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 a fracture 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. The post-cooled double-sided friction stir welding is performed on the basis of conditions such that the steel structures of the bonded portion and the hot-working-affected portion formed by the welding each become a ferrite-phase-oriented structure and the relationships of formulae (1) to (4) are satisfied 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 pass rate, 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 the 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 is used, or a powder filler containing Ni as a main component is supplied 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] represent the contents (weight %) of Ni, Si, Cr and Mo in the weld metal, respectively. "

[0008] Patent Document 2 discloses:

[0009] "A laser welding method, characterized in that, in a method of butting a leading plate and a trailing plate and performing laser welding using a filler wire, the ratio (Gap / DEPO) of the butt gap (Gap) between the leading plate and the trailing plate at the initial stage of welding to the 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, characterized in that, in a welded portion formed by laser welding a preceding thin plate and a succeeding thin plate made of special steel conveyed on a continuous cold rolling line,

[0012] If the minimum thickness of the above-mentioned base material existing on the lower side of the upper extension protrusion is set as L1, and the minimum thickness of the above-mentioned base material clamped by the lower extension protrusion and the above-mentioned upper extension protrusion is set as L2, at least one of L1 and L2 is greater than zero, wherein 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 molten 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) deteriorate. 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 as a coil joint of an electromagnetic steel strip as described in Patent Documents 1 to 3, there is a problem that on a production line, such as a continuous cold rolling line, the productivity decreases due to breakage at the coil joint and production line stoppage. 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.

[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 for the friction stir welding method of the above-mentioned 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 was applied to coil joints 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, about 2.0 to 5.0 mass %. 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 technologies of the above-mentioned patent documents 1 to 3, a filler (filler) containing 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 technologies 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 martensitic 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 variation of the gap between the preceding steel strip and the succeeding steel strip affects the height of the weld. For example, when the height of the weld becomes high and the weld becomes excessively convex, if a load is applied to the weld, stress is concentrated on the weld stop. Therefore, even at this point, the variation of the gap between the preceding steel strip and the succeeding steel strip causes the breakage of the coil joint on the production line. In addition, the height of the weld can be removed by grinding or the like. However, the increase of such processes leads to a significant decrease in productivity.

[0036] In view of the above-mentioned points, the inventors have further repeatedly conducted various studies, and as a result, the inventors have conceived of applying friction stir welding as coil joining of electrical steel strips.

[0037] Here, friction stir welding refers to solid phase welding that utilizes the friction heat between the rotating tool and the joined material and the plastic flow of the joined material. That is, the unjoined portion (joining predetermined area) of the joined material is frictionally stirred by the rotating tool. If the unjoined portion of the joined material is heated by friction heat, plastic flow begins. Then, the interface between the plastic flow area and the parent material portion is greatly extended. As a result, clean interfaces without oxides are in contact with each other, and the joined materials will not melt to form a joint. Here, the joint is an area that becomes a recrystallized structure due to thermal processing based on the friction heat and plastic flow of the rotating tool and the joined material, and there is also a situation called a stirring portion. 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 and cannot reach recrystallization. This area is called a hot working affected area. In addition, there is also an area in the joined material that is not affected by thermal processing based on friction heat and plastic flow. This area is called a parent material portion. 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 has been applied to coil welding of electromagnetic steel strips.

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

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

[0040] As the joining method, so-called double-sided friction stir welding is applied.

[0041] In the joining process, the steel structures of the joint and the hot working affected part formed by joining are respectively ferrite-based, and the steel structures of the joint and the hot working affected part are refined, and the hardness difference between the joint and the base material is reduced. Specifically, the joining is performed under the condition that the following equations (1) to (4) are satisfied at the same time.

[0042] After the above-mentioned joining process, the joined portion is cooled by a cooling device.

[0043] Therefore, even when an electromagnetic steel strip is used as the joined material, the shape of the coil joint portion will not be deteriorated, and the mechanical properties of the coil joint portion are improved, so that the occurrence of fractures in the coil joint portion on the production line can be 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. In addition, hereinafter, double-sided friction stir welding in which the joint portion is cooled by a cooling device after the joining process is also referred to as post-cooling double-sided friction stir welding.

[0044] Dsz≤100μm… (1)

[0045] Dhaz1≤Dbm1… (2)

[0046] Dhaz2≤Dbm2… (3)

[0047] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2… (4)

[0048] here,

[0049] Dsz is the average ferrite grain size of the joint (μm),

[0050] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0051] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0052] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0053] Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip,

[0054] Hsz is the average hardness of the joint.

[0055] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0056] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0057] (e) In addition, it is preferred to select a condition that satisfies the relationship of the above-mentioned formulas (1) to (4) at the same time and further satisfies the relationship of the following formulas (5) and (6) for joining. Thus, even when an electromagnetic steel strip is used as the joined material, the shape of the coil joint portion will not be 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 can be more effectively suppressed.

[0058] 0.8×TbmL≤TszL… (5)

[0059] TszH≤1.3×TbmH… (6)

[0060] here,

[0061] TszL is the minimum thickness of the joint (mm),

[0062] TszH is the maximum thickness of the joint (mm),

[0063] TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips.

[0064] TbmH is the plate thickness (mm) of the thicker one of the first electromagnetic steel strip and the second electromagnetic steel strip.

[0065] However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

[0066] The present invention has been completed as a result of further studies based on the above findings.

[0067] That is, the gist of the present invention is as follows.

[0068] 1. A friction stir welding method for electromagnetic steel strips, which comprises joining a first electromagnetic steel strip and a second electromagnetic steel strip as materials to be joined by a pair of rotating tools facing each other, wherein:

[0069] a joining step in which the rotating tool is pressed against the unjoined portions of the materials to be joined from both sides while rotating in opposite directions to each other, and the rotating tool is moved in a joining direction, thereby joining the first electromagnetic steel strip and the second electromagnetic steel strip to form a joined portion; and

[0070] a cooling step in which the joining portion is cooled by a cooling device disposed on at least one surface of the joined material and behind the joining direction of the rotating tool,

[0071] The unjoined portion of the joined materials 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.

[0072] The rotating tool is moved in conjunction with the cooling device in the joining direction, thereby continuously performing the joining process and the cooling process.

[0073] 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 ferrite phase and the relationships of the following equations (1) to (4) are satisfied.

[0074] Dsz≤100μm…(1)

[0075] Dhaz1≤Dbm1… (2)

[0076] Dhaz2≤Dbm2… (3)

[0077] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2… (4)

[0078] here,

[0079] Dsz is the average ferrite grain size of the joint (μm),

[0080] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0081] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0082] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0083] Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip,

[0084] Hsz is the average hardness of the joint.

