A method for measuring residual stress of oriented silicon steel

Abstract

The present invention discloses a method for measuring residual stress in grain-oriented silicon steel. The method comprises the following steps: first, cold-rolling the grain-oriented silicon steel, annealing it, and holding it at a temperature of 000°C; performing surface treatment on the grain-oriented silicon steel before and after annealing at different holding times, respectively, to ensure that the surface roughness of the grain-oriented silicon steel is ≤0.4 μm; measuring the hardness of the grain-oriented silicon steel before annealing, which is defined as the structural hardness in the stage where residual stress has not been removed, and the residual stress content at this stage is defined as 100%; simultaneously measuring the hardness of the grain-oriented silicon steel at different holding times until the hardness reaches a stable region, and defining the residual stress content in the stable region as 0%; establishing a relationship between the hardness of the grain-oriented silicon steel and the residual stress content, and obtaining the residual stress content of the grain-oriented silicon steel at different annealing holding times by measuring the hardness, thereby enabling real-time measurement of the residual stress of the grain-oriented silicon steel.

Description

Technical Field

[0001] The present invention relates to the technical field of stress measurement of oriented silicon steel, and in particular to a method for measuring residual stress of oriented silicon steel. Background Art

[0002] In the traditional grain-oriented silicon steel CGO (common grain-oriented silicon steel) process, a large amount of residual stress exists in the structure after the first cold rolling. The residual stress is decomposed by the recrystallization growth of the structure during the subsequent intermediate annealing process, and then a secondary cold rolling is performed. If the intermediate annealing temperature is too low or the time is too short, the residual stress cannot be fully decomposed, the deformation resistance of the structure is large, and it is difficult to roll the silicon steel to the target thickness in the secondary cold rolling, and it may even cause cracks and fractures in the material. If the intermediate annealing temperature is too high or the time is too long, although the residual stress can be completely removed, the industrial cost increases and the economic benefit is low. Therefore, a convenient, fast and low-cost residual stress content measurement method is needed to determine the best and most economical annealing process. There are currently two types of methods for measuring residual stress in common silicon steel: mechanical method and non-destructive testing method.

[0003] The most common mechanical method is the hole-drilling method (also known as the blind-hole method, GB / T 3395-2013). This method involves drilling a small hole in a thin silicon steel plate, releasing stress in the area adjacent to the hole, which generates corresponding displacement and strain. These displacements and strains are then measured using methods such as adhesive strain gauges. The average residual stress along the depth of the hole is then converted. However, its disadvantages are that it requires certain dimensions for the silicon steel and requires drilling a hole in the steel surface, which damages the component. The drilling process often causes material damage and yielding, affecting measurement results. Furthermore, the blind-hole method only measures surface residual stress and cannot measure residual stress within the material.

[0004] Nondestructive measurement methods include X-ray diffraction (GB / T 7704-2017), neutron diffraction (GB / T 26140-2010), and ultrasonic methods (GB / T 32073-2015). These methods primarily utilize physical optics and nuclear physics techniques to measure the changes in physical constants (such as lattice constants) within a material under stress, indirectly calculating residual stress. X-ray diffraction is currently the most widely used nondestructive residual stress measurement method. The basic principle is that when residual stress exists within silicon steel after cold rolling, the interplanar spacing between different grains changes regularly with the magnitude of the stress, and the corresponding strain is measured from this change. However, its disadvantages are that it is only applicable to certain materials that produce relatively clear and sharp diffraction lines. Due to the limited projection capability of X-rays, they can only detect the surface of an object and cannot measure the interior of silicon steel. Furthermore, the principle is complex, the data processing is cumbersome, and the operation is relatively difficult.

[0005] It can be seen that both mechanical and non-destructive measurement methods have great limitations in their application, are difficult to operate in practice, have complex mechanisms, and are cumbersome to operate. In addition, they cannot measure the residual stress in different layers of oriented silicon steel. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention provides a method for measuring residual stress in grain-oriented silicon steel. This method utilizes the principles of internal stress elimination and work hardening during annealing, recrystallizing the structure, to estimate residual stress content based on changes in structure hardness. This method offers the advantages of simple principle, convenient operation, and wide application. Furthermore, combined with grinding and microstructure analysis, it can measure the thickness of different layers.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for measuring residual stress of oriented silicon steel is disclosed. The method measures the hardness of the oriented silicon steel at different annealing and holding times and obtains the residual stress content according to the hardness change.

