Preparation method of standard sample for thin plate tensile detection

Abstract

The invention discloses a preparation method of a standard sample for thin plate tensile detection, which comprises the following steps: determining six constant value parameters, and the constant value range of r value is greater than or equal to 3.10; the method comprises the following steps: acquiring high-strength cold continuous rolling carbon structural steel for automobiles, which meets the requirements of constant value parameters and is smelted and produced by vanadium titano-magnetite, and continuously taking sample plates with preset widths in the middle of the high-strength cold continuous rolling carbon structural steel along the rolling direction; a sample is taken out from each sample plate in a laser cutting mode, the samples are subjected to finish machining and inspection, and qualified standard samples are obtained; carrying out primary homogeneity detection on the standard sample; and carrying out uniformity inspection and value determination on the standard sample subjected to the primary uniformity inspection. According to the method, the coverage of a high-section magnitude range of a plastic strain ratio index of a fixed value item can be realized, the influence of sample edge burrs, microcracks, distortion and processing precision on the performance of the standard sample can be eliminated, the uniformity, stability and fixed value accuracy of the sample are improved, and high-efficiency, low-cost and batch preparation of the standard sample is realized.

Description

Technical Field

[0001] This invention belongs to the technical field of standard sample preparation for testing instruments, and in particular relates to a method for preparing a standard sample for tensile testing of thin plates. Background Technology

[0002] In the testing of mechanical properties of materials, tensile testing is an important means of evaluating key indicators such as strength and ductility. The geometrical accuracy of the specimen directly affects the accuracy of the test results. Current methods for preparing standard samples for thin-plate tensile testing have the following problems: When preparing standard samples of thin plates, blanks are generally made using methods such as punching, shearing, or wire cutting. In this case, work hardening and deformation during punching and shearing (burrs and microcracks on the specimen edges) affect the stress distribution, which in turn affects the mechanical properties of the blank. When preparing standard samples in large batches, it is very easy to cause non-compliance in uniformity testing. Moreover, wire cutting has low efficiency, which prevents the batch production quantity from being increased; typically, the total number of thin-plate tensile standard samples prepared in each batch is less than 800. In summary, the existing techniques for preparing standard samples for tensile testing of thin plates have the following drawbacks: low preparation efficiency, small preparation quantity, and high cost. The high cost is due to the fact that if the uniformity test fails, it is necessary to re-sample and re-test the uniformity until it passes before the next step of value determination can be carried out. Moreover, the number of standard samples that can be prepared in each batch is relatively small, which leads to a much higher preparation cost per standard sample.

[0003] Furthermore, in existing technologies, to ensure the uniformity test passes and the accuracy of the assigned values, three to five elements are used for the same type of standard sample. This is because the uniformity test requires each item to pass the test. Generally, the more items assigned, the higher the probability of failing the test. Therefore, items with smaller performance fluctuations are usually used for assignment. This leads to problems such as missing assigned items or incomplete coverage of the assigned value range. When conducting traceability of metrological values ​​or verifying testing equipment, multiple standard samples are required. Moreover, the assigned value range of the plastic strain ratio (r value) of existing thin plate tensile standard samples is mostly concentrated around 2.5. For the assigned value range of r value ≥ 3.10, due to the uniformity test, there is a lack of standard samples in the higher range. This is because the high r value range fluctuates more and is more sensitive to the stability of the sample source and the quality of sample processing. The more samples there are, the lower the pass rate of the uniformity test. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a method for preparing standard samples for tensile testing of thin plates. This method covers a high range of values ​​for the plastic strain ratio index, and eliminates the influence of burrs, microcracks, torsional deformation, and processing precision on the performance of the standard samples. It improves the uniformity, stability, and accuracy of the samples, and can be used as a standard substance for rapid verification of equipment, achieving efficient, low-cost, and batch preparation of standard samples.

[0005] The present invention provides a method for preparing a standard sample for tensile testing of thin plates, comprising:

[0006] Determine that R is included p0.2 R m 、A 50 / 80mm 、A gt The parameters are fixed values ​​for n and r, and the fixed value range of r is ≥3.10;

[0007] Obtain high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite that meets the requirements of the specified parameters, and continuously take a first preset number of samples with a preset width along the rolling direction in the middle of the sample.

[0008] A second preset number of samples are taken from each of the templates by laser cutting, the samples are then finely processed and inspected to obtain no less than a third preset number of qualified standard samples;

[0009] The standard sample was subjected to an initial homogeneity test.

[0010] The standard samples, after initial homogeneity testing, are subjected to homogeneity testing and value determination.

