Friction stir welding method for electromagnetic steel strip, method for manufacturing electromagnetic steel strip, friction stir welding device, and device for manufacturing electromagnetic steel strip

Abstract

Provided is a friction stir welding method for an electromagnetic steel strip, with which it is possible to suppress the occurrence of breakage in a coiled material joint section on a production line due to deterioration in mechanical characteristics and deterioration in shape of the coiled material joint section, with high construction efficiency. Post-cooled double-sided friction stir welding is performed on the basis of conditions that satisfy the relationships of formula (1) and formula (2) at the same time.

Description

Technical Field

[0001] The present invention relates to a friction stir welding method for an electromagnetic steel strip, a method for manufacturing an electromagnetic steel strip, a friction stir welding device, and a device for manufacturing an electromagnetic steel strip. Background Art

[0002] In production lines for steel plates, such as pickling, cold rolling, annealing and plating, in order to improve productivity and yield, the steel strip is usually allowed to pass after the so-called coil joining is implemented. Here, coil joining refers to joining the end (rear end) of the preceding steel strip (hereinafter also referred to as the preceding steel strip) with the end (front end) of the steel strip following the preceding steel strip (hereinafter also referred to as the succeeding steel strip) on the production line. Hereinafter, the joint formed by coil joining is also referred to as a coil joining portion. In addition, the front end is the end on the side of the traveling direction of the steel strip on the production line. In addition, the rear end is the end on the opposite side of the traveling direction of the steel strip on the production line. By performing this coil joining, rolling can be performed over the entire length of the steel strip under a tensioned state. In addition, even at the front and rear ends of the steel strip, the plate thickness and shape can be controlled with high precision.

[0003] Conventionally, flash butt welding and the like have been generally used for coil joining. However, with the advancement of laser welding machines, for example, laser welding for coil joining has become mainstream even in production lines for electromagnetic steel sheets, stainless steel sheets, and high-tensile steel sheets.

[0004] As such a technology, for example, Patent Document 1 discloses:

[0005] "A laser welding method for high Si steel, characterized in that when welding high Si steel, a filler wire containing Ni as a main component or a powder filler containing Ni as a main component is used, and welding is performed in a manner such that the chemical composition of the weld metal satisfies the following formula (1).

[0006] X=[%Ni]-[%Si]×2.5-([%Cr]+[%Mo])×0.4≥0 ·· (1)

[0007] Here, [%Ni], [%Si], [%Cr] and [%Mo] respectively represent the contents (weight %) of Ni, Si, Cr and Mo in the weld metal. "

[0008] Patent Document 2 discloses:

[0009] "A laser welding method, in which a leading plate and a trailing plate are butted together and laser welded using a filler wire, characterized in that a ratio (Gap / DEPO) of a butt gap (Gap) between the leading plate and the trailing plate at the initial stage of welding to an average width (DEPO) of the weld metal is 0.3 to 0.8."

[0010] Patent Document 3 discloses:

[0011] "A welded portion of a thin plate, formed by laser welding a preceding thin plate and a succeeding thin plate made of special steel conveyed on a continuous cold rolling line, characterized in that:

[0012] If the minimum thickness of the above-mentioned base material existing on the lower side of the upper extension protrusion is set to L1, and the minimum thickness of the above-mentioned base material sandwiched by the lower extension protrusion and the above-mentioned upper extension protrusion is set to L2, then at least one of L1 and L2 is greater than zero, the above-mentioned upper extension protrusion is composed of weld metal extending and protruding to the upper surface side of the base material by cold rolling, and the above-mentioned lower extension protrusion is composed of weld metal extending and protruding to the lower surface side of the above-mentioned base material by cold rolling. ".

[0013] Patent Document 1: Japanese Patent Application Laid-Open No. 5-305466

[0014] Patent Document 2: Japanese Patent Application Publication No. 2004-25284

[0015] Patent Document 3: Japanese Patent Application Publication No. 2011-140026

[0016] Patent Document 4: Japanese Patent Publication No. 07-505090

[0017] Patent Document 5: Japanese Patent No. 3261433

[0018] Patent Document 6: Japanese Patent No. 4838385

[0019] Patent Document 7: Japanese Patent No. 4838388

[0020] Patent Document 8: Japanese Patent Application No. 2019-26864

[0021] Patent Document 9: Japanese Patent Application No. 2019-54400

[0022] Patent Document 10: Japanese Patent No. 6332561

[0023] Patent Document 11: Japanese Patent No. 6332562

[0024] Patent Document 12: Japanese Patent No. 6497451

[0025] Patent Document 13: Japanese Patent Application Publication No. 2020-124739

[0026] Non-patent document 1: Cui, L.; Fujii, H.; Tsuji, N.; Nogi, K. Scripta Mater. 2007, 56, p. 637-640.

[0027] However, since laser welding is fusion welding, embrittlement due to segregation of impurities during melting and solidification and embrittlement due to hydrogen intrusion occur. As a result, there are cases where the mechanical properties of the joint (weld portion) are deteriorated. In particular, since the composition of the electromagnetic steel sheet contains a large amount of Si, the deterioration of the mechanical properties of the coil joint is likely to become significant. Therefore, if laser welding is applied to the coil joining of the electromagnetic steel strip as described in Patent Documents 1 to 3, there is a problem of reduced productivity on the production line, such as a continuous cold rolling line, due to the occurrence of breakage at the coil joint, which causes the production line to stop. Summary of the invention

[0028] The present invention has been developed in view of the above-mentioned situation, and its purpose is to provide a friction stir welding method for electromagnetic steel strips, which can extremely effectively suppress the occurrence of breakage of the coil joint on the production line caused by the deterioration of the mechanical properties and shape of the coil joint at a high construction efficiency, and is also advantageous in terms of the durability of the rotating tool.

[0029] Another object of the present invention is to provide a method for producing an electromagnetic steel strip using the above-mentioned friction stir welding method for an electromagnetic steel strip.

[0030] Furthermore, an object of the present invention is to provide a friction stir welding device that can be suitably used in the above-mentioned friction stir welding method of electromagnetic steel strips.

[0031] Another object of the present invention is to provide an apparatus for producing electromagnetic steel sheets including the above-mentioned friction stir welding apparatus.

[0032] First, the inventors investigated and studied the reasons for the deterioration of mechanical properties and shape of the coil joint when laser welding is used for coil joining of electromagnetic steel strips, and obtained the following findings.

[0033] (a) As mentioned above, the composition of the electromagnetic steel sheet contains a large amount of Si, for example, specifically, about 2.0 to 5.0 mass % Si. Si is a ferrite stabilizing element. Therefore, if conventional laser welding is applied to the coil joining of the electromagnetic steel strip, the ferrite grains of the coil joining portion, which is the molten portion, and the ferrite grains of the heat-affected portion, will coarsen. As a result, the mechanical properties, especially the toughness and bending strength, of the coil joining portion are greatly deteriorated, resulting in the occurrence of fractures in the coil joining portion on the production line.

[0034] (b) In addition, in the techniques of the above-mentioned patent documents 1 to 3, a filler (filler) having Ni as a main component, which is an austenite stabilizing element, is used. Therefore, in the coil joint, an austenite phase is mainly obtained. However, in the techniques of the above-mentioned patent documents 1 to 3, it is necessary to eliminate the fluctuation of the butt gap between the preceding steel strip and the succeeding steel strip, to extremely strictly manage the fusion amount of the filler in the molten portion (weld metal) and the fusion amount of the steel plate, and to always properly control the balance of the Ni equivalent and the Cr equivalent in the molten portion (weld metal). That is, if the balance of the Ni equivalent and the Cr equivalent in the molten portion (weld metal) is not properly controlled, a martensite phase as a hard and brittle structure is formed in the coil joint. As a result, the mechanical properties, especially the toughness, of the coil joint are greatly deteriorated. In addition, in the heat-affected zone, the mechanical properties of the coil joint are greatly deteriorated due to the coarsening of the ferrite crystal grains. For these reasons, the fracture of the coil joint on the production line occurs.

[0035] (c) In addition, the above-mentioned change in the gap between the leading steel strip and the trailing steel strip affects the height of the welded portion. For example, when the welded portion has an excessively convex shape due to the height of the welded portion, if a load is applied to the welded portion, stress is concentrated on the weld toe. Therefore, the above-mentioned change in the gap between the leading steel strip and the trailing steel strip also causes the breakage of the coil joint on the production line. In addition, the welded portion can be removed by grinding or the like. However, the increase in such processes leads to a significant reduction in productivity.

[0036] Based on the above-mentioned points, the inventors have further conducted various studies and conceived the application of friction stir welding as coil joining of electromagnetic steel strips.

[0037] Here, friction stir welding refers to solid phase welding using friction heat between rotating tools and the joined parts and plastic flow of the joined parts. That is, friction stirring is performed on the unjoined part (joining predetermined area) of the joined parts by rotating tools. If the unjoined part of the joined parts is heated by friction heat, plastic flow begins. Moreover, the interface between the plastic flow area and the parent material part is greatly elongated. As a result, clean interfaces without oxides are in contact with each other, and the joined parts will not melt to form a joint. Here, the joint is an area that becomes a recrystallized structure due to thermal processing based on friction heat and plastic flow between the rotating tool and the joined parts, and there is also a situation called a stirring part. In addition, in the area adjacent to the joint, there is a region that becomes a structure that is affected by thermal processing based on friction heat and plastic flow, but the temperature and processing are insufficient to reach recrystallization. This area is called a hot working affected area. In addition, there is also an area in the joined parts that is not affected by thermal processing based on friction heat and plastic flow. This area is called a parent material part. Furthermore, technologies related to friction stir welding are disclosed in, for example, Patent Documents 4 to 13 and Non-Patent Document 1, but none of them is a technology applied to coil welding of electromagnetic steel strips.

[0038] Therefore, the inventors further repeated various studies based on the above-mentioned concept and obtained the following findings.

[0039] (d) In order to effectively solve the above-mentioned problems (a) to (c), the following points are important.

[0040] So-called double-sided friction stir welding is applied as the joining method.

[0041] On this basis, the diameter D (mm) of the shoulder of the rotary tool is set to satisfy the relationship of the following formula (1).

[0042] And the joining conditions are appropriately controlled. Specifically, RS×D expressed using the rotation speed RS (r / min) of the rotation tool, the diameter D (mm) of the shoulder of the rotation tool, and the joining speed JS (mm / min) 3 / JS satisfies the relationship of the following formula (2).

[0043] Therefore, even when an electromagnetic steel strip is used as the joined part, the shape of the coil joint will not deteriorate, the mechanical properties of the coil joint are improved, and the fracture of the coil joint on the production line is extremely effectively suppressed. In addition, it is possible to suppress the occurrence of defects and increase the joining speed, so the construction efficiency is excellent, which is also extremely advantageous in terms of productivity. It is also advantageous in terms of the durability of the rotating tool. In addition, the double-sided friction stir welding in which the joint is cooled by a cooling device after the joining process is also referred to as post-cooling double-sided friction stir welding.

[0044] 4×TJ≤D≤10×TJ…(1)

[0045] 200×TJ≤RS×D 3 / JS≤2000×TJ…(2)

[0046] Here, when the unjoined portion is a butted portion, TJ is an average value (mm) of the thickness of the first electromagnetic steel strip and the thickness of the second electromagnetic steel strip.

[0047] When the unjoined portion is an overlapping portion, TJ is the thickness (mm) of the overlapping portion.

[0048] (e) In addition, it is preferred that the steel structure of the joint and the hot working affected portion is a structure mainly composed of a ferrite phase, and that the steel structure of the joint and the hot working affected portion is refined and the hardness difference between the joint and the base material is reduced while simultaneously satisfying the above-mentioned equations (1) and (2). Specifically, it is preferred that the following equations (3) to (6) are satisfied at the same time.

[0049] Therefore, even when electromagnetic steel strips are used as the joined materials, the shape of the coil joint portion is not deteriorated, the mechanical properties of the coil joint portion are improved, and the occurrence of breakage in the coil joint portion on the production line is more effectively suppressed.

[0050] Dsz≤100μm…(3)

[0051] Dhaz1≤Dbm1…(4)

[0052] Dhaz2≤Dbm2…(5)

[0053] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2…(6)

[0054] here,

[0055] Dsz is the average ferrite grain size of the joint (μm),

[0056] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0057] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0058] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0059] Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip,

[0060] Hsz is the average hardness of the joint.

[0061] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0062] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0063] (f) In addition, it is preferred to simultaneously satisfy the relationships of the above-mentioned equations (3) to (6), and to select conditions that satisfy the relationships of the following equations (7) and (8) for joining. Thus, even when an electromagnetic steel strip is used as a joined material, the shape of the coil joint portion is not deteriorated, the mechanical properties of the coil joint portion are improved, and the occurrence of breakage at the coil joint portion on the production line is more effectively suppressed.

[0064] 0.8×TbmL≤TszL…(7)

[0065] TszH≤1.3×TbmH…(8)

[0066] here,

[0067] TszL is the minimum thickness of the joint (mm),

[0068] TszH is the maximum thickness of the joint (mm),

[0069] TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips.

[0070] TbmH is the plate thickness (mm) of the thicker one of the first and second electromagnetic steel strips.

