Sampling method for tensile property test of hot-rolled magnet yoke steel plate

Abstract

The invention discloses a hot-rolled magnet yoke steel plate tensile property test sampling method, which comprises the following steps: respectively extracting a steel coil from not less than three furnace batch numbers of the first batch of hot-rolled magnet yoke steel plates, sampling at 1 / 2 and 1 / 4 plate width positions and edge positions, and respectively carrying out tensile tests. Test results are compared and analyzed to find out the specific generality of the hot-rolled magnet yoke steel plate, namely the tensile properties of the hot-rolled magnet yoke steel plate at different positions in the longitudinal direction and the plate width, 1 / 4 part lt; 1 / 2 part; in-depth analysis finds that in the rolling process, the phenomena that the temperature of the edge of a steel belt is low, the number of separated second phases is small, strengthening is insufficient and the tensile property is low are easily caused, and therefore edge longitudinal sampling needs to be added in the hot-rolled magnet yoke steel plate tensile property test. The production process is improved, and the tensile property test verification is carried out again. According to the method, the manufacturing technology level and the quality control level of the hot-rolled magnet yoke steel plate are improved, the consistency and stability of product quality are ensured, potential quality hazards are eliminated, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of yoke steel plate sampling, in particular to a method for sampling hot-rolled yoke steel plate tensile performance test (see Figure 1 as shown). Background Art

[0002] Giant hydroelectric units (such as Figure 2 The rotor yoke size is φ16m×3.7m, and the weight is about 1300t. It is made of 22420 hot-rolled yoke steel plates (length 2400mm×width 1200mm×thickness 3mm) at the power station site. Figure 3 The yoke is made of a 2-axis magnetic field (as shown in the figure), and 56 magnetic poles (weight 1 t / each) are hung on the "T"-shaped slot on the outer circle of the yoke. The yoke is both the rotating magnetic circuit of the hydro-generator and an important rotating force-bearing component.

[0003] Generally, the tensile properties of steel plates for engineering structures are weaker in the transverse direction than in the longitudinal direction, and the properties at the edge of the plate width are higher, and the tensile properties gradually decrease from the edge of the plate width → 1 / 4 → 1 / 2. Therefore, the sampling position for the tensile properties test of steel plates for engineering structures shall be in accordance with GB / T 2975 "Sampling Position and Specimen Preparation for Mechanical Properties Test of Steel and Steel Products" - a compromise is made at the 1 / 4 position of the plate width, and a transverse sample (test specimen) is taken.

[0004] Q / CTG 26 standard stipulates that the sampling position of the hot-rolled yoke steel plate tensile performance test shall also be carried out in accordance with GB / T 2975. Considering that the "T"-shaped slot of the hot-rolled yoke steel plate is subjected to both radial force and tangential force during the operation of the hydropower unit (such as Figure 4 As shown), it is stipulated that in the tensile performance test of hot-rolled yoke steel plate, in addition to taking a transverse sample (test specimen) at the 1 / 4 position of the plate width, a longitudinal sample (test specimen) should also be taken (see Figure 5 As shown in Table 2), the tensile properties test results of the transverse and longitudinal specimens (test samples) should meet the requirements of Table 2.

[0005] Table 2 Tensile properties

[0006] For the first batch of hot-rolled yoke steel plates delivered, the steel mill took transverse and longitudinal samples (test specimens) at 1 / 4 of the plate width for each coil, and the tensile test results showed that the performance was qualified; however, the subsequent random inspection took longitudinal samples (test specimens) at the edge of the plate width, and the tensile test results showed that the yield strength R p0.2 All of them were below 750MPa and failed to meet the standards, resulting in all hot-rolled yoke steel plates in the same batch being scrapped, causing great losses. Summary of the invention

