Stirring friction welding tool, method for manufacturing such a tool, and method for joining components with such a tool

Description

[0001] The invention relates to a friction stir welding tool comprising a pin and a shoulder rigidly connected to the pin, for welding components made of a base material formed by a steel with a melting point of more than 900 °C according to the preamble of claim 1 (see e.g. WO 2008 / 102209 A2).

[0002] The invention further relates to a method for manufacturing a friction stir welding tool with a pin and a shoulder, with which components made of a base material formed by steel having a melting point of more than 900 °C can be joined by friction stir welding, see claim 6.

[0003] Furthermore, the invention relates to a method for joining components made of a base material formed by a steel, in particular a structural steel, or of several base materials formed by a steel, in particular a structural steel, with a melting temperature of more than 900 °C by friction stir welding, see claim 13.

[0004] Friction stir welding tools for joining components with a melting point above 900 °C, for joining components made of a single steel or several different steel alloys, are known in the art. Such tools have a pin and a shoulder, usually arranged perpendicular to the pin. When joining two adjacent components, a compressive force is applied to the components to be joined via the shoulder. Simultaneously, due to the rotation of the friction stir welding tool relative to the components about an axis of rotation, the components are heated, so that the components are plastically degraded and mixed in a joining zone within the area of ​​the friction stir welding tool, thereby creating the joint.The pin ensures the plasticized material is stirred in the joining zone and is therefore subjected to high mechanical and thermal stresses during friction stir welding, while the shoulder of the friction stir welding tool is responsible for a large part of the heat generation. The size of the shoulder is generally determined by the maximum surface pressure beneath it and the required axial compressive force on the components to be joined.

[0005] It has been shown that materials which have favorable properties for use as pin materials, for example a high melting temperature, lead to excessively high or insufficient heat generation when used in a friction stir welding tool at the shoulder due to excessive friction with the base material of the components to be joined, resulting in an unsatisfactory weld seam.

[0006] To avoid excessively high or low temperatures during the welding process, it is known in the art to make the shoulder correspondingly larger or smaller. However, this leads to suboptimal pressure in the joining zone, which in turn causes problems with the quality of the weld.

[0007] Furthermore, it is known from the prior art to form the shoulder and the pin from separate components and to drive the shoulder at a different speed than the pin in order to influence the heat input via the shoulder independently of its size by adjusting the rotational speed of the shoulder. However, it has been shown that while this achieves the desired effect when welding aluminum and other materials with low melting points, when welding base materials with a melting point above 900 °C, such as steel, plasticized material from the joining zone penetrates a gap between the pin and the shoulder, leading to damage to the tool and thus a reduced tool life.

[0008] This is where the invention comes in. The object is to provide a friction stir welding tool of the type mentioned above, with which a particularly high quality of the weld joint can be achieved even with a given geometry of the friction stir welding tool, while simultaneously ensuring a very long tool life.

[0009] Furthermore, a method for manufacturing a friction stir welding tool of the type mentioned above will be specified, with which such a friction stir welding tool can be manufactured.

[0010] Finally, a method for joining components of the type mentioned above will be specified, with which a particularly high quality of connection can be achieved in an efficient manner.

[0011] According to a first aspect of the invention, a friction stir welding tool is defined in claim 1.

[0012] Within the scope of the invention, it was recognized that the disadvantages of prior art friction stir welding tools can be overcome if the friction stir welding tool is made, at least partially, of a different material in the shoulder region than in a region of the pin. The first material differs from the second material, to which the first material is rigidly bonded, typically in terms of its chemical composition, mechanical properties, and / or thermal characteristics. This allows for the simple creation of an optimized friction stir welding tool, depending on the desired application.

[0013] It is advantageous if the first material has a melting temperature of more than 900 °C, preferably more than 2000 °C.

[0014] Preferably, the second material has a melting point of more than 900 °C, preferably more than 2000 °C, and particularly more than 3000 °C. This allows for a particularly long service life of the friction stir welding tool. Typically, the melting point of the second material is higher than that of the first material.

[0015] It has proven advantageous for the first and second materials to have different strengths. This allows for a tool that is particularly well-suited to the required conditions, especially since very high strength is usually necessary in the pin area, while lower strength is often sufficient in the shoulder area.