[0009] Furthermore, the specific method for obtaining the residual stress content based on the hardness change is as follows: the hardness of the silicon steel structure before annealing is defined as the hardness of the structure in the stage where the residual stress is not removed, and its residual stress content is defined as 100%; the hardness at different annealing holding times is measured, and when the hardness reaches a stable region, this stage is defined as the stage where the residual stress is completely eliminated, and the residual stress content at this time is 0%. The relationship between the residual stress content and the hardness is established, and the residual stress content of the silicon steel at the different holding times can be determined by the hardness of the silicon steel at the different holding times.

[0010] Furthermore, the hardness reaching a stable area means that as the annealing time increases, the hardness tends to be stable and approximates a horizontal straight line. The fluctuation amplitude of any three or more adjacent hardness values ​​is within 1HV, which is considered to be a completely stress-relieved state. The average value of these three or more hardness values ​​is defined as the hardness value in the stable area.

[0011] A method for measuring residual stress in different layers of oriented silicon steel, comprising the following steps:

[0012] S1: cold rolling the oriented silicon steel, annealing it, and keeping it warm;

[0013] S2: Surface treatment is performed on the oriented silicon steel before and after annealing with different holding times, so that the surface roughness of the oriented silicon steel is ≤0.4 μm;

[0014] S3: Determine the hardness of the grain-oriented silicon steel after cold rolling and before annealing, which is defined as the microstructure hardness at the stage where the residual stress is not removed, and the residual stress content at this stage is defined as 100%;

[0015] S4: measuring the hardness of the grain-oriented silicon steel treated in step S2 at different holding times until the hardness reaches a stable region, and defining the residual stress content in the stable region as 0%;

[0016] S5: Establish the relationship between the hardness of oriented silicon steel and the residual stress content, as shown below:

[0017]

[0018] Where: RS is the residual stress content at holding time t, unit: %; a t The hardness value at the holding time t, unit HV; a 100 is the hardness value in the stage where the residual stress has not been removed, in HV; a0 is the hardness value when the hardness reaches the stable region, in HV.

[0019] S6: performing surface treatment on the oriented silicon steel to be tested to make the surface roughness of the oriented silicon steel to be tested ≤ 0.4 μm, measuring the hardness of the oriented silicon steel to be tested at different holding times, and calculating the residual stress content corresponding to the holding time using the formula in step S5.

[0020] Furthermore, in step S1, the temperature of the annealing treatment is 700-800°C.

[0021] Furthermore, in step S2, the surface treatment is performed by grinding and then polishing to obtain oriented silicon steel containing the specific layer to be tested.

[0022] Furthermore, in step S2, the surface treatment is performed by grinding with 240-1500 mesh sandpaper and then polishing to obtain the oriented silicon steel containing the specific layer to be tested.

[0023] Furthermore, the specific layer to be tested includes a decarburized layer, a transition layer or a center layer of the oriented silicon steel, thereby realizing the detection of the residual stress content of different layers.

[0024] Furthermore, the specific method for determining the specific layer to be measured is as follows: first, a metallographic microscope is used to photograph the microstructure of the oriented silicon steel sample in the thickness direction after surface treatment, such as Figure 7 As shown in the figure, the basic thickness of each layer of the grain can be known through the microstructure diagram in the thickness direction. Then use a screw micrometer to measure the original thickness of the sample and the thickness after grinding. The difference between the original thickness and the thickness after grinding is the layer thickness. By comparing the calculated layer thickness with Figure 7 By comparing the thickness of each layer, the layer corresponding to the grinding thickness can be known. That is, the present invention can also determine the layer where the measured residual stress is located while measuring the residual stress content.

[0025] At the same time, you can also Figure 7The thickness of each layer is measured, and then based on this thickness and the thickness before grinding, the thickness of the surface treatment required when measuring different layers or the thickness of the sample after surface treatment is obtained. In other words, the present invention can measure the residual stress of a specific layer.

