Method for judging correlation between shear edge crack sensitivity and elongation flanging performance of high-strength steel

Abstract

The invention relates to the technical field of steel plate blanking quality detection. In particular to a method for judging the correlation between the shear edge crack sensitivity and the elongation flanging performance of high-strength steel. The method comprises the following steps: step 1, acquiring a crack sensitivity coefficient K at different included angles with the rolling direction of a steel plate; step 2, obtaining an included angle between a part side line at a position where the elongation flanging cracks or cracks risk and the rolling direction of the steel plate, wherein the included angle is a test included angle; comparing the test included angle with the crack sensitivity coefficient K under the included angle corresponding to the step 1, and judging whether the elongation flanging performance is related to the crack sensitivity of the shear edge of the high-strength steel or not; by designing the single-cycle tensile samples with different included angles, the shear edge crack sensitivity of the high-strength steel in different directions can be accurately evaluated; the included angle between the sideline of the cracking position of the part and the rolling direction can be measured; and judging whether the part crack is related to the shear edge crack sensitivity of the high-strength steel or not.

Description

Technical Field

[0001] The invention relates to the technical field of steel plate blanking quality detection; in particular, it relates to a method for determining the correlation between shear edge crack sensitivity and elongation and flanging performance of high-strength steel. Background Art

[0002] With the increasing development of lightweight automobiles, the application of high-strength steel is becoming more and more common.

[0003] However, in the application process of high-strength steel, elongation-type flange cracking often occurs. This is related to both the shear quality of the high-strength steel edge and the shear edge crack sensitivity of the high-strength steel itself.

[0004] The solution to the problem of cracking during shearing of elongation flanges mainly depends on the subjective judgment and personal experience of the mold debugging personnel, and the debugging effects vary greatly.

[0005] Existing patent CN116298170A discloses a method for predicting the quality of the blanking boundary of a steel plate under different blanking gaps. Multiple groups of specimens with different blanking gaps are blanked and tensile tests are performed using a tensile testing machine. The quality of the blanking boundary of the steel plate is predicted based on the maximum tensile force applied to the specimen when it breaks.

[0006] This method mainly focuses on the relationship between the blanking gap and the blanking quality, and does not clearly disclose the technical content for solving the above technical problems.

[0007] Therefore, in order to improve or solve at least one of the above technical problems, a method is needed to quickly determine the correlation between shear edge cracks and elongation flange cracking in high-strength steel. Summary of the Invention

[0008] The object of the present invention is to provide a method for determining whether the shear edge crack sensitivity of high-strength steel is correlated with the elongation and flanging performance.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel, the method comprising the following steps:

[0011] Step 1: Obtain the crack sensitivity coefficient K at different angles with the rolling direction of the steel plate;

[0012] Step 2: Obtain the angle between the edge of the part at the location where the elongation flange cracks or has a risk of cracking and the rolling direction of the steel plate. This angle is the test angle; and based on the comparison of the test angle with the crack sensitivity coefficient K at the corresponding angle in step 1, determine whether the elongation flange performance is related to the shear edge crack sensitivity of high-strength steel.

[0013] The test method of the crack sensitivity coefficient K comprises the following steps:

[0014] S1: multiple groups of test samples with different angles between shearing process and steel plate rolling direction; each group of test samples includes at least one single standard sample and one single shear sample;

[0015] S2: Perform a uniaxial tensile test on the single shear specimen to obtain the elongation Ac at the onset of local necking or fracture of the single shear specimen;

[0016] S3: Perform a uniaxial tensile test on a single standard specimen to obtain the elongation A during local necking;

[0017] S4: Calculate the crack sensitivity coefficient K of the same group of test samples; K = Ac / A.

[0018] In step S1, multiple groups of test samples are sheared at different angles to the rolling direction of the steel plate; each group of test samples includes at least two single test samples; half of each group of test samples are selected to obtain single standard samples by milling and grinding burrs; the remaining half of the test samples are single shear samples.

[0019] In the step S4, Ac is the average value of the Ac values of each monomer shear sample in the same group of samples to be tested; A is the average value of the A values of each monomer standard sample in the same group of samples to be tested.

[0020] The shearing process in S1 is required to be achieved by a trimming die, and the gap between the trimming dies is adjusted to ensure that the shearing edge quality of the single test sample is consistent with the shearing edge quality of the steel plate during actual production.

[0021] In step S2, if the single shear specimen does not show local necking, that is, the tensile fracture extends from the shear edge to the center, only the elongation at the beginning of the fracture of the single shear specimen can be obtained, and it can be determined that the high-strength steel in this direction is sensitive to shear edge cracks.

[0022] The standard for determining whether the elongation flanging performance is related to the shear edge crack sensitivity of high-strength steel in step 2 is: when the crack sensitivity coefficient K corresponding to the test angle is not less than 0.9, it is determined that at the test angle, the edge cracking during the elongation flanging is not related to the shear edge crack sensitivity of high-strength steel; when the crack sensitivity coefficient K corresponding to the test angle is less than 0.9, it is determined that at the test angle, the edge cracking during the elongation flanging is related to the shear edge crack sensitivity of high-strength steel.

