A 448mpa grade hot-rolled pickled steel sheet for automobiles and a method for producing the same

Abstract

The present application belongs to the field of metal materials, and particularly relates to a 448MPa-grade hot-rolled pickling steel plate for automobiles and a production method thereof. The steel plate of the present application is mainly suitable for manufacturing automobile chassis structural parts. The chemical components in the steel are designed as C, Si, Mn, Al, Nb, Ta, Zr, 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%, and N is limited to be less than or equal to 0.003%, and the balance is Fe and inevitable impurities. The yield strength of the steel plate of the present application is greater than or equal to 308MPa, the tensile strength is greater than or equal to 448MPa, the transverse elongation A is greater than or equal to 42%, the hole expansion ratio is greater than or equal to 125%, 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 1.00-1.40μm, 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 448MPa-grade hot-rolled pickled steel plate for automobiles 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, effectively reduces the procurement cost of users, and is one of the varieties with strong profitability for steel enterprises.

[0003] Chinese patent application with publication number CN108441759A discloses a 540MPa-grade hot-rolled pickled steel plate and a manufacturing method thereof. The hot-rolled pickled steel plate produced by adding a certain amount of Nb and / or Cr in the ordinary C-Mn component system has a longitudinal elongation A of not less than 26%, 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 CN109487153A discloses a 440MPa-grade high-expansion hot-rolled pickled steel plate. The hot-rolled pickled steel plate produced by using the ordinary C-Mn component system has a 50mm elongation A of not less than 30%, which does not meet the requirements of high-forming automobile chassis structural parts and does not have certain corrosion resistance and oxidation resistance. SUMMARY

[0005] In view of the development needs in the field of automobile steel, the present application provides a 448MPa-grade hot-rolled pickled steel plate for automobiles and a production method thereof. The yield strength is not less than 308MPa, the tensile strength is not less than 448MPa, the transverse elongation A is not less than 42%, the expansion rate is not less than 125%, the transverse cold bending 180° D=a is qualified, and the surface roughness Ra is 1.00-1.40μm. In a 168h test period, the corrosion rate of the steel plate is not more than 0.62g / (m 2 ·h) in the alkali solution with a concentration of 3.7g / L of NaOH, 10.5g / L of KOH and 2g / L of Ca(OH)2.

[0006] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0007] The application discloses a 448MPa-grade hot-rolled pickling steel plate for automobiles, and chemical components in the steel are as follows in percentage by weight: C: 0.042%-0.072%, Si: 0.010%-0.070%, Mn: 1.25%-1.53%, Al: 0.030%-0.050%, Nb: 0.007%-0.020%, Ta: 0.007%-0.012%, Zr: 0.010%-0.015%, Y: 0.003%-0.010%, 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 rest is Fe and inevitable impurities.

[0008] The finished steel plate has a ferrite volume percentage of 50%-60%, a bainite volume percentage of 25%-35% and a pearlite volume percentage of 5%-15%. The yield strength of the steel plate is greater than or equal to 308MPa, the tensile strength is greater than or equal to 448MPa, the transverse elongation A is greater than or equal to 42%, the hole expansion ratio is greater than or equal to 125%, and the transverse cold bending 180 D=a is qualified (a represents the nominal thickness of the sample). The finished steel plate has a thickness of 1.50-6.00mm, a surface roughness Ra of 1.00-1.40um, and a corrosion rate of the steel plate of less than or equal to 0.62g / (m 2 ·h) in a 168h test cycle in an alkaline solution with a concentration of 3.7g / L of NaOH+10.5g / L of KOH+2g / L of Ca(OH)2.

[0009] The main functions of the components of the 448MPa-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 certain lattice distortion in the matrix, thereby playing a solid solution strengthening role. The role of carbon in the 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 application cannot be obtained, if the content of carbon is too high, the steel plate will be embrittled, there will be a risk of delayed fracture and hot rolling edge cracking, and the welding performance, plasticity and toughness of the steel plate are also adversely affected. In the application, the overall content of carbon is required to be in the low carbon range, which is beneficial to reducing 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 application is 0.042%-0.072%.

