A method for evaluating the upsetting deformation capacity of wire rods used in fasteners

Abstract

The present invention provides an evaluation method for the upsetting deformation capacity of a wire rod for fasteners, comprising: measuring the tensile strength and compressive strength of the material to be evaluated; calculating the tensile and compressive asymmetry of the material to be evaluated based on the measured tensile strength and compressive strength; upsetting the material to be evaluated to form a fastener, and measuring the head non-roundness of the fastener head; and evaluating the upsetting deformation capacity of the material to be evaluated based on the measured or calculated tensile strength, compressive strength, tensile and compressive asymmetry, and head non-roundness. The evaluation method for the upsetting deformation capacity of a wire rod for fasteners described in the present invention combines tensile and compressive asymmetry and head non-roundness to evaluate the upsetting deformation capacity of the material. Through quantitative analysis of tensile and compressive asymmetry, the uniformity or consistency of the material's organization in the axial direction can be clearly indicated; through quantitative analysis of head non-roundness, the uniformity or consistency of the material's organization in the radial direction can be clearly indicated.

Description

Technical Field

[0001] The invention belongs to the technical field of material upsetting deformation capacity evaluation, and in particular relates to an evaluation method for the upsetting deformation capacity of a wire rod material for a fastener. Background Art

[0002] Fasteners are called "rice of industry" and are widely used in many important fields such as aerospace, high-speed rail, ships, etc. They are almost everywhere in the industry. As the basis for the development and production of fasteners, the performance of materials is directly related to the processing and final performance of fasteners. It is generally believed that raw materials that can be easily processed and can ensure the performance of fastener products are relatively ideal materials. This requires that the materials used for fasteners have both good upsetting deformation ability and high deformation resistance, which seems to pose a paradox.

[0003] At present, the evaluation of fastener materials is limited to testing according to material standards, and the test content mainly includes the main parameters indicating the strength-plasticity matching relationship of the material, namely: tensile strength, yield strength, cross-sectional shrinkage, elongation, shear strength, impact toughness, elastic modulus, etc. However, does meeting the values ​​required by the material standards really facilitate the processing of fasteners?

[0004] Facts have proved that simply meeting the performance requirements of material standards cannot guarantee the smooth processing of fastener products, especially the upsetting deformation capacity cannot be effectively evaluated. Often, the material strength and plasticity indicators meet the standard requirements, but the upsetting deformation effect is poor. There are even two materials with completely identical indicators that show completely different upsetting deformation capabilities under the same processing conditions, which is really confusing. At present, there is no method to effectively evaluate the upsetting deformation capacity of raw materials, nor is there an effective indicator to indicate the strength of the upsetting deformation capacity of materials. Summary of the invention

[0005] In view of this, the present invention aims to provide a method for evaluating the upsetting deformation capacity of a wire rod for fasteners, so as to solve the problem that there is currently no effective method for evaluating the upsetting deformation capacity of a wire rod.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A method for evaluating the upsetting deformation capacity of a wire rod material for fasteners comprises the following steps: measuring the tensile strength and compressive strength of the material to be evaluated;

[0008] Based on the measured tensile strength and compressive strength, calculate the tensile and compressive asymmetry of the material to be evaluated;

[0009] The material to be evaluated is upset to form a fastener, and the head out-of-roundness of the fastener head is measured;

[0010] The upsetting deformation capacity of the material to be evaluated is evaluated based on the measured or calculated tensile strength, compressive strength, tensile-compressive asymmetry, and head out-of-roundness.

[0011] Furthermore, the calculation formula of the tension-compression asymmetry W is as follows:

[0012] W = 100% × (σ b -σ') / σ b ;

[0013] Among them, σ b is the tensile strength of the material to be evaluated, σ' is the compressive strength of the material to be evaluated, and the above two strength values ​​are the maximum values ​​on the true stress-strain curve measured by the material.

[0014] Furthermore, when evaluating the upsetting deformation capacity of the material to be evaluated, it is necessary to select the tensile and compressive asymmetry of the benchmark material as a reference indicator for the material to be evaluated;

[0015] Among them, the benchmark material is a material that exhibits good upsetting deformation ability and good engineering application ability;

[0016] Compare the tensile and compressive asymmetry between the material to be evaluated and the benchmark material to determine the axial upsetting deformation capacity of the material to be evaluated.