[0085] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0086] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

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

[0088] In the above-mentioned bonding step, bonding is performed under the condition that the relationship of the following formulas (5) and (6) is satisfied.

[0089] 0.8×TbmL≤TszL… (5)

[0090] TszH≤1.3×TbmH… (6)

[0091] here,

[0092] TszL is the minimum thickness of the joint (mm),

[0093] TszH is the maximum thickness of the joint (mm),

[0094] TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips.

[0095] TbmH is the plate thickness (mm) of the thicker one of the first electromagnetic steel strip and the second electromagnetic steel strip.

[0096] However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

[0097] 3. The friction stir welding method for electromagnetic steel strips according to 1 or 2 above, wherein:

[0098] In the cooling step, cooling is performed under conditions satisfying the relationships of the following equations (7) to (9).

[0099] CR W＝0 ≥15… (7)

[0100] CR W＝0.2D ≥15… (8)

[0101] CR W＝0.5D ≥15… (9)

[0102] 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) from the joint center line of the materials to be joined to the vertical direction of the joint. D is the diameter (mm) of the shoulder of the rotating tool.

[0103] 4. The friction stir welding method for electromagnetic steel strips according to any one of 1 to 3 above, wherein:

[0104] The cooling device is an inert gas jet device, a liquid jet device, or a combination thereof.

[0105] 5. A method for manufacturing an electromagnetic steel strip, comprising:

[0106] A step of joining the first electromagnetic steel strip and the second electromagnetic steel strip by the friction stir welding method for electromagnetic steel strips according to any one of 1 to 4 above to obtain a joined steel strip; and

[0107] The step of cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

[0108] 6. A friction stir welding device used in the friction stir welding method of electromagnetic steel strips according to any one of 1 to 4 above, comprising:

[0109] A holding device, wherein the holding device holds the materials to be joined;

[0110] a pair of rotating tools disposed opposite to each other;

[0111] A driving device for the above-mentioned rotary tool;

[0112] a cooling device, the cooling device being arranged at the rear of the rotation tool in the joining direction on at least one surface of the materials to be joined; and

[0113] 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.

[0114] 7. The friction stir welding apparatus according to 6 above, wherein:

[0115] A cooling rate measuring device is provided for measuring CR on both sides of the joint portion formed by the materials to be joined. W＝0 , CR W＝0.2D and CR W＝0.5D .

[0116] 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) from the joint center line of the materials to be joined to the vertical direction of the joint. D is the diameter (mm) of the shoulder of the rotating tool.

[0117] 8. The friction stir welding device for electromagnetic steel strips according to 6 or 7 above, wherein:

[0118] The cooling device is an inert gas jet device, a liquid jet device, or a combination thereof.

[0119] 9. A device for manufacturing an electromagnetic steel strip, wherein:

[0120] A friction stir welding device according to any one of 6 to 8 above is provided.

[0121] 10. A device for manufacturing an electromagnetic steel strip, wherein:

[0122] In a continuous cold rolling line, the friction stir welding apparatus described in any one of 6 to 8 above is arranged upstream of a cold rolling apparatus, or upstream of a pickling apparatus and a cold rolling apparatus.

[0123] According to the present invention, even when an electromagnetic steel strip is used as the joined material, 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 can be 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0124] Figure 1A It is a schematic diagram for explaining a friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention, and is a side perspective view showing an example of butt-joining by after-cooling double-sided friction stir welding.

[0125] Figure 1B yes Figure 1A AA view.

[0126] Figure 1C yes Figure 1A Top view of the .

[0127] Figure 1D yes Figure 1A Cross-sectional view at the joint center line position ( Figure 1C AA view).

[0128] Figure 2A This is a schematic diagram showing an example of the shape of a rotating tool used in the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention.

[0129] Figure 2B This is a schematic diagram showing an example of the shape of a rotating tool used in the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention.

[0130] Figure 3 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.

[0131] Figure 4 It is a schematic diagram for explaining a friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention, and is a plan view showing an example of butt-joining by after-cooling double-sided friction stir welding. DETAILED DESCRIPTION

[0132] The present invention will be described based on the following embodiments.

[0133] [1] Friction stir welding method of electromagnetic steel strip

[0134] First, use Figure 1A to Figure 1D A friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention will be described. Figure 1A to Figure 1D is a schematic diagram for explaining a friction stir welding method for an electromagnetic steel strip 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.

[0135] In the figure, reference numeral 1 is a first electromagnetic steel strip (material to be joined), 2 is a second electromagnetic steel strip (material to be joined), 3-1 is a rotating tool (surface (front) side rotating tool), 3-2 is a rotating tool (back side rotating tool), 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 (surface (front) side cooling device), 10-2 is a cooling device (back side cooling device), 11 is a driving device for the rotating tool, and 12 is a motion control device. In addition, Figure 1A In 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 (surface), the first appearance of the description of the surface (front) surface (side) is marked as the surface (front) surface.

[0136] In addition, Figure 1A to Figure 1D middle,

[0137] by the direction of engagement (direction of travel of the rotating tool);

[0138] The direction perpendicular to the joint direction (the direction perpendicular to the joint direction and perpendicular to the plate thickness direction, in Figure 1A to Figure 1D The width direction of the joint portion and the traveling direction of the electromagnetic steel strip are consistent); and

[0139] The arrangement of each part and the like are shown in the plate thickness direction (a direction perpendicular to the surface of the materials to be joined).

[0140] 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 dotted line is located closer to the front side of the cooling areas H and I on the paper surface.

[0141] In addition, the electromagnetic steel strip mentioned here means an intermediate product that becomes a 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, 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, as described later. Hereinafter, the electromagnetic steel strip in the state after the first electromagnetic steel strip and the second electromagnetic steel strip are joined is also referred to as a joined steel strip, and the electromagnetic steel strip after cold rolling the joined steel strip is also referred to as a cold-rolled steel strip.

[0142] Furthermore, the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention is characterized in that, as described above, post-cooling double-sided friction stir welding is applied as coil welding of the electromagnetic steel strip. On this basis, it is characterized in that the steel structure of the joint part and the hot working affected part is mainly a ferrite phase structure, and the steel structure of the joint part and the hot working affected part is refined to reduce the hardness difference between the joint part and the base material part.

