System and method for reduction of welding residual stress

Abstract

One aspect of the present invention is to provide an apparatus and a method capable of effectively reducing welding residual stress without going through multiple post-welding processing steps after a weld is formed.

Description

Welding residual stress reduction device and method

[0001] The present invention relates to a device and method for reducing weld residual stress applicable to a welded joint.

[0002] Generally, large piping and other structures are installed in industrial plants to transport heat and fluids. Since these structures cannot be manufactured directly to the length or shape required by the equipment, construction methods such as welding are applied to manufacture them to fit the required length and shape.

[0003] Typically, welding refers to a process in which identical or similar metals are melted and joined together, and then the weldment is solidified to strengthen the bond between the two materials. In order to perform this welding, a welding material used as a joining medium for the two materials, a heat source capable of melting each material, and an inert gas to suppress welding defects generated when the weldment solidifies are required.

[0004] When the welding material is melted during the welding process, its volume (or surface area) expands, and when the molten material solidifies again, the expanded volume decreases. At this time, as the base material restrains the shrinkage of the welding material, tensile stress equivalent to the yield stress remains. This residual tensile stress can generally be divided into residual tensile stress perpendicular to the weld line and residual tensile stress along the weld line. The magnitude of the residual tensile stress perpendicular to the weld line is relatively small compared to the weld line direction because the amount of shrinkage caused by welding heat is small and it is significantly influenced by the restraint of the surrounding base material and angular deformation. On the other hand, it is known that a large stress remains along the weld line direction because the restraint of the base material is greater than that of the tensile stress perpendicular to the weld line.

[0005] If the magnitude of the residual tensile stress generated at this stage exceeds the yield stress of the welded materials, the equipment may easily fail even when used within the material's allowable stress range. Therefore, for equipment used after a welding process, reducing the residual tensile stress in the weld area after welding is completed is a critical issue related to the equipment's durability. As mentioned above, an even more critical task concerns methods to reduce residual tensile stress along the weld line.

[0006] To solve these problems, Patent Document 1 provides a method for reducing weld residual stress by redistributing and alleviating the weld residual stress by machining a stress relief hole, and then reducing the weld residual stress by quenching the area around the stress relief hole. However, Patent Document 1 has limitations in that the method is very complex, the amount of weld residual stress reduction is not significant, and it cannot directly reduce the source of the weld by utilizing the redistribution of uncertain residual stress.

[0007] [Prior Art Literature]

[0008] [Patent Literature]

[0009] (Patent Document 1) Republic of Korea Registered Patent Publication No. 10-1369221

[0010] According to one embodiment of the present invention, an apparatus and method capable of effectively reducing welding residual stress may be provided.

[0011] More specifically, according to one embodiment of the present invention, an apparatus and method can be provided that can effectively reduce weld residual stress without going through multiple steps after the weld is created.

[0012] The problems of the present invention are not limited to those described above. A person skilled in the art to which the present invention pertains will have no difficulty understanding additional problems of the present invention from the overall contents of this specification.

[0013] A method for reducing welding residual stress according to one embodiment of the present invention may include: a step of forming a weld metal by arc welding a welding base material and a welding material; a step of cooling the weld metal to a transformation end temperature; and a pressurization step of applying a compressive load to the weld metal using a disk.

[0014] The above-described disc may include one or more indenters formed on the circumferential surface of the disc, and the indenters may have a maximum height of 2.5 mm or more and less than twice the maximum height of the weld metal.

[0015] The curvature of the indenter described above may be 3 or more and 25 or less.

[0016] The above-described indenters may have a spacing between adjacent indenters of 5 mm or more and 20 mm or less.

[0017] The above-described indenter may have a semi-cylindrical shape.

[0018] The above-described welding base material may have a yield strength of 500 MPa or more and 1000 MPa or less.

[0019] The transformation completion temperature of the above-described welding base material may be 300°C or higher and 500°C or lower.

[0020] The surface temperature of the weld metal in the above-described pressurization step may be 25°C or higher and 500°C or lower.

[0021] The above-described method for reducing welding residual stress may additionally include a heat treatment step after the pressurization step.

