High-strength hot-rolled pickled steel sheet for automotive chassis and method for producing the same

Abstract

The present application belongs to the field of metal material, and particularly relates to a high-strength hot-rolled pickling steel plate for automobile chassis and a production method thereof. The steel plate of the present application is mainly used for manufacturing automobile chassis structural parts. The chemical composition of the steel is designed as C, Si, Mn, Al, V, Ni, Cu, Cr, Pt, Y, and P is limited to be less than or equal to 0.015%, S is limited to be less than or equal to 0.005%, N is limited to be less than or equal to 0.006%, and the balance is Fe and inevitable impurities. The yield strength of the steel plate of the present application is 498-552 MPa, the tensile strength is 608-643 MPa, the transverse elongation A is 33%-38%, the transverse cold bending 180 D=a is qualified, the surface quality is good, there are no iron oxide scale stripes and color difference defects, the surface roughness Ra is 1.10-1.35 microns, and the steel plate has excellent corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of metallic materials, and specifically relates to a high-strength hot-rolled pickled steel sheet for automotive chassis and its production method. The steel sheet of this invention is mainly suitable for manufacturing automotive chassis structural components. Background Technology

[0002] In recent years, with the development of the automotive industry, automakers have increasingly demanded more personalized steel materials. Hot-rolled pickled steel sheet is an intermediate product made from high-quality hot-rolled steel sheet. After removing the iron oxide scale through a pickling unit, its surface quality and usage requirements fall between those of hot-rolled and cold-rolled steel sheets. It is an ideal substitute for some hot-rolled and cold-rolled steel sheets. Currently, given the challenging steel market conditions, hot-rolled pickled steel sheet offers better surface quality than hot-rolled steel sheet and, while maintaining the required surface quality compared to cold-rolled steel sheet, effectively reduces procurement costs for users, making it one of the most profitable products for steel companies.

[0003] Chinese patent application CN108441759A discloses a 540MPa grade hot-rolled pickled steel plate and its manufacturing method. The hot-rolled pickled steel plate produced by adding a certain amount of Nb and / or Cr to the ordinary C-Mn composition system has a maximum strength of 601MPa, but does not have certain corrosion resistance and oxidation resistance.

[0004] Chinese patent application CN110484827A discloses a hot-rolled pickled steel sheet with a tensile strength of 600MPa and a low yield strength ratio. This invention primarily addresses the technical problem of mismatched stamping and hole-expanding properties in existing 600MPa-grade hot-rolled pickled steel sheets, which cannot meet the manufacturing requirements of complex-shaped automotive parts. The invention produces a 2.0–4.0mm thick hot-rolled pickled steel sheet with a yield strength ratio ≤0.80 and an elongation after fracture (A0.05). 50mm With a strength of 25-35% and a hole-expanding performance λ≥75%, this steel plate is used for manufacturing automotive structural components. However, it lacks resistance to alkali corrosion and oxidation, making it unsuitable for automotive chassis structural components. Summary of the Invention

[0005] To address the evolving needs of the automotive steel industry, this invention provides a high-strength hot-rolled pickled steel sheet for automotive chassis and its production method. The steel sheet exhibits a yield strength of 498–552 MPa, a tensile strength of 608–643 MPa, a transverse elongation A of 33%–38%, and meets the acceptable transverse cold bending standard (D=a at 180°). It also has a surface roughness Ra of 1.10–1.35 μm and excellent corrosion resistance. Using an alkaline solution of 3.7 g / L NaOH + 10.5 g / L KOH + 2 g / L Ca(OH)₂, the corrosion rate of the steel sheet is ≤0.60 g / (m²) over a 144-hour test period. 2 ·h).

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A high-strength hot-rolled pickled steel sheet for automobile chassis, wherein the chemical composition of the steel by weight percentage is: C: 0.051%~0.082%, Si: 0.29%~0.42%, Mn: 1.55%~1.70%, Al: 0.010%~0.040%, V: 0.20%~0.30%, Ni: 0~0.10%, Cu: 0~0.05%, Cr: 0.20%~0.80%, Pt: 0.001%~0.008%, Y: 0.003%~0.010%, with P≤0.015%, S≤0.005%, N≤0.006%, and the balance being Fe and unavoidable impurities.

