CN109689276B - Friction stir welding method and apparatus - Google Patents
Friction stir welding method and apparatus Download PDFInfo
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- CN109689276B CN109689276B CN201780055151.9A CN201780055151A CN109689276B CN 109689276 B CN109689276 B CN 109689276B CN 201780055151 A CN201780055151 A CN 201780055151A CN 109689276 B CN109689276 B CN 109689276B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
- B23K20/12—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating the heat being generated by friction; Friction welding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
- B23K20/26—Auxiliary equipment
Abstract
The present invention provides a friction stir welding method, wherein a preheating step of heating a steel sheet as a workpiece is performed by a heating mechanism provided in front of a rotary tool moving in a welding direction, and the surface temperature, area, position, and the like of a heating region in the preheating step are strictly controlled. In friction stir welding of structural steel, a rotary tool made of a material having a coefficient of dynamic friction with a steel plate of 0.6 or less is used, and 65% or more of the area of a heated region heated by a heating means provided in front of the rotary tool is located between a welding center line on the surface of the steel plate, which is a line passing through the rotation axis of the rotary tool and parallel to the welding direction, and a line parallel to the welding center line, which is a line spaced apart from the backward side only by the same distance as the maximum radius of the pin portion of the rotary tool.
Description
Technical Field
The present invention relates to a friction stir welding method in which a rotary tool is inserted into an unjoined portion between workpieces and moved while rotating, and the workpieces are welded without adding a filler by softening the workpieces by frictional heat with the rotary tool and by stirring plastic flow generated in the softened portion with the rotary tool, and an apparatus for implementing the friction stir welding method.
Background
As a friction welding method, patent document 1 discloses the following technique: when both or one of the pair of metal materials is rotated, frictional heat is generated in the metal materials to soften the metal materials, and the softened portions are stirred to cause plastic flow, thereby joining the metal materials.
However, since this technique is a technique of rotating a metal material to be joined, there is a limitation in the shape and size of the joined metal materials.
The friction welding method described in patent document 1 is a method of welding workpieces by rotating the workpieces and utilizing frictional heat between the workpieces. The friction stir welding method disclosed in patent document 2 is a method in which a tool is moved while being rotated in a state in which a welding member is fixed, thereby performing welding. In this way, since the friction stir welding method performs the welding by moving the tool, there is an advantage that the solid-phase welding can be continuously performed along the longitudinal direction even if the member is a member that is substantially infinitely long with respect to the welding direction. Further, since solid-phase bonding is performed by plastic flow of metal due to frictional heat of the tool and the bonding member, bonding can be performed without melting the bonding portion. Moreover, there are many advantages as follows: since the heating temperature is low, deformation after bonding is small; since the joint is not melted, there are few defects, and no filler is required; and so on.
Friction stir welding is a welding method of low melting point metal materials represented by aluminum alloys and magnesium alloys, and is being used in the fields of airplanes, ships, railway vehicles, automobiles, and the like. The reason for this is considered to be that these low melting point metal materials are difficult to obtain satisfactory characteristics of the joint by the conventional arc welding method, and the use of the friction stir welding method can improve productivity and obtain a high quality joint.
On the other hand, in the application of the friction stir welding method to structural steel mainly used as a material for structural materials such as buildings, ships, heavy machinery, pipelines, and automobiles, solidification cracking and hydrogen induced cracking, which have been problems in conventional melt welding, can be avoided, and structural change of steel material can be suppressed, so that excellent joint performance can be expected. In the friction stir welding method, since the clean surfaces are produced by stirring the welding interface with the rotating tool and are brought into contact with each other, there is also expected an advantage that a preliminary step such as diffusion welding is not required. Thus, many advantages can be expected in the application of the friction stir welding method to structural steels. However, the friction stir welding method has not been widely used in structural steels as compared with low-melting point metal materials, and has been problematic in terms of joint workability such as suppression of occurrence of defects at the time of joining and increase in joining speed.
In friction stir welding of structural steels, Polycrystalline Cubic Boron Nitride (PCBN) and silicon nitride (Si) are used as rotary tools as described in patent documents 3 and 43N4) High abrasion resistance materials. Since these ceramics are brittle, the thicknesses of the steel sheets to be joined and the working conditions thereof are significantly limited in order to prevent breakage of the rotary tool.
For example, patent document 5 discloses the following friction stir joining method: the joining apparatus is provided with a heating mechanism using an induction heating device, and the workpiece is heated before and after joining, thereby achieving high joining speed and elimination of cracks at the joined portion.
However, in the techniques of patent documents 5 and 6, the surface temperature, depth, and the like of the heated region of the workpiece due to heating before joining are not considered, and therefore sufficient joining workability cannot be obtained. Further, the microstructure around the heated region changes due to excessive heating, and the joint characteristics, particularly the joint strength, may be adversely affected.
Patent document 7 discloses a friction stir welding method in which a workpiece is partially heated immediately before welding, and the position, surface temperature, depth, and the like of a heated region are limited, thereby obtaining sufficient strength and improving the welding workability. However, no consideration is given to the influence of the relationship between the position of partial heating of the workpiece and the frictional heat generation (which is governed by the coefficient of dynamic friction between the material of the rotary tool or the material coated on the surface of the rotary tool and the workpiece) on the joining workability.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 62-183979
Patent document 2: japanese Kohyo publication Hei 7-505090
Patent document 3: japanese Kokai publication Hei-2003-532542
Patent document 4: japanese Kokai publication Hei-2003-532543
Patent document 5: japanese patent laid-open publication No. 2003-94175
Patent document 6: japanese patent laid-open publication No. 2005-288474
Patent document 7: international publication No. 2015/045299
Disclosure of Invention
Problems to be solved by the invention
The present invention has been made in view of the above-described situation, and an object thereof is to eliminate a plastic flow defect caused by insufficient heating of a workpiece at the time of friction stir welding, and to achieve sufficient strength and improvement of welding workability. In particular, an object of the present invention is to provide a friction stir welding method in which the conditions of the preheating process are strictly studied, taking into consideration the influence of the relationship between the position of partial heating of the workpiece and the frictional heat generation (which is caused by the coefficient of dynamic friction between the material of the rotary tool or the material coated on the surface of the rotary tool and the workpiece) on the workability of the welding, and to provide an apparatus for implementing the friction stir welding method.
Means for solving the problems
The inventors of the present application have made intensive studies to solve the above problems, and as a result, have obtained the following findings.
a) In general friction stir welding, the only heat source required for the welding is frictional heat generated between a rotating tool and a workpiece. Therefore, when structural steel is joined by friction stir welding, the amount of heat required to soften structural steel as a workpiece cannot be sufficiently secured. As a result, sufficient plastic flow cannot be obtained at the joint portion, and deterioration of joint workability such as reduction in joint speed and occurrence of joint defects may occur.
In order to avoid deterioration of the joining workability, which is very important for industrialization of the above-described technology, it is considered that the preheating step before friction stir joining is effective.
b) However, when the preheating process before friction stir welding is performed, if the preheating heat amount is too large, the microstructure around the heating region may be changed. In particular, in the case of a high-tensile steel sheet strengthened by a martensite structure, even if heating at a temperature equal to or lower than the ferrite-austenite transformation temperature is performed, the martensite annealing softens around the heated region, and the joint strength is significantly reduced.
