High-elongation 288mpa-grade hot-rolled pickled steel sheet for automobiles and method for producing the same

Abstract

The present application belongs to the field of metal material, and particularly relates to a high-elongation 288MPa-grade hot-rolled pickling steel plate for automobile and a production method thereof. The steel plate of the present application is mainly used for manufacturing automobile chassis structural parts. The chemical components of the steel are C, Si, Mn, Al, Ti, Zr, Ni, Pt, Y, and the content of P is limited to be less than or equal to 0.015%, the content of S is limited to be less than or equal to 0.005%, and the content of N is limited to be less than or equal to 0.003%, and the balance is Fe and inevitable impurities. The present application has excellent mechanical properties, the yield strength of the steel plate is greater than or equal to 238MPa, the tensile strength is greater than or equal to 288MPa, the transverse elongation A is greater than or equal to 48%, the hole expansion ratio is greater than or equal to 132%, 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 1.08-1.48μm, and the steel plate has good corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a 288MPa-grade hot-rolled pickled steel plate for automobiles with high elongation and a production method thereof. BACKGROUND

[0002] In recent years, with the development of the automobile industry, automobile manufacturers have increasingly high requirements for personalized steel materials. The hot-rolled pickled steel plate is an intermediate product between hot-rolled steel plates and cold-rolled steel plates in terms of surface quality and use requirements, and is an ideal substitute for part of hot-rolled steel plates and cold-rolled steel plates. At present, under the severe situation of the steel market, the hot-rolled pickled steel plate has better surface quality than the hot-rolled steel plate and, under the premise of ensuring the surface quality and use requirements, can effectively reduce the procurement cost of users, and is one of the varieties with strong profitability for steel enterprises.

[0003] Chinese patent application with publication number CN111926252A discloses a hot-rolled pickled steel plate for deep drawing purposes and a production method thereof. The hot-rolled pickled steel plate produced by adding a certain amount of Ti, Cu and B in a common C-Mn composition system has an elongation A50 of not less than 45%, which does not meet the requirements of high-forming automobile chassis structural parts and does not have certain corrosion resistance and oxidation resistance.

[0004] Chinese patent application with publication number CN115595503A discloses a hot-rolled pickled plate for high-hardness shaft nets and a preparation method thereof. The alloy components are as follows in terms of percentage by weight: 0.05-0.08% C, ≤0.05% Si, 0.2-0.4% Mn, 0.02-0.07% Als, P ≤0.025%, S ≤0.025%, N ≤0.007%, and the balance is Fe and unavoidable inclusions. The preparation method includes the process steps of hot rolling, cold rolling and pickling. The hot-rolled pickled plate has a yield strength of 200-280MPa, a tensile strength of 300-360MPa, an elongation of 40-50%, and a hardness value HRB of 100-125. It is a cold-rolled steel plate without a hole expansion rate index. It does not meet the requirements of high-forming automobile chassis structural parts and does not have certain corrosion resistance and oxidation resistance. SUMMARY

[0005] Aiming at the development demand of the field of automobile steel, the application discloses a high-elongation 288MPa-grade hot-rolled pickling steel plate for automobiles and a production method thereof, the yield strength of the steel plate is greater than or equal to 238MPa, the tensile strength is greater than or equal to 288MPa, the transverse elongation A is greater than or equal to 48%, the hole expansion ratio is greater than or equal to 132%, the transverse cold bending 180 D=a is qualified, and the surface roughness Ra is 1.08-1.48 microns. In a 168h test period, the corrosion rate of the steel plate is less than or equal to 0.45g / (m 2 ·h).

[0006] In order to achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0007] A high-elongation 288MPa-grade hot-rolled pickling steel plate for automobiles, the chemical components in the steel are as follows in percentage by weight: C: 0.005%-0.010%, Si: 0.20%-0.55%, Mn: 0.50%-1.08%, Al: 0.022%-0.040%, Ti: 0.010%-0.038%, Zr: 0.007%-0.012%, Ni: 0.012%-0.022%, Pt: 0.002%-0.007%, Y: 0.004%-0.009%, and the content of P is less than or equal to 0.015%, the content of S is less than or equal to 0.005%, the content of N is less than or equal to 0.003%, and the balance is Fe and inevitable impurities.