[0023] In the step S1, the shearing process is performed at different angles to the rolling direction of the steel plate, and the different angles are in the range of 0°-90°.

[0024] In step S1, the shearing process is performed at different angles to the rolling direction of the steel plate, where the different angles are selected as 0°, 45° and 90°.

[0025] In step 2, the angle between the edge line of the elongated flanging part and the rolling direction of the steel plate is obtained through stamping and forming simulation.

[0026] The advantages of the present invention are:

[0027] The invention discloses a method for determining the correlation between shear edge crack sensitivity and elongation and flanging performance of high-strength steel.

[0028] The present invention can accurately evaluate the shear edge crack sensitivity of high-strength steel in different directions by designing single-cycle tensile specimens with different angles.

[0029] The present invention can also determine whether the cracking of the part is related to the shear edge crack sensitivity of high-strength steel by measuring the angle between the edge line of the cracking position of the part and the rolling direction. The present invention can not only accurately evaluate the shear edge crack sensitivity of high-strength steel in different directions, but also provide specific guidance for solving the cracking problem in the elongation flanging forming of high-strength steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following is a brief description of the contents of the drawings in the specification of the present invention:

[0031] Figure 1 Schematic diagram of uniaxial tensile specimens at different angles along the rolling direction;

[0032] Figure 2 Schematic diagram of the starting point of local necking on the stress-strain curve;

[0033] Figure 3 A tensile fracture of a milling specimen provided by an embodiment of the present invention;

[0034] Figure 4 The tensile fracture of the shearing specimen provided in the embodiment of the present invention;

[0035] Figure 5 Stress-strain curves of milling and shearing samples provided by the embodiments of the present invention;

[0036] Figure 6 Typical parts with elongation-type flanging cracking and the angle between the part edge and the rolling direction provided in the embodiments of the present invention. DETAILED DESCRIPTION

[0037] The specific implementation of the present invention will be further explained in detail below by describing the best embodiment with reference to the accompanying drawings.

[0038] A method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel, the method comprising the following steps:

[0039] Step 1: Obtain the crack sensitivity coefficient K at different angles with the rolling direction of the steel plate;

[0040] Step 2: Obtain the angle between the edge of the part at the location where the elongation flange cracks or has a risk of cracking and the rolling direction of the steel plate. This angle is the test angle; and based on the comparison of the test angle with the crack sensitivity coefficient K at the corresponding angle in step 1, determine whether the elongation flange performance is related to the shear edge crack sensitivity of high-strength steel.

[0041] The present invention can accurately evaluate the shear edge crack sensitivity of high-strength steel in different directions by designing single-cycle tensile specimens with different angles.

[0042] The present invention can also determine whether the cracking of the part is related to the shear edge crack sensitivity of high-strength steel by measuring the angle between the edge line of the cracking position of the part and the rolling direction. The present invention can not only accurately evaluate the shear edge crack sensitivity of high-strength steel in different directions, but also provide specific guidance for solving the cracking problem in the elongation flanging forming of high-strength steel.

[0043] The determination method disclosed above in the present invention mainly comprises two main steps:

[0044] Step 1: Obtain the crack sensitivity coefficient K at different angles with the rolling direction of the steel plate;

[0045] The first step is sample preparation: multiple groups of test samples are cut at different angles to the rolling direction of the steel plate.

[0046] These angles usually include 0°, 45° and 90°, but other angles (such as 15°, 30°, 60°, 75°, etc.) can also be selected as needed.

[0047] Preparation of standard specimens: Half of each group of samples to be tested are selected and milled to obtain single standard specimens. These standard specimens are used to provide reference data to eliminate variables that may be introduced during the specimen processing process.

[0048] Shear specimen preparation: The remaining half of the specimen to be tested retains its shear edge and serves as a single shear specimen.

[0049] Uniaxial tensile test

[0050] Shear specimen test: Perform a uniaxial tensile test on a single shear specimen and record the elongation Ac at the onset of local necking or fracture of the specimen.

[0051] Standard specimen test: Perform a uniaxial tensile test on a single standard specimen and record the elongation A during local necking.

[0052] Special case handling: If the tensile fracture of a single shear specimen extends from the shear edge to the center without local necking, only the elongation at the beginning of the fracture of the single shear specimen can be obtained. At this time, it can be determined that the high-strength steel in this direction is sensitive to shear edge cracks.

[0053] Crack Sensitivity Calculation: Calculate the crack sensitivity coefficient K = Ac / A. This coefficient is used to quantify the shear edge crack sensitivity of high-strength steel at different shear angles.

[0054] Step 2: Obtain the test angle and determine the correlation;

[0055] Acquisition of test angle; actual part measurement: Through stamping, forming simulation or other methods, the angle between the edge of the part at the location where elongation flange cracking or cracking risk occurs and the rolling direction of the steel plate is obtained; this angle is called the test angle.