Therefore, the inventors of the present application have made various studies on the conditions of the preheating process before friction stir welding.
As a result, the following findings were obtained:
c) by using a heat source having high energy density such as a laser, the surface temperature, area, and position of the heating region in the preheating step are strictly controlled, and the temperature in the thickness direction of the heating region is also appropriately controlled as necessary. This can improve the joining workability without deteriorating the joint characteristics such as the strength of the joint.
d) In particular, the following findings were obtained: the position of the partial heating of the workpiece changes depending on the relationship with frictional heat generation (which is governed by the coefficient of dynamic friction between the material of the rotary tool or the material coated on the surface of the rotary tool and the workpiece), and the region in which the effect of improving the joining workability is produced changes.
e) The following insights were obtained: in general friction stir welding, since a welded portion is naturally cooled after completion of welding, there is a problem that micro-structural control based on thermal history management as performed in a rolling process in steel production cannot be applied. However, immediately after the joining is completed, the joining portion is subjected to a step of combining a heating treatment and a cooling treatment, whereby the properties of the joined joint can be further improved.
The present invention is based on the above-described findings, and in particular, can eliminate the plastic flow defect caused by insufficient heating of the workpiece, which may occur when the friction stir welding method is applied to the welding of structural steels, and can achieve sufficient strength and improvement in the welding workability.
That is, the gist of the present invention is as follows.
[1]A friction stir welding method in which a rotary tool is inserted into an unjoined portion between steel plates and the rotary tool is moved in a welding direction while rotating, and the softened portion is stirred by the rotary tool while softening the steel plates by frictional heat between the rotary tool and the steel plates, thereby generating plastic flow and welding the steel plates to each other, wherein the rotary tool has a shoulder portion and a pin portion disposed on the shoulder portion and sharing a rotation axis with the shoulder portion, the shoulder portion and the pin portion are formed of a material harder than a steel plate as a workpiece, and the material of the rotary tool or a material coated on the surface of the rotary tool has a coefficient of dynamic friction with the steel plate of 0.6 or less, and the temperature of the surface of the steel plate to be heated by a heating means provided forward in the joining direction of the rotary tool is set to be lower than that of the steel plate.Degree TS(DEG C) when a region satisfying the following formula (1) is used as the heating region, the minimum distance between the heating region and the rotating tool is less than or equal to the diameter of the shoulder part of the rotating tool, the area of the heating region is less than or equal to the area of the maximum diameter part of the pin part of the rotating tool, more than 65% of the area of the heating region is positioned between a joint center line of the surface of the steel plate and a straight line parallel to the joint center line, the joint center line passes through the rotating shaft of the rotating tool and is parallel to the joint direction, the straight line parallel to the joint center line is a straight line which is separated from the backward side by the same distance as the maximum radius of the pin part of the rotating tool,
TS≥0.8×TA1……(1)
TA1the temperature is represented by the following formula (2),
TA1(℃)＝723-10.7[％Mn]-16.9[％Ni]+29.1[％Si]+16.9[％Cr]+290[％As]+6.38[％W]……(2)
the above [% M ] is the content (% by mass) of the M element in the steel sheet as the workpiece, and is 0 in the absence of the M element.
[2]Such as [1]]The friction stir welding method described above, wherein the temperature T in the thickness direction of the heating region is set toD(DEG C) when the maximum depth from the surface of the steel sheet in a region satisfying the following formula (3) is taken as the depth D of the heated region, the depth D of the heated region is more than 30% of the thickness of the steel sheet,
TD≥0.8×TA1……(3)。
[3] the friction stir welding method according to [1] or [2], wherein the heating mechanism is a laser heating device.
[4] The friction stir welding method according to any one of [1] to [3], wherein a rear heating mechanism that heats a welded portion of the steel plates is provided behind the rotating tool in the welding direction.
[5] The friction stir welding method according to [4], wherein a cooling mechanism that cools the welded portion heated by the rear heating mechanism is provided behind the welding direction of the rear heating mechanism.
[6] The friction stir welding method according to any one of [1] to [3], wherein a cooling mechanism that cools a joint portion of the steel plates is provided rearward in a welding direction of the rotary tool.
[7] The friction stir welding method according to [6], wherein a rear heating means that heats the welded portion cooled by the cooling means is provided behind the cooling means in the welding direction.
[8] A friction stir welding apparatus for welding an unwelded portion between steel plates as workpieces, the friction stir welding apparatus comprising:
a rotating tool having a shoulder portion and a pin portion disposed on the shoulder portion and sharing a rotation axis with the shoulder portion, the shoulder portion and the pin portion being formed of a material harder than the steel plate, the rotating tool being moved in a joining direction while rotating in a state of being inserted into an unbonded portion between the steel plates, thereby generating a plastic flow while stirring a softened portion while softening the steel plates by frictional heat,
a heating means provided in front of the rotary tool in the joining direction for heating the steel plate,
a control means for controlling the rotary tool and the heating means so as to realize the following state 1,
the coefficient of dynamic friction between the material of the rotary tool or the material coated on the surface of the rotary tool and the steel plate is 0.6 or less,
(State 1)
A temperature T of a surface of the steel sheet to be heated by the heating meansS(DEG C) when a region satisfying the following formula (1) is used as a heating region, the minimum distance between the heating region and the rotating tool is less than or equal to the diameter of the shoulder of the rotating tool,
the area of the heating region is equal to or smaller than the area of the maximum diameter portion of the pin portion of the rotary tool,
wherein 65% or more of the area of the heating zone is located between a joining center line of the surface of the steel sheet, which is a straight line passing through the rotation axis of the rotating tool and parallel to the joining direction, and a straight line parallel to the joining center line, which is a straight line spaced apart from the backward side by the same distance as the maximum radius of the pin portion of the rotating tool,
TS≥0.8×TA1……(1)
TA1the temperature is represented by the following formula (2),
TA1(℃)＝723-10.7[％Mn]-16.9[％Ni]+29.1[％Si]+16.9[％Cr]+290[％As]+6.38[％W]……(2)
the above [% M ] is the content (% by mass) of the M element in the steel sheet as the workpiece, and is 0 in the absence of the M element.
[9] The friction stir welding apparatus according to [8], wherein the control means controls the rotary tool and the heating means so as to realize the following state 2,
(State 2)
Temperature T in the thickness direction of the heating regionD(DEG C) when the maximum depth from the surface of the steel sheet in a region satisfying the following formula (3) is taken as the depth D of the heated region, the depth D of the heated region is more than 30% of the thickness of the steel sheet,
TD≥0.8×TA1……(3)。
[10] the friction stir welding apparatus according to [8] or [9], wherein the heating mechanism is a laser heating device.
[11] The friction stir welding apparatus according to any one of [8] to [10], further comprising a rear heating mechanism that heats a welded portion of the steel plates,
the rear heating mechanism is disposed rearward in the joining direction of the rotary tool.