[0143] More specifically, the friction stir welding method of electromagnetic steel strips according to one embodiment of the present invention is:

[0144] A friction stir welding method for electromagnetic steel strips for welding a first electromagnetic steel strip and a second electromagnetic steel strip as welding materials by a pair of mutually opposed rotating tools in a continuous cold rolling line, wherein:

[0145] a joining step in which the rotating tool is pressed against the unjoined portions of the materials to be joined from both sides while rotating in opposite directions to each other, and the rotating tool is moved in a joining direction, thereby joining the first electromagnetic steel strip and the second electromagnetic steel strip to form a joined portion; and

[0146] a cooling step in which the joining portion is cooled by a cooling device disposed on at least one surface of the joined material and behind the joining direction of the rotating tool,

[0147] The unjoined portion of the joined materials 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.

[0148] The rotating tool is moved in conjunction with the cooling device in the joining direction, thereby continuously performing the joining process and the cooling process.

[0149] 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 ferrite phase structures and the relationships of the above formulas (1) to (4) are satisfied.

[0150] Here, as preferred examples of the joint form, butt joint and lap joint can be cited.

[0151] Butt joining means that the first electromagnetic steel strip and the second electromagnetic steel strip are joined by rotating a rotating tool while pressing the rotating tool against a butt joint including the 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. Then, in this state, the rotating tool is moved in a joining direction, thereby joining the first electromagnetic steel strip and the second electromagnetic steel strip.

[0152] Overlapping means overlapping at least a portion of the ends of the first electromagnetic steel strip and the second electromagnetic steel strip, 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.

[0153] The butt joint and the lap joint differ only in the form of the unjoined portion, and the other device structures are basically the same. Figure 1A to Figure 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 materials to be joined are joined using a pair of rotating tools that are opposed to each other, and after a joint is formed in the materials to be joined, the joint is cooled by a cooling device arranged behind 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.

[0154] 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:

[0155] A holding device (not shown) for holding the materials to be joined;

[0156] a pair of rotating tools disposed opposite to each other;

[0157] A driving device for the above-mentioned rotary tool;

[0158] a cooling device arranged on at least one surface (side) of the materials to be joined and behind the rotation tool in the joining direction; and

[0159] 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.

[0160] 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.

[0161] 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 materials to be joined) as the materials to be joined. In addition, the cooling device is arranged behind the joining direction of the rotating tool in at least one side of the materials to be joined. In addition, the rotating tool arranged on the surface side (upper side in the vertical direction) of the material to be joined 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 material to be joined 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 material to be joined 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 material to be joined 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 center line of the joining shown in the figure, and are respectively held by a holding device.

[0162] Here, the center line of the joint is a line connecting the rotation axis of the rotating tool during the joint (on the surface of the material to be joined) through the set (target) position, and is parallel to the joint direction. In addition. The center line of the joint can also be referred to as the trajectory of the rotation axis of the rotating tool during the joint (on the surface of the material to be joined), usually, passing through the center position of the width direction of the joint. In the case of butt joint, this position, for example, as shown in Figure 1, becomes 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 lap joint, this position, for example, becomes 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.

[0163] Then, the rotating tool is rotated in opposite directions from both sides while pressing against the unjoined portion (predetermined joining area) of the joined material located on the joining center line, that is, 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 material is softened by the friction heat between the joined material 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 material to obtain a joint. Next, the joint is cooled by a cooling device arranged behind the rotating tool in the joining direction on at least one side. In particular, by cooling the joint by 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 having an extremely fine ferrite structure can be obtained, and the joint characteristics are improved. As a result, the occurrence of fractures and defects in the coil joint on the production line can be 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.

[0164] Hereinafter, the joining step and the cooling step of the friction stir welding method of the electromagnetic steel strip according to one embodiment of the present invention will be described in detail.

[0165] [Joining process]

[0166] In the joining process, the rotating tool is pressed against the unjoined portion of the materials to be joined from both sides while rotating in opposite directions. Then, in this state, the rotating tool is moved in the joining direction, thereby joining the first electromagnetic steel strip and the second electromagnetic steel strip as the materials to be joined to form a joint.

[0167] Furthermore, in the joining process, it is important to perform the joining under the condition that the steel structures of the joint portion and the hot working affected portion formed by the joining are respectively ferrite phase-based structures and satisfy the relationship of the following equations (1) to (4). Thus, even when an electromagnetic steel strip is used as the 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 fractures in the coil joint portion on the production line can be effectively suppressed.

[0168] Dsz≤100μm… (1)

[0169] Dhaz1≤Dbm1… (2)

[0170] Dhaz2≤Dbm2… (3)

[0171] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2… (4)

[0172] here,

[0173] Dsz is the average ferrite grain size of the joint (μm),

[0174] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0175] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0176] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0177] Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip,

[0178] Hsz is the average hardness of the joint.

[0179] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0180] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0181] In the friction stir welding method for electromagnetic steel strips according to one embodiment of the present invention, it is preferable to perform welding under conditions satisfying the relationship of the following equations (5) and (6).

[0182] 0.8×TbmL≤TszL… (5)

[0183] TszH≤1.3×TbmH… (6)

[0184] here,

[0185] TszL is the minimum thickness of the joint (mm),

[0186] TszH is the maximum thickness of the joint (mm),

[0187] TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips.

[0188] TbmH is the plate thickness (mm) of the thicker one of the first electromagnetic steel strip and the second electromagnetic steel strip.

[0189] However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

[0190] Note that the descriptions of the joined materials (the first electromagnetic steel strip and the second electromagnetic steel strip), the joined portion and the hot working affected portion, and the above-mentioned equations (1) to (6) are as described in [2] Joined joint of electromagnetic steel strips described later.

[0191] In addition, the steel structure of the joint and the hot working affected part is also affected by the cooling after joining. Therefore, while considering the influence of the cooling after joining, the steel structure of the joint and the hot working affected part is a ferrite phase-based structure, and the conditions of satisfying the relationship of the above-mentioned formulas (1) to (4), preferably further satisfying the relationship of the above-mentioned formulas (5) and (6) are used for joining. For example, it is preferable to satisfy the following points.

[0192] RS×D represented by the rotation speed RS (turns / minute) of the rotary tool, the diameter D (mm) of the shoulder of the rotary tool, and the welding speed JS (mm / minute) 3 / JS satisfies the relationship of the following equations (10) and (11).

[0193] 4×TJ≤D≤10×TJ… (10)

[0194] 200×TJ≤RS×D 3 / JS≤2000×TJ… (11)

[0195] Here, when the unjoined portion is a butted portion, TJ in equations (10) and (11) is the average value (mm) of the thickness of the first electromagnetic steel strip and the thickness of the second electromagnetic steel strip,

[0196] When the unjoined portion is an overlapping portion, TJ in equations (10) and (11) is the thickness (mm) of the overlapping portion (i.e., the total thickness (mm) of the first electromagnetic steel strip and the thickness (mm) of the second electromagnetic steel strip).

