A method for producing a pickling high expansion steel for automobile structures

Abstract

The application discloses a production method of pickling high-hole-expanding steel for automobile structure and belongs to the technical field of metallurgical plates. The method comprises a steelmaking process, a hot rolling process and a pickling process. The chemical components in percentage by mass are as follows: C 0.040-0.080%, Si 0.04-0.06%, Mn 1.60-1.90%, P <=0.018%, S <=0.005%, Cr 0.40-0.60%, Al 0.015-0.050%, Nb 0.035-0.055%, Ti 0.035-0.060%, Ca 0.0008-0.0020%, N <=0.0050%, and the rest is Fe and impurities. The application aims to provide a production method of pickling high-hole-expanding steel for automobile structure to solve the stamping cracking problem of high-strength steel products in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical sheet technology, and particularly relates to a production method of pickled high-hole expanded steel for automotive structures. Background Technology

[0002] With the increasing demands for lightweighting and collision safety in automobiles, structural components require high strength, good formability, and high hole-expanding capacity to adapt to complex processing conditions such as stamping, punching, and flanging. Existing automotive structural steels suffer from significant technical defects: an imbalance between strength and hole-expanding capacity. Ordinary carbon manganese steel lacks sufficient strength and has poor hole-expanding performance, easily leading to edge cracks during hole-expanding. High-strength steels often face challenges in balancing strength and plasticity / hole-expanding capacity, and their high production costs make them incompatible with existing pickling and stamping production lines. Pickling, as a key process for steel surface purification, easily generates surface defects such as micropores, further deteriorating hole-expanding performance. Traditional post-treatment technologies such as passivation and shot peening may pose environmental risks or easily lead to work hardening, reducing ductility. To overcome these bottlenecks and meet the core requirements of high strength and high hole-expanding rate for components such as automotive chassis suspension arms and subframes, developing pickled high-hole-expanding steel for automotive structures and its production methods to achieve efficient matching of material properties and processing technology has become an important research and development direction in the field of automotive steels. Summary of the Invention

[0003] The purpose of this invention is to provide a method for producing pickled high-hole expanded steel for automotive structures, in order to solve the problem of stamping cracking in high-strength steel products in the prior art.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for producing pickled high-expansion steel for automotive structures, comprising: steelmaking process - hot rolling process - pickling process; wherein: the steelmaking process includes: converter top and bottom combined blowing smelting - LF refining - RH refining - slab continuous casting; the hot rolling process includes: billet heating - high-pressure water descaling - fixed-width press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - insulation cover - flying shear - high-pressure water descaling - F1-F7 finishing mill rolling - dense laminar flow cooling - coiling; the pickling process includes: pickling uncoiling - welding - tension leveling - pickling - rinsing - drying - edge trimming - oiling - coiling; characterized in that:

[0006] 1) Converter production

[0007] After desulfurization pretreatment, molten iron is smelted in a converter. The sulfur content of the molten iron entering the converter must be less than 0.005%, and the slag removal area must be greater than 90%. The tapping temperature of the converter must be ≥1620℃ to ensure that the composition and temperature are coordinated during tapping. The molten steel supplied to the converter for LF has the following composition: C≤0.060%, Si≤0.05%, Mn1.40-1.70%, P≤0.018%, S≤0.005%, Alt: ≥0.030%, Cr: 0.25-0.50%.

[0008] 2) LF production

[0009] LF furnace slag formation, deoxidation, and desulfurization; LF-supplied RH molten steel contains: C 0.040-0.080%, Si 0.04-0.06%, Mn 1.60-1.90%, P≤0.018%, S≤0.005%, Cr 0.40-0.60%, Alt: 0.015-0.050%, Nb 0.035-0.055%, Ca: 0.0008-0.0020%.

[0010] 3) RH production

[0011] The RH process involves vacuum treatment. The chemical composition of the molten steel supplied to the casting machine by the RH process is as follows (by weight percentage): C 0.040-0.080%, Si 0.04-0.06%, Mn 1.60-1.90%, P≤0.018%, S≤0.005%, Cr 0.40-0.60%, Alt 0.015-0.050%, Nb 0.035-0.055%, Ti 0.035-0.060%, Ca 0.0008-0.0020%, N≤0.0050%, with the remainder being Fe and impurities.

