Method for evaluating influence of predeformation on edge forming performance of high-strength steel

Abstract

The invention discloses a method for evaluating the influence of predeformation on the edge forming performance of high-strength steel. The method comprises the following steps: (1) processing a sample to be tested into a rectangular wide strip sample; (2) stretching the wide and long strip sample until the wide and long strip sample is broken, and determining the bearable maximum uniform deformation A of the wide and long strip sample; (3) taking a plurality of wide and long strip samples, and respectively applying different degrees of pre-deformation to obtain pre-deformed samples; (4) blanking each pre-deformed sample into a standard tensile sample; (5) directly stretching each standard tensile sample until fracture failure; (6) measuring the uniform elongation value Ag and the total elongation value A0 of each tensile test sample, and calculating to obtain the instability elongation PUE = A0-Ag of each tensile test sample; the unstable elongation is used as an evaluation index of the edge forming performance of the high-strength steel. The method is convenient, simple, convenient, high in operability, small in number of required samples, wide in application range and high in engineering application guidance.

Description

Technical Field

[0001] The invention relates to the technical field of plate formability testing, in particular to an evaluation method for the influence of pre-deformation on the edge formability of high-strength steel. Background Art

[0002] High-strength steel and advanced high-strength steel have high strength and good plasticity, and can meet the dual goals of automotive lightweight and collision safety requirements. They are increasingly used in white car bodies, and as a result, more and more quality problems such as edge cracking are exposed.

[0003] As the surface features of parts become more and more complex, single-pass forming can no longer obtain the target part features. Most high-strength steel parts can only be formed after five or six processes such as drawing-trimming-flanging / bending / expanding-shaping-punching. In the early drawing process, the sheet metal undergoes different degrees of pre-deformation. After blanking and punching, the edge forming performance of the sheet metal is different from that of the sheet metal without pre-deformation loading. At present, research generally believes that the hole expansion rate is the most direct and effective way to characterize the edge forming performance of the material, but the measured hole expansion rate is an indicator of the edge forming performance of the original sheet metal, which has little engineering guidance significance for parts that are pre-deformed and then bent / flanged. Therefore, it is urgent to develop a method that can evaluate the influence of pre-deformation on the edge forming performance of high-strength steel, and provide guidance and suggestions for the material selection recommendation and engineering application of complex high-strength steel parts. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for quickly and reasonably evaluating the influence of pre-deformation on the edge forming performance of high-strength steel.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention includes the following steps: (1) processing the sample to be tested into a rectangular wide and long strip sample; (2) Stretch the wide and long strip specimen until it breaks and determine the maximum uniform deformation A it can withstand; (3) Take a number of wide and long strip specimens and apply different degrees of pre-deformation to each specimen to obtain pre-deformed specimens; (4) Punching each pre-deformed specimen into a standard tensile specimen; (5) Directly stretch each standard tensile specimen until it breaks and fails; (6) Measure the uniform elongation value A of each tensile specimen g And the total elongation value A0, the instability elongation PUE of each broken specimen is calculated to be A0-A g ; The instability elongation is used as an evaluation index of the edge forming performance of high-strength steel.

[0006] Furthermore, in the step (3), the selection range of the pre-deformation amount is 0% to (A-2)%.

[0007] Furthermore, the pre-deformation amount is selected gradiently within a selection range.

[0008] Furthermore, in step (4), the blanking is performed using the same blanking gap as the trimming process at the production site.

[0009] Furthermore, the following steps are included: calculating and sorting out the instability elongation PUE values ​​under different pre-deformations, drawing a relationship curve between the pre-deformation and PUE, and obtaining a relationship curve of the influence of the pre-deformation on the edge forming performance.