[0008] The finished steel plate has the following organization: the volume percentage of ferrite is 90%-97%, the volume percentage of bainite is 1%-9%, and the volume percentage of pearlite is 0%-9%. The yield strength of the steel plate is greater than or equal to 238MPa, the tensile strength is greater than or equal to 288MPa, the transverse elongation A is greater than or equal to 48%, the hole expansion ratio is greater than or equal to 132%, and the transverse cold bending 180 D=a is qualified. The thickness of the finished steel plate is 1.50-6.00mm, the surface roughness Ra is 1.08-1.48 microns, and in a 168h test period, the corrosion rate of the steel plate is less than or equal to 0.45g / (m 2 ·h).

[0009] The main functions of the components of the high-elongation 288MPa-grade hot-rolled pickling steel plate for automobiles are as follows:

[0010] C: Carbon is a common strengthening element in steel, and the interstitial solid solution atom carbon causes a certain lattice distortion in the matrix, which plays a role in solid solution strengthening. The role of carbon in the present application can ensure the content of bainite, thereby improving the forming performance and hole expansion performance of the steel plate. If the content of carbon is too low, the mechanical properties of the steel plate in the present application cannot be obtained, and if the content is too high, the steel plate will be embrittled, there is a risk of delayed fracture and hot rolling edge cracking, and it is also not good for the welding performance, plasticity and toughness of the steel plate. In the present application, the overall carbon content is required to be in the low carbon range, which is beneficial to reduce the risk of delayed fracture and hot rolling edge cracking, and is also beneficial to the welding performance of the steel plate, therefore the optimal range of carbon in the present application is 0.005% to 0.010%.

[0011] Si: Silicon is one of the important elements in the present application, and sufficient silicon addition can ensure the strength of the ferrite matrix, and the role of silicon addition is also to reduce inclusions in the steel and inhibit the formation of inclusions, thereby avoiding the reduction of the mechanical properties and hole expansion performance of the steel plate due to the formation of inclusions. However, if the content of silicon is too low, it cannot guarantee the strength of the ferrite matrix and inhibit the formation of inclusions, and if the content is too high, it will affect the hot rolling surface quality and welding performance. Therefore, the content of silicon in the present application is 0.20% to 0.55%.

[0012] Mn: Manganese strengthens the solid solution in the form of lattice distortion caused by substitutional solid solution in steel, and is also an austenite stabilizing element in steel, which expands the austenite region, reduces the critical quenching speed of the steel, and delays the transformation of austenite to pearlite. However, if the content of manganese is too low, the supercooled austenite is unstable, which reduces the plasticity, toughness and hole expansion performance of the steel plate, and the content of manganese element should not exceed the range of the present application, mainly considering the problem of C or Mn segregation caused by too high content of manganese, which worsens the uniformity of the steel plate structure during hot rolling, and easily causes serious banding defects in the structure. In addition, too high content of manganese in the steel of the present application increases the hardenability and inhibits the formation of bainite, which is also not good for the hole expansion performance, and too high content of manganese will also cause the welding performance of the steel plate to deteriorate. Therefore, considering the above factors comprehensively, the content of manganese in the present application is selected to be 0.50% to 1.08%.

[0013] P: Phosphorus is an impurity element in steel, which is easily segregated at grain boundaries. When the content of phosphorus in steel is high, Fe2P particles are easily formed, which reduces the plasticity, toughness and hole expansion performance of the steel. Therefore, the lower the content of phosphorus, the better. In order to obtain high elongation, the content of phosphorus is limited to 0.015%.

[0014] S: Sulfur is an impurity element in steel, which easily combines with Mn to form MnS inclusions, becomes the starting point of cracks and deteriorates the processing performance, seriously affecting the plasticity, formability and hole expansion performance of the steel plate. Therefore, the lower the content of sulfur, the better, and the content of sulfur is limited to 0.005%.

[0015] Al: Al is a deoxidizer in the steelmaking process in the traditional process, Al can also combine with N in the steel to form AlN and refine the grain, while together with Si to inhibit the precipitation of cementite, increase the austenitizing temperature, facilitate better selection of process window, accelerate the bainite transformation. Too high Al content will cause the nozzle to be blocked during continuous casting, affecting production efficiency, increasing production cost, therefore, the Al content in the application is limited to 0.022%~0.040%.

