Method for testing cold bending properties of steel plates

Abstract

The present application discloses a method for testing the cold bending performance of steel plates. The method includes obtaining the thickness of the steel plate to be tested; classifying the steel plate to be tested according to a preset thickness classification standard based on the nominal thickness of the steel plate to be tested; preparing a cold-bending specimen according to a specimen preparation standard corresponding to the thickness classification of the steel plate to be tested for the steel plate to be tested classified according to the preset thickness classification standard; and performing a cold-bending performance test on the prepared cold-bending specimen to obtain an accurate cold-bending performance test result of the steel plate to be tested. The method for testing the cold-bending performance of steel plates in the present application provides a cold-bending specimen preparation standard of a corresponding width by refining the classification standard of the steel plate to prepare a cold-bending specimen to be tested of a width corresponding to the specimen thickness. This can more accurately detect the actual cold-bending performance of the steel plate, improve the accuracy of the cold-bending performance test result of the steel plate, and solve the problem that the cold-bending performance test result obtained according to the current testing method is too different from the actual cold-bending performance of the steel plate.

Description

Technical Field

[0001] The present application belongs to the field of material processing technology, and in particular relates to a method for testing the cold bending performance of a steel plate. Background Art

[0002] Cold bending performance is one of the most important process properties of steel plates. Using a steel plate bending machine to cold-bend steel plates is a common method for processing steel plates into components. However, cold bending performance generally decreases as the strength of the steel plate increases. Therefore, cold bending performance is often a difficulty in the development of high-strength steel products with a yield strength of 960 MPa and above.

[0003] While studying the cold bending performance of heat-treated high-strength steel plates, such as LG960QT and LG1100QT, the applicant discovered significant discrepancies between the cold bending test results conducted according to GB / T232-2010, "Methods for Testing Metallic Materials by Bend" (hereinafter referred to as "standard cold bending performance") and the actual cold bending performance experienced by users (hereinafter referred to as "actual cold bending performance"). For example, LG960QT steel plates with a thickness of 6 to 16 mm cracked when bent 90° with a 4a bend core diameter during user use. However, during production inspections conducted according to the test method in GB / T232-2010, cracking was never observed after bending 180° with a 4a bend core diameter on a SANS BHT5106 bend tester over tens of thousands of times according to the test method in GB / T232-2010. Therefore, it is necessary to improve the steel plate bending test method to better evaluate the actual bending or cold bending performance of steel plates, guide the improvement of steel plate production processes, and guide the selection of materials for users.

[0004] GB / T232-2010 requires that the width of the bending test specimen for sheet products should be in accordance with the requirements of the relevant product standards. If no specific requirements are specified, the following requirements should be followed:

[0005] a) When the product width is not greater than 20mm, the sample width is the original product width;

[0006] b) When the product width is greater than 20mm:

[0007] ——When the product thickness is less than 3mm, the specimen width is (20±5)mm;

[0008] ——When the product thickness is not less than 3mm, the specimen width is between 20mm and 50mm.

[0009] GB / T232-2010 stipulates that for sheet metal products, the specimen thickness should be the original product thickness. If the product thickness is 25mm or less, the specimen thickness may be machined to a minimum of 25mm, retaining the original thickness on one side. During the bending test, the retained surface of the specimen should be on the side subject to tensile deformation.

[0010] GB / T232-2010 stipulates that when sampling plate products for bending tests, the requirement for the roller spacing l of the sample is: l = bending core diameter + 3a±a / 2, where a is the thickness of the sample. Summary of the Invention

[0011] The present invention provides a method for testing the cold bending performance of steel plates. By refining the classification standards for steel plates and providing sample preparation standards corresponding to the steel plate thickness classification standards, the method can more accurately test the cold bending performance of steel plates and reduce the variance in the results of cold bending performance tests. This method solves the problem of a significant discrepancy between the cold bending performance test results obtained using current testing methods and the actual cold bending performance of steel plates.

[0012] In a first aspect, the present application provides a method for testing the cold bending performance of a steel plate, comprising:

[0013] S10, obtaining the nominal thickness of the steel plate to be tested;

[0014] S20, classifying the steel plate to be tested according to the nominal thickness of the steel plate to be tested according to a preset thickness classification standard;

[0015] S30, preparing a cold-bending specimen for the steel plate to be tested that has been classified according to a preset thickness classification standard according to a specimen preparation standard corresponding to the classification thickness of the steel plate to be tested;

[0016] S40. Perform a cold bending performance test on the prepared cold bending specimen to obtain accurate cold bending performance test results of the steel plate to be tested.