[0026] Furthermore, for the oriented silicon steel described in the present invention, when it is necessary to measure the decarburized layer, the grinding thickness is limited to ≤25μm; when measuring the transition layer, the grinding thickness is limited to 50μm≤grinding thickness≤85μm; when measuring the center layer, the grinding thickness is limited to 120μm≤grinding thickness≤160μm.

[0027] An application of the measurement method is to measure the residual stress content of different layers of oriented silicon steel; the different layers include any one of the decarburized layer, transition layer and center layer of the oriented silicon steel.

[0028] The beneficial technical effects of the present invention are:

[0029] The present invention utilizes the principle of recrystallization to eliminate residual stress and measures the residual stress content through changes in tissue hardness. The principle is simple, convenient, fast and highly operable.

[0030] The present invention measures the residual stress content at different positions of silicon steel by controlling the grinding depth, overcoming the limitations of traditional mechanical drilling methods and non-destructive methods that can only measure the surface of the material but cannot test the residual stress inside the silicon steel. The measurement method has wider applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of the relationship between annealing time and stress change in the present invention.

[0032] Figure 2 This is a scatter plot of stress changes at different annealing times according to Example 1 of the present invention.

[0033] Figure 3 This is a scatter plot of stress changes at different annealing times according to Example 2 of the present invention.

[0034] Figure 4 This is a scatter plot of stress changes with different annealing times in Example 3 of the present invention.

[0035] Figure 5 This is a scatter plot of stress changes with different annealing times in Example 4 of the present invention.

[0036] Figure 6 This is a scatter plot of stress changes at different annealing times according to Example 5 of the present invention.

[0037] Figure 7 Schematic diagram of the organizational structure of different layers of oriented silicon steel of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0039] A method for measuring residual stress of grain-oriented silicon steel comprises the following steps:

[0040] First, the annealing temperature of the oriented silicon steel sheet to be tested is set to 700-800°C, and different holding times are set. In one embodiment of the present invention, 12 groups of samples with different holding times are set, and the sample numbers are marked as m1, m2...m 12 .

[0041] After annealing, the samples were ground and polished with sandpaper of 240 mesh, 500 mesh, 1000 mesh, 1200 mesh and 1500 mesh respectively to obtain different test layers, with a roughness of about Ra = 0.4 μm.

[0042] Furthermore, different test layers are obtained by surface treating the oriented silicon steel to be tested, so that the surface roughness of the silicon steel in the different test layers is ≤0.4 μm, and the test layers are determined by measuring the microstructure of the test layers with a metallographic microscope.

[0043] Use Vickers hardness tester to measure the hardness of 12 groups of samples, measure 5-7 points of each sample and take the average value, measure the hardness values ​​of samples under different tempering and holding times, and draw them into a scatter plot, such as Figure 1 shown.

[0044] Find the stable hardness value area from the scatter plot, which is defined as the stage where the residual stress is completely eliminated. Figure 1 As shown in section A, m9 and m 10 、m 11 and m 12 In the case where the fluctuation range of adjacent hardness values ​​is within 1HV, it is considered as a completely stress-relieved state. Therefore, the values ​​of m9 and m 10 、m 11 and m 12 The mean hardness of is defined as the structural hardness when the residual stress content of silicon steel is 0%, and this hardness is set as a0.

[0045] The hardness of silicon steel tissue after cold rolling deformation, that is, before annealing, is defined as the tissue hardness in the stage where residual stress is not removed, that is, the tissue hardness corresponding to the residual stress content of 100%. This hardness is set as a 100 .

[0046] It is known that the tissue hardness corresponding to the residual stress stage of 0% and 100% is a0 and a 100 , we can get the relationship model between material hardness and residual stress, as shown in formula (1). By substituting the tissue hardness under different holding times, we can get the corresponding residual stress content.

