A method for measuring the limit strain of a micro-crack of an enamel layer of an enamel steel plate

Abstract

The application discloses a kind of enamelled steel plate enamel layer micro crack limit strain measurement method, mainly solve the technical problem that prior art cannot measure the limit strain of enamelled steel plate enamel layer.The technical scheme is, a kind of enamelled steel plate enamel layer micro crack limit strain measurement method, comprising the following steps:1) preparation sample, the measured enamelled steel plate is processed into tensile test parallel sample;2) measure the strain corresponding to yield strength on the measured enamelled steel plate;3) determine the optimum tensile speed Y1 of sample enamel layer in tensile test;4) measure the strain X1 corresponding to the micro crack of the enamel layer of the measured enamelled steel plate.The method of the application is simple and easy to operate, high efficiency, strong applicability, and the measurement result has little human influence factor, and the measurement result is accurate, reliable, and high reproducibility.

Description

Technical Field

[0001] This invention relates to an analytical method for the enamel layer of enamel-lined steel plates, and particularly to a method for measuring the ultimate strain of microcracks in the enamel layer of enamel-lined steel plates, belonging to the field of physical testing technology for metallic materials. Background Technology

[0002] Enameled material is a composite material made of metal and vitreous inorganic materials through high-temperature firing. Applying enamel enamel to the surface of steel plates prevents rusting, prevents the formation of an oxide layer when heated, and resists corrosion from various liquids. Enameled steel combines the mechanical strength of metal with the beautiful appearance of enamel enamel and resistance to chemical corrosion, making it widely used in light industry, home appliances, metallurgy, chemical industry, construction, and other sectors. Through market competition and technological upgrades, particularly in the home appliance and environmental protection industries, the enamel industry has experienced rapid development, especially in the manufacture of enamel-lined inner tanks for water heaters.

[0003] The performance requirements of enamel steel sheets mainly include strength, formability, resistance to blistering, adhesion, and weldability. Enamel steel sheets for different applications require different comprehensive properties.

[0004] Currently, the most common testing techniques for determining the surface coating of steel materials, both domestically and internationally, include metallographic methods, bending tests, hardness tests, tensile tests, and forming tests. However, these conventional methods all have certain limitations. They can perform relevant performance tests on the steel plate substrate, but they cannot meet the requirements for studying the extreme deformation process of microcracks in the enamel layer of enamel-lined steel plates.

[0005] Chinese patent application CN104931332A discloses a "time-based method for determining the forming limit of thin plates." This method involves conducting a steel ball mold bulging test on the sheet metal, photographing the bulged specimen, and continuing until the sheet fractures. This method can accurately determine the ultimate strain at which contraction or cracking just occurs, providing a time-based forming limit that fully reflects the in-situ deformation at the test point. However, because this method requires the sheet to fracture to obtain its forming limit, it can only test the forming limit of the entire thin plate and cannot test the forming limit of a specific coating or composite material on the thin plate.

[0006] Currently, there is a lack of ultimate strain testing methods for detecting microcracks in the enamel layer of enamel-lined steel plates under stress conditions, which cannot meet the urgent need for performance analysis of surface coatings on steel materials. Summary of the Invention

[0007] The purpose of this invention is to provide a method for measuring the ultimate strain of microcracks in the enamel layer of enamel-lined steel plates, mainly solving the technical problem that existing technologies cannot measure the ultimate strain of the enamel layer of enamel-lined steel plates.

[0008] The technical idea of ​​this invention is to conduct tensile tests on enamel-coated steel plates with different tensile speeds and strains, select the optimal test parameters, and accurately measure the ultimate strain of microcracks in the enamel layer of the enamel-coated steel plate.

[0009] The technical solution of the present invention is a method for measuring the ultimate strain of microcracks in the enamel layer of an enamel-lined steel plate, the method comprising the following steps:

[0010] 1) Prepare the test specimen by processing the enamel steel plate to be tested into a parallel specimen for tensile testing;

[0011] 2) Measure the strain corresponding to the yield strength on the enamel steel plate to be tested. Perform a tensile test on one parallel specimen using a tensile testing machine. Use the displacement control mode and set the tensile speed in the elastic modulus stage, the tensile speed Y in the yield strength range stage, and the tensile speed in the fracture stage. Record the strain X corresponding to the yield strength on the specimen.