[0011] Preferably, in the above method for preparing standard samples for tensile testing of thin plates, the first preset quantity is 80 to 200 sheets, and the preset width is 400 mm to 600 mm.

[0012] Preferably, in the above method for preparing standard samples for tensile testing of thin plates, the step of taking out a second preset number of samples from each of the sample plates by laser cutting is as follows:

[0013] Ten to 39 samples are continuously extracted from each of the four corners and the middle position of each template along the direction perpendicular to the rolling direction using laser cutting.

[0014] Preferably, in the above method for preparing standard samples for tensile testing of thin plates, the third preset quantity is 800 to 5000 pieces.

[0015] Preferably, in the above method for preparing standard samples for tensile testing of thin plates, the initial uniformity test of the standard sample includes:

[0016] Multiple samples are randomly selected from the sample set for consistency testing within and between units. Three samples are randomly selected from each sample set, and F-tests are performed on the composition and tensile properties. If the initial inspection is qualified, it proves that the selection of the sample set is feasible.

[0017] Preferably, in the above-mentioned method for preparing standard samples for tensile testing of thin plates, before obtaining high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite that meets the specified parameter requirements, the method further includes:

[0018] Select the corresponding raw materials according to the set parameters, and carry out continuous casting, hot rolling and cold rolling to obtain high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite.

[0019] Preferably, in the above method for preparing standard samples for tensile testing of thin plates, the step of selecting the corresponding raw materials according to the set parameter includes:

[0020] The impurity contents selected according to the specified parameters are as follows: V element is 0.0032%, Ti element is 0.0768%, C element is 0.0038%, Si element is 0.0078%, Mn element is 0.0700%, P element is 0.0105%, S element is 0.0057%, and Al element is 0.0453%.

[0021] Preferably, in the above-mentioned method for preparing standard samples for tensile testing of thin plates, before performing uniformity testing on the standard samples after the initial uniformity test, the method further includes:

[0022] The standard samples were numbered, their dimensions were measured, and they were treated with rust prevention.

[0023] Preferably, in the above-mentioned method for preparing standard samples for tensile testing of thin plates, after performing a uniformity test on the standard samples that have undergone initial uniformity testing, the method further includes:

[0024] The stability of the standard sample was monitored.

[0025] Preferably, in the above-mentioned method for preparing standard samples for tensile testing of thin plates, after performing uniformity testing and value determination on the standard samples that have undergone initial uniformity testing, the method further includes:

[0026] The standard sample is subjected to long-term stability monitoring. If it fails to meet the requirements, the standard sample is discontinued.

[0027] As can be seen from the above description, the method for preparing standard samples for tensile testing of thin plates provided by the present invention includes: determining R... p0.2 R m 、A50 / 80mm 、A gt The parameters for n and r are defined, with the value of r ≥ 3.10. High-strength cold-rolled carbon structural steel for automobiles produced from vanadium-titanium magnetite smelting that meets the requirements of the defined parameters are obtained. A first preset number of samples with a preset width are continuously taken from the middle along the rolling direction. A second preset number of samples are taken from each sample using laser cutting. The samples are then finely processed and inspected to obtain at least a third preset number of qualified standard samples. A preliminary uniformity test is performed on the standard samples. After the preliminary uniformity test, the standard samples undergo uniformity inspection and value determination. This allows for the coverage of a high range of values ​​for the plastic strain ratio index, and the laser cutting method eliminates the influence of burrs, microcracks, torsion deformation, and processing precision on the performance of the standard samples, improving the uniformity, stability, and accuracy of the values. It can serve as a standard material for rapid equipment verification, achieving high-efficiency, low-cost, and batch preparation of standard samples. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of an embodiment of a method for preparing a standard sample for tensile testing of thin plates provided by the present invention;

[0030] Figure 2 This is a sampling diagram;

[0031] Figure 3 This is a schematic diagram of a standard sample;

[0032] Figure 4 This is a flowchart of a fully automated laser cutting process. Detailed Implementation

[0033] The core of this invention is to provide a method for preparing standard samples for tensile testing of thin plates. This method can cover a high range of values ​​for the plastic strain ratio index of the specified test item. It can also eliminate the influence of burrs, microcracks, torsional deformation, and processing precision on the performance of the standard sample, improve the uniformity, stability, and accuracy of the sample, and can be used as a standard substance for rapid verification of equipment as a means of value transfer. This enables the preparation of standard samples with high efficiency, low cost, and large batch production.