[0071] However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

[0072] (g) In addition, double-sided friction stir welding is applied as a joining method, and the relationship between the above-mentioned formulas (1) and (2) is satisfied at the same time, thereby further improving the stirring energy. Therefore, a probeless rotating tool (hereinafter, also referred to as a probeless rotating tool) in which the front end of the rotating tool is only composed of a shoulder can be used. That is, in a conventional rotating tool (hereinafter, also referred to as a probe-equipped rotating tool), the probe (pin) is arranged at the front end of the rotating tool in a manner protruding from the shoulder. Therefore, a stress greater than that of the shoulder is applied to the probe, which is prone to breakage and wear. Therefore, the use of a probeless rotating tool is also extremely advantageous in terms of the durability and life extension of the rotating tool, and the reduction of the defective joining rate (caused by the wear and breakage of the rotating tool). Here, as a probeless rotating tool, for example, a probeless rotating tool in which the front end face (contact surface with the workpiece to be joined) of the rotating tool is a plane, a convex curved surface, or a concave curved surface can be cited.

[0073] (h) In addition, in the probeless rotating tool, it is preferable to provide a spiral step portion rotating in the opposite direction on the front end surface of the rotating tool. This can promote plastic flow, increase the joining speed, and further improve the construction efficiency.

[0074] The present invention has been completed as a result of further studies based on the above findings.

[0075] That is, the gist of the present invention is as follows.

[0076] 1. A friction stir welding method for electromagnetic steel strips, comprising: joining a first electromagnetic steel strip and a second electromagnetic steel strip as welded materials by a pair of rotating tools facing each other, wherein:

[0077] a joining step of pressing the rotating tool while rotating the rotating tool in opposite directions from both sides of the unjoined portion of the joined member and moving the rotating tool in a joining direction, thereby joining the first electromagnetic steel strip and the second electromagnetic steel strip to form a joined portion; and

[0078] a cooling step of cooling the joint portion by means of a cooling device disposed on at least one surface of the workpiece to be joined and behind the rotation tool in the joining direction;

[0079] The unjoined portion of the joined member is a butting portion or an overlapping portion between an end portion of the first electromagnetic steel strip and an end portion of the second electromagnetic steel strip following the first electromagnetic steel strip.

[0080] The joining process and the cooling process are continuously performed by moving the rotating tool and the cooling device in the joining direction in conjunction with each other.

[0081] In addition, the diameter D (mm) of the shoulder of the above-mentioned rotary tool satisfies the relationship of the following formula (1):

[0082] RS×D is expressed by the rotation speed RS (rpm) of the rotation tool, the diameter D (mm) of the shoulder of the rotation tool, and the joining speed JS (mm / min). 3 / JS satisfies the relationship of the following formula (2).

[0083] 4×TJ≤D≤10×TJ…(1)

[0084] 200×TJ≤RS×D 3 / JS≤2000×TJ…(2)

[0085] Here, when the unjoined portion is a butted portion, TJ is an average value (mm) of the thickness of the first electromagnetic steel strip and the thickness of the second electromagnetic steel strip.

[0086] When the unjoined portion is an overlapping portion, TJ is the thickness (mm) of the overlapping portion.

[0087] 2. The friction stir welding method for electromagnetic steel strips according to item 1 above, wherein:

[0088] In the joining step, the joining is performed under the condition that the steel structures of the joined portion and the hot working affected portion formed by joining the first electromagnetic steel strip and the second electromagnetic steel strip are mainly composed of a ferrite phase and satisfy the following relationships (3) to (6).

[0089] Dsz≤100μm…(3)

[0090] Dhaz1≤Dbm1…(4)

[0091] Dhaz2≤Dbm2…(5)

[0092] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2…(6)

[0093] here,

[0094] Dsz is the average ferrite grain size of the joint (μm),

[0095] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0096] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0097] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0098] Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip,

[0099] Hsz is the average hardness of the joint.

[0100] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0101] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0102] 3. The friction stir welding method for electromagnetic steel strips according to 1 or 2 above, wherein:

[0103] In the above-mentioned bonding step, bonding is performed under the condition that the relationship of the following formulas (7) and (8) is satisfied.

[0104] 0.8×TbmL≤TszL…(7)

[0105] TszH≤1.3×TbmH…(8)

[0106] here,

[0107] TszL is the minimum thickness of the joint (mm),

[0108] TszH is the maximum thickness of the joint (mm),

[0109] TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips.

[0110] TbmH is the plate thickness (mm) of the thicker one of the first and second electromagnetic steel strips.

[0111] However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

[0112] 4. The friction stir welding method for electromagnetic steel strips according to any one of 1 to 3 above, wherein:

[0113] In the above-mentioned joining step, the gap G (mm) between the shoulders of the above-mentioned rotating tools satisfies the relationship of the following formula (9).

[0114] 0.4×TJ≤G≤0.9×TJ…(9)

[0115] 5. The friction stir welding method for electromagnetic steel strips according to any one of 1 to 4 above, wherein:

[0116] The above-mentioned rotary tool is a probeless rotary tool.

[0117] 6. The friction stir welding method for electromagnetic steel strips according to 5 above, wherein:

[0118] The front end surface of the rotating tool is a plane, a convex curved surface or a concave curved surface.

[0119] 7. The friction stir welding method for electromagnetic steel strips according to 5 or 6 above, wherein:

[0120] The front end surface of the rotary tool has a spiral step portion rotating in opposite directions.

[0121] 8. The friction stir welding method for electromagnetic steel strips according to item 7 above, wherein:

[0122] The spiral step portion gradually becomes lower from the center of the front end surface of the rotation tool toward the outer periphery.

[0123] 9. The friction stir welding method for electromagnetic steel strips according to item 7 above, wherein:

[0124] The spiral step portion gradually increases in height from the center of the front end surface of the rotation tool toward the outer periphery.

[0125] 10. The friction stir welding method for electromagnetic steel strips according to any one of 5 to 9 above, wherein:

[0126] The tilt angle α of the above-mentioned rotating tool is 0°.

[0127] 11. The friction stir welding method for electromagnetic steel strips according to any one of 1 to 10 above, wherein:

[0128] In the cooling step, cooling is performed under conditions that satisfy the relationships of the following equations (10) to (12).

[0129] CR W＝0 ≥15…(10)

[0130] CR W＝0.2D ≥15…(11)

[0131] CR W＝0.5D ≥15…(12)

[0132] Here, CR W＝0 , CR W＝0.2D and CR W＝0.5D The cooling rate (°C / s) of the surface of the joint from the joint end temperature to 450°C at the positions of W=0, 0.2×D and 0.5×D respectively. In addition, W is the distance (mm) separated from the joint center line of the joined parts in the direction perpendicular to the joint. D is the diameter (mm) of the shoulder of the rotating tool.

[0133] 12. The friction stir welding method for electromagnetic steel strips according to any one of 1 to 11 above, wherein:

[0134] The cooling device is an inert gas jet device, a liquid jet device, or a combination thereof.

[0135] 13. A method for manufacturing an electromagnetic steel strip, comprising:

[0136] A step of joining a first electromagnetic steel strip and a second electromagnetic steel strip by the friction stir welding method for electromagnetic steel strips according to any one of 1 to 12 above to obtain a joined steel strip; and

[0137] A step of cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

[0138] 14. A friction stir welding device used in the friction stir welding method for electromagnetic steel strips according to any one of 1 to 12 above, comprising:

[0139] A holding device for holding the joined parts;

[0140] a pair of rotating tools disposed opposite to each other;

[0141] A driving device for the above-mentioned rotary tool;

[0142] a cooling device arranged on at least one surface of the workpiece to be joined and at the rear of the joining direction of the rotating tool; and

[0143] The above-mentioned holding device, the driving device of the above-mentioned rotating tool and the action control device of the above-mentioned cooling device.

[0144] 15. The friction stir welding device according to 14 above, comprising:

[0145] The cooling rate measuring device measures CR on both sides of the joint formed by the above-mentioned joined materials. W＝0 , CR W＝0.2D and CR W＝0.5D .

[0146] Here, CR W＝0 , CR W＝0.2D and CR W＝0.5D The cooling rate (°C / s) of the surface of the joint from the joint end temperature to 450°C at the positions of W=0, 0.2×D and 0.5×D respectively. In addition, W is the distance (mm) separated from the joint center line of the joined parts in the direction perpendicular to the joint. D is the diameter (mm) of the shoulder of the rotating tool.

[0147] 16. The friction stir welding device for electromagnetic steel strips according to 14 or 15 above, wherein:

[0148] The cooling device is an inert gas jet device, a liquid jet device, or a combination thereof.

[0149] 17. A device for manufacturing an electromagnetic steel strip, wherein:

[0150] A friction stir welding device according to any one of 14 to 16 above is provided.

[0151] According to the present invention, even when an electromagnetic steel strip is used as a workpiece to be joined, the mechanical properties and shape of the coil joint portion do not deteriorate, and the occurrence of fractures in the coil joint portion on the production line is effectively suppressed. In particular, the coarsening of ferrite recrystallized grains caused by plastic working at high temperatures during joining can be prevented, so the occurrence of fractures in the coil joint portion can be extremely effectively suppressed, which is extremely advantageous. In addition, along with this, the occurrence of defects can be suppressed and the joining speed can be increased to achieve high construction efficiency. As a result, the productivity of the electromagnetic steel sheet can be further improved, and the industrial utilization value is extremely high. In addition, in the friction stir joining method of the electromagnetic steel strip according to one embodiment of the present invention, a probeless rotating tool can be used, which is also extremely advantageous in terms of further improving the durability of the rotating tool and reducing the defective joining rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0152] Figure 1A This is a schematic diagram for explaining a friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention, and is a side perspective view showing an example of butt welding by after-cooling double-sided friction stir welding.

[0153] Figure 1B yes Figure 1A AA view.

[0154] Figure 1C yes Figure 1A Top view of the .

[0155] Figure 1D yes Figure 1A Cross-sectional view of the joint centerline position ( Figure 1C AA view).

[0156] Figure 2A This is a schematic diagram showing an example of the shape of a rotating tool with a probe used in the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention.

[0157] Figure 2B This is a schematic diagram showing an example of the shape of a rotating tool with a probe used in the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention.

[0158] Figure 3 This is a schematic diagram showing an example of the shape of a probeless rotating tool (rotating tool with a flat tip end) used in the friction stir welding method of an electromagnetic steel strip according to an embodiment of the present invention.

[0159] Figure 4This is a schematic diagram showing an example of the shape of a probeless rotating tool (front end convex rotating tool) used in the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention.

[0160] Figure 5 This is a schematic diagram showing an example of the shape of a probeless rotating tool (front end concave type rotating tool) used in the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention.

[0161] Figure 6 This is a schematic diagram showing an example of the shape of a probeless rotating tool (a rotating tool having a flat front end provided with a step portion) used in a friction stir welding method for an electromagnetic steel strip according to an embodiment of the present invention.

[0162] Figure 7 This is a schematic diagram showing an example of the shape of a probeless rotating tool (a convex-shaped rotating tool having a step portion) used in a friction stir welding method for an electromagnetic steel strip according to an embodiment of the present invention.

[0163] Figure 8 This is a schematic diagram showing an example of the shape of a probeless rotating tool (a concave-tip rotating tool provided with a step portion) used in the friction stir welding method of an electromagnetic steel strip according to an embodiment of the present invention.

[0164] Fig. 9 This is a diagram for explaining a method of dividing the vortex of the step portion into two and arranging (drawing) the vortices at equal intervals.

[0165] Fig.10 This is a diagram for explaining a method of dividing the vortex of the step portion into three and arranging (drawing) the vortices at equal intervals.

[0166] Fig.11 This is a diagram for explaining a method of dividing the vortex of the step portion into four and arranging (drawing) the vortices at equal intervals.

[0167] Fig.12 This is a diagram for explaining a method of dividing the step portion into five vortices and arranging (drawing) the vortices at equal intervals.

[0168] Fig.13 This is a diagram for explaining a method of dividing the step portion into six vortices and arranging (drawing) the vortices at equal intervals.

[0169] Fig.14 This is a schematic diagram showing an example of a convex-end type rotary tool provided with a stepped portion in a stepped shape.

[0170] Fig.15This is a schematic diagram showing an example of a convex-end type rotary tool provided with a groove-shaped step portion.

[0171] Fig.16 This is a schematic diagram showing an example of a front end flat rotating tool provided with a groove-shaped step portion.

[0172] Fig.17 Schematic diagram of a joined joint of electromagnetic steel strips obtained by a friction stir welding method of electromagnetic steel strips according to one embodiment of the present invention.

[0173] Fig.18 1 is a schematic diagram for explaining a friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention, and is a plan view showing an example of butt welding by after-cooling double-sided friction stir welding. DETAILED DESCRIPTION

[0174] The present invention will be described based on the following embodiments.

[0175] [1] Friction stir welding method of electromagnetic steel strip

[0176] First, use Figures 1A to 1D A friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention will be described. Figures 1A to 1D is a schematic diagram for explaining a friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention. Figure 1A It is a side view stereogram. Figure 1B yes Figure 1A AA view, Figure 1C yes Figure 1A A top view of Figure 1D yes Figure 1A Cross-sectional view at the location of the joining centerline.

[0177] In the figure, reference numeral 1 is a first electromagnetic steel strip (joined member), 2 is a second electromagnetic steel strip (joined member), 3-1 is a rotating tool (a rotating tool on the front side), 3-2 is a rotating tool (a rotating tool on the back side), 4 is a joining portion, 5-1 and 5-2 are shoulders (shoulders), 6-1 and 6-2 are probes (pins), 7 is a holding device, 9-1 and 9-2 are front ends, 10-1 is a cooling device (a cooling device on the front side), 10-2 is a cooling device (a cooling device on the back side), 11 is a driving device for the rotating tool, and 12 is a motion control device. In addition, in Figure 1AIn the figure, the holding device is omitted. In addition, α is the inclination angle of the rotating tool (°), a is the diameter of the probe part (hereinafter, also referred to as the pin diameter) (mm), b is the length of the probe part (hereinafter, also referred to as the pin length) (mm), D is the diameter of the shoulder of the rotating tool (mm), g is the gap between the probes (mm), G is the gap between the shoulders of the rotating tool, and H and I represent the cooling (predetermined) area based on the cooling device. In addition, from the perspective of easy observation, Figure 1C In the figure, the cooling device (surface side cooling device) of 10-1 is indicated by a dotted line. In addition, in order to distinguish the surface (outer surface (surface)) from the surface (front surface), the first appearance of the surface (front surface) is described as the surface (front surface).