[0007] The technical problem to be solved by the present invention is that although the tensile test results meet the set requirements by sampling at the 1 / 4 position of the plate width, it is found that the tensile performance at the edge position is lower than the tensile performance at the 1 / 4 position and is unqualified, resulting in the hot-rolled yoke steel plate detection being unrepresentative and causing scrap losses.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for sampling a hot-rolled yoke steel plate tensile property test, characterized in that it comprises the following steps: Step 1: Select one steel coil from each of the first batch of hot-rolled yoke steel plates supplied, no less than three heat batches; Step 2: Take samples at the 1 / 2 position, 1 / 4 position and edge position of the hot-rolled yoke steel plate to conduct tensile performance test; Step 3, comparing the average tensile properties of the samples (test specimens) at different positions of the same hot-rolled yoke steel plate, and comparing the average tensile properties of the samples (test specimens) at the same position of the hot-rolled yoke steel plates with different furnace batch numbers; Step 4: Based on the comparison results obtained in step 3, the manufacturing process of the samples (test pieces) at different positions of the same hot-rolled yoke steel plate and the samples (test pieces) at the same position of the hot-rolled yoke steel plates with different furnace batch numbers are compared; Step 5: Determine the correlation between the low tensile properties of the edge of the hot-rolled yoke steel plate and the manufacturing process, and improve the production process of the hot-rolled yoke steel plate; Step 6: Take samples of the improved hot-rolled yoke steel plate at the 1 / 2 position, 1 / 4 position and edge position of the plate width, and conduct a tensile performance test.

[0009] Preferably, in step 2, transverse and longitudinal samples (test specimens) are taken at the 1 / 2 position and the 1 / 4 position of the plate width, and a longitudinal sample (test specimen) is taken at the edge of the plate width.

[0010] Preferably, in step 2, samples are taken separately from areas of the hot-rolled yoke steel plate where color differences exist, including dark areas and light areas, and the tensile properties of the samples (test specimens) in the dark area and the light area are compared.

[0011] Preferably, the step three comprises: Step 3.1, compare the tensile properties of the dark-colored samples (test specimens) oxidized at the edges of the hot-rolled yoke steel plates and the light-colored samples (test specimens) that are not oxidized, to determine the effect of oxidation on the tensile properties of the hot-rolled yoke steel plates during stress relief heat treatment.

[0012] Preferably, the step 4 comprises: Step 4.1: According to the stress relief heat treatment process of the hot-rolled yoke steel plate, the space that originally caused the oxygen-containing gas to enter is eliminated.

[0013] Preferably, the step three comprises: Step 3.2, compare the microstructures of samples (specimens) with different tensile properties, including samples (specimens) at different positions of the same hot-rolled yoke steel plate and samples (specimens) at the same position of hot-rolled yoke steel plates with different furnace batch numbers.

[0014] Preferably, the step 4 comprises: Step 4.2, a high-strength manufacturing process is adopted according to the hot-rolled yoke steel plate, wherein the ferrite fine grain strengthening + precipitation second phase strengthening are simultaneously adopted, wherein the ferrite fine grain strengthening is achieved by the rolling process control and the ferrite phase transformation control, and the ferrite fine grain strengthening result is judged whether the strengthening effect is obvious by the ferrite grain size grade; the precipitation second phase strengthening is achieved by the chemical composition design and the rolling process temperature control, and the difference between the precipitation second phase result and the set chemical composition is compared, and the scanning electron microscope energy spectrum analysis is adopted.

[0015] Preferably, in step 4.3, the chemical composition of the second phase analyzed by scanning electron microscope energy spectrum is compared with the set chemical composition, and the set chemical composition is shown in reference table 1.

[0016] Table 1 Chemical composition (%)

[0017] Preferably, in step 4.4, the temperature distribution of the hot-rolled yoke steel plate during the rolling process is tested, and the temperatures at locations where differences in tensile properties exist are compared.

[0018] Preferably, in step 4.4, according to the locations where the temperature is low, the second phase precipitation is less, and the strengthening is insufficient during the rolling process of the hot-rolled yoke steel plate, a local heating device is correspondingly provided, and the overall temperature consistency of the hot-rolled yoke steel plate is controlled.

