Friction stir welding method, friction stir welding device, and method for manufacturing bonded member

Abstract

Provided is a friction stir welding method with which it is possible to obtain excellent welding efficiency while preventing the occurrence of roll scratches even when a high-Si steel sheet is used as a material to be welded. The method has a bonding step, a surface processing step, and a heating step, in which the maximum thickness reduction of the bonded member in the surface processing step is 5.0% or less of the thickness of the material to be bonded, and the maximum temperature reached in the heating step is 400-1000 DEG C.

Description

TECHNICAL FIELD

[0001] The present application relates to a friction stir joining method, a friction stir joining device, and a joining member manufacturing method. BACKGROUND

[0002] In friction stir joining, such as double-sided friction stir joining, joining of a joining material is performed in the following manner. That is, a pair of rotating tools is arranged on the surface side and the back side of a joining material having at least two or more metal sheets. Then, the rotating tools are pressed against the surface and the back of the joining material, respectively, and the rotating tools are moved in a joining direction while rotating. Thus, the metal sheets are softened by the frictional heat of the rotating tools and the softened portions thereof are stirred by the rotating tools. Then, plastic flow is generated in a region that becomes a joining portion of the joining material, and the joining material is joined. Hereinafter, a region in a portion where the joining material is butted or overlapped and is in a state of not yet being joined will be referred to as an "unjoined portion", and a region that is joined and integrated will be referred to as a "joined portion".

[0003] As a technique related to such friction stir joining, for example, Patent Literature 1 discloses: "A friction stir joining method characterized in that, when two steel sheets are butted or overlapped and subjected to friction stir joining, a rotation speed R of a tool that rotates in the friction stir joining is set to be more than 5 times / minute and less than 5000 times / minute, a front edge temperature T of the steel sheet that contacts a front side edge portion of the advancing direction of the tool is set to be 25°C or higher, a shoulder diameter D of the tool is set to be 8 to 40 mm, a joining speed V accompanying the progress of the tool is set to be 0.1 to 5 m / minute, and the friction stir joining is performed".

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Laid-Open No. 2019-166569 SUMMARY

[0007] However, in a production line of a steel sheet, such as a production line of pickling, cold rolling, annealing, and plating, in order to improve productivity and improve yield, the steel sheet (steel strip) is generally passed through after so-called coil joining is performed. Here, the coil joining refers to joining an end portion (rear end) of a preceding steel sheet or steel strip (hereinafter also referred to as a preceding steel sheet) and an end portion (front end) of a steel sheet or steel strip that follows the preceding steel sheet (hereinafter also referred to as a following steel sheet) as joining materials in the production line.

[0008] In the coil joining, generally, resistance seam welding, laser welding is applied. In addition, in recent years, application of friction stir joining in the coil joining is being studied. However, if the steel sheet having Si content: 2.0 to 12.0 mass% (hereinafter also referred to as high Si steel sheet), such as electromagnetic steel sheet, is subjected to the coil joining by the friction stir joining, equipment failure occurs, specifically, sometimes, a scratch (hereinafter also simply referred to as occurrence of roll scratch or occurrence of roll scratch) occurs in a roll through which the steel sheet passes on the downstream side of the joining process. Therefore, the current situation is that it is desired to improve this point.

[0009] The present application was developed in view of the above-described situation, and aims to provide a friction stir joining method capable of obtaining excellent joint efficiency while preventing occurrence of roll scratch even in a case where a high Si steel sheet is used as a joined material. In addition, the present application aims to provide a friction stir joining device which can be favorably used in the above-described friction stir joining method. Furthermore, the present application aims to provide a method for manufacturing a joined member. Note that in the present specification, the numerical range indicated using "~" means a range including the numerical values recited before and after "~" as lower limit value and upper limit value, respectively.

[0010] Thus, the inventors et al. repeatedly conducted intensive research in order to achieve the above-described object. First, the inventors et al. investigated the cause of occurrence of roll scratch in a case where a high Si steel sheet is used as a joined material. As a result, the inventors et al. found that burrs of a joined portion generated at the time of friction stir joining become the cause of occurrence of roll scratch. In particular, in a case where a high Si steel sheet is used as a joined material, the hardness of the burrs of the joined portion increases, and if a small amount of burrs remains, occurrence of roll scratch is caused.

[0011] The inventors et al. based on the above-described insight, tried to prevent occurrence of roll scratch by removing the burrs of the joined portion by grinding or the like. However, in this case, joint efficiency is significantly reduced.

[0012] Therefore, the inventors et al. repeatedly conducted research on the above-described cause, and further repeatedly conducted research in order to achieve the desired object. As a result, the following insight was obtained.

