WO2023032515A1 - 摩擦攪拌点接合継手およびその製造方法、ならびに、摩擦攪拌点接合方法 - Google Patents
摩擦攪拌点接合継手およびその製造方法、ならびに、摩擦攪拌点接合方法 Download PDFInfo
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- WO2023032515A1 WO2023032515A1 PCT/JP2022/028411 JP2022028411W WO2023032515A1 WO 2023032515 A1 WO2023032515 A1 WO 2023032515A1 JP 2022028411 W JP2022028411 W JP 2022028411W WO 2023032515 A1 WO2023032515 A1 WO 2023032515A1
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- 238000003756 stirring Methods 0.000 title claims abstract description 70
- 238000003466 welding Methods 0.000 title claims abstract description 58
- 238000000034 method Methods 0.000 title claims description 32
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
- B23K20/12—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding
Definitions
- the present invention relates to a friction stir spot welding joint, a manufacturing method thereof, and a friction stir spot welding method.
- the friction stir spot welding is a spot welding method using a friction stir phenomenon. Specifically, while rotating a tool having a shoulder portion and a pin portion protruding from the shoulder portion, the pin portion of the tool is press-fitted (pushed) into the material to be joined, which is made of a metal plate with which the pin portion is overlapped. As a result, the metal plates are softened and plastically flowed, and the superimposed metal plates are joined.
- Patent Document 1 As a technology related to such friction stir spot welding, for example, in Patent Document 1, "A first member and a second member made of a metal material are overlapped with a soft portion positioned at the boundary, and press-fitted from the first member to the second member while rotating the pin portion of the rotary tool, A friction stir spot welding method for spot welding by stirring the first member and the second member, At least one of the first and second members is made of a metal material having a tensile strength of 100 MPa or more at 800 ° C.
- the soft portion has a hardness lower than the base material hardness of the metal material having a tensile strength of 100 MPa or more at room temperature,
- the soft portion is a soft layer formed on a surface layer portion of the metal material having at least the tensile strength of 100 MPa or more,
- the metal material having a tensile strength of 100 MPa or more is carbon steel having a C content of 0.3% or more by mass, and the soft layer is a decarburized layer having a C content of 0.1% or less by mass.
- a friction stir spot welding method. is disclosed.
- the present invention has been developed to solve the above problems. It is an object of the present invention to provide a friction stir spot welded joint having tensile strength and a method for manufacturing the same. Another object of the present invention is to provide a friction stir spot welding method for obtaining the above friction stir spot welded joint.
- high cross tensile strength means a cross tensile strength of 8.0 kN or more as measured by a cross tension test conforming to JIS Z 3137.
- the inventors have made extensive studies in order to achieve the above object. As a result, the inventors ⁇ In addition to forming an annular groove on the upper surface of the joint, ⁇ Appropriately control the shape and hardness of the joint at the same time, specifically, satisfy the following (a) to (c) at the same time. As a result, it has been found that high joint strength can be obtained even when a steel plate having a soft surface layer is used as the material to be joined. (a) Regarding the vertical position of the deepest point of the concave portion of the joint, with the lower mating surface of the steel plate to be joined as the reference position, -0.5 mm or less and -TL x 0.50 or less satisfy at least one.
- the vertical position of the highest point of the joint interface is +TU ⁇ 0.50 or more with the upper mating surface of the steel plate to be joined as a reference position.
- R1 is the initial tool rotation speed (rpm)
- A1 is the tool press-in amount (mm) under the initial welding conditions
- P1 is the initial pressure (N).
- a n+1 is the tool press-fitting amount (mm) from the time when the n-th joining condition is switched to the time when the tool reaches the maximum press-fitting depth.
- a friction stir spot welded joint having two or more superimposed steel plates, a joint portion of the steel plates, and an annular groove portion on the upper surface of the joint portion, At least one of the steel plates has a surface soft layer,
- the junction includes a recess, a first flow section adjacent to the recess, a second flow section adjacent to the first flow section, and a joint between the first flow section and the second flow section.
- a bonding interface that is a boundary;
- the vertical position of the deepest point of the recess satisfies at least one of ⁇ 0.5 mm or less and ⁇ TL ⁇ 0.50 or less with the lower mating surface of the steel plate as a reference position,
- the vertical position of the highest point of the joint interface is +TU ⁇ 0.50 or more with the upper mating surface of the steel plate as a reference position, In the vertical position: +TU ⁇ 0.50 or +TU ⁇ 0.60, the difference between the hardness at the position of the bonding interface in the horizontal position and the hardness at the position +350 ⁇ m of the bonding interface is 80 HV or less. Friction stir spot welded fittings.
- the upper plate and the lower plate are respectively the steel plate positioned at the top and the steel plate positioned at the bottom among the two or more steel plates that are superimposed
- TU is the plate thickness (mm) of the steel plate of the upper plate
- TL is the plate thickness (mm) of the steel plate of the lower plate
- the upper mating surface is a mating surface between the upper plate and the steel plate adjacent to the upper plate
- the lower mating surface is the mating surface between the lower plate and the steel plate adjacent to the lower plate.
- the vertical position is + if it is above the reference position, and - if it is below the reference position.
- the horizontal position is the distance from the reference position.
- a friction stir point in which a tool having a shoulder portion and a pin portion protruding from the shoulder portion is rotated, and the pin portion is press-fitted into two or more superimposed steel plates to join the steel plates.
- a joining method comprising: At least one of the steel plates that are the materials to be joined has a surface soft layer, The vertical position of the maximum press-fit depth of the tool satisfies at least one of ⁇ 0.5 mm or less and ⁇ TL ⁇ 0.50 or less with the lower mating surface of the steel plate as a reference position, and , a state in which the shoulder and the upper plate are in contact when the tool reaches the maximum press-fit depth; The maximum temperature reached is 850 ° C.
- R1 is the initial tool rotation speed (rpm)
- A1 is the tool press-in amount (mm) under the initial welding conditions
- P1 is the initial pressure (N).
- a n+1 is the tool press-fitting amount (mm) from the time when the n-th joining condition is switched to the time when the tool reaches the maximum press-fitting depth.
- the upper plate and the lower plate are respectively the steel plate positioned at the top and the steel plate positioned at the bottom among the two or more steel plates that are superimposed
- TL is the plate thickness (mm) of the steel plate of the lower plate
- the lower mating surface is the mating surface between the lower plate and the steel plate adjacent to the lower plate.
- the vertical position is + if it is above the reference position, and - if it is below the reference position.
- a friction stir spot welded joint having high cross tensile strength can be obtained even when a steel plate having a soft surface layer is used as the material to be welded.
- friction stir spot welding can be applied to a wider range of steel plates, and the industrial utility value is extremely high.
