A method for preparing a high-formability rare earth microalloyed no-gap steel dc06 cold-rolled steel strip

Abstract

The application discloses a preparation method of high-formability rare earth micro-alloyed interstitial-atom-free steel DC06 cold-rolled steel strip, which comprises the following steps: smelting and continuous casting, heating and hot rolling process, acid rolling process, annealing process and flattening process; the hot rolling raw material quality percentage composition comprises the following components: C: <=0.0020%, Si: <=0.010%, Mn: <=0.12%, P: <=0.008%, S <=0.0065%, Ti: 0.055-0.070%, Alt: 0.020-0.055%, RE: 0.0005-0.015%, N <=0.003%, O <=0.003%, and the rest is iron and other inevitable impurities. The application aims to provide a preparation method of high-formability rare earth micro-alloyed interstitial-atom-free steel DC06 cold-rolled steel strip, so that the steel plate has good stamping forming performance.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical materials technology, and particularly relates to a method for preparing DC06 cold-rolled steel strip with high formability rare earth microalloyed interstitial atomic steel. Background Technology

[0002] As the automotive industry moves towards weight reduction and lightweighting, automotive sheet metal with both high strength and ultra-deep drawing performance has seen rapid development. Aluminum deoxidized IF steel, due to its excellent deep drawing performance and economy, has become a primary material for automotive outer panels produced by companies worldwide. Currently, new energy vehicles are designed with increasingly diverse and complex functions, placing ever-higher demands on the shapes and deformation of vehicle components. Therefore, DC06 cold-rolled steel strip, a high-formability rare-earth microalloyed gapless atomic steel, is of great significance for improving the performance of complex deformable automotive parts and for the iterative upgrading of new materials. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing high-formability rare-earth microalloyed gapless atomic steel DC06 cold-rolled steel strip, so that the steel sheet has good stamping and forming performance.

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

[0005] This invention discloses a method for preparing DC06 cold-rolled steel strip with high formability rare-earth microalloyed interstitial atom steel, comprising the following steps:

[0006] Smelting and continuous casting: Molten iron undergoes desulfurization pretreatment, with slag removal area exceeding 95%. The sulfur content of the molten iron entering the converter is less than 0.003%. After tapping from the converter, aluminum granules are added at 0.3-0.5 kg / ton of steel for top slag modification. After decarburization, deoxidation, and alloying in the RH process, aluminum granules are added at 0.15-0.20 kg / ton of steel for top slag modification. Vacuum degassing is performed in the RH furnace, and deep decarburization is carried out according to the composition and temperature of the RH steel. After decarburization, after circulation for more than 4 minutes, metallic manganese, ferrophosphorus, ferrotitanium, and ferroboron alloys are added to adjust the composition. After composition adjustment, vacuum circulation is ensured for more than 6 minutes. The casting machine adopts constant casting speed control, with a casting speed range of 1.2-1.6 m / min. Protective casting is used during the casting process.

[0007] Heating and hot rolling process: Heat to 1170℃~1200℃ and take out of the furnace. After descaling with high pressure water, roll. Rough rolling start temperature is 1160℃~1900℃, finish rolling finish temperature is 905℃~935℃, and coiling temperature is 705℃~735℃.

[0008] Pickling and rolling process: The pickling and rolling procedures for different thicknesses shall comply with the specifications in the table below:

[0009] Finished product thickness (mm) Raw material thickness (mm) ≥0.40-＜0.53 2.30 ≥0.53-＜0.59 2.50 ≥0.59-＜0.64 2.75 ≥0.64-＜0.70 3.00 ≥0.70-＜0.75 3.25 ≥0.75-＜0.81 3.50 ≥0.81-＜0.87 3.75 ≥0.87-＜0.93 4.00 ≥0.93-＜1.15 4.20 ≥1.15-＜1.25 4.50 ≥1.25-＜1.35 4.70 ≥1.35-＜1.50 4.80 ≥1.50-＜1.65 5.00 ≥1.65-＜1.80 5.30 ≥1.80-＜2.00 5.50 2.00 6.00

[0010] Annealing process: The annealing process shall be performed according to the specifications set in the table below:

[0011]

[0012]

[0013] Leveling process: The annealing process shall be performed according to the specifications set in the table below:

[0014]

[0015] Furthermore, the composition of the hot-rolled raw material by mass percentage includes: C: ≤0.0020%, Si: ≤0.010%, Mn: ≤0.12%, P: ≤0.008%, S≤0.0065%, Ti: 0.055-0.070%, Alt: 0.020-0.055%, RE: 0.0005-0.015%, N≤0.003%, O≤0.003%, with the remainder being iron and other unavoidable impurities.

