A high-precision evaluation method for forming ability of a rolled steel sheet for automobiles

Abstract

The application discloses a kind of high-precision evaluation methods of the forming capacity of rolled steel plate for automobile, using the following steps: 1) prepare uniaxial tensile sample, carry out uniaxial tensile test to sample at least three strain rates;2) with a certain strain rate as benchmark rate, calculate the formability index under benchmark rate according to the uniaxial tensile test result;3) calculate the ratio of the uniform elongation of each strain rate and the uniform elongation of benchmark rate;4) according to the same technical conditions and strain rate of uniaxial tensile test, carry out uniaxial tensile simulation under each strain rate;Calculate the ratio of each actual uniform elongation and simulation uniform elongation, and calculate the average ratio of actual and simulation;5) calculate the material overall forming capacity index.This method can conveniently obtain comprehensive forming capacity index according to the actual thickness of material and basic mechanical properties under different strain rates, and realize the quantitative characterization of forming capacity of different brand and specification materials.

Description

Technical Field

[0001] This invention belongs to the field of metal processing, and in particular, it is a high-precision evaluation method for the forming capability of rolled steel sheets for automobiles. Background Technology

[0002] The formability of rolled steel sheets for automobiles, as a comprehensive performance indicator, plays a crucial role in the entire automotive steel sheet industry chain, including material research and development, parts design, mold development, and production processing. Various measurement and evaluation methods have been established for formability testing and analysis. For example, GB / T24171.2-2009 and ISO12004-2:2008 specify the sheet metal fracture performance testing method using the FLD (Forming Limit Diagram), while GB / T15825.6-2008 specifies the specific method for measuring the formability of thin metal sheets using the "cone cup test."

[0003] The aforementioned standards specify the method for determining the forming limit of automotive sheet materials, solving the problem of measuring the forming performance of a single sample. However, automotive rolled steel sheets have a long production process. In a large-scale production environment, due to fluctuations in composition and processes, performance differences between batches of individual products are inevitable. Testing methods such as FLD forming limit testing or "cone cup test" have insurmountable practical problems in sample preparation, testing, and data processing. Furthermore, they do not consider the influence of deformation rate on the forming ability of materials, making it impossible to evaluate the forming ability of mass-produced materials in a timely and accurate manner. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a high-precision evaluation method for the forming capability of rolled steel sheets for automobiles, so as to accurately evaluate the forming capability.

[0005] To solve the above technical problems, the present invention adopts the following steps: 1) Prepare a uniaxial tensile specimen and subject the specimen to a uniaxial tensile test at at least three strain rates;

[0006] 2) Using a certain strain rate as the reference rate, calculate the formability index f at the reference rate according to formula (1) based on the uniaxial tensile test results:

[0007]

[0008] In equation (1): R m ρ is the tensile strength, MPa; r is the plastic strain ratio, A g The uniform elongation is given by t, where t is the thickness in mm; and S1 is the strain rate.

[0009] 3) Calculate the ratios λ2, λ3…λ of the uniform elongation at each strain rate to the uniform elongation at the reference rate. n ;

[0010] 4) Perform uniaxial tensile simulations at various strain rates under the same technical conditions and strain rates as the uniaxial tensile test; calculate the ratio of each actual uniform elongation to the simulated uniform elongation, and calculate the average ratio λ between the actual and simulated values.

[0011] 5) Calculate the overall forming capacity index of the material according to formula (2), denoted as F:

[0012]

[0013] In equation (2): f is the forming index at the reference rate; λ2, λ3…λ n λ is the ratio of the uniform elongation at each strain rate to the reference rate; λ is the average ratio of the actual and simulated values.

[0014] Furthermore, in step 1), uniaxial tensile tests are performed at three strain rates: 0.01 s⁻¹. -1 0.1s -1 and 1s -1 .

[0015] The beneficial effects of adopting the above technical solution are as follows: This invention is the first to use a method for rapid and accurate evaluation of material forming performance based on measured mechanical properties under mass production conditions. It fully considers the error between theoretical formulas and actual conditions and the influence of strain rate on forming capability, opens up a technical path for evaluating forming capability based on online performance data from mass production, and fills the gap in the field of capability testing and analysis of rolled steel sheets for automobiles.