[0178] In addition, Figures 1A to 1D middle,

[0179] According to the joining direction (the direction of rotation tool movement), the joining vertical direction (the direction perpendicular to the joining direction and perpendicular to the plate thickness direction), Figures 1A to 1D The configuration of each part is shown in the width direction of the joint and the running direction of the electromagnetic steel strip) and the plate thickness direction (a direction perpendicular to the surface of the joined material).

[0180] For example, in Figure 1B In the figure, the vertical direction is the plate thickness direction. The horizontal direction is the joint vertical direction. The direction on the inside of the paper is the joint direction. That is, Figure 1B The plane shown includes the direction perpendicular to the joint and the direction of the plate thickness. In addition, the cooling devices 10-1 and 10-2 are located closer to the front side of the paper than the rotating tools 3-1 and 3-2. Figure 1C The cooling device 10 - 1 indicated by the middle dotted line is located closer to the front side than the cooling areas H and I on the paper surface.

[0181] In addition, the electromagnetic steel strip mentioned here means an intermediate product that becomes a raw material for manufacturing an electromagnetic steel sheet, and in particular, refers to an intermediate product in the stage from the end of hot rolling to the heat treatment for primary recrystallization (for example, decarburization annealing or primary recrystallization annealing). In addition, as described later, the electromagnetic steel strip manufactured by the manufacturing method of the electromagnetic steel strip according to one embodiment of the present invention is obtained by cold rolling after joining the first electromagnetic steel strip and the second electromagnetic steel strip. Hereinafter, the electromagnetic steel strip in the state of joining the first electromagnetic steel strip and the second electromagnetic steel strip is also referred to as a joined steel strip, and the electromagnetic steel strip obtained by cold rolling the joined steel strip is also referred to as a cold-rolled steel strip.

[0182] Moreover, as described above, a friction stir welding method for an electromagnetic steel strip according to one embodiment of the present invention is characterized in that, based on the application of post-cooling double-sided friction stir welding as coil joining of the electromagnetic steel strip, the relationships of the above-mentioned equations (1) and (2) are simultaneously satisfied.

[0183] More specifically, a friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention is a friction stir welding method for electromagnetic steel strips in which a first electromagnetic steel strip and a second electromagnetic steel strip as welded materials are welded by a pair of rotating tools facing each other in a continuous cold rolling line, and comprises:

[0184] a joining step of pressing the rotating tool while rotating the rotating tool in opposite directions from both sides and moving the rotating tool in a joining direction at an unjoined portion of the joined member to join the first electromagnetic steel strip and the second electromagnetic steel strip to form a joined portion; and

[0185] a cooling step of cooling the joint portion by means of a cooling device disposed on at least one surface of the workpiece to be joined and behind the rotation tool in the joining direction;

[0186] The unjoined portion of the joined member is a butting portion or an overlapping portion between an end portion of the first electromagnetic steel strip and an end portion of the second electromagnetic steel strip following the first electromagnetic steel strip.

[0187] The joining process and the cooling process are continuously performed by moving the rotating tool and the cooling device in the joining direction in conjunction with each other.

[0188] In addition, the diameter D (mm) of the shoulder of the above-mentioned rotary tool satisfies the relationship of the above-mentioned formula (1),

[0189] RS×D is expressed by the rotation speed RS (rpm) of the rotation tool, the diameter D (mm) of the shoulder of the rotation tool, and the joining speed JS (mm / min). 3 / JS satisfies the relationship of the above formula (2).

[0190] Here, as preferred examples of the joint form, butt joint and overlap joint can be cited.

[0191] Butt joining refers to a joining method in which a rotating tool is rotated while being pressed against a butt joint including end faces (butt joint faces) of the first electromagnetic steel strip and the second electromagnetic steel strip while the end faces of the first electromagnetic steel strip and the second electromagnetic steel strip are opposed to each other, and then the first electromagnetic steel strip and the second electromagnetic steel strip are joined by moving the rotating tool in the joining direction in this state.

[0192] Overlapping joining refers to joining the first electromagnetic steel strip and the second electromagnetic steel strip by overlapping at least a portion of the ends of the first electromagnetic steel strip and pressing the rotating tool against the overlapping portion while rotating the rotating tool, and then moving the rotating tool in the joining direction in this state to join the first electromagnetic steel strip and the second electromagnetic steel strip.

[0193] For butt joint and overlap joint, only the shape of the unjoined part is different, and the structure of other devices is basically the same. Figures 1A to 1D The following describes a case where a butt joint is performed by post-cooling double-sided friction stir welding. The post-cooling double-sided friction stir welding method is a friction stir welding method in which a first electromagnetic steel strip and a second electromagnetic steel strip as the joined parts are joined using a pair of rotating tools facing each other, and after the joined parts form a joint, the joint is cooled by a cooling device arranged at the rear of the joining direction of the rotating tool. The first electromagnetic steel strip and the second electromagnetic steel strip are joined by the post-cooling double-sided friction stir welding method.

[0194] In such post-cooling double-sided friction stir welding, for example, Figure 1A As shown, a friction stir welding device is used, and the friction stir welding device has:

[0195] A holding device (not shown) for holding the joined parts;

[0196] a pair of rotating tools disposed opposite to each other;

[0197] A driving device for the above-mentioned rotary tool;

[0198] A cooling device is arranged on at least one surface (side) of the workpiece to be joined and behind the joining direction of the rotating tool; and

[0199] The above-mentioned holding device, the driving device of the above-mentioned rotating tool and the action control device of the above-mentioned cooling device.

[0200] In the motion control device, for example, the inclination angle α of the rotating tool, the position of the front end of the rotating tool and the distance g between the front ends (probes) (hereinafter also referred to as the gap g between probes), the gap G between the shoulders of the rotating tool, the joining speed (and the movement speed of the cooling device that moves in conjunction with the rotating tool in the joining direction), the pressing load, the rotation speed of the rotating tool, the rotational torque and the output of the cooling device are controlled.

[0201] In the post-cooling double-sided friction stir welding, the rotating tools of the friction stir welding device are respectively arranged on the two sides of the first electromagnetic steel strip and the second electromagnetic steel strip (hereinafter, also referred to as the joined parts) as the joined parts. In addition, the cooling device is arranged at the rear of the joining direction of the rotating tool on at least one side of the joined parts. In addition, the rotating tool arranged on the surface side (upper side in the vertical direction) of the joined parts is sometimes called the surface side rotating tool, and the rotating tool arranged on the back side (lower side in the vertical direction) of the joined parts is called the back side rotating tool. In addition, the cooling device arranged on the surface side (upper side in the vertical direction) of the joined parts is sometimes called the surface side cooling device, and the cooling device arranged on the back side (lower side in the vertical direction) of the joined parts is called the back side cooling device. The first electromagnetic steel strip and the second electromagnetic steel strip are arranged to be parallel to the joining center line shown in the figure, and are respectively held by the holding device.

[0202] Here, the joining center line is a line that passes through the set (target) position (on the surface of the joined part) of the rotation axis of the rotating tool during joining, and is parallel to the joining direction. In addition. The joining center line can also be referred to as the trajectory of the rotation axis of the rotating tool during joining (on the surface of the joined part), which usually passes through the center position of the width direction of the joint. In the case of butt joint, as shown in Figure 1, this position becomes, for example, the center position of the joint vertically of the joint between the end (rear end) of the first electromagnetic steel strip and the end (front end) of the second electromagnetic steel strip. In other words, this position becomes the midpoint between the end (rear end) of the first electromagnetic steel strip and the end (front end) of the second electromagnetic steel strip in the vertical direction of the joint. In addition, in the case of overlapping joints, this position becomes, for example, the center position of the width (width in the vertical direction of the joint) of the overlapping portion of the end (rear end) of the first electromagnetic steel strip and the end (front end) of the second electromagnetic steel strip.

[0203] Furthermore, the rotating tool is pressed while rotating the rotating tool from both sides in opposite directions to each other at the unjoined portion (joining area) of the joined parts located on the joining center line, i.e., the butt joint between the end (rear end) of the first electromagnetic steel strip and the end (front end) of the second electromagnetic steel strip. Then, in this state, the rotating tool is moved in the joining direction. At this time, the joined parts are softened by the friction heat between the joined parts and the rotating tool. Then, the softened portion is stirred by the rotating tool, thereby generating plastic flow to join the first electromagnetic steel strip and the second electromagnetic steel strip as the joined parts to obtain a joint. Next, the joint is cooled on at least one side by a cooling device arranged behind the rotating tool in the joining direction. In particular, the coarsening of ferrite recrystallized grains caused by plastic working at high temperature during joining can be prevented by cooling the joint by a cooling device after joining. That is, a joint having an extremely fine ferrite structure is obtained, and the joint characteristics are improved. As a result, the occurrence of fractures and defects in the coil joint on the production line is extremely effectively suppressed. In addition, the joining speed can be increased, and high construction efficiency can be achieved. In addition, a joining portion is formed at the joined portion. In addition, a hot working affected portion is formed adjacent to the joining portion.

[0204] Hereinafter, a joining step and a cooling step of a friction stir welding method of an electromagnetic steel strip according to an embodiment of the present invention will be described in detail.

[0205] [Joining process]

[0206] In the joining process, the rotating tool is pressed on the unjoined portion of the joined workpieces while rotating the rotating tool from both sides in opposite directions. Then, the rotating tool is moved in the joining direction in this state, thereby joining the first electromagnetic steel strip and the second electromagnetic steel strip as the joined workpieces to form a joined portion.

[0207] Furthermore, in this joining process,

[0208] The diameter D (mm) of the shoulder of the rotary tool satisfies the relationship of the above formula (1),

[0209] RS×D expressed by the rotation speed RS (rpm), the diameter D (mm) of the shoulder of the rotation tool, and the joining speed JS (mm / min) 3 It is important that / JS satisfies the relationship of the above formula (2).

[0210] That is, the diameter D of the shoulder of the rotating tool (hereinafter also referred to as the shoulder diameter D) is appropriately controlled according to the thickness of the unjoined portion. As a result, the temperature rise caused by the frictional heat generated between the rotating tool and the first and second electromagnetic steel strips as the joined parts and the shear stress generated by the frictional force can be effectively applied to the joined parts. Here, if the shoulder diameter D is less than 4×TJ (mm), there is a situation where sufficient plastic flow cannot be obtained and it is difficult to obtain the target mechanical properties. On the other hand, if the shoulder diameter D exceeds 10×TJ (mm), the area where plastic flow occurs is excessively expanded, and too much heat is input to the joint. As a result, there is a situation where the recrystallized structure of the joint is coarsened, and it is difficult to obtain the target mechanical properties. Therefore, the shoulder diameter D is made to satisfy the relationship of the above formula (1).

[0211] Furthermore, in the case of a probeless rotary tool, e.g. Figure 3 to Figure 5 The shoulder diameter D can also be called the tip diameter. The tip diameter is the diameter of the tip surface of the rotation tool in a plane perpendicular to the rotation axis (the diameter of the projection area when the tip surface of the rotation tool is projected in a direction parallel to the rotation axis).

[0212] In addition, RS×D 3 / JS is a parameter related to the heat generation per unit joint length. 3 The range of / JS is set to 200×TJ to 2000×TJ, which can effectively impart the temperature rise caused by the friction heat generated between the rotating tool and the first and second electromagnetic steel strips as the welded parts and the shear stress caused by the friction force to the welded parts. 3 When / JS is less than 200×TJ, the heat generation may be insufficient. Therefore, it may be difficult to form a metallurgically bonded interface between the first and second electromagnetic steel strips, and it may be difficult to obtain the target mechanical properties. On the other hand, if RS×D 3 If / JS exceeds 2000×TJ, the heat generated by friction stirring becomes too large, and too much heat is input to the joint. As a result, the peak temperature (maximum temperature reached) of the joint rises, or the cooling rate decreases, resulting in coarsening of the recrystallized structure of the joint. As a result, it is difficult to obtain the target mechanical properties. Therefore, RS×D 3 / JS satisfies the relationship of the above formula (2). RS×D 3 / JS is preferably 240×TJ or more. 3 / JS is preferably 1200×TJ or less.

[0213] When the rotation speed RS and / or shoulder diameter D of the rotation tool are different between the front side rotation tool and the back side rotation tool, it is preferable that the relationship of the above-mentioned equations (1) and (2) are satisfied in the front side rotation tool and the back side rotation tool, respectively.

[0214] In the friction stir welding method of the electromagnetic steel strip according to one embodiment of the present invention, it is preferable to perform the welding under the condition that the steel structure of the joint portion and the hot working affected portion formed by the welding of the first electromagnetic steel strip and the second electromagnetic steel strip is a structure mainly composed of a ferrite phase and satisfies the relationship of the above-mentioned equations (3) to (6). Thus, even when the electromagnetic steel strip is used as the welded material, the shape of the coil joint portion is not deteriorated, the mechanical properties of the coil joint portion are improved, and the occurrence of fracture of the coil joint portion on the production line is more effectively suppressed.