- FIG. 1 is a schematic diagram of a vertical cross-section of a friction stir spot welded joint according to one embodiment of the present invention
- FIG. Fig. 10 is a schematic diagram of a vertical cross section of a friction stir spot welded joint of sample number 13 (friction stir spot welded joint without an annular groove).
- FIG. 1 is a vertical cross section of the friction stir point welded joint passing through the center position of the concave portion of the joint (hereinafter also simply referred to as a vertical cross section), and the positions of each part are all shown in the vertical cross section. It is.
- the upper side in the vertical direction is the side into which the pin portion of the tool is press-fitted during friction stir spot welding.
- the lower side in the vertical direction is the side where the backing material is installed during friction stir spot welding (the side opposite to the side where the pin portion of the tool is press-fitted during friction stir spot welding).
- the upper side and the lower side in the vertical direction can be specified from the shape and the like, for example, the position of the recess.
- the uppermost steel plate (the steel plate positioned at the top) is the upper plate
- the lowermost steel plate (the steel plate positioned at the bottom) is the lower plate
- the top and bottom and the steel plate (steel plate other than the top and bottom) is also called a middle plate.
- the upper surface is the vertically upper surface and the lower surface is the vertically lower surface.
- a gap remaining (without being joined) between the superimposed steel sheets is referred to as an unjoined interface 4 .
- the junction includes a recess 2-1, a first flow section 2-2 adjacent to the recess, and a second flow section 2-3 adjacent to the first flow section. , and a joint interface 2-4 that is a boundary between the first flow section and the second flow section.
- the recess is formed by press-fitting the pin portion of the tool during joining.
- the recess is substantially circular when viewed from above in the vertical direction, and its diameter is approximately the same as the diameter of the pin portion of the tool.
- the center position of the recess is the center of the recess when viewed from above in the vertical direction.
- the first flow area is a flow area formed by plastic flow of the lower plate during joining, and is formed adjacent to the periphery of the recess.
- the second flow section is a flow region formed by plastic flow of the upper plate, and is formed adjacent to the first flow section. In the case where there are three or more steel plates to be joined, all the flow regions formed by the plastic flow of the intermediate plate shall be included in the second flow section.
- the first flow section and the second flow section are defined as follows.
- the joint interface which is the boundary between the first flow section and the second flow section. That is, the vertical cross section of the friction stir point welded joint passing through the center position of the recess of the joint is polished and etched with a picric acid saturated aqueous solution. Then, the vertical cross section is observed with an optical microscope, and the first and second fluidized portions are defined based on the structure of the base material and the degree of etching in the fluidized portions. Then, the determined boundary between the first fluidized portion and the second fluidized portion is defined as the bonding interface.
- the upper plate and the lower plate are respectively the steel plate positioned at the top and the steel plate positioned at the bottom among the two or more steel plates that are superimposed
- TU is the plate thickness (mm) of the steel plate of the upper plate
- TL is the plate thickness (mm) of the steel plate of the lower plate
- the upper mating surface is a mating surface between the upper plate and the steel plate adjacent to the upper plate
- the lower mating surface is the mating surface between the lower plate and the steel plate adjacent to the lower plate.
- the vertical position is + if it is above the reference position, and - if it is below the reference position.
- the horizontal position is the distance from the reference position (the reference position is set to 0 and does not become negative (negative values are not taken)).
- the level of the deepest point of the recess At least one of ⁇ 0.5 mm or less and ⁇ TL ⁇ 0.50 or less is satisfied with respect to the level of the deepest point of the recess, with the lower mating surface of the steel plate to be joined as a reference position. As a result, the joint interface is strengthened, and high cross tensile strength can be obtained even when a steel plate having a surface soft layer is used as the material to be joined.
- the level of the deepest point of the concave portion is preferably -TL ⁇ 0.90 or more.
- the level of the highest point of the joint interface is +TU ⁇ 0.50 or more with the upper mating surface of the steel plate to be joined as a reference position. +TU ⁇ 0.60 or more is preferable.
- the highest point of the joint interface is preferably as high as possible.
- the highest point of the joint interface may reach from the periphery of the shoulder portion of the tool to a region where burrs are discharged to the outside.
- the highest point level of the bonding interface is more preferably +TU ⁇ 0.98 or less.
- the joint interface usually has a shape curved upward in the vertical direction (a shape convex upward in the vertical direction) in a vertical cross section.
- the level of the deepest point of the recess and the level of the highest point of the joint interface can be measured with a vernier caliper or the like using a photographed image of a vertical cross section of the friction stir point welded joint used to specify the joint interface.
- the inventors found that when a steel plate having a soft surface layer is used as the material to be joined, the soft surface layer causes a decrease in hardness at the joint interface, and this causes a decrease in hardness when performing a cross tension test. It was found that fracture occurs along the soft portion located at the boundary between the first member and the second member. Based on this finding, the inventors conducted further studies, and found that the annular groove was formed on the upper surface of the joint, satisfying the above requirements (a) and (b), and at the same time, the joint was formed. It was found that by reducing the difference in hardness at a predetermined level, that is, the difference in hardness between the bonding interface and the second flow portion at the installation level of the upper plate, breakage along the above-described soft portion can be prevented.
- the difference in hardness at a predetermined level of the joint is 80 HV or less, breakage along the soft portion described above is effectively prevented, and the cross tensile strength is improved.
- the difference in hardness at the predetermined level of the joint exceeds 80 HV, it is not possible to sufficiently prevent breakage along the soft portion described above, resulting in a decrease in cross tensile strength. Therefore, the hardness difference at the predetermined level of the joint is set to 80 HV or less.
- the hardness difference at a given level of the joint is preferably 70HV or less, more preferably 60HV or less.
- the lower limit of the hardness difference at the predetermined level of the joint is not particularly limited, and may be zero.
- the hardness difference at a predetermined level of the joint is basically measured at the vertical position: +TU x 0.60. However, if the level of the highest point of the bond interface is less than +TU x 0.60, the hardness difference at the predetermined level of the bond is measured at the vertical position: +TU x 0.50.
- +TU ⁇ 0.60 is the position at which a strong bond can be sufficiently obtained at the bonding interface. Therefore, when the soft portion is not formed in the vicinity of the joint interface, breakage along the joint interface does not occur at that position. On the other hand, when a soft portion is formed in the vicinity of the joint interface, the soft tissue breaks along the joint interface at that position.
- +TU ⁇ 0.60 is the position where the difference in hardness between the position of the bonding interface and the position +350 ⁇ m of the bonding interface greatly affects the fracture path. Therefore, +TU ⁇ 0.60 is a suitable position for measuring the hardness difference (in other words, confirming whether or not a soft layer is formed in the vicinity of the bonding interface).
