strength R is... m 1000-1100 MPa, elongation after fracture It ranges from 16% to 25%.

[0014] The hot-rolled pickled steel sheet of this invention is used for the manufacture of vehicle coil springs. It can achieve direct slitting and blanking without annealing, and the edge quality is good.

[0015] The reason why the chemical composition of the hot-rolled pickled steel sheet for vehicle coil springs described in this invention is limited to the above-mentioned range is as follows:

[0016] C: Carbon is the main element affecting the strength and hardness of steel plates after annealing and quenching. However, the higher the C content, the greater the tendency for decarburization, which will affect the surface hardenability and fatigue resistance. The C content in this application is set at 0.56% to 0.63%.

[0017] Si (Si): Significantly increases the elastic limit of steel, making it the most important element for reducing spring tension in spring steel. Furthermore, due to its strong solid solution strengthening effect and significantly reduced critical cooling rate, Si improves the hardenability of steel. In this application, due to the ultra-low Al design, Si acts as a deoxidizer during smelting, enhancing deoxidation and desulfurization capabilities. However, high-Si steels tend to form ferrosilicon oxide scale on the steel plate surface during hot rolling, significantly increasing the difficulty of conventional pickling. Considering product performance requirements and consistent manufacturing process capabilities, the Si design in this application is 1.6%–2.0%.

[0018] Mn: Manganese is one of the most effective elements for improving hardenability and is also a solid solution strengthening element. Furthermore, when properly proportioned with silicon, it can reduce decarburization caused by silicon. However, excessive manganese content can easily cause segregation in the slab, affecting the uniformity of the microstructure of the hot-rolled plate. In this application, the Mn content is set at 0.7% to 1.0%.

[0019] S and P are impurity elements in steel, and their content should be as low as possible. At the same time, S easily forms MnS in steel, which affects fatigue performance. Considering economy and feasibility, this application uses S≤0.005% and P≤0.020%.

[0020] Al (Al) is a strong oxidizing element that can effectively reduce oxide inclusions in steel and purify the steel, often used as a deoxidizer. However, the resulting Al₂O₃ particles are relatively large and lack plasticity, making them difficult to deform during processing and use, leading to stress concentration and potentially affecting the fatigue strength of spring steel. This application employs an ultra-low aluminum and silicon deoxidation design, which can significantly improve the purity of the steel, controlling the total oxygen content to below 0.004%. This invention limits the Al content to ≤0.01%.

[0021] Cr is an element that significantly improves hardenability. It is also a strong carbide-forming element, strongly inhibiting carbon diffusion in austenite, thus reducing the carbon diffusion coefficient and the tendency for decarburization. Furthermore, during tempering, it makes the carbides in the steel fine and uniform, effectively suppressing the microstructure transformation during low-temperature tempering, resulting in good tempering stability. This invention limits the Cr content to 0.1%–0.2%.

[0022] N: In steel, it easily forms fine nitrides with alloying elements. During the tempering process of spring steel, it may precipitate again, which will reduce the toughness of the steel. Therefore, this invention limits N to ≤ 0.0040%.

[0023] A method for manufacturing hot-rolled pickled steel sheet for vehicle coil springs, the method comprising:

[0024] Molten steel is refined in a ladle furnace and degassed under vacuum before being continuously cast to obtain a continuously cast slab. The chemical composition of the molten steel is as follows (weight percentage): C: 0.56%–0.63%, Si: 1.6%–2.0%, Mn: 0.7%–1.0%, P≤0.020%, S≤0.005%, Al≤0.01%, N≤0.004%, Cr: 0.1%–0.2%, with the balance being Fe and unavoidable impurities. The thickness of the continuously cast slab is 210–230 mm, the width is 1000–1300 mm, and the length is 5000–8500 mm. The inclusion grade in the continuously cast slab is controlled to be ≤2.0.

[0025] The continuously cast slab is heated in a furnace and then hot-rolled. The slab is hot-charged and hot-delivered into the furnace, with an initial temperature ≥400℃. The furnace operates in a weakly reducing atmosphere, with an excess air coefficient of 0.95–1.0. The heating temperature is 1200–1260℃, and the heating time is 180–240 min. The hot rolling process is a two-stage rolling process: roughing is a 6-pass continuous rolling process, performed above the austenite recrystallization temperature, with a finishing temperature of 1040–1100℃; the intermediate slab thickness after roughing is controlled to be 38–42 mm; finishing is a 7-pass continuous rolling process, with a finishing temperature of 860–900℃; after finishing, the steel plate thickness is controlled to be 2.5–5.0 mm. Laminar flow cooling is performed using front-stage cooling at a rate of 5–10%. ℃ / s; laminar cooling end temperature is 610~650℃; hot-rolled steel coils are obtained at a coiling temperature of 600~640℃;

[0026] The hot-rolled steel coil is cooled slowly after being coiled, and the cooling rate of the hot-rolled steel coil to 200℃ is 6~9℃ / h.

