JP6497451B2 - Friction stir welding method and apparatus - Google Patents

Description

  According to the present invention, the rotary tool is inserted into an unjoined portion between the workpieces and moved while rotating, and the workpiece is softened by frictional heat with the rotary tool, and the softened portion is stirred by the rotary tool. The present invention relates to a friction stir welding method in which joining is performed without adding a filler material by using the generated plastic flow, and an apparatus for realizing the friction stir welding method.

  As a friction welding method, in Patent Document 1, by rotating both or one of a pair of metal materials, the metal material generates frictional heat and softens, while the softened portion is stirred to cause plastic flow. Thus, a technique for joining metal materials is disclosed.

  However, since this technique rotates the metal material to be joined, there is a limit to the shape and size of the metal material to be joined.

  In Patent Document 2, a tool made of a material that is substantially harder than a workpiece is inserted into an unjoined portion of the workpiece, and the tool is moved while being rotated. A method is disclosed in which workpieces are continuously joined in the longitudinal direction by heat and plastic flow.

  The friction welding method described in Patent Document 1 is a method in which workpieces are rotated and welded by frictional heat between workpieces. The friction stir welding method disclosed in Patent Document 2 is a method of joining by moving a tool while rotating a joining member in a fixed state. Thus, in the friction stir welding method, since the tool is moved and joined, even a member that is substantially infinitely long with respect to the welding direction has an advantage that it can be continuously solid-phase joined in the longitudinal direction. Moreover, since it is a solid-phase joining using the plastic flow of the metal by the frictional heat of a tool and a joining member, it can join, without melt | dissolving a junction part. Furthermore, since the heating temperature is low, deformation after joining is small, the joint is not melted, so there are few defects, and in addition, there are many advantages such as not requiring a filler material.

  The friction stir welding method is widely used in the fields of aircraft, ships, railway vehicles, automobiles and the like as a method of joining low melting point metal materials typified by aluminum alloys and magnesium alloys. The reason for this is that these low melting point metal materials are difficult to obtain satisfactory characteristics of the joints by conventional arc welding methods, and the productivity is improved and the quality is high by applying the friction stir welding method. It is because a junction can be obtained.

  On the other hand, the application of friction stir welding to structural steel, which is mainly applied as a structural material such as buildings, ships, heavy machinery, pipelines, and automobiles, is subject to solidification cracking and hydrogen cracking, which are problems in conventional fusion welding. Can be avoided, and the structural change of the steel material can be suppressed, so that it can be expected that the joint performance is excellent. Further, in the friction stir welding method, a clean interface is created by stirring the bonding interface with a rotating tool and the clean surfaces are brought into contact with each other. Therefore, an advantage that a preparatory step such as diffusion bonding is unnecessary can be expected. Thus, the application of the friction stir welding method to structural steel is expected to have many advantages. However, since there is a problem in joining workability such as suppression of defect generation during joining and an increase in joining speed, the friction stir welding method has not been widely used in structural steel compared to low melting point metal materials.

In friction stir welding of structural steel, as described in Patent Document 3 and Patent Document 4, high wear resistance such as polycrystalline boron nitride (PCBN) and silicon nitride (Si ₃ N ₄ ) is used as a rotating tool. Wearable material is used. Since these ceramics are brittle, the thickness of the steel plates to be joined and the construction conditions thereof are significantly limited in order to prevent damage to the rotary tool.

  Patent Document 5 and Patent Document 6 disclose a joining method in which a heating means is added for the purpose of improving joining workability.

  For example, Patent Document 5 includes a heating unit using an induction heating device, and by heating the workpieces before and after joining, friction that increases the joining speed and eliminates cracks in the joined part. A stir welding method is disclosed.

  Patent Document 6 has a heating means using a laser device, and the workpiece is partially heated immediately before joining, thereby suppressing the microstructure change around the heating region due to preheating and increasing the joining speed. A friction stir welding apparatus which is designed to be simplified is disclosed.

  Patent Document 7 has heating means using a laser device, and when the workpieces are partially heated immediately before joining, the surface temperature and depth of the heating region of the workpieces are strictly controlled. Thus, a friction stir welding apparatus is disclosed in which the plastic flow failure due to insufficient heating of the workpieces is eliminated, and the joining workability is improved with sufficient strength.

  In Patent Document 8 and Patent Document 9, one rotating tool is provided at the top and bottom, and a rotating tool is disposed on the front side and the back side of the overlapping portion of the two metal plates so as to face each other vertically. Use, press while rotating the rotating tool from the top and bottom, move in the joining direction and join to suppress joint failure, increase the joint strength, improve the reliability of the joint strength, further improve the tool life, A double-sided friction stir welding method and apparatus that improve the economics of the rotary tool is disclosed.

  In friction stir welding, plastic flow is generated by stirring with a rotating tool while softening the workpiece with frictional heat. When the workpiece is structural steel, the workpiece is stirred with the rotating tool. In some cases, a large load is applied to the pins of the rotating tool. This phenomenon has a major impact on the durability and life of rotating tools, and is a major factor limiting the workability of joints. Although it is thought that the method of adding heating means other than the frictional heat described in Patent Documents 5 to 7 is effective for overcoming the above problem, the surface side (for example, one surface side) of the workpiece, the back surface On the side (for example, the other side), if the side provided with the heating means and the side provided with the rotary tool are the same, the heat source is present only on one side. On the surface side not provided with the heating means and the rotating tool, the temperature becomes lower than that on the surface side provided with the heat generation source, and a temperature difference occurs in the thickness direction of the workpiece from the front surface side to the back surface side. Since the strength of the metal plate, which is a workpiece, decreases as the temperature increases, the load on the rotary tool in the friction stir welding is considered to decrease as the temperature increases. It is considered that the load applied to the tip of the rotating tool pin can be reduced by eliminating the temperature difference formed in the thickness direction of the workpiece, but in Patent Documents 5 to 7, the temperature difference in the thickness direction There is no consideration for resolution.

  In friction stir welding, the double-side friction stir welding method disclosed in Patent Document 8 and Patent Document 9 is considered effective as a method of eliminating the temperature difference formed in the thickness direction of the workpiece. However, in these joining methods, the improvement of joining workability and tool life by reducing the tool load using the pre-heat treatment process that heats the steel sheet as the workpiece by the heating means provided in front of the rotary tool is completely considered. It has not been.

JP 62-183979 A JP 7-505090 Gazette Special table 2003-532542 gazette Japanese translation of PCT publication No. 2003-532543 JP 2003-94175 A JP 2005-288474 A International Publication No. 2015/045299 Japanese Patent No. 3261433 Japanese Patent No. 4838385

  The present invention has been made in view of the above-mentioned present situation, and at the time of friction stir welding, an object of the present invention is to solve the plastic flow failure due to insufficient heating of work materials and to improve the joining workability with sufficient strength. To do. In particular, the relationship between the position of partial heating of the workpiece and the frictional heat generation due to the dynamic friction coefficient between the rotating tool material or the material coated on the surface of the rotating tool and the workpiece affects the workability. In view of this, it is an object of the present invention to provide a friction stir welding method in which the pre-heat treatment process conditions are closely scrutinized and an apparatus for realizing the friction stir welding method.

The inventors obtained the following knowledge as a result of intensive studies to solve the above problems.
a) In ordinary friction stir welding, the only heat source required for welding is frictional heat generated between the rotary tool and the workpiece. Therefore, when the structural steel is joined by the friction stir welding method, the amount of heat necessary to soften the structural steel that is the workpiece cannot be secured. As a result, a sufficient plastic flow cannot be obtained at the joint, and there is a concern about the deterioration of joining workability such as a reduction in joining speed and the occurrence of joining defects.

