Accurate detection method for tensile properties of natural aging swrh82b steel wire rod

Abstract

This invention discloses a precise testing method for the tensile properties of naturally aged SWRH82B steel wire rod, belonging to the field of metallic material performance testing technology. The method includes: sample preparation: selecting 12.5mm SWRH82B steel wire rods from the same batch, removing defects, and processing to uniform dimensions, then naturally aging them at 5℃ for at least 3 weeks; tensile parameter setting: adopting a two-stage control mode, using a strain control rate of 0.02-0.2%S, displacement control for tensile strength Rm testing, and simultaneous recording of reduction of area Z%; standardized testing: performing tensile tests on a microcomputer-controlled electro-hydraulic servo universal testing machine according to preset parameters; result correction: data correction based on the steel wire rod's microstructure, nitrogen and hydrogen content, and surface quality. This invention can accurately reflect the true tensile properties of SWRH82B steel wire rods, is suitable for factory quality control and engineering acceptance scenarios, and is suitable for standardized promotion and application.

Description

Technical Field

[0001] This invention belongs to the field of metal material performance testing technology, and in particular relates to a precise testing method for the tensile properties of naturally aged SWRH82B steel wire rod. Background Technology

[0002] SWRH82B steel wire rod, as the core material for making prestressed steel strands, is widely used in key engineering fields such as highways, railway bridges, seaports, and power plant dams. Its tensile properties (tensile strength Rm, yield strength Rp0.2, and reduction of area Z%) directly determine the safety and durability of the engineering structure. Therefore, the accuracy of factory testing is crucial.

[0003] However, existing methods for testing the tensile properties of SWRH82B steel wire rod have several technical drawbacks: First, the selection of tensile speed lacks scientific basis. Traditional testing often uses a single or arbitrarily selected tensile speed without considering the differential impact of speed on different strength indicators, resulting in significant deviations in test results and failing to reflect the true performance of the material. Second, the influence of natural aging is not fully considered. SWRH82B steel wire rod undergoes natural aging during storage, and its plasticity index is prone to change with aging time. However, existing testing methods often do not clearly define the aging stabilization period, which can easily lead to distorted test results due to improper sampling timing. Third, the testing process lacks standardization. There are no unified specifications for sample preparation, parameter setting, and result processing, making it highly susceptible to human operation and environmental factors, resulting in poor repeatability of test data. Fourth, there is insufficient coordinated control of influencing factors. The internal structure of the steel wire rod, residual stress, nitrogen and hydrogen content, and surface condition all affect the tensile test results, and existing methods have not established targeted control and correction mechanisms.

[0004] Currently, there are relevant tensile testing technologies for metallic materials, but none of them have developed a solution specifically tailored to the characteristics of SWRH82B steel wire rod. Some technologies only focus on the impact of a single tensile speed on ordinary steel, without addressing the performance changes at different aging stages over a wide speed range. Some testing methods ignore the significant impact of natural aging on the plasticity index of high-carbon steel wire rod and do not specify a stable aging period. Furthermore, some technologies do not consider the interference of the microstructure characteristics of SWRH82B steel wire rod (such as 85% sorbite content) and nitrogen and hydrogen content on the test results, resulting in testing accuracy that cannot meet engineering requirements. Therefore, there is an urgent need to develop a standardized and accurate testing method that takes into account tensile speed adaptation, aging period control, and correction for multiple influencing factors. Summary of the Invention

[0005] The purpose of this invention is to provide a precise testing method for the tensile properties of naturally aged SWRH82B steel wire rod, aiming to solve the technical problems in existing testing methods such as poor adaptability of tensile speed, insufficient stability of test results, and failure to consider the influence of natural aging. This method will enable accurate quantitative testing of the tensile properties of SWRH82B steel wire rod, providing reliable technical support for its factory quality control and engineering applications.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention provides a precise method for testing the tensile properties of naturally aged SWRH82B steel wire rod, comprising the following steps:

[0008] (1) Sample preparation: ① Select SWRH82B steel wire rods of the same specification produced in the same batch, cut off the defective section at the head, and continuously cut 350mm long blanks to process into standard tensile test specimens with a parallel length of 150mm, ensuring that the diameter fluctuation of the test specimen is ≤±0.1mm and the surface is free of scratches and microcracks; ② Place the test specimens in an environment with a temperature of 5℃±2℃ for natural aging, and the aging period is ≥3 weeks;

[0009] (2) Preparation of testing equipment and environment: ① Use a microcomputer-controlled electro-hydraulic servo universal testing machine. Before the test, use standard calibration parts to calibrate the equipment for accuracy; ② Maintain the test environment temperature at 5℃±2℃ and humidity at 40%-60% to avoid interference from environmental factors;

[0010] (3) Tensile parameter setting: A two-stage control mode is adopted. ① Yield strength Rp0.2 test: Strain control is adopted, with a strain rate of 0.02-0.2%S and a corresponding beam speed of 5-20mm / min; ② Tensile strength Rm test: Displacement control is adopted, with a displacement rate of 5-60mm / min; ③ The reduction of area Z% after the specimen fracture is recorded simultaneously.

[0011] (4) Standardized tensile test: ① Install the aged specimen into the testing machine clamp and ensure the alignment accuracy is ≤0.05mm; ② Start the tensile test according to the set parameters and collect stress-strain data in real time until the specimen breaks; ③ Prepare at least 3 parallel specimens for each test and repeat the test process.

[0012] (5) Results processing and correction: ① Calculate the average values ​​of tensile strength Rm, yield strength Rp0.2 and reduction of area Z% of parallel samples; ② Correct the data based on the nitrogen content of steel wire rod ≤0.008%, hydrogen content ≤2ppm and surface roughness Ra≤1.6μm, with a correction coefficient of 0.98-1.02; ③ When the relative standard deviation of the test results is >1.5%, re-prepare the sample for supplementary testing.

[0013] Furthermore, the 50mm defective section at the head is cut off.

[0014] Furthermore, the chemical composition of the SWRH82B steel wire rod mass meter mentioned in step (1) must meet the following requirements: C 0.79-0.86%, Si 0.15-0.35%, Mn 0.60-0.90%, S≤0.025%, P≤0.025%, Cr 0.10-0.35%, with the remainder being Fe and impurities.

[0015] Furthermore, the metallographic structure of the SWRH82B steel wire rod is sorbite + pearlite, with a sorbite content ≥85% and a total decarburized layer depth ≤0.1mm.

[0016] Furthermore, in step (1), the natural aging environment is a factory or constant temperature chamber in northern winter with temperature fluctuations ≤ ±2℃. During the aging period, the sample should be kept dry and free from mechanical collisions.

[0017] Furthermore, in step (3), when it is necessary to compare the performance differences at different speeds, the strain control speed can be extended to 0.02-1.0%S, and the displacement control speed can be extended to 5-60mm / min. Among them, the tensile strength Rm and yield strength Rp0.2 are most stable when the strain speed is ≤0.2%S and the beam speed is ≤20mm / min.

[0018] Furthermore, the data correction rules in step (5) are as follows: for every 0.001% increase in nitrogen content, the tensile strength test value is corrected by -0.5 MPa; for every 0.5 ppm increase in hydrogen content, the reduction of area test value is corrected by -0.8%; for every 0.2 μm increase in surface roughness Ra, the yield strength test value is corrected by +1.2 MPa.

[0019] Furthermore, the method is applicable to SWRH82B steel wire rods with chemical composition meeting the requirements and sorbite content of 75%-90%, and can be extended to the tensile property testing of similar high-carbon steel wire rods with a specification of 10-14mm.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] This invention achieves three key breakthroughs through the aforementioned core technological innovations: ① It clarifies the stable aging period (≥3 weeks) of SWRH82B steel wire rod at 5℃, solving the problem of detection distortion caused by aging; ② It establishes a suitable two-stage tensile parameter range, with a strength index detection error ≤1% at a strain rate of 0.02-0.2%S; ③ It constructs a multi-factor collaborative correction system, effectively offsetting interference from microstructure, composition, surface condition, etc., with a relative standard deviation of ≤1.5% for the test results, far superior to traditional methods (≤3%). Furthermore, the testing process of this invention is highly standardized, easy to operate, and suitable for industrial batch testing scenarios, and can be extended to the tensile performance testing of SWRH82B steel wire rods of different specifications. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings.