[0027] After the hot-rolled steel coil is recoiled, it undergoes push-pull pickling, rinsing, drying, and oiling to obtain the finished hot-rolled pickled steel sheet. The push-pull pickling uses hydrochloric acid pickling solution with a hydrochloric acid volume concentration of 15% to 20%, a pickling temperature of 75 to 90°C, a pickling time of 80 to 200 seconds, and a pickling squeeze roller pressure of 0.15 to 0.50 MPa.

[0028] The rationale for the production process adopted in this invention is as follows:

[0029] 1. Setting the temperature of the continuously cast slab entering the heating furnace, the heating temperature of the continuously cast slab, and the heating time.

[0030] Due to its high alloy content, spring steel is susceptible to thermal stress from rapid heating from a cold state, which can cause slab deformation or cracking. Therefore, it is generally required that continuously cast slabs be cut and then fed into the furnace while still hot. The slabs are typically charged and delivered hot into the furnace, with an entry temperature ≥400℃. As the temperature rises after entering the furnace, the slab gradually austenitizes, significantly improving the various compositional and structural segregations that occur during solidification. Generally, higher heating temperatures and longer holding times result in better compositional and structural uniformity. However, because spring steel has a high silicon content, it has an increased tendency to decarburize during heating, leading to a deeper decarburized layer, which is detrimental to surface quality. Therefore, this application primarily considers the austenitic microstructure and compositional uniformity in the first heating stage, setting the heating temperature at 1000-1100℃. The second heating stage's time and homogenization temperature are primarily determined by the rolling load of wide slab continuous rolling. Therefore, considering both cost and operability, this application sets the slab homogenization temperature at 1200-1260℃ and the total heating time at 180-240 minutes, with the second heating stage's homogenization time exceeding 80 minutes and the final temperature of the second heating stage exceeding 1220℃. Furthermore, the furnace atmosphere also has a certain impact on decarburization; this application sets the excess air coefficient at 0.95-1.0.

[0031] 2. Setting of finishing rolling end temperature, laminar flow cooling method, laminar flow cooling rate, laminar flow cooling end temperature, and coiling temperature.

[0032] The finishing rolling end temperature is generally set to ensure that the entire slab is rolled fully in the austenitic region, avoiding mixed crystals caused by rolling in the two-phase region at the end of the rolling process. The setting of the laminar cooling rate and coiling temperature after rolling mainly considers the final microstructure of the spring steel. Studies have shown that when the cooling rate is 1℃ / s, the ferrite phase transformation start temperature Ar3 is 720℃, and the phase transformation end temperature Ar1 is 670℃. The pearlite phase transformation start temperature is 670℃, and the phase transformation end temperature is 600℃. As the cooling rate increases, the phase transformation temperature decreases, the pearlite lamellar spacing decreases, and the strength increases. Therefore, in order to achieve the strength and plasticity of the steel plate of this application and realize direct slitting and blanking without annealing, this application, through repeated experiments, sets the finishing rolling end temperature to 860~900℃, uses front-stage cooling control for laminar cooling, the cooling rate is 5~10℃ / s, the laminar cooling end temperature is 610~650℃, and the coiling temperature is 600~640℃.

[0033] 3. Setting the cooling rate of hot-rolled steel coils

[0034] The design of the cooling process for spring steel mainly considers the microstructure transformation and uniformity during the subsequent gradual cooling process after the steel plate is coiled. Studies have shown that when the cooling rate is ≤7℃ / s, the microstructure of silicon-manganese spring steel is ferrite + pearlite. If the cooling rate is too slow, the proportion of ferrite increases, which may affect hardenability. If the cooling rate is too fast, the pearlite content increases accordingly, and the interlamellar spacing of the pearlite becomes finer, increasing strength but decreasing plasticity. At the same time, excessively fast cooling rates can also lead to varying degrees of uneven microstructure within the steel coil, resulting in increased internal stress and making it prone to brittle fracture or poor cut quality during slitting. Therefore, the cooling process design of this application requires the coil to enter the slow cooling wall or slow cooling hood for cooling as soon as possible, and the cooling rate for hot-rolled steel coils to 200℃ is 6~9℃ / h.