[0013] (1) In the process of removing the burrs, a deformed structure is formed in the joined portion. In particular, if a hardened phase, that is, a structure in which ductility is reduced with respect to the base material, exists in a region from the surface to a position of 1 / 10 of the thickness in the joined portion of the joined member (hereinafter also referred to as surface layer region of the joined portion), a defect is generated in this structure. Then, a crack is generated from this defect as a starting point, and joint efficiency is reduced.

[0014] (2) In order to obtain excellent joint efficiency while preventing occurrence of roll scratch, it is important to satisfy the following points at the same time.

[0015] In the surface processing step corresponding to the burr removing step, the maximum thickness reduction of the joined member is suppressed to 5.0% or less of the thickness of the joined material.

[0016] The heating of the joined member after the surface processing step is performed, and the heating conditions at this time are appropriately controlled to reduce the deformation strain in the surface layer region of the joined portion.

[0017] The present application was completed based on the above insight and further research.

[0018] That is, the gist of the present application is as follows.

[0019] 1. A friction stir joining method, comprising:

[0020] a joining step of pressing a rotating tool against a joined material and moving the rotating tool in a joining direction while rotating the rotating tool, thereby joining the joined material to obtain a joined member;

[0021] a surface processing step of subsequently performing surface processing on the joined member; and

[0022] a heating step of subsequently heating the joined member;

[0023] the joined material is a steel sheet having a Si content of 2.0 to 12.0 mass%,

[0024] the maximum thickness reduction of the joined member in the surface processing step is 5.0% or less of the thickness of the joined material, and

[0025] the maximum temperature reached in the heating step is 400°C to 1000°C.

[0026] 2. The friction stir joining method according to the above 1, wherein the surface processing is performed by grinding or pressing.

[0027] 3. The friction stir joining method according to the above 1 or 2, wherein the heating is performed by induction heating or resistance heating.

[0028] 4. The friction stir joining method according to any one of the above 1 to 3, wherein the hardness of the surface layer region of the joined portion of the joined member is in the range of 95 to 115% of the hardness of the base material of the joined member after the heating step.

[0029] The surface layer region of the joined portion of the joined member is a region from the surface to a position at 1 / 10 of the thickness in the joined portion of the joined member.

[0030] 5. The friction stir joining method according to any one of the above 1 to 4, wherein the joining process is further preceded by a preliminary surface processing process of at least removing a region of the joining material from the surface to a depth of 5 μm.

[0031] 6. A friction stir joining apparatus for use in the friction stir joining method according to any one of the above 1 to 4, the friction stir joining apparatus comprising, in the joining direction, in this order:

[0032] a joining apparatus that joins the joining materials to obtain a joined member;

[0033] a surface processing apparatus that performs surface processing of the joined member; and

[0034] a heating apparatus that heats the joined member.

[0035] 7. A friction stir joining apparatus for use in the friction stir joining method according to the above 5, the friction stir joining apparatus comprising, in the joining direction, in this order:

[0036] a preliminary surface processing apparatus that performs preliminary surface processing of the joining materials;

[0037] a joining apparatus that joins the joining materials to obtain a joined member;

[0038] a surface processing apparatus that performs surface processing of the joined member; and

[0039] a heating apparatus that heats the joined member.

[0040] 8. A method of manufacturing a joined member by the friction stir joining method according to any one of the above 1 to 5, the method comprising joining joining materials to obtain a joined member.

[0041] According to the present application, even in the case where a high Si steel sheet is used as the joining material, it is possible to obtain excellent joint efficiency while preventing the occurrence of roll marks. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 is a schematic view showing an example of a friction stir joining method according to an embodiment of the present application.

[0043] Figure 2 is a schematic view showing an example of double-sided friction stir joining. DETAILED DESCRIPTION

[0044] The present application will be described based on the following embodiments.

[0045] [1] Friction Stir Joining Method

[0046] First, a friction stirring bonding method according to one embodiment of the present invention will be described.

[0047] like Figure 1 As shown, a friction stirring bonding method according to one embodiment of the present invention includes:

[0048] In the joining process, a rotating tool is pressed against the material to be joined, and the rotating tool is moved in the joining direction while rotating, thereby joining the material to be joined to obtain a joined component.

[0049] Next, surface finishing is performed on the aforementioned mating components; and

[0050] Next, the heating process involves heating the aforementioned joining components.

[0051] Figure 1 In the diagram, symbol 1 represents a rotary tool (surface-side rotary tool), 3 represents the material being joined, 4 represents the joint, 5 represents the grinding device, and 6 represents the heating device. The following describes each of the above processes.