[0023] Figure 1 Microscopic morphology of SWRH82B steel wire rod (85% sorbite + pearlite, 100μm scale).

[0024] Figure 2 A graph showing the variation of tensile strength Rm at different stretching speeds (demonstrating the linear growth pattern across the speed range of V1-V8).

[0025] Figure 3 The graph shows the variation of yield strength Rp0.2 under different tensile speeds (reflecting the fluctuation in the V1-V4 range and the linear growth characteristics above V4).

[0026] Figure 4 A graph showing the relationship between the reduction of area Z% at different stretching speeds (indicating a decreasing trend as speed increases);

[0027] Figure 5 The graph shows the relationship between tensile strength Rm and aging time (showing the trend of stabilization after 3 weeks).

[0028] Figure 6 The graph shows the relationship between yield strength Rp0.2 and aging time (reflecting the small fluctuations during the aging process).

[0029] Figure 7 The graph shows the relationship between the cross-sectional shrinkage rate Z% and aging time (showing that it stabilizes in the 42%-45% range after 3 weeks). Detailed Implementation

[0030] This invention constructs a precise testing system adapted to SWRH82B steel wire rod through an integrated technical solution that optimizes aging cycle, classifies tensile parameters, standardizes processes, and corrects results. The specific technical solution is as follows:

[0031] 1. Sample preparation and aging cycle control technology

[0032] To address the impact of natural aging on plasticity indicators, a standardized sample preparation and aging control process was established:

[0033] Sampling specifications: Select SWRH82B steel wire rods produced in the same batch to ensure uniform chemical composition (within the range defined in claim 2). After cutting off the 50mm defective section at the head, continuously cut 350mm long billets to avoid interference from mixed batches and defective samples.

[0034] Uniform dimensions: The blank is processed into a standard tensile specimen with a diameter of 12.5 mm and a parallel length of 150 mm. Precision machining is used to ensure dimensional accuracy, with diameter fluctuation controlled within ±0.1 mm. After surface grinding, the roughness Ra≤1.6 μm is removed to eliminate stress concentration sources such as scratches and microcracks.

[0035] Aging stability: The sample was placed in an environment of 5℃±2℃ for natural aging. Through experimental verification, after aging for 3 weeks at this temperature, the section shrinkage rate Z% of the steel wire rod tended to stabilize (fluctuation ≤1%), and the tensile strength and yield strength fluctuated ≤3MPa. Therefore, it is clear that the aging period is ≥3 weeks to avoid the distortion of test results due to insufficient aging.

[0036] 2. Tensile parameter grading and adaptation technology

[0037] Based on the mechanical properties of SWRH82B steel wire rod, the two-stage tensile parameters were optimized:

[0038] Parameter classification: The yield strength Rp0.2 adopts strain control mode, and the applicable speed range is 0.02-0.2%S (corresponding to the beam speed of 5-20mm / min). This range can accurately capture the yield point and avoid misjudgment of yield strength due to excessive speed; the tensile strength Rm adopts displacement control and can be selected in the range of 5-60mm / min according to the testing requirements. Among them, the test results have the best stability at the speed of 5-20mm / min.

[0039] Synergistic Mode: The two-stage control mode takes into account both the accurate capture of yield strength and the efficient detection of tensile strength, avoiding insufficient detection accuracy of a certain indicator due to a single control mode; at the same time, the reduction of area Z% is recorded simultaneously to ensure that the three core indicators are detected in one go, thus improving detection efficiency.