[0022] The heat treatment described above can be performed for 5 hours or more and 7 hours or less at a temperature range of 550°C or higher and 650°C or lower.

[0023] A welding residual stress reduction device according to another embodiment of the present invention may include a disc that moves while rotating the surface of the weld along the welding direction around a rotation axis and applies a compressive load to the weld metal.

[0024] The above-described disc additionally includes one or more indenters formed on the circumferential surface of the disc, and the indenters may have a maximum height of 2.5 mm or more and less than twice the height of the weld metal.

[0025] The curvature of the indenter described above may be 3 or more and 25 or less.

[0026] The above-described indenters may have a spacing between adjacent indenters of 5 mm or more and 20 mm or less.

[0027] The above-described indenter may have a semi-cylindrical shape.

[0028] The aforementioned rotation axis may be eccentric.

[0029] The circumferential surface of the aforementioned disk may have a curved structure.

[0030] The aforementioned curved structure may be a U-shaped structure.

[0031] The above-described indenter can be formed on the inner curved surface of the circumferential surface of the disk.

[0032] The hardness of the indenter described above may be 56 HRC or higher.

[0033] The present invention can provide an apparatus and method capable of effectively reducing welding residual stress.

[0034] FIG. 1 is a perspective view of a welding residual stress reduction device according to an example of the present invention.

[0035] FIG. 2 is a cross-sectional view of a welding residual stress reduction device according to an example of the present invention.

[0036] Figure 3 is an image showing a welded test specimen.

[0037] Figure 4 is an image of the surface of a welded test specimen in which a press-fit into the weld metal has been implemented.

[0038] Figure 5 is a schematic diagram showing the weld line direction (x direction) and the weld line perpendicular direction (y direction) in this experiment.

[0039] Figure 6 is a graph showing the magnitude (σx, MPa) of the stress component in the weld line direction (x direction) of Example 1, Example 2 and Comparative Example according to the distance (mm) in the direction perpendicular to the weld line (y direction).

[0040] Figure 7 is a graph showing the magnitude (σx, MPa) of the stress component in the weld line direction (x direction) of Examples 3 and 4.

[0041] Preferred embodiments of the present invention will be described below with reference to the attached drawings. However, embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0042] In addition, embodiments of the present invention are provided to more fully explain the present invention to those with average knowledge in the relevant technical field.

[0043] In drawings, the shapes and sizes of elements may be exaggerated for clearer explanation.

[0044] In describing the embodiments of the present invention, if it is determined that a detailed description of known technology related to the present invention may unnecessarily obscure the essence of the present invention, such detailed description will be omitted. Furthermore, the terms described below are defined considering their functions in the present invention, and these may vary depending on the intentions or conventions of the user or operator. Therefore, such definitions should be based on the content throughout this specification. The terms used in the detailed description are merely for describing the embodiments of the present invention and should not be limited in any way. Unless explicitly stated otherwise, expressions in the singular form include the meaning of the plural form.

[0045] In this description, expressions such as “include” or “equipped” are intended to refer to certain characteristics, numbers, steps, actions, elements, parts or combinations thereof, and should not be interpreted to exclude the existence or possibility of one or more other characteristics, numbers, steps, actions, elements, parts or combinations thereof other than those described.

[0046] Unless otherwise specifically defined in the specification of the present invention, % units mean weight %.

[0047] In this specification, terms such as 'top', 'upper', 'upper surface', 'lower', 'lower surface', 'lower surface', and 'side surface' are based on the drawings and may actually vary depending on the direction in which the elements or components are arranged.

[0048] The present invention will be described in detail below through each embodiment or example of the invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may also be combined with other embodiments or examples. Accordingly, the citation of claims in the patent claims is merely an example of an embodiment, and the technical concept of the present invention should not be interpreted as being limited only to a combination with the cited claims; rather, combinations with various claims are also included within the scope of the technical concept of the present invention.

[0049] When cooling after welding, the weld metal and heat-affected zone shrink. As the weld base material restrains this shrinkage, tensile stress equivalent to the yield stress remains, which can result in weld residual stress.

[0050] The inventors of the present invention derived the present invention by recognizing that, as a method to reduce such welding residual stress, it is effective to apply an external force perpendicular to the weld metal to cause plastic deformation in the shrinkage direction.