[0016] According to the invention, a material pairing of the first material with the base material has a first coefficient of sliding friction. According to the invention, a material pairing of the second material with the base material also has a second coefficient of sliding friction.

[0017] The first coefficient of sliding friction is lower than the second coefficient of sliding friction according to the invention.

[0018] This allows the tool to be designed in such a way that, for example, it has a lower coefficient of sliding friction in the shoulder area than in the pin area. This ensures, in a simple manner, that while a sufficiently high pressing force can be applied via the shoulder with simultaneously low surface pressure, excessive heat generation does not occur, and sufficient friction is also present in the pin area to mix the plasticized components in the joining zone for a particularly good bond.

[0019] Depending on the desired conditions during the welding process or a required pressing force at the shoulder, the materials can of course also be chosen in such a way that the first coefficient of sliding friction is greater than the second coefficient of sliding friction.

[0020] While it may be intended that the shoulder is formed entirely from the first material and the pin entirely from the second, it is also possible to form the shoulder only partially from the first material and partially from the second material, and possibly one or more other materials. Similarly, the pin can also be formed only partially from the second material and the first material, and possibly from other materials. By appropriately dividing the shoulder or pin area into sections consisting of different materials with different coefficients of sliding friction relative to the base material, it is thus easily possible to achieve a desired coefficient of sliding friction in both the shoulder and pin areas, whereby the average coefficient of sliding friction for the shoulder typically differs from the average coefficient of sliding friction for the pin.

[0021] This can be achieved, for example, by having the first part be ring-shaped, with an outer diameter of this first part corresponding to the shoulder's outer diameter, but an inner diameter of this first part larger than the shoulder's inner diameter, which shoulder inner diameter can coincide with the pin's outer diameter. The first material then extends in the shoulder area from the shoulder's outer diameter to the inner diameter of the first part, forming a first section of the shoulder, and the second material extends in the shoulder area from the inner diameter of the first part to the shoulder's inner diameter or to the pin. Furthermore, the pin can also be formed by the second material, so that the second part can form a second section of the shoulder and partially or completely form the pin.

[0022] Normally, the average coefficient of sliding friction of the shoulder is lower than the average coefficient of sliding friction of the pin. An average coefficient of sliding friction can be achieved by considering the surface area. If the coefficient of sliding friction also depends on the relative speed of the friction stir welding tool relative to the base material, the speed of the respective surface areas during the friction stir welding process can also be taken into account when selecting the portion of the shoulder that consists of the first or second material.

[0023] Although a computational determination of the achievable average coefficient of sliding friction over the surfaces formed from the individual materials is preferred, a corresponding friction stir welding tool can of course also be formed by determining in experiments a composition of the shoulder area required for a desired weld quality, i.e. a size of that part of the shoulder which consists of the first material and optionally of a second and / or third material.

[0024] Preferably, the first material has a different, and in particular a lower, chemical affinity for the base material than the second material. Chemical affinity, in this context, refers to the tendency of the respective material to bond with the base material. For example, in the pin area, a high chemical affinity is advantageous to ensure thorough mixing and thus high weld strength. In the shoulder area, a lower affinity than in the pin area can be advantageous to achieve a weld with a smooth surface and to avoid excessive heat input and wear of the friction stir welding tool in the shoulder area. Therefore, it is beneficial if the first material has a lower chemical affinity for the base material than the second material.

[0025] To form the friction stir welding tool, the first material can be joined to the second material in any way possible, for example, by means of a force-fit, a form-fit, and / or a material-fit joining process. For instance, the friction stir welding tool can consist entirely of the second material and be partially or completely coated with the first material in the shoulder area. It is also conceivable that the first material is applied to a larger section of the friction stir welding tool made of the second material in the shoulder area by means of weld overlay.

[0026] Similarly, it is of course also possible that the pin, which consists of a second material, or a part of the pin consisting of the second material, is connected to a larger first part of the friction stir welding tool, which consists of the first material, in particular by force-fit, form-fit and / or material-fit, for example by welding or screwing.