[0052] (Jointing process)

[0053] In the joining process, a rotating tool is pressed against the material to be joined, and the rotating tool moves in the joining direction while rotating, thereby joining the materials to obtain a joined part.

[0054] There are no special restrictions on the joining conditions; the conventional method can be followed.

[0055] Alternatively, the joining method can be a single-sided friction stirring joining where a rotating tool is arranged on one side of the materials to be joined, or a two-sided friction stirring joining where a rotating tool is arranged on both the surface and the back side of the materials to be joined.

[0056] An example is given to illustrate the frictional mixing process on both sides, such as... Figure 2 As shown, a pair of rotary tools are positioned on the surface and back sides of a material to be joined, which has at least two metal plates. Hereinafter, the rotary tool positioned on the surface side of the material to be joined will be referred to as a surface-side rotary tool. The rotary tool positioned on the back side of the material to be joined will be referred to as a back-side rotary tool. Figure 2In the diagram, symbol 1 represents a rotating tool (surface-side rotating tool), 2 represents a rotating tool (back-side rotating tool), 3 represents the materials to be joined, and 4 represents the joint. Then, a pair of opposing rotating tools are pressed against the surface and back of the materials to be joined, respectively, and the rotating tools are moved in the joining direction while rotating. That is, the surface-side rotating tool is pressed against the surface of the materials to be joined, and the back-side rotating tool is pressed against the back of the materials to be joined, and these rotating tools are moved in the joining direction while rotating. Thus, the metal sheet is softened by the frictional heat between the rotating tools and the materials to be joined, while the softened areas are stirred by the rotating tools. Then, plastic flow occurs in the region that becomes the joint of the materials to be joined, thus joining the materials.

[0057] In addition, butt joint and overlap joint can be exemplified as joining methods. Butt joint refers to joining materials by rotating a rotating tool while pressing it against the butt joint containing the end faces (butt surfaces) of the materials being joined, with the end faces of the materials being joined facing each other, and then joining the materials by moving the rotating tool in the joining direction in this state. Overlap joint refers to joining materials by overlapping at least a portion of the ends of the materials being joined, rotating a rotating tool while pressing it against the overlapping portion, and then joining the materials by moving the rotating tool in the joining direction in this state.

[0058] (Surface finishing process)

[0059] In the surface finishing process, burrs on the surfaces of the joined parts generated during the joining process are removed. It should be noted that in... Figure 1 The description of the device on the back side is omitted. Moreover, at this time, it is important to suppress the amount of the jointing parts removed along with the burrs, especially to reduce the maximum thickness of the jointing parts to less than 5.0% of the thickness of the materials being joined.

[0060] Maximum thickness reduction of the joined parts: less than 5.0% of the thickness of the materials being joined.

[0061] When high-Si steel sheets are used as the bonding material for friction stir bonding, and burrs formed at the joint are removed, a microstructure with reduced ductility relative to the base material forms in the surface region of the joint, resulting in defects. Cracks then develop from these defects, reducing joint efficiency. As described above, to suppress deformation strain in this region, it is effective to heat the bonding components in the heating process described later, appropriately controlling the heating conditions. However, if the maximum thickness reduction of the bonding components exceeds 5.0% of the thickness of the bonded materials, i.e., the ratio of the maximum thickness reduction of the bonding components to the thickness of the bonded materials (=[Maximum thickness reduction of the bonding components (mm)] / [Thickness of the bonded materials (mm)]×100, hereinafter also referred to as the thickness reduction ratio of the bonding components) exceeds 5.0%, the joint efficiency decreases due to the thickness reduction. Furthermore, even if the bonding components are heated after the surface finishing process, the deformation strain in the aforementioned region cannot be sufficiently reduced, and excellent joint efficiency cannot be obtained. Therefore, the thickness reduction ratio of the bonding components is 5.0% or less. The thickness reduction ratio of the bonding components is preferably 3.0% or less. It should be noted that as long as the burrs generated in the joining process can be removed, the thickness reduction rate of the joined parts is not particularly limited and can be 0%. From the viewpoint of more reliably preventing the generation of roller scratches by sufficiently removing the burrs generated in the joining process, the thickness reduction rate of the joined parts is preferably 1.0% or more.