[0017] Furthermore, the method for evaluating the upsetting deformation capacity based on the tension-compression asymmetry is as follows:

[0018] Define the tensile and compressive asymmetry of the benchmark material as W 0 , the tensile and compressive asymmetry of the material to be evaluated is W x , the evaluation method is as follows:

[0019] If W x <W 0 , it is judged that the texture in the material to be evaluated is not conducive to the material's upsetting deformation in the axial direction relative to the texture in the benchmark material;

[0020] If W x >W 0 or W x =W 0 , it is judged that the texture in the material to be evaluated has better upsetting deformation ability in the axial direction than the texture in the benchmark material.

[0021] Furthermore, the calculation formula of the head out-of-roundness O is as follows:

[0022] O = 100% × (L1-L2) / L1;

[0023] Wherein, L1 is the length of the longest side of the arc of the fastener head, and L2 is the length of the shortest side of the arc of the fastener head;

[0024] The smaller the value of the head out-of-roundness O is, the stronger the structural consistency of the material to be evaluated in all radial directions is.

[0025] Furthermore, when measuring the out-of-roundness of the head, it is necessary to ensure that the head of the fastener formed by the material to be evaluated after the upsetting deformation does not crack. If the head cracks, it is directly concluded that the material to be evaluated cannot meet the upsetting deformation requirements;

[0026] During the upsetting process, the direction of the pressure on the material to be evaluated is the same as the axial direction of the material. When the head is deformed, the force on the material to be evaluated is perpendicular to the deformation direction, which is used to ensure the accuracy of the measurement result of the head out-of-roundness.

[0027] Furthermore, it also includes an evaluation method for the upsetting deformation capacity of the entire material, as follows:

[0028] Sampling uniformity of the material as a whole;

[0029] Conduct tension and compression tests on the selected test samples to obtain the tensile strength, compressive strength, tension and compression asymmetry, and head out-of-roundness of each sample;

[0030] The coefficient of variation of tensile strength, compressive strength, tensile-compressive asymmetry, and head out-of-roundness is calculated, and the consistency of the overall upsetting deformation capacity of the material is evaluated in combination with the coefficient of variation.

[0031] Furthermore, the coefficient of variation C V The calculation formula is as follows:

[0032] C V =100%×S d / mean;

[0033] Among them, S d represents the standard deviation, mean represents the mean value, C V The smaller the value of the material, the better the overall consistency of the material and the more stable the product quality.

[0034] Furthermore, when performing uniformity sampling, the following conditions must be met:

[0035] The number of sampling points shall be at least 10;

[0036] The sampling points need to include both ends;

[0037] At least 3 samples shall be taken from each sampling point;

[0038] Before the sample is subjected to tension and compression tests, the straightness of the sample should be ≤0.1mm. If the straightness does not meet the requirements, straightening treatment is required.

[0039] Compared with the prior art, the method for evaluating the upsetting deformation capacity of wire rods for fasteners according to the present invention has the following beneficial effects:

[0040] (1) The method for evaluating the upsetting deformation capacity of a wire rod for fasteners described in the present invention combines the tensile-compressive asymmetry and the head non-roundness to evaluate the upsetting deformation capacity of the material. The quantitative analysis of the tensile-compressive asymmetry can clearly indicate the uniformity or consistency of the material's structure in the axial direction; the quantitative analysis of the head non-roundness can clearly indicate the uniformity or consistency of the material's structure in the radial direction.

[0041] (2) In the present invention, the tensile-compression asymmetry is not only used to evaluate the material's upsetting deformation capacity, but can also be used to guide the manufacturing process. x <w 0 , the plasticity of the material can be improved by adjusting the upsetting deformation temperature to achieve the upsetting deformation effect. x =w 0 or x >w 0 , it can be processed according to the process parameters of the benchmark material. Even if the conditions are slightly worse, the required upsetting deformation effect can be achieved.