- the vertical position: +TU ⁇ 0.50 is also a suitable position for measuring the hardness difference for the same reason. Since it may be affected by segregation occurring in the central portion, it is preferable to measure at +TU ⁇ 0.60 if possible.
- hardness measurement at each position is performed in accordance with JIS Z 2244. Specifically, it is performed as follows. That is, the vertical cross section of the friction stir spot welded joint shown in FIG. to measure the Vickers hardness (HV).
- annular groove An annular groove is formed in the upper surface of the joint, as shown in FIG. Also, the annular groove is arranged so as to surround the recess on the upper surface of the joint. That is, the annular groove is formed by the contact between the shoulder of the tool and the upper plate during joining. The formation of the annular groove strengthens the bonding interface. As a result, high joint strength can be obtained even when a steel plate having a surface soft layer is used as the material to be joined.
- the presence or absence of the annular groove can be confirmed by visually observing the appearance of the upper surface of the friction stir spot welded joint and by observing the vertical cross section of the friction stir spot welded joint.
- At least one of the steel plates to be joined has a surface soft layer.
- the number of steel sheets having a soft surface layer is not particularly limited, and all of the steel sheets to be joined may have a soft surface layer.
- the soft surface layer is a region where the ferrite fraction is at least twice the ferrite fraction at the 1 ⁇ 3 position of the plate thickness.
- a surface soft layer having a thickness of 1 ⁇ m or more exists on at least one surface of the steel sheet, it is determined that the steel sheet has a surface soft layer. That is, "having a surface soft layer” means that at least one surface of the steel sheet has a region where the ferrite fraction is twice or more the ferrite fraction at the 1/3 position of the sheet thickness, and It means that the thickness of the region is 1 ⁇ m or more.
- the thickness of the surface soft layer is measured, for example, as follows. That is, a test piece is cut out from a steel plate so that an arbitrary cross section perpendicular to the surface of the steel plate serves as an observation surface. Then, the observation surface was polished, and 3 vol. Etch with % nital to expose the tissue. Next, the microstructure at various thickness positions from the top surface to the bottom surface of the steel sheet was photographed with a SEM (Scanning Electron Microscope) at a magnification of 2000 with a pitch (interval in the thickness direction) of 100 ⁇ m. do. From the obtained tissue images at various thickness positions, the area of ferrite at each thickness position is calculated using Adobe Photoshop of Adobe Systems.
- the area of ferrite at each thickness position is divided by the area of each viewing area, and these values are taken as the ferrite fraction at each thickness position.
- ferrite is a phase observed black on a relatively smooth surface.
- the deepest position hereinafter also referred to as the deepest position
- the thickness of the surface soft layer on each side (upper surface and lower surface) of the steel plate (distance from the upper surface to the deepest position (on the upper surface side) and from the lower surface to the deepest position (on the lower surface side) distance).
- the microstructure at various thickness positions near the upper surface and near the lower surface of the steel plate is examined by SEM at a magnification of 10000 times and pitch (interval in the thickness direction).
- SEM scan-electron emission computed tomography
- the starting point of the 1/3 plate thickness position may be any surface of the upper surface and the lower surface.
- the ferrite fraction at the 1 ⁇ 3 position of the plate thickness differs depending on whether the upper surface is the starting point or the lower surface is the starting point, it is preferable to adopt the value with the larger ferrite fraction.
- the average carbon concentration of the surface soft layer is preferably 80% or less of the carbon concentration of the chemical composition of the steel sheet having the surface soft layer.
- the average carbon concentration of the surface soft layer is measured by, for example, FE-EPMA. Specifically, a test piece is cut out from a steel plate so that an arbitrary cross section perpendicular to the surface of the steel plate serves as an observation surface. Then, using FE-EPMA, the carbon concentration at various depth positions of the test piece is measured to obtain the carbon concentration distribution in the depth direction of the steel sheet. Then, the average value of the carbon concentration at the depth position corresponding to the surface soft layer is obtained, and this value is taken as the average carbon concentration of the surface soft layer.
- the number of steel plates to be joined should be two or more. Although the upper limit of the number of steel plates to be joined is not particularly limited, the number of steel plates to be joined is preferably 5 or less. Steel plates of the same steel grade may be used for the steel plates to be joined materials, or steel plates of different steel grades may be used.
- the thickness of the steel plate to be joined is preferably 0.4 to 3.2 mm.
- Steel plates having the same thickness may be used as the steel plates to be joined, or steel plates having different thicknesses may be used.
- the chemical composition of the steel plate to be joined is, for example, in mass %, C: 0.05-0.6%, Si: 0.2-2.5%, Mn: 1.0-4.0%, P: 0.10% or less, S: 0.050% or less, Al : 0.01 to 0.80%, and N: 0.010% or less, optionally, Nb: 0.050% or less, Ti: 0.050% or less, B: 0.0050% or less, V: 0.05% or less, Cr: 0.50% or less, Mo: 0.50% or less, Co: One or more selected from 0.50% or less, Cu: 0.50% or less, Ni: 0.50% or less, Sb: 0.020% or less, and Ca and REM: 0.010% or less in total and the balance being Fe and unavoidable impurities.
- the tensile strength of the steel plate to be joined is preferably 980 MPa or more, more preferably 1470 MPa or more. Tensile strength is measured according to JIS Z 2241 (1998).
- the steel plate to be joined may have a plating layer on its surface.
- the plating layer may be provided on both sides of the steel sheet or may be provided on one side of the steel sheet.
- Examples of the plated layer include zinc-based plated layers.
- the zinc-based plating layer is a plating layer containing zinc as a main component (a plating layer having a zinc content of 50% by mass or more). A plating layer etc. are mentioned.
- the above steel plate can be manufactured according to a conventional method.
- Friction stir spot welding method and friction stir spot welding joint manufacturing method A manufacturing method will be described.
- a friction stir spot welding method comprises: A friction stir point in which a tool having a shoulder portion and a pin portion protruding from the shoulder portion is rotated, and the pin portion is press-fitted into two or more superimposed steel plates to join the steel plates.
- a joining method comprising: At least one of the steel plates that are the materials to be joined has a surface soft layer, The vertical position of the maximum press-fit depth of the tool satisfies at least one of ⁇ 0.5 mm or less and ⁇ TL ⁇ 0.50 or less with the lower mating surface of the steel plate as a reference position, and , a state in which the shoulder and the upper plate are in contact when the tool reaches the maximum press-fit depth; The maximum temperature reached is 850 ° C.
- a n+1 is the tool press-fitting amount (mm) from the time when the n-th joining condition is switched to the time when the tool reaches the maximum press-fitting depth.