[0215] In the friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention, it is preferable to perform the welding under the condition that the relationship of the above equations (7) and (8) is satisfied. This can further effectively suppress the occurrence of cracks in the coil joints on the production line.

[0216] Note that the descriptions of the joined materials (the first electromagnetic steel strip and the second electromagnetic steel strip), the joined portion, the hot working affected portion, and the above-mentioned equations (3) to (8) are as described in [2] Joined joint of electromagnetic steel strips described later.

[0217] In the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention, it is preferable that the gap G (mm) between the shoulders of the rotating tool satisfies the relationship of the following formula (9).

[0218] 0.4×TJ≤G≤0.9×TJ…(9)

[0219] That is, in double-sided friction stir welding, from the perspective of suppressing the generation of defects during welding and achieving a high welding speed, it is beneficial to appropriately control the gap G between the shoulders of the rotating tool (hereinafter, also referred to as the gap G between shoulders). In addition, the gap G between shoulders can also be referred to as the separation distance between the shoulder of the rotating tool on the surface side and the shoulder of the rotating tool on the back side in the plate thickness direction. In particular, if the gap G between shoulders is in the range of 0.4×TJ to 0.9×TJ, the shoulders of the rotating tools facing each other are pressed on the surface and back sides of the welded parts with sufficient load, fully promoting the heating of the welded parts and the plastic flow in the plate thickness direction. Thus, a better welded joint is obtained. On the other hand, if the gap G between shoulders exceeds 0.9×TJ, the shoulder of the rotating tool cannot be pressed on the surface and back sides of the welded parts with sufficient load, and there is a situation where the above-mentioned effect cannot be obtained. In addition, if the gap G between shoulders is less than 0.4×TJ, the surface and back of the welded part become excessively concave, which may have an adverse effect on the joint strength. Therefore, the shoulder gap G is preferably in the range of 0.4×TJ to 0.9×TJ. The shoulder gap G is more preferably 0.5×TJ or more. Furthermore, the shoulder gap G is more preferably 0.8×TJ or less.

[0220] In the friction stir welding method for electromagnetic steel strip according to one embodiment of the present invention, the inclination angle α of the rotating tool is not particularly limited. For example, it is preferred that both the front side rotating tool and the back side rotating tool satisfy the relationship of the following formula (13).

[0221] 0°≤α≤4°…(13)

[0222] Here, α is the inclination angle of the rotation axis of the rotating tool (hereinafter also referred to as the rotation axis of the tool) in the plane including the joining direction and the plate thickness direction (the direction perpendicular to the surface of the joined workpiece) relative to the plate thickness direction (the direction perpendicular to the surface of the joined workpiece). In addition, the direction (angle) of the front end of the rotating tool relative to the joining direction is set to +.

[0223] In addition, in the rotating tool with a probe commonly used in the double-sided friction stir welding method, the rotating axis of the tool is tilted on both the surface side rotating tool and the back side rotating tool. That is, it is more preferably set to 0°<α. As a result, the front end of the probe precedes the joining direction, so that the load on the rotating tool can be made into a component force compressed in the direction of the rotation axis and borne by the rotating tool. As a result, the force in the bending direction is reduced, reducing the risk of damage to the rotating tool. Therefore, when using a rotating tool with a probe, it is more preferably set to 0°<α. In addition, it is more preferably set to α≤2°.

[0224] On the other hand, in a rotary tool without a probe, there is no need to consider the breakage caused by the local stress concentration of the probe. Therefore, it is more preferred to make the inclination angle α of the rotary tool to be 0° on both the surface side rotary tool and the back side rotary tool, that is, to make the rotation axis of the tool parallel to the plate thickness direction on the surface including the joining direction and the plate thickness direction (the direction perpendicular to the surface of the joined member). As a result, the front and back sides of the joint become concave, and the ratio of the thickness of the joint to the thickness of the joined member is reduced. As a result, the tendency to adversely affect the strength of the joint can be avoided. In addition, there is also the advantage of being able to omit the control mechanism of the device for assigning and setting the inclination angle α of the rotary tool. Moreover, in this case, ±0.3° is the preferred allowable range.

[0225] The conditions other than the above are not particularly limited as long as they satisfy the relationship between the above formulae (1) and (2), and may be carried out in accordance with a conventional method.

[0226] For example, the rotation speed of the rotating tool is preferably 300 to 9000 r / min (revolutions per minute). By setting the rotation speed of the rotating tool within this range, it is advantageous because the surface shape can be well maintained and the reduction in mechanical properties caused by excessive heat input can be suppressed. The rotation speed of the rotating tool is more preferably 400 r / min or more. In addition, the rotation speed of the rotating tool is more preferably 8000 r / min or less.

[0227] The joining speed is preferably 800 to 5000 mm / min (mm / minute), and more preferably 1000 mm / min to 4000 mm / min.

[0228] The position of the tip of the rotation tool, the press-fit load, the rotation torque, the gap between the probes, and the like may be appropriately set according to a conventional method.

[0229] In addition, if Figures 1A to 1D As shown, in the post-cooling double-sided friction stir welding, the rotation direction of the surface side rotating tool and the rotation direction of the back side rotating tool are made to be opposite directions when viewed from the surface side (or back side) of the joined workpiece. In addition, it is preferred that the rotation speed of the surface side rotating tool is the same as the rotation speed of the back side rotating tool. Thus, the rotational torque applied to the joined workpiece from the surface side rotating tool and the back side rotating tool can be offset. As a result, compared with the single-sided friction stir welding method in which the unjoined part is joined by pressing from one side, the structure of the fixture constraining the joined workpiece can be simplified.

[0230] In addition, if the rotation direction of the surface side rotating tool and the rotation direction of the back side rotating tool are made to be the same direction when viewed from the surface side (or back side) of the joined parts, the relative speed of the rotating tool on one side relative to the rotating tool on the other side is close to zero. As a result, the plastic flow of the joined parts approaches a homogeneous state, and the plastic deformation also becomes smaller. Therefore, the heat generated by the plastic deformation of the material cannot be obtained, and it is therefore difficult to achieve a good joining state. Thus, from the viewpoint of obtaining a temperature rise and shear stress sufficient to achieve a good joining state homogeneously relative to the plate thickness direction of the joined parts, the rotation direction of the surface side rotating tool and the rotation direction of the back side rotating tool are made to be opposite directions when viewed from the surface side (or back side) of the joined parts.

[0231] The rotating tool used in the friction stir welding method of the electromagnetic steel strip according to one embodiment of the present invention is not particularly limited as long as it satisfies the relationship of the above formula (1), and a conventional method may be used.

[0232] For example, the front end portion of the rotating tool contacts the first electromagnetic steel strip and the second electromagnetic steel strip as the joined parts during joining. Therefore, the front end portion of the rotating tool is formed of a material that is harder than the first electromagnetic steel strip and the second electromagnetic steel strip under the high temperature state exposed during joining. As a result, the rotating tool can deform the first electromagnetic steel strip and the second electromagnetic steel strip while maintaining the shape of the front end portion unchanged during joining. As a result, a high stirring capacity can be continuously achieved, and appropriate joining can be performed. In addition, the hardness of the front end portion of the rotating tool, the first electromagnetic steel strip, and the second electromagnetic steel strip can be measured and compared by a high-temperature Vickers hardness test method. In addition, only the front end portion of the rotating tool can be formed of a material that is harder than the first electromagnetic steel strip and the second electromagnetic steel strip. In addition, the entire rotating tool can also be formed of a material that is harder than the first electromagnetic steel strip and the second electromagnetic steel strip.

[0233] Figure 2A and Figure 2B , respectively, represent examples of rotary tools with probes. Figure 2A and Figure 2B As shown, the rotary tool with a probe shows a shape in which the front end of the rotary tool has a shoulder (the range represented by the shoulder diameter in the figure) and a probe (the range represented by the pin diameter in the figure) arranged on the shoulder and sharing a rotation axis with the shoulder.

[0234] exist Figure 2A In the example of the rotation tool shown, the shape of the rotation tool is shoulder diameter D: 13 mm, pin diameter: 4 mm, pin length: 0.6 mm, and concave depth (not shown): 0.3 mm.

[0235] exist Figure 2BIn the example of the rotation tool shown, the shape of the rotation tool is shoulder diameter D: 27 mm, pin diameter: 8 mm, pin length: 0.9 mm, and concave depth (not shown): 0.3 mm.

[0236] In the rotating tool with a probe, the shoulder has a flat shape formed by a substantially flat surface or a gently curved surface. The shoulder has a function of generating frictional heat by contacting the first electromagnetic steel strip and the second electromagnetic steel strip while rotating during joining. In addition, the shoulder has a function of preventing the dispersion of the material and promoting plastic flow in the rotation direction by pressing the portion softened by heat.

[0237] The probe is discontinuous with the shoulder and protrudes approximately vertically toward the workpiece (not shown). The probe has a function of improving the stirring capacity near the center of the plate thickness by penetrating the softened portion of the first electromagnetic steel strip and the second electromagnetic steel strip toward the center of the plate thickness during joining. In addition, the probe is usually located at the center of the shoulder.

[0238] As described above, the shoulder diameter D (mm) is made to satisfy the relationship of the above formula (1). In addition, the pin diameter and pin length of the rotating tool are not particularly limited and can be appropriately set according to conventional methods. For example, when the first electromagnetic steel strip and the second electromagnetic steel strip have different plate thicknesses when butt-joining is performed, the pin diameter and pin length of the rotating tool according to conventional methods can be set by considering the average value of the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip. In addition, when the first electromagnetic steel strip and the second electromagnetic steel strip are overlapped and joined, the pin diameter and pin length of the rotating tool according to conventional methods can be set by considering the total value of the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip.

[0239] In addition, as described above, the probe has a function of improving the stirring capacity near the center of the plate thickness by penetrating the softened portion of the first electromagnetic steel strip and the second electromagnetic steel strip toward the center of the plate thickness during joining. However, a stress greater than that on the shoulder is applied to the probe. In this regard, in a friction stir joining method for an electromagnetic steel strip according to an embodiment of the present invention, the relationship between the above-mentioned equations (1) and (2) is satisfied at the same time, thereby further improving the stirring capacity. Therefore, a probeless rotating tool can be used. Compared with a probe-equipped rotating tool, a probeless rotating tool has excellent durability. Therefore, from the perspective of durability and life extension of the rotating tool and reduction in the defective joining rate (caused by wear and breakage of the rotating tool), it is preferred to use a probeless rotating tool.

[0240] Figure 3 to Figure 5 Each shows an example of a probeless rotation tool. Figure 3 This is an example of a probeless rotation tool whose front end surface is a flat surface (hereinafter also referred to as a front end flat surface rotation tool). Figure 4This is an example of a probeless rotary tool whose front end surface is a convex curved surface (hereinafter also referred to as a convex-front end rotary tool). Figure 5 This is an example of a probeless rotation tool whose front end surface is a concave curved surface (hereinafter also referred to as a concave-front end rotation tool).

[0241] like Figure 3 to Figure 5 As shown, the front end of the probeless rotary tool is composed only of a shoulder. That is, the front end of the probeless rotary tool is discontinuous with the shoulder and does not have a portion (probe) protruding substantially vertically toward the workpiece. The front end surface of the rotary tool is preferably Figure 3 That plane, Figure 4 Such convex surfaces, Figure 5 In addition, the shape of the front end portion in a plane perpendicular to the tool rotation axis (a projection area when the front end surface of the rotating tool is projected in a direction parallel to the rotation axis) is circular.

[0242] exist Figure 3 In such a front end plane rotation tool, for example, the front end surface that contacts the workpiece is constituted by a single plane that is perpendicular to the rotation axis of the tool.

[0243] exist Figure 4 In such a convex front end rotary tool, for example, the front end surface that contacts the workpiece becomes a continuous shape without a probe and becomes a substantially uniform inclined surface. More specifically, the front end surface constitutes a curved surface (paraboloid, ellipsoid or spherical surface) protruding from the periphery toward the center. In addition, as Figure 4 In this way, the cross section of the front end surface (a cross section including the rotation axis and parallel to the rotation axis) is a curve with substantially the same curvature radius. In addition, it is preferred that the curved surface height dv (mm) and the shoulder diameter D (mm) satisfy the relationship of the following formula (14).

[0244] dv / D≤0.06…(14)

[0245] That is, by setting dv / D to less than 0.06, when the front end of the rotating tool contacts the workpiece, pressure can be more effectively applied to the flow portion, and plastic flow can be more effectively generated. On the other hand, if dv / D exceeds 0.06, there is a situation where the surface and back of the joint become excessively concave, and the thickness of the joint becomes smaller relative to the thickness of the steel strip. In such a case, it is difficult to ensure the strength of the joint, so it is not preferred. In addition, the lower limit of dv / D is not particularly limited. However, from the viewpoint of applying pressure to the flow portion more effectively, dv / D is preferably greater than 0.01.

[0246] exist Figure 5In such a concave front end rotary tool, the front end surface that contacts the workpiece becomes a continuous shape without a probe and becomes a roughly uniform inclined surface. More specifically, the front end surface constitutes a curved surface (paraboloid, ellipsoid or spherical surface) that is concave from the periphery toward the center. In addition, as Figure 5 In this way, the cross section of the front end surface (a cross section including the rotation axis and parallel to the rotation axis) is a curve with substantially the same radius of curvature. In addition, it is preferred that the curved surface depth dc (mm) and the shoulder diameter D (mm) satisfy the relationship of the following formula (15).