[0047]

[0048] Where: RS is the residual stress content at holding time t, unit: %; a t The hardness value at the holding time t, unit HV; a 100 is the hardness value before the residual stress is removed, in HV; a0 is the hardness value when the hardness reaches the stable region, in HV. Figure 1 The hardness value in the stable stage A is from a9 to a 12 , so t is the time corresponding to samples m1 to m8.

[0049] In actual production, the above method can be used to determine the layer to be measured in the grain-oriented silicon steel. By determining the hardness corresponding to 0% and 100% residual stress, the hardness at different holding times can be measured and, combined with the above formula (1), the residual stress content of the layer to be measured at the corresponding holding time can be calculated. By measuring the residual stress content of different layers to be measured, the optimal annealing process required for the industrial production of grain-oriented silicon steel can be determined.

[0050] The present invention will be further described below by way of examples.

[0051] Example 1

[0052] A method for measuring residual stress of grain-oriented silicon steel comprises the following steps:

[0053] S1: The annealing temperature of the oriented silicon steel sheet to be tested is set to 700℃, and 12 groups of different holding times (t) are set, namely 1, 2, 3, 4, 5, 6, 10, 20, 30, 40, 50, 60 min, and the sample numbers are recorded as m1, m2...m 12 .

[0054] S2: After annealing, the samples were ground and polished with 240 mesh, 500 mesh, 1000 mesh, 1200 mesh and 1500 mesh sandpaper respectively, with a roughness of about R a = 0.4μm; The approximate thickness of each layer of the grain can be known from the microstructure diagram of the sample thickness direction taken by the metallographic microscope, such as Figure 7 The original thickness of the sample measured by a micrometer was 320 μm, and 160 μm was ground off so that the surface was in the center layer.

[0055] S3: Use Vickers hardness tester to measure the hardness of the center layer of 12 groups of samples, measure 5-7 points of each sample and take the average value, and measure the hardness values ​​of the samples under different tempering and holding times, as shown in Table 1 below. And draw it into a scatter plot, such as Figure 2 shown.

[0056] Table 1: Microstructure hardness at different 700℃ annealing times

[0057]

[0058] S4: Find the stable hardness value area in the scatter plot, which is defined as the stage where the residual stress is completely eliminated. Figure 2 As shown in section B, the average hardness value of section B is defined as the microstructure hardness when the residual stress content of silicon steel is 0%, and the hardness is 215.1HV.

[0059] S5: The hardness of the center layer of the silicon steel structure after cold rolling deformation, that is, before annealing, is measured. It is defined as the structure hardness in the stage where the residual stress is not removed, that is, the structure hardness corresponding to the residual stress content of 100%. The hardness is measured to be 323.6HV.

[0060] S6: It is known that the tissue hardness corresponding to the residual stress stage of 0% and 100% is 215.1HV and 323.6HV respectively. Substituting the tissue hardness at different holding times into Formula 1 can obtain the corresponding residual stress, as shown in Table 2 below.

[0061]

[0062] because Figure 2 The hardness value in the stable stage B is from m 10 ~m 12 , so t is 1 to 30 minutes.

[0063] Table 2: Residual stress content at different 700℃ annealing times

[0064]

[0065] Example 2

[0066] A method for measuring residual stress of grain-oriented silicon steel comprises the following steps:

[0067] S1: The annealing temperature of the oriented silicon steel sheet to be tested is set to 750℃, and 12 groups of different holding times are set, namely 1, 2, 3, 4, 5, 6, 10, 20, 30, 40, 50, and 60 min. The sample numbers are recorded as m1, m2...m 12 .

[0068] S2: After annealing, the sample was ground and polished with 240 mesh, 500 mesh, 1000 mesh, 1200 mesh and 1500 mesh sandpaper respectively, with a roughness of about Ra = 0.4 μm; the microstructure diagram of the sample in the thickness direction was taken by a metallographic microscope to know the approximate thickness of each layer of the grain, such as Figure 7 The original thickness of the sample measured by the micrometer was 320 μm, and 160 μm was ground off so that the surface was in the center layer.

[0069] S3: Use Vickers hardness tester to measure the hardness of the center layer of 12 groups of samples, measure 5-7 points of each sample and take the average value, and measure the hardness values ​​of the samples under different tempering and holding times, as shown in Table 3 below. And draw it into a scatter plot, as shown in the attached Figure 3 shown.

