Preparation method of high-strength anti-stamping deformation bake-hardening steel
By controlling specific chemical compositions and metallurgical processes, the contradiction between high strength and bake hardening properties in existing bake hardening steels has been resolved, providing low-cost, high-strength steel plates resistant to stamping deformation with excellent stamping forming performance, thus achieving a combination of low cost and high performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-31
- Publication Date
- 2026-04-07
AI Technical Summary
Existing bake-hardening steels, while ensuring high strength and bake-hardening properties, struggle to achieve both excellent stamping formability and low cost. In particular, their flanging and hole-expanding properties are poor, and the addition of microalloying elements such as Ti and Nb is costly.
By employing specific chemical compositions and metallurgical processes, including converter production, RH furnace deep decarburization treatment, continuous casting production, billet heating and hot rolling, cold rolling and continuous annealing processes, the formation of iron oxide scale and metallographic structure are controlled. C atoms are fixed by Ti element, avoiding the addition of other microalloying elements such as Nb and V, so as to achieve low cost, high strength, resistance to stamping deformation and high bake hardening effect.
This invention achieves a low-cost steel plate with high strength, resistance to stamping deformation, and high bake hardening performance. It possesses excellent stamping and forming properties, with a yield strength of 220-270 MPa, tensile strength of 320-400 MPa, elongation after fracture A80mm≥32%, r90≥1.5, n90≥0.16, and BH2≥30 MPa, reducing production costs by approximately 30 yuan/ton of steel.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of automobile steel, and particularly relates to a preparation method of high-strength stamping deformation resistant bake hardening steel. BACKGROUND
[0002] With the increasing requirements of light weight and safety in the automobile industry, high-strength steel plates are increasingly widely used. Bake hardening steel is an advanced automobile steel, which has a low yield strength before stamping forming and is easy to form; and in the coating and baking process after stamping, the yield strength is significantly improved due to the pinning effect of C atoms on dislocations, that is, the bake hardening effect is generated, thereby improving the service strength of the part.
[0003] However, the traditional bake hardening steel has a contradiction: in order to ensure the bake hardening property, a certain amount of solid solution C atoms are needed in the steel; but the solid solution C atoms also cause obvious yield platform and room temperature aging effect, that is, the strength increases and the plasticity decreases during storage, resulting in Luders band during stamping, which affects the surface quality. At the same time, with the increase of the strength level, the stamping formability of the steel plate, especially the flanging performance and the hole expansion performance, will decrease sharply.
[0004] In the prior art, Ti, Nb and other micro-alloying elements are used to fix C and N atoms to solve the aging problem, but it is difficult to ensure high strength while considering excellent bake hardening value and formability, and the cost will also increase accordingly. Therefore, it is of great significance to develop a low-cost steel plate which can simultaneously solve the problems of stamping deformation resistance, high strength and high bake hardening response and a preparation method thereof. SUMMARY
[0005] The purpose of the present application is to overcome the shortcomings of the prior art and high cost, and to provide a preparation method of a low-cost steel plate with high strength, high stamping deformation resistance and high bake hardening value.
[0006] To solve the above technical problems, the technical scheme is as follows:
[0007] The preparation method of the high-strength stamping deformation resistant bake hardening steel has the following chemical composition by weight percentage: C≤0.080%; Si≤0.50%; Mn≤0.70%; P≤0.085%; S≤0.030%; 0.015%≤Alt; 0.010%≤Ti≤0.020%; N≤0.0030%; the rest is Fe and impurities; and the preparation process comprises:
[0008] 1) Converter production
[0009] The hot metal needs to be desulfurized by KR, and the sulfur content of the hot metal entering the converter is required to be less than or equal to 0.002%, and the hot metal slag cleaning area is greater than 95%; the converter tapping temperature is greater than or equal to 1670℃, and a turnover ladle must be used for tapping, and the temperature drop requirement of tapping is less than 70℃, and the [C] in the RH molten steel is less than or equal to 0.04%, the [Mn] is less than or equal to 0.60%, and the [O] is less than or equal to 0.060%.