[0040] 3. Establishment of standardized testing procedures

[0041] Establish end-to-end standards from equipment calibration to result output:

[0042] Equipment calibration: Before the test, the microcomputer-controlled electro-hydraulic servo universal testing machine is calibrated with standard calibration parts to ensure that the force error is ≤ ±0.5% and the displacement error is ≤ ±0.1mm;

[0043] Environmental control: Maintain the test environment temperature at 5℃±2℃ and humidity at 40%-60%, consistent with the natural aging environment, to avoid performance fluctuations caused by temperature changes;

[0044] Operating procedures: When installing the sample, ensure that the centering accuracy of the clamps is ≤0.05mm to avoid errors introduced by eccentric stretching; during the stretching process, collect stress-strain data in real time with a sampling frequency ≥10Hz to ensure that no key data is missed;

[0045] Parallel testing: Prepare at least 3 parallel samples for each group, remove outlier data (deviations exceeding the average ±3%) and take the arithmetic mean to improve the repeatability of the test results.

[0046] 4. Multi-influencing factor correction technique

[0047] A multi-dimensional result correction mechanism was established based on the characteristics of SWRH82B steel wire rod:

[0048] Microstructure correction: Adjust the test results according to the sorbite content. For every deviation of 85%±5% in sorbite content, the tensile strength is corrected by ±2MPa. Since the spacing between sorbite lamellars directly affects the resistance to plastic deformation, it is necessary to combine the metallographic microstructure test results for correction.

[0049] Correction for the influence of composition: The pinning effect of nitrogen atoms on dislocations will improve the strength index, while excessive hydrogen content will reduce plasticity. According to the correction rule of claim 5, the test data are finely adjusted based on the actual nitrogen and hydrogen content.

[0050] Surface quality correction: Surface roughness and defects can lead to stress concentration and affect fracture behavior. Based on the surface roughness test results, the yield strength and reduction of area are corrected to eliminate errors caused by differences in surface condition.

[0051] Residual stress correction: For residual stress generated during the rolling process, aging treatment (more than 3 weeks) is used to fully release it, reducing the interference of stress concentration on the test results.

[0052] 5. Test Result Verification Technology

[0053] Establish a dual verification mechanism to ensure detection accuracy:

[0054] Repeatability verification: The same batch of samples is tested three times under the same conditions, and the relative standard deviation is ≤1.5% to ensure the stability of the test method;

[0055] Accuracy verification: Standard specimens (with known tensile properties) are used for comparative testing. The error in tensile strength and yield strength is ≤ ±5MPa, and the error in reduction of area is ≤ ±1%, to ensure the accuracy of the test results.

[0056] Example

[0057] 1. Preparation of reagents and equipment

[0058] 1.1 Sample Material

[0059] The SWRH82B steel wire rods produced in the same batch have the following chemical composition (mass fraction): C 0.83%, Si 0.25%, Mn 0.79%, S 0.006%, P 0.014%, Cr 0.195%, Ni 0.012%, V 0.014%, metallographic structure of 85% sorbite + pearlite, total decarburized layer depth of 0.078mm, nitrogen content of 0.005%, and hydrogen content of 1.2ppm.

[0060] 1.2 Equipment and Tools

[0061] Testing equipment: Microcomputer-controlled electro-hydraulic servo universal testing machine, standard calibration parts;

[0062] Processing equipment: precision machine tools, sandpaper (800-1200 grit), ultrasonic cleaning machine;

[0063] Auxiliary equipment: constant temperature chamber (temperature control accuracy ±2℃), electronic balance (accuracy 0.1mg), surface roughness tester, metallographic microscope.

[0064] 2. Sample preparation operation details

[0065] (1) Sampling: Select 12.5mm specification SWRH82B steel wire rod, cut off the 50mm defect section at the head, and continuously cut 12 billets with a length of 350mm to ensure that the billets are free from bending, rust and surface defects;

[0066] (2) Processing: The blank is processed into a standard tensile specimen with a parallel length of 150mm and a clamping end diameter of 16mm by a precision machining tool. After processing, the surface of the specimen is polished with 800-1200 grit sandpaper to remove oxide scale and processing marks, and to ensure that the surface roughness Ra≤1.6μm.

[0067] (3) Cleaning and drying: Place the processed sample into an ultrasonic cleaner and clean it with anhydrous ethanol for 5 minutes to remove surface oil. Then place it in a 105℃ oven to dry for 10 minutes and cool it to room temperature.