[0016] Ti: Titanium can effectively delay the recrystallization of deformed austenite, prevent austenite grain growth, increase austenite recrystallization temperature, refine the grain, and improve the strength and toughness of the steel. Since the free N atoms in the steel exist in the steel plate, the toughness of the steel plate is deteriorated, Ti combines with impurity element N in the steel to form TiN, so the formation of TiN has the effect of fixing N; In addition, Ti still forms Ti(C,N) with C and N, which plays a role in fine grain strengthening and precipitation strengthening. It can also strengthen ferrite and bainite, but too much Ti content will lead to too large TiN size, which will deteriorate the performance of the steel plate and make the toughness of the weld heat affected zone worse. In order to obtain excellent mechanical properties and hole expansion performance, therefore, the optimal range of Ti content in the application is between 0.010% and 0.038%.

[0017] Zr: Zirconium is a strong deoxidizer, which can generate stable ZrO2 with oxygen, effectively reduce the oxygen content in the steel, reduce oxide inclusions, and improve the purity of the steel. It can also generate ZrS with sulfur to reduce the sulfur content in the steel. When the steel solidifies, it can act as a heterogeneous core to promote grain nucleation and inhibit grain growth, refine the as-cast grain, and form stable carbides during hot rolling to hinder austenite grain growth, obtain fine and uniform grain structure, and improve the strength, toughness, plasticity and hole expansion performance of the steel. Therefore, the Zr content in the application is limited to 0.007%~0.012%.

[0018] Ni: Nickel element is a solid solution strengthening element, which can improve the hardenability of the material, prevent temper brittleness, improve the fatigue performance of the material, and has no adverse effect on the hardening and toughness of the steel weld heat affected zone, and improve the heat resistance and cold brittleness. However, too high Ni will increase the manufacturing cost, and nickel can promote the formation of a dense and stable oxide film (such as NiO) on the surface of the steel. This film is not easy to be damaged in an alkaline environment, and can effectively block the contact between the alkali and the steel matrix, reducing corrosion. Nickel can reduce the chemical reaction activity of the steel in concentrated alkali or high temperature alkali, especially has a significant inhibitory effect on intergranular corrosion and stress corrosion caused by strong alkalis such as sodium hydroxide, and maintains the stability of the steel structure. Therefore, the Ni content is limited to 0.012%~0.022%.

[0019] Pt: Platinum itself is a metal with extremely strong chemical inertness, has excellent chemical stability and corrosion resistance, platinum in steel can react with oxygen to form a dense oxide protective film, this protective film can isolate the steel and the corrosion medium direct contact, so as to slow down the corrosion process, and at room temperature to most lye (including strong base) show good corrosion resistance, not easy to chemical reaction. The addition of platinum can change the electrochemical properties of steel, may assist or strengthen the formation and stability of the passive film on the surface of steel, can reduce the electrochemical corrosion activity of steel in alkaline medium, improve the corrosion resistance and oxidation resistance of steel, improve the service life of steel in strong corrosion environment and high temperature, therefore, the content of Pt is limited to 0.002%~0.007% in the application.

[0020] Y: Y can refine the grain in steel, enhance the strength and plasticity of grain boundary, is beneficial to the improvement of hole expansion performance, can also improve the welding performance and oxidation resistance of steel, thereby improving the service life of steel at high temperature, therefore, the content of Y is limited to 0.004%~0.009% in the application.

[0021] N: for the content of N in steel, the lower the content of N is, the better, but too low will lead to production difficulty, increase cost, therefore, the content of N is ≤0.003% in the application.

[0022] A production method of a high-elongation 288MPa-grade hot-rolled pickled steel plate for automobile, comprising smelting, continuous casting, hot rolling and pickling processes, and the specific contents include:

[0023] (1)Smelting process: raw materials are pretreated by KR hot metal, S content is controlled below 0.005%, after slagging, they are put into converter, double slag method is used to remove P in converter smelting, P content is controlled below 0.015%, C content is controlled at 0.005-0.010% at converter smelting end point, argon is blown for more than 5 minutes when tapping (blowing argon to calm before continuous casting can promote the removal of inclusions in molten steel, improve the uniformity of molten steel composition), then LF+RH process is carried out, H and O content is strictly controlled, H≤0.0002%, O≤0.0015%, RH vacuum degassing is kept for more than 18 minutes, calcium treatment is carried out in refining LF process, then slab continuous casting is carried out, overheat degree is 16-21℃, continuous casting withdrawal rate is 0.9-1.4 m / min (reducing overheat degree and continuous casting withdrawal rate can improve macro-segregation of continuous casting billet, reduce secondary dendrite arm spacing in solidification structure of continuous casting billet, which is helpful to reduce segregation of steel billet and internal structure defects), current intensity of electromagnetic stirring in two cooling zone is controlled at 300-400 A, secondary cooling water quantity is 0.80 L / kg-1.10 L / kg (reducing average index of carbon segregation, inhibiting segregation, at the same time, secondary cooling intensity is limited, which inhibits the trend of center crack deterioration of cast billet), light press is put into in horizontal section of two cooling zone, i.e. solidification end, press down quantity of continuous casting billet is 3.0-5.0 mm (reducing center porosity level and segregation of cast billet), after offline, billet is stacked for more than 36 hours (reducing aggregation of residual H, inhibiting the generation of internal micro-cracks of steel billet, ensuring the toughness of steel plate).