[0019] 1. The present invention provides a sampling method for the tensile performance test of hot-rolled yoke steel plates, which reflects the essential laws of hot-rolled yoke steel plates. The implementation of this method is conducive to promoting the improvement of the manufacturing process technology level of hot-rolled yoke steel plates, and is conducive to promoting the improvement of the uniformity, consistency and stability of the tensile performance of hot-rolled yoke steel plates.

[0020] 2. A hot-rolled yoke steel plate tensile performance test sampling method is used for testing, which can reflect the true performance of the hot-rolled yoke steel plate, effectively control the quality of the hot-rolled yoke steel plate, and prevent the risk of unqualified products entering the subsequent stage.

[0021] 3. A sampling method for the tensile performance test of hot-rolled yoke steel plates is both scientific and reasonable, easy to implement, highly consistent, and has significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below in conjunction with the accompanying drawings and embodiments: Figure 1Schematic diagram of sampling positions according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of a giant hydroelectric unit.

[0024] Figure 3 This is a schematic diagram of the structure of the yoke steel plate laminations of a giant hydropower unit.

[0025] Figure 4 This is a schematic diagram of the "T"-shaped slot of the hot-rolled yoke steel plate being subjected to both radial force and tangential force.

[0026] Figure 5 This is a schematic diagram of taking transverse and longitudinal specimens (test samples) at 1 / 4 of the plate width for the tensile properties test of hot-rolled yoke steel plates as originally specified in the Q / CTG 26 standard.

[0027] Figure 6 This is the color difference diagram of the hot-rolled yoke steel plate of Steel Plant A.

[0028] Figure 7 This is a schematic diagram of the tensile properties of the first batch of hot-rolled yoke steel plates of Steel Plant A in the longitudinal direction, at the width edge, and at the 1 / 4 position.

[0029] Figure 8 This is a schematic diagram of the tensile properties of the first batch of hot-rolled yoke steel plates of Steel Plant B in the longitudinal direction, at the width edge, and at the 1 / 4 and 1 / 2 positions.

[0030] Fig. 9 This is a photo of the steel coil coming out of the furnace after stress relief heat treatment.

[0031] Fig.10 This is the microstructure picture of the first batch of hot-rolled yoke steel plates produced by Steel Plant A.

[0032] Fig.11 This is a picture of the ferrite grain size of the first batch of hot-rolled yoke steel plates produced by Steel Plant A.

[0033] Fig.12 This is a picture of the second phase chemical composition detection of the first batch of hot-rolled yoke steel plates of Steel Plant A using scanning electron microscope energy spectrum analysis.

[0034] Fig.13 This is a temperature difference diagram along the width of the steel strip for the first batch of hot-rolled yoke steel plates produced by Steel Plant A.

[0035] Fig.14 The width direction R of the first batch of hot-rolled yoke steel plates of Steel Plant A p0.2 Distribution map.

[0036] Fig.15 This is the tensile performance diagram of the hot-rolled yoke steel plate in the transverse direction and at 1 / 4 of the plate width of Steel Plant A after sampling analysis and modification of the production process.

[0037] Fig.16This is the tensile performance diagram of the longitudinal, width edge, 1 / 4, and 1 / 2 positions of the hot-rolled yoke steel plate of Steel Plant A after sampling analysis and modification of the production process.

[0038] Fig.17 To analyze the tensile properties of the hot-rolled yoke steel plate in the transverse direction and at 1 / 4 and 1 / 2 of the plate width of Steel Plant B after sampling and analysis and modification of the production process.

[0039] Fig.18 This is the tensile performance diagram of the longitudinal, width edge, 1 / 4, and 1 / 2 positions of the hot-rolled yoke steel plate of Steel Plant B after sampling analysis and modification of the production process. DETAILED DESCRIPTION

[0040] The invention provides a sampling method for a hot-rolled yoke steel plate tensile property test. 1. Technical background 1.1. Hot-rolled yoke steel plate is an important functional force-bearing material that integrates high strength, high magnetism and high-precision plate shape.