[0035] 4. Setting the pickling process

[0036] Due to its high Si content and the high furnace temperature used for spring steel, a layer of network-like iron silicate exists in the base layer of the iron oxide scale, making pickling difficult. Experiments revealed that the outer layer of the iron oxide scale containing iron silicate is sensitive to acid temperature and pickling time, but the residue adhering to the bottom layer is difficult to remove. Field tests showed that appropriately increasing the pressure of the squeeze rollers in the pickling tank can effectively remove the adhering substances through slight friction from the rollers. Therefore, under the process conditions of shallow tank turbulent push-pull hydrochloric acid pickling, a hydrochloric acid volume concentration of 15%–20%, a pickling temperature of 75–90℃, a pickling time of 80–200s, and a pickling squeeze roller pressure of 0.15–0.50MPa can meet both surface quality requirements and actual production requirements.

[0037] The metallographic structure of the hot-rolled pickled steel sheet produced by the method of this invention consists of a small amount of ferrite and pearlite. According to the American Society for Testing and Materials (ASTM) standard test method E45-13 for determining inclusion content in steel, method A is used to examine the inclusions in the steel sheet. Inclusions of types A, B, C, and D are all below grade 2.0; inclusions of types A, B, C, and D have a rating ≤ 2.0. The yield strength R of the hot-rolled pickled steel sheet with a thickness of 2.5–5.0 mm and a width of 1000–1300 mm is... p0.2 The tensile strength is 600-750 MPa, and the tensile strength R is... m 1000-1100 MPa, elongation after fracture It ranges from 16% to 25%.

[0038] Compared with existing technologies, this invention has the following positive effects: 1. The invention adopts a low-aluminum, low-oxygen design, significantly improving the purity of the steel and thus enhancing the fatigue performance of the spring steel. 2. This invention achieves uniformity of microstructure, strength, and plasticity requirements in wide-plate spring steel through process design including hot rolling heating, rolling, and slow cooling, improving edge trimming quality. 3. In the pickling process, the rational design of the pickling process achieves efficient removal of iron oxide scale from high-Si steel. 4. This invention produces wide-plate hot-rolled pickled steel sheets with a thickness of 2.5-5.0 mm and a width of 1000-1300 mm. Compared with hot-rolled narrow strip steel with a width of less than 600 mm, the steel sheet production efficiency is significantly improved. Furthermore, different specifications of products can be produced by slitting different dimensions at the user end, not only significantly improving production efficiency and yield but also effectively increasing production flexibility. Attached Figure Description

[0039] Figure 1 This is a metallographic photograph of the hot-rolled pickled steel plate of Example 3 of the present invention.

[0040] Figure 2 This is a scanning electron microscope (SEM) image of the metallographic structure of the hot-rolled pickled steel sheet in Example 3 of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to Examples 1-5, as shown in Tables 1-5.

[0042] Table 1 shows the chemical composition (by weight percentage) of the steel in the embodiments of the present invention, with the balance being Fe and unavoidable impurities.

[0043] Table 1 Chemical composition of steel in the embodiments of the present invention, unit: weight percentage.

[0044]

[0045] Molten steel that meets the chemical composition requirements is obtained through converter smelting. The molten steel is then refined in an LF ladle refining furnace by Ar blowing, followed by vacuum circulation degassing and composition fine-tuning in an RH furnace. The molten steel is then continuously cast under full Ar blowing protection to obtain a continuously cast slab with a thickness of 210-230 mm, a width of 1000-1300 mm, and a length of 5000-8500 mm. The inclusion grade in the continuously cast slab is controlled to be ≤2.0.

[0046] The continuously cast slab is directly fed into the heating furnace for heating, using a hot charging and hot delivery method. After heating in the furnace, the slab undergoes hot rolling, a two-stage rolling process controlled by a roughing and finishing continuous rolling mill. After laminar flow cooling, the slab is coiled, with the laminar flow cooling being front-stage cooling, producing qualified hot-rolled steel coils. The thickness of the hot-rolled steel plate is 2.5–5.0 mm. After coiling, the hot-rolled steel coil enters a slow cooling hood for slow cooling. The heating furnace process control parameters are shown in Table 2; the hot rolling process control parameters are shown in Tables 2 and 3.

[0047] Table 2 Process control parameters of the heating furnace in the embodiments of the present invention

[0048]

[0049] Table 3 Hot rolling process control parameters of the present invention embodiments

[0050]

[0051] After the hot-rolled steel coil is recoiled, it undergoes push-pull pickling, rinsing, drying, and oiling to obtain the finished hot-rolled pickled steel sheet. The push-pull pickling uses hydrochloric acid pickling solution with a hydrochloric acid volume concentration of 15%–20%, a pickling temperature of 75–90℃, a pickling time of 80–200s, and a pickling squeeze roller pressure of 0.15–0.50MPa. The pickling process control parameters are shown in Table 4.