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] An embodiment of the method for preparing a standard sample for tensile testing of thin plates provided by the present invention is as follows: Figure 1 As shown, Figure 1 This is a schematic diagram of an embodiment of a method for preparing a standard sample for tensile testing of thin plates provided by the present invention. The method may include the following steps:

[0036] S1: Determine whether R is included p0.2 R m 、A 50 / 80mm 、A gt The parameters are fixed values ​​for n and r, and the fixed value range of r is ≥3.10;

[0037] It should be noted that R p0.2 This is the plastic tensile strength, which is the stress corresponding to 0.2% irreversible plastic strain in the gauge length of the specimen, R. m It is tensile strength, which is the maximum engineering stress that occurs during the test. A 50 / 80mm It is elongation at break, specifically the percentage of permanent elongation within a 50mm (or 80mm) gauge length after the specimen breaks. A gt It is the maximum total elongation at maximum force, specifically the elongation at maximum force F. m At that time, the percentage of total strain (elastic + plastic) measured by the extensometer, where n is the work hardening index, specifically, in the uniform plastic deformation stage, the true stress σ and the true strain ε satisfy... The exponents n and r are plastic anisotropy coefficients, specifically the true strain ε in the width direction. w With respect to the true strain ε in the thickness direction t The ratio, r=ε w / ε t The standard sample was designed according to the parameters specified in product standard GB / T5213-2019 "Cold-rolled low carbon steel plate and strip" grade DC05. It also takes into account the commonly used mechanical property monitoring parameters of thin plates in the industry and the actual use of vanadium-containing automotive steel. The design of the fixed parameters can be seen in Table 1. Table 1 is the design table of fixed parameters.

[0038] Table 1 Design Table of Fixed Parameters

[0039]

[0040] S2: Obtain high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite that meets the requirements of the set parameters, and continuously take a first preset number of templates with a preset width along the rolling direction in the middle of the template.

[0041] It should be noted that the high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite has the characteristics of low anisotropy and good uniformity. By selecting different steel samples, which have significant vanadium and titanium characteristics, good uniformity and accurate values, it is possible to cover the high range of values ​​of the plastic strain ratio (r value) index of the standard sample.

[0042] In a specific example, the first preset quantity can preferably be 80 to 200 images, and more preferably 120 images; the preset width can preferably be 400mm to 600mm, and more preferably 500mm. Of course, these can all be selected according to actual needs.

[0043] S3: Take out a second preset number of samples from each template by laser cutting, refine and inspect the samples, and obtain no less than a third preset number of qualified standard samples;

[0044] In a specific example, 10 to 39 samples can be continuously extracted from each template at its four corners and the center position perpendicular to the rolling direction using laser cutting. More preferably, 30 samples can be selected from each template, and the third preset quantity can preferably be 800 to 5000 pieces. See details for further information. Figure 2 , Figure 2 This is a schematic diagram of a sampling process. The obtained standard sample can be obtained as follows: Figure 3 As shown, Figure 3 The diagram shows a standard sample, which can be manufactured according to the specification of sample number P6 in Appendix E of GB / T228.1-2021. The main parameters of this standard sample are as follows:

[0045] (1) Thickness and width: a0=0.80mm, b0=20mm;

[0046] (2) Transition arc: R = 25 mm;

[0047] (3) Parallel length: L c =120 mm;

[0048] (4) Gauge length: L0 = 80 mm;

[0049] (5) Parallelism: 0.02mm;

[0050] (6) Roughness: 0.80μm.

[0051] S4: Perform initial homogeneity checks on the standard samples;

[0052] Specifically, multiple samples can be randomly selected from the templates for consistency testing within and between units. Three samples are randomly selected from each template, and F-tests are performed on the composition and tensile properties. If the initial inspection is passed, the selection of the templates is deemed feasible. Before conducting a homogeneity test on the standard samples after the initial homogeneity test, the following steps can be taken: numbering the standard samples, measuring their dimensions, and applying rust-proofing treatment. Numbering ensures that each standard sample can be identified, preventing confusion. Dimensional measurement ensures that each standard sample meets the dimensional requirements, preventing performance inconsistencies due to size issues. Furthermore, applying rust-proofing oil can prevent corrosion from environmental moisture, thus ensuring that the samples maintain their properties in various environments and exhibit better stability.

[0053] In a specific example of this step, nine samples can be randomly selected from 120 initial samples for intra- and inter-unit consistency checks. Three samples are randomly selected from each sample, and the composition and tensile properties are tested. The preliminary test results are shown in Table 2 below, which is the preliminary uniformity test result table. Of course, other sampling methods can be used in other cases, and no restrictions are imposed here.