[0247] dc / D≤0.03…(15)

[0248] That is, by setting dc / D to less than 0.03, the softened metal during joining is filled in the concave curved surface of the front end. Thus, when the front end of the rotating tool contacts the workpiece, pressure can be applied to the flow portion more effectively, and plastic flow can be generated more effectively. On the other hand, if dc / D exceeds 0.03, it is difficult to effectively apply pressure to the flow portion to generate sufficient plastic flow, which is not preferred. In addition, the lower limit of dc / D is not particularly limited. From the viewpoint of applying pressure to the flow portion more effectively, dc / D is preferably greater than 0.01.

[0249] In addition, from the viewpoint of further promoting the flow of the material, it is preferred that the front end face of the rotating tool has a spiral (helical) step portion rotating in the opposite direction. The spiral step portion is formed, for example, by the center of the front end face of the rotating tool or by the Figures 6 to 8 The front end face of the rotating tool is divided into radial curves (vortices) starting from the periphery of the center circle of the front end face of the rotating tool and extending to the outer periphery of the front end face of the rotating tool. In addition, the center circle of the front end face of the rotating tool is a circle of any diameter centered at the center of the front end face of the rotating tool. Figures 6 to 8 In the figure, the number of vortices is 4.

[0250] The number of vortices that divide the step portion can be one or more. However, if the number of vortices that divide the step portion exceeds 6, the effect of promoting material flow is weakened. In addition, there is a concern that it is easy to break due to the complexity of the shape. Therefore, the number of vortices that divide the step portion is preferably 6 or less. In addition, Figures 9 to 13 Examples are shown in which the number of vortices that partition the step portion is 2 to 6.

[0251] In addition, from the viewpoint of improving the material flow and preventing the damage of the front end of the rotating tool, the number of vortices dividing the step portion is preferably adjusted according to the shoulder diameter. For example, it is preferred that the larger the shoulder diameter, the greater the number of vortices dividing the step portion, and the smaller the shoulder diameter, the less the number of vortices dividing the step portion. Specifically, when the shoulder diameter is less than 6 mm, it is preferred to set the number of vortices dividing the step portion to less than 2. On the other hand, when the shoulder diameter is greater than 6 mm, it is preferred to set the number of vortices dividing the step portion to 3 to 6.

[0252] When there are two vortices dividing the step portion and the vortices are arranged at equal intervals, as shown in FIG. Fig. 9 As shown, a semicircle with a radius of line segment AB is drawn with point A and point B as the starting point. Next, a semicircle with a radius of twice the length of line segment AB is drawn. Next, a semicircle with a radius of three times the length of line segment AB is drawn. By repeating the above operation, two vortices with equal intervals can be drawn.

[0253] When the number n of vortices dividing the step portion is 3 to 6 and the vortices are arranged at equal intervals, Figure 10 to Figure 13 As shown, draw a regular n-gon, with each vertex of the n-gon as the center, draw an arc of a radius equal to the length of the side of the regular n-gon to the point that intersects with the extension line of the side. Then, with the adjacent vertex of the previous vertex as the center, draw an arc of a radius twice the length of the side of the regular n-gon to the point that intersects with the extension line of the next side. Then, with the adjacent vertex of the previous vertex as the center, draw an arc of a radius three times the length of the side of the regular n-gon to the point that intersects with the extension line of the next side. By repeatedly performing the above operation, it is possible to draw n equally spaced vortices.

[0254] In addition, Figures 9 to 13 In the case of , the number of vortices can also be set to 1. Fig. 9 , Fig.11 and Fig.13 In the case of , the number of vortices can be set to 2, and the vortices can be formed at equal intervals. Fig.10 and Fig.13 In the case of , the number of vortices can be set to 3 and the vortices can be formed at equal intervals.

[0255] In addition, the length of each vortex is preferably more than 0.5 and less than 2 turns of the circumference of the front end surface. The length of the vortex is also preferably adjusted according to the shoulder diameter. For example, it is preferred that the larger the shoulder diameter, the longer the length of the vortex, and the smaller the shoulder diameter, the shorter the length of the vortex.

[0256] In an example of a convex front rotary tool, such as Fig.14As shown, the step portion is formed by changing the height position in a step-like manner according to each area between the vortices, for example, gradually becoming lower from the center of the front end face toward the periphery. In addition, in the case of a concave front end rotating tool, the step portion is formed by gradually becoming higher from the center of the front end face toward the periphery. Hereinafter, the shape of such a step portion is also referred to as a step-like shape. The number of steps of the step portion can be one or more. In addition, in a cross section ( Fig.14 In the cross section), each step portion may be substantially horizontal, for example.

[0257] In another example of a convex front rotary tool, such as Fig.15 As shown, the step portion is formed by providing an area (hereinafter, also referred to as a groove portion) that is recessed than the front end face at the position of the vortex. Thus, a step portion that gradually becomes lower from the center of the front end face toward the periphery is formed. In addition, in the case of a rotary tool with a concave front end, a step portion that gradually becomes higher from the center of the front end face toward the periphery is formed. Hereinafter, the shape of such a step portion is also referred to as a groove shape. In addition, as examples of the cross-sectional shape of the groove portion, a U-shape, a V-shape, a レ-shape, etc. can be exemplified. The number of the step portions may be one or more.

[0258] In an example of a front flat rotating tool, such as Fig.16 As shown, the step portion is formed by providing a groove portion at the position of the vortex. As the shape of the groove portion, a U-shape, a V-shape, a レ-shape, etc. can be exemplified. The number of steps of the step portion can be one or more.

[0259] By providing the step portion as described above, when the rotating tool presses and stirs the workpiece to be joined, the metal material softened by friction heat flows from the outside of the rotating tool to the inside. As a result, it is possible to suppress the metal material from flowing out to the outside of the pressing portion pressed by the rotating tool. As a result, the plastic flow of the pressing portion is promoted. In addition, it is possible to prevent the thickness of the joint portion from being reduced relative to the base material, and form a beautiful joint portion surface without burrs.

[0260] In addition, the root portion of the rotary tool on the opposite side to the front end portion can be attached to a conventionally generally used double-sided friction stir welding device, and the shape of the root portion is not particularly limited.

[0261] [Cooling process]

[0262] In the cooling process, a cooling device is arranged on at least one surface (side) of the joined parts behind the joining direction of the rotating tool, and the joint of the joined parts formed in the joining process is cooled by the cooling device. In addition, by moving the cooling device in the joining direction in conjunction with the rotating tool, the above-mentioned joining process and cooling process can be performed continuously. In addition, by cooling the joint part by using a cooling device after joining, the coarsening of ferrite recrystallized grains caused by plastic working at high temperature during joining can be prevented. That is, a joint part with extremely fine ferrite structure is obtained, and the joint characteristics are improved. As a result, the fracture and defect generation of the coil joint part on the production line are extremely effectively suppressed. In addition, the joining speed can be increased, and high construction efficiency can be achieved.

[0263] Next, use Figure 1C , taking the case where the cooling device is arranged on both sides of the joined parts (hereinafter also referred to as double-sided arrangement) as an example, the preferred cooling rate and the like are described. Here, the cooling rate is the cooling rate of the surface of the joint part from the joint end temperature to 450°C. In addition, the joint end temperature is the temperature of the surface of the joint part at the moment of joint end, that is, the moment of the passage of the rotating tool. That is, the cooling rate of each part can be calculated by the following formula.

[0264] [Cooling rate (°C / s)] = ([Joining end temperature (°C)] - 450°C) ÷ [Time from joining end to when the surface temperature of the joined portion reaches 450°C (s)] ... (18)

[0265] Moreover, it is preferred that the cooling rate satisfies the following requirements on both sides of the joint portion formed in the joined parts. In addition, when the cooling device is only configured on any one side of the joined parts, such as the surface (front) side (hereinafter, also referred to as single-sided configuration), as long as the cooling rate satisfies the following requirements on both sides of the joint portion formed in the joined parts, the same effect can also be obtained. Therefore, the description of the example of single-sided configuration is omitted.

[0266] CR W＝0 ≥15…(10)

[0267] CR W＝0.2D ≥15…(11)

[0268] CR W＝0.5D ≥15…(12)

[0269] In post-cooling double-sided friction stir welding, it is important to prevent the coarsening of ferrite recrystallized grains caused by plastic working at high temperature during welding by cooling the welded part with a cooling device after welding. Figure 1CThe cooling rates of the cooling area I (the area of ​​0≤W≤0.1×D on the surface of the joined material) and the cooling area H (0.1×D<W≤0.5×D on the surface of the joined material), especially the cooling rates of the positions of W=0, 0.2×D and 0.5×D as representative positions of these cooling areas, are effective. From such a viewpoint, it is preferred to control the cooling rate to satisfy the relationship of the above-mentioned formulas (10) to (12).

[0270] Here, W is the distance (mm) from the center line of the joined parts in the direction perpendicular to the joint, and CR W＝0 , CR W＝0.2D and CR W＝0.5D The cooling rate (°C / s) of the surface of the joint from the joint end temperature to 450°C at the positions of W=0, 0.2×D, and 0.5×D, respectively. In addition, D is the diameter (mm) of the shoulder of the rotating tool. In addition, the cooling area is the surface area of ​​the joint that is cooled by the cooling device.

[0271] 0.80≤CR W＝0.2D / CR W＝0 ≤1.20…(16)

[0272] 0.80≤CR W＝0.5D / CR W＝0 ≤1.20…(17)

[0273] In addition, in the cooling process, regarding the cooling rate of the joined parts, it is more preferable to further satisfy the relationship of the above-mentioned equations (16) and (17) on the basis of satisfying the relationship of the above-mentioned equations (10) to (12). That is, in order to obtain the effect of preventing the coarsening of ferrite recrystallized grains by cooling the joint part by a cooling device after joining, it is effective to increase the cooling rate of the joint part. However, if the cooling rate varies depending on the position on the surface of the joint part, the effect of preventing the coarsening of ferrite recrystallized grains also varies. As a result, there is a case where the ferrite grain size of the joint part also varies. The deviation in the ferrite grain size of the joint part leads to the deviation in the mechanical properties of the joint part, and therefore it is desired that the ferrite grain size of the joint part is uniform. Therefore, it is effective to control the cooling rate to be uniform in the cooling area I near the center line of the joint and the cooling area H away from the center line of the joint. In particular, with respect to the cooling rates at the positions of W=0, 0.2×D and 0.5×D, which are representative positions of the cooling area I and the cooling area H, CR W＝0.2D Relative to CR W＝0 CR W＝0.2D / CR W＝0 Set the range to 0.80 to 1.20, and set CR W＝0.5D Relative to CR W＝0 CRW＝0.5D / CR W＝0 It is effective to control the ratio to 0.80 to 1.20. Therefore, in the cooling step, it is more preferable to control the cooling rate to satisfy the relationship of the above-mentioned formulas (16) and (17).

[0274] In addition, the cooling device used in the cooling step is not particularly limited, and examples thereof include an inert gas spraying device and a liquid spraying device.

[0275] In the inert gas injection device, as an inert gas, for example, argon, helium, carbon dioxide (CO2), nitrogen (N2), etc. can be used. The injection amount of the inert gas can be adjusted in various ways according to the size of the cooling area of ​​the joint, the thermal conductivity of each gas, and the pressure. In addition, the shape and number of the gas injection ports can also be adjusted in various ways according to the size of the cooling area of ​​the joint. By making various adjustments to them, it is possible to ensure cooling capacity and uniform cooling. That is, the cooling rate can be controlled to satisfy the relationship between the above-mentioned equations (10) to (12), and further satisfy the relationship between the above-mentioned equations (16) and (17).

[0276] In addition, in the liquid injection device, as the liquid, for example, water, liquid carbon dioxide, liquid nitrogen, etc. can be used. The injection amount of the liquid, the shape of the liquid injection port, and the number can be adjusted in various ways according to the size of the cooling area of ​​the joint, taking into account the boiling phenomenon when each liquid contacts the surface of the joint, such as suppressing film boiling and promoting nucleate boiling. By making various adjustments to them, it is possible to ensure cooling capacity and uniform cooling. That is, the cooling rate can be controlled to satisfy the relationship between the above equations (10) to (12), and further satisfy the relationship between the above equations (16) and (17).

[0277] Furthermore, as the cooling device, a device combining a plurality of cooling devices, for example, a device combining the above-mentioned inert gas spraying device and liquid spraying device may be used.

[0278] In addition, as long as the cooling device is arranged behind the joining (progress) direction of the rotating tool on at least one surface of the joined parts, the distance between the rotating tool and the cooling device, and the range of the cooling area (hereinafter, also referred to as the cooling range) are not particularly limited. However, if the distance between the cooling device and the rotating tool is too small, there is a concern that defects may occur due to insufficient plastic flow in the joint. Therefore, it is preferred that the positional relationship between the cooling device and the rotating tool is determined based on the influence on the plastic flow at the joint and the cooling efficiency, etc., taking into account the joining speed. For example, when the joining speed is 1 to 4 m / min, it is preferred to set the distance between the rotating tool and the cooling device (the distance between the ends in the joining direction) to a range of 20 mm to 40 mm. In addition, the cooling range can be controlled, for example, by adjusting the type of gas and / or liquid ejected from the cooling device, and the shape, number and configuration of the ejection port.

[0279] [2] Joints of electrical steel strips

[0280] Next, use Fig.17 The joint of the electromagnetic steel strip is explained. In the figure, reference numeral 1 is the first electromagnetic steel strip (joined material), 2 is the second electromagnetic steel strip (joined material), 4 is the joint, 4-1 is the hot working affected part (on the first electromagnetic steel strip side), and 4-2 is the hot working affected part (on the second electromagnetic steel strip side). In addition, Fig.17 This is a cross-sectional view of the joint of the electromagnetic steel strip in the plate thickness direction. In the figure, the vertical direction is the plate thickness direction. The horizontal direction is the joint vertical direction. The direction near the front of the paper is the joint direction. That is, Fig.17 The shown plane (herein, the cross section in the plate thickness direction) includes the joining vertical direction and the plate thickness direction.