[0012] 4) Continuous casting production

[0013] For slab continuous casting, the superheat of the tundish during the casting process is controlled within the range of 15–30℃, and the production speed is 1.0–1.6 m / min;

[0014] 5) The heating temperature during billet heating is 1230-1290℃, the heating time is 170-270min, the soaking temperature is 1230-1290℃, the soaking time is 30-60min, and the furnace exit temperature is 1230-1290℃.

[0015] 6) The finishing rolling temperature is 865-905℃, and the coiling temperature is 450-510℃;

[0016] 7) The elongation rate of the straightening machine in the pickling process is 0.0-0.6%.

[0017] Furthermore, the chemical composition of the high-expansion steel by mass percentage is: C 0.061%, Si 0.048%, Mn 1.71%, P 0.016%, S 0.001%, Cr 0.50%, Alt 0.034%, Nb 0.045%, Ti 0.051%, Ca 0.0014%, N 0.0045%, with the remainder being Fe and impurities.

[0018] Furthermore, the chemical composition of the high-expansion steel by mass percentage is: C 0.057%, Si 0.056%, Mn 1.66%, P 0.013%, S 0.003%, Cr 0.51%, Alt 0.038%, Nb 0.039%, Ti 0.046%, Ca 0.0012%, N 0.0043%, with the remainder being Fe and impurities.

[0019] Furthermore, the chemical composition of the high-expansion steel by mass percentage is: C 0.059%, Si 0.053%, Mn 1.83%, P 0.013%, S 0.004%, Cr 0.46%, Alt 0.035%, Nb 0.051%, Ti 0.039%, Ca 0.0018%, N 0.0034%, with the remainder being Fe and impurities.

[0020] Furthermore, the billet heating regime is as follows: heating temperature 1230-1234℃; heating time 182-196min; soaking temperature 1239-1242℃; soaking time 57-59min; and furnace exit temperature 1242-1246℃.

[0021] Furthermore, the rolling process is as follows: roughing rolling temperature 1022-1029℃; finishing rolling temperature 869-884℃; coiling temperature 446-473℃.

[0022] Furthermore, its mechanical properties meet the following requirements: yield strength 600-800MPa, tensile strength ≥780MPa, elongation after fracture A ≥12%, and porosity ≥55%.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0024] Its mechanical properties meet the following requirements: yield strength 600-800MPa, tensile strength ≥780MPa, elongation after fracture A ≥12%, and hole expansion rate ≥55%. While improving strength, there are certain requirements for the hole expansion rate of the product to enhance hole expansion performance and reduce the risk of stamping cracking. Attached Figure Description

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] Figure 1 The metallographic structure of the finished product in Example 1. Detailed Implementation

[0027] A pickled high-expansion steel for automotive structures and its production method, the production method specifically includes the following steps: steelmaking process - hot rolling process - pickling process.

[0028] The steelmaking process includes: converter top and bottom blowing smelting—LF—RH—slab continuous casting. After desulfurization pretreatment, molten iron is smelted in a converter. The sulfur content of the molten iron entering the converter must be less than 0.005%, and the slag removal area must be greater than 90%. The converter tapping temperature must be ≥1620℃ to ensure that the composition and temperature are coordinated during tapping. The LF steel supplied to the converter contains [C] ≤0.060%, [Si] ≤0.05%, [Mn] 1.40-1.70%, [P] ≤0.018%, [S] ≤0.005%, [Alt] ≥0.030%, and [Cr] 0.25-0.50%. The LF furnace undergoes slagging, deoxidation, and desulfurization. The RH steel supplied by the LF furnace contains [C] 0.040-0.080%, [Si] 0.04-0.06%, [Mn] 1.60-1.90%, [P] ≤0.018%, [S] ≤0.005%, and [Cr] 0.40-0.60%. [Al]: 0.015-0.050%, [Nb]: 0.035-0.055%, [Ca]: 0.0008-0.0020%; RH-supplied molten steel for casting machines: [C] 0.040-0.080%, [Si] 0.04-0.06%, [Mn] 1.60-1.90%, [P] ≤0.018%, [S] ≤0.005%, [Cr] 0.4 0-0.60%, [Alt]: 0.015-0.050%, [Nb] 0.035-0.055%, [Ti] 0.035-0.060%, [Ca]: 0.0008-0.0020%, [N] ≤0.0050%; slab continuous casting, the superheat of the tundish during the casting process is controlled within the range of 15-30℃, and the production speed is 1.0-1.6m / min. According to the above steelmaking process requirements, the actual chemical composition (mass percentage) of the slab is shown in Table 1 below, with the balance being Fe and unavoidable impurities (Note: Due to the different composition design schemes of the comparative example and the embodiment, their production process parameters are also different from those described in this invention, and are only listed for comparison here).