[0054] Table 2 Initial Uniformity Inspection Results

[0055]

[0056] It can be seen that the F-test results for the proposed values ​​of the six parameters and the seven main chemical impurity components at the four corners and the middle position of the steel coil are all less than their critical values ​​F. 0.05 (8,18) = 2.51, therefore it is preliminarily considered that the uniformity of the material meets the requirements, and the entire material can be further processed into the smallest packaging unit (arranged in order, with each 3 samples as a smallest packaging unit).

[0057] S5: Perform uniformity testing and value determination on the standard samples after the initial uniformity test.

[0058] It should be noted that the mechanical properties of the samples are closely related to their processing precision. To ensure the accuracy of the standard samples, the processing quality must be controlled. After the initial uniformity inspection is passed, the preparation of the standard samples begins. Sample preparation utilizes a fully automated laser cutting system. According to regulations, 120 500mm wide templates are continuously taken from the middle of the steel coil along the rolling direction for later use. Each template is then laser-cut into 30 single tensile samples. The cutting process can be described as follows: Figure 4 As shown, Figure 4This is a flowchart of the fully automated laser cutting process. To ensure the quality of the cut edges, the corresponding piercing and cutting process parameters, such as the nozzle, cutting speed, focal length, focus, power, and gas pressure, are set according to the configuration of the laser cutting system, as shown in Table 3. Table 3 is the laser cutting process parameter table. During the cutting process, the samples are simultaneously coded and numbered using a laser. The samples are numbered according to BYCXXX-YY (XXX is the sequence number of the cutting block, a total of 120 blocks, e.g., 001; YY is the sequence number of each standard sample within each block, a total of 30 samples, e.g., 01) at the end. Three adjacent samples are packaged into a minimum packaging unit. Before measuring the sample dimensions, the sample surface should be visually inspected for integrity. Obvious defects or severe scratches are considered unqualified. Samples with poor surface roughness or damage / deformation are not used as standard samples. The resolution of the measuring instrument should not be less than 0.01 mm. The width and thickness should be measured at three points: both ends and the middle of the sample gauge length, and the arithmetic mean should be taken. The original cross-sectional area is calculated using the average value. Samples whose dimensions exceed the allowable tolerance specified in the specimen number P6 in Appendix E of GB / T228.1-2021 are considered unqualified and shall not be used as standard samples.

[0059] Table 3 Laser Cutting Process Parameters

[0060]

[0061] In accordance with the requirements of GB / T2975-2018 "Sampling Location and Specimen Preparation for Mechanical Property Testing of Steel and Steel Products", the laser cutting sampling method with no influence zone recommended in GB / T2975-2018 was used. This method ensures that the prepared specimens do not affect their mechanical properties. After laser cutting, the specimens are finished by milling in a tensile specimen machining center to eliminate work hardening caused by laser cutting. Samples are prepared directly from the sheet metal, retaining two original rolled surfaces. The prepared sample reduction portions are free of notches, tool marks, grooves, burrs, rough surfaces, and any defects that could affect performance determination. After machining, the samples are stored separately to avoid humid environments and protected from corrosion by applying rust-preventive oil.

[0062] As can be seen from the above description, in the embodiments of the method for preparing standard samples for tensile testing of thin plates provided by the present invention, since it includes: determining R p0.2 R m 、A 50 / 80mm 、A gtThe parameters for n and r are defined, with the value of r ≥ 3.10. High-strength cold-rolled carbon structural steel for automobiles produced from vanadium-titanium magnetite smelting that meets the parameter requirements are obtained. A first preset number of samples with a preset width are continuously taken from the middle along the rolling direction. A second preset number of samples are taken from each sample using laser cutting. The samples are then finely processed and inspected to obtain at least a third preset number of qualified standard samples. A preliminary uniformity test is performed on the standard samples. After the preliminary uniformity test, the standard samples undergo uniformity inspection and value determination. This allows for the coverage of a high range of values ​​for the plastic strain ratio index, and the laser cutting method eliminates the influence of burrs, microcracks, torsion deformation, and processing precision on the performance of the standard samples, improving the uniformity, stability, and accuracy of the values. It can serve as a standard substance for rapid equipment verification, achieving high-efficiency, low-cost, and batch preparation of standard samples.

[0063] In a specific embodiment of the above-mentioned method for preparing standard samples for tensile testing of thin plates, before obtaining high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite that meets the specified parameter requirements, the following steps may also be included:

[0064] Based on the set parameters, the corresponding raw materials are selected, and continuous casting, hot rolling and cold rolling are carried out to obtain high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite.