[0010] 2) RH furnace production
[0011] The RH furnace carries out deep decarburization treatment, after the decarburization is completed, according to the oxygen content, aluminum particles are added for deoxidization, and after circulating for more than 4 minutes, manganese iron, titanium iron and other alloys are added to adjust the composition. After the composition adjustment is completed, the vacuum circulation is ensured to be greater than or equal to 6 minutes;
[0012] 3) Continuous casting production
[0013] The slab is continuously cast, and the tundish superheat degree is controlled in the range of 30-45℃ during the casting process of the caster, and the production speed is 1.0-1.8m / min;
[0014] 4) The reheating temperature of the casting blank is 1200-1240℃, the heating time is 150-210min, the soaking temperature is 1215-1255, the soaking time is 30-60min, and the discharge temperature is 1215-1255℃;
[0015] 5) The finish rolling temperature of the finishing mill is 905-935℃, and the coiling temperature is 600-630℃;
[0016] 6) In the continuous annealing process, the annealing heating and soaking section temperature is 790-810℃, the slow cooling section outlet temperature is 650-700℃, the fast cooling section outlet temperature is 150-250℃, the overaging section temperature is 150-250℃, the final cooling section outlet temperature is less than or equal to 150℃, the elongation of the flattening machine is 1.15-1.55%, and the process section speed is 100-140m / min.
[0017] Further, the hot rolling thickness is: 2.7mm-6.0mm.
[0018] Further, the cold rolling thickness is 0.50-2.10mm.
[0019] Further, the steel strip surface quality is ferrite.
[0020] Further, the metallographic structure grain size is 8.0-10.0 levels.
[0021] Further, the mechanical properties of products of each thickness group are uniform, the steel strip surface quality is FD, and the surface roughness range is 0.6-1.9μm.
[0022] Further, the mechanical properties meet: yield strength 220-270MPa, tensile strength 320-400MPa, elongation A 80mm ≥ 32%, r 90 ≥ 1.5, n 90 ≥ 0.16, BH2 ≥ 30MPa.
[0023] Further, the weight percentage of the chemical composition includes: C 0.055%; Si 0.115%; Mn 0.52%; P 0.045%; S 0.0045%; Alt 0.045%; Ti 0.015%; N 0.0026%; and the rest is Fe and impurities.
[0024] The reasons for selecting the above process parameters are as follows:
[0025] The oxygen blowing amount is strictly controlled in the steelmaking process to reduce the generation of inclusions; the low heating temperature adopted in the hot rolling process is beneficial to control the generation of iron oxide scale and save energy consumption, and at the same time, the water pressure for descaling is increased to remove the iron oxide scale on the surface of the slab, and the surface quality of the steel strip after hot rolling is improved; high-temperature annealing is adopted in the continuous annealing process to realize rapid recrystallization, different tempering machine elongation rates are adopted according to the thickness group distance, and stable performance ranges of products of different thickness specifications are realized. 80mm ≥ 32% (transverse tensile test: L0=80mm, b0=20mm), n value ≥ 0.16, r value ≥ 1.5, surface roughness 0.6-1.9um, elongation after fracture and r value are high, so that excellent stamping forming performance is possessed.
[0026] Compared with the prior art, the beneficial technical effects of the present application are:
[0027] The high-strength stamping deformation bake hardening steel and the preparation method thereof provided by the present application meet the mechanical performance requirements of 180-grade high-strength stamping deformation bake hardening steel by adding only Ti (without adding other micro-alloy elements such as Nb and V), so as to realize the purpose of low cost (about 30 yuan per ton of steel cost reduction). 80mm ≥ 32%, r 90 ≥ 1.5, n 90 ≥ 0.16, BH2 ≥ 30MPa.
[0028] The preparation method provided by the present application provides a high-strength stamping deformation bake hardening steel preparation method by adopting new component design and metallurgical process parameters. BRIEF DESCRIPTION OF DRAWINGS
[0029] The application will be further described in connection with the accompanying drawings.