[12] The friction stir welding apparatus according to [11], further comprising a cooling mechanism that cools the welded portion,
the cooling mechanism is disposed rearward in the joining direction of the rear heating mechanism.
[13] The friction stir welding apparatus according to any one of [8] to [10], further comprising a cooling mechanism that cools a welded portion of the steel plates,
the cooling mechanism is disposed rearward in the joining direction of the rotary tool.
[14] The friction stir welding apparatus according to [13], further comprising a rear heating mechanism for heating the welded portion,
the rear heating mechanism is disposed rearward in the joining direction of the cooling mechanism.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a plastic flow defect caused by insufficient heating of a workpiece can be eliminated, and the joining workability of friction stir joining can be improved. Further, it is possible to suppress the change of the microstructure around the heating region, and to obtain high joint strength in the joint.
Drawings
Fig. 1 is a schematic diagram illustrating a friction stir welding method according to the present embodiment.
Fig. 2 is a view (plan view and a-a sectional view) showing an example of a heating region in the preheating step, a cooling region in the step performed after the joining, and a reheating region.
Fig. 3 is a graph showing a relationship between a temperature and a tensile strength of a steel sheet joined by the friction stir welding method according to the present embodiment.
FIG. 4 is a view showing the cross-sectional dimension of a rotary tool.
Detailed Description
The present invention will be specifically described below with reference to embodiments thereof. Fig. 1 is a schematic diagram illustrating a friction stir welding method and a friction stir welding apparatus according to the present embodiment. In the friction stir welding method according to the present embodiment, as shown in fig. 1, a rotary tool is inserted into an unwelded portion between steel plates, the rotary tool is moved in a welding direction while being rotated, the steel plates are softened by frictional heat of the rotary tool and the steel plates, and the softened portion is stirred by the rotary tool, thereby generating plastic flow, and the steel plates are welded to each other. Here, the rotary tool has a shoulder portion and a pin portion disposed on the shoulder portion and sharing a rotation axis with the shoulder portion, and at least the shoulder portion and the pin portion are formed of a material harder than a steel plate as a workpiece.
In fig. 1, reference numeral 1 denotes a rotary tool, 2 denotes a rotary shaft, 3 denotes a steel plate, 4 denotes a joining portion, 5 denotes a heating mechanism, 6 denotes a cooling mechanism, 7 denotes a rear heating mechanism, 8 denotes a shoulder portion of the rotary tool, 9 denotes a pin portion of the rotary tool, and 15 denotes a control mechanism. α represents the tilt angle of the rotating tool. "AS" indicates the forward side, and "RS" indicates the backward side. Here, the forward side refers to a side where the tool rotation direction coincides with the joining direction, and the backward side refers to a side opposite to the tool rotation direction and the joining direction, respectively.
In the present embodiment, the butted portion where only the steel plates 3 are butted and not joined is referred to as "unjoined portion", and the portion joined and integrated by plastic flow is referred to as "joined portion".
In the friction stir welding method of the present embodiment, a preheating step of heating the steel sheet 3 by the heating mechanism 5 provided in front of the rotary tool 1 moving in the welding direction is important. The conditions of the preheating step will be described below with reference to fig. 2.
Fig. 2 is a view (plan view and a-a sectional view) showing an example of a heating region in the preheating step, a cooling region in the step performed after the joining, and a reheating region. In fig. 2, a joint center line 10 indicates a straight line of the surface of the steel plate 3 passing through the rotation axis 2 of the rotary tool 1 and parallel to the joint direction. The RS line 11 is a straight line parallel to the joint center line 10 and spaced apart only to the backward side by the same distance as the maximum radius of the pin portion 9 of the rotary tool. Reference numeral 12 denotes a heating zone, 13 denotes a cooling zone, and 14 denotes a reheating zone. a represents the diameter of the shoulder 8 of the rotating tool, b represents the maximum diameter of the pin 9 of the rotating tool, X represents the minimum distance between the heated area 12 and the rotating tool 1, D represents the depth of the heated area 12, and t represents the thickness of the steel plate 3.
Surface temperature T of steel sheet in heating zoneS：TS≥0.8×TA1。
Fig. 3 is a graph showing a relationship between a temperature and a tensile strength of a steel sheet joined by the friction stir welding method according to the present embodiment. The steel sheets 3 joined by the friction stir welding method of the present embodiment are usually at a transformation temperature T of the steel as shown in fig. 3A1About 80% of the strength at room temperature, the strength becomes about 30% of the strength at room temperature. Further, above this temperature, the strength of the steel sheet 3 further decreases. Thereby, the surface temperature T of the steel plate 3 is satisfiedSIs 0.8 XTA1The steel sheet 3 is pre-softened at a temperature of not less than DEG C, and the steel sheet 3 is stirred to promote plastic flow. This reduces the load applied to the rotary tool 1, and increases the joining speed. Therefore, in the friction stir welding method of the present embodiment, the surface temperature T of the steel sheet 3 is set toSA region satisfying the following expression (1) is a heating region 12.
TS≥0.8×TA1…(1)
Transformation temperature T of steelA1The (. degree.C.) can be determined by the following formula (2).
TA1(℃)＝723-10.7[％Mn]-16.9[％Ni]+29.1[％Si]+16.9[％Cr]+290[％As]+6.38[％W]……(2)
The above [% M ] is the content (mass%) of the M element in the steel sheet 3 as the workpiece, and is 0 in the absence of M element.
Due to being higher than 0.8 XTA1Since the strength of the steel sheet 3 tends to decrease with an increase in temperature in the case of ° c, the surface temperature T of the steel sheet 3 in the hot zone 12 is preferably set to be equal toSThe adjustment is performed in a manner that does not excessively rise. Specifically, in order to secure the heated area 12 in the thickness direction, there may be a temperature gradient (variation in temperature in the surface) in the surface of the heated area 12, but at this time, it is preferable that the maximum surface temperature of the steel sheet 3 in the heated area 12 be 1.5 × TMBelow DEG C. Before contacting the rotating tool 1 passing through the heating zone 12, the steel sheet 3 in the heating zone 12 is preferably heatedSurface temperature less than TMDEG C. This can avoid damage to the rotary tool 1 due to an excessive increase in the temperature of the joint 4 and avoid deterioration of the microstructure around the heating region 12. T isMThe melting point (c) of the steel sheet 3 as the workpiece is shown.
Minimum distance X between the heated area of the steel plate surface and the rotating tool: under the diameter of the shoulder of the rotary tool
If the minimum distance X between the heated region 12 on the surface of the steel sheet 3 and the rotary tool 1 is too large, the temperature of the heated region 12 before joining is lowered, and the effect of preheating cannot be sufficiently obtained. Therefore, in the friction stir welding method according to the present embodiment, the minimum distance X between the heated region 12 on the surface of the steel sheet 3 and the rotary tool 1 moving in the welding direction is equal to or less than the diameter of the shoulder 8 of the rotary tool.
However, when the minimum distance X between the heated region 12 and the rotary tool 1 is too small, the rotary tool 1 may be damaged by heat generated by the heating means 5, and therefore the minimum distance X between the heated region 12 on the surface of the steel plate 3 and the rotary tool 1 moving in the joining direction is preferably 0.1 times or more the diameter of the shoulder 8 of the rotary tool. The diameter of the shoulder 8 of the rotary 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 rotary tool 1 is preferably 200mm/min to 3000 mm/min.