[0027] Preferably, the friction stir welding tool comprises a ring made of the first material, which is connected by a welding process, in particular a friction welding process, to a second part made of the second material, which forms the pin and a portion of the shoulder not formed by the ring. The ring made of the first material can form an outer end of the shoulder or can be arranged in a groove, such that the ring forms a central or inner first portion of the shoulder.

[0028] It is understood that a first part of the friction stir welding tool formed from the first material or a second part of the friction stir welding tool formed from the second material can also form a shaft of the friction stir welding tool, at least partially or completely.

[0029] Particularly for cost optimization, the friction stir welding tool can also be designed with a shank made of a third material, or even formed entirely from a third material. This minimizes the use of expensive materials for the shoulder and pin, for example, making the friction stir welding tool significantly cheaper to manufacture. The individual components, especially the pin, shoulder, and shank sections of the friction stir welding tool, can be joined to each other in any possible form-fit, force-fit, and / or material-fit manner, such as by friction welding.

[0030] Naturally, depending on the one or more different base materials from which the components to be welded are made, the friction stir welding tool can be made of a wide variety of materials, and the first material can be any material. However, to achieve favorable friction properties at the shoulder, it has proven particularly effective if the first material contains molybdenum, especially as a molybdenum alloy.

[0031] The second material can also be made from any material suitable for the intended application. To achieve a particularly long service life, even at high temperatures occurring in the joining zone, it is preferred that the second material contains tungsten, in particular tungsten-rhenium.

[0032] In order to achieve correspondingly advantageous properties, it may also be provided that the first material and / or the second material comprises a ceramic material, in particular an oxide ceramic material and / or a non-oxide ceramic material such as carbides, nitrides or silicides, or is formed by such a material.

[0033] A particularly long service life can be achieved if the first and / or second material is a refractory metal, a refractory metal alloy, a nickel alloy, a cobalt alloy, and / or an iron alloy, or is composed of such a material. Refractory metals, i.e., base metals of groups 4, 5, and 6, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten, exhibit a particularly high melting point and favorable mechanical properties for use as friction stir welding tools.

[0034] According to a second aspect of the invention, a method for manufacturing a friction stir welding tool with a pin and a shoulder is defined in claim 6.

[0035] This allows the properties of the friction stir welding tool in the shoulder area to be easily achieved independently of the properties in the pin area. In principle, the first part forming the friction stir welding tool can be connected to the second part in any way, for example, by a force-fit and / or form-fit connection. However, it is particularly preferred that the first part be joined to the second part by a material bond. This results in a particularly robust connection.

[0036] Although the first part can be joined to the second part, or vice versa, in principle by any material-bonding method, such as sintering, 3D printing, or the like, it is preferred that the first part be welded to the second part. Unlike a sintering process, a coating process, or a 3D printing process, it is therefore not essential that the outer contour of the first part be completely altered or that the first part be completely melted during the process. It is also possible for the first part and the second part to essentially retain their outer contours during the process of forming the friction stir welding tool. For example, the first part can be designed as a ring, which is welded onto the second part, which has the pin and part of the shoulder, particularly with a groove for the first part.Welding can in turn be carried out in a variety of ways known from the prior art, for example by laser welding, diffusion welding, electron beam welding or the like.

[0037] It has been shown that a particularly robust connection between the first part and the second part can be achieved if the first part is joined to the second part by a friction welding process.

[0038] Preferably, the first part is joined to the second part by a pressure welding process. However, a combination of friction welding and pressure welding is also conceivable.