[0281] The above-mentioned electromagnetic steel strip joint joins the first electromagnetic steel strip and the second electromagnetic steel strip, wherein:

[0282] The joint of the electromagnetic steel strip includes a joint portion and a hot working affected portion adjacent to the joint portion.

[0283] The steel structures of the joint and the hot working affected part are respectively mainly composed of ferrite phase.

[0284] The following relationships (3) to (6) are satisfied.

[0285] Dsz≤100μm…(3)

[0286] Dhaz1≤Dbm1…(4)

[0287] Dhaz2≤Dbm2…(5)

[0288] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2≤(Hbm1+Hbm2) / 2…(6)

[0289] here,

[0290] Dsz is the average ferrite grain size of the joint (μm),

[0291] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0292] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0293] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0294] Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip,

[0295] Hsz is the average hardness of the joint.

[0296] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0297] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0298] The above-mentioned joined joint of the electromagnetic steel strips can be obtained (produced), for example, by the friction stir welding method of the electromagnetic steel strips according to one embodiment of the present invention described above.

[0299] [Parts to be joined (first electromagnetic steel strip and second electromagnetic steel strip)]

[0300] The first and second electromagnetic steel strips are electromagnetic steel strips as joined materials. The composition of the first and second electromagnetic steel strips is not particularly limited as long as it is a common composition of an electromagnetic steel strip (electromagnetic steel sheet) in a cold-rolled stage.

[0301] As the composition of such an electrical steel strip, a composition containing Si in the range of 2.0 to 5.0 mass% can be exemplified. In addition, a composition containing C: 0.005 mass% or less, Si: 2.0 to 5.0 mass%, Al: 3.0 mass% or less, Mn: 2.00 mass% or less, P: 0.2 mass% or less, S: 0.01 mass% or less, and N: 0.01 mass% or less, and the remainder being Fe and inevitable impurities can be exemplified. In addition, the above composition can arbitrarily contain at least one selected from the group consisting of 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 in mass%. In addition, the above composition can arbitrarily contain at least one selected from the group consisting of Cr: 1% or less, Ni: 1% or less, and Cu: 1% or less in mass%. In addition, elements other than Si and Fe may all be 0%.

[0302] In addition, the component compositions of the first electromagnetic steel strip and the second electromagnetic steel strip may be the same or different.

[0303] The plate thickness t1 of the first electromagnetic steel strip and the plate thickness t2 of the second electromagnetic steel strip are not particularly limited, but t1 and t2 are preferably 1.2 to 3.2 mm, respectively. t1 and t2 may be the same or different.

[0304] In addition, a region of the first electromagnetic steel strip and the second electromagnetic steel strip as the joined materials which is not affected by the hot working due to friction heat and plastic flow is referred to as a base material portion.

[0305] In addition, the base material portion and the joined portion and hot working affected portion described later are divided as follows.

[0306] That is, the joint of the electromagnetic steel strip is Fig.17 The cut surface is cut in the plate thickness (vertical) direction so that the surface shown (i.e., the surface including the vertical direction of the joint and the plate thickness direction) becomes the cut surface. Next, the cut surface is polished and etched using a saturated aqueous solution of picric acid, nital (a solution of nitric acid and ethanol) or aqua regia (a solution obtained by mixing concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1). Next, the cut surface is observed under an optical microscope and the base material part, the joint part and the hot working affected part are divided according to the degree of etching.

[0307] [Joint]

[0308] The joined portion is a region that is subjected to thermal working due to frictional heat and plastic flow between the rotating tool and the joined materials and becomes a recrystallized structure.

[0309] The joint portion is composed of a steel structure mainly composed of a ferrite phase, specifically, a ferrite phase with an area ratio of 95% or more. The area ratio of the ferrite phase may be 100%. In addition, the area ratio of the remaining structure other than the ferrite phase is 5% or less. As the remaining structure other than the ferrite phase, for example, a second phase such as martensite, sulfide, nitride, carbide, etc. can be exemplified. The area ratio of the remaining structure may also be 0%.

[0310] In addition, the area ratio of the ferrite phase was measured as follows.

[0311] That is, a test piece is cut out from the joint of the electrical steel strip so that the measurement area of ​​the joint described later is included in the observation surface. Fig.17 The surface shown (i.e., including the surface in the direction perpendicular to the joint and the direction of the plate thickness). Next, after the observation surface of the test piece is polished, it is etched using 3 vol.% nitric acid ethanol, a saturated aqueous solution of picric acid, or aqua regia to make the structure visible. Next, in the measurement area of ​​the joint described later, a total of 10 fields of view are photographed using an optical microscope at a magnification of 500 times. Next, based on the obtained organizational image, Adobe Photoshop from Adobe Systems is used to calculate the area of ​​the ferrite phase in the 10 fields of view. Next, the area of ​​the ferrite phase calculated for each field of view is divided by the area of ​​the respective field of view and multiplied by 100. Then, the arithmetic mean of these values ​​is taken as the area ratio of the ferrite phase.

[0312] In addition, it is important to refine the steel structure of the joint, specifically, to reduce the particle size of the ferrite crystal grains (hereinafter also referred to as the ferrite particle size) constituting the steel structure of the joint and make it satisfy the relationship of the following formula (3). As a result, even when an electromagnetic steel strip is used as the joined material, the shape of the coil joint is not deteriorated, the mechanical properties of the coil joint are improved, and the occurrence of fractures in the coil joint on the production line is effectively suppressed.

[0313] Dsz≤100μm…(3)

[0314] here,

[0315] Dsz is the average value (μm) of the ferrite grain size in the joint.

[0316] Here, Dsz is measured in accordance with JIS G 0551. Specifically, it is measured as follows.

[0317] That is, the joint of the electromagnetic steel strip is Fig.17The plane shown (i.e., the plane including the direction perpendicular to the joint and the direction of the plate thickness) is cut in the plate thickness (vertical) direction so that it becomes a cut plane. In this cut plane, the direction perpendicular to the joint is set as the X axis, and the direction of the plate thickness is set as the Y axis. Moreover, the center position of the joint in the direction perpendicular to the joint and the center position of the plate thickness of the joined member in the plate thickness (vertical) direction are set as the origin of the X axis and the Y axis. The center position of the joint in the direction perpendicular to the joint is, for example, the center position of the butt gap in the case of a butt joint, and the center position of the overlap in the case of an overlap joint. The center position of the plate thickness of the joined member in the plate thickness (vertical) direction is, for example, the center position of the plate thickness of the first electromagnetic steel strip and the second electromagnetic steel strip with a smaller plate thickness in the case of a butt joint, and the center position of the plate thickness of the overlap in the case of an overlap joint. Furthermore, the region of X=-0.2×t to +0.2×t and Y=-0.2×t to +0.2×t is set as the measurement region. Here, t is the average value (mm) of the plate thickness of the first electromagnetic steel strip and the plate thickness of the second electromagnetic steel strip. However, when the measurement region includes a non-joining region such as a hot working affected portion or a base material portion, the region is excluded from the measurement region. In addition, + and - may be arbitrarily set for the X-axis and the Y-axis.

[0318] Then, at any position within the above-mentioned measurement area, the ferrite grain size of the joint is measured 5 times by the cutting method (evaluated based on the number of grains captured per 1 mm test line or the number of intersections P) according to JIS G 0551 "Steel-Grain Size Microscope Test Method", and their average value is taken as Dsz. In addition, hereinafter, the measurement area of ​​the ferrite grain size of the joint is also referred to as the measurement area of ​​the joint.

[0319] In addition, it is important to reduce the hardness difference between the joint and the base material, and more specifically, it is important to satisfy the relationship of the following formula (6). Therefore, even when an electromagnetic steel strip is used as the joined material, the shape of the coil joint will not be deteriorated, the mechanical properties of the coil joint are improved, and the occurrence of fractures in the coil joint on the production line is effectively suppressed.

[0320] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2…(6)

[0321] here,

[0322] Hsz is the average hardness of the joint.

[0323] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0324] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0325] Here, Hsz, Hbm1, and Hbm2 are measured in accordance with JIS Z 2244. Specifically, each is measured as follows.

[0326] That is, the Vickers hardness (HV) is measured at any five locations in the measurement region of the above-mentioned joint portion on the above-mentioned cut surface under the condition of a test force of 4.9 N. Then, the average value thereof is defined as Hsz.

[0327] In addition, in the above-mentioned cut surface, the Vickers hardness (HV) is measured at any five locations within the area of ​​±0.2×t1 of the center position of the plate thickness of the base material portion of the first electromagnetic steel strip (horizontal plane of the plate thickness (vertical) direction) and within the area of ​​±0.2×t2 of the center position of the plate thickness of the base material portion of the second electromagnetic steel strip (horizontal plane of the plate thickness (vertical) direction) under the condition of a test force of 4.9N. In addition, the position in the vertical (horizontal) direction of the joint can be arbitrarily selected as long as it is the base material portion. And the average values ​​of the Vickers hardness (HV) measured at the base material portion of the first electromagnetic steel strip and the base material portion of the second electromagnetic steel strip are respectively referred to as Hbm1 and Hbm2. Here, t1 and t2 are the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip, respectively.

[0328] In addition, the thickness of the joint is not particularly limited, but it is preferable to appropriately control the relationship with the thickness of the first electromagnetic steel strip and the second electromagnetic steel strip, specifically, to satisfy the relationship of the following equations (7) and (8). Thus, even when an electromagnetic steel strip is used as a joined member, the shape of the coil joint is not deteriorated, the mechanical properties of the coil joint are further improved, and the occurrence of breakage in the coil joint on the production line can be more effectively suppressed.

[0329] 0.8×TbmL≤TszL…(7)

[0330] TszH≤1.3×TbmH…(8)

[0331] here,

[0332] TszL is the minimum thickness of the joint (mm),

[0333] TszH is the maximum thickness of the joint (mm),

[0334] TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips.

[0335] TbmH is the plate thickness (mm) of the thicker of the first and second electromagnetic steel strips.

[0336] However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

[0337] In addition, TszL and TszH may be measured, for example, as follows. Fig.17 The sheet is cut in the sheet thickness (vertical) direction so that the indicated surface (i.e., the surface including the joining perpendicular direction and the sheet thickness direction) becomes a cut surface. Then, TszL and TszH are measured on the cut surface using a vernier caliper or the like.

[0338] [Affected by hot working]

[0339] The hot working affected portion is a region adjacent to the joint portion, which is affected by hot working based on friction heat and plastic flow, but the temperature and working are insufficient to achieve a recrystallized structure. In addition, the hot working affected portion is adjacent to the joint portion and is formed on both sides of the first electromagnetic steel strip and the second electromagnetic steel strip.

[0340] The hot working affected portion is composed of a steel structure mainly composed of a ferrite phase, as is the case with the joint, and specifically, is composed of a ferrite phase with an area ratio of 95% or more. The area ratio of the ferrite phase may also be 100%. In addition, the area ratio of the remaining structure other than the ferrite phase is 5% or less. As the remaining structure other than the ferrite phase, for example, a second phase such as martensite, sulfide, nitride, carbide, etc. can be exemplified. The area ratio of the remaining structure may also be 0%. The area ratio of the ferrite phase may be measured in the same manner as the above method.

[0341] Furthermore, even in the hot working affected portion, the steel structure is refined, and specifically, the ferrite grain size of the hot working affected portion is made smaller than the ferrite grain size of the base material portion. That is, it is important to satisfy the following relationships (4) and (5).

[0342] Dhaz1≤Dbm1…(4)

[0343] Dhaz2≤Dbm2…(5)

[0344] here,

[0345] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0346] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0347] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0348] Dbm2 is an average value (μm) of the ferrite grain size of the base material portion of the second electrical steel strip.

[0349] Here, Dhaz1, Dhaz2, Dbm1, and Dbm2 are measured in accordance with JIS G 0551 in the same manner as Dsz, which is the average value of the ferrite grain size in the joint portion.

[0350] In addition, the measurement area of ​​the ferrite grain size of the hot working affected portion on the first electromagnetic steel strip side (hereinafter also referred to as the measurement area of ​​the hot working affected portion on the first electromagnetic steel strip side) is set as follows. That is, the joint joint of the electromagnetic steel strip is set as Fig.17 The surface shown (i.e., the surface including the direction perpendicular to the joint and the direction of the plate thickness) is cut in the plate thickness (vertical) direction so as to become a cut surface. In the above-mentioned cut surface, the direction perpendicular to the joint is set as the X-axis, and the plate thickness direction is set as the Y-axis. In addition, the boundary position between the joint portion at the center position of the plate thickness of the first electromagnetic steel strip (horizontal plane) and the hot working affected portion on the first electromagnetic steel strip side is set as the origin of the X-axis and the Y-axis. With respect to the X-axis, the first electromagnetic steel strip side is set as +, the joint portion side is set as -, and the area of ​​X=0 to +0.4×t1, Y=-0.2×t1 to +0.2×t1 is set as the measurement area. Here, t1 is the plate thickness of the first electromagnetic steel strip. In addition, with respect to the Y-axis, + and - may be set arbitrarily. However, when the above-mentioned measurement area includes an area other than the hot working affected portion on the first electromagnetic steel strip side such as a joint portion and a base material portion, the area is excluded from the measurement area.