[0024] (2) in the hot rolling process: the (150-230) mm thick x (1040-2000) mm wide continuous casting slab is loaded into the walking beam furnace for heating, the heating temperature is 1150-1220℃, the holding time is 120-160 min, the rough rolling adopts a rolling process of 3+3 mode, (R1 adopts 3 passes of rolling, R2 adopts 3 passes of rolling) a total of 6 passes of rolling, the rough rolling outlet temperature is greater than or equal to 980℃, the intermediate blank thickness is 40.0-54.0 mm, the width is 1040-2000 mm, the intermediate blank is heated before entering the hot rolling finishing mill group by using a heat preservation cover to reduce the temperature drop of the intermediate blank on the delay roller way and the temperature difference of the head and tail and the plate width direction, the finishing rolling is 7-stand continuous rolling, high-pressure water descaling is carried out before the finishing rolling, the finishing rolling inlet temperature is less than or equal to 1030℃, the final rolling temperature is 838-925℃, after the final rolling, laminar flow cooling + air cooling + rapid cooling mode is adopted, the laminar flow cooling rate is greater than 18℃ / s, after cooling to 625-650℃, air cooling is carried out, after air cooling for 10-15s, rapid cooling is carried out, the rapid cooling rate is greater than 27℃ / s, after rapid cooling to 505-518℃, coiling is carried out. After laminar flow cooling to 625-650℃, air cooling is carried out for 10-15s, the purpose is to make ferrite generate rapidly, while inhibiting grain growth, and the content of ferrite is ensured, so that the ferrite grain is refined, and the purpose of rapid cooling to 505-518℃ is to make bainite generate rapidly, while inhibiting grain growth, and the content of bainite is ensured, so that the bainite grain is refined. The final organization of the rolled steel plate is that the volume percentage of ferrite is 90%-97%, the volume percentage of bainite is 1%-9%, and the volume percentage of pearlite is 0%-9%.

[0025] (3) the pickling process comprises: using hydrochloric acid to continuously clean the steel plate scale, the hot-rolled coiled steel plate is uncoiled and pickled in the pickling line, the steel plate is tensioned before pickling, the tensioning elongation is 0.5-1.0%, the pickling solution is hydrochloric acid, the pickling tank is divided into three tanks, the concentration of the No.1 tank is 70-115g / L, the temperature of the No.1 tank is 72.0-79.0℃, the concentration of the No.2 tank is 116-146g / L, the temperature of the No.2 tank is 68.0-72.0℃, the concentration of the No.3 tank is 146-164g / L, the temperature of the No.3 tank is 60.0-68.0℃, during pickling, the corrosion inhibitor accounts for 0.08-0.13% of the weight percentage of the pickling solution; the rinsing water temperature is 50-60℃, the pickling and rinsing speed is controlled at 100-140m / min; during pickling, it is tension pickling, the tension is 30-45KN, finally, oiling and coiling are carried out to obtain the finished product, the thickness of the finished product is 1.50-6.00mm, and the surface roughness Ra is 1.08-1.48μm.

[0026] Compared with the prior art, the beneficial effects of the present application are:

[0027] 1. Zirconium is a strong deoxidizer that can react with oxygen to form stable ZrO2, effectively reducing the oxygen content in steel, reducing oxide inclusions, and improving the purity of steel. It can also react with sulfur to form ZrS, reducing the sulfur content in steel. During steel solidification, it can act as a heterogeneous nucleus, promoting grain nucleation, inhibiting grain growth, and refining cast grains. Furthermore, during hot rolling, it forms stable carbides, hindering austenite grain growth, obtaining a fine and uniform grain structure, and improving the strength, toughness, plasticity, and porosity of steel.

[0028] 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.

[0029] 3. 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, assisting 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.

[0030] 4. The addition of Y can refine the grains in steel, enhance the strength and plasticity of grain boundaries, improve the hole expansion performance, and also improve the weldability and oxidation resistance of steel, thereby increasing the service life of steel at high temperatures.