[0065] In another specific embodiment of the above-mentioned method for preparing standard samples for tensile testing of thin plates, selecting the corresponding raw materials according to the set parameters may specifically include:

[0066] The impurity contents selected based on the set parameters are as follows: V 0.0032%, Ti 0.0768%, C 0.0038%, Si 0.0078%, Mn 0.0700%, P 0.0105%, S 0.0057%, and Al 0.0453%. Specifically, the main impurity components of the material are detected using GB / T4336-2016 "Determination of Multi-Element Content in Carbon Steel and Medium-Low Alloy Steel by Spark Discharge Atomic Emission Spectrometry (Conventional Method)". The smelting process can include: hot metal pretreatment → converter → ladle refining → slab continuous casting → finishing. The steel is smelted in a vacuum induction furnace, with the following steps: sample billet → two stabilization heat treatments → natural aging for at least 6 months → initial homogeneity inspection → sample billet shearing → machining → standard sample numbering and dimensional measurement → rust prevention treatment → homogeneity inspection → stability monitoring → set values ​​→ packaging.

[0067] In another specific embodiment of the method for preparing standard samples for tensile testing of thin plates described above, after performing a uniformity test on the standard sample following the initial uniformity test, the method may further include the following step: conducting stability monitoring on the standard sample. Additionally, after performing a uniformity test and value determination on the standard sample following the initial uniformity test, the method may further include the following step: conducting long-term stability monitoring on the standard sample; if the sample fails to meet the requirements, its use is discontinued.

[0068] The following is an explanation of the uniformity assessment:

[0069] 1. Model Design

[0070] The evaluation of inter-unit terms is adopted—basic design (basic homogeneity study design—single-round measurement in GB / T15000.3 "Guidelines for Standard Sample Work Part 3: Guidelines for Standard Sample Assignment and Homogeneity and Stability Evaluation"). Assuming there are m standard material units, n measurements were performed on unit i. i For a simple parallel design, the number of repetitions for all units is n (i=1,…,m). i They are all the same, that is, n1=n2=…=n m =n0. One-way ANOVA can be used for analysis. The statistical model is as follows:

[0071] X ij =µ+δ i +ε ij ………………………………………………(1),

[0072] In the formula: X ij —The j-th observation in the i-th unit;

[0073] µ—the sum of all possible outcomes (observation result X) ij Assume that a true mean is derived from it;

[0074] δ i —This represents the effect of unit i on the result, i.e., the (true) deviation between unit i and µ;

[0075] ε ij —The random error of the j-th observation in the i-th unit, also known as the residual term.

[0076] 2. Number of units sampled for average inspection

[0077] According to GB / T15000.3 "Standard Sample Working Guidelines Part 3: Standard Sample Value Determination and Homogeneity and Stability Assessment Guidelines", the minimum number of units to be sampled for homogeneity testing is:

[0078] N min =max(10, (2),

[0079] Where: N min —Minimum number of units extracted;

[0080] N prod —Total number of units (N here) prod =1200);

[0081] In accordance with the requirements of GB / T15000.3 "Standard Sample Working Guidelines Part 3: Guidelines for Standard Sample Value Determination and Homogeneity and Stability Assessment" and YB / T082-2016 "Technical Specifications for Standard Samples for Metallurgical Product Analysis", to ensure that the number of units sampled for homogeneity statistical sampling is sufficiently representative, this homogeneity test adopts a conservative strategy, sampling according to the maximum sample size, i.e., 3 × Sampling is performed according to the sampling rules. The total number of units is 1200, and the minimum number of units to be sampled is 3 × =31.8 units. To facilitate statistics, 35 of the smallest packaging units were selected for uniformity testing.

[0082] According to the random number table, 35 smallest packaging units were randomly selected from 1200 packaging units and numbered sequentially as 1, 2, 3...35. There were a total of 3 samples in each packaging unit. One sample in each packaging unit was measured in each round. A total of 3 rounds of measurement were conducted, and the total number of measurements was 35×3=105, resulting in 105 measurement data.

[0083] 3. Statistical basis for the F-test of uniformity

[0084] The measurement system in this study was stable throughout the required observation period, and all observations could be obtained in a single measurement cycle. One-way ANOVA (F-test) was used to statistically analyze the uniformity results. The relevant calculation formulas are as follows:

[0085] ………………………………(3),

[0086] …………………………………………………(4),

[0087] ……………………………………………(5),

[0088] …………………………………………………(6),

[0089] …………………………………(7),

[0090] …………………………………………(8),

[0091] ………………(9),

[0092] Of the above seven formulas:

[0093] — Arithmetic mean;

[0094] m — number of units;

[0095] S—Total standard deviation;

[0096] n i —The number of measurement groups within the unit is 3 in this case;

[0097] —The arithmetic mean of the measurements within the unit;

[0098] X ij —Measured values ​​within each unit;

[0099] F—F-test value;

[0100] MS between —Repeatability mean square of measurements in inter-unit homogeneity studies;

[0101] MS within — Repeatability mean square of measurements in intra-cell homogeneity studies.