[0011] Si: Silicon is one of the important elements of the present application, and sufficient silicon addition can ensure the strength of ferrite matrix, and the silicon addition can also reduce the inclusions in the steel, inhibit the formation of inclusions, and avoid the reduction of the mechanical properties and the hole expansion performance of the steel plate due to the formation of inclusions. However, if the silicon content is too low, it cannot guarantee the strength of the ferrite matrix and inhibit the formation of inclusions, and if the silicon content is too high, it will affect the surface quality of hot rolling and a large amount of iron oxide scale will appear. Therefore, the content of silicon in the present application is 0.010% to 0.070%.

[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 manganese content is too low, the supercooled austenite is unstable, which reduces the plasticity, toughness and hole expansion performance of the steel plate, and the manganese content should not exceed the range of the present application. The main consideration is that too high manganese content leads to C or Mn segregation, which deteriorates the uniformity of the steel plate structure during hot rolling, and easily causes serious banding defects in the structure. In addition, too high manganese content in the steel of the present application leads to increased hardenability and inhibited formation of bainite, which is also not conducive to the hole expansion performance. Moreover, too high manganese content will lead to poor welding performance of the steel plate. Therefore, the present application comprehensively considers and selects the manganese content to be 1.25% to 1.53%.

[0013] P: Phosphorus is an impurity element in steel, which is easily segregated at grain boundaries. When the phosphorus content 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, the better. In order to obtain higher elongation, the content 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 affects the plasticity, formability and hole expansion performance of the steel plate. Therefore, the lower the content, the better, and the content is limited to 0.005%.

[0015] Al: Al is a deoxidizer in the traditional steelmaking process. Al can also combine with N in steel to form AlN and refine the grains, and together with Si, it can inhibit the precipitation of cementite, increase the austenitizing temperature, facilitate better selection of process window and accelerate the bainite transformation. Too high Al content will cause nozzle blockage during continuous casting, affecting production efficiency and increasing production cost. Therefore, the Al content in the present application is limited to 0.030% to 0.050%.

[0016] Nb: niobium can effectively delay the recrystallization of deformed austenite, prevent austenite grain growth, improve austenite recrystallization temperature, refine grains, and improve the strength and toughness of the steel. Since the free N atoms in the steel deteriorate the toughness of the steel plate, Nb combines with the impurity element N in the steel to form NbN, so the formation of NbN has the effect of fixing N. In addition, Nb still forms Nb(C, N) with C and N, which has the effects of fine-grain strengthening and precipitation strengthening. It can also strengthen ferrite and bainite, but too much Nb content will lead to excessive size of NbN, 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, the optimal range of Nb content in the present application is between 0.007% and 0.020%.

[0017] Ta: tantalum has strong affinity with carbon, nitrogen and other elements in steel, and can form fine and dispersed carbides, nitrides or carbonitrides, which hinder grain growth and refine the grain of the steel, thereby improving the comprehensive mechanical properties and hole expansion rate of the steel. In addition, tantalum itself has high stability in strong alkali environment at room temperature to high temperature (such as sodium hydroxide solution), and is not easy to react with alkali. It can directly resist the corrosion of alkali. And tantalum is easy to form a dense and chemically stable oxide film (Ta2O5) on the surface of the steel, which is difficult to be dissolved in alkaline medium and can effectively block the contact between the alkali and the matrix, protecting the steel from corrosion. Therefore, the optimal range of Ta content in the present application is between 0.007% and 0.012%.

[0018] 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. During steel solidification, it can act as a heterogeneous core to promote grain nucleation and inhibit grain growth, refining the as-cast grain. In the hot rolling process, stable carbides are formed to hinder the growth of austenite grains, obtaining fine and uniform grain structure, improving the strength, toughness, plasticity and hole expansion performance of the steel. Therefore, the Zr content in the present application is limited to 0.010% to 0.015%.