In order to avoid the deterioration of joining workability, which is very important in industrializing the above technology, it is considered that a pre-heat treatment process before friction stir welding is effective.
b) However, in the workpiece, when the heating means for performing the pre-heat treatment process and the rotary tool are arranged on the same surface side (for example, the surface side), the heat source is present only on the same surface side of the workpiece. In this case, on the side not provided with the heating means and the rotating tool, that is, on the back side, the temperature is lower than that on the front side, and on the back side from the front side, a temperature difference occurs in the thickness direction of the workpiece. Since the strength of the metal plate, which is a workpiece, decreases as the temperature increases, the load on the rotary tool in the friction stir welding is considered to decrease as the temperature increases. Therefore, it is considered that the load applied to the tip of the rotating tool pin can be more effectively reduced by eliminating the temperature difference formed in the thickness direction of the workpiece.
Therefore, the inventors examined various preheat treatment process conditions before friction stir welding.

as a result,
c) In order to eliminate the temperature difference with respect to the thickness direction from the front surface side to the back surface side of the work material, in addition to performing the pre-heat treatment from one surface side before the friction stir welding, the rotary tool is attached to A mechanism that realizes friction stir welding that heats the workpiece by frictional heat from both the one side and the other side of the workpiece. Was found to be effective.
d) However, when preheating is performed before friction stir welding, if the amount of preheating heat is excessive, there is a problem that the microstructure around the heating region changes. In particular, in the case of a high-tensile steel sheet strengthened with a martensite structure, even when the periphery of the heating region is heated below the ferrite-austenite transformation temperature, softening occurs due to tempering of the martensite, and the joint joint strength Is significantly reduced.

  Therefore, the inventors examined various preheat treatment process conditions before friction stir welding.

as a result,
e) By using a heat source with a high energy density such as a laser, the surface temperature, area, and position of the heating region in the pre-heat treatment process are strictly controlled, and the temperature in the thickness direction of the heating region is also adjusted as necessary. Control appropriately. As a result, it has been found that the joining workability can be improved without causing deterioration of the jointed joint properties such as the jointed joint strength.
f) In particular, with respect to the position of partial heating of the workpiece, the relationship between the heat generated by the rotary tool or the material coated on the surface of the rotary tool and the frictional heating governed by the dynamic friction coefficient between the workpieces. Thus, the knowledge that the region where the effect of improving the bonding workability is generated is obtained.
g) In normal friction stir welding, since the joined portion is naturally cooled after the joining is completed, there is a problem that it is not possible to apply the microstructure control by the thermal history management performed in the rolling process at the time of manufacturing the steel material. there were. However, immediately after the completion of the joining, it was found that the joint joint characteristics can be further improved by performing a process that combines heat treatment and cooling treatment on the joint.

  The present invention is based on the above knowledge, and particularly arises from insufficient heating due to a temperature difference occurring in the plate thickness direction of the workpiece, which is a concern when the friction stir welding method is applied to the joining of structural steel. It is intended to eliminate the plastic flow failure and improve the joining workability with sufficient strength.

That is, the gist configuration of the present invention is as follows.
[1] A pair of rotary tools are arranged opposite to one side and the other side of a steel plate as a workpiece, respectively, and moved in the joining direction while rotating the pair of rotary tools at an unjoined portion between the steel plates. Friction stir to join steel plates by causing plastic flow by agitating the softened part with the pair of rotating tools while softening the steel plate by frictional heat between the pair of rotating tools and the steel plate In the joining method, the dynamic friction coefficient between the steel plate and the material of the pair of rotating tools or the material coated on the surface of the pair of rotating tools is 0.6 or less, and the rotation disposed on at least one surface side The tool includes a shoulder portion and a pin portion arranged on the shoulder portion and sharing the rotation axis with the shoulder portion, and the shoulder portion and the pin portion are formed of a material harder than the steel plate, Steel plate While rotating, the pair of rotating tools are pressed against the one surface side and the other surface side of the steel plate and moved in the joining direction while rotating the pair of rotating tools, and the rotation disposed on the one surface side When the area where the surface temperature T _S (° C.) of the steel sheet heated by the heating means provided in the front of the tool joining direction satisfies the following formula (1) is defined as the heating area, the heating area and the one surface The minimum distance from the rotary tool arranged on the side is equal to or less than the diameter of the shoulder of the rotary tool on the one surface side, and the area of the heating area is that of the pin portion of the rotary tool arranged on the one surface side. The area of the maximum diameter portion is less than or equal to 65% or more of the area of the heating area is a straight line parallel to the welding direction through the rotation axis of the rotary tool arranged on the one surface side of the surface of the steel plate Line and the junction center line And a straight line separated by the same distance as the maximum radius of the pin portion of the rotary tool arranged on the one surface side to the retreating side.
T _S ≧ 0.8 × T _A1 (1)
T _A1 is a temperature represented by the following formula (2).
T _A1 (° C.) = 723-10.7 [% Mn] −16.9 [% Ni] +29.1 [% Si] +16.9 [% Cr] +290 [% As] +6.38 [% W] · (2)
Said [% M] is content (mass%) of M element in the steel plate which is a workpiece, and is set to 0 when not containing.
[2] The friction stir welding method according to [1], wherein both of the pair of rotating tools include the shoulder portion and the pin portion, and the pair of rotating tools have the same pin length.
[3] Both of the pair of rotary tools include a shoulder portion and the pin portion, and the pin length of the rotary tool arranged on the one surface side is the pin length of the rotary tool arranged on the other surface side. The friction stir welding method according to [1], which is shorter.
[4] Any one of [1] to [3], wherein an axis of at least one rotary tool of the pair of rotary tools is inclined in a direction in which a pin portion precedes a joining direction of the rotary tools. The friction stir welding method described in 1.
[5] The rotation direction of the rotary tool arranged on the one surface side is the opposite direction to the rotation direction of the rotary tool arranged on the other surface side, according to any one of [1] to [4]. Friction stir welding method.
[6] When the depth from the surface of the steel sheet in the region where the temperature T _D (° C.) in the thickness direction of the heating region satisfies the following formula (3) is the depth D of the heating region, the heating region The depth D of the friction stir welding method according to any one of [1] to [5], which is 100% of the thickness of the steel plate.
T _D ≧ 0.8 × T _A1 (3)
[7] The friction stir welding method according to any one of [1] to [6], wherein the heating unit is a laser heating device.
[8] A rear heating means is provided behind the rotating tool disposed on the one surface side in the joining direction, and the rear heating means heats the joining portion of the steel sheet. The friction stir welding method according to one.
[9] The friction stir welding method according to [8], wherein a cooling means is provided behind the rear heating means in the joining direction, and the cooling means cools the joint heated by the rear heating means.
[10] A friction stir welding method according to any one of [1] to [7], wherein a cooling means is provided behind the rotating tool in the joining direction, and the cooling means cools the joining portion of the steel sheet. .
[11] A friction stir welding method according to [10], wherein a rear heating unit is provided behind the cooling unit in the bonding direction, and the rear heating unit heats the bonding portion cooled by the cooling unit.
[12] A friction stir welding apparatus that joins unjoined portions between steel plates that are workpieces, and is disposed so as to face a gripping device that fixes the steel plates, and one side and the other side of the steel plates A pair of rotary tools that can move in the joining direction while rotating at the unjoined portion between the steel plates, and a heating means that is provided in front of the joining direction of the rotary tool disposed on the one surface side and that heats the steel plates. The rotating tool and the control means for controlling the heating means so as to realize the following state 1, the rotating tool arranged on at least one side is disposed on the shoulder, The shoulder portion and the pin portion sharing the rotation axis, and the shoulder portion and the pin portion are formed of a material harder than the steel plate, and the material of the pair of rotating tools or the pair of rotating tools Surface coated material and front Friction stir welding apparatus dynamic friction coefficient between the steel sheet is 0.6 or less.
(State 1)
When the region where the temperature T _S (° C.) of the surface of the steel sheet heated by the heating unit satisfies the following formula (1) is defined as the heating region, the heating region and the rotating tool disposed on the one surface side; The minimum distance is equal to or less than the diameter of the shoulder portion of the rotary tool arranged on the one surface side, and the area of the heating region on the surface of the steel plate is the pin portion of the rotary tool arranged on the one surface side. The area of the maximum diameter portion is less than or equal to 65% or more of the area of the heating area is a straight line parallel to the welding direction through the rotation axis of the rotary tool arranged on the one surface side of the surface of the steel plate It is located between the line and a straight line that is parallel to the joining center line and that is separated from the retreating side by the same distance as the maximum radius of the pin portion of the rotary tool disposed on the one surface side.
T _S ≧ 0.8 × T _A1 (1)
T _A1 is a temperature represented by the following formula (2).
T _A1 (° C.) = 723-10.7 [% Mn] −16.9 [% Ni] +29.1 [% Si] +16.9 [% Cr] +290 [% As] +6.38 [% W] · (2)
Said [% M] is content (mass%) of M element in the steel plate which is a workpiece, and is set to 0 when not containing.
[13] The friction stir welding apparatus according to [12], wherein both of the pair of rotating tools include the shoulder portion and the pin portion, and the pair of rotating tools have the same pin length.
[14] Both of the pair of rotary tools include the shoulder portion and the pin portion, and the pin length of the rotary tool arranged on the one surface side is the pin of the rotary tool arranged on the other surface side. The friction stir welding apparatus according to [12], which is shorter than the length.
[15] The friction stirrer according to any one of [12] to [14], wherein an axis of at least one rotary tool in the pair of rotary tools is inclined in a direction in which the pin portion precedes the joining direction. Joining device.
[16] The rotation direction of the rotary tool arranged on the one surface side is the reverse direction of the rotation direction of the rotary tool arranged on the other surface side, according to any one of [12] to [15]. Friction stir welding equipment.
[17] The friction stir welding apparatus according to any one of [12] to [16], wherein the control unit controls the rotating tool and the heating unit so as to realize the following state 2.
(State 2)
When the depth from the surface of the steel sheet in the region where the temperature T _D (° C.) in the thickness direction of the heating region satisfies the following formula (3) is defined as the depth D of the heating region, the depth of the heating region D is 100% of the thickness t of the steel sheet.
T _D ≧ 0.8 × T _A1 (3)
[18] The friction stir welding apparatus according to any one of [12] to [17], wherein the heating means is a laser heating apparatus.
[19] The apparatus according to any one of [12] to [18], further including a rear heating unit that heats the joint portion of the steel plates, the rear heating unit being provided rearward in the joining direction of the rotary tool. Friction stir welding device.
[20] The friction stir welding apparatus according to [19], further including a cooling unit that cools the bonding portion, and the cooling unit is provided behind the rear heating unit in the bonding direction.
[21] The friction stirrer according to any one of [12] to [18], further including a cooling unit that cools a bonded portion of the steel plates, the cooling unit provided at a rear side in the bonding direction of the rotary tool. Joining device.
[22] The friction stir welding apparatus according to [21], further including a rear heating unit that heats the joint, and the rear heating unit is provided behind the cooling unit in the joining direction.