[0042] In order to improve electromagnetic efficiency, the hot-rolled yoke steel plate is required to have excellent magnetic properties, as shown in Table 3.

[0043] Table 3 Magnetic properties

[0044] In order to facilitate correction, laser cutting and improve the lamination quality, the thickness of the hot-rolled yoke steel plate is 3mm~4mm, and the plate unevenness is required to be no more than 1mm / m, see Table 4.

[0045] Table 4 Dimensional accuracy

[0046] During the operation of the hydropower unit, the "T" slot is subjected to both radial force and tangential force. Figure 4 As shown, it is stipulated that in the tensile property test of hot-rolled yoke steel plate, in addition to taking a transverse sample (test specimen) at the 1 / 4 position of the plate width, a longitudinal sample (test specimen) should also be taken (see Figure 4 As shown in Table 2), the tensile properties test results of transverse and longitudinal specimens shall meet the requirements of Table 2.

[0047] Table 2 Tensile properties

[0048] The hot-rolled yoke steel plates for giant hydropower unit A and giant hydropower unit B are supplied by two domestic steel mills, Steel Mill A and Steel Mill B.

[0049] 1.2. Appearance defects When testing the first batch of hot-rolled yoke steel plates for giant hydropower unit B supplied by Steel Plant A, it was found that the hot-rolled yoke steel plates had color differences. The color of the longitudinal sides was darker, and the color of the middle part was lighter. Figure 6 shown.

[0050] Before shipment, Steel Plant A took transverse and longitudinal samples (test specimens) at 1 / 4 of the plate width and conducted self-inspection on tensile properties, and both were qualified.

[0051] 2. Sampling verification Among the first batch of hot-rolled yoke steel plates for giant hydropower unit B supplied by Steel Plant A, one steel coil was selected from each of three furnace batches.

[0052] The tensile test results of transverse and longitudinal samples (test specimens) taken at the 1 / 4 position of the lighter color plate width are both qualified; and the tensile test results of longitudinal samples (test specimens) taken at the edge position of the darker color plate width are qualified. p0.2 The average tensile test results of the longitudinal specimens (test specimens) at the edge of the plate width and the longitudinal specimens (test specimens) at the 1 / 4 position of the plate width are shown in Figure 7 shown.

[0053] It was found that the longitudinal edge tensile properties R p0.2 After the failure, the first batch of hot-rolled yoke steel plates of giant hydropower unit B supplied by Steel Plant B were immediately inspected and the same color difference was found. At the same time, the tensile performance test results of the hot-rolled yoke steel plates of Steel Plant B were taken longitudinally, at the edge of the plate width, and at 1 / 4 and 1 / 2 positions. Figure 8 shown.

[0054] from Figure 8 It can be seen that although the longitudinal tensile performance of the hot-rolled yoke steel plate of Steel Plant B is qualified, the longitudinal edge tensile performance is also the lowest - among which R p0.2 , tensile strength R m Pass but with small margin.

[0055] Therefore, the unique commonality of hot-rolled yoke steel plates was discovered for the first time - the tensile properties at different positions in the longitudinal direction and across the plate width: edge < 1 / 4 < 1 / 2, which is completely opposite to the tensile properties distribution of general engineering structure steel plates.

[0056] Since both longitudinal edges of the hot-rolled yoke steel plate are key stress-bearing parts, the (inner circle) edge "T"-shaped slot is connected to the rotor bracket, and the (outer circle) edge "T"-shaped slot is used to hang the magnetic pole, all the hot-rolled yoke steel plates of the same batch with unqualified edge tensile properties are scrapped.