[0016] This invention establishes a formability evaluation method that considers the influence of strain rate and theoretical calculation errors through uniaxial tensile tests at different strain rates and uniaxial tensile simulation tests. This method allows for the convenient acquisition of comprehensive formability indices based on the actual material thickness and basic mechanical properties at different strain rates, enabling quantitative characterization of the formability of materials of different grades and specifications. It improves the accuracy of formability performance evaluation and provides quantitative data support for key aspects such as the research and development of automotive steel materials, performance optimization, and material selection and processing of automotive parts. Attached Figure Description

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a schematic diagram of the process structure of an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the uniaxial tensile specimen described in this invention;

[0020] Figure 3 This is a diagram showing the principal strain distribution of uniaxial tension obtained from a uniaxial tensile simulation test according to an embodiment of the present invention. Detailed Implementation

[0021] Example: The high-precision evaluation method for the forming capability of rolled steel sheets for automobiles adopts the following steps.

[0022] 1) Select 20 commonly used automotive steel grades, and apply the same technical conditions, such as... Figure 2 As shown, dumbbell-shaped tensile specimens with a gauge length of 20mm × 80mm were prepared, and their mechanical properties were tested at n different strain rates, where n ≥ 3 and is an integer. Referring to the actual deformation rate range during material application, this embodiment uses mechanical property testing at n = 3 different strain rates, with strain rate S... n S1 = 0.01s -1 S2 = 0.1s -1 and S3 = 1s -1 .

[0023] 2) Figure 1 As shown, with S1 = 0.01s -1 A tensile test was conducted using the reference strain rate, and a strain rate of 0.01 s⁻¹ was obtained. -1 Mechanical performance indicators, and the formability index f at the reference rate is calculated according to formula (1):

[0024]

[0025] In equation (1): R m ρ is the tensile strength, MPa; r is the plastic strain ratio, A g The uniform elongation is given by t, where t is the thickness in mm; and S1 is the strain rate.

[0026] This embodiment is as follows: The forming performance index f was calculated, and the results are shown in Table 1.

[0027] Table 1: Strain rate is 0.01 s. -1 Mechanical properties and forming properties f under the condition

[0028]

[0029]

[0030] 3) For the same batch of samples, dumbbell-shaped tensile specimens with a gauge length of 20mm × 80mm were prepared and subjected to tensile testing, obtaining a strain rate of 0.1s. -1 Mechanical performance indicators, and calculate the uniform elongation ratio according to formula (3):

[0031]

[0032] In equation (3), Strain rate S n Uniform elongation obtained from a tensile test, here representing the uniform elongation obtained from a tensile test at strain rate S2. The uniform elongation obtained from the above reference rate tensile test, i.e.

[0033] This embodiment is as follows: The uniform elongation ratio λ2 was calculated, and the results are shown in Table 2.

[0034] Table 2: Strain rate is 0.1 s. -1 Performance metrics and calculation results under the given conditions

[0035]

[0036]

[0037] 4) For the same batch of samples, dumbbell-shaped tensile specimens with a gauge length of 20mm × 80mm were prepared and subjected to tensile tests to obtain a strain rate of 1s. -1 Mechanical performance indicators, and calculate the uniform elongation ratio according to the above formula (3),

[0038] This embodiment is as follows: The uniform elongation ratio λ3 was calculated, and the results are shown in Table 3.

[0039] Table 3: Strain rate is 1s -1 Performance metrics and calculation results under the given conditions

[0040]

[0041]

[0042] 5) For the above 20 types of vehicle license plates, perform a 0.01s test on each. -1 0.1s -1 1s -1 Uniaxial tensile simulations at three strain rates were performed to compare with the above experiments, and the outputs were... That is, strain rate S n The elongation obtained from uniaxial tensile simulation, and the principal strain distribution diagram of uniaxial tensile test obtained in this embodiment are shown in the figure. Figure 3 ; Calculate the ratio of each actual uniform elongation to the simulated uniform elongation according to equation (4), and calculate the average ratio λ between the actual and simulated elongation according to equation (5):

[0043]

[0044]

[0045] In equations (4) and (5), Strain rate S n Uniform elongation obtained from tensile tests Strain rate S n Uniform elongation obtained from uniaxial tensile simulation; S1, S2, and S are strain rates respectively. n The ratio of the actual to the simulated value; λ is the average ratio of the actual to the simulated value;

[0046] This embodiment is as follows: λ=(λ 0.01 +λ 0.01 +λ 0.01 ) / 3; the calculation results are shown in Table 4.