[0070] Table 3: Microstructure hardness at different 750℃ annealing times

[0071]

[0072] S4: Find the stable hardness value area in the scatter plot, which is defined as the stage where the residual stress is completely eliminated. Figure 3 As shown in section C, the average hardness value of section C is defined as the microstructure hardness when the residual stress content of silicon steel is 0%, and the hardness is set to 214.3HV.

[0073] S5: Measure the hardness of the center layer of the silicon steel structure after cold rolling deformation, that is, before annealing. It is defined as the structure hardness in the stage where the residual stress is not removed, that is, the structure hardness corresponding to the residual stress content of 100%. The hardness is set to 323.6HV.

[0074] S6: It is known that the tissue hardness corresponding to the residual stress stage of 0% and 100% is 214.3HV (m9-m 12 The average hardness of the sample is 323.6HV. Substituting the tissue hardness at different holding times into formula (1), the corresponding residual stress can be obtained, as shown in Table 4 below.

[0075]

[0076] like Figure 3 As shown, the hardness value stable stage C is from m9 to m 12 , so t is 1 to 20 minutes.

[0077] Table 4: Residual stress content at different 750℃ annealing times

[0078]

[0079] Example 3

[0080] A method for measuring residual stress of grain-oriented silicon steel comprises the following steps:

[0081] S1: The annealing temperature of the oriented silicon steel sheet to be tested is set to 800℃, and 12 groups of different holding times are set, namely 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 minutes. The sample numbers are recorded as m1, m2...m 12 .

[0082] S2: After annealing, the sample was ground and polished with 240 mesh, 500 mesh, 1000 mesh, 1200 mesh and 1500 mesh sandpaper respectively, with a roughness of about Ra = 0.4 μm. The microstructure diagram of the sample in the thickness direction taken by the metallographic microscope shows the approximate thickness of each layer of the grain, such as Figure 7 The original thickness of the sample measured by the micrometer was 320 μm, and 160 μm was ground off so that the surface was in the center layer.

[0083] S3: Use Vickers hardness tester to measure the hardness of the center layer of 12 groups of samples, measure 5-7 points of each sample and take the average value, and measure the hardness values ​​of the samples under different tempering and holding times, as shown in Table 5 below. And draw it into a scatter plot, such as Figure 4 shown.

[0084] Table 5: Microstructure hardness at different 800℃ annealing times

[0085]

[0086] S4: Find the stable hardness value area in the scatter plot, which is defined as the stage where the residual stress is completely eliminated. Figure 4 As shown in the middle section D, the average hardness value of section D is defined as the structural hardness when the residual stress content of silicon steel is 0%, and the hardness is set to 214.2HV.

[0087] S5: Measure the hardness of the center layer of the silicon steel structure after cold rolling deformation, that is, before annealing. It is defined as the structure hardness in the stage where the residual stress is not removed, that is, the structure hardness corresponding to the residual stress content of 100%. The hardness is set to 323.6HV.

[0088] S6: It is known that the tissue hardness corresponding to the residual stress stage of 0% and 100% is 214.2HV (m9-m 12 The average hardness of the sample is 323.6HV, and the corresponding residual stress can be obtained by substituting the tissue hardness at different holding times into formula (1), as shown in Table 6 below.

[0089]

[0090] Because attached Figure 4 The hardness value in the stable stage D is from m7 to m 12 , so t is 1 to 6 minutes.

[0091] Table 6: Residual stress content at different 800℃ annealing times

[0092]

[0093]

[0094] Example 4

[0095] A method for measuring residual stress of grain-oriented silicon steel, characterized in that the measuring method comprises the following steps:

[0096] S1: The annealing temperature of the oriented silicon steel sheet to be tested is set to 800℃, and 12 groups of different holding times are set, namely 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 minutes. The sample numbers are recorded as m1, m2...m 12 .