[0042] (3) The method for evaluating the upsetting deformation capacity of wire rods for fasteners described in the present invention can clearly indicate the overall level of the material through analysis of the coefficient of variation CV of tensile and compressive asymmetry, head non-roundness, tensile strength, and compressive strength. It can evaluate the consistency of materials within a batch and the consistency of materials between batches, thereby achieving the purpose of evaluating the overall level of the material's deformation capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0044] Figure 1 It is a schematic diagram of the tension-compression asymmetry of the present invention;

[0045] Figure 2 This is a schematic diagram of the fishing line of the present invention;

[0046] Figure 3 This is a schematic diagram of the head non-roundness of the present invention. DETAILED DESCRIPTION

[0047] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0048] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0049] In the description of the invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the invention can be understood according to specific circumstances.

[0050] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0051] A method for evaluating the deformation capacity of wire rods for fasteners is introduced, which introduces a material evaluation index, namely "tension-compression asymmetry", represented by the letter w. Figure 1 As shown. The principle is mainly to characterize the deformation ability of the material during upsetting through the asymmetry of the tensile strength and compression strength of the material itself, that is, the difference. The greater the asymmetry of tension and compression, the better the upsetting deformation ability of the material during the upsetting deformation process. The calculation formula is:

[0052] w=100%×(σ b -σ') / σ b

[0053] where σ b is the tensile strength of the material, σ' is the compressive strength of the material, and the above two strength values ​​are the maximum values ​​on the true stress-strain curve of the material test.

[0054] In order to better reflect the characteristics of "tension-compression asymmetry", the "fishing line principle" is proposed here, as shown in the attached figure. Figure 2As shown. The texture in the material microstructure is regarded as a slender "fishing line" distributed in the material. When the material is subjected to tensile stress, the "fishing line" is tightened, which significantly increases the deformation resistance of the material in the tensile direction, and can meet the engineering application ability of the material. When the material is subjected to compressive stress, the "fishing line" facilitates deformation in the compression direction, making the material easier to process during compression deformation, and can meet the processing requirements of convenient processing of the material. According to the calculation method of tension and compression asymmetry, the w of the fishing line is 100%, which is the most ideal material.

[0055] In reality, there is no real "fishing line" in metal materials. Therefore, when evaluating the material's upsetting deformation capacity, this "fishing line material" with a tensile and compressive symmetry of 100% cannot be used as a reference indicator and has no practical significance. Therefore, when evaluating materials, it is necessary to provide a reference material as a benchmark. We use materials that show good upsetting deformation capacity and good engineering application capabilities in engineering applications as benchmarks, and define their tensile and compressive asymmetry as w. 0 , the tensile and compressive asymmetry of the material to be evaluated is defined as w x . The following three situations will occur, namely:

[0056] Evaluation materials are not as good as benchmark materials x <w 0

[0057] Evaluation materials are equivalent to benchmark materials x =w 0

[0058] Evaluation materials are better than benchmark materials x >w 0

[0059] According to the fishing line principle, when other conditions or mechanical performance indicators are exactly the same, if w x <w 0 , it is judged that the texture in the material to be evaluated is not conducive to the material's upsetting deformation in the axial direction relative to the texture in the benchmark material; if w x >w 0 or x =w 0 , it is judged that the texture in the material to be evaluated has better upsetting deformation ability in the axial direction than the texture in the benchmark material.

[0060] The tensile-compression asymmetry is not only an important index for evaluating the axial upsetting deformation capacity of the material in the present invention, but also can be used to guide the manufacturing process in the actual manufacturing process. For example, if w x <w 0, it is necessary to improve or optimize the texture morphology of the material through process adjustment or process optimization during the preparation of the raw materials. The value of the tensile and compressive asymmetry can be used to provide corresponding guidance on the process parameters of the raw materials during the upsetting deformation process. The benchmark material is used as the processing sample to adjust the process parameters during the upsetting deformation, such as deformation amount, deformation temperature, etc. If w x <w 0 , the plasticity of the material can be improved by adjusting the upsetting deformation temperature to achieve the upsetting deformation effect. x =w 0 or x >w 0 , it can be processed according to the process parameters of the benchmark material. Even if the conditions are slightly worse, the required upsetting deformation effect can be achieved.

[0061] Through the quantitative analysis of tension and compression asymmetry, the uniformity or consistency of the material's structure in the axial direction can be clearly indicated, thereby achieving the purpose of evaluating the material's deformation capacity.