[0197] 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 materials, and the shear stress generated by the friction force can be effectively applied to the joined material. 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 expands unnecessarily, and too much heat is input to the joint. As a result, the recrystallized structure of the joint is coarsened, and it is difficult to obtain the target mechanical properties. Therefore, the shoulder diameter D preferably satisfies the relationship of the above formula (10).

[0198] 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 materials to be joined, and the shear stress caused by the friction force to the materials to be joined. 3 If / 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 electromagnetic steel strip and the second electromagnetic steel strip, 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 the 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 preferably satisfies the relationship of the above formula (11). RS×D 3 / JS is more preferably 240×TJ or more. 3 / JS is more preferably 1200×TJ or less.

[0199] 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 front side rotation tool and the back side rotation tool satisfy the relationship of the above-mentioned equations (10) and (11), respectively.

[0200] In the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention, it is preferred that the inclination angle α of the rotating tool satisfies the relationship of the following formula (12).

[0201] 0°<α≤2°… (12)

[0202] 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 material) relative to the plate thickness direction (the direction perpendicular to the surface of the joined material). In addition, the direction (angle) of the front end of the rotating tool relative to the joining direction is set to +.

[0203] That is, the rotating tool is made of a material harder than the material being joined. However, in a rotating tool using a material that lacks toughness, such as ceramics, if a force in the bending direction is applied to the probe, there is a concern that stress will be locally concentrated, leading to damage. In this regard, if the rotation axis of the tool is tilted by α (°) from the plate thickness direction and the front end of the probe is advanced relative to the joining direction, the load relative to the rotating tool can be borne by the rotating tool as a component force compressed in the direction of the rotation axis. In this way, the force in the bending direction can be reduced and damage to the rotating tool can be avoided.

[0204] Here, if the inclination angle α of the rotating tool exceeds 0°, the above-mentioned effect can be obtained. However, if the inclination angle α of the rotating tool exceeds 2°, the front and back surfaces of the joint are likely to become concave. As a result, the minimum thickness of the joint is reduced relative to the thickness of the parent material. As a result, there is a situation where the joint strength is adversely affected, resulting in the occurrence of fractures in the coil joint on the production line. Therefore, the inclination angle α of the rotating tool is preferably set to the range of 0°<α≤2° for both the surface side rotating tool and the back side rotating tool.

[0205] In the friction stir welding method of an electromagnetic steel strip according to one embodiment of the present invention, it is preferred that the gap G (mm) between the shoulders of the rotating tool satisfies the relationship of the following formula (13).

[0206] 0.5×TJ-0.1×D×sinα≤G≤0.9×TJ-0.1×D×sinα… (13)

[0207] That is, in double-sided friction stir welding, from the viewpoint of suppressing the occurrence of defects during welding and increasing the welding speed, it is necessary to appropriately control Figure 1DThe gap G between the shoulders of the rotating tool shown (hereinafter, also referred to as the gap G between shoulders) is advantageous. 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 0.5×TJ-0.1×D×sinα to 0.9×TJ-0.1×D×sinα, the shoulders of the rotating tools facing each other are in close contact with the surface side and the back side of the material to be joined or are pressed into the surface side and the back side of the material to be joined. As a result, the material to be joined is pressed from the surface side and the back side by the shoulder of the rotating tool with sufficient load, which is advantageous in suppressing the generation of defects during joining and achieving a higher joining speed. Therefore, the gap G between shoulders is preferably in the range of 0.5×TJ-0.1×D×sinα to 0.9×TJ-0.1×D×sinα.

[0208] The conditions other than the above are not particularly limited as long as they satisfy the relationships of the above formulae (1) to (4), and may be carried out according to a conventional method.

[0209] For example, the rotation speed of the rotating tool is preferably 300 to 9000 r / min (turns / minute). By setting the rotation speed of the rotating tool within this range, the surface shape can be well maintained and the reduction in mechanical properties caused by excessive heat input can be suppressed, which is advantageous. 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.

[0210] The joining speed is preferably 800 to 5000 mm / min (mm / minute), and more preferably 1000 mm / min to 4000 mm / min.

[0211] 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.

[0212] 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 material. In addition, it is preferred that the rotation speed of the surface side rotating tool and the rotation speed of the back side rotating tool are the same. Thus, the rotational torque applied to the joined material by 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 portion is pressed from one surface to perform joining, the structure of the fixture that constrains the joined material can be simplified.

[0213] 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 observed from the surface side (or back side) of the material to be joined, 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 material to be joined is close to a homogeneous state, and the plastic deformation also becomes smaller. Therefore, the heat caused by the plastic deformation of the material cannot be obtained, and it is difficult to achieve a good joining state. Therefore, 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 material to be joined, 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 observed from the surface side (or back side) of the material to be joined.

[0214] In addition, 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, and a conventional method may be used.

[0215] For example, the front end portion of the rotating tool contacts the first electromagnetic steel strip and the second electromagnetic steel strip as the materials to be joined 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, high stirring capacity can be continuously achieved, and proper 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 be formed of a material that is harder than the first electromagnetic steel strip and the second electromagnetic steel strip.

[0216] As an example of a rotating tool used in double-sided friction stir welding, Figure 2A and Figure 2B The figure shows a shape in which the tip of the rotary tool includes a shoulder (a range indicated by the shoulder diameter in the figure) and a probe (a range indicated by the pin diameter in the figure) which is arranged on the shoulder and shares a rotation axis with the shoulder.

[0217] 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.

[0218] exist Figure 2B In the example of the rotation tool shown, the shape of the rotation tool is shoulder diameter D: 21 mm, pin diameter: 6.7 mm, pin length: 0.9 mm, and concave depth (not shown): 0.3 mm.

[0219] The shoulder has a flat shape formed by a substantially flat surface or a gently curved surface. The shoulder has the function of contacting the first electromagnetic steel strip and the second electromagnetic steel strip while rotating during joining to generate frictional heat. In addition, the shoulder has the function of preventing the material from dispersing by pressing the portion softened by heat and promoting plastic flow in the rotation direction.

[0220] The probe is discontinuous with the shoulder and protrudes approximately vertically toward the material to be joined (not shown). The probe has a function of penetrating the softened portion of the first and second electromagnetic steel strips toward the center of the plate thickness during joining, thereby improving the stirring capacity near the center of the plate thickness. In addition, the probe is usually located at the center of the shoulder.

[0221] As described above, the shoulder diameter D (mm) preferably satisfies the relationship of the above-mentioned equations (10) and (11). 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 average value of the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip can be considered, and the pin diameter and pin length of the rotating tool can be set according to conventional methods. In addition, when the first electromagnetic steel strip and the second electromagnetic steel strip are overlapped, the total value of the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip can be considered, and the pin diameter and pin length of the rotating tool can be set according to conventional methods.