- the upper plate and the lower plate are respectively the steel plate positioned at the top and the steel plate positioned at the bottom among the two or more steel plates that are superimposed
- TL is the plate thickness (mm) of the steel plate of the lower plate
- the lower mating surface is the mating surface between the lower plate and the steel plate adjacent to the lower plate.
- the vertical position is + if it is above the reference position, and - if it is below the reference position.
- a friction stir spot welding method is a method for obtaining (manufacturing) the friction stir spot welding joint according to one embodiment of the present invention described above.
- a method for manufacturing a friction stir spot welded joint according to one embodiment of the present invention is to join two or more superimposed steel plates by the friction stir spot welding method according to one embodiment of the present invention. be.
- a method for manufacturing a friction stir spot welded joint according to one embodiment of the present invention is a method for manufacturing the friction stir spot welded joint according to one embodiment of the present invention described above.
- Two or more superimposed steel plates, which are the materials to be joined, are joined with a tool having a shoulder portion and a pin portion protruding from the shoulder portion. Specifically, while rotating the tool, the pin portion of the tool is press-fitted into the workpiece to join the steel plates.
- the tool is not particularly limited, and general tools can be used.
- the shape of the shoulder portion and the pin portion for example, the diameter of the shoulder portion (hereinafter, also referred to as the shoulder diameter), the diameter of the pin portion (hereinafter, also referred to as the pin diameter), the length of the pin portion (hereinafter, also referred to as the pin length) ), and the angle of inclination of the side surface of the pin is also not particularly limited, and may be determined according to the steel type and thickness of the steel plate to be joined.
- the shoulder diameter is 6.0 to 16.0 mm
- the diameter of the pin is 3.0 to 8.0 mm
- the length of the pin is 2.0 to 3.5 mm
- the inclination angle of the side surface of the pin is 3 to 30°.
- a backing is provided on the lower surface of the material to be welded (the surface on the opposite side to which the pin part of the tool is press-fitted).
- a steel plate having a surface soft layer is used for at least one of the steel plates that are the materials to be joined.
- the definition of the surface soft layer and the method for measuring the thickness are as described above.
- the steel plate to be joined has a soft surface layer before joining, it can be generally determined that the steel plate has a soft surface layer after joining.
- the description of the steel plate, which is the material to be joined is also as described above.
- (d) Vertical position of the maximum press-fit depth of the tool About the vertical position of the maximum press-fit depth of the tool, with the lower mating surface of the steel plate as the reference position, -0.5 mm or less and -TL x 0.50 At least one of the following conditions is satisfied, and when the tool reaches the maximum press-fitting depth, the shoulder and the upper plate of the workpiece are brought into contact (the workpiece is pressed by the shoulder). Appropriate control of the vertical position of the press-fit depth of the tool facilitates material flow, making it possible to position the highest point of the joint interface at a higher position. Further, by bringing the shoulder into contact with the top plate of the material to be joined, the superimposed steel plates are brought into closer contact with each other and the joint interface is strengthened.
- the vertical position of the press-fitting depth of the tool is preferably -TL ⁇ 0.90 or more.
- the maximum reaching temperature of the joint during joining shall be 850°C or less.
- the hardness difference at the predetermined level of the joint can be 80 HV or less.
- the highest temperature reached is preferably 830° C. or lower, more preferably 810° C. or lower.
- the highest temperature is preferably 650° C. or higher.
- the maximum reaching temperature is measured as follows, for example. That is, a thermocouple is installed inside the tool, specifically near the tip of the pin portion of the tool that contacts the joint. Then, a thermocouple inside the tool continuously measures the temperature during bonding (the temperature that rises at the bonding portion). Then, the measured maximum temperature during bonding is taken as the maximum reached temperature.
- n is the number of switching times of bonding conditions
- R k+1 is the tool rotation speed (rpm) after the k-th switching of the welding conditions
- a k+1 is the tool press-fit amount (mm) from the k-th time of switching the bonding conditions to the k+1-th time of switching the bonding conditions
- P k+1 is the applied pressure (N) after the k-th switching of the bonding conditions is.
- R 1 is the initial tool rotation speed (rpm)
- a 1 is the tool press-in amount (mm) under the initial welding conditions (in other words, the tool press-in amount from the start of welding to the first switching of the welding conditions ( mm))
- P1 is the initial pressure (N).
- a n+1 is the tool press-fitting amount (mm) from the time when the n-th joining condition is switched to the time when the tool reaches the maximum press-fitting depth. At least one of the tool rotational speed and the applied pressure is used as the welding condition for switching.
- E is preferably 40 or less.
- E is preferably 10 or more.
- n (the number of switching times of bonding conditions) may be an integer of 0 or more. That is, the switching of the joining conditions (tool rotation speed and pressure) is optional and may or may not be performed.
- A1 which is the tool press-in amount under the initial welding conditions, is the tool press-in amount (mm) from the start of welding until the tool reaches the maximum press-in depth.
- n is preferably 5 times or less.
- the initial welding conditions that is, the initial tool rotational speed and the initial pressure, which are the welding conditions before the first switching of the welding conditions, set the maximum temperature to 850 ° C. or less, and the relationship of the above formula (1) is not particularly limited, and may be determined according to the steel type and thickness of the steel plate to be joined. For example, when using two steel plates having a surface soft layer, a tensile strength of 980 MPa or more, and a plate thickness of 1.6 mm as the materials to be joined, the initial tool rotation speed (R 1 ) is 200 to 2000 rpm is preferred. Also, the initial pressure (P 1 ) is preferably 10 to 60 kN.
- the tool rotation speed after switching is lower than the initial tool rotation speed, and the pressure after switching is higher than the initial pressure.
- the tool rotation speed (R 2 ) after switching is preferably 40 to 400 rpm.
- the applied pressure (P 2 ) after switching is preferably 20 to 70 kN.
- the timing for switching the tool rotation speed and the applied pressure is determined, for example, by using two steel plates having a surface soft layer, a tensile strength of 980 MPa or more, and a plate thickness of 1.6 mm as the materials to be welded.
- the timing can be set when the tool (pin portion) press-fit depth (A 1 ) from the upper surface of the upper plate reaches 0.8 to 2.4 mm. preferable.
- the bonding time is 3 to 60 seconds.
- the maximum temperature may be adjusted using an external heat source.
- conditions other than the above are not particularly limited, and conventional methods may be followed.