[0051] More specifically, the inventors of the present invention have discovered that when a compressive load is applied to the weld metal as described above, the weld metal can be elongated, and accordingly, the weld residual stress in the direction of the weld line can be offset.

[0052] In this regard, a method for reducing welding residual stress according to one embodiment of the present invention may include: a step of forming a weld metal by arc welding a weld base material and a weld material; a step of cooling the weld metal to a transformation end temperature; and a pressurization step of applying a compressive load to the weld metal using a disk.

[0053] Each step is described in detail below.

[0054] First of all, a welding residual stress reduction method according to one embodiment of the present invention can form welding metal by arc welding a welding base material and a welding material.

[0055] Throughout this specification, the weld metal refers to a metal that is melted and solidified during welding, and may mean a portion of the molten base metal fused with the weld metal.

[0056] In addition, the above arc welding may include, as examples, shielded metal arc welding, submerged arc welding, MIG welding, etc., but is not necessarily limited thereto.

[0057] After the weld metal is formed in this manner, the weld metal can be cooled to a transformation end temperature according to a welding residual stress reduction method according to a non-limiting example of the present invention.

[0058] During this cooling process, the weldment, including the weld metal and the heat-affected zone, may undergo transformation expansion through the martensitic transformation region, and a significant portion of the weld residual stress may be relieved. However, if cooling proceeds further and the temperature of the weldment falls below the transformation termination temperature, re-shrinkage of the weldment may occur.

[0059] Accordingly, the welding residual stress reduction method according to one embodiment of the present invention can effectively offset the welding residual stress by cooling the weld to a transformation end temperature to induce transformation expansion, and at the same time, by applying a compressive load at a temperature lower than the transformation end temperature to elongate the weld metal.

[0060] In particular, since high-strength steel is a steel material capable of effectively relieving residual stress through indentation, according to a non-limiting example of the present invention, the welding base material may be high-strength steel.

[0061] As a non-limiting example, the above high-strength steel may refer to steel with a yield strength of 315 MPa or more and 1000 MPa or less. As another example, the above high-strength steel may have a yield strength of 500 MPa or more and 1000 MPa or less. In this case, the yield strength may be determined by taking a tensile specimen of an annular or plate-shaped steel at a thickness of 1 / 4 T from the steel so that the length of the specimen is perpendicular to the rolling direction, processing it, and then conducting a tensile test at room temperature using the EN ISO 6892-1 test method. If a yield point phenomenon occurs during the tensile test, the upper yield point is used as the yield strength, and if no yield point phenomenon occurs, the 0.2% offset yield point is used as the yield strength.

[0062] In addition, the transformation termination temperature of the above-described high-strength steel may be 300°C or higher and 500°C or lower. More specifically, the transformation termination temperature may be 300°C to 400°C.

[0063] Meanwhile, the elongation of the steel at the point where plastic deformation of the weld metal begins may be 0.2% or more and 1% or less.

[0064] That is, the welding residual stress reduction method according to one embodiment of the present invention can effectively release tensile residual stress by elongating the base material of the steel and simultaneously elongating the weldment when the elongation rate of the steel at the point where plastic deformation of the weld metal begins is 0.2% or more and 1% or less.

[0065] Subsequently, a method for reducing welding residual stress according to one embodiment of the present invention may include a pressurization step of applying a compressive load to the weld metal using a disc.

[0066] In the corresponding pressurization step, as the disk rotates and moves along the welding line in the welding direction, a compressive load can be applied to the weld metal.

[0067] Through this, the welding residual stress reduction method according to one example of the present invention can elongate the weld metal and effectively reduce the welding residual stress.

[0068] Through such a pressurization step, the welding residual stress reduction method according to one example of the present invention can offset welding residual stress by directly controlling the cause of the welding residual stress generation without undergoing post-heat treatment.

[0069] Meanwhile, the disk according to a non-limiting example of the present invention may include one or more indenters formed on the circumferential surface of the disk. These indenters may serve to apply an additional load to the surface of the weld metal when the disk rotates in the welding direction.