[0031] 5. The microstructure of the steel of this invention consists of ferrite, bainite and pearlite, which significantly improves the hole expansion performance of the steel plate during the forming process.

[0032] 6. This invention possesses excellent mechanical properties: yield strength ≥ 238 MPa, tensile strength ≥ 288 MPa, transverse elongation A ≥ 48%, hole expansion rate ≥ 132%, transverse cold bending at 180° D=a is qualified, and surface roughness Ra is 1.08~1.48 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 ≤ 0.45 g / (m²) within a 168-hour test period. 2 ·h). Detailed Implementation

[0033] 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.

[0034] The embodiments of the invention are as follows:

[0035] 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. During converter smelting, a double-slag method is used to remove phosphorus (P), controlling the P content to ≤0.015%. At the end of converter smelting, the carbon content is controlled between 0.005% and 0.010%. Argon gas is blown for at least 5 minutes during tapping, followed by the LF+RH process. The H and O contents are strictly controlled: H ≤0.0002%, O ≤0.0015%. RH vacuum degassing is maintained for at least 18 minutes. In the refining LF process, calcium treatment is carried out, followed by slab continuous casting. The superheat of continuous casting is 16-21℃, the casting speed is 0.9-1.4m / min, the electromagnetic stirring current intensity in the secondary cooling zone is controlled at 300A-400A, the secondary cooling water volume is 0.80L / kg-1.10L / kg, and light pressure is applied in the horizontal section of the secondary cooling zone, i.e., at the end of solidification, the reduction of the continuous casting slab is 3.0-5.0mm, and the slabs are stacked for more than 36 hours after leaving the line. A continuously cast slab with a thickness of (150–230) mm and a width of (1040–2000) mm is loaded into a walking beam furnace for heating at a temperature of 1150–1220℃ for 120–160 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 ≥980℃. The intermediate slab has a thickness of 40.0–54.0 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 ≤1030℃, and the final rolling temperature is 838~925℃. After the final rolling, laminar flow cooling + air cooling + rapid cooling mode is adopted. The laminar flow cooling rate is greater than 18℃ / s. After cooling to 625~650℃, air cooling is performed. After air cooling for 10~15s, rapid cooling is performed. The rapid cooling rate is greater than 27℃ / s. After rapid cooling to 505~518℃, the plate is coiled.After hot rolling, the steel sheet is uncoiled on the pickling line and pickled with hydrochloric acid. Before pickling, the steel sheet is tension-straightened with an elongation of 0.5%–1.0%. The pickling solution is hydrochloric acid, and the pickling tanks are divided into three tanks: Tank 1 has a concentration of 70–115 g / L and a pickling solution temperature of 72.0–79.0℃; Tank 2 has a concentration of 116–146 g / L and a pickling solution temperature of 68.0–72.0℃; and Tank 3 has a concentration of 146–164 g / L and a pickling solution temperature of 60.0–68.0℃. During pickling, a corrosion inhibitor is added to the acid solution, with the inhibitor accounting for 0.08% to 0.13% of the pickling solution by weight. The rinsing water temperature is 50 to 60°C, and the pickling and rinsing speeds are controlled at 100 to 140 m / min. The pickling process is carried out under tension, with a tension of 30 to 45 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 1.08 to 1.48 μm, the surface quality is good, and there are no iron oxide scale streaks or color difference defects.

[0036] 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.

[0037] Table 1 Chemical composition (wt, %) of embodiments of the present invention

[0038]

[0039] Table 2 Smelting process of embodiments of the present invention

[0040]

[0041] Table 3 Hot rolling process of the present invention embodiments

[0042]

[0043] Table 4. Pickling process of the present invention embodiments

[0044]

[0045] Table 5 Mechanical performance parameters of embodiments of the present invention

[0046]

[0047] Table 6. Percentage of tissue volume in embodiments of the present invention

[0048]