[0016] Furthermore, the composition of the hot-rolled raw material by weight percentage includes: C: 0.0010%, Si: 0.005%, Mn: 0.10%, P: 0.006%, S: 0.0050%, Ti: 0.060%, Alt: 0.030%, Ce: 0.0015%, N: 0.0015%, with the remainder being iron and other unavoidable impurities.

[0017] Furthermore, it reduces the size of inclusions, optimizes the morphology of inclusions, increases the solidification nucleation rate, and refines the grains in both the cast and rolled states, thereby effectively improving the strength and toughness of the steel plate through the effect of grain refinement strengthening.

[0018] Furthermore, the average r90 value of the steel plate is 2.25.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] Traditional processes for producing interstitial atom-free steel DC06 fail to influence strip properties through microstructure control because the microstructure corresponding to this composition is ferrite. This invention, however, employs microalloying and a narrow-window process control throughout the entire rolling process. By adding rare earth element Ce, which combines with active oxygen and sulfur in the steel to achieve a lower Gibbs free energy, Ce readily forms rare earth oxides, aluminates, and sulfides such as CeAlO3, Ce2O2S, and Ce2O3. The rare earth compounds formed by Ce have high melting points and act as heterogeneous nucleation sites, increasing the nucleation rate and refining the solidification microstructure. Simultaneously, during rolling heat treatment, rare earth elements preferentially agglomerate at grain boundaries, slowing grain growth and increasing recrystallization time, thus reducing the average grain diameter and improving grain size at each rolling stage. This fine-grain strengthening increases both strength and plasticity, improving the r90 value (formability ratio) and effectively enhancing the stamping performance of ultra-low carbon IF steel.

[0021] This invention effectively utilizes the effects of rare earth elements and a rational composition design and narrow-window process control throughout the manufacturing process to achieve stable preparation of high-formability rare earth microalloyed gapless atomic steel DC06 cold-rolled strip. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings.

[0023] Figure 1 Comparison of grain size of strip steel in each rolling process (magnified 200 times), where: 1# without rare earth: (a) cold-rolled plate, (b) continuous annealed plate; 2# with rare earth: (c) cold-rolled plate, (d) continuous annealed plate;

[0024] Figure 2 A scatter plot comparing the r-values ​​of rare earth elements added and those not added. Detailed Implementation

[0025] Implementation Case 1:

[0026] A comparative analysis was conducted on DC06 cold-rolled steel strip with conventional composition and rare earth microalloyed interstitial atom-free steel (sample group 1) and cold-rolled steel strip with a Ce content of 15 ppm produced using this patent (sample group 2). Figure 1A comparison of grain size testing of strip steel at each rolling process shows that the grain size of sample #2 in the hot rolling, cold rolling, and continuous annealing processes is larger than that of the corresponding processes in sample #1. Grain size testing revealed that sample #1 had grain size ratings of 7 for cold rolling and 9.5 for continuous annealing, while sample #2 had ratings of 8.5 for cold rolling and 11 for continuous annealing. Comparative analysis indicates that the addition of rare earth elements results in a more uniform and denser strip steel microstructure with finer grain sizes. By implementing this patented technology and employing a rational composition design and narrow-window process control throughout the manufacturing process, the addition of rare earth elements and the resulting grain size rating improved by 1.5 levels, which is beneficial for enhancing the strength and plasticity of the metal.

[0027] Implementation Case 2:

[0028] The chemical composition of the continuously cast billet of the cold-rolled steel strip with a Ce content of 15 ppm produced using this patent is as follows:

[0029] Chemical composition of continuously cast billets (unit: %)

[0030] C Si Mn P S Alt Ti N Ce 0.0010 0.005 0.10 0.006 0.0050 0.030 0.060 0.0015 15ppm

[0031] Smelting and Continuous Casting: Molten iron undergoes desulfurization pretreatment, with 97% of the slag removed. The sulfur content of the molten iron entering the converter is 0.001%. After tapping from the converter, 0.4 kg / ton of steel-aluminum granules are added for top slag modification. After decarburization, deoxidation, and alloying in the RH process, 0.18 kg / ton of steel-aluminum granules are added for top slag modification. Vacuum degassing is performed in the RH furnace, and deep decarburization is carried out according to the composition and temperature of the RH steel. After decarburization, after 6 minutes of circulation, alloys such as metallic manganese, ferrophosphorus, ferrotitanium, and ferroboron are added to adjust the composition. After composition adjustment, vacuum circulation is ensured for at least 12 minutes. The casting machine uses constant casting speed control at 1.3 m / min, and protective casting is used during the casting process.