  ADVANTAGE OF THE INVENTION According to this invention, the plastic flow defect resulting from the heating shortage by the temperature difference produced in the plate | board thickness direction of a workpiece can be eliminated, and the joining workability of friction stir welding can be improved. Furthermore, a change in the microstructure around the heating region is also suppressed, and a high joint strength can be obtained at the joint.

FIG. 1 is a schematic diagram illustrating a friction stir welding method according to the present embodiment. FIG. 2 is a schematic diagram illustrating the gripping device. FIG. 3 is a diagram showing an example of a region in which a workpiece is frictionally stirred by a rotary tool from both the front side and the back side, a heating region in a preheating process, a cooling region after joining, and a reheating region (top view and A- (A sectional view). FIG. 4 is a diagram showing the relationship between the temperature and tensile strength of the steel plates to be joined by the friction stir welding method according to this embodiment. FIG. 5 is a diagram illustrating a cross-sectional dimension of the rotary tool.

  Hereinafter, the present invention will be specifically described through embodiments of the present invention. FIG. 1 is a schematic diagram illustrating a friction stir welding method according to the present embodiment, and FIG. 2 is a schematic diagram illustrating a gripping device. In FIG. 1, the description of the gripping device 21 is omitted, and in FIG. 2, only the steel plate 3 and the gripping device 21 are illustrated. In the friction stir welding method according to the present embodiment, as shown in FIG. 1, there is a pre-heat treatment process in which the steel plate is heated by a heating means provided in the front in the joining direction, and facing one side and the other side, respectively. Rotating tools that are arranged and moved in the joining direction while rotating by inserting the rotating tool into the unjoined part between the steel plates from both the one side and the other side with respect to the steel plate that is the work material. While the steel plates are softened by frictional heat between the steel plates and the steel plates, the softened portions are agitated with opposing rotating tools to cause plastic flow, thereby joining the steel plates together.

  In FIG. 1, reference numeral 1 is a surface-side rotating tool, 2 is a rotating shaft of the surface-side rotating tool, 3 is a steel plate, 4 is a joint, 5 is a heating means, and 6 is a cooling means. 7 is a rear heating means, 8 is a shoulder portion of the front surface side rotating tool, 9 is a pin portion of the front surface side rotating tool, 15 is a back surface side rotating tool, and 16 is a back surface side rotating tool. , 17 is a pin portion of the back surface side rotation tool, 19 is a rotation axis of the back surface side rotation tool, and 20 is a control means. α indicates the front surface side rotation tool inclination angle, and β indicates the rear surface side rotation tool inclination angle. “AS” indicates an advancing side, and “RS” indicates a retreating side. In the present embodiment, one side is described as the front side, and the other side is described as the back side. The front surface side rotation tool 1 and the back surface side rotation tool 15 may be collectively described as a pair of rotation tools.

  The advancing side is defined as the side where the tool rotation direction and the joining direction coincide with each other, and the retreating side is defined as the side where the tool rotation direction and the joining direction are opposite to each other.

  In the present embodiment, the butted portion that is not yet joined just by butting the steel plates 3 is described as “unjoined portion”, and the portion joined and integrated by plastic flow is described as “joined portion”. To do.

  In the present embodiment, as shown in FIG. 2, the steel plate 3 is fixed from the front and back surfaces using a gripping device 21. The gripping device 21 includes a lower jig 22 that fixes the back surface of the steel plate 3, an upper jig 23 that fixes the surface of the steel plate 3, and a clamp 24 that presses the upper jig 23 downward.

  From the front surface side and the back surface side of the steel plate 3 fixed by the gripping device 21, the pin portion 9 of the front surface side rotating tool and the pin portion 17 of the back surface side rotating tool are inserted into the unjoined portion, and the front surface The shoulder portion 8 of the side rotating tool and the shoulder portion 16 of the back surface side rotating tool are pressed and joined to the front surface side and the back surface side of the steel plate 3. The front end of the pin portion 9 of the front surface side rotary tool and the front end of the pin portion 17 of the back surface side rotary tool so that the friction by the shoulder portion and the stirring by the pin portion are appropriately performed and sound joining is possible. A gap δ may be provided between the two. The gap δ is preferably 0.1 mm or more. Thereby, the load of the surface side rotation tool 1 and the back surface side rotation tool 15 by the deformation resistance of the material at the time of stirring can be reduced. On the other hand, when the gap δ is too large, a portion that is not properly stirred by the pin portion becomes a defect. For this reason, the gap δ is preferably 0.3 mm or less.

  Of the pair of rotary tools, at least the surface-side rotary tool 1 includes a shoulder portion and a pin portion disposed on the shoulder portion and sharing the rotation axis with the shoulder portion, and at least the shoulder portion and the pin portion are covered. It is formed of a material harder than the steel plate 3 that is a processed material.

  Since the load applied to the rotating tool can be reduced by minimizing the stirring area plastically flowed by the pin part of the rotating tool, the shoulder of the rotating tool has a tapered shape that faces upward in the rotational direction. It is preferable to provide.

  In the conventional friction stir welding, a rotating tool is inserted from the surface side to perform bonding. Therefore, the pin length (pin length) needs to be equal to the thickness of the workpiece. However, the longer the pin length, the larger the load applied to the tip of the pin. Therefore, it is preferable that the pin length is shorter in order to improve the joining workability and tool life. In the present embodiment, the pin length is calculated by the difference in height between the tip of the pin portion and the highest position of the shoulder portion, as indicated by reference numeral c in (1) to (4) of FIG. Length.

  In this embodiment, when the pin length of a pair of rotary tools is the same length, the pin length is about half of the thickness of the steel plate 3, so the load applied to each rotary tool rotates only from one side. Lower than when tools are inserted and joined.

  Moreover, when the pin length of the front surface side rotary tool 1 is made shorter than the pin length of the back surface side rotary tool 15 among the pin lengths of the pair of rotary tools, the load on the front surface side rotary tool 1 can be reduced. Sufficient heat is applied by the heating means 5 to the joint near the tip of the pin portion 17 of the back surface side rotary tool, so that the load on the back surface side rotary tool 15 is also reduced.

  Furthermore, you may incline the axial center of a pair of rotary tool to the direction which a pin part precedes with respect to a joining direction. Since the pair of rotary tools is formed of a material harder than the steel plate 3, a material having poor toughness such as ceramic is used. For this reason, when a force in the bending direction is applied to the pin portions of the pair of rotating tools, the stress concentrates on the local portion and the pair of rotating tools is destroyed. On the other hand, by inclining the axis of the pair of rotating tools, the load applied to the rotating tools is set as a component force compressed in the axial direction, and the force in the bending direction can be reduced. Thereby, damage to the rotary tool 1 can be avoided. The inclination angle of the axis of the rotary tools 1 and 15 is, for example, not less than 1 ° and not more than 5 °.