[0008] The microstructure of the finished steel plate of this invention consists of 20%–35% ferrite, 65%–80% bainite, and 0%–3% retained austenite. The steel plate has a yield strength of 498–552 MPa, a tensile strength of 608–643 MPa, a transverse elongation A of 33%–38%, and passes the transverse cold bending test at 180° (D=a). The finished steel plate has a thickness of 1.50–6.00 mm and a surface roughness Ra of 1.10–1.35 μm. Using an alkaline solution of 3.7 g / L NaOH + 10.5 g / L KOH + 2 g / L Ca(OH)₂, the corrosion rate of the steel plate is ≤0.60 g / (m²) over a 144-hour test period. 2 ·h).

[0009] The main function of the composition of a high-strength hot-rolled pickled steel sheet for automobile chassis in this invention is as follows:

[0010] C: Carbon is a common strengthening element in steel. Interstitial carbon atoms cause certain lattice distortions in the matrix, playing a role in solid solution strengthening. In this invention, carbon ensures the bainite content, thereby improving the formability of the steel plate. Too low a carbon content will not yield the mechanical properties of the steel plate described in this invention, while too high a content will cause the steel plate to become brittle, posing a risk of delayed fracture and hot-rolling edge cracking, and also negatively impacting the weldability, plasticity, and toughness of the steel plate. In this invention, the overall carbon content is required to be within a low range, which helps reduce the risk of delayed fracture and hot-rolling edge cracking, and is also beneficial to the weldability of the steel plate. Therefore, the optimal range for carbon in this invention is 0.051% to 0.082%.

[0011] Silicon (Si): Silicon is one of the key elements in this invention. Sufficient silicon content ensures the strength of the ferrite matrix. Furthermore, adequate silicon content reduces inclusions in the steel, inhibits their formation, and prevents the steel plate's mechanical properties from being compromised by inclusions. However, too low a silicon content fails to guarantee the strength of the ferrite matrix and inhibit inclusion formation, while too high a content affects the surface quality of hot-rolled steel, resulting in excessive iron oxide scale and impaired weldability. Therefore, the silicon content in this invention is 0.29%–0.42%.

[0012] Mn: Manganese strengthens the solid solution in steel by inducing lattice distortion through substitution solid solution. It is also an austenite stabilizing element in steel, expanding the austenite region, reducing the critical quenching rate of steel, and delaying the transformation of austenite to pearlite. However, if the manganese content is too low, the supercooled austenite is unstable, reducing the plasticity and toughness of the steel plate. Furthermore, the added manganese content should not exceed the scope of this invention. The main consideration is that excessive manganese content will lead to C or Mn segregation, which will worsen the uniformity of the steel plate structure during hot rolling and easily cause severe banded defects in the structure. In addition, excessive manganese in the steel involved in this invention will increase hardenability and inhibit bainite formation, which is also not conducive to the comprehensive performance of the steel plate. In addition, excessive manganese content will lead to poor weldability of the steel plate. Therefore, considering all factors, this invention selects a manganese content of 1.55% to 1.70%.

[0013] P: Phosphorus is an impurity element in steel. It tends to agglomerate at grain boundaries. When the phosphorus content in steel is high, Fe2P particles are easily formed, which reduces the plasticity and toughness of the steel. Therefore, the lower its content, the better. In order to obtain a higher elongation, its upper limit is set at 0.015%.

[0014] S: Sulfur is an impurity element in steel. It easily combines with Mn to form MnS inclusions, which become the starting point of cracks and deteriorate the processing performance, seriously affecting the plasticity and formability of steel plates. Therefore, the lower the content, the better. The upper limit is set at 0.005%.

