Preparation method of low-residual-stress composite board

Abstract

The invention discloses a preparation method of a low-residual-stress composite board, which comprises the following steps of: 1) selecting a straightening process: setting the straightening times to be one-time straightening, two-time straightening and three-time straightening, and recording as one time when the composite board enters and exits from a straightening machine; 2) residual stress test: carrying out stress test on the composite boards in different states to obtain stress distribution data of the whole board; 3) stacking after straightening: straightening the composite board for different straightening times, then carrying out a stacking test in the same open-air environment for one month, and carrying out stress test and unevenness test on the composite board again after the stacking test is completed; and it is guaranteed that the residual stress of the straightened composite board is smaller than 250 Mpa. According to the method, the most appropriate straightening frequency of the rolled composite plate is confirmed, it is guaranteed that the residual stress of the straightened composite plate is smaller than 250 Mpa, it is guaranteed that the residual stress value of the straightened composite plate is low, and the long-time storage requirement of a user is met.

Description

Technical Field

[0001] The invention relates to the field of steel materials, and in particular to a method for preparing a low residual stress composite plate. Background Art

[0002] With the increase in China's steel production and the rapid development of various industries, the industry's requirements for the use of steel are constantly increasing. If steel is deformed or cracked during cutting, welding, and other processes, it will seriously affect subsequent use, delay construction, and cause huge economic losses. According to research, most of these problems are caused by excessive residual stress in steel. As an emerging product, rolled composite plates are produced by rolling substrates (generally various types of carbon steel, such as container plates, ship plates, etc.) and cladding materials (various types of stainless steel, such as 308L, 2205, etc.), taking into account the mechanical properties of the substrate and the corrosion resistance of the cladding, and are widely used in corrosion-resistant and acid-resistant working environments.

[0003] Before leaving the factory, composite panels are normally subjected to heat treatment, straightening and other measures to ensure that the panel shape and unevenness meet the user's agreement requirements. However, due to different manufacturing cycles in the actual production process, composite panels usually need to be placed on the user's site for a long time. As a result, some users have reported that composite panels have warped after being stacked on site, and the severely deformed positions even far exceed the unevenness requirements. This is usually because the residual stress in the composite panel relaxes due to the stress relaxation effect during the on-site stacking process, and the redistribution causes the panel shape to change, and some positions have obvious deformation.

[0004] Based on the above factors, controlling the residual stress value of the factory composite plate to the lowest possible level can effectively reduce the deformation problem caused by stress relaxation after long-term stacking. At present, steel mills usually use heat treatment, straightening and other means to reduce the residual stress of composite plate products, but the correspondence between each residual stress elimination method and the residual stress of the final composite plate is not clear, resulting in deformation and cracking of the composite plate during user use even after heat treatment or straightening process. However, simply increasing the heat treatment time or increasing the number of straightening passes not only increases the cost, but also affects the final performance. Multiple straightenings may also result in "over-straightening". The heat treatment process is generally determined by the specific performance required by the composite plate. Therefore, confirming the optimal number of straightening times is most suitable for controlling the residual stress of the composite plate product. It is necessary to develop a new method for preparing low residual stress composite plates in a targeted manner to effectively control the residual stress of composite plate products. Summary of the invention

[0005] Purpose of the invention: In view of the shortcomings and defects of the prior art, the present invention provides a method for preparing a low residual stress composite plate. By confirming the most suitable straightening times for the rolled composite plate, the residual stress of the composite plate after straightening is ensured to be less than 250Mpa, and the residual stress value of the composite plate after straightening is ensured to be low, thereby meeting the user's long-term storage requirements.

[0006] Technical solution: A method for preparing a low residual stress composite plate of the present invention is characterized by comprising the following steps:

[0007] 1) Straightening process selection: The straightening times are set to one straightening, two straightening and three straightening. The composite plate enters and exits the straightening machine once, which is counted as one time.

[0008] 2) Residual stress test: Perform stress tests on composite panels in different states to obtain stress distribution data of the entire panel;

[0009] 3) Stacking after straightening: After straightening, the composite panels with different straightening times are stacked in the same open air environment for one month. After the stacking test, the composite panels are subjected to stress test and unevenness test again to ensure that the residual stress of the composite panels after straightening is less than 250Mpa.

[0010] Wherein, the straightening machine in step 1) adopts a 7-9 roller straightening machine.

[0011] Wherein, in the step 2), X-ray diffraction or other non-destructive testing methods are used to perform stress tests on the composite plates in different states.