[0070] As one example, the indenter may be in the form of a circular protrusion. As another example, the indenter may be in the form of a semi-cylindrical shape. In this case, the semi-cylindrical shape may refer to a structure in which one side is a flat surface and the other side is an arc, and the arc-shaped surface may act as the indenter.

[0071] For example, the indenter may be 2.5 mm or larger and have a maximum height less than twice the maximum height of the weld metal. In this case, the maximum height of the indenter may be defined as the largest value among the heights of the indenter measured in a direction perpendicular to the circumferential surface of the disk. Additionally, the maximum height of the weld metal may be defined as the largest value among the heights of the weld metal measured in a direction perpendicular to the surface of the weld base material.

[0072] Specifically, to properly apply an additional compressive load to the surface of the weld metal, the maximum height of the indenter may be 2.5 mm or more. In another example, the lower limit of the maximum height of the indenter may be 3.0 mm, and in yet another example, the lower limit may be 3.5 mm. However, if the maximum height exceeds twice the maximum height of the weld metal, a problem may arise where excessive vibration occurs as the number of rotations of the disk increases; therefore, in a non-limiting embodiment of the present invention, the upper limit of the maximum height may be twice the maximum height of the weld metal. In another example, the upper limit of the maximum height of the indenter may be 10 mm.

[0073] In addition, the shape of the indenter is not specifically limited within the scope of achieving the purpose of the present invention, but as an example, in order to reduce the pressing power, the radius of curvature of the indenter may be 3 mm or more and 25 mm or less. In this case, the radius of curvature may refer to the radius of a virtual circle that the curve or curved surface has at a specific point. That is, the radius of curvature of the indenter may be at least 3 mm even at the place where the curvature of the curved surface or curve is steepest, and the radius of curvature may be at most 25 mm or less even at the place where the curved surface or curve is gentlest.

[0074] Meanwhile, for the purpose of continuously realizing the effect of generating compressive stress by indentation using the indenter, the present invention may set the spacing between adjacent indenters to 20 mm or less. At this time, the spacing between indenters may be measured based on the indenter, which is the highest part of the indenter. On the other hand, if the spacing between indenters is less than 5 mm, a problem of interference with surrounding indenters may occur at the maximum indentation depth; therefore, the lower limit of the spacing between indenters may be 5 mm. As another example, the spacing between indenters may be 7 mm or more and 18 mm or less, and 9 mm or more and 16 mm or less.

[0075] During the aforementioned pressurization, frictional heat may be generated between the weld metal and the disc, and as a result, the surface temperature of the weld metal may rise locally. Accordingly, as an example, the surface temperature of the weld metal during the pressurization step may be 25°C or higher. At this time, the surface temperature of the weld metal may be the average value obtained by measuring the temperature of any 10 points on the surface of the weld metal using a thermal imaging camera.

[0076] In addition, as described above, since the weld may undergo transformation expansion during the cooling process up to the transformation end temperature, it may be more desirable to perform the pressurization in a temperature range lower than that. Accordingly, a method for reducing welding residual stress according to a non-limiting example of the present invention may limit the rotational speed so that the surface temperature of the weld metal during the pressurization step is 500°C or lower. More specifically, the surface temperature of the weld metal during pressurization may be 300°C or lower or 250°C or lower.

[0077] Although this step is not necessarily required after the pressurization step, for the purpose of increasing the ductility of the surface structure of the hardened weld metal, the welding residual stress reduction method according to one embodiment of the present invention may include a heat treatment step on the weld metal after welding and pressurization.

[0078] The above heat treatment may be performed according to conditions typically carried out to achieve the above-described purpose. However, as a non-limiting example, the heat treatment may be performed for 5 to 7 hours at a temperature range of 550°C or higher and 650°C or lower.

[0079] The present invention can effectively reduce welding residual stress without using post-heat treatment through such a welding residual stress reduction method, thereby simplifying the post-treatment process performed after welding.

[0080] In particular, since this method of reducing welding residual stress directly controls the source of the stress, it enables more accurate reduction of welding residual stress.

[0081] Hereinafter, a welding residual stress reduction device according to another embodiment of the present invention will be described in detail with reference to FIG. 1. FIG. 1 is a perspective view of a welding residual stress reduction device according to an example of the present invention.