[0068] (4) Aging treatment: Place the sample in a 5℃ constant temperature chamber for natural aging for 4 weeks. During the aging period, check the ambient temperature regularly to ensure that the fluctuation is ≤±2℃.

[0069] 3. Calibration and parameter setting of testing equipment

[0070] (1) Equipment calibration: Turn on the microcomputer-controlled electro-hydraulic servo universal testing machine, preheat for 30 minutes, and then use standard calibration parts to calibrate the force and displacement accuracy to ensure that the force error is ≤ ±0.5% and the displacement error is ≤ ±0.1mm;

[0071] (2) Parameter settings: ① Strain control parameters: The strain rate of 0.1%S is used for the yield strength Rp0.2 test, corresponding to a beam speed of 15mm / min; ② Displacement control parameters: The displacement rate of 20mm / min is used for the tensile strength Rm test; ③ Data acquisition parameters: The sampling frequency is 10Hz, and the stress, strain and displacement data are recorded synchronously.

[0072] 4. Standardized tensile testing procedure

[0073] (1) Environmental preparation: Adjust the temperature of the test environment to 5℃ and the humidity to 50% to ensure that it is consistent with the aging environment;

[0074] (2) Sample installation: Install the aged sample into the upper and lower clamps of the testing machine, and adjust the coaxiality of the sample through the centering device to ensure that the centering accuracy is ≤0.05mm;

[0075] (3) Tensile test: Start the testing machine and perform tensile test according to the set parameters. During the yield stage, strain control is used and the yield strength Rp0.2 is recorded. Then switch to displacement control until the specimen breaks and record the tensile strength Rm.

[0076] (4) Cross-sectional measurement: After the specimen breaks, the minimum cross-sectional area of ​​the specimen after breakage is measured with an electronic balance, and the reduction of area Z% is calculated.

[0077] (5) Parallel test: Repeat the above steps to complete the tensile test of 12 specimens, with 3 specimens as a group, for a total of 4 groups.

[0078] 5. Result Processing and Correction

[0079] (1) Data statistics: Calculate the average values ​​of tensile strength Rm, yield strength Rp0.2 and reduction of area Z% for each group of specimens, and remove abnormal data that exceed the average value ±3%;

[0080] (2) Multi-factor correction: Based on the actual detected nitrogen content (0.005%), hydrogen content (1.2ppm) and surface roughness (Ra=1.2μm), the data is fine-tuned according to the correction rules of claim 5. No additional correction is required for the test data (all within the specified range).

[0081] (3) Results output: The final test results are: tensile strength Rm=1215±10MPa, yield strength Rp0.2=765±8MPa, reduction of area Z%=43.5±0.5%, relative standard deviation=1.2%, which meets the accuracy requirements.

[0082] Example verification

[0083] Three batches of SWRH82B steel wire rods from different furnace batches were selected and tested according to the method of this invention. The results were also compared using traditional methods. The results are as follows:

[0084] The method of this invention: the relative standard deviations of tensile strength of the three batches of samples were 1.0%, 1.1%, and 1.3%, respectively; the relative standard deviations of yield strength were 0.9%, 1.2%, and 1.0%, respectively; and the relative standard deviations of reduction of area were 0.8%, 1.0%, and 0.9%, respectively.

[0085] Traditional method: The relative standard deviations of tensile strength of the three batches of samples were 2.8%, 3.1%, and 2.9%, respectively; the relative standard deviations of yield strength were 2.5%, 2.7%, and 2.6%, respectively; and the relative standard deviations of reduction of area were 2.3%, 2.5%, and 2.4%, respectively.

[0086] The verification results show that the detection accuracy of the method of the present invention is significantly better than that of the traditional method, which can effectively reduce the error caused by multi-factor interference, and the detection results are stable and reliable, which is suitable for industrial batch detection needs.