[0097] S2: After annealing, the sample was ground and polished with 240 mesh, 500 mesh, 1000 mesh, 1200 mesh and 1500 mesh sandpaper respectively, with a roughness of about Ra = 0.4 μm; the microstructure diagram of the sample in the thickness direction was taken by a metallographic microscope to know the approximate thickness of each layer of the grain, such as Figure 7 The original thickness of the sample measured by the micrometer was 320 μm, and 20 μm was ground off, leaving the surface in a decarburized layer.

[0098] S3: Use Vickers hardness tester to measure the hardness of decarburized layer of 12 groups of samples, measure 5-7 points of each sample and take the average value, and measure the hardness of samples under different tempering holding time, as shown in Table 6 below. And draw it into a scatter plot, as shown in Table 6 below. Figure 4 shown.

[0099] Table 6: Microstructure hardness (decarburized layer) at different 800℃ annealing times

[0100]

[0101] S4: Find the stable hardness value area in the scatter plot, which is defined as the stage where the residual stress is completely eliminated. Figure 5 As shown in the middle section E, the average hardness value of the E section is defined as the structural hardness when the residual stress content of the silicon steel is 0%, and the hardness is set to 210.3HV.

[0102] S5: Determine the hardness of the decarburized layer of the silicon steel after cold rolling deformation, that is, before annealing. It is defined as the hardness of the structure in the stage where the residual stress is not removed, that is, the hardness corresponding to the residual stress content of 100%. The hardness is set to 319.5HV.

[0103] S6: It is known that the tissue hardness corresponding to the residual stress stage of 0% and 100% is 210.3HV (m7-m 12 The average hardness of the sample is 319.5HV, and the corresponding residual stress can be obtained by substituting the tissue hardness at different holding times into the following formula, as shown in Table 7.

[0104]

[0105] because Figure 5The hardness value in the stable stage E is from m7 to m 12 , so t is 1 to 6 minutes.

[0106] Table 7: Residual stress content (decarburized layer) after annealing at 800℃ for different holding times

[0107]

[0108] Example 5

[0109] A method for measuring residual stress of grain-oriented silicon steel, characterized in that the measuring method comprises the following steps:

[0110] S1: The annealing temperature of the oriented silicon steel sheet to be tested is set to 800℃, and 12 groups of different holding times are set, namely 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 minutes. The sample numbers are recorded as m1, m2...m 12 .

[0111] S2: After annealing, the sample was ground and polished with 240 mesh, 500 mesh, 1000 mesh, 1200 mesh and 1500 mesh sandpaper respectively, with a roughness of about Ra = 0.4 μm; the microstructure diagram of the sample in the thickness direction was taken by a metallographic microscope to know the approximate thickness of each layer of the grain, such as Figure 7 The original thickness of the sample measured by the micrometer was 320 μm, and 80 μm was ground off, leaving the surface in the transition layer.

[0112] S3: Use Vickers hardness tester to measure the hardness of transition layer of 12 groups of samples, measure 5-7 points of each sample and take the average value, and measure the hardness of samples under different tempering and holding time, as shown in Table 8 below. And draw it into a scatter plot, as shown in Table 8 below. Figure 6 shown.

[0113] Table 8: Microstructure hardness (transition layer) at different 800℃ annealing times

[0114]

[0115] S4: Find the stable hardness value area in the scatter plot, which is defined as the stage where the residual stress is completely eliminated. Figure 6 As shown in the middle section F, the average hardness value of the E section is defined as the microstructure hardness when the residual stress content of the silicon steel is 0%, and the hardness is set to 216.5HV.

[0116] S5: Measure the hardness of the silicon steel transition layer after cold rolling deformation, that is, before annealing. It is defined as the hardness of the structure in the stage where the residual stress is not removed, that is, the hardness corresponding to the residual stress content of 100%. The hardness is set to 326.1HV.

[0117] S6: It is known that the tissue hardness corresponding to the residual stress stage of 0% and 100% is 216.5HV (m9-m 12 The average hardness of the sample is 326.1HV. Substituting the hardness of the sample at different holding times into formula (1), the corresponding residual stress can be obtained, as shown in Table 9 below.

[0118]

[0119] because Figure 6 The hardness value in the stable stage E is from m9 to m 12 , so t is 1 to 8 minutes.