[0222] As a rotating tool, in addition to using a rotating tool whose front end portion is composed of a shoulder and a probe (hereinafter, also referred to as a rotating tool with a probe), a probeless rotating tool whose front end portion is composed of only a shoulder (hereinafter, also referred to as a probeless rotating tool) can also be used. As a probeless rotating tool, for example, a probeless rotating tool can be cited in which the front end face of the rotating tool (the contact surface with the material to be joined) is a plane, a convex curved surface, or a concave curved surface. In addition, in the case of a probeless rotating tool, the shoulder diameter D can also be referred to as the front end diameter. The front end diameter is the diameter of the front end face of the rotating tool on the plane perpendicular to the rotation axis (the diameter of the projection area when the front end face of the rotating tool is projected in a direction parallel to the rotation axis).

[0223] [Cooling process]

[0224] In the cooling process, a cooling device is arranged on at least one surface (side) of the joined material behind the joining direction of the rotating tool, and the joint portion of the joined material 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 portion by means of 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 portion having an extremely fine ferrite structure can be obtained, and the joint characteristics are improved. As a result, the occurrence of fractures and defects in the joint portion of the coil on the production line can be extremely effectively suppressed. In addition, the joining speed can be increased, and high construction efficiency can be achieved.

[0225] Next, use Figure 1C , taking the case where the cooling device is arranged on both sides of the joined material (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 portion from the joint end temperature to 450°C. In addition, the joint end temperature is the temperature of the surface of the joint portion at the moment of joint end, that is, the moment of passage of the rotating tool. That is, the cooling rate of each part can be calculated by the following formula.

[0226] [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)]… (16)

[0227] Moreover, it is preferred that the cooling rate satisfies the following requirements on both sides of the joint portion formed in the joined materials. In addition, when the cooling device is only arranged on any one side of the joined materials, such as the surface (front) side (hereinafter, also referred to as single-sided arrangement), as long as the cooling rate satisfies the following requirements on both sides of the joint portion formed in the joined materials, the same effect can be obtained. Therefore, the description of the example of single-sided arrangement is omitted.

[0228] CR W＝0 ≥15… (7)

[0229] CR W＝0.2D ≥15… (8)

[0230] CR W＝0.5D ≥15… (9)

[0231] 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 using 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 at the positions of W=0, 0.2×D and 0.5×D as representative positions of these cooling areas, are effective. From this point of view, it is preferred to control the cooling rate to satisfy the relationship of the above-mentioned formulas (7) to (9).

[0232] Here, W is the distance (mm) from the center line of the materials to be joined 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.

[0233] 0.80≤CR W＝0.2D / CR W＝0 ≤1.20… (14)

[0234] 0.80≤CR W＝0.5D / CR W＝0 ≤1.20… (15)

[0235] Furthermore, in the cooling process, it is more preferable that the cooling rate of the joined materials further satisfies the relationship of the above-mentioned equations (14) and (15) on the basis of satisfying the relationship of the above-mentioned equations (7) to (9). That is, in order to obtain the effect of preventing the coarsening of ferrite recrystallized grains by cooling the joint using a cooling device after joining, it is effective to increase the cooling rate of the joint. However, if the cooling rate varies due to the position of the surface of the joint, 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 also varies. The deviation in the ferrite grain size of the joint leads to the deviation in the mechanical properties of the joint, so it is desired that the ferrite grain size of the joint is uniform. For this reason, it is effective to uniformly control the cooling rate 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, for 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 (14) and (15).

[0236] 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.

[0237] In the inert gas injection device, as the 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, etc. 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 (7) to (9), and further satisfy the relationship between the above-mentioned equations (14) and (15).

[0238] 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 and number of the liquid injection ports can be adjusted in accordance with the size of the cooling area of ​​the joint, etc., 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 (7) to (9), and further satisfy the relationship between the above equations (14) and (15).

[0239] Furthermore, as the cooling device, a device in which a plurality of cooling devices are combined may be used, for example, a device in which the above-mentioned inert gas spraying device and liquid spraying device are combined.

[0240] In addition, as long as the cooling device is arranged behind the joining (progress) direction of the rotating tool in at least one surface of the joined material, 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, the positional relationship between the cooling device and the rotating tool is preferably 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.

[0241] [2] Joints of electrical steel strips

[0242] Next, use Figure 3 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 (first electromagnetic steel strip side), and 4-2 is the hot working affected part (second electromagnetic steel strip side). In addition, Figure 3 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, Figure 3 The shown plane (herein, the cross section in the plate thickness direction) includes the joining vertical direction and the plate thickness direction.

[0243] The above-mentioned electromagnetic steel strip joint joins the first electromagnetic steel strip and the second electromagnetic steel strip, wherein:

[0244] The joint of the electromagnetic steel strip includes a joint portion and a hot working affected portion adjacent to the joint portion.

[0245] The steel structures of the joint and the hot working affected part are mainly ferrite phase.

[0246] The following relationships (1) to (4) are satisfied.

[0247] Dsz≤100μm… (1)

[0248] Dhaz1≤Dbm1… (2)

[0249] Dhaz2≤Dbm2… (3)

[0250] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2≤(Hbm1+Hbm2) / 2… (4)

[0251] here,

[0252] Dsz is the average ferrite grain size of the joint (μm),

[0253] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0254] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0255] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0256] Dbm2 is the average value (μm) of the ferrite grain size of the base material portion of the second electromagnetic steel strip,

[0257] Hsz is the average hardness of the joint.

[0258] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0259] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0260] 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.

[0261] [Materials to be joined (first electromagnetic steel strip and second electromagnetic steel strip)]

[0262] The first and second electromagnetic steel strips are electromagnetic steel strips as materials to be joined. 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.

[0263] 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, in the above composition, 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 can be arbitrarily contained in terms of mass%. In addition, in the above composition, at least one selected from the group consisting of Cr: 1% or less, Ni: 1% or less, and Cu: 1% or less can be arbitrarily contained in terms of mass%. Furthermore, elements other than Si and Fe may be 0%.

[0264] In addition, the component compositions of the first electromagnetic steel strip and the second electromagnetic steel strip may be the same or different.

[0265] 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.

[0266] In addition, in the first and second electromagnetic steel strips as the materials to be joined, a region that is not affected by hot working due to frictional heat and plastic flow is referred to as a base material portion.

[0267] In addition, the base material portion and the joined portion and hot working affected portion described later are divided as follows.

[0268] That is, the joint of the electromagnetic steel strip is Figure 3 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.

[0269] [Joint]

[0270] 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.

[0271] 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%.