[0017] Compared with the test method in the existing test standard GB / T232-2010, the method for testing the cold bending performance of steel plates in the embodiment of the present application refines the classification standards of steel plates and provides sample preparation standards of width corresponding to the classification standards of the nominal thickness of steel plates, so as to prepare cold-bent samples to be tested with a certain width corresponding to the nominal thickness of the samples, that is, the width of the cold-bent samples to be tested is determined according to the nominal thickness of the cold-bent samples steel plates to be tested, so as to more accurately detect the actual bending or cold-bending performance of the cold-bent samples steel plates to be tested, reduce the difference in the cold-bending performance test results of the steel plates, and solve the problem that the cold-bending performance test results obtained according to the current testing method are too different from the actual cold-bending performance of the steel plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1This is the morphology of an LG1100QT rectangular cold-bent specimen with a thickness * width * length of 10 * 20 * 160 mm in one embodiment of the present application after being bent 90° with a roller spacing of 46 mm and a bending core diameter of 1.6a (16 mm). There are no cracks on the outer arc surface of the bent part, and the width is reduced from the actual 19.5 mm to 15.5 mm, a reduction of 4.0 mm, and a reduction ratio of 20.51%. That is, the lateral deformation rate is as high as 20.51%. The lateral flow of metal inward on the outer arc surface has a significant "filling" effect on the longitudinal extension and is not prone to cracking;

[0020] Figure 2 This is the morphology of two LG1100QT cold-bent specimens with a thickness of 10 mm and a width of 100 mm (width-to-thickness ratio of 10) in one embodiment of the present application after being bent 90° with a bending core diameter of 4a (40 mm). R20 represents a bending core radius of 20 mm, and 34 min and 39 min are tempering times, respectively. The roller spacing of the cold-bent specimen on the left is 100 mm, and the roller spacing of the cold-bent specimen on the right is 80 mm. The outer arc width of the bending part of the two cold-bent specimens is reduced from the actual 100.0 mm to 98.5 mm, a reduction of 1.5%. That is, the lateral deformation rate is only 1.5%, indicating that the "filling" effect of the metal lateral flow on the longitudinal extension has been significantly weakened, making it more prone to cracking. As a result, a small crack appeared in the middle of the outer arc surface of the bending part of the cold-bent specimen on the left; however, there was no crack in the width of about 10mm on both sides of the left specimen, indicating that there was an "edge effect" in the cold-bent specimen with a width-to-thickness ratio of 10. That is, because the width-to-thickness ratio of the cold-bent specimen is large enough, the inward lateral flow of metal on the outer arc surface of the bending part mainly occurs within a width of about 10mm on both sides, resulting in no crack in the width of about 10mm on each side. This further shows that the width-to-thickness ratio of the cold-bent specimen must be large enough to detect the cold-bending performance of the steel plate; the cold-bent specimen on the right has better cold-bending performance due to the improved tempering process of the original plate. After being bent 90° with a 4a bending core diameter, there were no cracks on the edges and middle of the outer arc surface of the bending part.

[0021] Figure 3 The results of a transverse cold bending performance test of a 10*2000*12000 mm LG1100QT hot-rolled steel plate provided in one embodiment of the present application after being subjected to quenching at 870°C for 29 minutes and tempering at 220°C for 39 minutes were obtained. Three cold-bent specimens (thickness*width*length) of 10*20*160 mm were cold-bent 90° with a bending core diameter of 1.6a (16 mm) and roller spacings of 46 mm, 41 mm, and 36 mm, respectively. The cold-bent specimen with a roller spacing of 46 mm had no cracks, the cold-bent specimen with a roller spacing of 41 mm had cracks, and the cold-bent specimen with a roller spacing of 36 mm broke, with a fracture depth exceeding 2 / 3 of the thickness. This indicates that the roller spacing has a significant effect on the cold-bending test results of heat-treated high-strength steel plates.

[0022] Figure 4 This is a diagram of the testing method for the cold-bent specimen to be tested in the embodiment of the present application. DETAILED DESCRIPTION

[0023] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present application by illustrating the examples of the present application.

[0024] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, the elements defined by the phrase "comprising..." do not exclude the presence of other identical elements in the process, method, article, or device comprising the elements.