- a steel having the chemical composition shown in Table 1 (the balance being Fe and unavoidable impurities) was melted and continuously cast into a slab. Then, the slab was hot rolled to obtain a hot rolled steel sheet. Then, the hot-rolled steel sheet was pickled. Then, the hot-rolled steel sheet was cold-rolled and annealed to obtain a cold-rolled steel sheet (thickness: 1.2 to 1.6 mm). Next, a JIS No. 5 tensile test piece was taken from the obtained steel sheet so that the direction perpendicular to the rolling was the longitudinal direction (tensile direction). Then, using the sampled test piece, a tensile test was performed according to JIS Z 2241 (1998) to measure the tensile strength (TS). In addition, the presence or absence of the surface soft layer was confirmed and the average carbon concentration of the surface soft layer was measured by the method described above. The results are also shown in Table 1.
- a test piece of 50 mm ⁇ 150 mm was cut out from the obtained steel plate, and the combinations shown in Table 2 were overlapped in a cross shape.
- the upper plate and the middle plate were superimposed crosswise, and the middle plate and the lower plate were superimposed in parallel (that is, in the measurement of the cross tensile strength described later, the upper plate-middle plate The cross tensile strength was measured between.).
- friction stir spot welding was applied to the center of the cross-lapped portion of the test piece under the conditions shown in Table 2 to obtain a friction stir spot welded joint.
- the shape of the tool was a shoulder diameter of 10 mm, a pin diameter of 4.8 mm, an inclination angle of the pin side surface of 10°, and a pin length of 1.8 mm to 4.6 mm depending on the joining conditions. Further, in sample numbers 1 to 5, 9 to 14 and 16 to 21, the tool rotation speed and the pressure were switched once during joining. In sample number 6, only the applied pressure was switched once during bonding.
- the timing for switching the tool rotation speed and pressure is based on the tool press-in depth from the upper surface of the upper plate ("Tool press-in depth at switching" in Table 2 is from the upper surface of the upper plate. is the tool insertion depth of ).
- FIG. 2 shows a schematic diagram of a vertical cross section of a friction stir spot welded joint of sample number 13 (a friction stir spot welded joint without an annular groove).
- the level of the deepest point of the recess, the level of the highest point of the weld interface, the hardness at a predetermined level of the weld, and the hardness of the annular groove were measured by the methods described above.
- Table 3 shows the results.
- the hardness at a predetermined level of the joints shown in Table 3 is No. Measured at vertical position: +TU ⁇ 0.60 for Nos. 1-9 and 13-21; For 10 and 12, the values measured at the vertical position: +TU ⁇ 0.50 are described. In addition, No. For all of 1 to 4, 9 to 10 and 12 to 21, the hardness difference measured at vertical position: +TU ⁇ 0.50 or vertical position: +TU ⁇ 0.60 was 80 HV or less.
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Abstract
Description
「金属材料からなる第1部材および第2部材をその境界部に軟質部を位置させた状態で重ね合わせ、回転工具のピン部を回転させながら前記第1部材から前記第2部材まで圧入し、前記第1部材および前記第2部材を攪拌することによって点接合する摩擦攪拌点接合方法であって、
前記第1および第2部材のうちの少なくとも一方が、800℃かつ歪み速度10-3s-1での引張強度が100MPa以上の金属材料からなり、
前記軟質部が、室温において前記引張強度が100MPa以上の前記金属材料の母材硬度よりも低い硬度を有するものであり、