[0062] Here, the maximum thickness reduction of the joining parts is the maximum reduction in thickness in each region of the joining parts where surface finishing has been performed. Furthermore, in the case of butt joints, the thickness of the joined materials is the thickness of each individual steel plate used as the joined material. However, if the thicknesses of the steel plates used as joined materials differ, the thickness of the joined materials is the average thickness of the steel plates used as joined materials. Additionally, in the case of overlap joints, it is the thickness of the overlapping portion of the joined materials (i.e., the total thickness of the steel plates overlapping in the overlapping portion).

[0063] There are no particular limitations on the surface finishing method. From the viewpoint of processing efficiency, grinding or pressing is preferred. In order to control the maximum thickness reduction of the joint parts, it is preferable to check the surface condition of the joint parts (the degree of burrs, etc.) before surface finishing and then adjust the position and height of the surface finishing.

[0064] It should be noted that in the joining process, when performing two-sided friction stir joining, the aforementioned surface processing is performed on both sides of the joining components. Alternatively, in the joining process, when performing one-sided friction stir joining, the aforementioned surface processing can be performed on only one side of the joining components (the side with the rotating tool (the side with the weld bead)) or on both sides of the joining components. From an efficiency standpoint, the former is advantageous. Furthermore, when the aforementioned surface processing is performed on both sides of the joining components, the thickness reduction rate of the joining components on each side can be controlled within the aforementioned range. It should be noted that in the heating process described later, similarly, heating can be performed on one or both sides of the joining components depending on the joining method.

[0065] There are no special restrictions on conditions other than those mentioned above; the conventional methods can be followed.

[0066] (Heating process)

[0067] In the heating process, the joining components are heated. As described above, when removing burrs formed at the joint after friction stir bonding using high-Si steel sheets as the bonding material, a microstructure with reduced ductility relative to the base material is formed in the surface region of the joint, resulting in defects. Cracks then originate from these defects, reducing joint efficiency. To reduce deformation strain in the surface region of the joint, it is important to heat the joining components after burr removal, controlling the heating conditions as follows.

[0068] Maximum temperature reached: 400℃~1000℃

[0069] By setting the maximum reaching temperature to 400°C or higher, deformation strain in the surface region of the joint is reduced, resulting in excellent joint efficiency. However, if the maximum reaching temperature exceeds 1000°C, grain coarsening occurs. Therefore, the maximum reaching temperature is between 400°C and 1000°C. The maximum reaching temperature is preferably 700°C or higher. Furthermore, the maximum reaching temperature is preferably 900°C or lower.

[0070] Furthermore, during the heating process, the following conditions are preferably met. This more advantageously reduces deformation strain in the surface region of the aforementioned joint, resulting in excellent joint efficiency.

[0071] Average heating rate (hereinafter also referred to as heating rate) in the temperature range of 100–400℃: 10–300℃ / second

[0072] Holding time at the highest reached temperature (hereinafter also referred to as holding time): 0.1 to 10 seconds

[0073] Average cooling rate (hereinafter also referred to as cooling rate) in the temperature range of 400–100°C: 10–300°C / second

[0074] The temperatures mentioned here are all based on the surface temperature of the joint of the joining components. It should be noted that when performing single-sided friction stir bonding, and only one side of the joining components (the side with the rotating tool (the side with the weld bead)) undergoes the aforementioned surface processing, the highest temperature reached on that side of the joint of the joining components will be controlled within the aforementioned range. In this case, it is preferable to control the heating rate, holding time, and cooling rate within the aforementioned range on that side of the joint of the joining components. Furthermore, when performing two-sided friction stir bonding, and both sides of the joining components undergo the aforementioned surface processing, the highest temperature reached on both sides of the joint of the joining components will be controlled within the aforementioned range. In this case, it is preferable to control the heating rate, holding time, and cooling rate within the aforementioned range on both sides of the joint of the joining components.

[0075] Furthermore, there are no particular limitations on the heating method. From the viewpoint of heating efficiency, high-frequency induction heating or resistance heating (using electrodes clamped and energized) is preferred.

[0076] There are no special restrictions on conditions other than those mentioned above; the conventional methods can be followed.

[0077] (Pre-surface processing steps)

[0078] In friction stir bonding, if oxide films or contaminants remain on the surfaces of the materials being bonded, it can sometimes lead to a decrease in joint strength. To avoid this, the friction stir bonding method according to one embodiment of the present invention may optionally include a pre-surface processing step prior to the aforementioned bonding step, which removes at least a region of the materials being bonded from the surface to a depth of 5 μm. It should be noted that the region of the materials being bonded removed in the pre-surface processing step is, at most and preferably, a region of the materials being bonded from the surface to a depth of 50 μm. Furthermore, the aforementioned pre-surface processing may be performed on only one side of the materials being bonded, or on both sides, depending on the surface condition of the materials being bonded.