[0056] Correlation determination

[0057] Comparative analysis: Compare the test angle with the crack sensitivity coefficient K at the corresponding angle in step 1.

[0058] Judgment criteria: If the crack sensitivity coefficient K corresponding to the test angle is ≥ 0.9, it is determined that at this test angle, edge cracking during elongation flanging has nothing to do with the shear edge crack sensitivity of high-strength steel.

[0059] If the crack sensitivity coefficient K corresponding to the test angle is less than 0.9, it is determined that at this test angle, edge cracking during elongation flanging is related to the shear edge crack sensitivity of high-strength steel.

[0060] Advantages of the above determination method:

[0061] Accuracy: By designing uniaxial tensile specimens with different angles, the shear edge crack sensitivity of high-strength steel in different directions can be accurately evaluated.

[0062] Practicality: Combined with the geometric characteristics of actual parts, it is possible to determine whether the cracking of parts is related to the shear edge crack sensitivity of high-strength steel, providing specific guidance for solving problems in actual production.

[0063] Flexibility: Different angles can be selected according to actual needs to adapt to different high-strength steel materials and part shapes.

[0064] Economical: By optimizing the test plan, the test workload and cost can be reduced while ensuring the evaluation accuracy.

[0065] Furthermore, the test method of the crack sensitivity coefficient K in the present invention includes the following steps:

[0066] S1: multiple groups of test samples with different angles between shearing process and steel plate rolling direction; each group of test samples includes at least one single standard sample and one single shear sample;

[0067] S2: Perform a uniaxial tensile test on the single shear specimen to obtain the elongation Ac at the onset of local necking or fracture of the single shear specimen;

[0068] S3: Perform a uniaxial tensile test on a single standard specimen to obtain the elongation A during local necking;

[0069] S4: Calculate the crack sensitivity coefficient K of the same group of test samples; K = Ac / A.

[0070] Based on the disclosure of the above test method, the determination of the crack sensitivity coefficient K can be achieved.

[0071] specific:

[0072] Step S1: shearing multiple groups of test samples at different angles to the rolling direction of the steel plate;

[0073] Shearing: Multiple sets of test specimens are sheared at different angles to the rolling direction of the steel plate; these angles typically include 0°, 45°, and 90°, but other angles (such as 15°, 30°, 60°, 75°, etc.) can also be selected as needed.

[0074] Specimen type: Each group of test specimens shall include at least one single standard specimen and one single shear specimen.

[0075] The single standard specimens were obtained by milling the edges and grinding the burrs, while the single shear specimens kept their shear edges.

[0076] Step S2: Perform uniaxial tensile test on the single shear specimen

[0077] Tensile test: Perform a uniaxial tensile test on a single shear specimen and record the elongation Ac at the onset of local necking or fracture of the specimen.

[0078] Special case handling: If the tensile fracture of a single shear specimen extends from the shear edge to the center without local necking, only the elongation at the beginning of the fracture of the single shear specimen can be obtained. At this time, it can be determined that the high-strength steel in this direction is sensitive to shear edge cracks.

[0079] Step S3: Perform uniaxial tensile test on single standard specimen

[0080] Tensile test: Perform a uniaxial tensile test on a single standard specimen and record the elongation A during local necking.

[0081] Step S4: Calculating the crack sensitivity coefficient K of the same group of test samples;

[0082] Average value calculation: For each group of samples to be tested, take the average value of the Ac values of each monomer shear specimen and the average value of the A values of each monomer standard specimen.

[0083] Crack sensitivity coefficient calculation: Calculate the crack sensitivity coefficient K = Ac / A; this coefficient is used to quantify the shear edge crack sensitivity of high-strength steel at different angles.

[0084] Furthermore, in step S1 of the present invention, multiple groups of test samples are sheared at different angles to the rolling direction of the steel plate; each group of test samples includes at least two single test samples; half of each group of test samples are selected by milling and grinding burrs to obtain single standard samples; the remaining half of the test samples are single shear samples; based on the above operations, the calculation of the crack sensitivity coefficient K can be guaranteed to be more accurate and reliable.

[0085] In the present invention, multiple groups of test samples are sheared at different angles to the rolling direction of the steel plate; these angles usually include 0°, 45° and 90°, but other angles (such as 15°, 30°, 60°, 75° and 90°, etc.) can also be selected as needed.

[0086] Each group of test samples includes at least two individual test samples, which means there are at least two specimens in each group for subsequent different processing and testing.

[0087] Half of each set of test specimens were milled and deburred to create single standard specimens. These standard specimens provide reference data to eliminate variables that may be introduced during specimen processing. The remaining half of each set of test specimens were kept on their sheared edges as single shear specimens. These shear specimens are used to directly evaluate the shear edge crack susceptibility of high-strength steel.

[0088] Specific operation process

[0089] Material selection: Select high-strength steel materials and ensure that their rolling direction is clear.