[0062] For the evaluation of the raw material's ability to be deformed by upsetting, in addition to the data indication of the asymmetry of tension and compression, the most direct upsetting deformation effect can be combined to further give a more intuitive and accurate evaluation of the material. Here, the head out-of-roundness formed after the fastener material is upset and deformed is introduced as an evaluation indicator, represented by the letter O. Figure 3 As shown in the figure, the asymmetry between the longest side L1 and the shortest side L2 of the bolt head arc is defined as the head out-of-roundness, and its calculation formula is:

[0063] O = 100% × (L1-L2) / L1

[0064] The premise of testing the head out-of-roundness is that after the material is deformed by upsetting, the head does not crack and can form the head shape required by the fastener. Because if cracking occurs, it can be directly concluded that the material cannot meet the requirements of upsetting deformation. If the influencing factors other than the material are not considered, and only the characteristics of the material itself during upsetting deformation are considered, the deformation range is the mold space of the upsetting deformation, and the pressure on the material is in the direction consistent with the axial direction of the material. When the head is deformed, the force on the material is perpendicular to the deformation direction (i.e. radial direction). Therefore, if the material has uniform organization in all directions in the radial direction, then the flow deformation trend of the material in all directions during deformation remains at the same level. After upsetting deformation, the head shape of the fastener is a perfect circle, at this time L1 = L2, and the head out-of-roundness is 0. When the material has different organization in the radial direction and exhibits anisotropic characteristics, then in one direction, there will be characteristics that are more conducive to material deformation, and in another direction, there will be characteristics that prevent material deformation. In general, when the material is deformed, two different deformation characteristics will appear, that is, different results of L1 and L2 will appear. Therefore, it can be judged that when the radial structure difference of the material is large, the difference between L1 and L2 will be larger, resulting in an increase in the head out-of-roundness O value.

[0065] Through the quantitative analysis of the head out-of-roundness O, the uniformity or consistency of the material's structure in the radial direction can be clearly indicated, thereby achieving the purpose of evaluating the material's deformation capacity.

[0066] The above invention content discusses in detail the method of evaluating the axial and radial deformation capacity of materials, but the above content only describes the evaluation of the upsetting deformation capacity of materials at a certain point or a certain local area, and does not describe the evaluation of the material as a whole. Therefore, in order to further evaluate the material as a whole, the present invention also provides a method for evaluating the consistency of the upsetting deformation capacity of the material as a whole, in which the coefficient of variation C is introduced. V Value, that is, standard deviation S d The ratio to the mean value, expressed as a percentage, is calculated as: C V =100%×S d / mean. C V The smaller the value, the better the overall consistency of the material, which is more conducive to batch processing and stable product quality.

[0067] Considering that there may be differences in various areas of the material, in order to obtain more accurate evaluation results, it is necessary to regulate the sampling process. The specific sampling requirements are as follows:

[0068] a) Uniformity sampling is performed at regular intervals, with a minimum of 10 sampling points. The more data points sampled, the more accurate the evaluation results will be;

[0069] b) The sampling points must include both ends of the material;

[0070] c) At each sampling point, no less than 3 samples are taken to ensure the accuracy of the test results. There is no requirement for data processing. When calculating, all 3 data points can be fully included in the calculation, or the average value can be calculated. Of course, the median value can also be selected, which will not affect the evaluation results;

[0071] d) Before the raw materials are subjected to tension and compression tests, the straightness of the test samples must be ≤0.1mm, which can ensure the accuracy of the test results. If the straightness does not meet the requirements, straightening is required;

[0072] e) The length of the raw material sample cut should meet the length requirements of the test.

[0073] In combination with the material standard requirements and the basic material properties required during the fastener upsetting deformation process, when conducting material consistency evaluation, at least the following properties need to be tested: V The performance of the test, as well as the sampling method and quantity, are shown in Table 1.