[0010] The beneficial effects of adopting the above technical scheme are as follows: the present invention first applies a certain pre-deformation to a larger rectangular wide strip sample to simulate the drawing deformation at the production site, and then punches out a tensile sample to simulate the edge quality of the blanking at the production site, and uses the instability elongation PUE calculated after tensile failure to evaluate the local forming performance after pre-deformation; the present invention is convenient, simple and fast, has strong operability, requires a small number of samples, has a wide range of applications, can effectively simulate the edge forming ability of high-strength steel parts with edge deformation after drawing and trimming, and has strong guidance for engineering applications; the forming performance of all parts obtained by trimming and punching after drawing and then bending / flanging / flanging and other edge forming methods can be evaluated by this method, with high test efficiency, less human intervention and short test cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0012] Figure 1 1 is a diagram of a rectangular strip sample after different pre-deformations are applied in Example 1 of the present invention; Figure 2 This is a diagram of a tensile specimen punched out from a rectangular strip specimen in Example 1 of the present invention; Figure 3 This is a sample diagram of Example 1 of the present invention after being directly broken without grinding the edge; Figure 4 is a curve diagram showing the relationship between the pre-deformation amount and the edge forming performance obtained in Example 1 of the present invention; Figure 5 It is a curve diagram showing the relationship between the pre-deformation amount and the edge forming performance obtained in Example 2 of the present invention. DETAILED DESCRIPTION

[0013] Example 1: The evaluation method for the effect of pre-deformation on the edge forming performance of high-strength steel is based on 1.2 mm thick 590DP produced by a steel material supplier as an example, and the following steps are adopted.

[0014] (1) The sample to be tested is processed into a rectangular wide strip specimen. The size of the wide strip specimen can be any size as long as the middle of the specimen can be uniformly deformed and the uniformly deformed area can be punched out into a tensile specimen. The specific length and width of the specimen can be adjusted in combination with the shape of the chuck of the tensile testing machine, that is, the width of the specimen must be greater than the width of the punched tensile specimen after pre-stretching, and the length of the specimen must be such that the uniformly deformed area during the pre-stretching process covers the stress area of ​​the subsequent punched specimen, preferably covering the clamping end. In this embodiment, the width of the wide strip specimen is 40 mm and the length is 400 mm.

[0015] (2) The wide strip specimen is stretched on a tensile testing machine until it breaks, and the maximum uniform deformation A that it can withstand is determined to be 14.32%.

[0016] (3) Take a number of wide and long strip specimens and apply different degrees of pre-deformation in the selection range from 0% to (A-2)% to obtain pre-deformed specimens; the interval gradient of the pre-deformation can be equal or unequal, as long as the deformation at each location in the deformation area is uniform and equal; it is best to repeat the test three or more times for each pre-deformation. Figure 1 As shown, this embodiment selects 7 different pre-deformations of 0%, 1%, 3%, 5%, 7%, 9%, and 12% in the range of 0% to 12.32%, and each pre-deformation is subjected to the following three repeated tests. Therefore, this embodiment takes 21 wide and long strip specimens and conducts a total of 21 tests.

[0017] (4) Using the same blanking gap as the production site, punch each pre-deformed specimen into a standard tensile specimen, such as Figure 2 As shown, in actual production, the blanking gap is generally 10% to 15% of the material thickness, which can be adjusted according to actual conditions. In this embodiment, a gap of 0.1 times the material thickness is used for blanking, and the gap is 0.12mm.

[0018] (5) After punching, each standard tensile specimen is stretched directly without grinding the edges until it breaks and fails. Figure 3 shown.

[0019] (6) Measure the uniform elongation value A of each tensile specimen g And the total elongation value A0, and calculate the unstable elongation PUE = A0-A g ; The average value of the repeated tests for each pre-deformation amount is used as a material performance evaluation index; the measurement and calculation results of 21 tests in this embodiment are shown in Table 1; Table 1: Measurement and calculation results of Example 1

[0020] In Table 1, the average PUE is the average of the PUEs obtained from three tests.

[0021] (7) According to the measurement in step (6), the instability elongation PUE values ​​under different pre-deformation are calculated and sorted, and the average value of three tests is taken as the final instability elongation of the material, see Table 1; the relationship curve between pre-deformation and PUE is plotted to obtain the relationship curve of the influence of pre-deformation on edge forming performance, such as Figure 4 shown.

[0022] Example 2: The evaluation method for the effect of pre-deformation on the edge forming performance of high-strength steel is based on 980QP with a thickness of 1.0 mm produced by a steel material supplier, and the following steps are adopted.