  For the pair of rotary tools, only the axis of one rotary tool may be tilted, or the axes of both rotary tools may be tilted. The angle of inclination of the axis of the pair of rotary tools may be different.

  By rotating the pair of rotary tools in the opposite direction between the front and back sides, the rotational torque applied to the material to be joined from the pair of rotary tools can be canceled, and the rotary tool is pressed only from one side. Thus, the structure of the gripping device 21 for fixing the steel plate 3 can be simplified as compared with the friction stir welding method for joining.

  In the friction stir welding method of the present embodiment, a pre-heat treatment process in which the steel plate 3 is heated by the heating means 5 provided in front of the surface side rotary tool 1 moving in the joining direction is important. Hereinafter, the preheat treatment process conditions will be described with reference to FIG.

  FIG. 3 is a diagram showing an example of a region in which a workpiece is frictionally stirred by a rotary tool from both the front side and the back side, a heating region in a preheating process, a cooling region after joining, and a reheating region (top view and A- (A sectional view). In FIG. 3, the joining center line 10 indicates a straight line passing through the rotation axis 2 of the surface-side rotating tool 1 on the surface of the steel plate 3 and parallel to the joining direction. The RS line 11 is a straight line parallel to the joining center line 10 and separated to the retreating side by the same distance as the maximum radius of the pin portion 9 of the rotary tool, 12 is a heating area, and 13 is a cooling area. , 14 is a reheating region. a indicates the diameter of the shoulder portion 8 of the surface-side rotating tool, b indicates the maximum diameter of the pin portion 9 of the surface-side rotating tool, X indicates the minimum distance between the heating region 12 and the surface-side rotating tool 1, and D Indicates the depth of the heating region 12, and t indicates the thickness of the steel plate 3.

Surface temperature T _S of steel plate in heating region: T _S ≧ 0.8 × T _A1
FIG. 4 is a diagram showing the relationship between the temperature and tensile strength of the steel plates to be joined by the friction stir welding method according to this embodiment. As shown in FIG. 4, the steel plate 3 to be joined by the friction stir welding method of the present embodiment is usually about 30% strength at room temperature at a temperature of about 80% of _TA1 , which is the transformation temperature of steel. It becomes. Moreover, when it becomes higher than this temperature, the intensity | strength of the copper plate 3 will fall further. Therefore, the steel plate 3 is previously softened so that the surface temperature T _S of the steel plate 3 satisfy the above 0.8 × T _A1 ° C., and stirred the steel plate 3, to promote plastic flow. Thereby, the load concerning a pair of rotary tool is reduced and a joining speed can be made high-speed. Therefore, in the friction stir welding method in this embodiment, the surface temperature T _S of the steel plate 3 is the heating region 12 a region which satisfies the following formula (1).

T _S ≧ 0.8 × T _A1 (1)
The transformation temperature T _A1 (° C.) of steel can be obtained by the following formula (2).

T _A1 (° C.) = 723-10.7 [% Mn] −16.9 [% Ni] +29.1 [% Si] +16.9 [% Cr] +290 [% As] +6.38 [% W] · (2)
Said [% M] is content (mass%) of M element in the steel plate 3 which is a workpiece, and is set to 0 when not containing.

If the temperature exceeds 0.8 × T _A1 ° C., the strength of the steel plate 3 tends to decrease as the temperature increases. Therefore, it is preferable to adjust so that the surface temperature T _S of the steel plate 3 in the heating region 12 does not increase excessively. Specifically, in order to secure the heating region 12 in the thickness direction, a temperature gradient (temperature variation on the surface) may exist on the surface of the heating region 12. The high surface temperature is preferably 1.5 × T _M ° C. or less. Furthermore, it is preferable that the surface temperature of the steel plate 3 in the heating region 12 is less than T _M ° C. until the surface temperature of the steel plate 3 contacts the surface-side rotating tool 1 passing through the heating region 12. Thereby, damage to a pair of rotating tools due to excessive increase in the temperature of the joint portion 4 and alteration of the microstructure around the heating region 12 can be avoided. T _M (° C.) is the melting point of the steel plate 3 that is the workpiece.

Minimum distance X between the heating region on the surface of the steel plate and the rotating tool on the side provided with the heating device: not more than the diameter of the shoulder of the rotating tool The minimum distance X between the heating region 12 on the surface of the steel plate 3 and the surface side rotating tool 1 is large. If it becomes too much, the temperature in the heating region 12 is lowered before joining, and the effect of preheating cannot be sufficiently obtained. For this reason, in the friction stir welding method according to the present embodiment, the minimum distance X between the heating region 12 on the surface of the steel plate 3 and the surface-side rotating tool 1 moving in the joining direction is equal to or less than the diameter of the shoulder 8 of the rotating tool. It is.

  However, if the minimum distance X between the heating region 12 and the rotating tool 1 becomes too small, the surface-side rotating tool 1 may be damaged by the heat of the heating means 12, so that the heating region 12 on the surface of the steel plate 3 is joined in the joining direction. It is preferable that the minimum distance X with the moving surface-side rotating tool 1 is not less than 0.1 times the diameter of the shoulder portion 8 of the surface-side rotating tool. The diameter of the shoulder portion 8 of the surface-side rotating tool in the present embodiment is, for example, about 8 to 60 mm. In order to sufficiently obtain the effect of preheating, the moving speed of the surface-side rotating tool 1 is preferably 200 mm / min or more and 3000 mm / min or less.

Area of the heating region on the surface of the steel plate: not more than the area of the maximum diameter portion of the pin portion of the rotary tool on the side provided with the heating device When the heating region 12 becomes too large, the microstructure of the heating region 12 and its peripheral region changes. In particular, in the case of a high-tensile steel sheet strengthened by a martensite structure, even when heating at a temperature below the ferrite-austenite transformation temperature, the martensite is tempered to cause softening and greatly reduce the joint strength. . For this reason, in the friction stir welding method according to the present embodiment, the area of the heating region 12 on the surface of the steel plate 3 is equal to or less than the area of the maximum diameter portion of the pin portion 9 of the rotary tool.

  On the other hand, if the area of the heating region 12 becomes too small, the effect of preheating cannot be sufficiently obtained. Therefore, it is preferable that the area of the heating region 12 on the surface of the steel plate 3 is 0.1 times or more the area of the maximum diameter portion in the pin portion 9 of the surface-side rotating tool.

  The maximum diameter of the pin portion 9 of the surface-side rotating tool in the present embodiment is, for example, about 2 to 50 mm. The maximum diameter of the pin portion 9 of the surface-side rotating tool is the maximum diameter among the diameters obtained at the cut surface when one pin portion is cut in a cross section perpendicular to the axial direction.

  FIG. 5 is a diagram illustrating a cross-sectional dimension of the rotary tool. As shown in FIGS. 5 (1) to (4), when the diameter of the pin portion 9 of the surface-side rotating tool does not change along the axial direction, the diameter of the upper surface of the pin portion (4 mm in the figure) is changed to the pin portion. The maximum diameter may be used. When the pin portion 9 of the rotary tool has a tapered shape or the like and the pin diameter varies depending on the position in the axial direction, the largest diameter may be set as the maximum diameter of the pin portion. The shape of the heating region 12 may be any shape such as a circle, an ellipse, or a rectangle.

On the surface of the steel plate, the area of the heating region located between the joining center line and the RS wire: 65% or more of the area of the heating region on the surface of the steel plate. As described above, along the rotation direction of the surface-side rotating tool 1, the front side of the joining direction, the retreating side, and the rear side of the joining direction pass, and the advanced side is the end point. Since the advanced side is the starting point of plastic flow, insufficient heating of the steel plate 3 as the workpiece is likely to occur. For this reason, when plastic flow is insufficient and defects occur, most of them occur on the advanced side. Therefore, on the surface of the steel plate 3, the advancing side is preferentially heated and the steel plate is softened to promote plastic flow, suppress the occurrence of defects, and increase the joining speed.