[0082] Specifically, a welding residual stress reduction device (10) according to one embodiment of the present invention may include a disk (11) that moves while rotating on the surface of the weld metal (30) along the welding direction around a rotation axis and applies a compressive load to the weld metal (30).

[0083] As described above, the disk (11) can rotate the surface of the weld metal (30) according to the welding direction around the rotation axis and apply a compressive load to the weld metal (30) in the vertical direction of the weld base material (20). Through this, the disk (11) according to one embodiment of the present invention can press and elongate the surface of the weld metal (30) in the vertical direction of the weld base material (20) and can offset residual stress generated after welding.

[0084] The shape of the disk (11) used for the above-described pressurization is not significantly limited as long as it can achieve the purpose of the present invention as described above; however, for ease of pressurization, the disk (11) may be in the shape of a disc, and the bottom surface of the disc may be elliptical or circular. Hereinafter, according to one embodiment of the present invention, the description will be based on the premise of a disk (11) in which the bottom surface of the disc is circular.

[0085] As a more specific example, the circumferential surface (A-plane) of the disk (11) may have a curved structure. The curved structure may be a U-shaped structure. FIG. 2 shows a cross-sectional view of the welding residual stress reduction device (10) of the present invention, cut perpendicular to the bottom surface and passing through the center of the circle that is the bottom surface (X-plane). Looking at FIG. 2, it can be seen that the circumferential surface (A-plane) of the disk (11) has a U-shaped structure.

[0086] In particular, as a non-limiting example, the inner curvature of the U-shaped structure may be set so that the disk (11) does not detach from the weld metal (30) when the disk (11) is rotated and a compressive load is applied. At this time, since the specific numerical range of the inner curvature can be appropriately adopted within the range that can achieve the above purpose, it is not described in detail in this specification.

[0087] Additionally, as a non-limiting example, the rotation axis of the disk (11) may be eccentric. This is to improve the press-fitting effect. An eccentric rotation axis means that, when the circular disk is made of a uniform material, the rotation axis of the disk is partially misaligned with the axis passing through the center of the circle and perpendicular to the bottom surface of the circle. The direction and degree of misalignment are not significantly limited as long as the purpose of improving the press-fitting effect is achieved.

[0088] Meanwhile, one or more indenters (12) may be formed on the circumferential surface (A surface) of the disk (11). As described above, these indenters (12) can serve to apply an additional load to the surface of the weld metal (30) when the disk (11) rotates in the welding direction.

[0089] As an example, as shown in FIG. 1, the indenter (12) may be formed on the circumferential surface (A-side) of the disk (11). As described above, in the case where the circumferential surface has a U-shaped structure according to one example of the present invention, the indenter (12) may be formed on the inner curved surface. In this case, the indenter (12) can apply a load to the side of the weld metal (30), thereby effectively functioning to reduce weld residual stress. However, the position of the indenter (12) is not necessarily limited to this.

[0090] As described above, the indenter (12) may be in the shape of a circular protrusion or a semi-cylindrical shape.

[0091] In addition, the maximum height (B height) of the indenter (12) may be 2.5 mm or more and less than twice the height of the weld metal, the radius of curvature of the indenter may be 3 mm or more and 25 mm or less, and the spacing between adjacent indenters may be 5 mm or more and 20 mm or less. As this has been described above in the welding residual stress reduction method of the present invention, further details will be omitted.

[0092] In addition, as an example, the hardness of the indenter (12) may be 56 to 60 HRC.

[0093] That is, the indenter (12) may have a hardness of 56 HRC to maintain the shape of the indenter (12) despite being pressed multiple times. To secure such high hardness, the indenter (12) may be a heat-treated metal material, but is not limited thereto. Since the higher the hardness of the indenter (12), the more advantageous it is for pressing, the present invention does not separately limit the upper limit of the hardness of the indenter (12), but as an example, the hardness of the indenter (12) may be 60 HRC or less.

[0094] When using the welding residual stress reduction device of the present invention, welding residual stress can be effectively reduced despite using a device with a relatively simple structure.