Area of heating area of steel sheet surface: the maximum diameter part of the pin part of the rotary tool has an area below
When the heating zone 12 is too large, the micro-tissue tends to deteriorate in the heating zone 12 and its peripheral area. In particular, in the case of a high-tensile steel sheet strengthened by a martensite structure, even when heating at a temperature of not higher than the ferrite-austenite transformation temperature, martensite annealing occurs and softening occurs, and the joint strength is significantly reduced. Therefore, in the friction stir welding method according to the present embodiment, the area of the heated region 12 on the surface of the steel plate 3 is equal to or smaller than the area of the maximum diameter portion of the pin portion 9 of the rotary tool.
On the other hand, when the area of the heating zone 12 is too small, the effect of preheating cannot be sufficiently obtained. Accordingly, the area of the heated region 12 of the surface of the steel plate 3 is preferably 0.1 times or more the area of the maximum diameter portion of the pin 9 of the rotating tool.
The maximum diameter of the pin 9 of the rotary tool in the present embodiment is, for example, about 2 to 50 mm. The maximum diameter of the pin 9 of the rotary tool is the maximum diameter among diameters obtained in a cross-sectional plane when 1 pin is cut in a cross-sectional plane perpendicular to the axial direction.
Fig. 4 is a view showing the cross-sectional dimension of the rotary tool. As shown in fig. 4, in the case where the diameter of the pin portion 9 of the rotary tool does not change in the axial direction, the diameter (4 mm in the drawing) of the upper surface of the pin portion 9 of the rotary tool can be set as the maximum diameter of the pin portion 9 of the rotary tool. When the pin portion 9 of the rotary tool has a taper shape or the like and the pin diameter differs depending on the position in the axial direction, the maximum diameter can be set as the maximum diameter of the pin portion 9 of the rotary tool. Reference symbol c in fig. 4 denotes a probe length (probe length) which is calculated from a height difference between the tip end portion of the pin portion 9 of the rotary tool and the highest position of the shoulder portion 8 of the rotary tool.
The shape of the heating region 12 may be any shape such as a circle, an ellipse, and a rectangle. The pin portion 9 of the rotary tool has a maximum diameter portion which is generally circular or elliptical in shape.
Area of a heating region located between the joining center line and the RS line in the surface of the steel sheet: the area of the heating zone on the surface of the steel plate is more than 65 percent
In the friction stir welding of the steel plates 3, the plastic flow starts at the forward side, passes through the forward side in the welding direction, the backward side, and the backward side in the welding direction along the rotation direction of the rotary tool 1, and ends at the forward side. Since the advancing side becomes a starting point of the plastic flow, the steel sheet 3 as the work material is likely to be insufficiently heated. Therefore, when defects are generated due to insufficient plastic flow, they almost all occur on the advancing side. Therefore, the surface of the steel sheet 3 is preferentially heated on the advancing side to soften the steel sheet, thereby promoting plastic flow, suppressing the occurrence of defects, and increasing the joining speed.
However, when the coefficient of kinetic friction between the material of the rotary tool 1 or the material coated on the surface of the rotary tool 1 and the steel plate 3 as the material to be joined is 0.6 or less, frictional heat and plastic flow generated between the rotary tool 1 and the steel plate 3 become small. The forward side is a region which is a starting point of plastic flow in front of the rotary tool 1 and in which a large amount of frictional heat is generated between the rotary tool 1 and the steel plate 3. However, the dynamic friction coefficient tends to decrease in a high temperature state, and if the portion is preheated to a high temperature, sufficient frictional heat generation cannot be obtained when the dynamic friction coefficient between the rotary 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 is insufficient, the occurrence of a defect on the advancing side which becomes the end point of the plastic flow is greatly influenced. In particular, when the coefficient of dynamic friction between the rotary tool 1 and the steel plate 3 is small, sufficient plastic flow cannot be obtained.
Therefore, when the coefficient of dynamic friction between the steel plate 3 and the material of the rotary tool 1 or the material coated on the surface of the rotary tool 1 is 0.6 or less, 65% or more of the area of the heated region 12 is positioned between the joining center line 10 and the RS line 11 parallel to the joining center line 10 on the surface of the steel plate 3, and the retreating side is preferentially heated. This can promote the plastic flow on the backward side, which is the middle of the plastic flow, while ensuring frictional heat generation on the forward side, which becomes the starting point of the plastic flow, and suppress the occurrence of defects, thereby increasing the joining speed. The area range of the heating region 12 located between the joining center line 10 and the RS line 11 is preferably 70% or more, more preferably 80% or more, and may be 100%.
From the viewpoint of heating the retreating side preferentially, the center of the heating region 12 is located between the RS line 11 and a straight line passing through the midpoint between the joining center line 10 and the RS line 11. In other words, the center of the heating zone 12 is preferably located closer to the retreating side than the joining center line 10, and more preferably, the distance from the center of the heating zone 12 to the joining center line 10 is 0.5 times or more and 1 time or less the maximum radius of the pin portion 9 of the rotating tool.
Heating ofTemperature T in a region in the thickness direction of the regionD：TD≥0.8×TA1
As described above, the steel sheets 3 joined by the friction stir welding method according to the present embodiment have a transformation temperature T of steelA1About 80% of the strength at room temperature, the strength becomes about 30% of the strength at room temperature. Further, above this temperature, the strength of the steel sheet 3 further decreases. Accordingly, it is preferable that the temperature is set to 0.8 × T also in the region in the thickness direction of the heating zone 12A1The steel sheet 3 is softened in advance at a temperature of not less than DEG C. This further reduces the load applied to the rotary tool 1, thereby further increasing the joining speed. Therefore, the temperature T in the thickness direction region of the region 12 is to be heatedDThe depth from the surface of the steel sheet 3 in the region satisfying the following expression (3) is defined as the depth D of the heated region 12.
TD≥0.8×TA1…(1)
TA1The (. degree. C.) can be determined by the following formula (2).
TA1(℃)＝723-10.7[％Mn]-16.9[％Ni]+29.1[％Si]+16.9[％Cr]+290[％As]+6.38[％W]……(2)
The above [% M ] is the content (mass%) of the M element in the steel sheet 3 as the workpiece, and is 0 in the absence of M element.
However, since it is higher than 0.8 XTA1In the case of c, since the strength of the steel sheet 3 tends to decrease with an increase in temperature, it is preferable to adjust the temperature of the steel sheet 3 in the hot zone 12 so as not to increase excessively. Specifically, in order to secure the heated zone 12 in the thickness direction, there may be a temperature gradient (variation in temperature in the thickness direction) in the thickness direction of the heated zone 12, but at this time, the maximum temperature of the steel sheet 3 in the thickness direction in the heated zone 12 is preferably 1.5 × TMBelow DEG C. In order to avoid damage to the rotary tool 1 due to excessive temperature rise of the joint 4 and to avoid alteration of the microstructure around the heating zone 12, it is preferable that the temperature in the thickness direction of the steel sheet 3 in the heating zone 12 is set to be lower than T before the rotary tool 1 passing through the heating zone 12 comes into contact with the steel sheet 3M℃。TMThe melting point (DEG C) of the steel sheet 3 as the material to be processed is shown.