  However, when the dynamic friction coefficient between the material of the surface-side rotating tool 1 or the material coated on the surface of the surface-side rotating tool 1 and the steel plate 3 to be joined is 0.6 or less, the surface-side rotating tool 1 and the steel plate Friction heat and plastic flow generated between the two are reduced. The advanced side located in front of the surface-side rotating tool 1 is a portion that becomes a starting point of plastic flow, and is a region where frictional heat between the surface-side rotating tool 1 and the steel plate 3 is greatly generated. However, since the dynamic friction coefficient tends to decrease in a high temperature state, if this part is heated to a high temperature by preheating, sufficient frictional heat generation cannot be obtained when the dynamic friction coefficient between the surface-side rotating tool 1 and the steel plate 3 is small. On the other hand, since the retreating side is located in the middle of the plastic flow, if the plastic flow at this position becomes insufficient, the occurrence of defects on the advanced side that is the end point of the plastic flow is greatly affected. In particular, when the dynamic friction coefficient between the surface-side rotating tool 1 and the steel plate 3 is small, sufficient plastic flow cannot be obtained.

  Therefore, when the dynamic friction coefficient between the material of the surface-side rotating tool 1 or the material coated on the surface of the surface-side rotating tool 1 and the steel plate 3 is 0.6 or less, 65% or more of the area is positioned between the joint center line 10 and the RS wire 11 parallel to the joint center line 10, and the retreating side is preferentially heated. This promotes plastic flow on the retreating side, which is the middle of plastic flow, while ensuring frictional heat generation on the advanced side, which is the starting point of plastic flow, suppresses the occurrence of defects, and increases the joining speed. You can plan. The area range of the heating region 12 located between the bonding center line 10 and the RS wire 11 is more preferably 80% or more, and may be 100%.

  Further, from the viewpoint of preferentially heating the retreating side, the center of the heating region 12 is positioned between the RS line 11 and a straight line passing through an intermediate point between the junction center line 10 and the RS line 11. In other words, the center of the heating region 12 is positioned on the retreating side with respect to the bonding center line 10, and the distance from the center of the heating region 12 to the bonding center line 10 is set to 0 of the maximum radius in the pin portion 9 of the rotary tool. It is preferable to be 5 times or more and 1 time or less.

Temperature T _D in the thickness direction region of the heating region: T _D ≧ 0.8 × T _A1
As described above, the steel plate 3 to be joined by the friction stir welding method of the present embodiment usually has a strength of about 30% of the strength at normal temperature at a temperature of about 80% of _TA1 , which is the transformation temperature of the steel. . Moreover, when it becomes higher than this temperature, the intensity | strength of the steel plate 3 will fall further. Therefore, it is preferable to soften the steel plate 3 in advance in the thickness direction region of the heating region 12 at a temperature of 0.8 × T _A1 ° C. or higher. Thereby, the load concerning the surface side rotation tool 1 is further reduced, and the joining speed can be further increased. Accordingly, the temperature T _D in the thickness direction of the region of the heating region 12 has the depth D of the following formula (3) heating region 12 a depth from the surface of the steel plate 3 in satisfying region.

T _D ≧ 0.8 × T _A1 (3)
T _A1 (° C.) can be obtained by the following formula (2).

T _A1 (° C.) = 723-10.7 [% Mn] −16.9 [% Ni] +29.1 [% Si] +16.9 [% Cr] +290 [% As] +6.38 [% W] · (2)
Said [% M] is content (mass%) of M element in the steel plate 3 which is a workpiece, and is set to 0 when not containing.

However, since the strength of the steel plate 3 tends to decrease as the temperature rises if it exceeds 0.8 × T _A1 ° C, it is preferable to adjust so that the temperature of the steel plate 3 in the heating region 12 does not rise too much. Specifically, in order to secure the heating region 12 in the thickness direction, there may be a temperature gradient (temperature variation along the thickness direction) in the thickness direction of the heating region 12, but in that case, the heating region 12 12, the highest temperature in the thickness direction of the steel plate 3 is preferably 1.5 × T _M ° C. or less. Furthermore, in order to avoid damage to the surface-side rotary tool 1 due to excessive increase in the temperature of the joint 4 and alteration of the microstructure around the heating region 12, the temperature in the thickness direction of the steel plate 3 in the heating region 12 is avoided. Is preferably less than T _M ° C. before contacting the surface-side rotating tool 1 passing through the heating region 12. T _M (° C.) is the melting point of the steel sheet 3 as the workpiece.

Heating zone depth D: 100% of steel sheet thickness t
The depth D of the heating zone 12, the temperature T _D in the thickness direction of the pressurized heat region 12 is defined by the maximum depth from 0.8 × T _A1 ° C. or higher and a region surface of the steel plate 3 of the. The depth D of the heating region 12 is preferably 50% or more of the thickness t of the steel plate 3, and ideally 100%. By setting the depth D of the heating region 12 to 50% or more of the thickness t of the steel plate 3, the plastic flow is promoted to the maximum, which is advantageous for reducing the load on the rotary tool 1 and increasing the joining speed. . In the friction stir welding method in which the rotary tool is pressed and joined only from one side where the heating means 5 for performing the pre-heat treatment is provided, a support having a hardness equal to or higher than the material to be joined on the other side is used. It is necessary to support the material to be bonded, and if the depth D of the heating region 12 exceeds 90% of the thickness t of the steel plate 3, the material to be bonded and the support may be fixed. However, in this embodiment, since the opposite side (the other surface side) of the heating region 12 is in a hollow state, there is a risk of sticking even when the depth D of the heating region 12 is 50 to 100% of the total thickness of the steel plate 3. There is no.

  In order to realize the above-described conditions, the friction stir welding apparatus according to this embodiment includes a control unit 20. The control means 20 controls the operation of the rotary tool and the heating means. The control unit 20 may control operations of the rear heating unit 7 and the cooling unit 6.

  Further, the heating means 5 used in the preheat treatment process is not particularly limited, but is preferably a laser heating apparatus. By using a laser having a high energy density as a heat source, it is possible to more accurately control the preheat treatment process conditions, and it is possible to improve the joining workability without impairing the joint characteristics.

  The joining conditions other than those described above are not particularly limited. For example, the moving speed of the heating means 5 used in the preheat treatment process may be approximately the same as the joining speed. Moreover, when using a laser heating apparatus for this heating means 5, the laser output and beam diameter may be suitably set according to joining conditions.

  The preheat treatment process in the friction stir welding method and apparatus of the present embodiment has been described above. However, in the friction stir welding method and apparatus of the present embodiment, the cooling means 6 is disposed behind the surface-side rotary tool 1 that moves in the joining direction. The joint joint strength may be improved by providing the cooling means 6.

  Usually, after joining is completed, the joint 4 is naturally cooled, so that the strength of the joint joint cannot be sufficiently obtained when the hardenability of the steel plate 3 as the workpiece is low. On the other hand, the cooling means 6 is provided at the rear side in the joining direction of the surface-side rotating tool 1 moving in the joining direction, the joint 4 of the steel plate 3 is cooled by the cooling means 6, and the cooling rate is appropriately controlled. The strength can be improved by quenching. As the specific cooling means 6, for example, it is preferable to use a cooling device that ejects an inert gas. In this case, for example, argon gas, helium gas, or the like can be used as the inert gas that is preferably 30 to 300 ° C./s in the range of 800 ° C. to 500 ° C., for example.

  On the other hand, when the hardenability of the steel plate 3 which is a workpiece is high, there is a possibility that the steel plate 3 is excessively hardened, thereby reducing the toughness of the joint joint. On the other hand, the rear heating means 7 for heating the rear portion adjacent to the surface-side rotating tool 1 is provided behind the surface-side rotating tool 1 in the joining direction, and the cooling rate is appropriately controlled to gradually cool. Can be suppressed. As the specific rear heating means 7, it is preferable to use, for example, a high-frequency induction heating or a heating device using a laser as a heat source. The slow cooling rate in this case is preferably 10 to 30 ° C./s in the range of 800 ° C. to 500 ° C., for example.

  A rear heating means 7 may be provided behind the rotating tool moving in the joining direction and behind the cooling means 6 in the joining direction, and the joining portion 4 of the steel sheet 3 may be reheated by the rear heating means 7. Thereby, when the joining part 4 is quenched by cooling by the cooling means 6 and excessively cured, the hardness is suppressed by tempering by the rear heating means 7 and joint characteristics having both strength and toughness can be obtained. The cooling rate in this case is preferably 30 to 300 ° C./s in the range of 800 ° C. to 500 ° C., for example, and the reheating temperature is preferably 550 to 650 ° C., for example.