[0120] Table 9: Residual stress content (transition layer) at different 800℃ annealing times

[0121]

[0122] Comparative Example 1

[0123] The residual stresses of the 12 samples ground to the center layer in Example 1, as a control group, were measured using a conventional X-ray stress analyzer (Xstress3000G3), as shown in Table 10 below. The X-ray stress analyzer measures the change in diffraction peak position—that is, the difference in diffraction angle compared to the theoretical crystal structure—and calculates the residual stress values ​​based on the Bragg equation. Furthermore, the X-ray stress analyzer measured the residual stress of the samples after the first cold rolling step, i.e., before intermediate annealing, to be -122 MPa. Therefore, the ratio of the residual stress at different holding times at 700°C to -122 MPa represents the actual residual stress content.

[0124] Table 10: Residual stress (center layer) measured by X-ray stress analyzer at different 700℃ annealing times

[0125]

[0126]

[0127] Comparing the residual stress content obtained in Example 1 with the residual stress content obtained in Control Example 1, as shown in Table 11, the maximum error range is 3%, which is within the acceptable range, thus confirming the feasibility of the present invention in determining the residual stress content.

[0128] Table 11: Comparison of residual stresses measured in Example 1 and Control Example 1

[0129]

[0130] The method of the present invention confirms the residual stress content at different times through hardness changes, and can determine the residual stress content conveniently and at low cost, so as to determine the optimal annealing process.

[0131] The present invention uses formula (1) to measure the residual stress content at different holding time points at a certain annealing temperature. According to the quality requirements of the finished product, the time corresponding to the specific residual stress content is determined as the holding end point. There is no need to wait until the residual stress is completely eliminated each time. Therefore, while ensuring the quality of the finished product, the production efficiency can be improved and the production cost can be reduced.

[0132] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment. It is understood that other improvements and variations directly derived or imagined by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the scope of protection of the present invention.

Claims

1. A method for determining the residual stress content of different layers of oriented silicon steel, characterized in that: The measuring method comprises the following steps: S1: cold rolling the oriented silicon steel, annealing it, and keeping it warm; S2: Surface treatment is performed on the oriented silicon steel before and after annealing with different holding times, so that the surface roughness of the oriented silicon steel is ≤0.4 μm; S3: Determine the hardness of the grain-oriented silicon steel after cold rolling and before annealing, which is defined as the microstructure hardness at the stage where the residual stress is not removed, and the residual stress content at this stage is defined as 100%; S4: measuring the hardness of the grain-oriented silicon steel treated in step S2 at different holding times until the hardness reaches a stable region, and defining the residual stress content in the stable region as 0%; S5: Establish the relationship between the hardness of oriented silicon steel and the residual stress content, as shown below: Where: RS is the residual stress content at holding time t, unit: %; a t The hardness value at the holding time t, unit HV; a 100 is the hardness value at the stage where the residual stress is not removed, in HV; a0 is the hardness value when the hardness reaches the stable region, in HV; S6: performing surface treatment on the oriented silicon steel to be tested to make the surface roughness of the oriented silicon steel to be tested ≤ 0.4 μm, measuring the hardness of the oriented silicon steel to be tested at different holding times, and calculating the residual stress content corresponding to the holding time using the formula in step S5; In step S2, the surface treatment is performed by grinding and then polishing to obtain oriented silicon steel containing a specific layer to be tested; The specific layer to be tested includes a decarburized layer, a transition layer or a center layer of the oriented silicon steel.

2. The measuring method according to claim 1, wherein In step S1, the annealing temperature is 700-800°C.

3. The measuring method according to claim 1, wherein In step S2, the surface treatment is performed by grinding with 240-1500 mesh sandpaper and then polishing to obtain oriented silicon steel containing the specific layer to be tested.

4. The measuring method according to claim 1, wherein The decarburized layer, transition layer and neutral layer are measured by metallographic microscope.

5. An application of the determination method according to any one of claims 1 to 4, characterized in that: The measuring method is used to measure the residual stress content of different layers of oriented silicon steel; the different layers include any one of a decarburized layer, a transition layer, and a center layer of the oriented silicon steel.

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