[0090] Shearing: Use a trimming die to shear multiple groups of test specimens at different angles to the rolling direction of the steel plate; each group includes at least two individual test specimens.

[0091] Assignment of specimens: Half of the specimens from each group to be tested are selected, and the single standard specimens are obtained by milling the edges and grinding the burrs; the remaining half retains its shear edge and is used as a single shear specimen.

[0092] Assume that we select three angles of 0°, 45° and 90° for testing, and the number of test specimens in each group is 6 (3 standard specimens and 3 shear specimens in each group).

[0093] 0° direction: standard specimens: 3; shear specimens: 3.

[0094] 45° direction: standard specimens: 3; shear specimens: 3.

[0095] 90° direction: standard specimens: 3; shear specimens: 3.

[0096] The present invention requires trimming die adjustment: ensuring that the trimming die gap is adjusted so that the trimming edge quality of the single test sample is consistent with the trimming edge quality of the steel plate during actual production, thereby reducing experimental errors.

[0097] Furthermore, in step S4 of the present invention, Ac is the average value of the Ac values of each monomer shear specimen in the same group of samples to be tested; A is the average value of the A values of each monomer standard specimen in the same group of samples to be tested; the Ac value of each monomer shear specimen in the same group of samples to be tested is collected; and the A value of each monomer standard specimen in the same group of samples to be tested is collected; in addition, when calculating the above data, it is necessary to ensure that all data come from the same group of samples to be tested to ensure the accuracy of the calculation.

[0098] In addition, when a data value differs greatly from other values, it is necessary to check and process the outliers before calculating the average value to avoid excessive impact on the results.

[0099] Through the above steps, the calculation of the crack sensitivity coefficient K can be ensured to be more accurate and reliable, providing a solid foundation for evaluating the shear edge crack sensitivity of high-strength steel.

[0100] This provides an accurate quantitative indicator for the subsequent determination of the correlation between the elongation and flanging performance and the shear edge crack sensitivity of high-strength steel.

[0101] Furthermore, in S1 of the present invention, the shearing process is required to be implemented by a trimming die, and the gap of the trimming die is adjusted to ensure that the shear edge quality of the single test sample is consistent with the shear edge quality of the steel plate during actual production; the shearing process is implemented by a trimming die, and the design and use of the trimming die can ensure that the shear edge quality of the sample is consistent with the shear edge quality of the steel plate during actual production; by adjusting the gap of the trimming die, the shear edge quality of the single test sample is consistent with the shear edge quality of the steel plate during actual production.

[0102] This step is crucial because the quality of the sheared edge directly affects the accuracy and reliability of subsequent test results.

[0103] Die selection: Choose a suitable trimming die to ensure that it can accurately adjust the gap.

[0104] Gap adjustment: According to the shearing process in actual production, the gap of the trimming die is accurately adjusted to ensure that the shear edge quality of the specimen is consistent with the actual production.

[0105] Ensure that each group of specimens is consistent in size, shape and processing conditions to reduce experimental errors.

[0106] Through the above-mentioned limitations, the present invention can ensure that subsequent uniaxial tensile tests and calculations of the crack sensitivity coefficient K are more accurate and reliable; this provides a solid foundation for evaluating the shear edge crack sensitivity of high-strength steel, while also ensuring that the experimental results are representative of actual production.

[0107] Furthermore, in step S2 of the present invention, if local necking does not occur in the single shear specimen, that is, when the tensile fracture extends from the shear edge to the center, only the elongation at the beginning of the fracture of the single shear specimen can be obtained, and it can be determined that the high-strength steel is sensitive to shear edge cracks in this direction; through this detailed step S2, it is possible to ensure that the sensitivity of high-strength steel to shear edge cracks in different directions is accurately identified in the uniaxial tensile test; this provides important data support for the subsequent calculation of the crack sensitivity coefficient K and the correlation determination of the elongation and flanging performance.

[0108] The tensile test process is as follows:

[0109] Test equipment: Use standard uniaxial tensile testing equipment, such as a universal testing machine.

[0110] Test steps:

[0111] Install the single shear specimen on the testing machine.

[0112] The test was carried out according to the standard tensile test procedure, and the stress-strain curve of the specimen was recorded during the tensile process.

[0113] Observe the deformation of the specimen during the stretching process, especially the local necking and fracture behavior.

[0114] Special Case Handling: No Localized Neck: If a single shear specimen exhibits no localized necking during tension, but instead exhibits a tensile fracture extending directly from the shear edge toward the center, this indicates that stress concentration at the shear edge leads to premature fracture. Recording the fracture elongation: In this case, only the elongation Ac at the onset of fracture of the single shear specimen is available. Based on this phenomenon, it can be directly determined that the high-strength steel in this direction is sensitive to shear edge cracking. This means that cracks are likely to form and propagate along the shear edge of the high-strength steel during tension in this direction, leading to premature fracture.

[0115] Specific operation process:

[0116] Install the specimen: Install the single shear specimen on the testing machine to ensure that the specimen does not slide or deflect during the test.