  Further, a cooling means 6 is provided behind the front side rotating tool 1 moving in the joining direction and behind the rear heating means 7, and the joining portion 4 of the steel plate 3 is cooled by the cooling means 6. Good.

  In this case, immediately after joining, slow cooling is performed by the rear heating means 7 and then rapid cooling is performed by the cooling means 6 so that the structure can be combined, and joint characteristics having both strength and ductility can be obtained. The cooling rate in this case is, for example, about 0 to 30 ° C./s in the range of 800 ° C. to 600 ° C. (gradual cooling range), and then 30 to 30 in the range of 600 ° C. to 400 ° C. (rapid cooling range). It is preferably about 300 ° C./s.

  The joining conditions other than those described above may be in accordance with ordinary methods. However, the greater the torque of the pair of rotating tools, the lower the plastic fluidity of the steel plate 3, and thus defects and the like are likely to occur.

  Therefore, in the friction stir welding method and apparatus of the present embodiment, the rotational speed of the pair of rotary tools is set in the range of 100 to 1000 rpm, the torque of the pair of rotary tools is suppressed, and the joining speed is increased to 1000 mm / min or more. To the goal. When the joining speed is increased from 500 mm / min to 1000 mm / min or more, it is preferable to suppress the torque of the pair of rotary tools to 90 N · m or less. As a result, it is possible to avoid a state in which the pair of rotary tools are damaged during bonding or an unbonded portion remains. When the joining speed is 500 mm / min or less, it is preferable to suppress the torque of the pair of rotary tools to 75 N · m or less. Thereby, the load of a pair of rotary tools can be eased, ensuring plastic fluidity.

  In addition, as a target steel type of the friction stir welding method of the present embodiment, general structural steel and carbon steel, for example, rolled steel for welded structure of JIS (Japanese Industrial Standard) G 3106, carbon for mechanical structure of JIS G 4051 Steel or the like can be used. It can also be applied to high-strength structural steel having a tensile strength of 800 MPa or more, and a strength of 85% or more of the tensile strength of the steel plate (base material), and further a strength of 90% or more can be obtained at the joint 4.

Example 1
Friction stir welding was performed using a steel plate having a plate thickness of 1.6 mm and having a chemical composition and tensile strength shown in Table 1 below. The joint butting surfaces were joined by pressing a rotating tool from both the one side and the other side of the steel sheet according to the surface state of a so-called I-shaped groove and milling with no angle. Table 2 shows the welding conditions of the friction stir welding. In Example 1, the rotary tool having the cross-sectional dimensions shown in FIGS. 5 (1) to (4) was used. The rotary tool used in Example 1 is a rotary tool whose surface is coated with titanium nitride (TiN) by physical vapor deposition (PVD) using tungsten carbide (WC) as a raw material. At the time of bonding, the bonded portion was shielded with argon gas to prevent surface oxidation. The coefficient of dynamic friction between the surface of the rotating tool of WC having a TiN coating treatment on the surface and the steel sheet was 0.6 or less.

  The dynamic friction coefficient between the tool material surface and the steel sheet was measured by the following measuring method. Using a ball-on-disk friction and wear tester, a disk made of the target material was pressed against a steel ball having a diameter of 6 mm while rotating with a load of 5 N, and the test was performed at a rotational speed of 100 mm / s and a sliding distance of 300 m. The test was performed at room temperature and without lubrication. The steel ball used for the test is a steel ball made of a material having a chemical component of SUJ2 defined by JIS G 4805 and processed as a steel ball for bearings.

  Prior to the bonding, in order to confirm the heating region by preheating using a laser as a heat source, the steel plate I in Table 1 was subjected to laser irradiation under the irradiation conditions (laser moving speed, laser output, and beam diameter) shown in Table 3. Light was irradiated and the surface temperature was measured by thermography. Furthermore, the cross section of the laser irradiation part was observed, and the microstructure was observed with a nital etchant.

Here, the region having the transformation point (T _A1 ° C) or higher is darkest, and is less than the transformation point (T _A1 ° C) existing outside, but a high hardness structure such as martensite in the base material is tempered. Since the region is etched relatively thin, the region where the transformation point (T _A1 ° C) or higher, the tempering region below the transformation point (T _A1 ° C), and the base material region can be distinguished. is there. Furthermore, from the knowledge of heat treatment of steel, it is known that the tempering region below the transformation point (T _A1 ° C) coincides with the region of 0.8 x T _A1 ° C or more and less than T _A1 ° C. Based on the microstructure observation with such a nital corrosion solution, the depth D _{0 of the} region where the transformation point (T _A1 ° C) or higher and the depth of the region where the temperature becomes 0.8 × T _A1 ° C or higher (of the heating region) Depth D) was measured.

  These measurement results are shown in Table 4.

As shown in Table 4, from the surface temperature measurement result by thermography, in the irradiation condition A, the region of 0.8 × T _A1 ° C or more was a circular shape with a diameter of 2.4 mm. Since the maximum diameter of the pin portion of the rotating tool used here is 4.0 mm, the area of the heating region in the irradiation condition A is equal to or less than the area of the maximum diameter portion of the pin portion of the rotating tool.

In the irradiation condition B, the region of 0.8 × T _A1 ° C. or higher was a circular shape having a diameter of 2.0 mm. Therefore, similarly to the above, the area of the heating region in the irradiation condition B is equal to or smaller than the area of the maximum diameter portion of the pin portion of the rotary tool.

In the irradiation condition C, the region of 0.8 × T _A1 ° C or higher was a circular shape having a diameter of 5.4 mm. Since the maximum diameter of the pin part of the rotary tool used here is 4.0 mm, the area of the heating region in the irradiation condition C exceeds the area of the maximum diameter part of the pin part of the rotary tool.

In the irradiation condition D, the region where the temperature is 0.8 × T _A1 ° C or more has an elliptical diameter in which the laser moving direction is the major axis and the direction perpendicular to the laser moving direction is the minor axis, the major axis is 1.8 mm, and the minor axis is 1. It was 2 mm. Since the maximum diameter of the pin portion of the rotating tool used here is 4.0 mm, the area of the heating region in the irradiation condition D is equal to or less than the area of the maximum diameter portion of the pin portion of the rotating tool.

In the irradiation condition E, the region where the temperature is 0.8 × T _A1 ° C. or more has an elliptical diameter in which the laser moving direction is the major axis and the direction perpendicular to the laser moving direction is the minor axis, the major axis is 2.3 mm and the minor axis is 1. It was 9 mm. Therefore, similarly to the above, the area of the heating region under the irradiation condition E is equal to or smaller than the area of the maximum diameter portion of the pin portion of the rotary tool.

Further, as shown in Table 4, the cross-section observation of the laser irradiation unit, the irradiation condition A, the depth of the region becomes T _A1 ° C. or higher and the depth of the turned region D ₀ and 0.8 × T _A1 ° C. or higher The depth (depth D of the heating region) was 1.60 mm and 1.60 mm, respectively, and regions having a temperature equal to or higher than T _A1 ° C. were formed over the entire thickness of the steel sheet. Therefore, the depth D of the heating region, which is the depth of the region of 0.8 × T _A1 ° C or higher, is 100% of the thickness t of the steel plate.

Under irradiation condition B, the depth D _{0 of the} region where T _A1 ° C or higher and the depth of the region where 0.8 × T _A1 ° C or higher (depth D of the heating region) are 0.47 mm and 0, respectively. .50 mm. Since the thickness t of the steel plate as the workpiece is 1.6 mm, the depth D of the heating region is about 31.3% of the thickness t of the steel plate.

Under irradiation condition C, the depth D _{0 of the} region where T _A1 ° C or higher and the depth of 0.8 × T _A1 ° C or higher (depth D of the heating region) are 0.28 mm and 0, respectively. .30 mm. Since the thickness t of the steel plate as the workpiece is 1.6 mm, the depth D of the heating region is about 18.8% of the thickness t of the steel plate.

Under irradiation condition D, the depth D _{0 of the} region where T _A1 ° C. or higher and the depth of the region where 0.8 × T _A1 ° C. or higher (depth D of the heating region) are 1.60 mm, 1 A region of .60 mm and T _A1 ° C or higher was formed in the entire thickness of the steel sheet. Therefore, the depth D of the heating region, which is the depth of the region of 0.8 × T _A1 ° C or higher, is 100% of the thickness t of the steel plate.