[0039] It has proven effective that, depending on the desired average coefficient of sliding friction, which acts when the shoulder contacts the base material and lies between a first coefficient of sliding friction (existing when the first material is in contact with the base material) and a second coefficient of sliding friction (existing when the second material is in contact with the base material), a first section of the shoulder is formed by the first material and a second section by the second material to achieve the desired average coefficient of sliding friction. In other words, the size of the section of the shoulder formed by the first material (if the shoulder is not entirely formed by the first material) is chosen according to the desired average coefficient of sliding friction in the shoulder area.For example, if the average coefficient of sliding friction of the first material in a material pairing with the base material, particularly in a material pairing with steel, especially a high-strength structural steel such as that used for pipeline pipes, is 0.1, and the coefficient of sliding friction of the second material in a material pairing with the same base material is 0.3, then an average coefficient of sliding friction of the shoulder of, for example, 0.2 can be achieved by forming a shoulder surface in contact with the components to be welded during the welding process that is 50% made of the first material and 50% of the second material. A shoulder surface then consists of the first sub-area and the second sub-area, although, in principle, further sub-areas made of other materials are also possible. After a speed of the shoulder in a pin-near or...Since the coefficient of sliding friction is lower in the area near the axis of rotation than at an outer edge, and since the coefficient of sliding friction can also depend on a relative velocity, different ratios of the areas of the shoulder formed by the first material and the second material can result, depending on whether the first material is located inside or outside the shoulder.

[0040] To achieve a particularly high effect when using the first material, which preferably has a lower coefficient of sliding friction than the second material, the first material is typically positioned at an outer edge of the shoulder, for example as an outer ring. Thus, not only the surface area of ​​the shoulder formed by the first or second material is relevant for the quality of the weld or the heat input into the components to be welded, but also, at least to a small extent, the position at which the shoulder is formed by the first or second material, or the distance of the corresponding position from an axis of rotation of the friction stir welding tool.

[0041] Preferably, the friction stir welding tool is designed to be approximately rotationally symmetrical.

[0042] To achieve particularly simple manufacturing, it is advantageously provided that, before joining the first part to the second part, the first part is formed with a contour that corresponds to the shoulder section formed from the first material. The first part can thus, for example, be designed as a ring that is positioned in a groove in the second part to form a corresponding part of the shoulder. Of course, the first part can also be designed as a polygon or the like to achieve a positive-locking connection with the second part. The second part can form part of the pin, the complete pin, or the partial or complete shank of the tool. Preferably, the first part has a substantially rotationally symmetrical outer contour, in particular, it is ring-shaped.This allows for a particularly simple manufacturing process for the friction stir welding tool.

[0043] It is understood that a friction stir welding tool designed according to the invention can be formed by a method according to the invention.

[0044] According to a third aspect of the invention, a method for joining components using a tool according to the first aspect in claim 13 is defined.

[0045] This results in a weld seam of particularly high quality while simultaneously ensuring a long service life for the friction stir welding tool.

[0046] Although any component can, in principle, be joined using a friction stir welding tool according to the invention, it has been shown that such a tool is particularly suitable for use in a process where the components to be joined are tubular. For example, pipes forming a pipeline can be welded without having to change the friction stir welding tool during the formation of a weld seam running along a circumferential direction. This is crucial for the particularly efficient formation of a pipeline, which, for example, may be laid at a depth of 3000 m below the sea surface.

[0047] The method is particularly preferred when the components have a wall thickness of more than 10 mm, and especially more than 20 mm, with a weld seam extending over the entire wall thickness. The components, which are typically flat, preferably tubular, are thus placed next to each other along their narrow sides before welding, so that the weld seam, if it extends from one surface of the components to an opposite surface, has a height corresponding to the wall thickness or to the height of the adjacent narrow sides of the components.

[0048] To achieve a stable friction stir weld even with correspondingly large wall thicknesses, the application of a precisely defined amount of heat is required, since an excessively high or low heat input would result in the friction stir weld being suboptimal, at least over a portion of the weld thickness. Such a precisely defined heat input is easily achieved with a friction stir welding tool according to the invention, particularly since a sliding friction coefficient of the shoulder can be achieved independently of the sliding friction coefficient and material of the pin.

[0049] Further features, advantages, and effects of the invention will become apparent from the exemplary embodiments described below. The drawings referenced therein show: Fig. 1 bis 3 various friction stir welding tools designed according to the invention; Fig. 4 a friction stir welding tool according to the invention during the welding of two components; Fig. 5 bis 7 other friction stir welding tools; Fig. 8 another friction stir welding tool during the joining of two components.