[0025] As noted in the Background Technology section, cold bending performance of steel plates is a challenging aspect of high-strength steel manufacturing. Without accurate testing of this performance, effective guidance for improving high-strength steel plate manufacturing processes and guidance for users on appropriate material selection and use are both limited. Based on this, the applicant conducted the following research to improve this aspect.

[0026] LG1100QT high-strength steel is a hot-rolled, heat-treated plate with a yield strength of 1100 MPa developed and produced by the applicant in recent years. Made from hot-rolled plate, it undergoes quenching and low-temperature tempering. It is primarily used in engineering machinery, for example, in the bending process for crane booms. The QT in the steel designation stands for quenching and tempering. The basic requirement for cold bending performance of LG1100QT steel plate in actual use is that the plate exhibits no cracking when bent 90° transversely (with the bend line parallel to the rolling direction) with a core diameter of D = 8a (a is the nominal thickness of the plate, and a will represent the nominal thickness of the plate in the following text). Some users require no cracking when bending 90° transversely with a core diameter of D = 6a.

[0027] The standard cold bending performance is the result of cold bending performance tests conducted in accordance with GB / T232-2010, "Metallic Materials Bending Test Methods." This standard stipulates that for steel plates with a width greater than 20 mm and a thickness of at least 3 mm, the cold bending specimen width shall be 20 mm to 50 mm. For steel plates with a thickness of 25 mm or less, full-thickness cold bending specimens shall be taken.

[0028] While researching the cold-bending performance of heat-treated high-strength steel plates such as LG960QT and LG1100QT, the applicant discovered significant discrepancies between the cold-bending test results conducted in accordance with GB / T232-2010, "Methods for Testing Metallic Materials by Bend" (hereinafter referred to as "standard cold-bending performance") and the actual cold-bending performance during use (hereinafter referred to as "actual cold-bending performance"). For example, cracking occasionally occurred when LG960QT steel plates with a thickness of 6mm to 16mm were bent 90° with a bend core diameter of 4a during user use. However, during production inspections conducted according to the test method in GB / T232-2010, cracking was never observed in tens of thousands of tests conducted using a SANS BHT5106 bend tester with a bend core diameter of 4a.

[0029] Furthermore, samples of LG960QT parts that cracked during 90° bending with a core diameter of D = 4a on a steel plate bending machine were subjected to standard cold bending performance tests with the same core diameter (D = 4a) and no cracking occurred during 90° to 180° bending on a SANS BHT5106 bend tester. Therefore, accurately testing the actual cold bending performance of LG960QT and LG1100QT products became a critical issue.

[0030] To investigate the causes of the discrepancy between standard cold-bending performance and actual cold-bending performance, the applicant conducted a series of experimental studies and purchased a UBB-500 / 3200 steel plate bending machine manufactured by Ruitie CNC Machine Tool Co., Ltd. for the experimental studies. The inventors provide the following improved technical solutions.

[0031] Improvement of the method for testing the cold bending performance of steel plates

[0032] The inventors have discovered that the width of the LG1100QT steel plate cold-bend specimen significantly affects the cold-bend performance test results. Transverse cold-bend specimens of varying widths were cut from the same LG1100QT steel plate (thickness * width * length = 10 * 2000 * 12000 mm) at 1 / 4 of its width. The sampling and cold-bend specimen testing methods were as follows:

[0033] 1) Use wire cutting to process rectangular cold-bent specimens with widths and lengths of 20 / 40 / 60 / 80 / 100 / 120 / 140*160mm respectively. The width-to-thickness ratios of the cold-bent specimens are 2, 4, 6, 8, 10, 12, and 14;

[0034] 2) The bending line is parallel to the rolling direction of the steel plate;

[0035] 3) The spacing between the support rollers in Tables 1 and 2 below is l = bending core diameter + 3 times the nominal thickness of the cold-bent specimen, that is, l = D + 3a;

[0036] 4) Matters not listed shall be handled in accordance with the provisions of GB / T232-2010.

[0037] Then, the cold bending specimens were subjected to cold bending tests on a SANS BHT5106 bending test machine and a UBB-500 / 3200D steel plate bending machine produced by Ruitie CNC Machine Tool Co., Ltd., respectively, according to the above method. The test results are shown in Tables 1 and 2 below:

[0038] Table 1 Influence of cold-bending specimen width on test results

[0039]

[0040] Note: The test equipment used in Table 1 is the UBB-500 / 3200D steel plate bending machine produced by Ruitie CNC Machine Tool Co., Ltd.