[0047] Table 4: λ 0.01 , λ 0.1 , λ 1 and λ calculation results

[0048] Brand 0.01 ]]> ​ <![CDATA[λ 0.1 ]]> <![CDATA[λ 1 ]]> λ DC01 1.10 1.06 0.90 1.02 DC03 1.15 1.05 0.96 1.05 DC04 1.17 1.10 0.93 1.07 DC05 1.16 1.12 0.92 1.07 DC06 1.13 1.01 0.91 1.02 DX51D+Z 1.05 1.00 0.92 0.99 DX52D+Z 1.15 1.13 0.93 1.07 DX53D+Z 1.09 1.02 0.95 1.02 DX54D+Z 1.10 1.03 0.97 1.03 DX56D+Z 1.20 1.10 0.89 1.06 DX57D+Z 1.13 1.05 0.99 1.06 CR180IF 1.12 1.04 0.92 1.03 CR260IF 1.20 1.06 0.98 1.08 HC340LA 1.02 1.16 0.78 0.99 HC180YD+Z 1.25 1.05 0.90 1.07 HC220YD+Z 1.06 1.02 0.91 1.00 HC180BD+Z 1.13 1.10 0.98 1.07 HX220BD+Z 0.98 1.20 0.90 1.03 HC340LAD+Z 1.11 1.01 0.89 1.00 HC340 / 590DP 0.90 0.85 0.83 0.86

[0049] 6) Calculate the overall forming capacity index of the material according to formula (2), denoted as F:

[0050]

[0051] In equation (2): f is the forming index at the reference rate; λ2, λ3…λ n λ is the ratio of the uniform elongation at each strain rate to the reference rate; λ is the average ratio of the actual and simulated values.

[0052] This embodiment is as follows: The calculation results are shown in Table 5.

[0053] Table 5: Calculation Results of Forming Capacity for 20 Common Automotive Sheet Metal Grades with Different Thicknesses

[0054]

[0055]

[0056] 7) Forming ability evaluation: As shown in Tables 1 and 5, the F value shows a significant downward trend as the tensile strength of the material increases. This does not indicate that the forming ability of the material deteriorates while the strength increases, which is consistent with the general law of strength-plastic change of rolled steel plates.

[0057] Comparing different grades, the larger the F value, the better the formability. In Table 5, classified by steel type, ultra-deep drawing IF steel (DC03-DC06, DX54D+Z-DX57D+Z) has the best formability. Aluminum killed steel (DC01-DC03, DX51D+Z-DX53D+Z), high-strength IF steel (CR180IF, CR260IF, HC180YD+Z, HC220YD+Z), and bake-hardening steel (HC180BD+Z, HC220BD+Z) have similar formability and are all better than low-alloy high-strength steel (HC340LAD+Z) and duplex steel (HC340 / 590DP).

[0058] However, the actual forming capability of a material is affected by a combination of factors such as material thickness, mechanical properties, and strain rate. According to this method, based on the mechanical property indicators provided by the material supplier, necessary uniaxial tensile tests and simulation benchmarks can be supplemented to accurately and quantitatively evaluate the forming capability of rolled steel sheets for automobiles of different thicknesses and grades. This method is widely used in the material selection and lightweight design of new models by automobile OEMs.

Claims

1. A high-precision evaluation method for the forming capability of rolled steel sheets for automobiles, characterized in that, The following steps are adopted: 1) Prepare a uniaxial tensile specimen and subject the specimen to uniaxial tensile tests at at least three strain rates; 2) Using a certain strain rate as the reference rate, calculate the formability index f at the reference rate according to formula (1) based on the uniaxial tensile test results: In equation (1): R m ρ is the tensile strength, MPa; r is the plastic strain ratio, A g The uniform elongation is given by t, where t is the thickness in mm; and S1 is the strain rate. 3) Calculate the ratios λ2, λ3…λ of the uniform elongation at each strain rate to the uniform elongation at the reference rate. n ; 4) Perform uniaxial tensile simulations at various strain rates under the same technical conditions and strain rates as the uniaxial tensile test; calculate the ratio of each actual uniform elongation to the simulated uniform elongation, and calculate the average ratio λ between the actual and simulated values. 5) Calculate the overall forming capacity index of the material according to formula (2), denoted as F: In equation (2): f is the forming index at the reference rate; λ2, λ3…λ n This is the ratio of the uniform elongation at each strain rate to that at the reference rate. λ is the average ratio of the actual value to the simulation value.

2. The high-precision evaluation method for the forming capability of rolled steel sheets for automobiles according to claim 1, characterized in that: In step 1), uniaxial tensile tests are performed at three strain rates: 0.01 s⁻¹. -1 0.1s -1 and 1s -1 .

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