[0015] Al: In traditional steelmaking processes, Al is a deoxidizer. Al can also combine with nitrogen in steel to form AlN, refining the grain size. Simultaneously, together with Si, it inhibits cementite precipitation, increases the austenitizing temperature, facilitates better selection of the process window, and accelerates bainite transformation. Excessive Al content will cause nozzle blockage during continuous casting, affecting production efficiency and increasing production costs. Therefore, in this invention, the Al content is limited to 0.010%–0.040%.

[0016] Vanadium (V) has significant precipitation strengthening and grain refinement effects. Its effect is mainly achieved through the formation of precipitates with carbon and nitrogen, especially the VN precipitation formed with nitrogen, which greatly improves the strength of the steel plate. In addition, the retention of a large amount of V precipitates within the steel plate microstructure acts as a hydrogen trap, reducing the risk of delayed cracking during use and giving the steel plate excellent mechanical properties and resistance to hydrogen-induced cracking. Higher V content also leads to poorer toughness in the weld heat-affected zone; therefore, the V addition amount in this invention is 0.20%–0.30%.

[0017] Ni: Nickel is a solid solution strengthening element that can improve the hardenability of materials, prevent temper brittleness, and improve the fatigue performance of materials. It has no adverse effect on the hardening and toughness of the weld heat-affected zone of steel, and improves heat resistance and cold brittleness. However, excessive Ni will lead to increased manufacturing costs. Nickel can promote the formation of a dense and stable oxide film (such as NiO) on the steel surface. This film is not easily destroyed in alkaline environments and can effectively block the contact between alkaline solutions and the steel matrix, reducing corrosion. Nickel can reduce the chemical reactivity of steel in concentrated alkali or high-temperature alkaline solutions, especially significantly inhibiting intergranular corrosion and stress corrosion caused by strong alkalis such as sodium hydroxide, maintaining the stability of the steel structure. Therefore, the optimal range of Ni content in this invention is between 0% and 0.10%.

[0018] Cu (Cu) plays a role in solid solution strengthening and precipitation strengthening. However, when the Cu content is too high, it can easily lead to copper embrittlement on the steel plate surface and the risk of hot-rolling edge cracking. In addition, Cu can reduce work hardening, improve the plasticity of the steel plate, and in an alkaline environment, copper will form a protective film containing copper oxide (CuO) or basic copper salts on the steel surface. This film has a relatively dense structure, which can slow down the erosion rate of alkaline solution on the steel substrate. Copper can reduce the electrochemical corrosion activity of steel in alkaline media, especially in medium-low temperature and medium concentration alkaline environments, it can inhibit uniform corrosion and localized corrosion (such as pitting corrosion) of steel, and enhance overall corrosion resistance. Therefore, the optimal range of Cu content in this invention is between 0% and 0.05%.

[0019] Cr: Chromium is a carbide-forming element that can delay the pearlite transformation and improve the hardenability of steel. It also refines the microstructure, resulting in a strengthening effect. Furthermore, it enhances the stability of austenite, inhibiting the transformation of austenite to other phases during coiling and improving the stability of residual austenite after coiling, ensuring a certain amount of residual austenite in the final microstructure. Chromium readily forms a dense and chemically stable oxide film (Cr2O3) on the steel surface. This film is not easily dissolved or destroyed in alkaline environments, effectively preventing contact between alkaline solutions and the steel matrix, fundamentally slowing down corrosion. In high-temperature or concentrated alkaline environments, chromium can inhibit the formation of harmful compounds (such as carbides) between carbon and other elements in steel, reducing intergranular corrosion and maintaining the integrity of the steel's microstructure. Chromium can increase the electrochemical potential of steel in alkaline media, reducing the corrosion rate, especially in strongly alkaline (such as sodium hydroxide) and high-temperature alkaline environments. Therefore, the optimal range of Cr content in this invention is between 0.20% and 0.80%.