[0012] 3) Determine the optimal tensile speed Y1 for the enamel layer of the specimen in the tensile test. Perform tensile tests on two parallel specimens using a tensile testing machine, employing strain control mode and setting the strain to 0.50×X~X. The tensile speeds for the two parallel specimens are 0.10×Y~0.49×Y mm / min and 0.50×Y~Y mm / min, respectively. Record whether cracks occur in the enamel layer of the two parallel specimens. Determine the optimal tensile speed based on the occurrence of cracks in the enamel layer of the specimens. If neither specimen develops cracks, the larger tensile speed is the optimal tensile speed. If one specimen does not develop cracks, its tensile speed is the optimal tensile speed. If both specimens develop cracks, repeat the tensile test on the parallel specimens with a lower strain until the optimal tensile speed is determined.

[0013] 4) Measure the strain X1 corresponding to the microcrack in the enamel layer of the enamel steel plate to be tested. Perform tensile tests on 4 parallel specimens using a tensile testing machine. Use strain control mode, set the data storage displacement interval of the specimen elastic modulus stage and the optimal tensile speed Y1 of the specimen enamel layer; use the bisection asymptotic method to set the strain data interval between 0.5×X and X; record the strain X1 corresponding to the microcrack in the specimen enamel layer.

[0014] Further, step 1) of preparing the sample includes:

[0015] 1.1) The enamel-coated steel sheet to be tested is processed into a long strip tensile specimen by wire cutting;

[0016] 1.2) The long strip tensile specimen is finished by milling to obtain a tensile specimen of standard size;

[0017] 1.3) Remove burrs from the parallel section of the tensile specimen.

[0018] Further, step 2) involves measuring the strain rate corresponding to the yield strength of the enamel-coated steel plate to be tested, including:

[0019] A tensile test was performed on one parallel specimen using a tensile testing machine. The displacement control mode was adopted, and the tensile speed for the specimen's yield range and the tensile speed for the specimen's yield point were set. The sensitivity for detecting the yield point on the specimen was set according to the attenuation value of the tensile force on the specimen. The force limit of the specimen's yield strain at the end of the tensile test was set. The tensile force attenuation threshold corresponding to the termination of the tensile test, the tensile force threshold corresponding to specimen fracture, and the displacement of the specimen after fracture were set. The strain X corresponding to the yield strength on the specimen during the tensile test was recorded.

[0020] When preparing the sample using the method of this invention, the enamel steel plate to be tested is rough-machined by wire cutting according to the dimensions of the tensile sample. The purpose is to prevent cracking due to deformation during the surface enamel processing.

[0021] The method of this invention is based on the applicant's research as follows:

[0022] 1) In order to ensure more accurate acquisition of the strain corresponding to the upper yield point, a displacement control mode is adopted, the yield point speed and the yield range speed are set, and the upper yield point detection sensitivity is set according to the percentage of force attenuation.

[0023] 2) In order to ensure more accurate acquisition of the ultimate strain of microcracks in the enamel layer of the enamel steel plate, a strain control mode is adopted, a reasonable displacement interval for data storage is set when measuring the elastic modulus, the optimal tensile speed is measured in advance, and the strain setting adopts the bisection method.

[0024] The method of this invention utilizes a conventional tensile testing machine and accurately measures the ultimate strain of microcracks in the enamel layer of enamel-lined steel plates by setting test parameters for the elastic modulus measurement stage and the yield measurement stage. This method is time-saving, labor-saving, and provides reliable results, solving the technical problem of the inability to measure the ultimate strain of microcracks in the enamel layer of enamel-lined steel plates.

[0025] Compared with the prior art, the present invention has the following advantages: 1. The method described in the present invention can be implemented on a conventional tensile testing machine and has universal operability. 2. The method described in the present invention, by measuring the optimal tensile speed and setting the strain using the bisection method, can accurately measure the ultimate strain of microcracks in the enamel layer of enamel-lined steel plates, saving time and effort, minimizing the influence of human factors on the analysis and testing results, and ensuring accurate, reliable, and highly reproducible results. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, as shown in Tables 1 and 2.

[0027] Example 1: The enamel steel plate to be tested is a BTC245R enamel steel plate with a thickness of 2.3mm. The enamel layer of the enamel steel plate is applied in one coat.

[0028] A method for measuring the ultimate strain of microcracks in the enamel layer of an enamel-lined steel plate includes the following steps:

[0029] 1) Sample preparation: The enamel-lined steel plate to be tested is processed into parallel specimens for tensile testing, with the original gauge length L0 being 80 mm and the specimen width b0 being 20 mm.