[0272] In addition, the area ratio of the ferrite phase was measured as follows.

[0273] That is, a test piece was cut out from the joint of the electrical steel strip so that the measurement area of ​​the joint described later was included in the observation surface. Figure 3 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.

[0274] 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 ferrite particle size) constituting the steel structure of the joint so as to satisfy the relationship of the following formula (1). Thus, 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 can be effectively suppressed.

[0275] Dsz≤100μm…(1)

[0276] here,

[0277] Dsz is the average value (μm) of the ferrite grain size in the joint.

[0278] Here, Dsz is measured in accordance with JIS G 0551. Specifically, it is measured as follows.

[0279] That is, the joint of the electromagnetic steel strip is Figure 3The 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, which is the center position of the plate thickness of the materials to be joined in the plate thickness (vertical) direction, is 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 a lap joint. The center position of the plate thickness of the materials to be joined 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 a lap 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 region other than a joining portion such as a hot working affected portion or a base material portion, the region is excluded from the measurement region. In addition, with respect to the X-axis and the Y-axis, + and - may be arbitrarily set.

[0280] Then, at any position within the above-mentioned measurement area, the ferrite grain size of the joint is measured 5 times in total 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-Microscope test method for grain size", and their average value is set 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.

[0281] In addition, it is important to reduce the hardness difference between the joint and the base material, specifically to satisfy the relationship of the following formula (4). Thus, 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 can be effectively suppressed.

[0282] 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2… (4)

[0283] here,

[0284] Hsz is the average hardness of the joint.

[0285] Hbm1 is the average hardness of the base material portion of the first electromagnetic steel strip.

[0286] Hbm2 is an average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0287] Here, Hsz, Hbm1, and Hbm2 are measured in accordance with JIS Z 2244. Specifically, each is measured as follows.

[0288] 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.

[0289] 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. Then, the average values ​​of the Vickers hardness (HV) measured in the base material portion of the first electromagnetic steel strip and the base material portion of the second electromagnetic steel strip are set to Hbm1 and Hbm2, respectively. Here, t1 and t2 are the plate thicknesses of the first electromagnetic steel strip and the second electromagnetic steel strip, respectively.

[0290] In addition, the thickness of the joint is not particularly limited, but it is preferable to appropriately control the relationship between the thickness of the first electromagnetic steel strip and the second electromagnetic steel strip, specifically, to satisfy the relationship of the following equations (5) and (6). Thus, even when an electromagnetic steel strip is used as the material to be joined, the shape of the coil joint is not deteriorated, the mechanical properties of the coil joint are further improved, and the occurrence of breakage at the coil joint on the production line can be more effectively suppressed.

[0291] 0.8×TbmL≤TszL… (5)

[0292] TszH≤1.3×TbmH… (6)

[0293] here,

[0294] TszL is the minimum thickness of the joint (mm),

[0295] TszH is the maximum thickness of the joint (mm),

[0296] TbmL is the thickness (mm) of the thinner one of the first and second electromagnetic steel strips.

[0297] TbmH is the plate thickness (mm) of the thicker of the first and second electromagnetic steel strips.

[0298] However, when the first electromagnetic steel strip and the second electromagnetic steel strip have the same thickness, TbmL=TbmH.

[0299] In addition, TszL and TszH may be measured, for example, as follows. Figure 3 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.

[0300] [Parts affected by hot working]

[0301] The hot working affected portion is a region adjacent to the joint portion, and although it is affected by hot working based on friction heat and plastic flow, it does not reach a recrystallized structure due to insufficient temperature and working. In addition, the hot working affected portion is formed adjacent to the joint portion on both sides of the first electromagnetic steel strip and the second electromagnetic steel strip.

[0302] The hot working affected portion is similar to the joint portion, and 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 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 can be measured in the same manner as the above method.

[0303] Furthermore, even in the hot working affected portion, it is important to refine the steel structure, and specifically, to make the ferrite grain size of the hot working affected portion smaller than the ferrite grain size of the base material portion, that is, to satisfy the following relationships (2) and (3).

[0304] Dhaz1≤Dbm1… (2)

[0305] Dhaz2≤Dbm2… (3)

[0306] here,

[0307] Dhaz1 is the average value (μm) of the ferrite grain size of the hot working affected zone on the first electromagnetic steel strip side,

[0308] Dhaz2 is the average value (μm) of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side,

[0309] Dbm1 is the average value (μm) of the ferrite grain size of the base material portion of the first electromagnetic steel strip,

[0310] Dbm2 is an average value (μm) of the ferrite grain size of the base material portion of the second electrical steel strip.

[0311] 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.

[0312] 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 Figure 3 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. Then, 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 - can be set arbitrarily. However, in the above-mentioned measurement area, when an area that is not the hot working affected portion on the first electromagnetic steel strip side, such as a joint portion and a base material portion, is included, the area is excluded from the measurement area.

[0313] As mentioned above, the joint portion refers to a region that is subjected to thermal processing by friction heat and plastic flow between the rotating tool and the material to be joined and becomes a recrystallized structure. The hot working affected portion refers to a region adjacent to the joint portion, which is affected by thermal processing based on friction heat and plastic flow, but does not reach a recrystallized structure due to insufficient temperature and processing. The parent material refers to a region that is not affected by thermal processing based on friction heat and plastic flow.

[0314] 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. Figure 3The 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. Then, the boundary position of 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 - can be set arbitrarily. However, in the above-mentioned measurement area, when an area that is not the hot working affected portion on the second electromagnetic steel strip side, such as a joint portion and a base material portion, is included, the area is excluded from the measurement area.

[0315] 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) can be set to the area of ​​±0.2×t1 (horizontal plane in the plate thickness (vertical) direction) 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 and the area of ​​±0.2×t2 (horizontal plane in the plate thickness (vertical) direction) of the center position of the plate thickness of the base material part of the second electromagnetic steel strip. 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.

[0316] In addition, as the joint form, a butt joint and a lap joint can be exemplified.

[0317] [3] Method for manufacturing electromagnetic steel strip

[0318] Next, a method for producing an electrical steel strip according to one embodiment of the present invention will be described.

[0319] A method for manufacturing an electrical steel strip according to one embodiment of the present invention comprises:

[0320] 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

[0321] The step of cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

[0322] Here, the joined steel strip preferably 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.

[0323] In addition, the cold rolling conditions are not particularly limited, and may be carried out according to a conventional method. In addition, after the first electromagnetic steel strip and the second electromagnetic steel strip are joined, pickling may be arbitrarily performed before cold rolling.

[0324] [4] Friction stir welding equipment

[0325] Next, a friction stir welding apparatus according to an embodiment of the present invention will be described.