[0057] 3. Experimental verification of the correlation between low tensile properties and specific manufacturing processes 3.1 Analysis of the correlation between surface color difference and tensile properties The hot-rolled yoke steel plate structure design is based on the tensile performance R at 1 / 4 of the plate width. p0.2 , R m The tensile properties of the key stress-bearing parts on both sides of the longitudinal direction are calculated to be lower than the position R of 1 / 4 of the plate width.p0.2 Assessment of technical indicators is not allowed.

[0058] After finishing rolling, the hot-rolled yoke steel plate is rolled into a coil and subjected to stress relief heat treatment in a furnace (such as a bell-type furnace). Fig. 9 The figure shows 4 steel coils strung together and taken out of the furnace after stress relief heat treatment. In order to maintain the plate shape, the coiling tension is reduced during coiling, resulting in an increase in the interlayer interval at the edge of the steel coil. During the stress relief heat treatment, high-temperature oxygen-containing gas can easily enter, causing the edge surface to be oxidized and its color to darken; while the middle part of the steel coil has no intermittent high-temperature oxygen-containing gas and cannot enter, so the surface of the middle part is not oxidized, retaining the original color after fine rolling, that is, light color.

[0059] After testing, the thickness of the oxide scale on the edge is about 0.01mm. The oxide scale partially falls off and pits are visible to the naked eye. After pickling, all the pits are eliminated. After testing, the depth of the single-sided oxide deoxidation layer on the edge is about 0.15mm, and the depth of the deoxidation layer on both sides is about 0.3mm in total. The deoxidation of the edge has a certain adverse effect on the strength. For hot-rolled yoke steel plates with a thickness of only 3mm to 4mm, this problem cannot be ignored.

[0060] Based on the above analysis, the stress relief heat treatment process of hot-rolled yoke steel plate and coil causes the edge surface to oxidize, making its color darker and forming color difference; the oxidation and decarbonization of the edge surface has a certain adverse effect on its strength, but it is not the main reason for the low tensile properties of the edge.

[0061] 3.2 Analysis of correlation between organization and tensile properties In order to obtain a high-precision plate shape with an unevenness of ≤1mm / m, the yoke steel plate is used directly in the hot-rolled state to avoid the deterioration of the plate shape caused by quenching and tempering. In other words, in order to maintain the plate shape accuracy, the yoke steel plate does not obtain high strength through quenching and tempering heat treatment.

[0062] In order to obtain high magnetic properties and to facilitate correction to obtain a high-precision plate shape with an unevenness of ≤1mm / m, the matrix structure of the hot-rolled yoke steel plate is designed to be ferrite.

[0063] However, the strength of ferrite is too low. In order to obtain high strength of 750MPa, it is necessary to adopt both fine grain strengthening and precipitation of second phase strengthening.

[0064] The test results of the first batch of hot-rolled yoke steel plates for giant hydropower unit B supplied by Steel Plant A show that its microstructure is ferrite + second phase. Fig.10 shown.

[0065] In addition to composition factors, ferrite fine grain strengthening is achieved through the control of steel strip rolling process and ferrite phase transformation. The test results of the first batch of giant hydropower unit B hot-rolled yoke steel plates supplied by Steel Plant A show that the ferrite grain size is finer than level 9, and the strengthening effect is obvious. Fig.11 shown.

[0066] 2) Precipitation of the second phase strengthening is achieved through the following two ways: a) Chemical composition design. The Q / CTG 26 standard requires the addition of appropriate amounts of microalloying elements such as Nb and Ti (see Table 5). Nb, Ti and elements such as C, Mn, and N form a second phase to achieve strengthening. The chemical composition test results of the first batch of giant hydropower unit B hot-rolled yoke steel plates supplied by Steel Plant A, among which the content of some elements is shown in Table 5; the chemical composition of the second phase analyzed by scanning electron microscope energy spectrum: C 0.31%, Mn 1.15%, Nb 6.17%, Ti 7.07%, etc., see Fig.12 Place.