[0095] Furthermore, since residual stress can be reduced by a mechanical method when using the above-mentioned welding residual stress reduction device, the post-welding treatment process can be simplified, thereby providing the advantage of reducing the time and cost required for the process.

[0096] The present invention will be described in detail below through examples. However, it should be noted that the examples described below are intended merely to illustrate and embody the present invention and are not intended to limit the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the patent claims and matters reasonably inferred therefrom.

[0097] [Explanation of the symbol]

[0098] 10: Welding residual stress reduction device

[0099] Disk 11:

[0100] 12: Indenter

[0101] 30: Welding metal

[0102] 20: Welding base material

[0103] (Example)

[0104] First, a welding residual stress reduction device (10) according to one embodiment of the present invention was prepared. Next, SM570 steel (thickness: 50 mm) according to JIS G 3106 was prepared as the welding base material (20). The yield strength (YS) of the steel was 535 MPa, and the tensile strength (TS) and elongation (EL) were 636 MPa and 18%, respectively. Next, the welding base material (20) was welded with a welding material using a submerged arc welding (SAW) method with a heat input of 50 KJ to form a weld metal (30). The SAW WIRE from Oerlikon was OE-SD3 1Ni1 / 2Mo (4Ψ), and the yield strength (YS) of the SAW WIRE was 550 MPa, and the tensile strength (TS) was 620 to 760 MPa. And, the welding material was Oerlikon's OP 121TT. After that, the formed weld metal (30) was cooled to room temperature (23℃), and then only half of the weld line was pressed in using the disc (11) of the weld residual stress reduction device (10) to obtain a weld test specimen.

[0105] Figure 3 is an image showing the welded test specimen. As can be seen in Figure 3, the welded test specimen was a specimen having a weld line with one long weld line (1m) welded by X-beam welding, half of the weld line was a press-fit section, and the other half was in an as-welded state. Through the welded test specimen, the residual stress reduction effect due to the press-fit effect and the residual stress in the as-welded state can be simultaneously verified in this experiment using one welded test specimen.

[0106] Figure 4 is an image of the surface of a welded test specimen in which a press-fit is implemented in the weld metal. Through Figure 4, it can be seen that the surface of the welded test specimen has become uneven due to the press-fit.

[0107] Meanwhile, Figure 5 is a schematic diagram showing the weld line direction (x direction) and the weld line perpendicular direction (y direction) in this experiment.

[0108] To explain the experiment in more detail with reference to Figs. 3 and 5, the portion of the weld line where an indenter was applied to verify the indentation effect was the section between 0 ≤ x ≤ 500 mm and -10 mm ≤ y ≤ 10 mm, and the portion of the weld line in the As-welded state where no indenter was applied was 500 mm. <x≤1000mm인 부분이었다.

[0109] FIG. 6 is a graph showing the magnitude (σx, MPa) of the stress component in the weld line direction (x direction) of Example 1, Example 2 and Comparative Example according to the distance (mm) in the direction perpendicular to the weld line (y direction). In the welded specimens described above, Example 1 and Example 2 represent the magnitude (σx) of the stress component in the weld line direction measured at points x=350mm and x=200mm, respectively, i.e., the part where the indentation is implemented, and Comparative Example represents the magnitude (σx) of the stress component in the weld line direction measured at point x=750mm, i.e., the part in the As-welded state where the indentation is not implemented.

[0110] Looking at Fig. 6, it can be seen that in both Examples 1 and 2, the weld metal part where the maximum tensile residual stress typically occurs has a final compressive stress due to elongation and plastic deformation caused by indentation, and the surrounding stress is also released.

[0111] Figure 7 is a graph showing the magnitude (σx, MPa) of the stress component in the weld line direction (x-direction) of Examples 3 and 4. Example 4 shows the magnitude of the x-direction stress component measured in the weld metal; specifically, the magnitude of the x-direction stress component was measured with a gaugh length of 2 mm at the point where y=0 mm. In addition, Example 3 shows the magnitude of the x-direction stress component of the base material adjacent to the weld metal; specifically, the magnitude of the x-direction stress component was measured with a gaugh length of 1 mm at the point where y=15 mm.