前記軟質部は、少なくとも前記引張強度が100MPa以上の前記金属材料の表層部に形成される軟質層であり、
前記引張強度が100MPa以上の前記金属材料は、質量%でC含有量が0.3%以上の炭素鋼であり、前記軟質層は、質量%でC含有量が0.1%以下の脱炭層である、摩擦攪拌点接合方法。」
が開示されている。
また、本発明は、上記の摩擦攪拌点接合継手を得るための摩擦攪拌点接合方法を提供することを目的とする。
・接合部の上面に環状溝部を形成するとともに、
・接合部の形状と硬度とを同時に適切に制御する、具体的には、以下の(a)~(c)を同時に満足させる、
ことによって、被接合材として表層軟質層を有する鋼板を使用する場合にも、高い継手強度を得られる、との知見を得た。
(a)接合部の凹部の最深点の鉛直方向位置について、被接合材となる鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足させる。
(b)接合界面の最高点の鉛直方向位置を、被接合材となる鋼板の上側合せ面を基準位置として、+TU×0.50以上とする。
(c)鉛直方向位置:+TU×0.50または+TU×0.60において、水平方向位置で接合界面の位置の硬度と、接合界面の位置+350μmの位置の硬度との差を、80HV以下とする。
(d)ツールの圧入最大深さの鉛直方向位置について、鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足させつつ、ツールが圧入最大深さに到達した際にショルダーと被接合材の上板とが接触する(ショルダーにより被接合材が押圧されている)状態とする。
(e)最高到達温度を850℃以下とする。
(f)接合条件を適正に制御する、具体的には、ツール回転速度、ツール圧入量および加圧力について、次式(1)の関係を満足させる。
nは、接合条件の切り替え回数、
Rk+1は、k回目の接合条件の切り替え後のツール回転速度(rpm)、
Ak+1は、k回目の接合条件の切り替え時点からk+1回目の接合条件の切り替え時点までのツール圧入量(mm)、
Pk+1は、k回目の接合条件の切り替え後の加圧力(N)
である。
ただし、R1は初期ツール回転速度(rpm)、A1は初期接合条件でのツール圧入量(mm)、P1は初期加圧力(N)とする。また、An+1は、n回目の接合条件の切り替え時点からツールの圧入最大深さ到達時点までのツール圧入量(mm)とする。
本発明は、上記の知見に基づき、さらに検討を加えて完成されたものである。
1.重ね合わせた2枚以上の鋼板と、該鋼板の接合部と、該接合部の上面の環状溝部と、を有する、摩擦攪拌点接合継手であって、
前記鋼板のうちの少なくとも1枚が表層軟質層を有し、
前記接合部は、凹部と、該凹部に隣接する第1の流動部と、該第1の流動部に隣接する第2の流動部と、該第1の流動部と該第2の流動部の境界である接合界面と、を有し、
前記凹部の最深点の鉛直方向位置が、前記鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足し、
前記接合界面の最高点の鉛直方向位置が、前記鋼板の上側合せ面を基準位置として、+TU×0.50以上であり、
鉛直方向位置:+TU×0.50または+TU×0.60において、水平方向位置で前記接合界面の位置の硬度と、前記接合界面の位置+350μmの位置の硬度との差が、80HV以下である、摩擦攪拌点接合継手。
ここで、上板および下板はそれぞれ、重ね合わせた2枚以上の鋼板のうち、最上部に位置する鋼板および最下部に位置する鋼板であり、
TUは、上板の鋼板の板厚(mm)、
TLは、下板の鋼板の板厚(mm)、
上側合せ面は、上板と、該上板に隣接する鋼板との合せ面、
下側合せ面は、下板と、該下板に隣接する鋼板との合せ面
である。
また、鉛直方向位置は、基準位置よりも上側の場合を+、下側の場合を-とする。水平方向位置は、基準位置からの距離とする。
前記被接合材である鋼板のうちの少なくとも1枚が表層軟質層を有し、
前記ツールの圧入最大深さの鉛直方向位置が、前記鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足し、かつ、前記ツールが圧入最大深さに到達した際に前記ショルダーと上板とが接触する状態であり、
最高到達温度が850℃以下であり、
次式(1)の関係を満足する、摩擦攪拌点接合方法。
nは、接合条件の切り替え回数、
Rk+1は、k回目の接合条件の切り替え後のツール回転速度(rpm)、
Ak+1は、k回目の接合条件の切り替え時点からk+1回目の接合条件の切り替え時点までのツール圧入量(mm)、
Pk+1は、k回目の接合条件の切り替え後の加圧力(N)
である。
ただし、R1は初期ツール回転速度(rpm)、A1は初期接合条件でのツール圧入量(mm)、P1は初期加圧力(N)とする。また、An+1は、n回目の接合条件の切り替え時点からツールの圧入最大深さ到達時点までのツール圧入量(mm)とする。
また、上板および下板はそれぞれ、重ね合わせた2枚以上の鋼板のうち、最上部に位置する鋼板および最下部に位置する鋼板であり、
TLは、下板の鋼板の板厚(mm)、
下側合せ面は、下板と、該下板に隣接する鋼板との合せ面
である。
さらに、鉛直方向位置は、基準位置よりも上側の場合を+、下側の場合を-とする。
[1]摩擦攪拌点接合継手
まず、本発明の一実施形態に従う摩擦攪拌点接合継手について、図1を用いて説明する。なお、図1では、被接合材となる鋼板が2枚の場合を例としている。ここで、図1は、接合部の凹部の中心位置を通る、摩擦攪拌点接合継手の鉛直断面(以下、単に鉛直断面ともいう)であり、各部の位置などは、いずれも当該鉛直断面でのものである。
接合部は、図1に示すように、凹部2-1と、該凹部に隣接する第1の流動部2-2と、該第1の流動部に隣接する第2の流動部2-3と、該第1の流動部と該第2の流動部の境界である接合界面2-4と、を有する。
すなわち、接合部の凹部の中心位置を通る、摩擦攪拌点接合継手の鉛直断面を研磨し、ピクリン酸飽和水溶液でエッチングする。ついで、当該鉛直断面を光学顕微鏡で観察し、母材組織と流動部におけるエッチングの度合いなどから、第1の流動部および第2の流動部を画定する。そして、確定した第1の流動部と第2の流動部の境界を接合界面とする。
ここで、上板および下板はそれぞれ、重ね合わせた2枚以上の鋼板のうち、最上部に位置する鋼板および最下部に位置する鋼板であり、
TUは、上板の鋼板の板厚(mm)、
TLは、下板の鋼板の板厚(mm)、
上側合せ面は、上板と、該上板に隣接する鋼板との合せ面、
下側合せ面は、下板と、該下板に隣接する鋼板との合せ面
である。
また、鉛直方向位置は、基準位置よりも上側の場合を+、下側の場合を-とする。水平方向位置は、基準位置からの距離(基準位置を0とし、-にはならない(負の値はとらない)もの)とする。
凹部の最深点のレベルについて、被接合材となる鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足させる。これにより、接合界面が強化され、被接合材として表層軟質層を有する鋼板を使用する場合にも、高い十字引張強さが得られる。なお、特に限定されるものではないが、凹部の最深点のレベルは-TL×0.90以上とすることが好ましい。
接合界面の最高点のレベルは、被接合材となる鋼板の上側合せ面を基準位置として、+TU×0.50以上とする。好ましくは+TU×0.60以上とする。これにより、接合界面が強化され、被接合材として表層軟質層を有する鋼板を使用する場合にも、高い十字引張強さが得られる。なお、接合界面の最高点のレベルは高いほど好ましく、例えば、ツールのショルダー部の周囲からバリとして外部に排出される領域まで接合界面の最高点が到達していてもよい。接合界面の最高点のレベルは、より好ましくは+TU×0.98以下である。