[0074] Table 1 Required Test C V Test contents and sampling requirements of the value

[0075] Serial number Test Project Sampling location Sampling quantity Remark 1 Tension and compression asymmetry Any 10 locations 3 per location The sampling position should include the beginning and the end 2 Head out of roundness Any 10 locations 3 per location The sampling position should include the beginning and the end 3 tensile strength Any 10 locations 3 per location The sampling position should include the beginning and the end 4 Compressive strength Any 10 locations 3 per location The sampling position should include the beginning and the end

[0076] Through the tension and compression asymmetry, head out of roundness, tensile strength, and compressive strength coefficient of variation C V The analysis can clearly indicate the overall level of the material, and can evaluate both the consistency of the material within a batch and the consistency of the material between batches, thereby achieving the purpose of evaluating the overall level of the material's deformation capacity.

[0077] Embodiment 1:

[0078] First, titanium alloy wire A with the same brand, state and specification as the material is selected as the benchmark material. Wire A has been widely used in engineering applications and has good upsetting deformation ability. The material to be evaluated is recorded as B. The tensile strength, yield strength, cross-sectional shrinkage, elongation, compressive strength, elastic modulus and other data of materials A and B are tested and recorded in Table 2.

[0079] Table 2 Material evaluation test items and their data

[0080]

[0081] From the test data, the plasticity index of the evaluated material is more advantageous than that of the benchmark material. For example, the elongation after fracture and the cross-sectional shrinkage are higher than those of the benchmark material, and the elastic modulus of A and B are at the same level. The tensile strength of A is significantly higher than that of B. According to the requirements of the material standard, the processing deformation ability of the evaluated material B should be better than that of A.

[0082] The upsetting deformation test of materials A and B showed that the results were completely opposite to the test data. The head forming effect of material A was good, showing a relatively regular circle, and the head out of roundness was O A =0.6%. However, the head of material B, which uses the same upsetting process parameters, cracks directly, indicating that the upsetting deformation capacity of material B is not as good as that of material A. This phenomenon shows that the plasticity index specified in the material standard alone cannot truly reflect the upsetting deformation capacity of the material.

[0083] Using the present invention, a group of data with the smallest cross-sectional shrinkage is selected for comparison. Test the tension and compression asymmetry of material A, denoted as w A .w A =100%×(1151-823) / 1151=28.5%, test the tension and compression asymmetry of material B, recorded as w b .w b =100%×(1012-853) / 1012=15.7%, which is only 55% of material A. This indicates that the upsetting deformation capacity of the evaluated material B is not as good as that of the benchmark material A.

[0084] Based on the value of the tension-compression asymmetry, the manufacturing process is adjusted to increase the upsetting temperature, so that material B can be formed (upsetting to form a fastener with a head that does not crack). Using the present invention, the head out-of-roundness of material B is evaluated, and it is found that material B has a head out-of-roundness of 0. B =1.73%, which is nearly three times that of material A. This further illustrates that the upsetting deformation capacity of the evaluated material B is not as good as that of the benchmark material A.

[0085] It can be seen that the use of tensile-compression asymmetry and head out-of-roundness indicators to evaluate the material's upsetting deformation capacity is more suitable for fastener materials than traditional plasticity indicators.

[0086] The consistency of the evaluated material B was evaluated and the consistency evaluation index was obtained, as shown in Table 3.

[0087] Table 3 Material consistency evaluation

[0088] Serial number Test Project Maximum Minimum average value Standard Deviation Coefficient of variation 1 Tension and compression asymmetry 15.92％ 19.25％ 17.79％ 0.017 9.5 2 Head out of roundness 1.53％ 0.6％ 1.06％ 0.002 12.5 3 tensile strength 1079MPa 1032MPa 1054.93MPa 13.66 1.29 4 Compressive strength 882MPa 832MPa 856MPa 8.93 1.04