[0012] Wherein, during the test in step 2), each test point needs to be tested in both width and length directions respectively.

[0013] Among them, when selecting the test points in the step 2), the points are divided into intervals according to 1 / 5 of the length and width of the composite board, and the points are rounded down if they are less than the integer, and no points are taken at the head and tail.

[0014] Among them, when selecting the test points in the step 2), for the composite board with excessive unevenness or abnormal positions, after confirming the range size, the point intervals are still divided according to 1 / 5 of the area size.

[0015] Among them, when selecting the test points in the step 2), if any point in the unevenness area exceeds 1 / 5 of the length or width dimension, the excess part should be further subdivided according to 1 / 10 size until no size exceeds the preset range.

[0016] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: After a large amount of data analysis and research, the present invention has found that controlling the residual stress of the composite plate product within 250Mpa is most beneficial for subsequent production and use. Therefore, by confirming the most appropriate straightening times for the rolled composite plate, the residual stress of the composite plate after straightening is ensured to be less than 250Mpa, and the residual stress value of the composite plate after straightening is ensured to be low, meeting the user's long-term storage requirements, and ensuring that the user does not produce deformation, cracking, and other problems that affect the use of the above-mentioned composite plate after straightening. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a stress distribution diagram of the composite plate in the width direction after one-time straightening of the present invention;

[0018] Figure 2 This is a stress distribution diagram of the composite plate in the length direction after one-time straightening of the present invention;

[0019] Figure 3 This is a stress distribution diagram of the composite plate in the width direction after secondary straightening of the present invention;

[0020] Figure 4 This is a stress distribution diagram of the composite plate in the length direction after secondary straightening of the present invention;

[0021] Figure 5 This is a stress distribution diagram of the composite plate in the width direction after three straightenings of the present invention;

[0022] Figure 6 This is a stress distribution diagram of the composite plate in the length direction after three straightenings of the present invention;

[0023] Figure 7 This is a stress distribution diagram of the composite plate in the width direction after being stacked for one month after one straightening of the present invention;

[0024] Figure 8 This is a stress distribution diagram of the composite plate in the length direction after being stacked for one month after the single straightening of the present invention;

[0025] Fig. 9 It is a schematic diagram of the position where the unevenness exceeds the standard of the present invention;

[0026] Fig.10 It is a point selection diagram of the unevenness exceeding standard area of ​​the present invention;

[0027] Fig.11 This is a stress distribution diagram of the composite plate in the width direction after one straightening in Example 1;

[0028] Fig.12 This is a stress distribution diagram of the composite plate in the length direction after one straightening in Example 1;

[0029] Fig.13 This is the stress distribution diagram of the composite plate in the width direction after secondary straightening in Example 2;

[0030] Fig.14 This is the stress distribution diagram of the composite plate in the length direction after secondary straightening in Example 2;

[0031] Fig.15 This is the stress distribution diagram of the composite plate in the width direction after secondary straightening in Example 3;

[0032] Fig.16 This is the stress distribution diagram of the composite plate in the length direction after secondary straightening in Example 3. DETAILED DESCRIPTION

[0033] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific implementation methods.

[0034] The method for preparing a low residual stress composite plate of the present invention comprises the following steps:

[0035] 1) Straightening process selection: The specific straightening process, including parameters such as pressure, does not need to be changed deliberately, and a common 7-9 roller straightening machine can be used. The straightening times can be set to one straightening, two straightening and three straightening (one time the composite plate enters and exits the straightening machine is counted as one time). More straightening times will affect the production rhythm and increase costs.

[0036] 2) Residual stress test: Use X-ray diffraction method to perform stress test on composite plates in different states to obtain stress distribution data of the whole plate. Other non-destructive test methods are also acceptable. Due to the different deformation conditions of the composite plate in width and length, the width and length directions of each point need to be tested separately during the test. The selection of test points requires a comprehensive design of test efficiency and unevenness index. Usually, the point intervals are divided according to 1 / 5 of the length and width dimensions, and the points are rounded down if they are less than the specified value, and no points are taken at the head and tail. For unevenness exceeding the standard or abnormal position, after confirming the range size, the point intervals are still divided according to 1 / 5 of the area size. If any part of the unevenness area exceeds 1 / 5 of the length or width dimension, the excess part should be further subdivided according to the size of 1 / 10 until no size exceeds the preset range.

[0037] 3) Stacking after straightening: After straightening, the composite boards with different straightening times are tested against each other in the same open air environment and stacked for one month. After the stacking test, stress test and unevenness test of the composite board are carried out again to compare the effect of different straightening processes on the control of residual stress level of the composite board.