[0326] 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 includes:

[0327] A holding device, wherein the holding device holds the materials to be joined;

[0328] a pair of rotating tools disposed opposite to each other;

[0329] A driving device capable of rotating the rotary tool and moving it in a joining direction;

[0330] a cooling device, the cooling device being arranged on at least one surface of the materials to be joined and at the rear of the rotating tool in the joining advancing direction; and

[0331] 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.

[0332] Here, as the form of the holding device, for example, there can be cited:

[0333] A holding device having a movable holding member and a sliding device for the movable holding member; and

[0334] A configuration having a fixed holding member, a movable holding member, and a sliding device for the movable holding member.

[0335] The form of the rotating tool is as exemplified in the friction stir welding method of electromagnetic steel strips described in [1] above.

[0336] The driving device of the rotary tool may include a rotary drive unit for the rotary tool and a moving device for moving 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 an electric drive method, for example.

[0337] The cooling device is in the form of the friction stir welding method for 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 and the rotating tool in the welding direction in conjunction with each other. The driving method of the moving device is not particularly limited, and an electric driving method may be used, for example.

[0338] As a form of motion control device, there can be cited a form 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 in the calculation unit.

[0339] In addition, from the viewpoint of controlling the cooling rate of the surface of the joining portion of the materials to be joined within the range of the above-mentioned formulas (7) to (9), (14), and (15), it is preferable to further include a cooling rate measuring device that measures CR on both sides of the materials to be joined. W＝0 , CR W＝0.2D and CR W＝0.5D .

[0340] The cooling rate measuring device is, for example, a temperature measuring device that continuously measures the temperature of the surface of the joint. Examples of the temperature measuring device include a device that has a plurality of radiation-type thermometers for measuring the temperature of the surface of the joint at positions W=0, 0.2×D, and 0.5×D, and a thermal imager (set to capture and measure the temperature of a range including positions W=0, 0.2×D, and 0.5×D). Then, based on the temperature measured by the temperature measuring device and the time from the end of the joint to the time when the temperature of the surface of the joint reaches 450°C, CR is calculated according to the above formula (16) using, for example, a computing function attached to a computing device or a thermal imager. W＝0 , CR W＝0.2D and CR W＝0.5D .

[0341] In addition, the device structure and the like other than the above are not particularly limited, and any device structure of a conventionally known friction stir welding device may be used.

[0342] [5]Equipment for manufacturing electrical steel strip

[0343] Next, a manufacturing apparatus for an electrical steel strip according to an embodiment of the present invention will be described.

[0344] 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].

[0345] In addition, in the manufacturing apparatus of the electromagnetic steel strip according to one embodiment of the present invention, the friction stir welding apparatus described in [4] is arranged on the upstream side of the cold rolling apparatus, or on the upstream side of the pickling apparatus and the cold rolling apparatus (from the upstream side, in the order of the friction stir welding apparatus, the pickling apparatus, and the cold rolling apparatus). In addition, the pickling apparatus and the cold rolling apparatus can be appropriately used as the apparatus commonly used in the continuous cold rolling line of the electromagnetic steel strip.

[0346] In addition, a continuous cold rolling line refers to a production line that continuously cold rolls a steel strip through a cold rolling device. A continuous cold rolling line, for example, includes a conveying device for the steel strip and a cold rolling device. In the continuous cold rolling line, there is also a case where a pickling device, an annealing furnace, a coating device, etc. are further attached.

[0347] In addition, the device configuration other than the above is not particularly limited, and may be a device configuration of a conventionally known electrical steel strip manufacturing device.

[0348] Example

[0349] 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.

[0350] The electromagnetic steel strips having the component composition shown in Table 1 (the remainder is Fe and inevitable impurities) are used as the materials to be joined (the first electromagnetic steel strip and the second electromagnetic steel strip). And, by post-cooling friction stir joining under the joining conditions and cooling conditions described in Table 2, the first electromagnetic steel strip (previous 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 of the electromagnetic steel strips is manufactured. Here, in the case of butt-joining, the groove is 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 materials to be joined, 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 of the parent material 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 parent material of the electromagnetic steel strip are obtained by the above-mentioned method. In addition, the Erichsen cupping value is a value measured according to the Erichsen cupping test method specified in JISZ 2247. In addition, the conditions not explicitly described were set according to the conventional methods.

[0351] 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 2A and Figure 2BAny one of the two types of rotating tools with cross-sectional dimensions and shapes shown. In addition, rotating tools with the same cross-sectional dimensions and shapes are used for the surface side rotating tool and the back side rotating tool. In addition, these rotating tools are all made of tungsten carbide (WC) with a Vickers hardness of HV1090, which is harder than the material to be joined. In addition, when the plate thickness of the first electromagnetic steel strip and the second electromagnetic steel strip is different, in the joint portion of the first electromagnetic steel strip and the second electromagnetic steel strip, the back side (the surface on the side where the back side rotating tool is configured) is set to a state without steps, and the surface (the surface on the side where the surface side rotating tool is configured) is set to a state with steps. In addition, the joining is carried out in such a manner that the first electromagnetic steel strip (the leading steel strip) becomes the advancing side and the second electromagnetic steel strip (the trailing steel strip) becomes the retreating side.

[0352] In the case of lap jointing, 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 direction of rotation of the rotating tool and the shape of the rotating tool are the same as those in the case of butt jointing.

[0353] 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, Figure 4 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 injection port (front end) of the front end of the cooling device is ( Figure 4 L in the figure) and the (center point) spacing of each injection port ( Figure 4 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 materials to be joined by a thermal imager provided in the friction stir welding apparatus, and the cooling rate at each position on the surface of the joint is determined. The measured cooling rates are shown in Table 2. In addition, CR W＝0 .2 and CR W＝0 .5 The cooling speeds on both the forward side (first electromagnetic steel strip side) and the backward side (second electromagnetic steel strip side) were measured across the center line of the joint, but they were almost the same. Therefore, here, as a representative, only the cooling speed on the forward side is recorded. In addition, for comparison, cooling by the cooling device was not performed under some conditions.

[0354] 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 procedure.

[0355] In addition, according to the above method,

[0356] Dsz: average ferrite grain size of the joint (μm),

[0357] Dhaz1: average value of the ferrite grain size of the hot working affected portion on the first electromagnetic steel strip side (μm),

[0358] Dhaz2: average value of the ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side (μm),

[0359] Dbm1: average value of ferrite grain size of the base material portion of the first electromagnetic steel strip (μm),

[0360] Dbm2: average value of the ferrite grain size of the base material portion of the second electrical steel strip (μm),

[0361] Hsz: average hardness of the joint,

[0362] Hbm1: average value of hardness of the base material portion of the first electromagnetic steel strip,

[0363] Hbm2: Average value of the hardness of the base material portion of the second electromagnetic steel strip.