[0102] Based on the chosen significance level α, F is obtained from the F critical value table. α Compare F and F α Make a judgment:

[0103] If F≤F α=0.05 If no statistically significant difference is found within or between groups, then it is considered that there are no statistically significant differences.

[0104] If F α=0.05 <F≤F α=0.01 If the statistical difference is within and between groups, it is suspected that there is a systematic error between groups, that is, there are certain differences within and between groups, but they do not exceed the statistical outlier threshold.

[0105] If F>F α=0.01 If the results are statistically significant, then it is considered that there are statistically significant differences within and between groups, and further evaluation is needed to determine whether the uncertainty caused by the inhomogeneity will affect the expected use.

[0106] It should satisfy the condition that F≤F as much as possible. α=0.05 This ensures that there are no significant differences between or within units.

[0107] 4. F-test analysis

[0108] According to the design scheme, the F test was performed on each of the fixed parameters of this standard sample. The measurement method was the same as that for the initial uniformity test. The F test results are shown in Table 4 below. Table 4 is the F test result table.

[0109] Table 4. Results of the F-test

[0110]

[0111] The F-test indicates that the constant parameter R m ,R p0.2 A 80mm ,n 10-20 A gt The F-test values ​​are all less than the critical value F. 0.05 (34,70), therefore it can be considered that there are no statistically significant differences in the six fixed parameters between and within units.

[0112] The specific process of setting a constant value is described below:

[0113] 1. Measurement methods and sample distribution

[0114] Each designated collaborative laboratory is randomly assigned two minimum packaging units and given a unique number. Each designated collaborative laboratory reports two independent measurement data points for each minimum packaging unit, for a total of four independent measurement data points. Significant figures for the designated parameter results are in the format XXX.XX, XX.XX, X.XXX, 0.XXXX. The designated measurement methods are GB / T228.1—2021 "Metallic materials, tensile testing—Part 1: Test methods at room temperature", GB / T5027—2016 "Determination of plastic strain ratio (r value) of thin plates and strips of metallic materials", and GB / T5028—2008 "Determination of tensile strain hardening index (n value) of thin plates and strips of metallic materials".

[0115] Quality control requirements: The instrument should be calibrated to its optimal state. Quality control samples should be tested along with the sample. Alternatively, quality control samples from a designated laboratory (which must be certified reference materials / samples) can be used for quality control. Test results should be filled out according to the fixed format. The designated data is valid only after quality control is passed.

[0116] 2. Data statistics and processing

[0117] After the data from each laboratory are compiled, the quality control data are checked first, followed by a technical review. If no quality issues are found, the data within a group are tested using the Grubbs test, the data between groups are tested using the Grubbs test and the Cochrane test, and then all data are tested using the Shapiro-Wilke normality test. The statistical calculation formulas and critical values ​​for each test are given in Appendix B to D of JJF1343—2022 "Guidelines for the Determination of Standard References and Evaluation of Homogeneity and Stability".

[0118] The above test statistics are compared with the critical values ​​at the 0.05 and 0.01 significance levels, respectively, and outliers are removed as follows:

[0119] (1) When the statistic exceeds the critical value of the 0.01 significance level, the value is an outlier and should be removed without a reasonable retention technique explanation, and is judged as unqualified;

[0120] (2) When the statistic is between the significance level of 0.05 and 0.01, the value is a discrepancy value and has not exceeded the degree of outlier. If there is no reasonable explanation for the rejection technique, it should be retained and judged as qualified.

[0121] (3) When the statistical value exceeds the critical value of 0.05 significance level, it should be retained and judged as qualified;

[0122] (4) Both Grubbs' and Dixon's tests were used to determine the consistency of data between groups. If both tests show outliers, the outlier should be removed and deemed unqualified; otherwise, if there is no reasonable technical explanation, the outlier should be retained and deemed qualified.

[0123] 3. Determination of standard values

[0124] The processed data were statistically analyzed for standard values ​​and uncertainties of constant values ​​as follows:

[0125] (1) When the mean of the measured data sets follows an approximately normal distribution and the data sets have equal precision, the mean of the m data sets is... The unweighted arithmetic mean is used as the assigned value y. char :

[0126] ………………………………………………(10),

[0127] In the formula:

[0128] y char —The value assigned to the fixed parameter;

[0129] m — number of valid data sets;

[0130] —The average value of each data set;

[0131] —The average of the averages of each data set, i.e., the total arithmetic average.