[0050] Fig. 1 Figure 1 shows a cross-section through a friction stir welding tool 1 designed according to the invention. As can be seen, the friction stir welding tool 1, which is essentially rotationally symmetrical about an axis of rotation 9, has a shank 4, a pin 2, and a shoulder 3. The shoulder 3 is oriented approximately perpendicular to the axis of rotation 9 and is formed by a first part 5 made of a first material, here a molybdenum alloy, and the pin 2 and the shank 4 by a second part 6 made of a second material, here tungsten-rhenium. The first part 5 is ring-shaped, as shown, with an inner diameter 13 of the first part 5 corresponding to a pin outer diameter 11, which in turn corresponds to the shoulder inner diameter 13. An outer diameter of the ring-shaped first part 5 corresponds to a shoulder outer diameter 12. The shoulder 3 is thus formed entirely by the first part 5 or the first material.

[0051] Due to the use of tungsten-rhenium in the pin 2 area, such a tool achieves high temperature resistance. The use of the molybdenum alloy in the shoulder 3 area results in a lower coefficient of sliding friction at the shoulder 3 than at the pin 2 area when welding components 7 made of steel, particularly structural steel. Therefore, compared to a friction stir welding tool 1 made entirely of tungsten-rhenium, with the same process parameters such as axial contact pressure, rotational speed of the friction stir welding tool 1 around the axis of rotation 9, and feed rate, less heat is introduced via the shoulder 3. In the pin 2 area, the higher coefficient of sliding friction exhibited by the tungsten-rhenium / structural steel material pairing is advantageous for achieving thorough stirring in the joining zone.This allows components 7 with a large wall thickness 10 to be welded together by friction stir welding in such a way that both a long service life of the friction stir welding tool 1 and a high quality of the weld joint are achieved.

[0052] Fig. 2 Figure 1 shows another friction stir welding tool according to the invention. Again, the shoulder 3 is formed entirely by an annular first part 5 made of a molybdenum alloy, while the pin 2 and a portion of the shaft 4 are formed by a second part 6 made of tungsten-rhenium. In contrast to the one shown in Figure 1, the shoulder 3 is formed entirely by an annular first part 5 made of a molybdenum alloy, while the pin 2 and a portion of the shaft 4 are formed by a second part 6 made of tungsten-rhenium alloy. Fig. 1 In the depicted friction stir welding tool 1, the shaft 4 is only partially formed by the second part 6 and partially by a third part 8 made of a third material, which third material may be cheaper than tungsten-rhenium in terms of manufacturing costs, for example.

[0053] Fig. 3 Figure 1 shows a further embodiment of a friction stir welding tool 1 according to the invention. In this embodiment, the first part 5 does not extend over the entire shoulder 3, but only forms a first partial region 14 of the shoulder 3, such that a second partial region 15 of the shoulder 3 is formed by the second part 6, which also forms the pin 2. Thus, only an outer first partial region 14 of the shoulder 3 is formed by the first part 5, which is also ring-shaped and made of a molybdenum alloy. The ring-shaped first part 5 therefore does not extend from the shoulder outer diameter 12 to the pin 2 or to the pin outer diameter 11, but only to an inner diameter 13, which lies approximately midway between the shoulder inner diameter 13 and the shoulder outer diameter 12. The shoulder inner diameter 13 also corresponds to the pin outer diameter 11.Thus, by changing the inner diameter 13 of the first part 5 or by changing the first sub-section 14 formed by the first material and the second sub-section 15 formed by the second material of the shoulder 3, a desired average coefficient of sliding friction of the shoulder 3, which results when used on a base material such as steel, can be set arbitrarily between a first coefficient of sliding friction of a material pairing of the first material with the base material and a second coefficient of sliding friction of a material pairing of the second material with the base material. In the exemplary embodiment, the first coefficient of sliding friction of the material pairing molybdenum alloy with steel is lower than the second coefficient of sliding friction of the material pairing tungsten-rhenium with steel, so that in the case of the Fig. 3 In the illustrated embodiment, a mean coefficient of sliding friction is achieved in the area of ​​shoulder 3, which is higher than the coefficient of sliding friction of the material pairing molybdenum alloy with steel and lower than the coefficient of sliding friction of the material pairing tungsten-rhenium with steel.