[0117] Start the test: Start the testing machine and conduct the test at the set tensile speed.

[0118] Observe and record:

[0119] Observe the deformation of the specimen during the stretching process, especially the stress concentration at the shear edge.

[0120] Record the stress-strain curve of the sample during the stretching process, especially the elongation Ac at fracture.

[0121] Furthermore, the standard for determining whether the elongation flanging performance is related to the shear edge crack sensitivity of high-strength steel in step 2 of the present invention is: when the crack sensitivity coefficient K corresponding to the test angle is not less than 0.9, it is determined that at the test angle, the edge cracking during the elongation flanging is not related to the shear edge crack sensitivity of high-strength steel; when the crack sensitivity coefficient K corresponding to the test angle is less than 0.9, it is determined that at the test angle, the edge cracking during the elongation flanging is related to the shear edge crack sensitivity of high-strength steel.

[0122] The core content of the judgment criteria;

[0123] The relationship between the test angle and the crack sensitivity coefficient K;

[0124] Test angle: This is the angle between the edge of the part where the elongated flange cracks or has the risk of cracking in the actual part and the rolling direction of the steel plate.

[0125] Crack sensitivity coefficient K: This is calculated in step 1 and is used to quantify the shear edge crack sensitivity of high-strength steel at different angles.

[0126] Decision rules

[0127] When K ≥ 0.9:

[0128] At this test angle, edge cracking during elongation flanging has nothing to do with the shear edge crack sensitivity of high-strength steel.

[0129] This means that in this direction, the shear edge crack sensitivity of high-strength steel has little effect on the cracking during elongation flanging, and the cracking may be related to other factors (such as material uniformity, processing technology, etc.).

[0130] When K<0.9:

[0131] At this test angle, edge cracking during elongation flanging is related to the shear edge crack sensitivity of high-strength steel.

[0132] This indicates that the shear edge crack sensitivity of high-strength steel in this direction is an important factor leading to edge cracking during elongation flanging.

[0133] Detailed description of the judgment criteria

[0134] Calculation of crack sensitivity coefficient K

[0135] K is calculated from the elongation of the monomer shear specimen and the monomer standard specimen in step 1. The specific formula is: K = Ac / A; where: Ac is the elongation of the monomer shear specimen at the beginning of local necking or fracture; A is the elongation of the monomer standard specimen at the beginning of local necking.

[0136] Acquisition of the test angle: The angle between the edge of the part at the location where elongation flanging cracks or cracking risks occur in the actual part and the rolling direction of the steel plate is obtained through stamping, forming simulation or other methods; this angle is called the test angle and is a key parameter for determining the correlation between elongation flanging performance and crack sensitivity.

[0137] The comparative analysis compares the test angle with the crack sensitivity coefficient K at the corresponding angle in step 1; through the comparison, it is determined whether the shear edge crack sensitivity of high-strength steel at the test angle has a significant effect on edge cracking during elongation flanging.

[0138] By quantifying the crack sensitivity coefficient K, the shear edge crack sensitivity of high-strength steel in different directions can be accurately evaluated.

[0139] 0.9 serves as a clear threshold and provides a clear standard for judgment.

[0140] This judgment standard, combined with the geometric characteristics of actual parts, can be directly applied to quality control and process optimization in actual production.

[0141] By determining whether cracking is related to shear edge crack sensitivity, targeted measures (such as adjusting the shearing process, optimizing part design, etc.) can be taken to reduce the cracking problem.

[0142] Through clear judgment criteria, unnecessary testing and analysis work is reduced and production efficiency is improved.

[0143] The example description is as follows:

[0144] Suppose that in actual production, a part cracks at the elongated flange position in the test angle of 45°.

[0145] Through the test in step 1, the crack sensitivity coefficient K in the 45° direction is obtained to be 0.85.

[0146] According to the judgment criteria:

[0147] Because K = 0.85 < 0.9, it is determined that the edge cracking during elongation flanging in the 45° direction is related to the shear edge crack sensitivity of high-strength steel.

[0148] This means that measures need to be taken to address the shear edge crack sensitivity in this direction, such as optimizing the shearing process or adjusting the part design to reduce the risk of cracking.

[0149] Furthermore, in step S1 of the present invention, the shearing process has different angles with the rolling direction of the steel plate, and the different angles here range from 0° to 90°; this indicates that when performing the shearing process, any angle between 0° and 90° with the rolling direction of the steel plate can be selected to process the sample.

[0150] 0° means that the processing direction of the sample is completely consistent with the rolling direction of the steel plate, 90° means that the processing direction of the sample is completely perpendicular to the rolling direction of the steel plate, and other angles between 0° and 90° mean that the processing direction of the sample forms a certain angle with the rolling direction of the steel plate.

[0151] The reason for choosing the range of 0°-90° is that this range can cover various tensile directions that high-strength steel may encounter in actual applications. By selecting different angles within this range for testing, the shear edge crack sensitivity of high-strength steel in different directions can be comprehensively evaluated, providing more comprehensive data support for subsequent judgments.