[0132] Type A uncertainty based on statistical methods, standard uncertainty of the arithmetic mean of each data set. The standard deviation is:

[0133] …………………………………………(11),

[0134] In the formula:

[0135] —Standard uncertainty (standard deviation) of the average value of each array.

[0136] Based on statistical methods, the Type A uncertainty is assigned the value y. char Standard uncertainty u char The standard deviation is:

[0137] ……………………………(12),

[0138] In the formula:

[0139] u char —The assigned value y char The standard uncertainty (standard deviation);

[0140] —Standard uncertainty (standard deviation) of the total arithmetic mean.

[0141] (2) When the measured data sets follow an approximately normal distribution, but the data sets have different precisions, the assigned value y char The weighted average of the groups can be used:

[0142] …………………………………………(13),

[0143] ………………………………………………(14),

[0144] In the above two equations:

[0145] w i —Weight value;

[0146] u i —Precision (standard deviation) of each data point.

[0147] Based on the statistical method for Type A uncertainty, the uncertainty of the weighted average of all groups is:

[0148] …………………………(15).

[0149] 4. Uncertainty assessment

[0150] The standard uncertainty of the standard value is synthesized from the following aspects:

[0151] (1) Standard uncertainty (u) caused by measurementchar );

[0152] (2) Standard uncertainty (u) caused by homogeneity hom );

[0153] (3) Standard uncertainty (u) caused by short-term (instability) sts );

[0154] (4) Standard uncertainty (u) caused by long-term (instability) lts ).

[0155] The formula for calculating the standard uncertainty of the standard value is:

[0156] ………………………(16),

[0157] In the formula:

[0158] u hom — Uncertainty caused by (non)uniformity;

[0159] u lts —The standard uncertainty of long-term stability is relatively stable for metallurgical products and can be ignored;

[0160] u sts —Short-term stability standard uncertainty is relatively stable for metallurgical products and can be ignored;

[0161] The formula for calculating the expanded uncertainty U of the standard value is:

[0162] U=k·u CRM ……………………………………………(17),

[0163] In the formula:

[0164] k – expansion factor, k=2 at 95% confidence interval.

[0165] 5. Error Assessment

[0166] (1) Accuracy check

[0167] Typically, the accuracy of metallurgical chemical composition measurements is verified using certified reference materials (CRMs), and the laboratory's final results are compared with the standard values ​​y of the CRM or RM. char Comparison. Two scenarios will emerge:

[0168] ①|μ c -y char |≤C, there is no significant difference between the measured value and the standard value.

[0169] ②|μ c -ychar |>C, There is a significant difference between the measured value and the standard value.

[0170] In the formula:

[0171] μ c —CRM measurement values;

[0172] y char —Standard values ​​for CRM;

[0173] C – This value depends on the type of CRM used.

[0174] The formula for calculating C is as follows:

[0175] ………………………………(18),

[0176] In the formula:

[0177] R—Reproducibility limit;

[0178] r—repeatability limit;

[0179] u—the standard uncertainty of the CRM.

[0180] (2) Calculation of error

[0181] Unlike the metallurgical chemical composition measurement standards, the measurement standards for each parameter of thin plate tensile samples do not provide the reproducibility limit R and repeatability limit r of the measurement method (see GB / T228.1—2021 "Metallic materials, tensile testing—Part 1: Test methods at room temperature", GB / T5027—2016 "Metallic materials, thin plates and strips, determination of plastic strain ratio (r value)", GB / T5028—2008 "Metallic materials, thin plates and strips, determination of tensile strain hardening index (n value)"). Therefore, it is impossible to perform the accuracy verification according to formula (18). In view of this, it is necessary to provide the measurement error E of the standard sample to facilitate the accuracy verification according to the following formula:

[0182] ①|μ c -y char If |≤|E|, there is no significant difference between the measured value and the standard value.

[0183] ②|μ c -y char |>|E|, indicating a significant difference between the measured value and the standard value.

[0184] In the formula:

[0185] μ c —CRM measurement values;

[0186] y char —Standard values ​​for CRM;

[0187] E – Error of the standard sample.

[0188] The formula for calculating the error E of the standard sample is as follows:

[0189] E=±k·S R …………………………………………………(19),

[0190] In the formula:

[0191] k – expansion factor, taken as 2 at 95% confidence level, and as 3 at 99% confidence level; here, we take 2.