Depth D of the heating region: the thickness t of the steel plate is more than 30 percent
The depth D of the heating zone 12 is determined by the temperature T in the thickness direction of the heating zone 12DIs 0.8 XTA1The maximum depth from the surface of the steel sheet 3 in the region of not less than DEG C is defined. The depth D of the heated zone 12 is preferably 30% or more of the thickness t of the steel sheet 3. By setting the depth D of the heated region 12 to 30% or more of the thickness t of the steel sheet 3, the plastic flow is further promoted, which contributes to a reduction in the load applied to the rotary tool 1 and an increase in the joining speed. The depth D of the heating zone 12 is more preferably 50% or more of the thickness of the steel sheet 3.
However, when the depth D of the heating zone 12 is greater than 90% of the thickness t of the steel sheet 3, the heating becomes excessive, and the microstructure around the heating zone 12 may change, and therefore the depth D of the heating zone 12 is preferably 90% or less of the thickness t of the steel sheet 3.
In order to achieve the above conditions, the friction stir welding apparatus according to the present embodiment includes a control mechanism 15. The control mechanism 15 controls the operations of the rotary tool 1 and the heating mechanism 5. The control means 15 can also control the operations of the rear heating means 7, the cooling means 6, and the like.
The heating mechanism 5 used in the preheating step is not particularly limited, and a laser heating device is preferable. By using a laser having a high energy density as a heat source, the conditions of the preheating process can be controlled more accurately, and the joining workability can be improved without impairing the characteristics of the joined joint.
The joining conditions other than the above are not particularly limited, and for example, the moving speed of the heating mechanism 5 used in the preheating step may be about the same as the joining speed. When a laser heating device is used as the heating means 5, the laser output power and the beam diameter can be set appropriately according to the bonding conditions.
While the preheating step in the friction stir welding method and apparatus of the present embodiment has been described above, in the friction stir welding method and apparatus of the present embodiment, the cooling mechanism 6 may be provided behind the welding direction of the rotary tool 1 moving in the welding direction, and the strength of the welded joint may be improved by the cooling mechanism 6.
Normally, after the joining is completed, the joint 4 is naturally cooled, and therefore, when the hardenability of the steel sheet 3 as the workpiece is low, the strength of the joined joint cannot be sufficiently obtained. On the other hand, by providing the cooling mechanism 6 at the rear side in the joining direction of the rotary tool 1 moving in the joining direction, and cooling the joined portion 4 of the steel sheet 3 by the cooling mechanism 6, the cooling rate is appropriately controlled, and the strength by quenching can be improved. As the cooling mechanism 6, for example, a cooling device that ejects an inert gas is preferably used. The cooling rate in this case is preferably in the range of, for example, 800 to 500 ℃ at 30 to 300 ℃/s. As the inert gas, for example, argon gas, helium gas, or the like can be used.
When the hardenability of the steel plate 3 as the work material is high, excessive hardening may occur to lower the toughness of the joined joint. On the other hand, the excessive hardening can be suppressed by providing the rear heating means 7 for heating the rear portion close to the rotary tool 1 at the rear in the joining direction of the rotary tool 1 and performing slow cooling while appropriately controlling the cooling rate. As the back heating means 7, for example, a heating device using high-frequency induction heating and laser as a heat source is preferably used. The slow cooling rate in this case is preferably 10 to 30 ℃/s in the range of 800 to 500 ℃, for example.
A rear heating mechanism 7 may be provided behind the joining direction of the rotary tool moving in the joining direction and behind the joining direction of the cooling mechanism 6, and the joined portion 4 of the steel plates 3 may be reheated by the rear heating mechanism 7. Thus, when the joint portion 4 is quenched by cooling by the cooling mechanism 6 and is excessively hardened, the hardness is suppressed by annealing by the rear heating mechanism 7, and joint characteristics having both strength and toughness can be obtained. The cooling rate in this case is preferably 30 to 300 ℃/s in the range of 800 to 500 ℃ for example, and the reheating temperature is preferably 550 to 650 ℃ for example.
Further, a cooling mechanism 6 may be provided behind the joining direction of the rotary tool 1 moving in the joining direction and behind the joining direction of the rear heating mechanism 7, and the joined portion 4 of the steel plate 3 may be cooled by the cooling mechanism 6.
In this case, the structure can be combined by gradually cooling by the rear heating means 7 immediately after joining and then rapidly cooling by the cooling means 6, and joint characteristics having both strength and ductility can be obtained. The cooling rate in this case is preferably about 10 to 30 ℃/s in the range of 800 to 600 ℃ (slow cooling range), and then about 30 to 300 ℃/s in the range of 600 to 400 ℃ (rapid cooling range), for example.
In the joining conditions other than the above, it is preferable to perform the joining according to a conventional method, because the larger the torque of the rotary tool 1 is, the lower the plastic fluidity of the steel sheet 3 is, and therefore, defects and the like are likely to occur.
Therefore, the friction stir welding method and apparatus of the present embodiment aim to set the rotation speed of the rotary tool 1 in the range of 100 to 1000rpm, suppress the torque of the rotary tool 1, and increase the welding speed to 1000mm/min or more. When the joining speed is increased to more than 500mm/min and 1000mm/min or less, the torque of the rotary tool 1 is preferably suppressed to 90N · m or less. This can avoid a situation in which the rotary tool 1 is broken during the joining process or an unjoined portion remains. When the joining speed is set to 500mm/min or less, the torque of the rotary tool 1 is preferably suppressed to less than 75N · m. This can reduce the load on the rotary tool 1 while ensuring plastic fluidity.
As the steel type to be subjected to the friction stir welding method of the present embodiment, ordinary structural steel or carbon steel, for example, rolled steel for welded structure according to JIS (japanese industrial standards) G3106, carbon steel for machine structure according to JIS G4051, or the like can be used. Steel for high-strength structural use having a tensile strength of 800MPa or more can also be used, and a strength of 85% or more, and further 90% or more of the tensile strength of the steel sheet (base material) can be obtained in the joint 4.
Examples
(example 1)
The steel sheets having a thickness of 1.6mm and having the chemical composition and tensile strength shown in table 1 below were used to carry out friction stir welding. The joint mating surfaces are joined by a so-called I-groove (groove) having no angle, in a surface state of a degree of polishing, in a single surface 1 pass. The joining conditions of the friction stir joining are shown in table 2. In example 1, a rotary tool having a cross-sectional dimension shape (shoulder diameter a: 12mm, maximum diameter b: 4mm of pin portion, probe length c: 1.4mm) shown in FIG. 4 was used. The rotary tool used in example 1 was a rotary tool having a surface coated with titanium nitride (TiN) by Physical Vapor Deposition (PVD) using tungsten carbide (WC) as a material. At the time of bonding, the bonding portion is masked with argon gas, thereby preventing oxidation of the surface. The coefficient of dynamic friction between the surface of a WC rotary tool, the surface of which has been coated with TiN, and a steel plate is 0.6 or less.