[0041] Table 2 Influence of cold-bending specimen width on test results

[0042]

[0043] Note: The test equipment used in Table 2 is a SANS BHT5106 bending tester.

[0044] In Tables 1 and 2, 1.6a, 2a, 3a, 4a, and 5a represent the core diameters used in the 90° cold bend test, respectively. For a given cold-bend specimen, when the specimen width b is less than 10a, the influence of the specimen width on the cold-bend performance test results is significant. As the width-to-thickness ratio increases, that is, as the width increases, the 90° cold-bend test results of the steel plate change from no cracks to cracks. However, when the specimen width b is ≥ 10a, as the width-to-thickness ratio continues to increase, the 90° cold-bend test results of the steel plate all show cracks, and the width has no effect on the cold-bend performance test results.

[0045] Comparing Table 1 and Table 2, we can see that specimens with the same width-to-thickness ratio have the same test results on different testing machines. In the past, users cracked LG960QT components when bending them 90° with a core diameter of D=4a on a steel plate bending machine. However, when samples were bent 90° to 180° with the same core diameter (D=4a) on a SANS BHT5106 bending tester for standard cold bending performance, no cracking occurred. This shows that this phenomenon is not caused by different testing equipment.

[0046] The test results in Tables 1 and 2 show that the cold bending performance test results conducted in accordance with the current national standard GB / T232-2010 "Metallic Materials Bending Test Methods" do not necessarily reflect the actual cold bending performance of steel plate materials. The main reason for this is the unreasonable specification of the specimen width. Because the standard does not set clear requirements for the width-to-thickness ratio, the width of the cold bending performance test specimen for steel plate products with a width of 3mm to 25mm is usually taken as the middle value of the standard's width range of 20mm to 50mm, that is, 35mm. In this case, the width-to-thickness ratio of the cold bending specimen for 10mm thick steel plate products is only 3.5, and only the cold bending specimens for steel plate products with a thickness of 3.0mm to 3.5mm meet the requirement of a width-to-thickness ratio of ≥10. The basic principle that the width-to-thickness ratio of cold-bent specimens of steel plate products needs to be ≥10 is: when the width-to-thickness ratio of the cold-bent specimen is less than 10, during the bending deformation process, the surface metal of the outer arc surface not only has longitudinal extension deformation, but also has obvious lateral flow inward, thereby "filling" the longitudinally extended metal and making the cold-bent specimen less likely to crack.

[0047] For example, when a LG1100QT steel plate cold-bent specimen with a specification of thickness * width * length = 10 * 20 * 160 mm, that is, a cold-bent specimen with a width of 2a is bent 90° through a bending core diameter of 1.6a, Figure 1 As shown in the figure, the width of the outer arc surface changes from the actual width of 19.5mm to 15.5mm, that is, the width of the outer arc surface is reduced by 4.0mm, and the reduction ratio of the outer arc surface width is 20.51%, that is, the lateral deformation rate is as high as 20.51%. The inward lateral flow of the metal on the outer arc surface has a significant filling effect on the longitudinal extension and is not easy to crack.

[0048] When the width-to-thickness ratio of the cold-bent specimen increases, the flow of metal from the outer side of the cold-bent specimen to the inner side becomes more difficult and more prone to cracking. During bending deformation, the reduction ratio of the width of the outer arc surface, that is, the lateral deformation rate, is significantly reduced, that is, the filling effect of the inward lateral flow of the outer arc surface on the longitudinal extension is significantly weakened, making it easy to crack.

[0049] For another example, a LG1100QT steel plate cold-bent specimen with a specification of thickness * width * length = 10 * 100 * 160 mm, that is, a cold-bent specimen with a width of 10a, is bent 90° through a 4a bending core diameter. Figure 2As shown: R20 is the bending core radius of 20mm, 34min and 39min are the tempering times respectively, the roller spacing of the cold-bent specimen on the left is 100mm, and the roller spacing of the cold-bent specimen on the right is 80mm; the width of the outer arc surface of the bending part of the two cold-bent specimens is reduced from the actual width of 100.0mm to 98.5mm, a reduction of 1.5%, that is, the transverse deformation rate is only 1.5%, indicating that the "filling" effect of the transverse flow of metal on the longitudinal extension has been significantly weakened and is more prone to cracking, resulting in a small crack in the middle of the outer arc surface of the bending part of the cold-bent specimen on the left; about 10 on both sides of the left specimen There are no cracks on the width of mm, which shows that there is an "edge effect" in the cold-bent specimen with a width-to-thickness ratio of 10, that is, since the width-to-thickness ratio of the cold-bent specimen is large enough, the inward lateral flow of metal on the outer arc surface of the bending part mainly occurs within a width of about 10mm on both sides, resulting in no cracks on the edges of about 10mm width. This further shows that the width-to-thickness ratio of the cold-bent specimen must be large enough to detect the cold-bending performance of the steel plate; the cold-bent specimen on the right has better cold-bending performance due to the improved tempering process of the original plate. After being bent 90° with a 4a bending core diameter, there are no cracks on the edge and middle of the outer arc surface of the bending part.