[0023] (1) The sample to be tested is processed into a rectangular wide strip specimen. The size of the wide strip specimen can be any size as long as the middle of the specimen can be uniformly deformed and the uniformly deformed area can be punched out into a tensile specimen. The specific length and width of the specimen can be adjusted in combination with the shape of the chuck of the tensile testing machine, that is, the width of the specimen must be greater than the width of the punched tensile specimen after pre-stretching, and the length of the specimen must be such that the uniformly deformed area during the pre-stretching process covers the stress area of ​​the subsequent punched specimen, preferably covering the clamping end. In this embodiment, the width of the wide strip specimen is 40 mm and the length is 400 mm.

[0024] (2) The wide strip specimen is stretched on a tensile testing machine until it breaks, and the maximum uniform deformation A that it can withstand is determined to be 13.49%.

[0025] (3) Take a number of wide and long strip specimens and apply different degrees of pre-deformation in the selection range from 0% to (A-2)% to obtain pre-deformed specimens; the interval gradient of the pre-deformation can be equal or unequal, as long as the deformation at each location in the deformation area is uniform and equal; it is best to repeat the test three or more times for each pre-deformation. Figure 1 As shown, this embodiment selects 6 different pre-deformations of 0%, 2%, 4%, 6%, 8%, and 10% in the range of 0% to 11.49%, and each pre-deformation is subjected to the following three repeated tests. Therefore, this embodiment takes 18 wide and long strip specimens, and a total of 18 tests are conducted.

[0026] (4) Using the same blanking gap as the production site, punch each pre-deformed specimen into a standard tensile specimen, such as Figure 2 As shown, in actual production, the blanking gap is generally 10% to 15% of the material thickness, which can be adjusted according to actual conditions. In this embodiment, a gap of 0.1 times the material thickness is used for blanking, and the gap is 0.10 mm.

[0027] (5) After punching, each standard tensile specimen is stretched directly without grinding the edges until it breaks and fails. Figure 3 shown.

[0028] (6) Measure the uniform elongation value A of each tensile specimeng And the total elongation value A0, and calculate the unstable elongation PUE = A0-A g ; The average value of the repeated tests for each pre-deformation amount is used as a material performance evaluation index; the measurement and calculation results of 18 tests in this embodiment are shown in Table 2; Table 2: Measurement and calculation results of Example 2

[0029] In Table 2, the average PUE is the average of the PUEs obtained from three tests.

[0030] (7) According to the measurement in step (6), the instability elongation PUE values ​​under different pre-deformation are calculated and sorted, and the average value of three tests is taken as the final instability elongation of the material, see Table 2; the relationship curve between pre-deformation and PUE is plotted to obtain the relationship curve of the influence of pre-deformation on edge forming performance, such as Figure 5 shown.

Claims

1. A method for evaluating the effect of pre-deformation on the edge forming performance of high-strength steel, characterized in that: The method comprises the following steps: (1) processing the sample to be tested into a rectangular wide and long strip sample; (2) Stretch the wide and long strip specimen until it breaks and determine the maximum uniform deformation A it can withstand; (3) Take a number of wide and long strip specimens and apply different degrees of pre-deformation to each specimen to obtain pre-deformed specimens; (4) Punching each pre-deformed specimen into a standard tensile specimen; (5) Directly stretch each standard tensile specimen until it breaks and fails; (6) Measure the uniform elongation value A of each tensile specimen g And the total elongation value A0, the instability elongation PUE of each broken specimen is calculated to be A0-A g ; The instability elongation is used as an evaluation index of the edge forming performance of high-strength steel.

2. The method for evaluating the effect of pre-deformation on the edge forming performance of high-strength steel according to claim 1, characterized in that: In the step (3), the selection range of the pre-deformation amount is 0% to (A-2)%.

3. The method for evaluating the effect of pre-deformation on the edge forming performance of high-strength steel according to claim 2, characterized in that: The pre-deformation amount is selected gradiently within a selection range.

4. The method for evaluating the effect of pre-deformation on the edge forming performance of high-strength steel according to claim 1, characterized in that: In the step (4), the blanking is performed using the same blanking gap as the trimming process at the production site.

5. A method for evaluating the effect of pre-deformation on edge forming performance of high-strength steel according to any one of claims 1 to 4, characterized in that: The method also includes the following steps: calculating and sorting out the instability elongation PUE values ​​under different pre-deformations, drawing a relationship curve between the pre-deformation and PUE, and obtaining a relationship curve of the influence of the pre-deformation on the edge forming performance.

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