[0029] Table 1: Chemical Composition (%)

[0030] element C Si Mn P S Cr Nb Ti Alt Ca N scope 0.040-0.080 0.04-0.06 1.60-1.90 ≤0.018 ≤0.005 0.40-0.60 0.035-0.055 0.035-0.060 0.015-0.050 0.0008-0.0020 ≤0.0050 Example 1 0.061 0.048 1.71 0.016 0.001 0.50 0.045 0.051 0.034 0.0014 0.0045 Example 2 0.57 0.056 1.66 0.013 0.003 0.51 0.039 0.046 0.038 0.0012 0.0043 Example 3 0.59 0.053 1.83 0.013 0.004 0.46 0.051 0.039 0.035 0.0018 0.0034

[0031] The hot rolling process includes: billet heating—high-pressure water descaling—width-fixed press—E1R1 roughing mill rolling—E2R2 roughing mill rolling—flying shear—high-pressure water descaling—F1-F7 finishing mill rolling—densified laminar flow cooling—coiling; this process uses a walking beam furnace to heat the billet (heating process is shown in Table 2), roughing uses a double-stand R1 and R2 reciprocating rolling process, and finishing uses a continuous rolling process from F1 to F7. Specific hot rolling processes are shown in Table 3.

[0032] Table 2 Heating Regime for Cast Billets

[0033] Example Heating temperature / ℃ Heating time / min Isotropic temperature / ℃ Soaking time / min Furnace temperature / ℃ Example 1 1230 192 1240 59 1245 Example 2 1233 192 1239 57 1242 Example 3 1234 186 1242 59 1246

[0034] Table 3 Rolling Process

[0035] Example Rolled thickness / mm Roughing and finishing rolling temperatures / ℃ Finishing rolling temperature / ℃ Winding temperature / ℃ Example 1 4.00 1025 875 460 Example 2 3.50 1022 869 446 Example 3 3.00 1029 884 473

[0036] The pickling process includes: pickling and uncoiling—welding—straightening—pickling—rinsing—drying—edge trimming—oiling—winding; the specific process of the pickling process is shown in Table 4.

[0037] Table 4: Pickling Process

[0038] Example Cold rolled thickness / mm Elongation of leveling machine / % Example 1 4.00 0.33 Example 2 3.50 0.31 Example 3 3.00 0.39

[0039] The room temperature tensile mechanical properties of the finished product after steelmaking, hot rolling and pickling processes are shown in Table 5.

[0040] Table 5: Room Temperature Tensile Properties of Finished Products

[0041] Thickness / mm Yield strength / MPa Tensile strength / MPa Elongation / % Hole expansion rate / % Example 1 4.00 648 780 16.2 56.7 Example 2 3.50 652 791 15.4 55.9 Example 3 3.00 655 794 15.3 56.4

[0042] In summary, this product has passed performance testing and meets all performance requirements. User trial molding has also met molding requirements, making it suitable for widespread use.