The coefficient of dynamic friction between the tool material surface and the steel plate was measured by the following measurement method. While rotating a disk made of a target material, a ball having a fixed diameter of 6mm was pressed with a load of 5N by using a ball-and-disk type friction wear tester, and a test was performed at a rotation speed of 100mm/s and a sliding distance of 300 m. The test was performed at room temperature without lubrication. The steel balls used in the tests were formed of a material having a chemical composition of SUJ2 defined in JIS G4805 and were processed as bearing steel balls.
[ Table 1]
[ Table 2]
In addition, in order to confirm the heated region formed by preheating using laser light as a heat source before joining, laser light was irradiated to the steel sheets I of table 1 under the irradiation conditions (laser moving speed, laser output power, and beam diameter) shown in table 3, and the surface temperature was measured by thermal imaging (Thermography). Then, the cross section of the laser irradiated portion was observed, and microstructure observation using a nital etching solution was performed.
[ Table 3]
Here, at the phase transition point (T)A1A region above) is etched deepest, and a region existing outside the region and below a phase transition point (T DEG C)A1C) of the base material, and the region where the high-hardness structure such as martensite in the base material is annealed is relatively shallowly etched, and therefore, can be recognized as being at the transformation point (T) respectivelyA1DEG C) or more, and below the transformation point (T)A1DEG C) and a region of the base material. Further, from the knowledge of the heat treatment of steel, it is found that the temperature is lower than the transformation point (T)A1deg.C) and 0.8 XT) annealing regionA1At a temperature of not less than TA1The region at DEG C was uniform. The microstructure observation using the nitroethanol etching solution measured the phase transition point (T)A1C) or more, D) of the region0And at 0.8 XTA1The depth of the region at or above DEG C (depth D of the heated region).
The measurement results are shown in table 4.
[ Table 4]
As shown in Table 4, from the results of surface temperature measurement by thermal imaging, it was found that the surface temperature was 0.8 XT under the irradiation condition AA1The region at or above DEG C is a circle having a diameter of 3.5 mm. Here, since the maximum diameter of the pin portion of the rotary tool used is 4.0mm, the area of the heated region under the irradiation condition a is equal to or smaller than the area of the maximum diameter portion of the pin portion of the rotary tool.
Under irradiation condition B, the temperature became 0.8 XTA1Above DEG CThe area of (2) is a circle with a diameter of 2.0 mm. Therefore, as described above, the area of the heated region under 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.
Under irradiation condition C, the molecular weight of the resin composition became 0.8 XTA1The region at or above DEG C is a circle having a diameter of 4.5 mm. Here, since the maximum diameter of the pin portion of the rotary tool used is 4.0mm, the area of the heating region under the irradiation condition C is larger than the area of the maximum diameter portion of the pin portion of the rotary tool.
Under irradiation condition D, the temperature became 0.8 XTA1The region at a temperature of not less than DEG C is an ellipse having a major axis in the laser moving direction and a minor axis in the direction perpendicular to the laser moving direction, and the major axis is 3.8mm and the minor axis is 3.2 mm. Here, since the maximum diameter of the pin portion of the rotary tool used is 4.0mm, the area of the heating region under the irradiation condition D is equal to or smaller than the area of the maximum diameter portion of the pin portion of the rotary tool.
Under irradiation condition E, the temperature became 0.8 XTA1The region at a temperature of not less than DEG C is an ellipse having a major axis in the laser moving direction and a minor axis in the direction perpendicular to the laser moving direction, and the major axis is 2.2mm and the minor axis is 1.8 mm. Therefore, as described above, the area of the heated 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.
Under the irradiation condition F, the temperature became 0.8 XTA1The region at a temperature of not less than DEG C is an ellipse having a long diameter in the laser moving direction and a short diameter in the direction perpendicular to the laser moving direction, and the long diameter is 4.9mm and the short diameter is 4.1 mm. Here, since the maximum diameter of the pin portion of the rotary tool used is 4.0mm, the area of the heated region under the irradiation condition F is larger than the area of the maximum diameter portion of the pin portion of the rotary tool.
Further, as shown in Table 4, it was found from the cross-sectional view of the laser irradiated portion that T was formed under the irradiation condition AA1Depth D of region of not less than DEG C0And becomes 0.8 XTA1The depth of the region at a temperature of not less than DEG C (depth D of the heating region) was 0.28mm and 0.30mm, respectively. The thickness T of the steel sheet as a work material is 1.6mm, and hence 0.8 XTA1At a temperature of higher than DEG CThe depth D of the heated zone, which is the depth of the zone, is about 18.8% of the steel sheet thickness t.
Under irradiation condition B, it becomes TA1Depth D of region of not less than DEG C0And becomes 0.8 XTA1The depth of the region at a temperature of not less than DEG C (depth D of the heating region) was 0.47mm and 0.50mm, respectively. Since the thickness t of the steel sheet as a workpiece is 1.6mm, the depth D of the heated zone is about 31.3% of the thickness t of the steel sheet.
Under the irradiation condition C, it becomes TA1Depth D of region of not less than DEG C0And becomes 0.8 XTA1The depth of the region at a temperature of not less than DEG C (depth D of the heating region) was 0.09mm and 0.10mm, respectively. Since the thickness t of the steel sheet as the workpiece was 1.6mm, the depth D of the heated zone was about 6.3% of the thickness t of the steel sheet.
Under the irradiation condition D, it becomes TA1Depth D of region of not less than DEG C0And becomes 0.8 XTA1The depth of the region at a temperature of not less than DEG C (depth D of the heating region) was 0.30mm and 0.32mm, respectively. The thickness T of the steel plate as the workpiece was 1.6mm, and therefore, it was 0.8 XTA1The depth D of the heated region, which is the depth of the region at or above DEG C, is about 20.0% of the thickness t of the steel plate.
Under irradiation condition E, it becomes TA1Depth D of region of not less than DEG C0And becomes 0.8 XTA1The depth of the region at a temperature of not less than DEG C (depth D of the heating region) was 0.51mm and 0.54mm, respectively. Since the thickness t of the steel plate as the workpiece is 1.6mm, the depth D of the heated zone is about 33.8% of the thickness t of the steel plate.
Under the irradiation condition F, the molecular weight is TA1Depth D of region of not less than DEG C0And becomes 0.8 XTA1The depth of the region at a temperature of not less than DEG C (depth D of the heating region) was 0.10mm and 0.11mm, respectively. Since the thickness t of the steel plate as the workpiece is 1.6mm, the depth D of the heated zone is about 6.9% of the thickness t of the steel plate.
The preheating process conditions by laser irradiation performed before the joining of the materials to be processed are shown in table 5, and the process conditions performed after the joining are shown in table 6. Here, cooling in the step performed after bonding is performed by gas ejection, and heating (and reheating) is performed by induction heating.
In tables 5 and 6, "-" in the preheating step conditions and the step conditions performed after bonding indicates the case where the preheating step and the step after bonding such as cooling and heating are not performed, respectively. The descriptions of "(AS)" and "(RS)" in the distance from the joining center line to the center of the heating region indicate that the center of the heating region is on the forward side and the backward side with respect to the joining center line, respectively.