[0089] Through the present invention, it can be judged that although the evaluated material B is at a good level in terms of consistency of basic mechanical properties of the material, it has certain deficiencies in upsetting deformation ability. Through the analysis of tensile and compressive asymmetry, it can be judged that in the preparation process of the evaluated material B, the process did not give full play to the radial cold working effect, but excessively used axial deformation to achieve the required size of the material; it can be further inferred that the texture organization in the evaluated material B was destroyed during the material preparation process due to excessive axial deformation. Although the tensile strength is lower, the compressive strength is at a higher level, which is not conducive to the upsetting deformation of the fastener product.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating the upsetting deformation capacity of a wire rod for a fastener, characterized in that: include: Measure the tensile strength and compressive strength of the material to be evaluated; Based on the measured tensile strength and compressive strength, calculate the tensile and compressive asymmetry of the material to be evaluated; The material to be evaluated is upset to form a fastener, and the head out-of-roundness of the fastener head is measured; Evaluate the upsetting deformation capacity of the material to be evaluated based on the measured or calculated tensile strength, compressive strength, tensile and compressive asymmetry, and head out-of-roundness; The calculation formula of tension and compression asymmetry W is as follows: W=100%×(σ b -s') / s b ; Among them, σ b is the tensile strength of the material to be evaluated, σ' is the compressive strength of the material to be evaluated, and the above two strength values ​​are the maximum values ​​on the true stress-strain curve measured by the material; When evaluating the upsetting deformation capacity of the material to be evaluated, it is necessary to select the tensile and compressive asymmetry of the benchmark material as a reference indicator for the material to be evaluated; Among them, titanium alloy wire with the same brand, state and specification as the material to be evaluated is selected as the benchmark material; Compare the tensile and compressive asymmetry between the material to be evaluated and the benchmark material to determine the axial upsetting deformation capacity of the material to be evaluated; The calculation formula of head out-of-roundness O is as follows: O = 100% × (L1-L2) / L1; Wherein, L1 is the length of the longest side of the arc of the fastener head, and L2 is the length of the shortest side of the arc of the fastener head; The smaller the value of the head out-of-roundness O is, the stronger the structural consistency of the material to be evaluated in all radial directions is.

2. The method for evaluating the upsetting deformation capacity of a wire rod for a fastener according to claim 1, characterized in that: The method for evaluating the deformation capacity of upsetting based on the asymmetry of tension and compression is as follows: Define the tensile and compressive asymmetry of the benchmark material as W0, and the tensile and compressive asymmetry of the material to be evaluated as W x , the evaluation method is as follows: If W x <W0, it is judged that the texture in the material to be evaluated is not conducive to the material's upsetting deformation in the axial direction relative to the texture in the benchmark material; If W x >W0 or W x =W0, it is judged that the texture in the material to be evaluated has better upsetting deformation ability in the axial direction than the texture in the benchmark material.

3. The method for evaluating the upsetting deformation capacity of a wire rod for a fastener according to claim 1, characterized in that: When measuring the out-of-roundness of the head, it is necessary to ensure that the head of the fastener formed by the material to be evaluated after upsetting deformation does not crack. If the head cracks, it is directly concluded that the material to be evaluated cannot meet the upsetting deformation requirements; During the upsetting process, the direction of the pressure on the material to be evaluated is the same as the axial direction of the material. When the head is deformed, the force on the material to be evaluated is perpendicular to the deformation direction, which is used to ensure the accuracy of the measurement result of the head out-of-roundness.

4. The method for evaluating the upsetting deformation capacity of a wire rod for a fastener according to claim 1, characterized in that: It also includes an evaluation method for the upsetting deformation capacity of the entire material, as follows: Sampling uniformity of the material as a whole; Conduct tension and compression tests on the selected test samples to obtain the tensile strength, compressive strength, tension and compression asymmetry, and head out-of-roundness of each sample; The coefficient of variation of tensile strength, compressive strength, tensile-compressive asymmetry, and head out-of-roundness is calculated, and the consistency of the overall upsetting deformation capacity of the material is evaluated in combination with the coefficient of variation.

5. The method for evaluating the upsetting deformation capacity of a wire rod for a fastener according to claim 4, characterized in that: Coefficient of variation C V The calculation formula is as follows: C V =100%×S d / mean; Among them, S d represents the standard deviation, mean represents the mean value, C V The smaller the value of the material, the better the overall consistency of the material and the more stable the product quality.

6. The method for evaluating the upsetting deformation capacity of a wire rod for a fastener according to claim 4, characterized in that: When sampling for uniformity, the following conditions must be met: The number of sampling points shall be at least 10; The sampling points need to include both ends; At least 3 samples shall be taken from each sampling point; Before the sample is subjected to tension and compression tests, the straightness of the sample should be ≤0.1mm. If the straightness does not meet the requirements, straightening treatment is required.

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