[0351] As mentioned above, the joint portion refers to a region that is subjected to thermal processing based on frictional heat and plastic flow between the rotating tool and the workpiece to form a recrystallized structure. The hot working affected area is a region adjacent to the joint portion, which is affected by thermal processing based on frictional heat and plastic flow but the temperature and processing are insufficient to achieve a recrystallized structure. The parent material refers to a region that is not affected by thermal processing based on frictional heat and plastic flow.

[0352] Similarly, the measurement region of the ferrite grain size of the hot working affected portion on the second electromagnetic steel strip side (hereinafter also referred to as the measurement region of the hot working affected portion on the second electromagnetic steel strip side) is set as follows. Fig.17The surface shown (i.e., the surface including the direction perpendicular to the joint and the direction of the plate thickness) is cut in the plate thickness (vertical) direction so as to become a cut surface. In the above-mentioned cut surface, the direction perpendicular to the joint is set as the X-axis, and the plate thickness direction is set as the Y-axis. In addition, the boundary position between the joint portion at the center position of the plate thickness of the second electromagnetic steel strip (horizontal plane) and the hot working affected portion on the second electromagnetic steel strip side is set as the origin of the X-axis and the Y-axis. With respect to the X-axis, the second electromagnetic steel strip side is set as +, the joint portion side is set as -, and the area of ​​X=0 to +0.4×t2, Y=-0.2×t2 to +0.2×t2 is set as the measurement area. Here, t2 is the plate thickness of the second electromagnetic steel strip. In addition, with respect to the Y-axis, + and - may be set arbitrarily. However, when the above-mentioned measurement area includes an area other than the hot working affected portion on the second electromagnetic steel strip side such as a joint portion and a base material portion, the area is excluded from the measurement area.

[0353] In addition, the measurement area of ​​the ferrite grain size of the base material part of the first electromagnetic steel strip and the second electromagnetic steel strip (hereinafter, also referred to as the measurement area of ​​the base material part of the first electromagnetic steel strip and the second electromagnetic steel strip) is set to the area of ​​±0.2×t1 of the center position of the plate thickness of the base material part of the first electromagnetic steel strip in the above-mentioned cut surface (the horizontal plane in the plate thickness (vertical) direction) and the area of ​​±0.2×t2 of the center position of the plate thickness of the base material part of the second electromagnetic steel strip (the horizontal plane in the plate thickness (vertical) direction). In addition, the position in the vertical (horizontal) direction of the joint can be arbitrarily selected as long as it is the base material part. Here, t1 and t2 are the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip, respectively.

[0354] In addition, as the joint form, a butt joint and an overlap joint can be exemplified.

[0355] [3] Method for manufacturing electromagnetic steel strip

[0356] Next, a method for producing an electrical steel strip according to one embodiment of the present invention will be described.

[0357] A method for manufacturing an electrical steel strip according to one embodiment of the present invention comprises:

[0358] a step of joining a first electromagnetic steel strip and a second electromagnetic steel strip by the friction stir welding method of electromagnetic steel strips according to one embodiment of the present invention to obtain a joined steel strip; and

[0359] A step of cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

[0360] Here, it is preferred that the joined steel strip has a joint of the first electromagnetic steel strip, the second electromagnetic steel strip, and the electromagnetic steel strip described in [2] above, and the first electromagnetic steel strip and the second electromagnetic steel strip are joined via the joint of the electromagnetic steel strip.

[0361] In addition, the cold rolling conditions are not particularly limited and may be carried out according to a conventional method. In addition, pickling may be arbitrarily performed after the first electromagnetic steel strip and the second electromagnetic steel strip are joined and before cold rolling.

[0362] [4] Friction stir welding equipment

[0363] Next, a friction stir welding apparatus according to one embodiment of the present invention will be described.

[0364] A friction stir welding device according to one embodiment of the present invention is a friction stir welding device used in the friction stir welding method of the electromagnetic steel strip described in [1], and comprises:

[0365] A holding device for holding the joined parts;

[0366] a pair of rotating tools disposed opposite to each other;

[0367] A driving device capable of realizing the rotation of the rotating tool and the movement in the joining direction;

[0368] A cooling device is arranged on at least one surface of the workpiece to be joined and at the rear of the joining direction of the rotating tool; and

[0369] The above-mentioned holding device, the driving device of the above-mentioned rotating tool and the action control device of the above-mentioned cooling device.

[0370] Here, as the form of the holding device, for example, there can be cited:

[0371] A structure having a movable holding member and a sliding device for the movable holding member; and

[0372] A structure having a fixed holding member, a movable holding member, and a sliding device for the movable holding member.

[0373] The form of the rotating tool is as exemplified in the friction stir welding method of electromagnetic steel strips described in [1] above.

[0374] The driving device of the rotary tool may include a rotary drive unit for the rotary tool and a moving device for the rotary tool in the joining direction. The driving method of the rotary drive unit and the moving device is not particularly limited, and may be, for example, an electric driving method.

[0375] The cooling device is in the form of the method for friction stir welding of electromagnetic steel strips as exemplified in the above-mentioned [1]. In addition, the cooling device is provided with a moving device for moving the cooling device in conjunction with the rotating tool in the welding direction. The driving method of the moving device is not particularly limited, and may be, for example, an electric driving method.

[0376] As a form of motion control device, there can be cited a structure having an input unit for inputting data such as various set values, a calculation unit for performing calculations on the input data, a storage device for storing data, and an output unit for outputting motion signals to a holding device, a driving device of a rotating tool, and a cooling device based on the calculation results of the calculation unit.

[0377] In addition, from the viewpoint of controlling the cooling rate of the surface of the joining portion of the joined workpieces within the range of the above-mentioned formulas (10) to (12), (16), and (17), it is preferable to further include a cooling rate measuring device that measures CR on both surfaces of the joined workpieces. W＝0 , CR W＝0.2D and CR W＝0.5D .

[0378] The cooling rate measuring device is, for example, a temperature measuring device that continuously measures the temperature of the surface of the joint. As a form of the temperature measuring device, for example, there can be cited a structure in which a plurality of radiation thermometers are provided for measuring the temperature of the surface of the joint at the positions of W=0, 0.2×D and 0.5×D, a thermal imager (set to measure the temperature in a range including the positions of W=0, 0.2×D and 0.5×D), etc. Then, based on the temperature measured by the temperature measuring device and the time from the end of the joining to the time when the temperature of the surface of the joint reaches 450°C, for example, using a computing function attached to a computing device or a thermal imager, CR is calculated according to the above formula (18): W＝0 , CR W＝0.2D and CR W＝0.5D .

[0379] The device configurations other than those described above are not particularly limited, and may be the device configurations of conventionally known friction stir welding devices.

[0380] [5]Equipment for manufacturing electrical steel strip

[0381] Next, a manufacturing apparatus for an electrical steel strip according to an embodiment of the present invention will be described.

[0382] An apparatus for producing an electrical steel strip according to one embodiment of the present invention includes the friction stir welding apparatus described in [4].

[0383] In addition, in the manufacturing apparatus of the electromagnetic steel strip according to one embodiment of the present invention, the friction stir welding apparatus of [4] is arranged on the upstream side of the cold rolling apparatus or the upstream side of the pickling apparatus and the cold rolling apparatus (from the upstream side, the friction stir welding apparatus, the pickling apparatus, and the cold rolling apparatus, in that order). In addition, the pickling apparatus and the cold rolling apparatus can appropriately use apparatuses commonly used in the continuous cold rolling line of the electromagnetic steel strip.

[0384] In addition, a continuous cold rolling line refers to a production line that continuously cold rolls a steel strip by a cold rolling device. The continuous cold rolling line, for example, includes a conveying device for the steel strip and a cold rolling device. There are also cases where a pickling device, an annealing furnace, a coating device, etc. are optionally attached to the continuous cold rolling line.

[0385] In addition, the device configuration other than the above is not particularly limited, and the device configuration of a conventionally known electrical steel strip manufacturing device may be used.

[0386] Example

[0387] Hereinafter, the function and effect of the present invention will be described using examples. In addition, the present invention is not limited to the following examples.

[0388] The electromagnetic steel strips having the component composition shown in Table 1 (the remainder is Fe and inevitable impurities) are used as the joined parts (the first electromagnetic steel strip and the second electromagnetic steel strip). Furthermore, by post-cooling friction stir joining under the joining conditions and cooling conditions described in Table 2, the first electromagnetic steel strip (preceding steel strip) and the second electromagnetic steel strip (following steel strip) are simulated to be joined on a continuous cold rolling line, and a joint joint of the electromagnetic steel strips is manufactured. Here, in the case of butt-joining, the groove is set as a so-called I-type groove in which a groove angle is not formed on the end faces of the two electromagnetic steel strips as the joined parts, and the two electromagnetic steel strips are butted and joined in a surface state of milling degree. In addition, the average value of the ferrite grain size, the average value of the hardness, and the Erichsen cupping value (Erichsen value) of the base material part of the electromagnetic steel strip are also marked in Table 1. Here, the average value of the ferrite grain size and the average value of the hardness of the base material part of the electromagnetic steel strip are obtained by the above-mentioned method. The Erichsen cupping value is a value measured according to the Erichsen cupping test method specified in JIS Z 2247. In addition, conditions not explicitly described were set according to conventional methods.

[0389] In addition, during the joining process, the surface-side rotating tool arranged on the upper side in the vertical direction is rotated clockwise when viewed from the upper side in the vertical direction, and the back-side rotating tool arranged on the lower side in the vertical direction is rotated counterclockwise when viewed from the upper side in the vertical direction. That is, when the front end of each rotating tool is viewed from the front, they all rotate counterclockwise. Figure 8Any one of the rotating tools of the shape shown. In addition, the surface side rotating tool and the back side rotating tool use rotating tools with the same cross-sectional size and shape. In addition, these rotating tools are all made of tungsten carbide (WC) with a Vickers hardness of HV1090, which is harder than the workpiece to be joined. In addition, when the plate thickness of the first electromagnetic steel strip and the second electromagnetic steel strip is different, the butt joint of the first electromagnetic steel strip and the second electromagnetic steel strip is made so that the back side (the surface on the side where the back side rotating tool is configured) is in a state without steps, and the surface (the surface on the side where the surface side rotating tool is configured) is in a state with steps. In addition, the first electromagnetic steel strip (advancing steel strip) is joined to the advancing side (advancing side) and the second electromagnetic steel strip (retreating side) is joined to the retreating side (retreating side).

[0390] In the case of overlapping joining, the first electromagnetic steel strip (preceding steel strip) is overlapped on the upper side and the second electromagnetic steel strip (following steel strip) is overlapped on the lower side. The rotation direction and shape of the rotating tool are the same as those in the case of butt joining.

[0391] In the cooling process, a cooling device arranged behind the rotation tool in the joining direction is moved in conjunction with the rotation tool (at the same speed as the joining speed) in the joining direction. In addition, an inert gas injection device is used in the cooling device. In addition, carbon dioxide is used as the inert gas. More specifically, Fig.18 As shown in FIG. 1 , the cooling device has a structure in which five nozzles are arranged in a vertical row at the center of the joining line, and the nozzles have a circular injection port with a diameter of 4 mm. In addition, the distance from the rear end of the rotating tool to the frontmost injection port (front end) of the cooling device is ( Fig.18 L in the figure) and the (center point) spacing of each injection port ( Fig.18 The M in the friction stir welding apparatus is 30 mm. In addition, the distance from the surface of the joint to the injection port is 20 mm. Moreover, carbon dioxide gas is injected from each injection port at a pressure of 1 MPa. In addition, the surface temperature of the joint is measured on both sides of the joined parts by a thermal imager installed in the friction stir welding apparatus, and the cooling rate of the surface of the joint at each position is measured. The measured cooling rates are shown in Table 2. In addition, CR W＝0.2 and CR W＝0.5 The cooling rates were measured on both the forward side (first electromagnetic steel strip side) and the backward side (second electromagnetic steel strip side) with the center line of the joint sandwiched, but they were almost the same. Therefore, here, as a representative, only the cooling rate on the forward side is recorded. In addition, for comparison, cooling by the cooling device was not performed under some conditions.

[0392] The thus-obtained joined joint of the electrical steel strip is divided into a joined portion, a hot working affected portion, and a base material portion according to the above-described method.

[0393] In addition, the following values ​​were determined according to the above method:

[0394] Dsz: average ferrite grain size of the joint (μm),

[0395] Dhaz1: average value of the ferrite grain size of the hot working affected portion on the first electromagnetic steel strip side (μm),

[0396] Dhaz2: average value of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side (μm),

[0397] Dbm1: average value of ferrite grain size of the base material portion of the first electromagnetic steel strip (μm),

[0398] Dbm2: average value of the ferrite grain size of the base material portion of the second electrical steel strip (μm),

[0399] Hsz: average hardness of the joint,

[0400] Hbm1: average value of hardness of the base material portion of the first electromagnetic steel strip,

[0401] Hbm2: Average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0402] In addition, in the vertical direction cut surface ( Fig.17 On the surface shown (ie, the surface including the direction perpendicular to the joint and the plate thickness direction), TszL: the minimum value (mm) of the thickness of the joint portion and TszH: the maximum value (mm) of the thickness of the joint portion were measured.

[0403] The results are shown in Table 3. In the confirmation of surface defects and internal defects described below, if defects were confirmed, the above-mentioned measurement was omitted. In addition, if surface defects were confirmed, the confirmation of internal defects was also omitted.

[0404] In addition, the joints of the obtained electrical steel strips were checked for (I) the presence of surface defects and (II) the presence of internal defects in the following manner. The results are shown in Table 4.