[0050] In order to test the effect of roller spacing on the cold bending performance test results, six transverse cold bending specimens with the same width of 20 mm were cut from the 1 / 4 width of the LG1100QT steel plate with the specifications of thickness * width * length = 10 * 2000 * 12000 mm. The sampling method and cold bending test method are as follows:

[0051] 1) Use wire cutting to cut 6 transverse rectangular cold-bend specimens with a size of width * length * thickness = 20 * 160 * 10 mm;

[0052] 2) The test roller spacings are D+3a, D+3a-a / 2, and D+3a-a respectively;

[0053] 3) The diameter of the bending core D = 1.6a, i.e. 16 mm;

[0054] 4) The bending line is parallel to the rolling direction of the steel plate;

[0055] 5) For matters not mentioned, GB / T232-2010 shall apply.

[0056] Then, the six cold-bending specimens were subjected to cold-bending tests on a SANA BHT5106 bending test machine and a UBB-500 / 3200D steel plate bending machine produced by Ruitie CNC Machine Tool Co., Ltd., respectively, according to the above method. The test results are shown in Tables 3 and 4 below:

[0057] Table 3 Effect of roller spacing on cold bending performance test results

[0058]

[0059] Note: The test equipment used in Table 3 is a SANS BHT5106 bending tester.

[0060] Table 4 Effect of roller spacing on cold bending performance test results

[0061]

[0062] Note: The test equipment used in Table 4 is the UBB-500 / 3200D steel plate bending machine produced by Ruitie CNC Machine Tool Co., Ltd.

[0063] As shown in Table 3, when the support roller spacing is the bend core diameter plus 3 times the thickness, the cold-bent specimen has no cracks; when the support roller spacing is 2.5 times the thickness of the bend core diameter, microcracks appear on the surface of the cold-bent specimen; when the support roller spacing is 2 times the thickness of the bend core diameter, the cold-bent specimen breaks, and the crack depth exceeds 2 / 3 of the thickness of the cold-bent specimen; the test comparison results of the support roller spacing of the cold-bent specimen show that the support roller spacing has a significant impact on the test results of the cold-bending performance test.

[0064] Therefore, in order to test the true cold bending performance of steel plate materials, the specimen width needs to be ≥10 times the thickness, and the support roller spacing needs to be D+3a, instead of D+3a±a / 2 specified in GB / T232-2010.

[0065] Based on the above findings, the inventors propose the following technical solutions:

[0066] In order to solve the problems in the prior art, the present invention provides a method for testing the cold bending performance of a steel plate. The method for testing the cold bending performance of a steel plate provided in the present invention is first introduced below.

[0067] The embodiment of the present application provides a method for testing the cold bending performance of a steel plate, comprising:

[0068] S10. Obtaining the nominal thickness of the steel plate whose cold bending performance is to be measured (hereinafter referred to as the steel plate to be measured);

[0069] S20, classifying the steel plate to be tested according to the nominal thickness of the steel plate to be tested according to a preset thickness classification standard;

[0070] S30, preparing a cold-bending specimen for the steel plate to be tested that has been classified according to a preset thickness classification standard according to a specimen preparation standard corresponding to the thickness classification of the steel plate to be tested;

[0071] S40. Perform a cold bending performance test on the prepared cold bending specimen to obtain accurate cold bending performance test results of the steel plate to be tested.