[0019] Y: yttrium can refine the grains in the steel, enhance the strength and plasticity of the grain boundary, and improve the hole expansion performance, welding performance and oxidation resistance of the steel, thereby improving the service life of the steel at high temperature. Therefore, the Y content in the present application is limited to 0.003% to 0.010%.

[0020] N: the lower the N content in the steel, the better, but too low will lead to production difficulties and increase the cost. Therefore, the N content in the present application is ≤0.003%.

[0021] A production method of a 448MPa grade hot-rolled pickled steel plate for automobile, comprising smelting, continuous casting, hot rolling, pickling processes, the specific content comprising:

[0022] (1) smelting process: the raw material is pretreated by KR molten iron, the content of S is controlled below 0.005%, after slagging, it enters the converter, double slag method is used to remove P in the converter smelting, the content of P is controlled ≤0.015%, the content of C is controlled at 0.045%-0.072% at the end of converter smelting, argon is blown for more than 11min when tapping (the argon blowing and settling before continuous casting can promote the removal of inclusions in molten steel and improve the composition uniformity of molten steel), then LF+RH process is carried out, the contents of H and O are strictly controlled, H≤0.0002%, O≤0.0015%, RH vacuum degassing is kept for more than 22min, calcium treatment is carried out in the refining LF process, then slab continuous casting is carried out, the superheat is 15-20℃, the casting speed is 0.8-1.3m / min (reducing the superheat and the casting speed can improve the macrosegregation of continuous casting slab, reduce the secondary dendrite arm spacing in the solidification structure of the slab, which is helpful to reduce the segregation of the slab and the internal structure defects), the current intensity of electromagnetic stirring in the secondary cooling zone is controlled at 300-400A, the secondary cooling water quantity is 0.85-1.15L / kg (reducing the average index of carbon segregation, suppressing segregation, at the same time, the secondary cooling intensity is limited, which suppresses the trend of center crack deterioration of the casting slab), the light press-down is put into the horizontal section of the secondary cooling zone, i.e. the solidification end, the press-down amount of the continuous casting slab is 3.2-4.6mm (reducing the center porosity level and segregation of the slab), the slab is stacked for more than 36 hours after being discharged (reducing the aggregation of residual H, suppressing the generation of internal micro-cracks of the slab, and ensuring the toughness of the steel plate).

[0023] (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 128-158 min, the rough rolling adopts the 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 38.0-57.0 mm, the width is 1040-2000 mm, the intermediate blank is heated before entering the hot rolling finishing mill group by using the 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, the 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 845-915℃, the laminar flow cooling + air cooling + rapid cooling mode is adopted after the final rolling, the laminar flow cooling rate is greater than 15℃ / s, after being cooled to 645-670℃, air cooling is carried out, after air cooling for 10-15 s, rapid cooling is carried out, the rapid cooling rate is greater than 22℃ / s, after being cooled to 525-545℃ by rapid cooling, coiling is carried out. After laminar flow cooling to 645-670℃, air cooling is carried out for 10-15 s, the purpose is to make the ferrite generate rapidly, while inhibiting the grain growth, and the content of the ferrite is ensured, so that the ferrite grain is refined, the purpose of rapid cooling to 525-545℃ is to make the bainite generate rapidly in a large amount, while inhibiting the grain growth, and the content of the 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 50%-60%, the volume percentage of bainite is 25%-35%, and the volume percentage of pearlite is 5%-15%.