Claims

1. A high-elongation 288MPa grade hot-rolled pickled steel sheet for automotive applications, characterized in that, The chemical composition of the steel, by weight percentage, is as follows: C: 0.005%–0.010%, Si: 0.20%–0.55%, Mn: 0.50%–1.08%, Al: 0.022%–0.040%, Ti: 0.010%–0.038%, Zr: 0.007%–0.012%, Ni: 0.012%–0.022%, Pt: 0.002%–0.005%, Y: 0.004%–0.009%, with P ≤ 0.015%, S ≤ 0.005%, N ≤ 0.003%, and the balance being Fe and unavoidable impurities. The production method of high-elongation 288MPa grade hot-rolled pickled steel sheet for automotive applications includes smelting, continuous casting, hot rolling, and pickling processes, specifically including: In the hot rolling process: the heating temperature is 1150~1220℃, the holding time is 120~160min, the roughing mill exit temperature is ≥980℃, the intermediate billet is kept warm by a heat insulation cover before entering the hot rolling finishing mill, the finishing mill inlet temperature is ≤1030℃, the final rolling temperature is 838~925℃, after final rolling, laminar flow cooling + air cooling + rapid cooling mode is adopted, the laminar flow cooling rate is greater than 18℃ / s, after cooling to 625~650℃, air cooling is carried out, after air cooling for 10~15s, rapid cooling is carried out, the rapid cooling rate is greater than 27℃ / s, after rapid cooling to 505~518℃, the billet is coiled. The finished steel plate has a thickness of 1.50–6.00 mm and a surface roughness Ra of 1.08–1.48 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 ≤0.45 g / (m²) over a 168-hour test period. 2 ·h); The microstructure of the finished steel plate consists of 90%–97% ferrite, 1%–9% bainite, and 0%–9% pearlite. The steel plate has a yield strength ≥238MPa, tensile strength ≥288MPa, transverse elongation A ≥48%, hole expansion rate ≥132%, and transverse cold bending 180° D=a is qualified.

2. A method for producing high-elongation 288MPa grade hot-rolled pickled steel sheet for automobiles as described in claim 1, characterized in that, It includes smelting, continuous casting, hot rolling, and pickling processes, specifically: In the hot rolling process: the heating temperature is 1150~1220℃, the holding time is 120~160min, the roughing mill exit temperature is ≥980℃, the intermediate billet is kept warm by an insulation cover before entering the hot rolling finishing mill, the finishing mill inlet temperature is ≤1030℃, the final rolling temperature is 838~925℃, after final rolling, laminar flow cooling + air cooling + rapid cooling mode is adopted, the laminar flow cooling rate is greater than 18℃ / s, after cooling to 625~650℃, air cooling is carried out, after air cooling for 10~15s, rapid cooling is carried out, the rapid cooling rate is greater than 27℃ / s, after rapid cooling to 505~518℃, coiling is carried out.

3. The method for producing high-elongation 288MPa grade hot-rolled pickled steel sheet for automobiles according to claim 2, characterized in that, In the smelting process: Argon gas is blown for more than 5 minutes when the converter taps out steel, and RH vacuum degassing is maintained for more than 18 minutes.

4. The method for producing high-elongation 288MPa grade hot-rolled pickled steel sheet for automobiles according to claim 2, characterized in that, In the continuous casting process: the superheat of continuous casting is 16-21℃, the continuous casting billet pulling speed is 0.9-1.4m / min, the electromagnetic stirring current intensity in the secondary cooling zone of the continuous casting stage is controlled at 300-400A, the secondary cooling water volume is 0.80-1.10L / kg, light pressure is applied at the end of solidification, the reduction of the continuous casting billet is 3.0-5.0mm, and the billets are stacked for more than 36 hours after leaving the line.

5. The method for producing high-elongation 288MPa grade hot-rolled pickled steel sheet for automobiles according to claim 2, characterized in that, The specifications of the continuously cast billet are 150-230mm thick and 1040-2000mm wide. The thickness of the intermediate billet between the roughing and finishing rolling is 40.0-54.0mm and the width is 1040-2000mm.

6. The method for producing high-elongation 288MPa grade hot-rolled pickled steel sheet for automobiles according to claim 2, characterized in that, The pickling process includes: pre-pickling straightening of the steel plate with an elongation rate of 0.5%–1.0%; three pickling tanks: tank 1 has a concentration of 70–115 g / L and a pickling solution temperature of 72.0–79.0℃; tank 2 has a concentration of 116–146 g / L and a pickling solution temperature of 68.0–72.0℃; tank 3 has a concentration of 146–164 g / L and a pickling solution temperature of 60.0–68.0℃; during pickling, a corrosion inhibitor is added to the acid solution, with the inhibitor accounting for 0.08–0.13% of the pickling solution by weight; the rinsing water temperature is 50–60℃; and the pickling and rinsing speeds are controlled at 100–140 m / min. The pickling process is tension pickling with a tension of 30–45 kN; the pickling solution is hydrochloric acid.

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