[0405] (I) Presence of surface defects

[0406] The joint portion and the front and back surfaces of the hot working affected zone of the joint joint of the obtained electrical steel strip were visually observed to confirm the non-joined state and the presence of cracks. Then, the presence of surface defects was determined based on the following criteria.

[0407] No surface defects: No unbonded state or cracks were confirmed.

[0408] Surface defects: At least one of a non-bonded state and a crack is observed.

[0409] (II) Presence of internal defects

[0410] The obtained joint of the electromagnetic steel strip is Fig.17 The test piece was collected by cutting along the plate thickness (vertical) direction so that the surface shown (i.e., the surface including the vertical direction of the joint and the plate thickness direction) becomes the observation surface. In addition, the cutting position in the joining direction is a position 20 mm from the end of the joined part on the joining (welding) start side, a position 20 mm from the end of the joined part on the joining (welding) end side, and a position in the middle of the two ends of the joined part. Moreover, a total of 3 test pieces were collected so that the cut surface at the cutting position became the observation surface. Next, the observation surface of the obtained test piece was observed using an optical microscope (magnification: 10 times). Moreover, the presence or absence of internal defects was determined based on the following criteria.

[0411] No internal defects: No unbonded state or cracks were observed in the bonded portion in any of the three test pieces.

[0412] Internal defect: At least one of a non-bonded state and a crack was observed in the bonded portion of at least one test piece.

[0413] In addition, the effect of suppressing the occurrence of breakage at the coil joint on the production line (hereinafter also referred to as breakage suppression effect) was evaluated for the obtained joint joints of the electrical steel strips according to the following procedure.

[0414] That is, from the joint joint of the obtained electromagnetic steel strip, a test piece was collected in a manner including the joint portion, the hot working affected portion and the base material on the first electromagnetic steel strip side, and the hot working affected portion and the base material on the second electromagnetic steel strip side. Next, the collected test pieces were used to measure the Erichsen cupping value of the joint joint according to the Erichsen cupping test method specified in JIS Z 2247. In addition, the fracture suppression effect was evaluated according to the following criteria based on the ratio of the Erichsen cupping value of the joint joint to the Erichsen cupping value of the base material portion (hereinafter also referred to as the Erichsen cupping value ratio). The results are shown in Table 4.

[0415] [Ratio of Erichsen cupping value (%)] = [Erichsen cupping value of joint] / [Erichsen cupping value of parent material] × 100

[0416] Pass: Eriksson cupping value ratio is 90% or more

[0417] Disqualified: Erickson cupping value ratio is less than 90%

[0418] In addition, when the Erichsen cupping value of the base material portion of the first electromagnetic steel strip is different from the Erichsen cupping value of the base material portion of the second electromagnetic steel strip, the Erichsen cupping value of the base material portion is the smaller value of the Erichsen cupping value of the base material portion of the first electromagnetic steel strip and the Erichsen cupping value of the base material portion of the second electromagnetic steel strip.

[0419] In addition, the durability of the rotation tool was evaluated according to the following procedure.

[0420] That is, if the rotating tool is damaged or worn, there is a high probability that a poor joint will occur due to internal defects. Therefore, joints with a joint length of 0.5 m were repeatedly performed under the same conditions as above, and the presence of internal defects was determined for the obtained joints according to the determination method shown in the above "(II) Presence of internal defects".

[0421] Furthermore, the durability of the rotary tool was evaluated based on the maximum number of joints that maintained 90% or more of the total number of joints judged to be free of internal defects (hereinafter referred to as the 90% maintenance maximum number of joints). The 90% maintenance maximum number of joints is also noted in Table 4. In addition, when the 90% maintenance maximum number of joints is 15 times or more, the durability (life) of the rotary tool is judged to be excellent (qualified), and when the 90% maintenance maximum number of joints is less than 15 times, it is judged that the durability (life) of the rotary tool cannot be said to be sufficient (unqualified).

[0422] Here, 90% maintenance of the maximum number of joints means the maximum value of N that satisfies the following formula (a) when the number of joints for which the presence of internal defects is confirmed is N.

[0423] [The number of joints determined to have no internal defects among the joints whose internal defects were confirmed] ÷ [the number of joints whose internal defects were confirmed] × 100 ≥ 90 ... formula (a)

[0424] For example, when it is determined that the joints obtained by the first to fourth joining processes have no internal defects and the joints obtained by the fifth joining process have internal defects,

[0425] When N=4,

[0426] [Total number of joints without internal defects among the joints for which the presence or absence of internal defects was confirmed] ÷ [Number of joints for which internal defects were confirmed] × 100

[0427] =4÷4×100=100≥90,

[0428] When N=5,

[0429] [Total number of joints without internal defects among the joints for which the presence or absence of internal defects was confirmed] ÷ [Number of joints for which internal defects were confirmed] × 100

[0430] =4÷5×100=80<90.

[0431] That is, in this case, the formula (a) is satisfied until N=4, and the formula (a) is not satisfied for the first time when N=5, so the maximum number of engagements is maintained at 4 at 90%.

[0432] In addition, when it is determined that there is no internal defect in the joints obtained by the first to tenth and twelfth to nineteenth joinings, and when it is determined that there is an internal defect in the joints obtained by the eleventh, twentieth, and twenty-first joinings,

[0433] When N=11,

[0434] [Total number of joints without internal defects among the joints for which the presence or absence of internal defects was confirmed] ÷ [Number of joints for which internal defects were confirmed] × 100

[0435] =10÷11×100≈90.9≥90,

[0436] When N=20,

[0437] [Total number of joints without internal defects among the joints for which the presence or absence of internal defects was confirmed] ÷ [Number of joints for which internal defects were confirmed] × 100

[0438] =18÷20×100=90≥90,

[0439] When N=21,

[0440] [Total number of joints without internal defects among the joints for which the presence or absence of internal defects was confirmed] ÷ [Number of joints for which internal defects were confirmed] × 100

[0441] =18÷21×100=85.7<90.

[0442] That is, in this case, the formula (a) is satisfied until N=20, and the formula (a) is not satisfied for the first time when N=21, so the maximum number of engagements is maintained at 20 at 90%.

[0443] In addition, 90% of the joints determined to be defective in the above-mentioned (I) presence of surface defects or (II) presence of internal defects maintained the maximum number of joints at 0.

[0444]

[0445]

[0446]

[0447]

[0448]

[0449] According to Table 4, in all the inventive examples, high-efficiency joining was performed at a joining speed of 1000 mm / min or more, and a joined joint of an electromagnetic steel strip having no defects and an Erichsen cupping value ratio of 90% or more with an extremely excellent fracture suppression effect was obtained. In addition, the durability (life) of the rotating tool was also excellent.

[0450] On the other hand, in the comparative example, when the joining was performed at a joining speed of 1000 mm / min or more, a sufficient fracture suppression effect was not obtained.

[0451] Description of Reference Numerals

[0452] 1…first electromagnetic steel strip (joined workpiece); 2…second electromagnetic steel strip (joined workpiece); 3-1…rotating tool (rotating tool on the surface side); 3-2…rotating tool (rotating tool on the back side); 4…joining portion; 4-1…portion affected by thermal working (first electromagnetic steel strip side); 4-2…portion affected by thermal working (second electromagnetic steel strip side); 5-1, 5-2…shoulder portion; 6-1, 6-2…probe; 7…holding device; 9-1, 9-2…front end portion; 10-1…cooling device (cooling device on the surface side); 10-2…cooling device (cooling device on the back side); 11…driving device for the rotating tool; 12…motion control device.

Claims

1. A friction stir welding method for electromagnetic steel strips, wherein a first electromagnetic steel strip and a second electromagnetic steel strip as welded materials are welded by a pair of rotating tools facing each other, wherein: have: a joining step of pressing the rotating tool while rotating the rotating tool from both sides in opposite directions to each other at an unjoined portion of the joined members and moving the rotating tool in a joining direction, thereby joining the first electromagnetic steel strip and the second electromagnetic steel strip to form a joined portion; and a cooling step of cooling the joining portion by a cooling device disposed on at least one surface of the joined workpiece and behind the joining direction of the rotating tool; The unjoined portion of the joined member is a butting portion or an overlapping portion between an end portion of the first electromagnetic steel strip and an end portion of the second electromagnetic steel strip following the first electromagnetic steel strip. The joining process and the cooling process are continuously performed by moving the rotating tool and the cooling device in the joining direction in conjunction with each other. In addition, the diameter D (mm) of the shoulder of the rotary tool satisfies the following equation (1): RS×D is expressed by the rotation speed RS (r / min) of the rotation tool, the diameter D (mm) of the shoulder of the rotation tool, and the joining speed JS (mm / min). 3 / JS satisfies the following relationship (2): 4×TJ≤D≤10×TJ …(1) 200×TJ≤RS×D 3 / JS≤2000×TJ …(2) Here, when the unjoined portion is a butted portion, TJ is an average value (mm) of the thickness of the first electromagnetic steel strip and the thickness of the second electromagnetic steel strip. When the unjoined portion is an overlapping portion, TJ is the thickness (mm) of the overlapping portion.

2. The friction stir welding method for electromagnetic steel strip according to claim 1, characterized in that: In the joining step, the joining is performed under the condition that the steel structures of the joint portion and the hot working affected portion formed by joining the first electromagnetic steel strip and the second electromagnetic steel strip are respectively structures mainly composed of a ferrite phase and satisfy the relationship of the following equations (3) to (6). Dsz≤100μm …(3) Dhaz1≤Dbm1 …(4) Dhaz2≤Dbm2 …(5) 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2…(6) here, Dsz is the average ferrite grain size of the joint (μm), Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side, Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side, Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip, Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip, Hsz is the average hardness of the joint. Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip. Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

3. The friction stir welding method of electromagnetic steel strip according to claim 2, characterized in that: In the bonding step, bonding is performed under the condition that the relationship between the following equations (7) and (8) is satisfied: 0.8×TbmL≤TszL …(7) TszH≤1.3×TbmH …(8) here, TszL is the minimum thickness of the joint (mm), TszH is the maximum thickness of the joint (mm), TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips. TbmH is the thickness (mm) of the thicker of the first and second electromagnetic steel strips. However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

4. The friction stir welding method for electromagnetic steel strips according to any one of claims 1 to 3, characterized in that: In the joining process, the gap G (mm) between the shoulders of the rotating tool satisfies the following equation (9): 0.4×TJ≤G≤0.9×TJ …(9).

5. The friction stir welding method for electromagnetic steel strips according to any one of claims 1 to 3, characterized in that: The rotary tool is a probeless rotary tool.

6. The friction stir welding method of electromagnetic steel strip according to claim 5, characterized in that: The front end surface of the rotating tool is a plane, a convex curved surface or a concave curved surface.

7. The friction stir welding method of electromagnetic steel strip according to claim 6, characterized in that: The front end surface of the rotary tool has a spiral step portion rotating in opposite directions.

8. The friction stir welding method of electromagnetic steel strip according to claim 7, characterized in that: The spiral step portion gradually becomes lower from the center of the front end surface of the rotation tool toward the outer periphery.

9. The friction stir welding method for electromagnetic steel strips according to claim 7, characterized in that: The spiral step portion gradually increases in height from the center of the front end surface of the rotation tool toward the outer periphery.

10. The friction stir welding method for electromagnetic steel strips according to claim 5, characterized in that: The tilt angle α of the rotating tool is 0°.

11. The friction stir welding method for electromagnetic steel strips according to any one of claims 1 to 3, characterized in that: In the cooling step, cooling is performed under the conditions satisfying the relationship of the following equations (10) to (12): CR W＝0 ≥15 …(10) CR W＝0.2D ≥15 …(11) CR W＝0.5D ≥15 …(12) Here, CR W＝0 , CR W＝0.2D and CR W＝0.5D are the cooling rates (°C / s) of the surface of the joint from the end-of-joining temperature to 450°C at the positions of W=0, 0.2×D and 0.5×D respectively; W is the distance (mm) separated from the center line of the joint in the vertical direction of the joint; and D is the diameter of the shoulder of the rotating tool (mm).

12. The friction stir welding method for electromagnetic steel strips according to claim 11, characterized in that: The cooling device is an inert gas spraying device, a liquid spraying device or a device combining these.

13. A method for manufacturing an electromagnetic steel strip, characterized in that: have: A step of joining the first electromagnetic steel strip and the second electromagnetic steel strip by the friction stir welding method of electromagnetic steel strips according to claim 11 to obtain a joined steel strip; and A step of cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

14. A friction stir welding device used in the friction stir welding method of electromagnetic steel strips according to claim 11, characterized in that: have: A holding device for holding the joined parts; a pair of rotating tools disposed opposite to each other; a driving device for the rotating tool; a cooling device, arranged on at least one surface of the workpiece to be joined and behind the rotation tool in the joining direction; as well as The holding device, the driving device of the rotating tool and the motion control device of the cooling device.

15. The friction stir welding device according to claim 14, characterized in that: have: The cooling rate measuring device measures CR on both sides of the joint formed by the joined materials. W＝0 , CR W＝0.2D and CR W＝0.5D , Here, CR W＝0 , CR W＝0.2D and CR W＝0.5D are the cooling rates (°C / s) of the surface of the joint from the end-of-joining temperature to 450°C at the positions of W=0, 0.2×D and 0.5×D respectively; W is the distance (mm) separated from the center line of the joint in the vertical direction of the joint; and D is the diameter of the shoulder of the rotating tool (mm).

16. The friction stir welding device for electromagnetic steel strip according to claim 15, characterized in that: The cooling device is an inert gas spraying device, a liquid spraying device or a device combining these.

17. A manufacturing device for an electromagnetic steel strip, characterized in that: A friction stir welding device according to claim 15 is provided.

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