[0024] (3) the pickling process comprises: using hydrochloric acid to continuously clean the steel plate scale, the hot rolled coiling is opened in the pickling line for pickling, the steel plate is tensioned before pickling, the tensioning elongation is 0.6%-2.0%, the pickling liquid is hydrochloric acid, the pickling tank is divided into three tanks, the concentration of the No.1 tank is 75-125 g / L, the pickling liquid temperature of the No.1 tank is 82.0-88.0℃, the concentration of the No.2 tank is 125-155 g / L, the pickling liquid temperature of the No.2 tank is 77.0-82.0℃, the concentration of the No.3 tank is 155-175 g / L, the pickling liquid temperature of the No.3 tank is 70.0-77.0℃, the corrosion inhibitor is added in the acid solution during pickling, the weight percentage of the corrosion inhibitor in the pickling solution is 0.08%-0.13%; the rinsing water temperature is 50-60℃, the pickling and rinsing speed is controlled at 80-120 m / min; the tension pickling is carried out in the pickling process, the tension is 30-60 KN, finally the oiling and coiling are carried out to obtain the finished product, the finished product thickness is 1.50-6.00 mm, and the surface roughness Ra is 1.00-1.40 μm.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] 1. Tantalum has strong affinity with carbon, nitrogen and other elements in steel, and can form fine and dispersed carbides, nitrides or carbonitrides, which hinder grain growth, refine the grain of the steel, and thus improve the comprehensive mechanical properties and hole expansion rate of the steel, such as strength, toughness, plasticity, etc. In addition, tantalum itself has very high stability in strong alkali environment at room temperature to high temperature (such as sodium hydroxide solution), is not easy to chemically react with alkali, and can directly resist the corrosion of alkali. And tantalum can easily form a dense and chemically stable oxide film (Ta2O5) on the surface of the steel, which is difficult to be dissolved in alkaline medium and can effectively block the contact between the alkali and the matrix, protecting the steel from corrosion.

[0027] 2. 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. Zirconium can also generate ZrS with sulfur to reduce the sulfur content in the steel. During the solidification of the steel, zirconium can act as a heterogeneous core to promote grain nucleation and inhibit grain growth, thereby refining the as-cast grain. In the process of hot rolling, zirconium can form stable carbides to hinder the growth of austenite grains, resulting in fine and uniform grain structure, and improving the strength, toughness, plasticity and hole expansion performance of the steel.

[0028] 3. The addition of Y can refine the grain of the steel, enhance the strength and plasticity of the grain boundary, and improve the hole expansion performance, welding performance and oxidation resistance of the steel, thereby improving the service life of the steel at high temperature.

[0029] 4. The microstructure of the steel in the present application is ferrite, bainite and pearlite, which can significantly improve the hole expansion performance of the steel sheet during forming.

[0030] 5. The steel sheet of the present application has excellent mechanical properties, with yield strength ≥ 308 MPa, tensile strength ≥ 448 MPa, transverse elongation A ≥ 42%, hole expansion rate ≥ 125%, transverse cold bending 180° D=a (a represents the nominal thickness of the sample), surface roughness Ra is 1.00-1.40 μm, and in a 168 h test period, the corrosion rate of the steel sheet in an alkaline solution of NaOH with a concentration of 3.7 g / L + KOH with a concentration of 10.5 g / L + Ca(OH)2 with a concentration of 2 g / L is ≤ 0.62 g / (m 2 ·h). DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the specific embodiments of the present application will be further described below in combination with examples. The following examples are used to specifically illustrate the content of the present application, and these examples are only a general description of the content of the present application, and do not limit the content of the present application.

[0032] The inventive examples are as follows:

[0033] The smelting raw material is pretreated by KR hot metal, the content of S is controlled below 0.005%, and then enters the converter after slagging. The double slag method is used to remove P in the converter smelting, the content of P is controlled below 0.015%, the content of C is controlled at 0.045-0.072% at the end of the converter smelting, argon is blown for more than 11 minutes when tapping, then LF+RH process is carried out, the content of H and O is strictly controlled, H≤0.0002%, O≤0.0015%, RH vacuum degassing is kept for more than 22 minutes, calcium treatment is carried out in the refining LF process, then slab continuous casting is carried out, the overheat degree is 15-20℃, the continuous casting withdrawal rate is 0.8-1.3m / min, the current intensity of electromagnetic stirring in the secondary cooling zone is controlled at 300A-400A, the secondary cooling water quantity is 0.85L / kg-1.15L / kg, the light press-down is carried out in the horizontal section of the secondary cooling zone, i.e. the solidification end, the press-down amount of the continuous casting slab is 3.2-4.6mm, the slab is stacked for more than 36 hours after being discharged. The continuous casting slab with a thickness of (150-230)mm and a width of (1040-2000)mm is loaded into a walking beam heating furnace for heating, the heating temperature is 1150-1220℃, the holding time is 128-158min, the rough rolling adopts a 3+3 mode rolling process, i.e. 3 passes for R1 and 3 passes for R2, a total of 6 passes, the rough rolling exit temperature is≥980℃, the intermediate slab thickness is 38.0-57.0mm, the width is 1040-2000mm, the intermediate slab is kept in a holding cover before entering the hot rolling finishing mill train, so as to reduce the temperature drop of the intermediate slab on the delay roller way and the temperature difference of the head and tail and the 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≤1030℃, the finish rolling temperature is 845-915℃, after finish rolling, laminar flow cooling+air cooling+rapid cooling mode is adopted, the laminar flow cooling rate is greater than 15℃ / s, after cooling to 645-670℃, air cooling is carried out, after air cooling for 10-15s, rapid cooling is carried out, the rapid cooling rate is greater than 22℃ / s, after rapid cooling to 525-545℃, coiling is carried out.The hot-rolled coil is opened and pickled in hydrochloric acid in the pickling line, the steel plate is tension-straightened before pickling, the tension-straightening elongation is 0.6-2.0%, the pickling liquid is hydrochloric acid, the pickling tank is divided into three tanks, the concentration of the No.1 tank is 75-125 g / L, the temperature of the pickling liquid of the No.1 tank is 82.0-88.0 ℃, the concentration of the No.2 tank is 125-155 g / L, the temperature of the pickling liquid of the No.2 tank is 77.0-82.0 ℃, the concentration of the No.3 tank is 155-175 g / L, the temperature of the pickling liquid of the No.3 tank is 70.0-77.0 ℃, the corrosion inhibitor is added in the pickling liquid, the weight percentage of the corrosion inhibitor in the pickling solution is 0.08%-0.13%, the rinsing water temperature is 50-60 ℃, the pickling and rinsing speed is controlled at 80-120 m / min, the pickling process is tension pickling, the tension is 30-60 KN, finally, the oiling and dividing are carried out, the finished product is obtained, the thickness of the finished product is 1.50-6.00 mm, the surface roughness Ra is 1.00-1.40 μm, and the surface quality is good without iron oxide scale stripe and color difference defects.

[0034] The specific components, smelting process system, hot-rolling process system, pickling process system, performance and volume percentage of the organization of the six embodiments of the application are shown in Tables 1-6.

[0035] Table 1 Chemical components (wt, %) of the embodiments of the application

[0036]

[0037] Table 2 Smelting process of the embodiments of the application

[0038]

[0039] Table 3 Hot-rolling process system of the embodiments of the application

[0040]

[0041] Table 4 Pickling process system of the embodiments of the application

[0042]

[0043] Table 5 Mechanical property parameters of the embodiments of the application

[0044]

[0045] Table 6 Volume percentage of the organization in the embodiments of the application

[0046]

Claims

1. A hot-rolled pickled steel sheet for a 448 MPa grade automobile characterized by, The chemical composition of the steel is as follows in terms of percentage by weight: C: 0.042%-0.072%, Si: 0.010%-0.070%, Mn: 1.25%-1.53%, Al: 0.030%-0.050%, Nb: 0.007%-0.020%, Ta: 0.007%-0.012%, Zr: 0.010%-0.015%, Y: 0.003%-0.010%, and the limitation of P≤0.015%, S≤0.005%, N≤0.003%, and the balance of Fe and inevitable impurities.

2. The 448 MPa grade hot-rolled pickled steel plate for automobiles according to claim 1, characterized by, The volume percentage of ferrite of the finished steel plate is 50%-60%, the volume percentage of bainite is 25%-35%, and the volume percentage of pearlite is 5%-15%.