[0152] In step S1 of the present invention, the shearing process is performed at different angles with the rolling direction of the steel plate, where the different angles are selected as 0°, 45° and 90°; in actual operation, these three specific angles of 0°, 45° and 90° are usually selected to process the sample.

[0153] 0°: This angle can be used to evaluate the shear edge crack sensitivity of high-strength steel in the rolling direction. In actual production, the processing direction of many parts may be consistent with the rolling direction of the steel plate. Therefore, the test results at this angle are important for assessing the cracking risk of these parts.

[0154] 45°: This angle can be used to evaluate the shear edge crack sensitivity of high-strength steel at a 45° angle to the rolling direction. 45° is an intermediate angle that can reflect the performance characteristics of high-strength steel during oblique processing. In the processing of some complex parts, processing at a certain angle to the rolling direction may be involved, and the test results at a 45° angle can provide a reference for these situations.

[0155] 90°: This angle can be used to evaluate the sensitivity of high-strength steel to shear edge cracks perpendicular to the rolling direction. In actual production, some parts may be processed perpendicular to the rolling direction of the steel plate. The test results at a 90° angle are also important for evaluating the cracking risk of these parts.

[0156] The reason for choosing these three angles is that they are representative and can better reflect the performance differences of high-strength steel in different directions. Through the tests at these three angles, the changing trend of shear edge crack sensitivity of high-strength steel in different directions can be preliminarily judged, providing key data points for subsequent judgments.

[0157] Moreover, the tests at these three angles are relatively simple and easy to perform, which can reduce the experimental workload to a certain extent while meeting the needs of most practical applications.

[0158] Furthermore, in step 2 described in the present invention, the angle between the edge line of the elongated flange part and the rolling direction of the steel plate is obtained through stamping and forming simulation; in the present invention, the angle between the edge line of the part manufactured by the stamping process and the rolling direction of the steel plate can be obtained by measuring the actual part.

[0159] Forming simulation is a technology that uses computers to simulate the metal forming process. It can predict the deformation, stress distribution, cracking risk, etc. of parts during the processing process; it runs simulations through forming simulation software to simulate the forming process of parts; and extracts the angle between the edge line of the elongated flange part and the rolling direction of the steel plate from the simulation results.

[0160] specific:

[0161] The invention discloses a method for determining the correlation between shear edge crack sensitivity and elongation and flanging performance of high-strength steel.

[0162] The present invention provides a method for considering the anisotropy and shear edge crack sensitivity of high-strength steel, and determining the correlation between the shear edge crack sensitivity of high-strength steel and the elongation and flanging performance;

[0163] Here are the steps:

[0164] 1) Take the sample in the uniaxial tensile strain state and conduct a uniaxial tensile test.

[0165] 2) Shear uniaxial tensile specimens at angles of 0°, 45°, and 90° to the rolling direction of the steel plate. Adjust the gap between the trimming dies to ensure that the shear edge quality of the specimens is consistent with the shear edge quality of the steel plate during actual production. Perform a uniaxial tensile test on the specimens to obtain the elongation Ac at the onset of local necking or fracture of the specimens.

[0166] 3) Process uniaxial tensile specimens with angles of 0°, 45°, and 90° to the rolling direction of the steel plate, mill the edges of the specimens and grind off the burrs to obtain standard specimens, and then perform uniaxial tensile tests on the standard specimens to obtain the elongation A during local necking;

[0167] 4) The crack sensitivity coefficient K = Ac / A, which is the ratio of the elongation Ac of the sheared specimen with the same rolling direction as the steel plate when local necking or fracture begins to occur to the elongation A of the standard specimen when local necking occurs, is used as a parameter to determine the crack sensitivity of the shear edge of the steel plate at 0°, 45°, and 90° to the rolling direction of the steel plate;

[0168] 5) Punch or perform forming simulation on the blank with the rolling direction mark engraved on the surface to obtain the angle between the edge line of the part at the position where elongation-related flange cracking or cracking risk occurs and the rolling direction mark line. Compare this angle with the previously obtained shear edge crack sensitivity test results of the steel plate at 0°, 45°, and 90° to the rolling direction of the steel plate to determine whether elongation-related flange cracking is related to the shear edge crack sensitivity of high-strength steel plates.

[0169] In the above steps, the uniaxial tensile strain state specimens include single standard specimens and single shear specimens.

[0170] In the steps 2) and 3), the uniaxial tensile specimens with angles of 0°, 45°, and 90° to the rolling direction of the steel plate can be optimized to uniaxial tensile specimens with angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90° to the rolling direction of the steel plate.

[0171] In step 2), when the sheared sample is subjected to a uniaxial tensile test, if the sample does not show local necking stress-strain curve, i.e., an abnormal decrease, or the tensile fracture extends from the shear edge to the center, only the elongation at the beginning of the sample fracture can be obtained, and it can be determined that the high-strength steel in this direction is sensitive to shear edge cracks.