[0067] Table 5 Chemical composition (%)

[0068] b) The temperature distribution of the steel strip during the rolling process has a great influence on the precipitation of the second phase. Due to water spraying for descaling and controlled rolling during the rolling process, the temperature of the edge of the steel strip is 50℃~80℃ lower than the temperature in the middle of the steel strip. The actual temperature difference in the width direction of the steel strip is shown in Fig.13 As shown in the figure, the lower temperature at the edge of the steel strip leads to less precipitation of the second phase, and less precipitation of the second phase leads to insufficient strengthening. This is the fundamental reason for the low tensile properties of the edge of the hot-rolled yoke steel plate. The width direction R p0.2 Distribution Fig.14 shown.

[0069] 4. Test conclusions and process modifications This discovery reveals the essence of the low tensile properties at the edges of hot-rolled yoke steel plates: the rolling process causes the edges of the steel strip to: have low temperature → less precipitation of the second phase → insufficient strengthening → low tensile properties.

[0070] According to the results of sampling and testing, targeted adjustments are made to the production process of hot-rolled yoke steel plates, including: 1. Use edge heating device to increase the edge temperature by about 30℃.

[0071] 2. The descaling water between the finishing mill stands and the cooling water between the stands are shielded by the edges to reduce the direct spraying of water on the edge of the steel strip, reduce the cooling speed of the edge of the steel strip, and make the edge temperature of the steel strip consistent with the middle temperature.

[0072] 3. After rough rolling, the steel strip quickly enters the finishing mill to reduce the temperature drop of the intermediate billet.

[0073] 4. Increase the coiling tension of the steel coil and reduce the interval between steel strip layers.

[0074] 5. The heat treatment furnace is filled with protective gas.

[0075] 5. Application effect After improving the production process of hot-rolled yoke steel plate, samples were taken again for testing. The tensile properties of hot-rolled yoke steel plate in the transverse direction and at 1 / 4 of the plate width of Steel Plant A are shown in Fig.15 As shown, the tensile properties of the hot-rolled yoke steel plate of Steel Plant A in the longitudinal direction, the width edge, 1 / 4, and 1 / 2 positions are shown in Fig.16 As shown; the tensile properties of the hot-rolled yoke steel plate of Steel Plant B at the 1 / 4 and 1 / 2 positions of the plate width are shown in the figure Fig.17 As shown, the tensile properties of the hot-rolled yoke steel plate in the longitudinal direction, the width edge, 1 / 4 and 1 / 2 of the plate are shown in Fig.18 As shown. Figure 15 to Figure 18 It can be seen that: 1. Tensile properties R of hot-rolled yoke steel plates of Steel Plant A and Steel Plant B p0.2 , R m All increased significantly.

[0076] 2. The tensile properties of the hot-rolled yoke steel plates in the longitudinal direction, the width edge, 1 / 4 and 1 / 2 of the steel plates in Steel Plant A and Steel Plant B are R p0.2 , or R m The differences are very small, that is, the uniformity of tensile properties at different positions in the longitudinal direction and the width of the board is greatly improved.

[0077] 3. The consistency of tensile properties of hot-rolled yoke steel plates of Steel Plant A and Steel Plant B has been greatly improved.

[0078] 4. The tensile performance stability of the hot-rolled yoke steel plates of Steel Plant A and Steel Plant B has been greatly improved.

[0079] 5. The tensile properties of hot-rolled yoke steel plates are improved, which significantly improves the manufacturing quality of the rotor yokes of giant hydropower units A and B.