[0079] There are no particular restrictions on the surface finishing method. From the point of view of processing efficiency, grinding or lapping is the preferred surface finishing method.

[0080] It should be noted that when pre-surface processing is performed, the thickness of the material to be joined, which is the denominator of the thickness reduction ratio of the joining parts, is the thickness of the material to be joined after pre-surface processing. That is, the thickness of the material to be joined, which is the denominator of the thickness reduction ratio of the joining parts, is the thickness of the material to be joined supplied for the joining process.

[0081] There are no special restrictions on conditions other than those mentioned above; the conventional methods can be followed.

[0082] (Materials to be joined)

[0083] The material to be joined is a steel sheet with a Si content of 2.0 to 12.0% by mass. The content of elements other than Si is not particularly limited. Examples of such a steel sheet composition include, by mass%, C: 0.1% or less, Si: 2.0 to 12.0%, Al: 2.0% or less, and Mn: 1.0% or less, with the remainder being Fe and unavoidable impurities. Unavoidable impurities include, for example, P: 0.2% or less, S: 0.01% or less, and N: 0.01% or less. In the above composition, at least one element selected from Cr: 1% or less, Ni: 1% or less, Cu: 1% or less, Sn: 0.2% or less, Sb: 0.2% or less, Ca: 0.01% or less, REM: 0.05% or less, and Mg: 0.01% or less may be present by mass%. It should be noted that elements other than Si and Fe can be 0% by mass. The Si content is preferably 3.0% by mass or more. Furthermore, the Si content is preferably 8.0% by mass or less, more preferably 5.0% by mass or less. The C content is more preferably 0.001% by mass or more. The Mn content and Al content are each more preferably 0.01% by mass or more. Additionally, the steel plates used for the joined materials can be of the same steel grade or different steel grades. Furthermore, the thickness of each steel plate used for the joined materials is preferably 0.2 to 3.2 mm.

[0084] (Jointing components)

[0085] The joined component obtained by the friction stir joining method according to one embodiment of the present invention has two or more base materials (materials to be joined) and joints between the base materials (joints between the joining base materials). Here, each base material is composed of a steel plate that is a material to be joined. The joint is a region that has become a recrystallized structure due to heat treatment based on frictional heat and plastic flow between a rotating tool and the materials to be joined. In addition, for the above-mentioned joined component, the hardness of the surface region of the joint is preferably in the range of 95 to 115% of the hardness of the base material, more preferably in the range of 100 to 110% of the hardness of the base material. In other words, the conditions of each of the above-mentioned processes, especially the conditions in the heating process, are controlled in such a way that the hardness of the surface region of the joint of the finally obtained joined component is preferably in the range of 95 to 115% of the hardness of the base material, more preferably in the range of 100 to 110% of the hardness of the base material.

[0086] Here, the surface region refers to the area from the surface to a depth of 1 / 10 of the thickness in the joint of the joining components. It should be noted that when performing single-sided friction stir bonding, and only on one side of the joining components (the side with the rotating tool (the side with the weld bead)) the aforementioned surface processing and heating are performed, the hardness of the surface region of the joint is preferably in the range of 95-115% of the hardness of the base material, more preferably in the range of 100-110% of the hardness of the base material, at least on that side of the joint of the joining components. Furthermore, when performing two-sided friction stir bonding, and on both sides of the joining components the aforementioned surface processing and heating are performed, the hardness of the surface region of the joint is preferably in the range of 95-115% of the hardness of the base material, more preferably in the range of 100-110% of the hardness of the base material, on both sides of the joint of the joining components.

[0087] The hardness of the surface area of ​​the joint and the hardness of the base material were determined by Vickers hardness test according to JIS Z 2244 (2009). The test force was 100 gf.

[0088] Specifically, the joint component is cut along the thickness (vertical) direction with a joint cross-section (the surface of the joint component including the joint vertical direction and the thickness direction, where the joint vertical direction is the direction perpendicular to both the joint direction and the thickness direction). Then, in the surface region of the joint at the cut surface, starting from a position 50 μm deep from the surface of the joint and 50 μm apart from the boundary between the base material and the joint in the joint vertical direction (joint side), Vickers hardness is measured at intervals of 50 μm in the thickness direction and 50 μm in the joint vertical direction, according to the above conditions. Additionally, Vickers hardness is measured at the thickness center of the base material at the cut surface under the same conditions. Furthermore, if the Vickers hardness measured in the surface region of the joint at the cut surface is within 95% to 115% of the Vickers hardness measured at the thickness center of the base material at the cut surface, it is determined that the hardness of the surface region of the joint is within 95% to 115% of the hardness of the base material. It should be noted that when the Vickers hardness differs due to the different base materials joined via the joint, the above judgment is made based on the Vickers hardness of each base material joined via the joint. For example, in a joint component where a first base material and a second base material are joined via the joint, if the Vickers hardness measured in the surface region of the joint at the cut surface is in the range of 95% to 115% of the Vickers hardness measured at the center of the thickness of the first base material at the cut surface, and the Vickers hardness measured at the center of the thickness of the second base material at the cut surface is also in the range of 95% to 115%, then the hardness of the surface region of the joint is judged to be in the range of 95% to 115% of the hardness of the base material.