[0054] Fig. 4 shows a friction stir welding tool 1 after Fig. 1 The welding of the second components 7 is shown again in a sectional view. As can be seen, the pin 2 extends essentially over the entire wall thickness 10 of the components 7, which here, for example, are plate-shaped and are made of steel, preferably pipeline steel, and have a melting point of more than 900 °C. By using the first material in the area of ​​the shoulder 3, a lower coefficient of sliding friction is achieved in the area of ​​the shoulder 3 than in the area of ​​the pin 2, so that advantageously strong mixing of the base materials of the components 7 is achieved in the area of ​​the pin 2, while a comparatively low heat input occurs via the shoulder 3.

[0055] The ring-shaped first part 5, from which the shoulder 3 extends into the Fig. 1 bis Fig. 4 The second part 6, which forms the pin 2 and at least a partial area of ​​the shaft 4, is at least partially formed in the illustrated embodiments by means of a friction welding process.

[0056] This results in a rigid, stable connection, which also ensures that there is no gap between the first part 5 and the second part 6 and thus no plasticized material from the weld can penetrate into such a gap, as would be the case with a multi-part friction stir welding tool 1, in which, for example, the shoulder 3 rotates at a lower speed than the pin 2.

[0057] Fig. 5 bis 7 Figure 1 shows further embodiments of a friction stir welding tool 1 according to the invention in sectional view. In these embodiments, the shoulder 3 and the pin 2 of a friction stir welding tool 1, which is essentially made of a third material, are at least partially coated with different materials in order to achieve different friction properties in the area of ​​the pin 2 and in the area of ​​the shoulder 3 when carrying out a friction stir welding process. The friction stir welding tool 1 can consist essentially of a third material and be coated only in the area of ​​the shoulder 3 and in the area of ​​the pin 2 as shown, in order to achieve the desired properties in these partial areas. In the embodiment shown in Figure 1, the shoulder 3 and the pin 2 are coated in the area of ​​the shoulder 3 and the area of ​​the pin 2 in the third material. Fig. 5 In the illustrated embodiment, a surface forming the shoulder 3 is completely coated with a first material, and a surface forming the pin 2 is completely coated with a second material. The first part 5 is thus, in the Fig. 5 In the illustrated embodiment, the first part 5 is formed as a coating in the area of ​​the shoulder 3 and the second part 6 as a coating in the area of ​​the pin 2, wherein the first part 5 can again be made of a molybdenum alloy and the second part 6 can again be made of a tungsten alloy.

[0058] In the Fig. 6 In the illustrated embodiment, the first part 5, which is also formed by a coating, only partially covers a surface in the area of ​​the shoulder 3. A portion of the shoulder 3 not formed by the coating made of the first material, or by the first part 5, is formed by a coating made of the second material, or by a second part 6, which also forms a surface of the pin 2. In this way, a coefficient of sliding friction for the shoulder 3 can again be achieved that lies between the coefficients of sliding friction of the first and second materials.

[0059] Fig. 7 Figure 1 shows a further embodiment in which a surface in the area of ​​the shoulder 3 is formed by a first part 5 consisting of a first material, which is designed as a coating. Here, a surface of the pin 2 is partially coated with the first material and partially with the second material in order to achieve properties that lie between those of the first material and those of the second material.

[0060] Fig. 8 . shows the use of a friction stir welding tool 1 according to Fig. 5 during a process for joining corresponding components 7, again in sectional view.

[0061] As in the Fig. 5 bis 8 As can be seen, the friction stir welding tool 1 can therefore also be essentially formed by a third material or a third part 8, which is coated at its end in the area of ​​the shoulder 3 and the pin 2 with a first material, which forms a first part 5, and a second material, which forms a second part 6, in order to achieve corresponding properties. In contrast to the in Fig. 1 bis 4 The illustrated embodiments are used in the Fig. 5 bis 8 In the illustrated embodiments, the contours of the first part 5 and the second part 6 are thus only formed during the manufacture of the friction stir welding tool 1, namely by coating a surface of the third part 8.

[0062] Preferably, a suitable tool is used to weld structural steel, especially higher-strength and ultra-high-strength steels, as well as thick-walled pipes, which, for example, consist of structural steel and can have a wall thickness of more than 10 mm, together along a circumferential weld seam. These pipes can be used, for example, for a pipeline at great depth. Thick-walled steel pipes can thus be welded with a single friction stir welding tool 1 without changing tools, enabling the construction of such a pipeline in a particularly cost-effective manner.