[0043] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing pickled high-permeability steel for automotive structures, comprising: Steelmaking process - hot rolling process - pickling process; wherein: the steelmaking process includes: converter top and bottom blowing smelting - LF refining - RH refining - slab continuous casting; the hot rolling process includes: billet heating - high-pressure water descaling - fixed width press - E1R1 roughing mill rolling - E2R2 roughing mill rolling - insulation cover - flying shear - high-pressure water descaling - F1-F7 finishing mill rolling - dense laminar flow cooling - coiling; the pickling process includes: pickling uncoiling - welding - tension leveling - pickling - rinsing - drying - edge trimming - oiling - coiling; characterized in that: 1) Converter production After desulfurization pretreatment, molten iron is smelted in a converter. The sulfur content of the molten iron entering the converter must be less than 0.005%, and the slag removal area must be greater than 90%. The tapping temperature of the converter must be ≥1620℃ to ensure that the composition and temperature are coordinated during tapping. The molten steel supplied to the converter for LF has the following composition: C≤0.060%, Si≤0.05%, Mn1.40-1.70%, P≤0.018%, S≤0.005%, Alt: ≥0.030%, Cr: 0.25-0.50%. 2) LF production LF furnace slag formation, deoxidation, and desulfurization; LF-supplied RH molten steel contains: C 0.040-0.080%, Si 0.04-0.06%, Mn 1.60-1.90%, P≤0.018%, S≤0.005%, Cr 0.40-0.60%, Alt: 0.015-0.050%, Nb 0.035-0.055%, Ca: 0.0008-0.0020%. 3) RH production The RH process involves vacuum treatment. The chemical composition of the molten steel supplied to the casting machine by the RH process is as follows (by weight percentage): C 0.040-0.080%, Si 0.04-0.06%, Mn 1.60-1.90%, P≤0.018%, S≤0.005%, Cr 0.40-0.60%, Alt 0.015-0.050%, Nb 0.035-0.055%, Ti 0.035-0.060%, Ca 0.0008-0.0020%, N≤0.0050%, with the remainder being Fe and impurities. 4) Continuous casting production For slab continuous casting, the superheat of the tundish during the casting process is controlled within the range of 15–30℃, and the production speed is 1.0–1.6 m / min; 5) The heating temperature during billet heating is 1230-1290℃, the heating time is 170-270min, the soaking temperature is 1230-1290℃, the soaking time is 30-60min, and the furnace exit temperature is 1230-1290℃. 6) The finishing rolling temperature is 865-905℃, and the coiling temperature is 450-510℃; 7) The elongation rate of the straightening machine in the pickling process is 0.0-0.6%.

2. The production method of pickled high-perforation steel for automotive structures according to claim 1, characterized in that, The chemical composition of the high-expansion steel by mass percentage is: C 0.061%, Si 0.048%, Mn 1.71%, P 0.016%, S 0.001%, Cr 0.50%, Alt 0.034%, Nb 0.045%, Ti 0.051%, Ca 0.0014%, N 0.0045%, with the remainder being Fe and impurities.

3. The method for producing pickled high-perforation steel for automotive structures according to claim 1, characterized in that, The chemical composition of the high-expansion steel by mass percentage is: C 0.057%, Si 0.056%, Mn 1.66%, P 0.013%, S 0.003%, Cr 0.51%, Alt 0.038%, Nb 0.039%, Ti 0.046%, Ca 0.0012%, N 0.0043%, with the remainder being Fe and impurities.

4. The method for producing pickled high-perforation steel for automotive structures according to claim 1, characterized in that, The chemical composition of the high-expansion steel by mass percentage is: C 0.059%, Si 0.053%, Mn 1.83%, P 0.013%, S 0.004%, Cr 0.46%, Alt 0.035%, Nb 0.051%, Ti 0.039%, Ca 0.0018%, N 0.0034%, with the remainder being Fe and impurities.

5. The method for producing pickled high-perforation steel for automotive structures according to claim 1, characterized in that, Heating regime for billet casting: heating temperature 1230-1234℃; heating time 182-196min; soaking temperature 1239-1242℃; soaking time 57-59min; tapping temperature 1242-1246℃.

6. The method for producing pickled high-perforation steel for automotive structures according to claim 1, characterized in that, Rolling process: Roughing rolling temperature 1022-1029℃; Finishing rolling temperature 869-884℃; Coiling temperature 446-473℃.

7. The method for producing pickled high-perforation steel for automotive structures according to claim 1, characterized in that, Its mechanical properties meet the following requirements: yield strength 600-800MPa, tensile strength ≥780MPa, elongation after fracture A ≥12%, and expansion rate ≥55%.

Images