[0030] 1.1) First, the enamel steel plate to be tested is processed into a long strip tensile specimen with a size of 270mm×30mm by wire cutting.

[0031] 1.2) The long strip tensile specimen was precision machined using a milling machine to obtain a standard-sized tensile specimen of 270mm×20mm with a parallel section length of 100mm.

[0032] 1.3) Remove burrs from the parallel section of the tensile specimen;

[0033] 2) Measure the strain corresponding to the yield strength on the enamel steel plate to be tested. Perform a tensile test on one parallel specimen using a tensile testing machine. Use displacement control mode and set the tensile speed to 6 mm / min in the elastic modulus stage, 6 mm / min in the yield strength stage, and 16 mm / min in the fracture stage. Based on the attenuation value of the tensile force on the specimen, set the yield point detection sensitivity on the specimen to 0.5% Fmax. Set the force limit of the specimen's yield strain at the end of the tensile test to exceed 3% of the yield strength. Set the tensile force attenuation threshold corresponding to the termination of the tensile test to 80% Fmax, the tensile force threshold corresponding to specimen fracture to 0.1% Fmax, and the displacement after specimen fracture to 5 mm. Record the strain corresponding to the yield strength on the specimen as 0.1% during the tensile test.

[0034] 3) Determine the optimal tensile speed of the enamel layer of the specimen in the tensile test. Tensile tests were performed on two parallel specimens using a tensile testing machine. The strain control mode was adopted and the strain was set to 0.07. The tensile speeds of the two parallel specimens were 1 mm / min and 5 mm / min, respectively. No cracks were generated in the enamel layer of the two parallel specimens. The optimal tensile speed of the specimen was determined to be 5 mm / min.

[0035] 4) Measure the strain corresponding to the microcracks in the enamel layer of the enamel-coated steel plate to be tested. Tensile tests were performed on four parallel specimens using a tensile testing machine. The strain control mode was adopted, and the data storage displacement interval for the elastic modulus stage of the specimen was set to 1 μm. The optimal tensile speed of the enamel layer of the specimen was set to 5 mm / min. The bisection asymptotic method was adopted, and the strain data interval between 0.5×X and X was set to 0.05%, 0.0625%, 0.075%, and 0.0875%, respectively. The strain corresponding to the microcracks in the enamel layer of the specimen was recorded as 0.0875.

[0036] The crack data of the enamel layer of the tensile specimens under different strain rates in Example 1 are shown in Table 1.

[0037] Table 1. Data on enamel layer cracks in tensile specimens under different strain rates in Example 1 of the present invention.

[0038]

[0039] Example 2: The enamel steel plate to be tested is a BTC340R enamel steel plate with a thickness of 3.6mm. The enamel layer of the enamel steel plate is applied by a two-stage enamel coating method.

[0040] A method for measuring the ultimate strain of microcracks in the enamel layer of an enamel-lined steel plate includes the following steps:

[0041] 1) Sample preparation: The enamel-lined steel plate to be tested is processed into parallel specimens for tensile testing, with the original gauge length L0 being 80 mm and the specimen width b0 being 20 mm.

[0042] 1.1) First, the enamel steel plate to be tested is processed into a long strip tensile specimen with a size of 270mm×30mm by wire cutting.

[0043] 1.2) The long strip tensile specimen was precision machined using a milling machine to obtain a standard-sized tensile specimen of 270mm×20mm with a parallel section length of 100mm.

[0044] 1.3) Remove burrs from the parallel section of the tensile specimen;

[0045] 2) Measure the strain corresponding to the yield strength on the enamel steel plate to be tested. Perform a tensile test on one parallel specimen using a tensile testing machine. Use displacement control mode and set the tensile speed to 5 mm / min in the elastic modulus stage, 5 mm / min in the yield strength stage, and 25 mm / min in the fracture stage. Based on the attenuation value of the tensile force on the specimen, set the sensitivity of the yield point detection on the specimen to 0.4% Fmax. Set the force limit of the specimen's yield strain at the end of the tensile test to exceed 3% of the yield strength. Set the tensile force attenuation threshold corresponding to the termination of the tensile test to 80% Fmax, the tensile force threshold corresponding to specimen fracture to 0.1% Fmax, and the displacement of the specimen after fracture to 4 mm. Record the strain corresponding to the yield strength on the specimen during the tensile test as 0.15%.