Claims

1. A method for sampling hot-rolled yoke steel plate tensile properties test, characterized in that: The steps include: Step 1: Select one steel coil from each of the first batch of hot-rolled yoke steel plates supplied, no less than three heat batches; Step 2: Take samples at the 1 / 2 position, 1 / 4 position and edge position of the hot-rolled yoke steel plate to conduct tensile performance test; Step 3: Compare the average tensile properties of the samples (test specimens) at different plate width positions of the same hot-rolled yoke steel plate, and compare the average tensile properties of the samples (test specimens) at the same position of the hot-rolled yoke steel plates with different furnace batch numbers; Step 4: Based on the comparison results obtained in step 3, the manufacturing process of the samples (test pieces) at different positions of the same hot-rolled yoke steel plate and the samples (test pieces) at the same position of the hot-rolled yoke steel plates with different furnace batch numbers are compared; Step 5: Determine the correlation between the low tensile properties of some areas of the hot-rolled yoke steel plate and the manufacturing process, and improve the production process of the hot-rolled yoke steel plate; Step 6: Take samples of the improved hot-rolled yoke steel plate at the 1 / 2 position, 1 / 4 position and edge position of the plate width, and conduct a tensile performance test.

2. A method for sampling a hot-rolled yoke steel plate for tensile properties test according to claim 1, characterized in that: In the step 2, transverse and longitudinal samples (test specimens) are taken at the 1 / 2 position and the 1 / 4 position of the plate width, and the longitudinal sample (test specimen) is taken at the edge of the plate width.

3. A method for sampling a hot-rolled yoke steel plate for tensile properties test as claimed in claim 2, characterized in that: In the step 2, samples are taken from the areas of the hot-rolled yoke steel plate where color differences exist, including dark areas and light areas, and the tensile properties of the samples (test specimens) in the dark area and the light area are compared.

4. A method for sampling a hot-rolled yoke steel plate for tensile properties test according to claim 1, characterized in that: The step three comprises: Step 3.1, compare the tensile properties of the dark-colored samples (test specimens) oxidized at the edges of the hot-rolled yoke steel plates and the light-colored samples (test specimens) that are not oxidized, to determine the effect of oxidation on the tensile properties of the hot-rolled yoke steel plates during stress relief heat treatment.

5. A method for sampling a hot-rolled yoke steel plate for tensile properties test as claimed in claim 4, characterized in that: The fourth step comprises: Step 4.1: According to the stress relieving heat treatment process of the hot-rolled yoke steel plate, the space that originally caused the oxygen-containing gas to enter is eliminated.

6. A method for sampling a hot-rolled yoke steel plate for tensile properties test according to claim 1, characterized in that: The step three comprises: Step 3.2, compare the microstructures of the samples (specimens) with different tensile properties, including samples (specimens) at different positions of the same hot-rolled yoke steel plate and samples (specimens) at the same position of different hot-rolled yoke steel plates.

7. A method for sampling a hot-rolled yoke steel plate for tensile properties test according to claim 6, characterized in that: The fourth step comprises: Step 4.2, according to the process of hot-rolled yoke steel plate, fine grain strengthening + precipitation second phase strengthening are simultaneously adopted to obtain high strength, wherein ferrite fine grain strengthening is achieved by rolling process control and phase change temperature control, and the result is judged whether the strengthening effect is obvious by the ferrite grain size grade; precipitation of the second phase is achieved by chemical composition design and rolling process temperature control, and the difference between the precipitation second phase result and the set chemical composition is compared, and scanning electron microscope energy spectrum analysis is used.

8. A method for sampling a hot-rolled yoke steel plate for tensile properties test according to claim 7, characterized in that: Step 4.3: Compare the chemical composition of the second phase by SEM energy spectrum analysis with the set chemical composition. The set chemical composition is shown in Reference Table 1. Table 1 Chemical composition (%) 。 9. A method for sampling a hot-rolled yoke steel plate for tensile properties test according to claim 7, characterized in that: Step 4.4: Test the temperature distribution of the hot-rolled yoke steel plate during the rolling process, and compare the temperatures at locations where there are differences in tensile properties.

10. A method for sampling a hot-rolled yoke steel plate for tensile properties test according to claim 9, characterized in that: Step 4.4: According to the locations where the temperature is relatively low during the rolling process of the hot-rolled yoke steel plate, a local heating device is correspondingly provided, and the overall temperature of the hot-rolled yoke steel plate is controlled to be consistent.

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