3. The 448 MPa grade hot-rolled and pickled steel plate for automobiles according to claim 1, characterized by, The yield strength of the steel plate is ≥308 MPa, the tensile strength is ≥448 MPa, the transverse elongation A is ≥42%, the hole expansion ratio is ≥125%, and the transverse cold bending 180° D=a is qualified.

4. The 448 MPa grade hot-rolled pickled steel plate for automobiles according to claim 1, characterized by, The finished steel plate has a thickness of 1.50-6.00 mm and a surface roughness Ra of 1.00-1.40 μm, and in a 168 h test period, the corrosion rate of the steel plate is ≤0.62 g / (m 2 ·h) in an alkaline solution of NaOH at a concentration of 3.7 g / L, KOH at a concentration of 10.5 g / L and Ca(OH)2 at a concentration of 2 g / L.

5. A method of producing a 448 MPa grade hot-rolled pickled steel sheet for automobiles as claimed in any one of claims 1 to 4, characterized in that, The process includes smelting, continuous casting, hot rolling and pickling, and the specific contents include: In the hot rolling process, the heating temperature is 1150-1220℃, the holding time is 128-158 min, the rough rolling outlet temperature is ≥980℃, the finish rolling inlet temperature is ≤1030℃, the final rolling temperature is 845-915℃, the laminar flow cooling+air cooling+rapid cooling mode is adopted after the final rolling, the laminar flow cooling rate is greater than 15℃ / s, air cooling is carried out after cooling to 645-670℃, rapid cooling is carried out after air cooling for 10-15 s, the rapid cooling rate is greater than 22℃ / s, and coiling is carried out after rapid cooling to 525-545℃.

6. The production method of a 448 MPa grade hot-rolled pickled steel sheet for automobiles according to claim 5, characterized in that, In the smelting process, argon blowing is carried out for more than 11 min when the converter is tapped, and the RH vacuum degassing is maintained for more than 22 min.

7. The method of producing a 448 MPa grade hot-rolled pickled steel sheet for automobiles according to claim 5, characterized in that, In the continuous casting process, the continuous casting superheat is 15-20℃, the continuous casting withdrawal rate is 0.8-1.3 m / min, the electromagnetic stirring current intensity in the secondary cooling zone is 300-400 A, the secondary cooling water quantity is 0.85-1.15 L / kg, the light press-down is put into the solidification end, the press-down amount of the continuous casting blank is 3.2-4.6 mm, and the blank is stacked for more than 36 hours after being discharged.

8. The production method of a 448 MPa grade hot-rolled pickled steel sheet for automobiles according to claim 5, characterized in that, The continuous casting blank specification is (150-230) mm thick x (1040-2000) mm wide, the intermediate blank thickness between rough rolling and finish rolling is 38.0-57.0 mm, and the width is 1040-2000 mm.

9. The production method of a 448 MPa grade hot-rolled pickled steel sheet for automobiles according to claim 5, characterized in that, The pickling process comprises: tension leveling the steel plate before pickling, the tension leveling elongation being 0.6-2.0%, the pickling tank is divided into three tanks, the concentration of the No.1 tank is 75-125 g / L, the temperature of the pickling solution of the No.1 tank is 82.0-88.0 ℃, the concentration of the No.2 tank is 125-155 g / L, the temperature of the pickling solution of the No.2 tank is 77.0-82.0 ℃, the concentration of the No.3 tank is 155-175 g / L, the temperature of the pickling solution of the No.3 tank is 70.0-77.0 ℃, and an inhibitor is added in the pickling solution during pickling, the weight percentage of the inhibitor in the pickling solution being 0.08-0.13%; the rinsing water temperature is 50-60 ℃, the pickling and rinsing speed is controlled in 80-120 m / min; the pickling process is under tension, the tension being 30-60 KN; and the pickling solution is hydrochloric acid.

Images