[0072] Compared with the test method in the existing test standard GB / T232-2010, the method for testing the cold bending performance of steel plates in the embodiment of the present application classifies steel plates by refining the thickness classification standard of steel plates, and provides a sample preparation standard corresponding to the steel plate thickness classification standard to prepare the cold bending sample to be tested, that is, the width of the cold bending sample is determined according to the nominal thickness of the steel plate, so that the cold bending performance of the steel plate can be more accurately tested during the cold bending performance test, the difference in the cold bending performance test results of the steel plate is reduced, the accuracy of the test results is improved, and the problem of excessive difference between the test results obtained according to the current test method GB / T232-2010 and the actual cold bending performance of the steel plate is solved.

[0073] According to an embodiment of the present application, step S20 includes:

[0074] Classify the steel plates to be tested with a nominal thickness of less than 10 mm into the first thickness classification standard;

[0075] The steel plates to be tested with a nominal thickness equal to or greater than 10 mm are classified as the second thickness classification standard.

[0076] In order to carry out detailed classification of steel plates to be tested of different thicknesses, and then select and prepare cold-bending specimens of steel plates to be tested of different widths according to the thickness classification standards of the steel plates to be tested for cold-bending performance tests, detect the cold-bending performance of the steel plates to be tested, and reduce or minimize the problem of excessive difference between the test results obtained according to GB / T232-2010 and the cold-bending performance test results of the steel plates during actual use by users, so as to guide the improvement of steel plate production technology and the selection of materials by users.

[0077] According to an embodiment of the present application, step S30 includes:

[0078] S301. For a steel plate to be tested of a first thickness classification standard, prepare a first standard cold-bent specimen, where the width of the first standard cold-bent specimen is 100 mm.

[0079] S302. For the steel plate to be tested of the second thickness classification standard, prepare a second standard cold-bent specimen, wherein the width of the second standard cold-bent specimen is equal to or greater than 10 times the nominal thickness of the steel plate to be tested.

[0080] That is, when the nominal thickness of the steel plate to be tested is less than 10 mm, the width of the cold-bent specimen is uniformly specified to be 100 mm; for example, when the nominal thickness of the steel plate to be tested is 5 mm to 9 mm, a cold-bent specimen with a width of 100 mm is selected for cold-bending performance testing;

[0081] When the nominal thickness of the steel plate to be tested is equal to or greater than 10mm, the width of the cold-bend specimen is uniformly stipulated to be 10 times the nominal thickness of the steel plate to be tested. For example, when the steel plate thickness is 10mm or above, a cold-bend specimen with a width of 10 times the nominal thickness is selected for cold-bend performance testing, or a cold-bend specimen with a width greater than 10 times the nominal thickness is selected for cold-bend performance testing.

[0082] Specifically, step S302 includes:

[0083] S3021. For the steel plate to be tested with a nominal thickness of 10 mm in the second thickness classification standard, prepare a second standard cold-bent specimen, wherein the width of the second standard cold-bent specimen is equal to 10 times the nominal thickness of the steel plate to be tested, i.e., 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, etc.;

[0084] S3022. For the steel plate to be tested with a nominal thickness greater than 10 mm in the second thickness classification standard, prepare a second standard cold-bent specimen. The width of the second standard cold-bent specimen is equal to 10 times the nominal thickness of the steel plate to be tested. For example, when the thickness of the cold-bent specimen is 11 mm, the width of the cold-bent specimen is 110 mm, 120 mm, 130 mm, 140 mm, etc.

[0085] This is to ensure that the specimen preparation standards for cold bending performance testing of steel plates of different thicknesses have corresponding widths under the corresponding thickness classification standards, so as to obtain more accurate cold bending performance test results of steel plates and reduce the differences in cold bending performance test results caused by different width-to-thickness ratios of cold bending specimens of steel plates.

[0086] According to an embodiment of the present application, step S40, performing a cold bending performance test on the prepared cold bending specimen to obtain an accurate cold bending performance test result of the steel plate to be tested, includes:

[0087] S401, place the prepared cold bending specimen 3 on a roller bending device equipped with two rollers 1 and a bending pressure head 2, as shown in FIG. Figure 4 As shown in the left figure, the axes of the two arms of the cold-bent specimen 3 are kept in a plane perpendicular to the bending axis. The cold-bent specimen 3 is taken from the steel plate to be tested as described above.

[0088] S402, use the bending indenter 2 to apply a force on the cold-bent specimen 3, such as Figure 4 As shown in the figure on the right, the cold-bend sample 3 is bent to a specified angle to complete the cold-bend performance test of the cold-bend sample 3.