[0172] In the steps 2) and 3), in order to accurately determine the sensitive range of the steel plate to shear edge cracks, the uniaxial tensile specimens with angles of 0°, 45°, and 90° to the rolling direction of the steel plate are optimized to uniaxial tensile specimens with angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90° to the rolling direction of the steel plate, but the workload of specimen processing and testing is increased.

[0173] To this end, the present invention proposes 30 possible test schemes to facilitate the economical and rapid completion of the work of determining the sensitive range of steel plates to shear edge cracks.

[0174] The test method is explained using Scheme 1 and Scheme 2, which have the least amount of tests.

[0175] Priority is given to conducting uniaxial tensile tests on shear specimens in the 0°, 45°, and 90° directions. Whether the elongation of the specimens in the three directions is significantly weakened indicates that the steel plate is insensitive to shear edge cracks in the 0° to 90° direction; if the elongation of the specimens in the three directions is significantly weakened, it indicates that the steel plate is sensitive to shear edge cracks in the 0°-90° direction.

[0176] Table 1 Test scheme for the sensitivity and range of steel plate to shear edge cracks

[0177]

[0178]

[0179] In the above step 4), the crack sensitivity of the material is evaluated by the formula K=Ac / A. If the shear crack sensitivity coefficient K is less than 0.9, it is determined that the steel plate is sensitive to shear edge cracks.

[0180] In the above step 5), the angle between the edge line of the elongation flanging part and the rolling direction is obtained through stamping and forming simulation, and the angle is compared with the sensitivity or range of the steel plate to shear edge cracks. It can be determined whether the forming performance of the elongation flanging is related to the shear edge crack sensitivity of high-strength steel, thereby providing a reference for determining a solution to the problem of shear edge cracking of elongation flanging.

[0181] Example 1:

[0182] See also Figure 1-4 , the present invention discloses a method for determining the correlation between shear edge crack sensitivity and elongation flanging performance of high-strength steel;

[0183] The determination method includes the following steps:

[0184] 1) Multiple groups of test specimens with different angles between shearing and rolling direction; each group of test specimens includes at least two individual test specimens; half of each group of test specimens are selected by milling and grinding burrs to obtain individual standard specimens; the remaining half of the test specimens are individual shear specimens;

[0185] 2) Perform a uniaxial tensile test on a single shear specimen to obtain the elongation Ac at the onset of local necking or fracture of the specimen. If no local necking occurs, the stress-strain curve shows an abnormal drop, or the tensile fracture extends from the shear edge to the center, it is determined that the high-strength steel is sensitive to shear edge cracks in this direction, and the range of the steel plate's sensitivity to shear edge cracks is then determined.

[0186] 3) Perform a uniaxial tensile test on a single standard specimen to obtain the elongation A during local necking;

[0187] 4) When the rolling direction is the same and the ratio of the elongation Ac of the shear processed sample to the elongation A of the standard sample is less than 0.9, the steel plate is determined to be sensitive to shear edge cracks.

[0188] 5) Obtain the angle between the edge of the part at the location where the elongation flange cracks or has the risk of cracking and the rolling direction mark line, and compare the angle with the test results of the steel plate's sensitivity to shear edge cracks to determine whether the elongation flange performance is related to the shear edge crack sensitivity of high-strength steel.

[0189] Example 2:

[0190] A high-strength steel part that cracked during elongation flanging forming was taken as an example.

[0191] 1) Select a low-alloy high-strength steel plate with a thickness of 1.8 mm. First, shear three groups of uniaxial tensile specimens at angles of 0°, 45°, and 90° to the rolling direction of the steel plate, with each group containing six uniaxial tensile specimens. Take three uniaxial tensile specimens at angles of 0°, 45°, and 90° to the rolling direction of the steel plate, mill the edges of the specimens, and grind off the burrs to obtain single standard specimens. The remaining specimens are single shear specimens.

[0192] 2) Uniaxial tensile tests were conducted on single shear specimens at angles of 0°, 45°, and 90° to the rolling direction of the steel plate. The elongation of the single shear specimens at local necking in the 0° and 45° directions was 21.0% and 25.6%, respectively. The single shear specimen at 90° showed no local necking, and the stress-strain curve showed an abnormal decrease. The tensile fracture extended from the shear edge to the center, indicating that the shear edge of the steel plate is sensitive to cracks at an angle of 90° to the rolling direction of the steel plate.

[0193] 3) Uniaxial tensile tests were carried out on single standard specimens at angles of 0°, 45°, and 90° to the rolling direction of the steel plate. The elongations of the single standard specimens during local necking at 0°, 45°, and 90° directions were 20.9%, 25.1%, and 19.2%, respectively.