[0087] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A precise method for testing the tensile properties of naturally aged SWRH82B steel wire rod, characterized in that, Includes the following steps: (1) Sample preparation: ① Select SWRH82B steel wire rods of the same specification produced in the same batch, cut off the defective section at the head, and continuously cut 350mm long blanks to process into standard tensile test specimens with a parallel length of 150mm, ensuring that the diameter fluctuation of the test specimen is ≤±0.1mm and the surface is free of scratches and microcracks; ② Place the test specimens in an environment with a temperature of 5℃±2℃ for natural aging, and the aging period is ≥3 weeks; (2) Preparation of testing equipment and environment: ① Use a microcomputer-controlled electro-hydraulic servo universal testing machine. Before the test, use standard calibration parts to calibrate the equipment for accuracy; ② Maintain the test environment temperature at 5℃±2℃ and humidity at 40%-60% to avoid interference from environmental factors; (3) Tensile parameter setting: A two-stage control mode is adopted. ① Yield strength Rp0.2 test: Strain control is adopted, with a strain rate of 0.02-0.2%S and a corresponding beam speed of 5-20mm / min; ② Tensile strength Rm test: Displacement control is adopted, with a displacement rate of 5-60mm / min; ③ The reduction of area Z% after the specimen fracture is recorded simultaneously. (4) Standardized tensile test: ① Install the aged specimen into the testing machine clamp and ensure the alignment accuracy is ≤0.05mm; ② Start the tensile test according to the set parameters and collect stress-strain data in real time until the specimen breaks; ③ Prepare at least 3 parallel specimens for each test and repeat the test process. (5) Results processing and correction: ① Calculate the average values ​​of tensile strength Rm, yield strength Rp0.2 and reduction of area Z% of parallel samples; ② Correct the data based on the nitrogen content of steel wire rod ≤0.008%, hydrogen content ≤2ppm and surface roughness Ra≤1.6μm, with a correction coefficient of 0.98-1.02; ③ When the relative standard deviation of the test results is >1.5%, re-prepare the sample for supplementary testing.

2. The method for accurately testing the tensile properties of naturally aged SWRH82B steel wire rod according to claim 1, characterized in that, Cut off the 50mm defective section at the head.

3. The method for accurately testing the tensile properties of naturally aged SWRH82B steel wire rod according to claim 1, characterized in that, The chemical composition of the SWRH82B steel wire rod mass meter mentioned in step (1) must meet the following requirements: C 0.79-0.86%, Si 0.15-0.35%, Mn 0.60-0.90%, S≤0.025%, P≤0.025%, Cr 0.10-0.35%, with the remainder being Fe and impurities.

4. The method for accurately testing the tensile properties of naturally aged SWRH82B steel wire rod according to claim 1, characterized in that, The metallographic structure of the SWRH82B steel wire rod is sorbite + pearlite, with sorbite content ≥85% and total decarburized layer depth ≤0.1mm.

5. The method for accurately testing the tensile properties of naturally aged SWRH82B steel wire rod according to claim 1, characterized in that, In step (1), the natural aging environment is a factory or constant temperature chamber in northern winter with temperature fluctuations ≤ ±2℃. During the aging period, the sample should be kept dry and free from mechanical collisions.

6. The method for accurately testing the tensile properties of naturally aged SWRH82B steel wire rod according to claim 1, characterized in that, In step (3), when it is necessary to compare the performance differences at different speeds, the strain control speed can be extended to 0.02-1.0%S, and the displacement control speed can be extended to 5-60mm / min. Among them, the tensile strength Rm and yield strength Rp0.2 are most stable when the strain speed is ≤0.2%S and the beam speed is ≤20mm / min.

7. The method for accurately testing the tensile properties of naturally aged SWRH82B steel wire rod according to claim 1, characterized in that, The data correction rules in step (5) are as follows: for every 0.001% increase in nitrogen content, the tensile strength test value is corrected by -0.5 MPa; for every 0.5 ppm increase in hydrogen content, the reduction of area test value is corrected by -0.8%; for every 0.2 μm increase in surface roughness Ra, the yield strength test value is corrected by +1.2 MPa.

8. The method for accurately testing the tensile properties of naturally aged SWRH82B steel wire rod according to claim 1, characterized in that, The method is applicable to SWRH82B steel wire rods with chemical composition meeting the requirements and sorbite content of 75%-90%, and can be extended to the tensile property testing of similar high-carbon steel wire rods with specifications of 10-14mm.

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