[0112] Looking at the results in Fig. 7, in the MSR indentation test section (MSR Treated side, 0≤x≤500mm), which corresponds to half of the weld line, the maximum tensile residual stress was converted into compressive stress due to the indentation effect, and in the other half (500mm <x≤1000mm)은 용접한 그대로의 상태(As-Welded)로, 잔류응력은 소재의 항복응력에 상당하는 수치를 나타내었다. 통상, 용접잔류응력은 소재의 항복응력에 상당하는 응력이 용접선을 따라 잔류하여 피로 등의 파괴현상을 일으키는 바, 실시예 3 및 4을 통해 용접금속에 압축하중을 부여하는 경우 효과적으로 용접잔류응력을 저감할 수 있어 용접부의 피로균열을 방지할 수 있다.

[0113] Meanwhile, the results of the MSR indentation test section in Fig. 7 show a discontinuous graph shape, but this is a result caused by the center of the disk being eccentric and the indentation depth changing at x = 380 mm, and it can be seen that the degree of compressive residual stress generation may vary depending on the indentation depth.

Claims

1. A step of forming weld metal by arc welding the base material and the welding material; A step of cooling the weld metal to a transformation termination temperature; and A method for reducing weld residual stress, comprising a pressurization step of applying a compressive load to the weld metal using a disc.

2. In Paragraph 1, The above disk includes one or more indenters formed on the circumferential surface of the disk, and A method for reducing weld residual stress, wherein the indenter is 2.5 mm or larger and has a maximum height of less than twice the maximum height of the weld metal.

3. In Paragraph 2, A method for reducing welding residual stress, wherein the radius of curvature of the above-mentioned indenter is 3 mm or more and 25 mm or less.

4. In Paragraph 2, A welding residual stress reduction method in which the above-mentioned indenters have a spacing between adjacent indenters of 5 mm or more and 20 mm or less.

5. In Paragraph 2, A welding residual stress reduction method in which the above-mentioned indenter has a circular protrusion shape or a semi-cylindrical shape.

6. In Paragraph 1, A welding residual stress reduction method in which the above-mentioned welding base material has a yield strength of 315 MPa or more and 1000 MPa or less.

7. In Paragraph 1, A method for reducing weld residual stress, wherein the transformation completion temperature of the above-mentioned weld base material is 300°C or higher and 500°C or lower.

8. In Paragraph 1, A method for reducing weld residual stress, wherein the surface temperature of the weld metal in the above pressurization step is 25°C or higher and 500°C or lower.

9. In Paragraph 1, A method for reducing weld residual stress, additionally comprising a heat treatment step after the above-mentioned pressurization step.

10. In Paragraph 9, A method for reducing weld residual stress, wherein the above heat treatment is performed for 5 hours or more and 7 hours or less at a temperature range of 550°C or more and 650°C or less.

11. A welding residual stress reduction device comprising a disc that moves while rotating on the surface of the weld metal along the welding direction around a rotation axis and applies a compressive load to the weld metal.

12. In Paragraph 11, The above disk additionally includes one or more indenters formed on the circumferential surface of the disk, and A welding residual stress reduction device having a maximum height of less than twice the height of the weld metal, wherein the indenter is 2.5 mm or larger.

13. In Paragraph 12, A welding residual stress reduction device having a radius of curvature of 3 mm or more and 25 mm or less of the indenter.

14. In Paragraph 12, The above-mentioned indenter is a welding residual stress reduction device in which the spacing between adjacent indenters is 5 mm or more and 20 mm or less.

15. In Paragraph 12, The above-mentioned indenter is a welding residual stress reduction device having a circular protrusion shape or a semi-cylindrical shape.

16. In Paragraph 11, The above-mentioned rotating shaft is an eccentric welding residual stress reduction device.

17. In Paragraph 11, A welding residual stress reduction device in which the circumferential surface of the above-mentioned disk has a curved structure.

18. In Paragraph 17, The above curved structure is a U-shaped structure, a welding residual stress reduction device.

19. In Paragraph 12, A welding residual stress reduction device in which the above-mentioned indenter is formed on the inner curved surface of the circumferential surface of the above-mentioned disk.

20. In Paragraph 12, A welding residual stress reduction device having a hardness of 56 HRC or higher for the indenter.

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