Under irradiation condition E, the depth D _{0 of the} region where T _A1 ° C or higher and the depth of 0.8 × T _A1 ° C or higher (depth D of the heating region) are 0.58 mm and 0, respectively. .63 mm. Since the thickness t of the steel plate as the workpiece is 1.6 mm, the depth D of the heating region is about 39.4% of the thickness t of the steel plate.

  Table 5 shows preheating process conditions by laser irradiation performed before joining the workpieces, and Table 6 shows process conditions performed after joining. Here, in the process performed after joining, cooling by gas ejection was performed, and in the heating (and reheating), induction heating was performed.

  In Tables 5 and 6, “-” in the preheating process condition and the process condition performed after bonding indicates a case where the preheating process and the process after bonding such as cooling and heating are not performed, respectively. In addition, in the description of “(AS)” and “(RS)” in the distance from the junction center line to the center of the heating area, the center of the heating area is located on the advancing side and the retreating side from the junction center line, respectively. Indicates.

  Table 7 shows the measured value of the torque of the rotating tool when the joining is performed and the measured value of the tensile strength of the obtained joint. The tensile strength of the joint joint is the result of taking a tensile test piece having the size of No. 1 test piece defined in JIS Z 3121 and conducting a tensile test. The greater the torque of the rotating tool, the lower the plastic fluidity and the more likely to cause defects.

  From Table 7, in invention examples 1-11, even if it was a case where a joining speed was 400 mm / min, the joint joint intensity | strength 90% or more of the tensile strength of the steel plate used as a base material was obtained. The torques of the rotary tools on the front and back sides of Invention Examples 1 to 11 were both 72 N · m or less, and the plastic fluidity was also good. In particular, in Invention Examples 7 to 10 in which only cooling / reheating, cooling or reheating was performed after joining, a strength equivalent to the tensile strength of the base material was obtained. In Invention Example 11 in which reheating and cooling were performed after joining, a strength of 96% or more of the tensile strength of the base material was obtained.

  The friction stir welding conditions of Comparative Examples 1 to 4 are conditions for joining by pressing the rotary tool from both one side and the other side of the steel sheet that satisfies the scope of the present invention, and the preheating process conditions are the present invention. This is a condition that does not satisfy the range. In Comparative Examples 1 to 4, the torques of both the front and back rotary tools were greater than 75 N · m, and the plastic fluidity was poor.

  The friction stir welding condition of Comparative Example 5 is a condition for joining by pressing a rotating tool from one side of a steel sheet that does not satisfy the scope of the present invention, and the preheating process condition is a condition for satisfying the scope of the present invention. . In Comparative Example 5, the torque of the rotary tool on the surface side was greater than 75 N · m, and the plastic fluidity was poor.

  In Invention Examples 12 to 21, even when the joining speed is increased to 1000 mm / min, a joint joint strength of 90% or more of the tensile strength of the base material is obtained, and each of the front side and the back side is obtained. The torque of the rotary tool was 90 N · m or less. In particular, in Inventive Examples 17 to 20 in which only cooling / reheating, cooling or reheating was performed after joining, joint joint strength equivalent to the tensile strength of the base material was obtained. In Invention Example 21, in which reheating and cooling were performed after joining, a joint joint strength of 99% or more of the tensile strength of the base material was obtained.

  The friction stir welding conditions of Comparative Example 6 and Comparative Example 7 are conditions in which the rotary tool is pressed from both the one side and the other side of the steel sheet that satisfies the scope of the present invention, and the preheating process conditions are This is a condition that does not satisfy the scope of the present invention. In Comparative Example 6 and Comparative Example 7, unjoined portions remained and could not be joined. For this reason, in the comparative example 6 and the comparative example 7, measurement of rotating tool torque etc. is not performed.

The friction stir welding conditions of Comparative Example 8 are conditions in which the rotating tool is pressed from one side of the steel sheet that does not satisfy the scope of the present invention and the preheating process conditions do not satisfy the scope of the present invention. . In Comparative Example 8, a joint strength of 90% or more of the tensile strength of the base material was obtained, but the torque of the rotary tool on the surface side was greater than 100 N · m, and the plastic fluidity was poor.
(Example 2)
Friction stir welding was performed using a steel plate having a plate thickness of 1.6 mm and a chemical composition and tensile strength shown in Table 1 above. The joint butting surfaces were joined by pressing a rotating tool from both the one side and the other side of the steel sheet according to the surface state of a so-called I-shaped groove and milling with no angle. The welding conditions for friction stir welding are shown in Table 2 above. In Example 2, the rotary tool having the cross-sectional dimensions (shoulder diameter a: 12 mm, pin portion maximum diameter b: 4 mm, probe length c: 1.4 mm) shown in FIG. 5 was used. The rotary tool used in Example 2 has a surface that is coated with titanium nitride (TiN) by physical vapor deposition (PVD) using tungsten carbide (WC) as a raw material without being coated with tungsten carbide (WC). , Coated with aluminum nitride nitride (AlCrN) using tungsten carbide (WC) as a material, or made of cubic boron nitride (CBN) as a material.

  At the time of bonding, the bonded portion was shielded with argon gas to prevent surface oxidation. The coefficient of dynamic friction between the surface of the rotating tool and the steel sheet is 0.7 when tungsten carbide (WC) is not used as a raw material, and titanium nitride (TiN) is formed by physical vapor deposition (PVD) using tungsten carbide (WC) as a raw material. ) Is 0.5, and tungsten carbide (WC) is made of aluminum nitride nitride (AlCrN), and 0.4 is made of cubic boron nitride (CBN). In the case of the above, it was 0.3.

  The dynamic friction coefficient between the tool material surface and the steel plate was measured by the same measurement method as in Example 1.

  Table 8 shows preheating process conditions by laser irradiation performed before joining the workpieces.

  In Table 8, “WC” is a rotating tool that is not coated with tungsten carbide (WC) as a material, and titanium nitride (TiN) is coated by physical vapor deposition (PVD) with tungsten carbide (WC) as a material. “WC + TiN” as the rotary tool, “WC + AlCrN” as the rotary tool coated with aluminum chromium nitride (AlCrN) using tungsten carbide (WC) as the raw material, and “CBN” as the rotary tool using cubic boron nitride (CBN) as the raw material. ". The laser irradiation conditions in the preheating process conditions are as shown in Table 3 above, and the surface shape and depth of the heating region formed by each laser irradiation condition are as shown in Table 4 above.

  In Example 2, the process after joining was not performed. “(AS)” and “(RS)” in the distance from the junction center line to the center of the heating region indicate that the center of the heating region is located on the advansing side and the retreating side from the junction center line, respectively.

  Table 9 shows the measured values of the torque of the rotating tool and the measured values of the tensile strength of the obtained joints when the joining is performed. The tensile strength of the joint joint is the result of taking a tensile test piece having the size of No. 1 test piece defined in JIS Z 3121 and conducting a tensile test. The greater the torque of the rotating tool, the lower the plastic fluidity and the more likely to cause defects.

  From Table 9, in the invention examples 22-27, even if it was a case where a joining speed was 400 mm / min, the joint joint intensity | strength 90% or more of the tensile strength of the steel plate used as a base material was obtained. The torques of the rotating tools on the front side and the back side of Invention Examples 22 to 27 were all 65 N · m or less, and the plastic fluidity was also good.

  On the other hand, in Comparative Examples 9 and 10, the torque of the rotary tool on both the front and back rotary tools was greater than 75 N · m, and the plastic fluidity was poor.

  In Invention Examples 28 to 33, even when the joining speed is increased to 1000 mm / min, a joint joint strength of 93% or more of the tensile strength of the steel sheet as the base material can be obtained. The torque of each of the rotary tools was 86 N · m or less. On the other hand, in Comparative Examples 11 and 12, the torque of the rotary tool on both the front and back rotary tools was greater than 90 N · m, and the plastic fluidity was poor.