[0089] In one embodiment, in step S401, the prepared cold-bend specimen is placed on a roller-type bending device equipped with two supporting rollers 1 and a bending pressure head 2, so that the axes of the two arms of the cold-bend specimen 3 are maintained in a plane perpendicular to the bending axis. The distance l between the two supporting rollers should satisfy the formula (1):

[0090] l=D+3a (1);

[0091] In formula (1), D is the diameter of the bending core, unit: mm; a is the nominal thickness of the prepared cold-bending specimen, unit: mm; the distance between the two support rollers remains unchanged during the cold-bending test of the cold-bending specimen.

[0092] In one embodiment, the distance l between the support rollers satisfies formula (1), and the values ​​of the bending core diameter D are 1.6a, 2a, 3a, 4a, and 5a, respectively.

[0093] In one embodiment, the distance l between the support rollers satisfies formula (2):

[0094] l= (D+3a) ±a / 2 (2);

[0095] The meanings and units of the symbols in formula (2) are the same as those in formula (1). The values ​​of the bending core diameter D are 1.6a, 2a, 3a, 4a, and 5a, respectively, and the cold bending is 90°.

[0096] In one embodiment, the distance l between the support rollers should satisfy formula (3):

[0097] l=(D+3a)+a (3);

[0098] The meaning and units of the symbols in formula (3) are the same as those in formula (1), the bending core diameter is 4a, and the cold bending is 90°

[0099] In one embodiment, the distance l between the support rollers should satisfy formula (4):

[0100] l=(D+3a)+3a (4);

[0101] The meaning and units of the symbols in formula (4) are the same as those in formula (1), the bending core diameter is 4a, and the cold bending is 90°

[0102] In one embodiment, the distance l between the support rollers should satisfy formula (5):

[0103] l=( D+3a)-a (5);

[0104] The meaning and units of the symbols in formula (5) are the same as those in formula (1), the bending core diameter is 1.6a, and the cold bending is 90°

[0105] In one embodiment, S402 uses a bending press to apply a force to the cold-bend specimen to bend the cold-bend specimen to a specified angle, thereby completing the cold-bend performance test of the cold-bend specimen, including:

[0106] The bending pressure head is placed at the midpoint of the cold-bent sample between the two supporting rollers, and a force is continuously applied to the cold-bent sample to bend the cold-bent sample to 90°, thereby completing the cold-bending performance test of the cold-bent sample.

[0107] In one embodiment, S402 uses a bending press to apply a force to the cold-bend specimen to bend the cold-bend specimen to a specified angle, thereby completing the cold-bend performance test of the cold-bend specimen, including:

[0108] Place the bending head at the midpoint of the cold-bend specimen between the two support rollers and continuously apply force to the cold-bend specimen to bend the specimen to a target angle greater than 90° and less than or equal to 180° to complete the cold-bend performance test of the cold-bend specimen. That is, the target angle α satisfies: 90°≤α≤180°.

[0109] In one embodiment, the target angle is 100°, 120°, 150°, 160°, 175°, or 180°, or any value between 90° and 180°.

[0110] Specifically, the target angle can be given by relevant product technical standards or determined according to user technical requirements to complete the cold bending performance test of the cold bending specimen.

[0111] According to an embodiment of the present application, the method for testing the cold bending performance of a steel plate further includes:

[0112] S50. After the cold-bend test, if no cracks are visible on the outer surface of the cold-bend specimen, the specimen shall be deemed qualified. If no cracks are visible on the outer surface of the cold-bend specimen, the specimen shall be deemed unqualified. The magnifying instrument shall be a magnifying glass.

[0113] By adopting the improved method for testing the cold bending performance of steel plates in this application, the cold bending performance test of LG1100QT steel plates of different thicknesses and widths was carried out using the above-mentioned two testing machines, and the problem of different results did not occur.

[0114] Matters not mentioned in the test method for cold bending performance of steel plates in this application shall be carried out in accordance with GB / T232-2010.

[0115] Compared with the test method in the existing test standard GB / T232-2010, the method for testing the cold bending performance of steel plates in the embodiment of the present application refines the classification standards of steel plates and provides sample preparation standards corresponding to the steel plate thickness classification standards to prepare the cold bending samples to be tested, that is, the width of the cold bending sample is determined according to the nominal thickness of the steel plate, so as to more accurately detect the cold bending performance of the steel plate, reduce the difference in the cold bending performance test results of the steel plate, and solve the problem of excessive difference between the test results obtained according to the current test method GB / T232-2010 and the cold bending performance results of the steel plate in actual use by users.