[0052] Table 4. Pickling process control parameters in embodiments of the present invention

[0053] Hot rolling parameters Thickness of hot-rolled pickled steel plate / mm Pickling temperature / ℃ Pickling time / s Squeeze roller pressure / MPa This invention 2.5-5.0 75-90 80-200 0.15-0.5 Example 1 4.0 80 155 0.35 Example 2 3.5 82 150 0.45 Example 3 5.0 88 195 0.28 Example 4 2.5 78 100 0.38 Example 5 4.8 85 175 0.18

[0054] For hot-rolled pickled steel sheets obtained using the above method, see [link / reference]. Figure 1 , Figure 2 The microstructure of hot-rolled pickled steel sheet consists of a small amount of ferrite and pearlite. According to ASTM E45-13, "Standard Test Method for Determination of Inclusion Content in Steel," method A is used to examine inclusions in hot-rolled pickled steel sheet. Inclusions of types A, B, C, and D are all below grade 2.0; inclusion grades A, B, C, and D are ≤2.0. The yield strength R of hot-rolled pickled steel sheet with a thickness of 2.5–5.0 mm and a width of 1000–1300 mm is... p0.2The tensile strength is 600-750 MPa, and the tensile strength R is... m 1000-1100 MPa, elongation after fracture It ranges from 16% to 25%.

[0055] The hot-rolled pickled steel sheet obtained by this invention was subjected to tensile testing according to GB / T228.1-2010 Metallic Materials - Tensile Testing - Part 1: Test Method at Room Temperature; the inclusions in the hot-rolled pickled steel sheet were examined using Method A according to ASTM E45-13 Standard Test Method for Determination of Inclusion Content in Steel; the decarburized layer thickness was determined according to GB / T 224-2008 Determination of Decarburized Layer Depth in Steel, and its mechanical properties are shown in Table 5.

[0056] Table 5 Mechanical properties, inclusion grades, and decarburized layer parameters of hot-rolled pickled steel sheets according to embodiments of the present invention.

[0057]

[0058] Table 5 shows the results of testing the elongation after fracture of hot-rolled pickled steel sheets, using the gauge length... S0 is the cross-sectional area of ​​the sample steel plate.

[0059] 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 hot-rolled pickled steel sheet for vehicle coil springs, comprising the following chemical composition by weight percentage: C: 0.56%–0.63%, Si: 1.6%–2.0%, Mn: 0.7%–1.0%, P≤0.020%, S≤0.005%, Al≤0.01%, N≤0.004%, Cr: 0.1%–0.2%, with the balance being Fe and unavoidable impurity elements; the yield strength R of the hot-rolled pickled steel sheet having a thickness of 2.5–5.0 mm and a width of 1000–1300 mm is... p0.2 The tensile strength is 600-750 MPa, and the tensile strength R is... m 1000-1100 MPa, elongation after fracture The content is 16% to 25%; the manufacturing method of hot-rolled pickled steel sheet is characterized by, Includes the following steps: Molten steel is refined in a ladle furnace and degassed under vacuum before being continuously cast to obtain a continuously cast slab. The chemical composition of the molten steel is as follows (weight percentage): C: 0.56%–0.63%, Si: 1.6%–2.0%, Mn: 0.7%–1.0%, P≤0.020%, S≤0.005%, Al≤0.01%, N≤0.004%, Cr: 0.1%–0.2%, with the balance being Fe and unavoidable impurities. The thickness of the continuously cast slab is 210–230 mm, the width is 1000–1300 mm, and the length is 5000–8500 mm. The inclusion grade in the continuously cast slab is controlled to be ≤2.

0. The continuously cast slab is heated in a furnace and then hot-rolled. The slab is fed into the furnace using a hot-charging and hot-delivery method. The slab's temperature upon entering the furnace is ≥400℃. The furnace heats the slab in a weakly reducing atmosphere with an air excess coefficient of 0.95–1.