[0020] Pt: Platinum itself is a chemically inert metal with excellent chemical stability and corrosion resistance. In steel, platinum reacts with oxygen to form a dense oxide protective film. This film isolates the steel from direct contact with corrosive media, thus slowing down the corrosion process. Furthermore, it exhibits good corrosion resistance to most alkaline solutions (including strong alkalis) at room temperature and is not prone to chemical reactions. The addition of platinum can alter the electrochemical properties of steel, potentially aiding or enhancing the formation and stability of the passivation film on the steel surface. It can reduce the electrochemical corrosion activity of steel in alkaline media, improve the corrosion resistance and oxidation resistance of steel, and extend the service life of steel in highly corrosive environments and at high temperatures. Therefore, this invention limits the Pt content to 0.001%–0.008%.

[0021] Y: Yttrium can refine the grains in steel, enhance the strength and plasticity of grain boundaries, which is beneficial to the improvement of mechanical properties. It can also improve the weldability and oxidation resistance of steel, thereby increasing the service life of steel at high temperatures. Therefore, the Y content is limited to 0.003% to 0.010% in this invention.

[0022] N: For the N content in steel, the lower the N content, the better. However, too low a content will lead to production difficulties and increased costs. However, this invention requires the precipitation of VN formed with V to carry out precipitation strengthening and grain refinement strengthening, thereby improving the strength of the steel plate. Therefore, the N content in this invention is ≤0.006%.

[0023] A method for producing high-strength hot-rolled pickled steel sheet for automobile chassis includes smelting, hot rolling, and pickling processes, specifically comprising:

[0024] (1) Smelting process: The raw materials are pretreated with KR hot metal to control the S content to be less than 0.005%. After slag removal, they enter the converter. In the converter smelting, the double slag method is used to remove P, and the P content is controlled to be ≤0.015%. At the end of the converter smelting, the C content is controlled to be 0.051% to 0.082%. Argon gas is blown for more than 7 minutes when tapping the steel (the argon blowing and sedation before continuous casting can promote the removal of inclusions in the molten steel and improve the uniformity of the steel composition). Then, the LF+RH process is carried out, and the H and O contents are strictly controlled, H≤0.0002% and O≤0.0015%. The RH vacuum degassing is maintained for more than 15 minutes. Calcium treatment is carried out in the refining LF process. After that, the slab is continuously cast. The superheat of continuous casting is 15 to 20℃, and the continuous casting drawing speed is 1.1 to 1.6 m / min. (Reducing superheat and casting speed can improve macroscopic segregation of the billet, reduce the spacing of secondary dendrite arms in the solidification structure of the billet, and help reduce billet segregation and internal structural defects.) Control the electromagnetic stirring current intensity in the secondary cooling zone of the continuous casting stage to 200-300A, and the secondary cooling water volume to 0.75-1.00L / kg (to reduce the average carbon segregation index, suppress segregation, and limit the intensity of secondary cooling to suppress the tendency of central cracks in the billet to worsen). In the horizontal section of the secondary cooling zone, i.e., at the end of solidification, apply light pressure, and reduce the billet by 3.0-4.0mm (to reduce the central porosity and segregation of the billet). Stack the billets after casting for more than 36 hours (to reduce the accumulation of residual H, suppress the generation of microcracks inside the billet, and ensure the toughness of the steel plate).

[0025] (2) In the hot rolling process: The continuously cast slab with a thickness of (170-235) mm and a width of (1040-2000) mm is loaded into a walking beam furnace for heating at a temperature of 1190-1250℃ and a holding time of 150-180 min. The roughing process adopts a 3+3 rolling process (R1 is rolled in 3 passes and R2 is rolled in 3 passes) for a total of 6 passes. The exit temperature of the roughing mill is ≥1000℃. The thickness of the intermediate slab is 37.0-55.0 mm and the width is 1040-2000 mm. The intermediate slab is kept warm by a heat insulation cover before entering the hot rolling finishing mill to reduce the temperature drop of the intermediate slab on the delay roller table and the temperature difference in the head, tail and width directions. The finishing mill is a 7-stand continuous rolling process. High-pressure water descaling is performed before finishing milling. The entry temperature of the finishing mill is ≤1050℃. The final rolling temperature is 838–888℃. After final rolling, a laminar flow cooling + air cooling + rapid cooling mode is adopted. The laminar flow cooling rate is greater than 16℃ / s. After cooling to 675–725℃, air cooling is performed for 15–20 seconds, followed by rapid cooling at a rate greater than 25℃ / s. After rapid cooling to 488–520℃, the steel is coiled. The purpose of laminar flow cooling to 675–725℃ followed by air cooling for 15–20 seconds is to promote rapid ferrite formation, inhibiting grain growth while ensuring ferrite content, thus refining the ferrite grains. Rapid cooling to 488–520℃ aims to promote rapid bainite formation, inhibiting grain growth while ensuring bainite content, thus refining the bainite grains. The final microstructure of the rolled steel plate has a ferrite volume percentage of 20%–35%, a bainite volume percentage of 65%–80%, and a retained austenite volume percentage of 0%–3%.