[0116] The above description is only a specific embodiment of the present application. Those skilled in the art will clearly understand that for the convenience and brevity of description, the method described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here. It should be understood that the scope of protection of the present application is not limited to this. Any person skilled in the art can easily think of various equivalent modifications or replacements within the technical scope disclosed in this application, and these modifications or replacements should be included in the scope of protection of this application.

Claims

1. A method for testing the cold bending performance of a steel plate, characterized in that: include: S10, obtaining the nominal thickness of the steel plate to be tested; S20, classifying the steel plates to be tested according to a preset thickness classification standard based on the nominal thickness of the steel plates to be tested, including: classifying the steel plates to be tested with a nominal thickness of less than 10 mm into a first thickness classification standard; and classifying the steel plates to be tested with a nominal thickness equal to or greater than 10 mm into a second thickness classification standard; S30, preparing a cold-bending specimen for the steel plate to be tested that has been classified according to a preset thickness classification standard according to a specimen preparation standard corresponding to the thickness classification of the steel plate to be tested, including: S301. For a steel plate to be tested of a first thickness classification standard, prepare a first standard cold-bent specimen, where the width of the first standard cold-bent specimen is 100 mm. S302. For the steel plate to be tested of the second thickness classification standard, prepare a second standard cold-bent specimen, wherein the width of the second standard cold-bent specimen is equal to or greater than 10 times the nominal thickness of the steel plate to be tested; S40. Perform a cold bending performance test on the prepared cold bending specimen to obtain accurate cold bending performance test results of the steel plate to be tested.

2. The method according to claim 1, characterized in that The step S302 includes: S3021. For a steel plate to be tested having a nominal thickness of 10 mm in the second thickness classification standard, prepare a second standard cold-bent specimen, wherein the width of the second standard cold-bent specimen is equal to 10 times the nominal thickness of the steel plate to be tested; S3022. For the steel plate to be tested with a nominal thickness greater than 10 mm in the second thickness classification standard, prepare a second standard cold-bent specimen, wherein the width of the second standard cold-bent specimen is equal to 10 times the nominal thickness of the steel plate to be tested.

3. The method according to claim 1, characterized in that The step S40 of performing a cold bending performance test on the prepared cold bending specimen to obtain accurate cold bending performance test results of the steel plate to be tested includes: S401, placing the prepared cold-bend specimen on a roller-type bending device equipped with two rollers and a bending pressure head, so that the axes of the two arms of the cold-bend specimen remain in a plane perpendicular to the bending axis; S402: Use a bending press to apply a force on the cold-bend specimen to bend the cold-bend specimen to a specified angle, thereby completing a cold-bend performance test of the cold-bend specimen.

4. The method according to claim 3, characterized in that In the step of placing the prepared cold-bent specimen on a roller-type bending device equipped with two supporting rollers and a bending pressure head in S401, so that the axes of the two arms of the cold-bent specimen are maintained in a plane perpendicular to the bending axis, the distance l between the two supporting rollers should satisfy formula (1): l=D+3a (1); In formula (1), D is the diameter of the bending core, unit: mm; a is the nominal thickness of the prepared cold-bending specimen, unit: mm; the distance between the two support rollers remains unchanged during the cold-bending test of the cold-bending specimen.

5. The method according to claim 3, characterized in that The step of completing the cold bending performance test of the cold bending specimen in S402 includes: The bending pressure head is placed at the midpoint of the cold-bent sample between the two support rollers, and a force is continuously applied to the cold-bent sample to bend the cold-bent sample to 90°, thereby completing the cold-bending performance test of the cold-bent sample.

6. The method according to claim 3, characterized in that The step of completing the cold bending performance test of the cold bending specimen in S402 includes: The bending pressure head is placed at the midpoint of the cold-bent sample between the two support rollers to continuously apply force to the cold-bent sample so that the cold-bent sample is bent to a target angle greater than 90° and less than or equal to 180°, thereby completing the cold-bending performance test of the cold-bent sample.

7. The method according to claim 1, characterized in that Also includes: S50. After completing the cold bending performance test of the cold-bend specimen, if no cracks are visible on the outer surface of the cold-bend specimen when observed without a magnifying instrument, the specimen shall be evaluated as qualified; or if cracks are visible on the outer surface of the cold-bend specimen when observed without a magnifying instrument, the specimen shall be evaluated as unqualified.

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