0. The heating temperature is 1200–1260℃, and the heating time is 180–240 min. The hot rolling is a two-stage rolling process, with the rough rolling being a six-pass continuous rolling process, during austenite recrystallization. The rolling process is carried out above the specified temperature, with the roughing rolling ending temperature at 1040–1100℃; the thickness of the intermediate slab after roughing rolling is controlled at 38–42 mm; the finishing rolling is a 7-pass continuous rolling process, with the finishing rolling ending temperature at 860–900℃; after finishing rolling, the steel plate thickness is controlled at 2.5–5.0 mm; laminar flow cooling adopts front-stage cooling, with a cooling rate of 5–10℃ / s; the laminar flow cooling ending temperature is 610–650℃; hot-rolled steel coils are obtained at a coiling temperature of 600–640℃. The hot-rolled steel coil is cooled slowly after being coiled, and the cooling rate of the hot-rolled steel coil to 200℃ is 6~9℃ / h. After the hot-rolled steel coil is recoiled, it undergoes push-pull pickling, rinsing, drying, and oiling to obtain the finished hot-rolled pickled steel sheet. The push-pull pickling uses hydrochloric acid pickling solution with a hydrochloric acid volume concentration of 15% to 20%, a pickling temperature of 75 to 90°C, a pickling time of 80 to 200 seconds, and a pickling squeeze roller pressure of 0.15 to 0.50 MPa.

2. The hot-rolled pickled steel sheet for vehicle coil springs as described in claim 1, characterized in that, The metallographic structure of hot-rolled pickled steel sheet is a small amount of ferrite + pearlite; according to the American Society for Testing and Materials (ASTM) standard test method for determining inclusion content in steel (E45-13), method A is used to test the inclusions in hot-rolled pickled steel sheet. Among them, inclusions of categories A, B, C and D are all below grade 2.0; inclusions of categories A, B, C and D are ≤2.

0.

3. A method for manufacturing hot-rolled pickled steel sheet for vehicle coil springs, characterized in that, Includes the following steps: Molten steel is refined in a ladle furnace and degassed under vacuum before being continuously cast to obtain a continuously cast slab. The chemical composition of the molten steel is as follows (weight percentage): C: 0.56%–0.63%, Si: 1.6%–2.0%, Mn: 0.7%–1.0%, P≤0.020%, S≤0.005%, Al≤0.01%, N≤0.004%, Cr: 0.1%–0.2%, with the balance being Fe and unavoidable impurities. The thickness of the continuously cast slab is 210–230 mm, the width is 1000–1300 mm, and the length is 5000–8500 mm. The inclusion grade in the continuously cast slab is controlled to be ≤2.

0. The continuously cast slab is heated in a furnace and then hot-rolled. The slab is fed into the furnace using a hot-charging and hot-delivery method. The slab's temperature upon entering the furnace is ≥400℃. The furnace heats the slab in a weakly reducing atmosphere with an air excess coefficient of 0.95–1.

0. The heating temperature is 1200–1260℃, and the heating time is 180–240 min. The hot rolling is a two-stage rolling process, with the rough rolling being a six-pass continuous rolling process, during austenite recrystallization. The rolling process is carried out above the specified temperature, with the roughing rolling ending temperature at 1040–1100℃; the thickness of the intermediate slab after roughing rolling is controlled at 38–42 mm; the finishing rolling is a 7-pass continuous rolling process, with the finishing rolling ending temperature at 860–900℃; after finishing rolling, the steel plate thickness is controlled at 2.5–5.0 mm; laminar flow cooling adopts front-stage cooling, with a cooling rate of 5–10℃ / s; the laminar flow cooling ending temperature is 610–650℃; hot-rolled steel coils are obtained at a coiling temperature of 600–640℃. The hot-rolled steel coil is cooled slowly after being coiled, and the cooling rate of the hot-rolled steel coil to 200℃ is 6~9℃ / h. After the hot-rolled steel coil is recoiled, it undergoes push-pull pickling, rinsing, drying, and oiling to obtain the finished hot-rolled pickled steel sheet. The push-pull pickling uses hydrochloric acid pickling solution with a hydrochloric acid volume concentration of 15% to 20%, a pickling temperature of 75 to 90°C, a pickling time of 80 to 200 seconds, and a pickling squeeze roller pressure of 0.15 to 0.50 MPa.

4. The method for manufacturing hot-rolled pickled steel sheet for vehicle coil springs as described in claim 3, characterized in that, The microstructure of the hot-rolled pickled steel sheet is a small amount of ferrite + pearlite; according to the American Society for Testing and Materials (ASTM) standard test method E45-13 for determining inclusion content in steel, method A is used to test the inclusions in the hot-rolled pickled steel sheet, wherein inclusions of types A, B, C, and D are all below grade 2.0; the yield strength R of the hot-rolled pickled steel sheet with a thickness of 2.5-5.0 mm and a width of 1000-1300 mm is... p0.2 The tensile strength is 600-750 MPa, and the tensile strength R is... m 1000-1100 MPa, elongation after fracture It ranges from 16% to 25%.

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