[0089] Alternatively, the base material and the joint can be separated, for example, as follows: The joint is cut along its thickness (vertical) direction with the joint cross-section as the cut surface. Then, the cut surface is ground and etched using 3 vol.% nitric acid ethanol (a solution of nitric acid and ethanol), a saturated aqueous solution of picric acid, or aqua regia (a solution of hydrochloric acid and nitric acid mixed in a 3:1 volume ratio). The cut surface is then observed using an optical microscope, and the base material and the joint are separated according to the degree of etching, etc.

[0090] It should be noted that the joining component can be a single-sided friction stir joint or a double-sided friction stir joint. Here, a single-sided friction stir joint is a joining component obtained by joining materials using a single-sided friction stir joint with a rotating tool positioned on one side of the materials being joined. That is, the single-sided friction stir joint has a weld bead only on one surface of the joint. In a single-sided friction stir joint, it is preferable to control the conditions of the aforementioned processes, particularly the conditions in the heating process, in such a way that the aforementioned surface layer area is obtained at least on one surface side of the joint. Conversely, a double-sided friction stir joint is a joining component obtained by joining materials using a double-sided friction stir joint with a rotating tool positioned on both the front and back sides of the materials being joined. That is, the double-sided friction stir joint has weld beads on both surfaces of the joint. When the joining component is a double-sided friction stir joint, it is preferable to control the conditions of the aforementioned processes, particularly the conditions in the heating process, in such a way that the aforementioned surface layer area is obtained near both surfaces of the joint.

[0091] [2] Friction stirring joint device

[0092] Next, a friction stirring and joining device according to one embodiment of the present invention will be described.

[0093] A friction stirring joining device according to one embodiment of the present invention can be well used in the friction stirring joining method described above [1], wherein the friction stirring joining device is characterized in that it has the following components in sequence in the joining direction:

[0094] Any pre-surface processing device performs pre-surface processing on the materials to be joined;

[0095] A joining device joins the aforementioned materials to be joined, thereby obtaining a joined component;

[0096] A surface processing apparatus performs surface processing on the aforementioned joining components; and

[0097] A heating device is used to heat the aforementioned joint components.

[0098] It should be noted that a surface shape measuring device may be provided between the aforementioned joining device and the aforementioned surface processing device as needed.

[0099] Here, the form of the pre-surface processing apparatus is not particularly limited as long as it can perform surface processing on the materials to be joined and partially remove the materials to be joined. Examples of pre-surface processing apparatuses include grinding apparatuses or polishing apparatuses such as grinding machines.

[0100] The form of the joining device is not particularly limited as long as it is a device for friction stirring joining. Examples of joining devices include those having a rotating tool and a drive mechanism for that tool.

[0101] The form of the surface shape measuring device is not particularly limited as long as it can confirm the degree of burrs on the surface of the joint of the joint parts. Examples of surface shape measuring devices include contact type (tracing the surface of the sample with a stylus) or non-contact type (laser, etc.) surface shape measuring machines.

[0102] The form of a surface finishing apparatus is not particularly limited as long as it is capable of performing surface finishing on the joint parts and removing burrs from the joint surfaces of the joint parts. Examples of surface finishing apparatuses include grinding apparatuses such as grinding machines or pressing apparatuses.

[0103] The form of the heating device is not particularly limited. Examples of heating devices include atmosphere furnaces (devices that heat the joint by means of an atmosphere covering the entire joint), induction heating devices and resistance heating devices that provide non-contact localized heating. In addition, the heating device preferably includes a device for measuring the surface temperature of the joint components, such as a temperature recorder.

[0104] Furthermore, the friction stirring bonding apparatus according to one embodiment of the present invention preferably includes a driving device that causes any pre-surface processing device, bonding device, any surface shape measuring device, surface processing device, and heating device to move integrally in the bonding direction in accordance with the bonding speed. This allows for a series of processes to be performed continuously, thus offering significant advantages in terms of efficiency.