[0026] (3) The pickling process includes: continuously cleaning the iron oxide scale of the steel plate with hydrochloric acid; uncoiling the hot-rolled coil for pickling on the pickling line; leveling the steel plate before pickling, with a leveling elongation of 0.7% to 1.2%; using hydrochloric acid as the pickling solution; and dividing the pickling tank into four tanks: tank 1 has a concentration of 45 to 65 g / L and a pickling solution temperature of 78.0 to 88.0℃; tank 2 has a concentration of 75 to 105 g / L and a pickling solution temperature of 70.0 to 78.0℃; and tank 3 has a concentration of 125 to 145 g / L and a pickling solution temperature of 65.0℃. The pickling temperature in tank 4 is 55.0-65.0℃, with a concentration of 155-170 g / L. During pickling, a corrosion inhibitor is added to the acid solution, accounting for 0.09%-0.14% of the total weight. The rinsing water temperature is 50-60℃, and the pickling and rinsing speeds are controlled at 80-120 m / min. The pickling process is conducted under tension, with a tension of 40-55 KN. Finally, the product is coated with oil and rolled up to obtain a finished product with a thickness of 1.50-6.00 mm and a surface roughness Ra of 1.10-1.35 μm.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. The addition of vanadium mainly enhances the strength of the steel plate by forming VN precipitation with nitrogen. It can also retain a large amount of V precipitation phase inside the steel plate structure as a hydrogen trap, reducing the risk of delayed cracking in the steel plate during use, thereby obtaining a steel plate with excellent mechanical properties and resistance to hydrogen-induced cracking.

[0029] 2. Nickel can improve the hardenability of materials, prevent temper brittleness, and improve the fatigue performance of materials. It has no adverse effect on the hardening properties and toughness of the weld heat-affected zone of steel, and improves heat resistance and cold brittleness. Furthermore, nickel can promote the formation of a dense and stable oxide film (such as NiO) on the steel surface. This film is not easily destroyed in alkaline environments and can effectively prevent contact between alkaline solutions and the steel substrate, reducing corrosion. Nickel can reduce the chemical reactivity of steel in concentrated alkalis or high-temperature alkaline solutions, especially significantly inhibiting intergranular corrosion and stress corrosion caused by strong alkalis such as sodium hydroxide, thus maintaining the stability of the steel structure.

[0030] 3. Copper plays a role in solid solution strengthening and precipitation strengthening. Simultaneously, it significantly improves the corrosion resistance of steel plates, reduces work hardening, and enhances the plasticity of the steel plates. Furthermore, in alkaline environments, copper forms a protective film containing copper oxide (CuO) or basic copper salts on the steel surface. This film has a relatively dense structure, which slows down the erosion rate of alkaline solutions on the steel substrate. Copper can reduce the electrochemical corrosion activity of steel in alkaline media, especially in medium- and low-temperature, medium-concentration alkaline environments, inhibiting uniform and localized corrosion (such as pitting corrosion) and enhancing overall corrosion resistance.