[ Table 5]
[ Table 6]
Cooling rate of 1 from 800 ℃ to 650 ℃
Cooling rate of 2 from 800 ℃ to 600 ℃
Cooling rate of from 600 ℃ to 400 ℃
Table 7 shows measured values of the torque of the rotary tool at the time of joining and the obtained measured values of the tensile strength of the joined joint. The tensile strength of the joint was measured by taking a tensile test specimen having a size of No. 1 specimen prescribed in JIS Z3121 and performing a tensile test. The larger the torque of the rotary tool, the lower the plastic fluidity, and thus defects and the like are more likely to occur.
[ Table 7]
As is clear from Table 7, in the invention examples 1 to 10, even when the joining speed was 400mm/min, the joint strength of 90% or more of the tensile strength of the steel sheet as the base material was obtained. The torque of the rotary tool of the invention examples 1 to 10 was 72N · m or less, and the plastic fluidity was also good. In particular, in invention examples 6, 7, and 8 in which cooling and reheating or only cooling was performed after joining, the strength of the joined joint was obtained to be equivalent to the tensile strength of the base material. In invention examples 9 and 10 in which heating and cooling or heating alone was performed after joining, a joint strength of 93% or more of the tensile strength of the base material was obtained.
On the other hand, in comparative examples 1 to 6, the torque of the rotary tool was 75N · m or more, and the plastic flowability was poor.
In invention examples 11 to 20, even when the joining speed was increased to 1000mm/min, the joint strength of 85% or more of the tensile strength of the base material was obtained, and the torque of the rotary tool was 90N · m or less. In particular, in invention examples 16, 17 and 18 in which cooling and reheating or only cooling was performed after joining, a joint strength of 99% or more of the tensile strength of the base material was obtained. In invention examples 19 and 20 in which reheating and cooling were performed after joining or only reheating was performed, the joint strength of 95% or more of the tensile strength of the base material was obtained.
On the other hand, in comparative example 7, the rotary tool was broken during the bonding and was not bonded. In comparative examples 8 to 12, the unjoined portion remained and could not be joined, and thus, a perfect joint could not be obtained. Therefore, in comparative examples 7 to 12, the torque of the rotary tool and the like were not measured.
(example 2)
The friction stir welding was performed using steel sheets having a thickness of 1.6mm and having the chemical composition and tensile strength shown in table 1. In the joint mating surface, the joint is joined by 1-pass on one surface in a surface state of a degree of grinding using a so-called I-groove to which no angle is given. The joining conditions of the friction stir joining were as shown in table 2 above. In example 2, a rotary tool having a cross-sectional size shape (shoulder diameter a: 12mm, maximum diameter b: 4mm of pin portion, probe length c: 1.4mm) shown in FIG. 4 was used. The rotary tool used in example 2 was a rotary tool made of tungsten carbide (WC) and not subjected to a coating treatment; a rotary tool having a surface coated with titanium nitride (TiN) by Physical Vapor Deposition (PVD) using tungsten carbide (WC) as a material; a rotary tool made of tungsten carbide (WC) and having a surface coated with chromium aluminum nitride (AlCrN); or a Cubic Boron Nitride (CBN) material.
At the time of bonding, the bonding portion is masked with argon gas, thereby preventing oxidation of the surface. The coefficient of dynamic friction between the surface of the rotary tool and the steel plate was 0.7 in the case of the rotary tool made of tungsten carbide (WC) and not subjected to the coating treatment, 0.5 in the case of the rotary tool made of tungsten carbide (WC) and subjected to the coating treatment of titanium nitride (TiN) by Physical Vapor Deposition (PVD), 0.4 in the case of the rotary tool made of tungsten carbide (WC) and subjected to the coating treatment of chromium aluminum nitride (AlCrN), and 0.3 in the case of the rotary tool made of Cubic Boron Nitride (CBN).
The coefficient of dynamic friction between the tool material surface and the steel plate was measured by the same measurement method as in example 1.
The preheating process conditions by laser irradiation performed before joining the materials to be processed are shown in table 8.
[ Table 8]
In table 8, a rotary tool made of tungsten carbide (WC) without being coated is denoted by "WC", a rotary tool made of tungsten carbide (WC) and coated with titanium nitride (TiN) by Physical Vapor Deposition (PVD) is denoted by "WC + TiN", a rotary tool made of tungsten carbide (WC) and coated with chromium aluminum nitride (AlCrN) is denoted by "WC + A1 CrN", and a rotary tool made of Cubic Boron Nitride (CBN) is denoted by "CBN". The laser irradiation conditions in the preheating step conditions are shown in table 3, and the surface shape and depth of the heated region formed by each laser irradiation condition are shown in table 4.
In example 2, the post-bonding step was not performed. "AS" and "RS" in the distance from the joining center line to the center of the heating region indicate that the center of the heating region is located on the forward side and the backward side with respect to the joining center line, respectively.
Table 9 shows measured values of the torque of the rotary tool when the joining was performed, and the obtained measured values of the tensile strength of the joined joint. The tensile strength of the joint was measured by taking a tensile test specimen having a size of No. 1 specimen prescribed in JIS Z3121 and performing a tensile test. The larger the torque of the rotary tool, the lower the plastic fluidity, and thus defects and the like are more likely to occur.
[ Table 9]
As is clear from Table 9, in invention examples 21 to 26, even when the joining speed was set to 400mm/min, the joint strength of 90% or more of the tensile strength of the steel sheet as the base material was obtained. The torque of the rotary tool of the invention examples 21 to 26 was 65N · m or less, and the plastic fluidity was also good.
On the other hand, in comparative examples 13 and 14, the torque of the rotary tool was 75N · m or more, and the plastic flowability was poor.
As is clear from Table 9, in invention examples 27 to 32, even when the joining speed was increased to 1000mm/min, the joint strength of 85% or more of the tensile strength of the base material could be obtained, and the torque of the rotary tool was 81N · m or less.
On the other hand, in comparative examples 15 and 16, the unjoined portion remained and could not be joined. Therefore, in comparative examples 15 and 16, the torque of the rotary tool and the like were not measured.