[0038] The stress state of the composite plate after one straightening is as follows Figure 1 , Figure 2 As shown;

[0039] The stress state of the composite plate after secondary straightening is as follows Figure 3 , Figure 4 As shown;

[0040] The stress state of the composite plate after three straightenings is as follows Figure 5 , Figure 6 shown.

[0041] After one, two, and three straightenings, the composite boards were stacked for one month and then tested for unevenness and residual stress again. The unevenness of the single straightening test board increased to 20mm / 2m in the width direction, and the unevenness in the length direction did not change much. The unevenness of the double straightening test board and the triple straightening test board did not change much. Figure 7 , Figure 8 .

[0042] The thermal expansion coefficient of duplex stainless steel is greater than that of ordinary A36 steel. During the cooling process, the deformation of duplex stainless steel is greater than that of A36 steel, so the composite plate will bend toward the stainless steel side.

[0043] Therefore, 1) the unevenness of the composite plate in the width direction after the first straightening is 14mm / 2mm, and the unevenness of the composite plate in the width direction increases to 20mm / 2m after being placed for 1 month. Combined with the stress test results after the first straightening and placement for 1 month, it shows that the first straightening of the composite plate is not in place and the stress is not well eliminated. Therefore, when cutting and blanking, the stress release causes serious deformation of the composite plate.

[0044] 2) The test results after the second and third straightening show that straightening can effectively reduce the stress of the composite plate. Only two straightenings are required for the composite plate used in this patent to meet user requirements. After three straightenings, some areas of the composite plate are over-straightened. Therefore, composite plates of different plate thicknesses and materials need to use the residual stress test method of this patent to accurately obtain the stress distribution after different straightening processes, so as to formulate a reasonable straightening process. Otherwise, it is easy to over-straighten and introduce more unevenly distributed residual stress.

[0045] Fig. 9 This is a schematic diagram of the location where the unevenness exceeds the standard. Fig.10 This is a point selection diagram for the area where the unevenness exceeds the standard (the area exceeding the standard shall be based on the actual situation and is not necessarily a circular area).

[0046] Embodiment 1:

[0047] In the method for producing a low residual stress composite plate of this embodiment, the composite plate is selected from ordinary A36 composite duplex stainless steel 2205 composite plate, and the surface of the test plate does not need additional treatment, but it cannot be obviously oily to avoid affecting the residual stress test results.

[0048] Conduct unevenness test on composite plates, keep the test plate coating on top and the base layer on the bottom, and use X-ray diffraction method to perform stress test on composite plates in different states to obtain stress distribution data of the whole plate. Other non-destructive test methods are also acceptable. The unevenness requirement of the composite plate is 5mm / 2m. The selection of test points requires a comprehensive design of test efficiency and unevenness index. Usually, the point intervals are divided according to 1 / 5 of the length and width dimensions. If the length and width are less than 1 / 5, the points are rounded down and no points are taken at the head and tail. For unevenness exceeding the standard or abnormal position, after confirming the range size, the point intervals are still divided according to 1 / 5 of the area size.

[0049] The stress distribution diagram of the whole plate is drawn according to the residual stress test results. The stress distribution in the rolling direction and width direction after one straightening is as follows: Fig.11 , Fig.12 shown.

[0050] The test results show that the tensile stress value of more than 250MPa mainly appears in the width direction, which provides the basic conditions for the redistribution of residual stress during the storage of the composite plate and causes secondary deformation. Therefore, the one-time straightening process of the composite plate cannot fully meet the use requirements such as low residual stress and unevenness.

[0051] Embodiment 2:

[0052] In the method for producing a low residual stress composite plate of this embodiment, the composite plate is selected from ordinary A36 composite duplex stainless steel 2205 composite plate, and the surface of the test plate does not need additional treatment, but it cannot be obviously oily to avoid affecting the residual stress test results.

[0053] Conduct unevenness test on composite plates, keep the test plate coating on top and the base layer on the bottom, and use X-ray diffraction method to perform stress test on composite plates in different states to obtain stress distribution data of the whole plate. Other non-destructive test methods are also acceptable. The unevenness requirement of the composite plate is 5mm / 2m. The selection of test points requires a comprehensive design of test efficiency and unevenness index. Usually, the point intervals are divided according to 1 / 5 of the length and width dimensions. If the length and width are less than 1 / 5, the points are rounded down and no points are taken at the head and tail. For unevenness exceeding the standard or abnormal position, after confirming the range size, the point intervals are still divided according to 1 / 5 of the area size.