[0030] Figure 1 The finished product has a metallographic structure. DETAILED DESCRIPTION
[0031] The application relates to a high-strength stamping-deformation-resistant bake hardening steel for automobiles and a preparation method thereof, and the production method specifically comprises the following steps: a steelmaking process, a hot rolling process, a cold rolling process and a continuous annealing process.
[0032] The steelmaking process comprises KR desulfurization, a converter, RH and slab continuous casting. After desulfurization pretreatment, the molten iron is subjected to converter smelting, the sulfur content of the molten iron entering the converter is required to be less than 0.002%, and the molten iron slag cleaning area is greater than 95%; the converter tapping temperature is greater than or equal to 1670 DEG C, a turnover ladle must be used for tapping, the tapping temperature drop is required to be less than 70 DEG C, and the [C] in the RH molten steel is less than or equal to 0.04%, the [Mn] is less than or equal to 0.60%, and the [O] is less than or equal to 0.060%. The RH furnace is subjected to deep decarburization treatment, after the decarburization is finished, aluminum particles are added for deoxidization according to the oxygen content, and after circulating for more than 4 minutes, manganese iron, titanium iron and other alloys are added for adjusting the composition. After the composition is adjusted, the vacuum circulation is ensured to be greater than or equal to 6 minutes; the slab is continuously cast, and the tundish overheating degree is controlled to be in the range of 30-45 DEG C during the casting process of the caster, and the production drawing speed is 1.0-1.8 m / min. According to the above steelmaking process requirements, the actual slab chemical composition (mass percentage) is shown in Table 1 below, and the balance is Fe and inevitable impurities (note: since the component design scheme of the comparative example is different from that of the example, the production process parameters are also different from those described in the application, which are only listed for comparison here).
[0033] Table 1: Chemical composition (%)
[0034]
[0035] The hot rolling process comprises slab heating, high-pressure water descaling, width setting press, E1R1 rough rolling mill rolling, E2R2 rough rolling mill rolling, flying shear, high-pressure water descaling, F1-F7 finishing rolling mill rolling, encryption type laminar cooling and coiling, and the process adopts a step-by-step heating furnace to heat the slab (the heating process is shown in Table 2), the rough rolling adopts a double-rack R1 and R2 shuttle type rolling, and the finishing rolling adopts a F1-F7 continuous rolling process. The specific hot rolling process is shown in Table 3.
[0036] Table 2: Slab heating system
[0037] Heating temperature / °C Heating time / min Soaking temperature / °C Soaking time / min Discharge temperature / °C 1235 228 1253 47 1235
[0038] Table 3: Rolling process
[0039] Rolling thickness / mm Finish rolling temperature / °C Coiling temperature / °C 5.3 936 629
[0040] The cold rolling process includes: acid pickling uncoiling-welding-straightening-acid pickling-rinsing-drying-trimming-cold rolling of continuous rolling mill-coiling;
[0041] The continuous annealing process includes: continuous annealing uncoiling-welding-cleaning-inlet loop-annealing furnace-outlet loop-tempering-trimming-surface inspection-oiling-sampling-coiling-weighing-packaging; the annealing uses vertical continuous annealing furnace, and the furnace uses reducing atmosphere and nitrogen-hydrogen mixed protective atmosphere for cooling. The specific process system of the continuous annealing process is shown in Table 4.
[0042] Table 4: Annealing process
[0043]
[0044] Through the hot rolling, cold rolling and continuous annealing processes, the room temperature tensile mechanical properties of the finished product are shown in Table 5, the metallographic structure is equiaxed ferrite, the grain size is 8.0-10.0 grade, and the structure morphology is shown in Figure 1 .
[0045] Table 5: Room temperature tensile properties of finished product
[0046]
[0047] In summary, the product passes the performance test, and each performance meets the requirements, and after being used by the user for trial molding, the product meets the forming requirements, and can be widely used.