[0105] It should be noted that there are no special limitations other than those mentioned above, and the device configuration can be the same as that of conventionally known devices.

[0106] [3] Manufacturing method of joint components

[0107] Next, a method for manufacturing a joining member according to one embodiment of the present invention will be described.

[0108] According to one embodiment of the present invention, a method for manufacturing a joining component involves joining materials using the friction stir joining method described in [1] above to obtain a joining component. The resulting joining component is as described in [1] above. Furthermore, as a specific example of the resulting joining component, a coil having a joint portion for joining a preceding steel plate and a following steel plate can be cited. There are no particular limitations on conditions other than those described above; conventional methods may be used.

[0109] Example

[0110] Two steel plates with the Si content and thickness listed in Table 1, used as the bonding materials, were joined together and subjected to two-sided friction stirring to obtain a bonded component (bonding process). In all cases, the rotation speed on both sides was 1000 rpm, and the bonding speed was 2 m / min. A ceramic tool with a shoulder diameter of 16 mm, a probe diameter of 8 mm, and a probe length of 1 mm was used for both sides of the resulting bonded component under the conditions shown in Table 1, to remove burrs from the joint area (surface finishing process). The maximum thickness reduction of the bonded component was measured using a laser displacement gauge. Next, the bonded component was heated under the conditions shown in Table 1 (heating process). Heating was performed using an atmosphere furnace. The highest reached temperature was measured on both sides of the bonded component using a temperature recorder. For conditions not explicitly stated, the above-described or conventional methods were followed. It should be noted that the surface finishing process was not performed in No. 15. No heating process was performed in No. 16. Furthermore, in all cases, the conditions of the surface finishing process and the heating process, as well as the hardness of the surface area of ​​the joint (described later) / hardness of the base material × 100, are approximately the same on both sides; therefore, only one of these is representatively recorded in Table 1. In addition, the prevention of roller scratches (described later) was confirmed on both sides of the joint of the joint components.

[0111] For the jointed parts obtained in this way, the hardness of the surface area of ​​the joint and the hardness of the base material are measured according to the above-described method, and it is determined whether the hardness of the surface area of ​​the joint is within the range of 95% to 115% of the hardness of the base material. The hardness of the surface area of ​​the joint / the hardness of the base material × 100 is recorded in Table 1.

[0112] In addition, the joint efficiency of the obtained joint components was evaluated. In the evaluation of joint efficiency, a joint efficiency (= fracture strength of the joint / fracture strength of the base material × 100) exceeding 95% was rated as "excellent," 95% to 90% was rated as "good," and below 90% was rated as "poor." The results are recorded in Table 1.

[0113] Here, the fracture strength of the joint is determined as follows. Specifically, from the obtained friction-stirred joint, a test piece of the same shape as test piece No. 1 as specified in JIS Z 3121 (2013) is collected, with the joint direction and thickness direction perpendicular to the long side direction of the test piece and the joint located at the center of the parallel portion. Then, a tensile test according to JIS Z 3121 (2013) is performed using the collected test piece to determine the maximum test force (N). The determined maximum test force (N) is then divided by the cross-sectional area (mm²) of the parallel portion of the test piece. 2 The value obtained is used as the fracture strength of the joint.

[0114] The fracture strength of the base material can also be referred to as the tensile strength (TS) of the base material (the joined materials). That is, the fracture strength of the base material can be determined by a tensile test according to JIS Z 2241 (2022). For example, a JIS 5 test piece is collected from the base material or a material identical to the base material. Then, using the collected test piece, a tensile test is performed at a crosshead speed of 10 mm / min to determine the tensile strength (TS). It should be noted that when the fracture strength varies depending on the base material, the highest fracture strength among the fracture strengths of each base material is used in the evaluation of joint efficiency.

[0115] To confirm the effectiveness of preventing roller scratches, the joint of the mating component was pressed against a surface of polished high-carbon chromium bearing steel (SUJ-2, hereinafter also referred to as bearing steel) (simulating a roller) and slid for 100 cycles. The pressing pressure (the applied pressure when pressing the joint of the mating component against the bearing steel) was 400 MPa. Next, the presence or absence of scratches on the bearing steel was visually checked. Furthermore, if scratches were found, the depth of the scratches was measured by cross-sectional observation using an optical microscope. The effectiveness of preventing roller scratches was evaluated according to the following criteria. The results are recorded in Table 1.

[0116] Good: No scratches deeper than 50μm were detected.

[0117] Defect: Scratches exceeding 50μm in depth were confirmed.