[0192] S R —The reproducibility standard deviation is calculated using the method described in GB / T6379.2-2004 "Accuracy (correctness and precision) of measurement methods and results - Part 2: Basic methods for determining the repeatability and reproducibility of standard measurement methods".

[0193] 6. Expression of standard values

[0194] After statistical analysis, the processed data follows a (approximate) normal distribution, and each data group has the same precision. Therefore, the standard value and uncertainty of the standard sample are calculated with the same precision.

[0195] Uncertainty u caused by (non)homogeneity hom Equal to inter-unit uncertainty u bb The expanded uncertainty is generally retained to one significant figure, with a maximum of two. The number of significant figures for the standard value and the error is aligned with that of the expanded uncertainty. The characteristic values ​​are shown in Table 5. Table 5 is a table of characteristic values.

[0196] Table 5 Characteristic Values

[0197]

[0198] In summary, the standard samples prepared using the methods described in the above embodiments exhibit good homogeneity, and the values ​​of relevant components are accurate and reliable. Stability testing results show that the standard samples demonstrate good stability. These standard samples exhibit significant vanadium and titanium characteristics, have a wide range of defined parameters, and are highly practical. The breakthrough in the range of plastic strain ratio (r-value) values ​​fills the gap in defining high-range r-values ​​for thin-plate tensile standards.

[0199] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a standard sample for tensile testing of thin plates, characterized in that, include: Determine that R is included p0.2 R m A 50 / 80mm A gt The parameters are fixed values ​​for n and r, and the fixed value range of r is ≥3.10; Obtain high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite that meets the requirements of the specified parameters, and continuously take a first preset number of samples with a preset width along the rolling direction in the middle of the sample. A second preset number of samples are taken from each of the templates by laser cutting, the samples are then finely processed and inspected to obtain no less than a third preset number of qualified standard samples; The standard sample was initially tested for homogeneity. The standard samples, after initial homogeneity testing, are subjected to homogeneity testing and value determination.

2. The method for preparing standard samples for tensile testing of thin plates according to claim 1, characterized in that, The first preset quantity is 80 to 200 sheets, and the preset width is 400mm to 600mm.

3. The method for preparing standard samples for tensile testing of thin plates according to claim 2, characterized in that, The step of removing a second preset number of samples from each of the templates by laser cutting is as follows: Ten to 39 samples are continuously extracted from each of the four corners and the middle position of each template along the direction perpendicular to the rolling direction using laser cutting.

4. The method for preparing standard samples for tensile testing of thin plates according to claim 3, characterized in that, The third preset quantity is 800 to 5000.

5. The method for preparing a standard sample for tensile testing of thin plates according to claim 4, characterized in that, The initial homogeneity check of the standard sample includes: Multiple samples are randomly selected from the sample set for consistency testing within and between units. Three samples are randomly selected from each sample set, and F-tests are performed on the composition and tensile properties. If the initial inspection is qualified, it proves that the selection of the sample set is feasible.

6. The method for preparing a standard sample for tensile testing of thin plates according to claim 5, characterized in that, Before obtaining high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite that meets the specified parameter requirements, the process also includes: Select the corresponding raw materials according to the set parameters, and carry out continuous casting, hot rolling and cold rolling to obtain high-strength cold-rolled carbon structural steel for automobiles produced by smelting vanadium-titanium magnetite.

7. The method for preparing a standard sample for tensile testing of thin plates according to claim 6, characterized in that, The step of selecting the corresponding raw material according to the fixed parameter includes: The impurity contents selected according to the specified parameters are as follows: V element is 0.0032%, Ti element is 0.0768%, C element is 0.0038%, Si element is 0.0078%, Mn element is 0.0700%, P element is 0.0105%, S element is 0.0057%, and Al element is 0.0453%.

8. The method for preparing a standard sample for tensile testing of thin plates according to claim 7, characterized in that, Before performing homogeneity testing on the standard sample after the initial homogeneity test, the method further includes: The standard samples were numbered, their dimensions were measured, and they were treated with rust prevention.

9. The method for preparing a standard sample for tensile testing of thin plates according to claim 8, characterized in that, After performing a homogeneity test on the standard sample that has undergone an initial homogeneity test, the method further includes: The stability of the standard sample was monitored.

10. The method for preparing a standard sample for tensile testing of thin plates according to claim 9, characterized in that, After performing homogeneity testing and value determination on the standard sample that has undergone initial homogeneity testing, the method further includes: The standard sample is subjected to long-term stability monitoring. If it fails to meet the requirements, the standard sample is discontinued.

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