[0194] 4) The formula K = Ac / A is used to calculate the shear crack sensitivity coefficient of the steel plate in the directions of 0°, 45°, and 90° to the rolling direction of the steel plate. The shear crack sensitivity coefficient K of the steel plate in the directions of 0° and 45° is greater than 1, while the shear crack sensitivity coefficient K of the steel plate in the direction of 90° is K = 0.71 < 0.9, which indicates that the steel plate in the direction of 90° is sensitive to shear cracks;

[0195] Table 2 Shear crack sensitivity coefficients of steel plates at 0°, 45°, and 90° directions

[0196]

[0197] Using simulation analysis and experiments, the crack position of a high-strength steel part that cracked during elongation flanging was measured. The angle between the part edge and the rolling direction was approximately 10°. Since the steel plate is not sensitive to shear edge cracks in the direction of 0° to 45°, it was determined that the edge cracking of the part during elongation flanging has nothing to do with the sensitivity of high-strength steel to shear edge cracks.

[0198] During mold debugging, shear edge grinding, laser blanking and other methods were used on site, but the problem of edge cracking during the part's elongation and flanging was not significantly improved. Finally, the edge cracking problem of the part was solved by changing the forming process from pressing + flanging to drawing + trimming.

[0199] The method provided by the present invention for testing the shear edge crack sensitivity and elongation flanging forming performance of high-strength steel plates mainly consists of two parts. One part is a testing method that takes into account the anisotropy of high-strength steel and the shear edge crack sensitivity. The other part is based on the angle between the edge line with high cracking risk or cracking risk and the rolling direction of the steel plate during elongation flanging forming of the part, and compares the test results of the shear edge crack sensitivity of high-strength steel to determine the correlation between the elongation flanging performance and the shear edge crack sensitivity of high-strength steel, providing a more detailed and feasible solution for analyzing and solving the problem of shear edge cracking of elongation flanging.

[0200] Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, they are all within the scope of protection of the present invention.

Claims

1. A method for determining the correlation between shear edge crack sensitivity and elongation flanging performance of high-strength steel, characterized in that: The determination method comprises the following steps: Step 1: Obtain the crack sensitivity coefficient K at different angles with the rolling direction of the steel plate; Step 2: Obtain the angle between the edge of the part at the location where the elongation flange cracks or has a risk of cracking and the rolling direction of the steel plate. This angle is the test angle; and based on the comparison of the test angle with the crack sensitivity coefficient K at the corresponding angle in step 1, determine whether the elongation flange performance is related to the shear edge crack sensitivity of high-strength steel.

2. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 1, characterized in that: The test method of the crack sensitivity coefficient K comprises the following steps: S1: multiple groups of test samples with different angles between shearing process and steel plate rolling direction; each group of test samples includes at least one single standard sample and one single shear sample; S2: Perform a uniaxial tensile test on the single shear specimen to obtain the elongation Ac at the onset of local necking or fracture of the single shear specimen; S3: Perform a uniaxial tensile test on a single standard specimen to obtain the elongation A during local necking; S4: Calculate the crack sensitivity coefficient K of the same group of test samples; K = Ac / A.

3. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 2, characterized in that: In step S1, multiple groups of test samples are sheared at different angles to the rolling direction of the steel plate; each group of test samples includes at least two single test samples; half of each group of test samples are selected to obtain single standard samples by milling and grinding burrs; the remaining half of the test samples are single shear samples.

4. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 3, characterized in that: In the step S4, Ac is the average value of the Ac values of each monomer shear sample in the same group of samples to be tested; A is the average value of the A values of each monomer standard sample in the same group of samples to be tested.

5. A method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to any one of claims 2 to 4, characterized in that: The shearing process in S1 is required to be achieved by a trimming die, and the gap between the trimming dies is adjusted to ensure that the shearing edge quality of the single test sample is consistent with the shearing edge quality of the steel plate during actual production.

6. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 2, characterized in that: In step S2, if the single shear specimen does not show local necking, that is, the tensile fracture extends from the shear edge to the center, only the elongation at the beginning of the fracture of the single shear specimen can be obtained, and it can be determined that the high-strength steel in this direction is sensitive to shear edge cracks.

7. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 1, characterized in that: The criterion for determining whether the elongation flanging performance is related to the shear edge crack sensitivity of the high-strength steel in step 2 is: when the crack sensitivity coefficient K corresponding to the test angle is not less than 0.9, it is determined that at the test angle, edge cracking during elongation flanging forming is not related to the shear edge crack sensitivity of the high-strength steel; When the crack sensitivity coefficient K corresponding to the test angle is less than 0.9, it is determined that at this test angle, the edge cracking during elongation flanging is related to the shear edge crack sensitivity of high-strength steel.

8. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 2, characterized in that: In the step S1, the shearing process is performed at different angles to the rolling direction of the steel plate, and the different angles are in the range of 0°-90°.

9. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 8, characterized in that: In step S1, the shearing process is performed at different angles to the rolling direction of the steel plate, where the different angles are selected as 0°, 45° and 90°.

10. The method for determining the correlation between shear edge crack sensitivity and elongation-flanging performance of high-strength steel according to claim 1, characterized in that: In step 2, the angle between the edge line of the elongated flanging part and the rolling direction of the steel plate is obtained through stamping and forming simulation.

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