[0031] 4. Chromium is a carbide-forming element that can delay the pearlite transformation and improve the hardenability of steel. It also refines the microstructure, resulting in a strengthening effect. Furthermore, it enhances the stability of austenite, inhibiting the transformation of austenite to other phases during coiling and improving the stability of residual austenite after coiling, ensuring a certain amount of residual austenite in the final microstructure. Chromium readily forms a dense and chemically stable oxide film (Cr2O3) on the steel surface. This film is not easily dissolved or destroyed in alkaline environments, effectively preventing contact between alkaline solutions and the steel matrix, fundamentally slowing down corrosion. In high-temperature or concentrated alkaline environments, chromium can inhibit the formation of harmful compounds (such as carbides) between carbon and other elements in steel, reducing intergranular corrosion and maintaining the integrity of the steel's microstructure. Chromium can increase the electrochemical potential of steel in alkaline media, reducing the corrosion rate, especially in strongly alkaline (such as sodium hydroxide) and high-temperature alkaline environments.

[0032] 5. Platinum possesses excellent chemical stability and corrosion resistance. In steel, platinum reacts with oxygen to form a dense oxide protective film. This film isolates the steel from direct contact with corrosive media, thus slowing down the corrosion process. Furthermore, it exhibits good corrosion resistance to most alkaline solutions (including strong alkalis) at room temperature and is not prone to chemical reactions. The addition of platinum can alter the electrochemical properties of steel, potentially aiding or enhancing the formation and stability of the passivation film on the steel surface. It can reduce the electrochemical corrosion activity of steel in alkaline media, improve its corrosion resistance and oxidation resistance, and extend its service life in highly corrosive environments and at high temperatures.

[0033] 6. The addition of Y can refine the grains in steel, enhance the strength and plasticity of grain boundaries, which is beneficial to the improvement of mechanical properties. It can also improve the weldability and oxidation resistance of steel, thereby increasing the service life of steel at high temperatures.

[0034] 7. The microstructure of the steel of this invention consists of ferrite, bainite and retained austenite, which significantly improves the comprehensive mechanical properties of the steel plate during the forming process.

[0035] 8. This invention possesses excellent mechanical properties, with a yield strength of 498–552 MPa, a tensile strength of 608–643 MPa, a transverse elongation A of 33%–38%, a qualified transverse cold bending 180° D=a, and a surface roughness Ra of 1.10–1.35 μm. Using an alkaline solution of 3.7 g / L NaOH + 10.5 g / L KOH + 2 g / L Ca(OH)₂, the corrosion rate is ≤0.60 g / (m²) within a 144-hour test period. 2 ·h). Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0037] The embodiments of the invention are as follows:

[0038] The smelting raw materials undergo KR hot metal pretreatment to control the sulfur content below 0.005%. After slag removal, the material enters the converter. In the converter smelting, a double-slag method is used to remove phosphorus (P), controlling the P content to ≤0.015%. At the end of the converter smelting, the carbon content is controlled between 0.051% and 0.082%. Argon gas is blown for at least 7 minutes during tapping, followed by the LF+RH process, with strict control of H and O contents: H ≤0.0002%, O ≤0.0015%. RH vacuum degassing is maintained for at least 15 minutes. In the refining LF process, calcium treatment is carried out, followed by slab continuous casting. The superheat of continuous casting is 15-20℃, the casting speed is 1.1-1.6m / min, the electromagnetic stirring current intensity in the secondary cooling zone is controlled at 200A-300A, the secondary cooling water volume is 0.75L / kg-1.00L / kg, and light pressure is applied in the horizontal section of the secondary cooling zone, i.e., at the end of solidification, the continuous casting billet reduction is 3.0-4.0mm, and the billets are stacked for more than 36 hours after leaving the line. A continuously cast slab with a thickness of (170–235) mm and a width of (1040–2000) mm is loaded into a walking beam furnace for heating at a temperature of 1190–1250℃ for 150–180 min. The roughing process uses a 3+3 rolling pattern (R1 is rolled in 3 passes, R2 in 3 passes), for a total of 6 passes. The roughing mill exit temperature is ≥1000℃. The intermediate slab has a thickness of 37.0–55.0 mm and a width of 1040–2000 mm. The intermediate slab is kept warm before entering the hot finishing mill. The shroud is used for heat preservation to reduce the temperature drop of the intermediate billet on the delay roller table and the temperature difference between the head and tail and the width of the plate. The finishing rolling is a 7-stand continuous rolling process. High-pressure water descaling is performed before finishing rolling. The entry temperature of the finishing rolling is ≤1050℃, and the final rolling temperature is 838~888℃. After the final rolling, laminar flow cooling + air cooling + rapid cooling mode is adopted. The laminar flow cooling rate is greater than 16℃ / s. After cooling to 675~725℃, air cooling is performed. After air cooling for 15~20s, rapid cooling is performed. The rapid cooling rate is greater than 25℃ / s. After rapid cooling to 488~520℃, the plate is coiled. After hot rolling, the steel plate is uncoiled on the pickling line and pickled with hydrochloric acid. Before pickling, the steel plate is tension-straightened with an elongation of 0.7% to 1.2%. The pickling solution is hydrochloric acid, and the pickling tank is divided into 4 tanks. The concentration of pickling solution in tank 1 is 45 to 65 g / L, and the temperature of pickling solution in tank 1 is 78.0 to 88.0℃. The concentration of pickling solution in tank 2 is 75 to 105 g / L, and the temperature of pickling solution in tank 2 is 70.0 to 78.0℃. The concentration of pickling solution in tank 3 is 125 to 145 g / L, and the temperature of pickling solution in tank 3 is 65.0 to 70.0℃. The concentration of pickling solution in tank 4 is 155 to 170 g / L, and the temperature of pickling solution in tank 4 is 55.0 to 65.0℃.During pickling, a corrosion inhibitor is added to the acid solution, with the inhibitor accounting for 0.09% to 0.14% of the pickling solution by weight. The rinsing water temperature is 50 to 60°C, and the pickling and rinsing speeds are controlled at 80 to 120 m / min. The pickling process is carried out under tension, with a tension of 40 to 55 kN. Finally, the product is coated with oil and rolled up to obtain the finished product. The finished product thickness is 1.50 to 6.00 mm, the surface roughness Ra is 1.10 to 1.35 μm, the surface quality is good, and there are no iron oxide scale streaks or color difference defects.

[0039] The specific components, smelting process, hot rolling process, pickling process, steel plate properties, and volume percentage of the six embodiments of the present invention are shown in Tables 1-6.

[0040] Table 1 Chemical composition (wt, %) of embodiments of the present invention

[0041]

[0042] Table 2 Smelting process of embodiments of the present invention

[0043]

[0044] Table 3 Hot rolling process of the present invention embodiments

[0045]

[0046] Table 4. Pickling process of the present invention embodiments

[0047]

[0048] Table 5 Mechanical performance parameters of embodiments of the present invention

[0049]

[0050] Table 6. Percentage of tissue volume in embodiments of the present invention

[0051] .

Claims

1. A high-strength hot-rolled pickled steel sheet for automobile chassis, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.051%–0.072%, Si: 0.29%–0.42%, Mn: 1.55%–1.70%, Al: 0.010%–0.040%, V: 0.20%–0.30%, Ni: 0.04%–0.10%, Cu: 0%–0.05%, Cr: 0.56%–0.80%, Pt: 0.001%–0.008%, Y: 0.003%–0.010%, with P ≤ 0.015%, S ≤ 0.005%, N ≤ 0.006%, and the balance being Fe and unavoidable impurities. The production method of high-strength hot-rolled pickled steel sheet for automobile chassis includes smelting, hot rolling, and pickling processes, specifically: In the hot rolling process: the heating temperature is 1190~1250℃, the holding time is 150~180min, the roughing mill exit temperature is ≥1000℃, the intermediate billet is kept warm by an insulation cover before entering the hot rolling finishing mill, the finishing mill inlet temperature is ≤1050℃, the final rolling temperature is 838~888℃, after final rolling, laminar flow cooling + air cooling + rapid cooling mode is adopted, the laminar flow cooling rate is greater than 16℃ / s, after cooling to 675~725℃, air cooling is carried out, after air cooling for 15~20s, rapid cooling is carried out, the rapid cooling rate is greater than 25℃ / s, after rapid cooling to 488~520℃, coiling is carried out.