[0046] 3) Determine the optimal tensile speed of the enamel layer of the specimen in the tensile test. Tensile tests were performed on two parallel specimens using a tensile testing machine. The strain control mode was adopted and the strain was set to 0.1. The tensile speeds of the two parallel specimens were 0.5 mm / min and 4 mm / min, respectively. No cracks were generated in the enamel layer of the two parallel specimens. The optimal tensile speed of the specimen was determined to be 4 mm / min.

[0047] 4) Measure the strain corresponding to the microcracks in the enamel layer of the enamel-coated steel plate to be tested. Tensile tests were performed on four parallel specimens using a tensile testing machine. The strain control mode was adopted, and the data storage displacement interval for the elastic modulus stage of the specimen was set to 0.5 μm. The optimal tensile speed of the enamel layer of the specimen was set to 4 mm / min. The bisection asymptotic method was adopted, and the strain data interval between 0.5×X and X was set to 0.075%, 0.094%, 0.1125%, and 0.131%, respectively. The strain corresponding to the microcracks in the enamel layer of the specimen was recorded as 0.131.

[0048] The crack data of the enamel layer of the tensile specimens under different strain rates in Example 2 are shown in Table 2.

[0049] Table 1. Crack data of enamel layer in tensile specimens under different strain rates in Example 2 of the present invention.

[0050]

[0051] In addition to the embodiments described above, the present invention may have other implementations. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for measuring the ultimate strain of microcracks in the enamel layer of an enamel-lined steel plate, characterized in that, The method includes the following steps: 1) Prepare the test specimen by processing the enamel steel plate to be tested into a parallel specimen for tensile testing; 2) Measure the strain corresponding to the yield strength on the enamel steel plate to be tested. Perform a tensile test on one parallel specimen using a tensile testing machine. Use the displacement control mode and set the tensile speed in the elastic modulus stage, the tensile speed Y in the yield strength range stage, and the tensile speed in the fracture stage. Record the strain X corresponding to the yield strength on the specimen. 3) Determine the optimal tensile speed Y1 for the enamel layer of the specimen in the tensile test. Perform tensile tests on two parallel specimens using a tensile testing machine, employing strain control mode and setting the strain to 0.50×X~X. The tensile speeds for the two parallel specimens are 0.10×Y~0.49×Y mm / min and 0.50×Y~Y mm / min, respectively. Record whether cracks occur in the enamel layer of the two parallel specimens. Determine the optimal tensile speed based on the occurrence of cracks in the enamel layer of the specimens. If neither specimen develops cracks, the larger tensile speed is the optimal tensile speed. If one specimen does not develop cracks, its tensile speed is the optimal tensile speed. If both specimens develop cracks, repeat the tensile test on the parallel specimens with a lower strain until the optimal tensile speed is determined. 4) Measure the strain X1 corresponding to the microcrack in the enamel layer of the enamel steel plate to be tested. Perform tensile tests on 4 parallel specimens using a tensile testing machine. Use strain control mode, set the data storage displacement interval of the specimen elastic modulus stage and the optimal tensile speed Y1 of the specimen enamel layer; use the bisection asymptotic method to set the strain data interval between 0.5×X and X; record the strain X1 corresponding to the microcrack in the specimen enamel layer.

2. The method for measuring the ultimate strain of microcracks in the enamel layer of an enamel-lined steel plate as described in claim 1, characterized in that, Step 1) The preparation of the sample includes: 1.1) The enamel-coated steel sheet to be tested is processed into a long strip tensile specimen by wire cutting; 1.2) The long strip tensile specimen is finished by milling to obtain a tensile specimen of standard size; 1.3) Remove burrs from the parallel section of the tensile specimen.

3. The method for measuring the ultimate strain of microcracks in the enamel layer of an enamel-lined steel plate as described in claim 1, characterized in that, Step 2) involves measuring the strain corresponding to the yield strength of the enamel-coated steel plate to be tested, including: A tensile test was performed on one parallel specimen using a tensile testing machine. The displacement control mode was adopted, and the tensile speed for the specimen's yield range and the tensile speed for the specimen's yield point were set. The sensitivity for detecting the yield point on the specimen was set according to the attenuation value of the tensile force on the specimen. The force limit of the specimen's yield strain at the end of the tensile test was set. The tensile force attenuation threshold corresponding to the termination of the tensile test, the tensile force threshold corresponding to specimen fracture, and the displacement of the specimen after fracture were set. The strain X corresponding to the yield strength on the specimen during the tensile test was recorded.

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