[0048] The above-described embodiments are only used to describe the preferred modes of the present application, and do not limit the scope of the present application, and various deformations and improvements on the technical solutions of the present application made by the ordinary skilled in the art without departing from the design spirit of the present application should fall within the protection scope of the present application defined by the claims.
Claims
1. A method for preparing high-strength, stamping-resistant, bake-hardening steel, characterized in that, Its chemical composition by weight percentage includes: C≤0.080%; Si≤0.50%; Mn≤0.70%; P≤0.085%; S≤0.030%; 0.015%≤Al; 0.010%≤Ti≤0.020%; N≤0.0030%; the remainder is Fe and impurities; its preparation process includes: 1) Converter production Molten iron must undergo desulfurization treatment via KR. The sulfur content of the molten iron entering the converter must be less than or equal to 0.002%, and the slag removal area must be greater than 95%. The tapping temperature of the converter must be ≥1670℃. A turnover ladle must be used for tapping, and the temperature drop at tapping must be less than 70℃. The RH molten steel supplied to the converter must contain [C] ≤0.04%, [Mn] ≤0.60%, and [O] ≤0.060%. 2) RH furnace production The RH furnace undergoes deep decarburization treatment. After decarburization, aluminum particles are added for deoxidation based on the oxygen content. After circulating for more than 4 minutes, ferromanganese and ferrotitanium alloys are added to adjust the composition. After adjusting the composition, ensure vacuum circulation for ≥6 minutes. 3) Continuous casting production For slab continuous casting, the superheat of the tundish during the casting process is controlled within the range of 30-45℃, and the production speed is 1.0-1.8m / min; 4) The heating temperature during billet heating is 1200-1240℃, the heating time is 150-210min, the soaking temperature is 1215-1255℃, the soaking time is 30-60min, and the furnace exit temperature is 1215-1255℃. 5) The finishing rolling temperature is 905-935℃, and the coiling temperature is 600-630℃; 6) In the continuous annealing process, the annealing heating and soaking temperature is 790-810℃, the slow cooling section outlet temperature is 650-700℃, the rapid cooling section outlet temperature is 150-250℃, the over-aging section temperature is 150-250℃, the final cooling section outlet temperature is ≤150℃, the leveling machine elongation rate is 1.15-1.55%, and the process section speed is 100-140m / min.
2. The method for preparing high-strength, impact-resistant, bake-hardening steel according to claim 1, characterized in that, Hot-rolled thickness: 2.7mm-6.0mm.
3. The method for preparing high-strength, impact-resistant, bake-hardening steel according to claim 1, characterized in that, The thickness of cold-rolled steel is 0.50-2.10 mm.
4. The method for preparing high-strength, impact-resistant, bake-hardening steel according to claim 1, characterized in that, The metallographic structure of the steel coil is ferrite.
5. The method for preparing high-strength, impact-resistant, bake-hardening steel according to claim 4, characterized in that, The metallographic grain size is 8.0-10.0 grade.
6. The method for preparing high-strength, impact-resistant, bake-hardening steel according to claim 1, characterized in that, To achieve uniformity of mechanical properties for products of various thickness groups, the surface quality FD of the steel strip is achieved, and the surface roughness ranges from 0.6 to 1.9 μm.
7. The method for preparing high-strength, impact-resistant, bake-hardening steel according to claim 1, characterized in that, Its mechanical properties meet the following requirements: yield strength 220-270 MPa, tensile strength 320-400 MPa, and elongation after fracture A. 80mm ≥32%, r 90 ≥1.5, n 90 ≥0.16, BH2≥30MPa.
8. The method for preparing high-strength, impact-resistant, bake-hardening steel according to claim 1, characterized in that, Its chemical composition by weight percentage includes: C 0.055%; Si 0.115%; Mn 0.52%; P 0.045%; S 0.0045%; Alt 0.045%; Ti 0.015%; N 0.0026%; the remainder being Fe and impurities.