[0032] Heating and hot rolling process: Heated to 1190℃ and removed from the furnace, descaled by high pressure water and then rolled. The roughing rolling temperature is 1170℃, the finishing rolling temperature is 925℃, and the coiling temperature is 725℃.

[0033] Pickling and rolling process: The pickling and rolling procedures for different thicknesses shall be in accordance with the specifications in Table 1 below.

[0034] Table 1 Product Raw Material Thickness

[0035] Finished product thickness (mm) Thickness of hot-rolled raw material (mm) 0.70 3.5

[0036] Annealing process: The annealing process shall be performed in accordance with Table 2 below.

[0037] Table 2 Annealing Furnace Process Parameters

[0038]

[0039] Leveling process: The annealing process shall be performed in accordance with the specifications set in Table 3 below.

[0040] Table 3. Process parameters of the leveling machine

[0041] steel grades Thickness (mm) Elongation of leveling machine (%) DC06 0.7 0.3

[0042] Through sample processing tests, the r90 value, representing the forming performance index of this batch of rare earth steel strip samples, was tested. The average r90 value reached 2.25, which shows that the steel coil has strong stamping forming performance. Other mechanical properties are shown in Table 4. This product meets the requirements of users through performance testing and user use.

[0043] Table 4 Mechanical Properties of Steel Strip

[0044]

[0045] Implementation Case 3:

[0046] The addition of rare earth element Ce reduces the size and morphology of inclusions, increases the solidification nucleation rate, and refines the grains in both cast and rolled states. This, in turn, effectively improves the strength and toughness of the steel plate through grain refinement. Figure 2 The results show a comparative analysis of conventionally designed rare-earth microalloyed interstitial steel DC06 cold-rolled steel strip (sample group 1) and cold-rolled steel strip with a Ce content of 15ppm produced using this patent (sample group 2). The r90 value, representing the forming performance index of the strip in sample group 2 with added rare earth, is significantly greater than that in sample group 1 without added rare earth. The average r90 value of the steel plate with added rare earth is 2.25, while the average r90 value of the product without added rare earth is 1.96.

[0047] 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 the production of a high formability rare earth microalloyed gap-free steel DC06 cold rolled steel strip, characterized in that, Comprising the following steps: Smelting and continuous casting: the molten iron is pretreated by desulfurization, the molten slag is cleaned with an area requirement of greater than 95%, the sulfur content of the molten iron entering the converter is required to be less than 0.003%, and after the converter tapping is completed, aluminum particles are added at 0.3-0.5 kg / ton of steel for top slag modification; after the RH process decarburization, deoxidization and alloying are completed, aluminum particles are added at 0.15-0.20 kg / ton of steel for top slag modification; the RH furnace is vacuum degassed, deep decarburization treatment is performed according to the RH molten steel composition and temperature; after decarburization is completed, metal manganese, phosphorus iron, ferrotitanium, ferroboron alloy is added after circulating for more than 4 minutes to adjust the composition, and after the composition is adjusted, vacuum circulation is ensured for more than 6 minutes; the casting machine uses constant speed control, the speed range is 1.2-1.6 m / min, and the casting machine uses protective casting during casting; Heating and hot rolling process: heating to 1170-1200°C and discharging, high-pressure water descaling and then rolling, rough rolling opening temperature 1160-1900°C, finishing rolling final rolling temperature 905-935°C, coiling temperature 705-735°C; Pickling process: the following table specifies the specifications for different thickness pickling rolling procedures: ； Annealing process: the following table specifies the specifications for annealing process: ； ； Skin pass process: the following table specifies the specifications for annealing process: ； The hot rolled raw material composition by mass percentage is composed of the following components: C: ≤0.0020%, Si: ≤0.010%, Mn: ≤0.12%, P: ≤0.008%, S ≤0.0065%, Ti: 0.055-0.070%, Alt: 0.020-0.055%, RE: 0.0005-0.015%, N ≤0.003%, O ≤0.003%, the rest is iron and other unavoidable impurities.

2. Process for the production of a high-formability interstitial-free steel DC06 cold-rolled strip of rare earth microalloyed according to claim 1, characterized in that, The hot rolled raw material composition by mass percentage is further selected as: C: 0.0010%, Si: 0.005%, Mn: 0.10%, P: 0.006%, S: 0.0050%, Ti: 0.060%, Alt: 0.030%, Ce: 0.0015%, N: 0.0015%.

3. Process for the production of a high-formability interstitial-free steel DC06 cold-rolled strip of rare earth microalloyed according to claim 2, characterized in that, The average r90 value of the steel plate is 2.25.

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