Description of the reference numerals
1 rotating tool
2 rotating shaft
3 Steel plate
4 joint part
5 heating mechanism
6 Cooling mechanism
7 rear heating mechanism
8 shoulder of rotary tool
9 Pin part of rotary tool
10 center line of junction
11 RS line
12 heating zone
13 cooling zone
14 reheating zone
15 control mechanism
a shoulder diameter of rotary tool
b maximum diameter of pin of rotary tool
c probe length of rotary tool
Minimum distance of X heating zone from rotating tool
Depth of D heating zone
thickness of t-steel plate
Angle of inclination of alpha rotary tool
Claims (16)
1. A friction stir welding method in which a rotary tool having a shoulder portion and a pin portion disposed on the shoulder portion and sharing a rotation axis with the shoulder portion is inserted into an unbonded portion between steel plates and moved in a welding direction while rotating, and the rotary tool stirs the softened portion with the rotary tool while softening the steel plates by frictional heat of the rotary tool and the steel plates, thereby generating plastic flow to weld the steel plates to each other, wherein the shoulder portion and the pin portion are formed of a material harder than the steel plate as a workpiece material,
the coefficient of dynamic friction between the material of the rotary tool or the material coated on the surface of the rotary tool and the steel plate is 0.6 or less,
a temperature T of a surface of the steel sheet to be heated by a heating mechanism provided forward in a joining direction of the rotary toolS(DEG C) when a region satisfying the following formula (1) is used as a heating region, the minimum distance between the heating region and the rotating tool is the rotating toolIs below the diameter of the shoulder portion of the body,
the area of the heating region is equal to or smaller than the area of the maximum diameter portion of the pin portion of the rotary tool,
wherein 65% or more of the area of the heating zone is located between a joining center line of the surface of the steel sheet, which is a straight line passing through the rotation axis of the rotating tool and parallel to the joining direction, and a straight line parallel to the joining center line, which is a straight line spaced apart from the backward side by the same distance as the maximum radius of the pin portion of the rotating tool,
TS≥0.8×TA1……(1)
TA1the temperature is represented by the following formula (2),
TA1(℃)＝723-10.7[％Mn]-16.9[％Ni]+29.1[％Si]+16.9[％Cr]+290[％As]+6.38[％W]……(2)
the above [% M ] is the mass% of the M element in the steel sheet as the workpiece, and is 0 in the absence of the M element.
2. The friction stir welding method according to claim 1, wherein a temperature T in a thickness direction of the heating region is set toD(DEG C) when the maximum depth from the surface of the steel sheet in a region satisfying the following formula (3) is taken as the depth D of the heated region, the depth D of the heated region is more than 30% of the thickness of the steel sheet,
TD≥0.8×TA1……(3)。
3. the friction stir welding method according to claim 1, wherein the heating mechanism is a laser heating device.
4. The friction stir welding method according to claim 2, wherein the heating mechanism is a laser heating device.
5. The friction stir welding method according to any one of claims 1 to 4, wherein a rear heating mechanism that heats a welded portion of the steel plates is provided behind the rotating tool in the welding direction.
6. The friction stir welding method according to claim 5, wherein a cooling mechanism that cools the welded portion that is heated by the rear heating mechanism is provided rearward in a welding direction of the rear heating mechanism.
7. The friction stir welding method according to any one of claims 1 to 4, wherein a cooling mechanism that cools a welded portion of the steel plates is provided behind a welding direction of the rotary tool.
8. The friction stir welding method according to claim 7, wherein a rear heating means that heats the welded portion cooled by the cooling means is provided behind the cooling means in the welding direction.
9. A friction stir welding apparatus for welding an unwelded portion between steel plates as workpieces, the friction stir welding apparatus comprising:
a rotating tool having a shoulder portion and a pin portion disposed on the shoulder portion and sharing a rotation axis with the shoulder portion, the shoulder portion and the pin portion being formed of a material harder than the steel plate, the rotating tool being moved in a joining direction while rotating in a state of being inserted into an unbonded portion between the steel plates, thereby generating a plastic flow while stirring a softened portion while softening the steel plates by frictional heat,
a heating means provided in front of the rotary tool in the joining direction for heating the steel plate,
a control means for controlling the rotary tool and the heating means so as to realize the following state 1,
the coefficient of dynamic friction between the material of the rotary tool or the material coated on the surface of the rotary tool and the steel plate is 0.6 or less,
(State 1)
A temperature T of a surface of the steel sheet to be heated by the heating meansS(DEG C) when a region satisfying the following formula (1) is used as a heating region, the minimum distance between the heating region and the rotating tool is less than or equal to the diameter of the shoulder of the rotating tool,
the area of the heating region is equal to or smaller than the area of the maximum diameter portion of the pin portion of the rotary tool,
wherein 65% or more of the area of the heating zone is located between a joining center line of the surface of the steel sheet, which is a straight line passing through the rotation axis of the rotating tool and parallel to the joining direction, and a straight line parallel to the joining center line, which is a straight line spaced apart from the backward side by the same distance as the maximum radius of the pin portion of the rotating tool,
TS≥0.8×TA1……(1)
TA1the temperature is represented by the following formula (2),
TA1(℃)＝723-10.7[％Mn]-16.9[％Ni]+29.1[％Si]+16.9[％Cr]+290[％As]+6.38[％W]……(2)
the above [% M ] is the mass% of the M element in the steel sheet as the workpiece, and is 0 in the absence of the M element.
10. The friction stir welding apparatus according to claim 9, wherein the control means controls the rotating tool and the heating means so as to realize the following state 2,
(State 2)
Temperature T in the thickness direction of the heating regionD(DEG C) when the maximum depth from the surface of the steel sheet in a region satisfying the following formula (3) is taken as the depth D of the heated region, the depth D of the heated region is more than 30% of the thickness of the steel sheet,
TD≥0.8×TA1……(3)。
11. the friction stir welding apparatus according to claim 9, wherein the heating mechanism is a laser heating apparatus.
12. The friction stir welding apparatus according to claim 10, wherein the heating mechanism is a laser heating apparatus.
13. The friction stir welding apparatus according to any one of claims 9 to 12, further comprising a rear heating mechanism that heats a welded portion of the steel plates,
the rear heating mechanism is disposed rearward in the joining direction of the rotary tool.
14. The friction stir welding apparatus as recited in claim 13, further comprising a cooling mechanism that cools said welded portion,
the cooling mechanism is disposed rearward in the joining direction of the rear heating mechanism.
15. The friction stir welding apparatus according to any one of claims 9 to 12, further comprising a cooling mechanism that cools a welded portion of the steel plates,
the cooling mechanism is disposed rearward in the joining direction of the rotary tool.
16. The friction stir welding apparatus as recited in claim 15, further comprising a rear heating mechanism that heats said welded portion,
the rear heating mechanism is disposed rearward in the joining direction of the cooling mechanism.
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|---|---|---|---|---|
| CN1443102A (en) * | 2000-07-25 | 2003-09-17 | Eads德国有限公司 | Laser supported friction stir welding method |
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| CN1443102A (en) * | 2000-07-25 | 2003-09-17 | Eads德国有限公司 | Laser supported friction stir welding method |
| CN1503711A (en) * | 2001-03-07 | 2004-06-09 | �Ѻ͵繤��ʽ���� | Friction agitation joining method, method for manufacturing joined butted members and friction agitation joining apparatus |
| CN101203352A (en) * | 2005-04-14 | 2008-06-18 | 通用汽车环球科技运作公司 | Method for friction stir welding of different materials |
| CN105579183A (en) * | 2013-09-30 | 2016-05-11 | 杰富意钢铁株式会社 | Friction stir welding method for steel sheets and method of manufacturing joint |
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| KR20190039743A (en) | 2019-04-15 |
| CN109689276A (en) | 2019-04-26 |
| KR102173603B1 (en) | 2020-11-03 |
| WO2018070316A1 (en) | 2018-04-19 |
| JPWO2018070316A1 (en) | 2018-10-11 |
| JP6493564B2 (en) | 2019-04-03 |
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