DESCRIPTION OF SYMBOLS 1 Surface side rotary tool 2 Rotating shaft of surface side rotary tool 3 Steel plate 4 Joint part 5 Heating means 6 Cooling means 7 Backward heating means 8 Shoulder part of surface side rotary tool 9 Pin part of surface side rotary tool 10 Joining center line 11 RS Line 12 Heating area 13 Cooling area 14 Reheating area 15 Back surface side rotating tool 16 Shoulder portion of back surface side rotating tool 17 Pin portion of back surface side rotating tool 19 Rotating shaft of back surface side rotating tool 20 Control means 21 Gripping device 22 Lower jig 23 Upper jig 24 Clamp a Diameter of shoulder part of surface side rotating tool b Maximum diameter of pin part of surface side rotating tool c Length of pin of surface side rotating tool X Distance between heating area and rotating tool D Depth of heating area t Steel plate thickness α Front side rotation tool inclination angle β Back side rotation tool inclination angle

Claims (22)

A pair of rotary tools are respectively arranged facing the one side and the other side of the steel plate as a workpiece, and moved in the joining direction while rotating the pair of rotary tools at the unjoined portion between the steel plates, A friction stir welding method in which the steel plates are softened by frictional heat between a pair of rotating tools and the steel plate, and the softened portions are stirred by the pair of rotating tools to cause plastic flow and join the steel plates together. There,
The dynamic friction coefficient between the steel plate and the material of the pair of rotary tools or the material coated on the surface of the pair of rotary tools is 0.6 or less,
The rotating tool disposed on at least one surface side includes a shoulder portion and a pin portion arranged on the shoulder portion and sharing the rotation axis with the shoulder portion,
The shoulder portion and the pin portion are formed of a material harder than the steel plate,
While fixing the steel plate, pressing the pair of rotary tools against one side and the other side of the steel plate, moving the pair of rotary tools in the joining direction while rotating,
A region in which the temperature T _S (° C.) of the surface of the steel sheet heated by the heating means provided in front of the rotating tool arranged on the one surface side satisfies the following formula (1) is defined as a heating region. When the minimum distance between the heating area and the rotating tool disposed on the one surface side is equal to or less than the diameter of the shoulder of the rotating tool on the one surface side,
The area of the heating region is equal to or less than the area of the maximum diameter portion of the pin portion of the rotary tool disposed on the one surface side,
65% or more of the area of the heating region is parallel to the joining center line, which is a straight line passing through the rotation axis of the rotary tool arranged on the one surface side of the steel plate and parallel to the joining direction. And a straight line separated by the same distance as the maximum radius of the pin portion of the rotary tool arranged on the one surface side to the retreating side.
T _S ≧ 0.8 × T _A1 (1)
T _A1 is a temperature represented by the following formula (2).
T _A1 (° C.) = 723-10.7 [% Mn] −16.9 [% Ni] +29.1 [% Si] +16.9 [% Cr] +290 [% As] +6.38 [% W] · (2)
Said [% M] is content (mass%) of M element in the steel plate which is a workpiece, and is set to 0 when not containing.   The friction stir welding method according to claim 1, wherein both of the pair of rotating tools include the shoulder portion and the pin portion, and the pair of rotating tools have the same pin length.   Both of the pair of rotary tools include a shoulder portion and the pin portion, and the pin length of the rotary tool arranged on the one surface side is shorter than the pin length of the rotary tool arranged on the other surface side. The friction stir welding method according to claim 1.   4. The axial center of at least one rotary tool of the pair of rotary tools is tilted in a direction in which the pin portion precedes the joining direction of the rotary tool. Friction stir welding method.   The friction stirrer according to any one of claims 1 to 4, wherein a rotation direction of the rotary tool arranged on the one surface side is a direction opposite to a rotation direction of the rotary tool arranged on the other surface side. Joining method. When the depth from the surface of the steel sheet in the region where the temperature T _D (° C.) in the thickness direction of the heating region satisfies the following formula (3) is defined as the depth D of the heating region, the depth of the heating region The friction stir welding method according to any one of claims 1 to 5, wherein D is 100% of the thickness of the steel plate.
T _D ≧ 0.8 × T _A1 (3)   The friction stir welding method according to any one of claims 1 to 6, wherein the heating means is a laser heating device.   The back heating means is provided in the joining direction rear side of the rotary tool arranged on the one surface side, and the back heating means heats the joining portion of the steel sheet. The friction stir welding method described.   The friction stir welding method according to claim 8, wherein a cooling means is provided behind the rear heating means in the joining direction, and the cooling means cools the joint heated by the rear heating means.   The friction stir welding method according to any one of claims 1 to 7, wherein a cooling means is provided behind the rotating tool in the joining direction, and the cooling means cools the joining portion of the steel sheet.   The friction stir welding method according to claim 10, wherein a rear heating means is provided at the rear of the cooling means in the joining direction, and the rear heating means heats the joining portion cooled by the cooling means. A friction stir welding apparatus that joins unjoined portions between steel plates that are workpieces,
A gripping device for fixing the steel plate;
A pair of rotating tools that are arranged opposite to the one surface side and the other surface side of the steel plate and are movable in the joining direction while rotating in the unjoined portion between the steel plates,
A heating means for heating the steel plate, provided in front of the rotating direction of the rotary tool disposed on the one surface side;
Control means for controlling the rotating tool and the heating means so as to realize the following state 1;
The rotating tool disposed on at least one surface side includes a shoulder portion and a pin portion arranged on the shoulder portion and sharing the rotation axis with the shoulder portion,
The shoulder portion and the pin portion are formed of a material harder than the steel plate,
The friction stir welding apparatus, wherein a dynamic friction coefficient between the steel plate and the material of the pair of rotary tools or the material coated on the surface of the pair of rotary tools is 0.6 or less.
(State 1)
When the region where the temperature T _S (° C.) of the surface of the steel sheet heated by the heating unit satisfies the following formula (1) is defined as the heating region, the heating region and the rotating tool disposed on the one surface side; The minimum distance is less than or equal to the diameter of the shoulder of the rotating tool disposed on the one surface side,
The area of the heating region on the surface of the steel sheet is equal to or less than the area of the maximum diameter portion of the pin portion of the rotary tool disposed on the one surface side,
65% or more of the area of the heating region is parallel to the joining center line, which is a straight line passing through the rotation axis of the rotary tool arranged on the one surface side of the steel plate and parallel to the joining direction. And a straight line separated from the retreating side by the same distance as the maximum radius of the pin portion of the rotary tool arranged on the one surface side.
T _S ≧ 0.8 × T _A1 (1)
T _A1 is a temperature represented by the following formula (2).
T _A1 (° C.) = 723-10.7 [% Mn] −16.9 [% Ni] +29.1 [% Si] +16.9 [% Cr] +290 [% As] +6.38 [% W] · (2)
Said [% M] is content (mass%) of M element in the steel plate which is a workpiece, and is set to 0 when not containing.   The friction stir welding apparatus according to claim 12, wherein both of the pair of rotating tools include the shoulder portion and the pin portion, and the pair of rotating tools have the same pin length.   Both of the pair of rotary tools include the shoulder portion and the pin portion, and the pin length of the rotary tool arranged on the one surface side is larger than the pin length of the rotary tool arranged on the other surface side. The friction stir welding apparatus according to claim 12, which is short.   The friction stir welding apparatus according to any one of claims 12 to 14, wherein an axis of at least one rotary tool in the pair of rotary tools is inclined in a direction in which the pin portion precedes the joining direction.   The friction stirrer according to any one of claims 12 to 15, wherein a rotation direction of the rotary tool arranged on the one surface side is a direction opposite to a rotation direction of the rotary tool arranged on the other surface side. Joining device. The friction stir welding apparatus according to any one of claims 12 to 16, wherein the control means controls the rotating tool and the heating means so as to realize the following state 2.
(State 2)
When the depth from the surface of the steel sheet in the region where the temperature T _D (° C.) in the thickness direction of the heating region satisfies the following formula (3) is defined as the depth D of the heating region, the depth of the heating region D is 100% of the thickness t of the steel sheet.
T _D ≧ 0.8 × T _A1 (3)   The friction stir welding apparatus according to any one of claims 12 to 17, wherein the heating means is a laser heating apparatus. It further has a rear heating means for heating the joined portion of the steel sheet,
The friction stir welding apparatus according to any one of claims 12 to 18, wherein the rear heating means is provided rearward in the joining direction of the rotary tool. A cooling means for cooling the joint;
The friction stir welding apparatus according to claim 19, wherein the cooling means is provided behind the rear heating means in the joining direction. A cooling means for cooling the joint of the steel plates;
The friction stir welding apparatus according to any one of claims 12 to 18, wherein the cooling means is provided behind the rotating tool in the joining direction. A rear heating means for heating the joint;
The friction stir welding apparatus according to claim 21, wherein the rear heating means is provided rearward in the joining direction of the cooling means.

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