[0364] In addition, in the vertical direction cut surface ( Figure 3 In the shown surface (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.

[0365] The results are shown in Table 3. In the confirmation of surface defects and internal defects described below, when defects were confirmed, the above-mentioned measurement was omitted. In addition, when surface defects were confirmed, the confirmation of internal defects was also omitted.

[0366] 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.

[0367] (I) Presence of surface defects

[0368] 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.

[0369] No surface defects: No unbonded state or cracks were confirmed.

[0370] Surface defects: At least one of a non-bonded state and a crack is observed.

[0371] (II) Presence of internal defects

[0372] The obtained joint of the electromagnetic steel strip is Figure 3 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 material on the joining (welding) start side, a position 20 mm from the end of the joined material on the joining (welding) end side, and a position in the middle of the two ends of the joined material. Then, 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). Then, the presence or absence of internal defects was determined based on the following criteria.

[0373] No internal defects: No unbonded state or cracks were observed in the bonded portion in any of the three test pieces.

[0374] 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.

[0375] 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.

[0376] That is, from the obtained joint of the 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 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 to the Erichsen cupping value of the base material portion (hereinafter also referred to as the ratio of the Erichsen cupping value). The results are shown in Table 4.

[0377] [Ratio of Erichsen cupping value (%)] = [Erichsen cupping value of joint] / [Erichsen cupping value of parent material] × 100

[0378] Pass: Eriksson cupping value ratio is 90% or more

[0379] Disqualified: Eriksson cupping value ratio is less than 90%

[0380] 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.

[0381] [Table 1]

[0382]

[0383] [Table 2]

[0384]

[0385]

[0386] [Table 3]

[0387]

[0388] [Table 4]

[0389]

[0390] 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 electrical steel strips having no defects and an Erichsen cupping value ratio of 90% or more and an extremely excellent fracture suppression effect was obtained.

[0391] 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.

[0392] Description of Reference Numerals

[0393] 1…first electromagnetic steel strip (material to be joined); 2…second electromagnetic steel strip (material to be joined); 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, comprising: joining a first electromagnetic steel strip and a second electromagnetic steel strip as materials to be joined by a pair of rotating tools facing each other; The friction stir welding method of the electromagnetic steel strip is characterized by comprising: a joining step in which the rotating tool is pressed against the unjoined portion of the materials to be joined from both sides while rotating in opposite directions to each other, and the rotating tool is moved 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 in which the joining portion is cooled by a cooling device disposed at the rear of the rotation tool in the joining direction on at least one surface of the joined material; The unjoined portion of the joined materials 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 rotating tool is moved in the joining direction in conjunction with the cooling device, thereby continuously performing the joining process and the cooling process. 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 ferrite phase structures and the following relationships (1) to (4) are satisfied. Dsz≤100μm…(1) Dhaz1≤Dbm1…(2) Dhaz2≤Dbm2…(3) 0.9×(Hbm1+Hbm2) / 2≤Hsz≤1.2×(Hbm1+Hbm2) / 2…(4)Here, Dsz is the average ferrite grain size of the joint. Dhaz1 is the average value of the ferrite grain size in the hot working affected portion on the first electromagnetic steel strip side, Dhaz2 is the average ferrite grain size of the hot working affected zone on the second electromagnetic steel strip side, Dbm1 is the average value of the ferrite grain size of the base material portion of the first electromagnetic steel strip, Dbm2 is the average value 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 the average hardness of the base material portion of the second electromagnetic steel strip. The units of Dsz, Dhaz1, Dhaz2, Dbm1 and Dbm2 are μm.

2. The friction stir welding method for electromagnetic steel strip according to claim 1, characterized in that: In the bonding step, bonding is performed under the condition that the relationship between the following equations (5) and (6) is satisfied: 0.8×TbmL≤TszL…(5) TszH≤1.3×TbmH…(6) here, TszL is the minimum thickness of the joint, TszH is the maximum thickness of the joint, TbmL is the thickness of the thinner one of the first electromagnetic steel strip and the second electromagnetic steel strip. TbmH is the thickness 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. Wherein, the unit of TszL, TszH, TbmL and TbmH is mm.

3. The friction stir welding method for electromagnetic steel strips according to claim 1 or 2, characterized in that: In the cooling step, cooling is performed under the conditions satisfying the relationship of the following equations (7) to (9): CR W＝0 ≥15…(7) CR W＝0.2D ≥15…(8) CR W＝0.5D ≥15…(9) Here, CR W＝0 , CR W＝0.2D and CR W＝0.5D are the cooling rates 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 from the joint center line of the materials to be joined in the direction perpendicular to the joint, and D is the diameter of the shoulder of the rotating tool. Among them, the CR W＝0 , CR W＝0.2D and CR W＝0.5D The unit of is °C / s, and the unit of W and D is mm.

4. The friction stir welding method for electromagnetic steel strips according to claim 3, characterized in that: The cooling device is an inert gas spraying device, a liquid spraying device or a device combining these.

5. 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 3 to obtain a joined steel strip; and The step of cold-rolling the joined steel strip to obtain a cold-rolled steel strip.

6. A friction stir welding device used in the friction stir welding method of the electromagnetic steel strip according to claim 3, The friction stir welding device is characterized by comprising: A holding device for holding the materials to be joined; a pair of rotating tools disposed opposite to each other; a driving device for the rotating tool; a cooling device, the cooling device being arranged behind the rotation tool in the joining direction on at least one surface of the materials to be joined; as well as The holding device, the driving device of the rotating tool and the motion control device of the cooling device.

7. The friction stir welding device according to claim 6, characterized in that: A cooling rate measuring device is provided for measuring CR on both sides of the joint portion formed by the materials to be joined. 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 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 from the joint center line of the materials to be joined in the direction perpendicular to the joint, and D is the diameter of the shoulder of the rotating tool. Among them, the CR W＝0 , CR W＝0.2D and CR W＝0.5D The unit of is °C / s, and the unit of W and D is mm.

8. The friction stir welding device for electromagnetic steel strip according to claim 7, characterized in that: The cooling device is an inert gas spraying device, a liquid spraying device or a device combining these.

9. A manufacturing device for an electromagnetic steel strip, characterized in that: A friction stir welding device according to claim 7 is provided.

10. A manufacturing device for an electromagnetic steel strip, characterized in that: In the continuous cold rolling line, the friction stir welding apparatus according to claim 7 is arranged upstream of the cold rolling apparatus, or upstream of the pickling apparatus and the cold rolling apparatus.

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