発明者らは、上掲特許文献1の技術により得られる擦攪拌点接合継手を用いて十字引張試験を行う場合に、第1部材と第2部材の境界部に位置する軟質部に沿って破断が生じ、十分な十字引張強さが得られないという問題が生じる原因について調査した。その結果、発明者らは、被接合材として表層軟質層を有する鋼板を使用すると、表層軟質層の影響により接合界面において硬度低下が生じ、これが原因となって、十字引張試験を行う場合に、第1部材と第2部材の境界部に位置する軟質部に沿って破断が生じることを知見した。そして、発明者らは、この知見を基にさらに検討を重ねたところ、接合部の上面に環状溝部を形成するとともに、上記(a)および(b)の要件を満足させ、同時に、接合部の所定レベルでの硬度差、つまり、上板の設置レベルでの接合界面と第2の流動部の硬度差を低減することにより、上記した軟質部に沿った破断が防止されることを知見した。
すなわち、健全な摩擦攪拌点継手の場合、+TU×0.60は接合界面に強固な接合が十分に得られる位置である。そのため、接合界面近傍に軟質部が形成されない場合には、当該位置において接合界面に沿った破断が生じない。一方、接合界面近傍に軟質部が形成される場合には、当該位置において接合界面に沿って軟質な組織が破断する。つまり、+TU×0.60は、接合界面の位置の硬度と、接合界面の位置+350μmの位置の硬度との差が、破断経路に大きく影響を与える位置である。そのため、+TU×0.60は、硬度差の測定(換言すれば、接合界面近傍における軟質層の形成有無の確認)に適した位置である。また、鉛直方向位置:+TU×0.50も、同様の理由で硬度差の測定に適した位置である、ただし、鉛直方向位置:+TU×0.50では、硬度の測定値が鋼板の板厚中央部に生じる偏析の影響を受ける可能性があるため、可能な場合には+TU×0.60で測定することが好ましい。
すなわち、図1に示す摩擦攪拌点接合継手の鉛直断面(接合部の凹部の中心位置を通る、摩擦攪拌点接合継手の鉛直断面)を測定面とし、各位置において試験力:2.942Nの条件でビッカース硬さ(HV)を測定する。
環状溝部は、図1に示すように、接合部の上面に形成される。また、環状溝部は、接合部の上面において、凹部を取り囲むように配置される。すなわち、環状溝部は、接合時に、ツールのショルダー部と上板とが接触することにより形成される。環状溝部が形成されることにより、接合界面が強化される。これにより、被接合材として表層軟質層を有する鋼板を使用する場合にも、高い継手強度が得られる。
被接合材となる鋼板のうち、少なくとも1枚が表層軟質層を有する。なお、表層軟質層を有する鋼板の枚数は特に限定されず、被接合材となる鋼板がいずれも表層軟質層を有していてもよい。
すなわち、「表層軟質層を有する」とは、鋼板の少なくとも一方の面において、フェライト分率が、板厚1/3位置のフェライト分率の2倍以上となる領域が存在しており、かつ、その領域の厚さが1μm以上であることを意味する。
すなわち、鋼板から、鋼板表面と垂直な任意の断面が観察面となるように、試験片を切り出す。ついで、観察面を研磨し、3vol.%ナイタールでエッチングし、組織を現出させる。ついで、鋼板の上面から下面までの種々の厚さ位置におけるミクロ組織を、ピッチ(厚さ方向の間隔):100μmピッチとして、SEM(Scanning Electron Microscope;走査電子顕微鏡)により、倍率:2000倍で撮影する。得られた種々の厚さ位置における組織画像から、Adobe Systems社のAdobe Photoshopを用いて、各厚さ位置におけるフェライトの面積を算出する。ついで、各厚さ位置におけるフェライトの面積をそれぞれの視野領域の面積で除し、それらの値を、各厚さ位置におけるフェライト分率とする。ここで、比較的平滑な面で黒く観察される相をフェライトとする。ついで、フェライト分率が、板厚1/3位置のフェライト分率の2倍以上になる厚さ位置の最深位置(以下、最深位置ともいう)を鋼板の両面(上面および下面)それぞれで特定し、これらの厚さ位置から、鋼板の両面(上面および下面)それぞれにおける表層軟質層の厚さ(上面から(上面側の)最深位置までの距離、および、下面から(下面側の)最深位置までの距離)を特定する。また、表層軟質層の厚さが10μm以下の場合には、鋼板の上面近傍および下面近傍の種々の厚さ位置におけるミクロ組織を、SEMにより、倍率:10000倍、ピッチ(厚さ方向の間隔):5μmとして1~3枚撮影し、同様にAdobe Systems社のAdobe Photoshopを用いて、各厚さ位置におけるフェライトの面積およびフェライト分率を算出する。これにより、表層軟質層の厚さを特定する。なお、板厚1/3位置の起点(板厚0位置)は、上面および下面の任意の面とすればよい。ただし、上面を起点とする場合と、下面を起点とする場合とで、板厚1/3位置のフェライト分率が異なる際には、フェライト分率が大きい方の値を採用することが好ましい。
具体的には、鋼板から、鋼板表面と垂直な任意の断面が観察面となるように試験片を切り出す。ついで、FE-EPMAを用いて、試験片の種々の深さ位置における炭素濃度を測定し、鋼板の深さ方向における炭素濃度分布を求める。そして、表層軟質層に当たる深さ位置での炭素濃度の平均値を求め、その値を、表層軟質層の平均炭素濃度とする。
C:0.05~0.6%、Si:0.2~2.5%、Mn:1.0~4.0%、P:0.10%以下、S:0.050%以下、Al:0.01~0.80%、および、N:0.010%以下
であり、
任意に、
Nb:0.050%以下、Ti:0.050%以下、B:0.0050%以下、V:0.05%以下、Cr:0.50%以下、Mo:0.50%以下、Co:0.50%以下、Cu:0.50%以下、Ni:0.50%以下、Sb:0.020%以下、ならびに、CaおよびREM:合計で0.010%以下
から選択される1種以上を有し、残部がFeおよび不可避的不純物である成分組成を例示できる。
つぎに、本発明の一実施形態に従う摩擦攪拌点接合方法、および、本発明の一実施形態に従う摩擦攪拌点接合継手の製造方法について、説明する。
ショルダー部と該ショルダー部から突出するピン部とを有するツールを回転させながら、該ピン部を被接合材である重ね合わせた2枚以上の鋼板に圧入し、該鋼板を接合する、摩擦攪拌点接合方法であって、
前記被接合材である鋼板のうちの少なくとも1枚が表層軟質層を有し、
前記ツールの圧入最大深さの鉛直方向位置が、前記鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足し、かつ、前記ツールが圧入最大深さに到達した際に前記ショルダーと上板とが接触する状態であり、
最高到達温度が850℃以下であり、
次式(1)の関係を満足する、というものである。
nは、接合条件の切り替え回数、
Rk+1は、k回目の接合条件の切り替え後のツール回転速度(rpm)、
Ak+1は、k回目の接合条件の切り替え時点からk+1回目の接合条件の切り替え時点までのツール圧入量(mm)、
Pk+1は、k回目の接合条件の切り替え後の加圧力(N)
である。
ただし、R1は初期ツール回転速度(rpm)、A1は初期接合条件でのツール圧入量(mm)、P1は初期加圧力(N)とする。また、An+1は、n回目の接合条件の切り替え時点からツールの圧入最大深さ到達時点までのツール圧入量(mm)とする。
また、上板および下板はそれぞれ、重ね合わせた2枚以上の鋼板のうち、最上部に位置する鋼板および最下部に位置する鋼板であり、
TLは、下板の鋼板の板厚(mm)、
下側合せ面は、下板と、該下板に隣接する鋼板との合せ面
である。
さらに、鉛直方向位置は、基準位置よりも上側の場合を+、下側の場合を-とする。