[0118]

[0119] As shown in Table 1, in the inventive examples, excellent jointing efficiency is achieved while preventing the generation of roller scratches. On the other hand, in the comparative examples, roller scratches occur or sufficient jointing efficiency cannot be obtained.

[0120] Furthermore, when the jointing parts are manufactured in the same manner as described above, except for the pre-surface processing step, excellent joint efficiency is obtained in the method where the thickness reduction rate of the jointing parts in the surface processing step is 5.0% or less and the maximum temperature reached in the heating step is 400°C to 1000°C, while preventing the generation of roller scratches.

[0121] Furthermore, when using various steel plates with a Si content of 2.0 to 12.0% by mass and a thickness of 0.2 to 3.2 mm as the joining material, and manufacturing the joining parts by butt jointing or overlap jointing under various joining conditions, excellent joint efficiency is obtained while preventing the generation of roll scratches in methods where the thickness reduction rate of the joining parts is 5.0% or less and the maximum temperature reached in the heating process is 400°C to 1000°C.

[0122] Symbol Explanation

[0123] 1. Rotation tool (surface-side rotation tool)

[0124] 2 Rotation tool (backside rotation tool)

[0125] 3. Materials to be joined

[0126] 4. Joint

[0127] 5 Grinding device

[0128] 6. Heating device

Claims

1. A friction stirring bonding method, comprising: In the joining process, a rotating tool is pressed against the materials to be joined, and the rotating tool moves in the joining direction while rotating, thereby joining the materials to obtain a joined component. Then... The surface finishing process involves performing surface finishing on the joining components, and then, The heating process involves heating the joining components; The material to be joined is a steel plate with a Si content of 2.0–12.0% by mass. The maximum thickness reduction of the joining component in the surface processing step is less than 5.0% of the thickness of the materials being joined, and... The maximum temperature reached in the heating process is 400℃~1000℃.

2. The friction stirring bonding method according to claim 1, wherein, The surface processing is performed by grinding or pressing.

3. The friction stirring bonding method according to claim 1, wherein, The heating is performed by induction heating or resistance heating.

4. The friction stirring bonding method according to claim 2, wherein, The heating is performed by induction heating or resistance heating.

5. The friction stirring bonding method according to claim 1, wherein, After the heating process, the hardness of the surface region of the joint of the joining components is in the range of 95% to 115% of the hardness of the base material of the joining components. The surface region of the joint of the joining component is the area from the surface to a position of 1 / 10 of the thickness in the joint of the joining component.

6. The friction stirring bonding method according to claim 2, wherein, After the heating process, the hardness of the surface region of the joint of the joining components is in the range of 95% to 115% of the hardness of the base material of the joining components. The surface region of the joint of the joining component is the area from the surface to a position of 1 / 10 of the thickness in the joint of the joining component.

7. The friction stirring bonding method according to claim 3, wherein, After the heating process, the hardness of the surface region of the joint of the joining components is in the range of 95% to 115% of the hardness of the base material of the joining components. The surface region of the joint of the joining component is the area from the surface to a position of 1 / 10 of the thickness in the joint of the joining component.

8. The friction stirring bonding method according to claim 4, wherein, After the heating process, the hardness of the surface region of the joint of the joining components is in the range of 95% to 115% of the hardness of the base material of the joining components. The surface region of the joint of the joining component is the area from the surface to a position of 1 / 10 of the thickness in the joint of the joining component.

9. The friction stirring bonding method according to any one of claims 1 to 8, wherein, Prior to the bonding process, there is a pre-surface processing step that removes at least a 5 μm area from the surface to the depth of the materials to be bonded.

10. A friction stirring joining device for use in the friction stirring joining method according to any one of claims 1 to 8, wherein the friction stirring joining device comprises, in sequence in the joining direction: A joining device joins materials to be joined, resulting in a joined component; A surface processing apparatus performs surface processing on the joining components; as well as A heating device is used to heat the joining components.

11. A friction stirring joining device for use in the friction stirring joining method of claim 9, wherein the friction stirring joining device comprises, in sequence in the joining direction: A pre-surface processing device for performing pre-surface processing on the materials to be joined; A joining device joins the materials to be joined to obtain a joined component; A surface processing apparatus performs surface processing on the joining components; as well as A heating device is used to heat the joining components.

12. A method for manufacturing a joining component, wherein the joining components are obtained by joining materials by friction stirring joining method according to any one of claims 1 to 8.

13. A method for manufacturing a joining component, wherein the materials to be joined are joined by the friction stirring joining method as described in claim 9, thereby obtaining the joining component.

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