[0054] The stress distribution diagram of the whole plate is drawn according to the residual stress test results. The stress distribution in the rolling direction and width direction after secondary straightening is as follows: Fig.13 , Fig.14 shown.

[0055] The test results show that the tensile stress value in the rolling direction and width does not exceed 250MPa, and the residual stress change is not obvious after stacking for one month. Therefore, the secondary straightening process of the composite plate can ensure the use requirements of low residual stress and unevenness.

[0056] Embodiment 3:

[0057] In the method for producing a low residual stress composite plate of this embodiment, the composite plate is selected from ordinary A36 composite duplex stainless steel 2205 composite plate, and the surface of the test plate does not need additional treatment, but it cannot be obviously oily to avoid affecting the residual stress test results.

[0058] Conduct unevenness test on composite plates, keep the test plate coating on top and the base layer on the bottom, and use X-ray diffraction method to perform stress test on composite plates in different states to obtain stress distribution data of the whole plate. Other non-destructive test methods are also acceptable. The unevenness requirement of the composite plate is 5mm / 2m. The selection of test points requires a comprehensive design of test efficiency and unevenness index. Usually, the point intervals are divided according to 1 / 5 of the length and width dimensions. If the length and width are less than 1 / 5, the points are rounded down and no points are taken at the head and tail. For unevenness exceeding the standard or abnormal position, after confirming the range size, the point intervals are still divided according to 1 / 5 of the area size.

[0059] The stress distribution diagram of the whole plate is drawn according to the residual stress test results. The stress distribution in the rolling direction and width direction after secondary straightening is as follows: Fig.15 , Fig.16 shown.

[0060] The test results show that compressive stress areas begin to appear at the rolling edge, and tensile stress areas exceeding 250MPa appear in the width, indicating that the composite plate is over-straightened in the rolling and width directions after three straightenings, and the residual stress is unevenly distributed, which also provides the basic conditions for the redistribution of residual stress during storage of the composite plate and causes secondary deformation. Therefore, the three-time straightening process of the composite plate has exceeded the actual use requirements and does not meet the use requirements such as low residual stress and unevenness.

[0061] After a large amount of data analysis and research, the present invention has found that controlling the residual stress of the composite plate product within 250Mpa is most beneficial for subsequent production and use. Therefore, by confirming the most appropriate straightening times for the rolled composite plate, the residual stress of the composite plate after straightening is ensured to be less than 250Mpa, and the residual stress value of the composite plate after straightening is ensured to be low, meeting the user's long-term storage requirements, and ensuring that the user does not produce deformation, cracking, and other problems that affect the use of the above-mentioned composite plate after straightening.

Claims

1. A method for preparing a low residual stress composite plate, characterized in that: The steps include: 1) Straightening process selection: The straightening times are set to one straightening, two straightening and three straightening. The composite plate enters and exits the straightening machine once, which is counted as one time. 2) Residual stress test: Perform stress tests on composite panels in different states to obtain stress distribution data of the entire panel; 3) Stacking after straightening: After straightening, the composite panels with different straightening times are stacked in the same open air environment for one month. After the stacking test, the composite panels are subjected to stress test and unevenness test again to ensure that the residual stress of the composite panels after straightening is less than 250Mpa.

2. The method for preparing a low residual stress composite plate according to claim 1, characterized in that: In the step 1), the straightening machine adopts a 7-9 roller straightening machine.

3. The method for preparing a low residual stress composite plate according to claim 1, characterized in that: In the step 2), X-ray diffraction or other non-destructive testing methods are used to perform stress tests on the composite plates in different states.

4. The method for preparing a low residual stress composite plate according to claim 3, characterized in that: When testing in step 2), each test point needs to be tested in both width and length directions.

5. The method for preparing a low residual stress composite plate according to claim 4, characterized in that: When selecting the test points in step 2), the points are divided into intervals at 1 / 5 of the length and width of the composite board, and if the interval is less than 1 / 5, the points are rounded down, and no points are taken at the head and tail.

6. The method for preparing a low residual stress composite plate according to claim 5, characterized in that: When selecting the test points in step 2), for the composite board with unevenness exceeding the standard or abnormal position, after confirming the range size, the point intervals are still divided according to 1 / 5 of the area size.

7. The method for preparing a low residual stress composite plate according to claim 6, characterized in that: When selecting the test points in step 2), if any part of the unevenness area exceeds 1 / 5 of the length or width, the excess part should be further subdivided according to 1 / 10 until no size exceeds the preset range.

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