2. The high-strength hot-rolled pickled steel sheet for automobile chassis according to claim 1, characterized in that, The microstructure of the finished steel plate is 20%–35% ferrite, 65%–80% bainite, and 0%–3% retained austenite.

3. The high-strength hot-rolled pickled steel sheet for automobile chassis according to claim 1, characterized in that, The steel plate has a yield strength of 498–552 MPa, a tensile strength of 608–643 MPa, a transverse elongation A of 33%–38%, and a transverse cold bending of 180° with D=a is qualified.

4. The high-strength hot-rolled pickled steel sheet for automobile chassis according to claim 1, characterized in that, The finished steel plate has a thickness of 1.50–6.00 mm and a surface roughness Ra of 1.10–1.35 μm. Using an alkaline solution of 3.7 g / L NaOH + 10.5 g / L KOH + 2 g / L Ca(OH)₂, the corrosion rate of the steel plate is ≤0.60 g / (m²) over a 144-hour test period. 2 ·h).

5. A method for producing high-strength hot-rolled pickled steel sheet for automobile chassis as described in any one of claims 1-4, characterized in that, This includes smelting, hot rolling, and pickling processes, specifically: In the hot rolling process: the heating temperature is 1190~1250℃, the holding time is 150~180min, the roughing mill exit temperature is ≥1000℃, the intermediate billet is kept warm by an insulation cover before entering the hot rolling finishing mill, the finishing mill inlet temperature is ≤1050℃, the final rolling temperature is 838~888℃, after final rolling, laminar flow cooling + air cooling + rapid cooling mode is adopted, the laminar flow cooling rate is greater than 16℃ / s, after cooling to 675~725℃, air cooling is carried out, after air cooling for 15~20s, rapid cooling is carried out, the rapid cooling rate is greater than 25℃ / s, after rapid cooling to 488~520℃, coiling is carried out.

6. The method for producing high-strength hot-rolled pickled steel sheet for automobile chassis according to claim 5, characterized in that, In the smelting process: Argon gas is blown for more than 7 minutes when the converter taps out steel, and RH vacuum degassing is maintained for more than 15 minutes.

7. The method for producing high-strength hot-rolled pickled steel sheet for automobile chassis according to claim 5, characterized in that, In the smelting process: the superheat of continuous casting is 15-20℃, the continuous casting billet pulling speed is 1.1-1.6m / min, the electromagnetic stirring current intensity in the secondary cooling zone is 200-300A, the secondary cooling water volume is 0.75-1.00L / kg, light pressure is applied at the end of solidification, the reduction of the continuous casting billet is 3.0-4.0mm, and the billets are stacked for more than 36 hours after leaving the line.

8. The method for producing high-strength hot-rolled pickled steel sheet for automobile chassis according to claim 5, characterized in that, The specifications of the continuously cast billet are 170-235mm thick × 1040-2000mm wide. The thickness of the intermediate billet between the roughing and finishing rolling is 37.0-55.0mm and the width is 1040-2000mm.

9. The method for producing high-strength hot-rolled pickled steel sheet for automobile chassis according to claim 5, characterized in that, The pickling process includes: pre-pickling straightening of the steel plate with an elongation of 0.7%–1.2%; the pickling tank is divided into four tanks: tank 1 has a concentration of 45–65 g / L and a pickling solution temperature of 78.0–88.0℃; tank 2 has a concentration of 75–105 g / L and a pickling solution temperature of 70.0–78.0℃; and tank 3 has a concentration of 125–145 g / L and a pickling solution temperature of 65.0–78.0℃. The concentration in tank 4 is 155–170 g / L, and the temperature of the pickling solution in tank 4 is 55.0–65.0℃. During pickling, a corrosion inhibitor is added to the acid solution, and the corrosion inhibitor accounts for 0.09%–0.14% of the weight of the pickling solution. The rinsing water temperature is 50–60℃, and the pickling and rinsing speeds are controlled at 80–120 m / min. The pickling process is under tension, with a tension of 40–55 kN. The pickling solution is hydrochloric acid.

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