加えて、本発明の一実施形態に従う摩擦攪拌点接合方法は、上記の本発明の一実施形態に従う摩擦攪拌点接合継手を得る(製造する)ための方法である。
加えて、本発明の一実施形態に従う摩擦攪拌点接合継手の製造方法は、上記の本発明の一実施形態に従う摩擦攪拌点接合継手を製造するための方法である。
ツールの圧入最大深さの鉛直方向位置について、鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足させつつ、ツールが圧入最大深さに到達した際にショルダーと被接合材の上板とが接触する(ショルダーにより被接合材が押圧されている)状態とする。ツールの圧入深さの鉛直方向位置を適切に制御することにより、材料流動を促進して、接合界面の最高点を、より高い位置とすることが可能となる。また、ショルダーと被接合材の上板とを接触させることにより、重ね合わせた鋼板同士がより密着し、接合界面が強化される。なお、特に限定されるものではないが、ツールの圧入深さの鉛直方向位置は、-TL×0.90以上とすることが好ましい。
接合中の接合部の最高到達温度を850℃以下とする。これにより、接合部の所定レベルでの硬度差を80HV以下とすることが可能となる。最高到達温度は、好ましくは830℃以下、より好ましくは810℃以下である。また、最高到達温度は、好ましくは650℃以上である。
すなわち、ツールの内部、具体的には、接合部と接触するツールのピン部先端近傍に、熱電対を設置する。そして、ツール内部の熱電対により、接合中の温度(接合部で上昇した温度)を連続的に計測する。そして、計測した接合中の最高温度を、最高到達温度とする。
接合条件を適正に制御する、具体的には、ツール回転速度、ツール圧入量および加圧力について、次式(1)の関係を満足させることが重要である。なお、式(1)の左辺を、以下、Eともいう。
nは、接合条件の切り替え回数、
Rk+1は、k回目の接合条件の切り替え後のツール回転速度(rpm)、
Ak+1は、k回目の接合条件の切り替え時点からk+1回目の接合条件の切り替え時点までのツール圧入量(mm)、
Pk+1は、k回目の接合条件の切り替え後の加圧力(N)
である。
ただし、R1は初期ツール回転速度(rpm)、A1は初期接合条件でのツール圧入量(mm)(換言すれば、接合開始時点から1回目の接合条件の切り替え時点までのツール圧入量(mm))、P1は初期加圧力(N)とする。また、An+1は、n回目の接合条件の切り替え時点からツールの圧入最大深さ到達時点までのツール圧入量(mm)とする。
なお、切り替えを行う接合条件は、ツール回転速度および加圧力のうちの少なくとも一方とする。
例えば、被接合材として、表層軟質層を有し、引張強さが980MPa以上で、板厚が1.6mmの鋼板を2枚使用し、n(接合条件の切り替え回数)を1回とする場合、切り替え後のツール回転速度(R2)は40~400rpmとすることが好ましい。また、切り替え後の加圧力(P2)は、20~70kNとすることが好ましい。
なお、ツールの形状は、ショルダー径:10mm、ピン径:4.8mm、ピン側面の傾斜角:10°とし、ピン長は接合条件に応じて1.8mm~4.6mmとした。また、試料番号1~5、9~14および16~21では、接合中、ツール回転速度および加圧力の切り替えを同時に1回行った。試料番号6では、接合中、加圧力のみ切り替えを1回行った。ここで、ツール回転速度および加圧力を切り替えるタイミングは、上板の上面からのツール圧入深さを基準とした(表2に記載の「切替時のツール圧入深さ」は、上板の上面からのツール圧入深さである。)。
また、ツールが圧入最大深さに到達した際に、目視により、ショルダーの外周部と上板の接触状態を確認したところ、試料番号13では、ショルダーの外周部と上板とが接触していなかった。一方、試料番号13以外のものはいずれも、ツールが圧入最大深さに到達した際にショルダーの外周部と上板とが接触していた。参考のため、図2に、試料番号13の摩擦攪拌点接合継手(環状溝部を有さない摩擦攪拌点接合継手)の鉛直断面の模式図を示す。
一方、比較例では、十分な継手強度が得られなかった。
2 接合部
3 環状溝部
4 未接合界面
2-1 凹部
2-2 第1の流動部
2-3 第2の流動部
2-4 接合界面
Claims (5)
- 重ね合わせた2枚以上の鋼板と、該鋼板の接合部と、該接合部の上面の環状溝部と、を有する、摩擦攪拌点接合継手であって、
前記鋼板のうちの少なくとも1枚が表層軟質層を有し、
前記接合部は、凹部と、該凹部に隣接する第1の流動部と、該第1の流動部に隣接する第2の流動部と、該第1の流動部と該第2の流動部の境界である接合界面と、を有し、
前記凹部の最深点の鉛直方向位置が、前記鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足し、
前記接合界面の最高点の鉛直方向位置が、前記鋼板の上側合せ面を基準位置として、+TU×0.50以上であり、
鉛直方向位置:+TU×0.50または+TU×0.60において、水平方向位置で前記接合界面の位置の硬度と、前記接合界面の位置+350μmの位置の硬度との差が、80HV以下である、摩擦攪拌点接合継手。
ここで、上板および下板はそれぞれ、重ね合わせた2枚以上の鋼板のうち、最上部に位置する鋼板および最下部に位置する鋼板であり、
TUは、上板の鋼板の板厚(mm)、
TLは、下板の鋼板の板厚(mm)、
上側合せ面は、上板と、該上板に隣接する鋼板との合せ面、
下側合せ面は、下板と、該下板に隣接する鋼板との合せ面
である。
また、鉛直方向位置は、基準位置よりも上側の場合を+、下側の場合を-とする。水平方向位置は、基準位置からの距離とする。 - 前記表層軟質層の平均炭素濃度が、前記表層軟質層を有する鋼板の成分組成の炭素濃度の80%以下である、請求項1に記載の摩擦攪拌点接合継手。
- ショルダー部と該ショルダー部から突出するピン部とを有するツールを回転させながら、該ピン部を被接合材である重ね合わせた2枚以上の鋼板に圧入し、該鋼板を接合する、摩擦攪拌点接合方法であって、
前記被接合材である鋼板のうちの少なくとも1枚が表層軟質層を有し、
前記ツールの圧入最大深さの鉛直方向位置が、前記鋼板の下側合せ面を基準位置として、-0.5mm以下、および、-TL×0.50以下のうちの少なくとも一方を満足し、かつ、前記ツールが圧入最大深さに到達した際に前記ショルダーと上板とが接触する状態であり、
最高到達温度が850℃以下であり、
次式(1)の関係を満足する、摩擦攪拌点接合方法。
nは、接合条件の切り替え回数、
Rk+1は、k回目の接合条件の切り替え後のツール回転速度(rpm)、
Ak+1は、k回目の接合条件の切り替え時点からk+1回目の接合条件の切り替え時点までのツール圧入量(mm)、
Pk+1は、k回目の接合条件の切り替え後の加圧力(N)
である。
ただし、R1は初期ツール回転速度(rpm)、A1は初期接合条件でのツール圧入量(mm)、P1は初期加圧力(N)とする。また、An+1は、n回目の接合条件の切り替え時点からツールの圧入最大深さ到達時点までのツール圧入量(mm)とする。
また、上板および下板はそれぞれ、重ね合わせた2枚以上の鋼板のうち、最上部に位置する鋼板および最下部に位置する鋼板であり、
TLは、下板の鋼板の板厚(mm)、
下側合せ面は、下板と、該下板に隣接する鋼板との合せ面
である。
さらに、鉛直方向位置は、基準位置よりも上側の場合を+、下側の場合を-とする。 - 前記表層軟質層の平均炭素濃度が、前記表層軟質層を有する鋼板の成分組成の炭素濃度の80%以下である、請求項3に記載の摩擦攪拌点接合方法。
- 請求項3または4に記載の摩擦攪拌点接合方法により、重ね合わせた2枚以上の鋼板を接合する、摩擦攪拌点接合継手の製造方法。
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