Claims

1. A friction stir welding tool (1), which has a pin (2) and a shoulder (3) connected rigidly to the pin (2), for welding components (7) consisting of a parent material that is composed of steel and has a melting point of more than 900°C, wherein said friction stir welding tool (1) particularly is produced in a method according to one of claims 6 to 15, and wherein the shoulder (3) consists at least partially of a first material and the pin (2) consists at least partially of a second material, characterized in that a material pairing of the first material with the parent material has a first coefficient of sliding friction and a material pairing of the second material with the parent material has a second coefficient of sliding friction, wherein the first coefficient of sliding friction is lower than the second coefficient of sliding friction.

2. The friction stir welding tool (1) according to claim 1, characterized in that the friction stir welding tool (1) has a shaft (4) that contains a third material, particularly is composed of a third material.

3. The friction stir welding tool (1) according to claim 1 or 2, characterized in that the first material contains molybdenum, particularly is realized in the form of a molybdenum alloy, and / or in that the second material contains tungsten, particularly is composed of tungsten-rhenium.

4. The friction stir welding tool (1) according to one of claims 1 to 3, characterized in that the first material and / or the second material contains a ceramic material, particularly an oxide ceramic material and / or a nonoxide ceramic material such as carbides, nitrides or silicides or is composed of such a material.

5. The friction stir welding tool (1) according to one of claims 1 to 4, characterized in that the first material and / or the second material contains a refractory metal, a refractory metal alloy, a nickel alloy, a cobalt alloy and / or an iron alloy or is composed of such a material.

6. A method for producing a friction stir welding tool (1) that has a pin (2) and a shoulder (3), which friction stir welding tool is capable of connecting components (7) consisting of a parent material that is composed of steel, particularly construction steel, and has a melting temperature of more than 900°C by means of friction stir welding, particularly for producing a friction stir welding tool (1) according to one of claims 1 to 5, wherein a first part (5), which consists of a first material, is connected rigidly to a second part (6), which consists of the second material, such that at least a section of the shoulder (3) is composed of the first material and at least a section of the pin (2) is composed of the second material, characterized in that a material pairing of the first material with the parent material has a first coefficient of sliding friction and a material pairing of the second material with the parent material has a second coefficient of sliding friction, wherein the first coefficient of sliding friction is lower than the second coefficient of sliding friction.

7. The method according to claim 6, characterized in that the first part (5) is connected integrally to the second part (6), wherein the first part (5) preferably is welded to the second part (6).

8. The method according to claim 6 or 7, characterized in that the first part (5) is connected to the second part (6) by means of a friction welding process.

9. The method according to one of claims 6 to 8, characterized in that the first part (5) is connected to the second part (6) by means of a pressure welding process.

10. The method according to one of claims 6 to 9, characterized in that, depending on a desired average coefficient of sliding friction that acts during a contact of the shoulder (3) with the parent material and lies between a first coefficient of sliding friction of a material pairing of the first material with the parent material and a second coefficient of sliding friction of a material pairing of the second material with the parent material, a first section (14) of the shoulder (3) is composed of the first material and a second section (15) of the shoulder (3) is composed of the second material in order to achieve the desired average coefficient of sliding friction.

11. The method according to one of claims 6 to 10, characterized in that the first part (5) is produced with a contour that corresponds to the section of the shoulder (3) composed of the first material prior to connecting the first part (5) to the second part (6).

12. The method according to one of claims 6 to 11, characterized in that the first part (5) essentially has a rotationally symmetrical outer contour, particularly an approximately annular design.

13. A method for connecting components (7) consisting of a parent material or multiple parent materials that is / are composed of steel, particularly construction steel, and has / have a melting temperature of more than 900°C by means of friction stir welding, characterized in that a friction stir welding tool (1) according to one of claims 1 to 5 is used for connecting these components (7).

14. The method according to claim 13, characterized in that the components (7) have a tubular design.

15. The method according to claim 13 or 14, characterized in that the components (7) have a wall thickness (10) of more than 10 mm.