阅读说明：本技术 摩擦搅拌接合工具 (Friction stir welding tool ) 是由 船平伸之 宫本卓弥 河原亮 宫胁章嘉 佐山满 茑佳佑 兵藤安正 于 2020-04-02 设计创作，主要内容包括：一种摩擦搅拌接合工具,其在铁基合金和铝合金的摩擦搅拌接合时,即使高硬度的凝聚物附着在前端部,也抑制缺损。作为具备小径部和与之连续地被形成的大径部的高速工具钢制的摩擦搅拌接合用工具,使硬度随着从小径部到大径部去而减小。另外,也可以使小径部的硬度按照洛氏硬度C刻度在65HRC以上,使大径部的硬度按照洛氏硬度C刻度在60HRC以下。(A friction stir welding tool which suppresses chipping even when a high-hardness aggregate adheres to a tip portion at the time of friction stir welding of an iron-based alloy and an aluminum alloy. A tool for friction stir welding made of high-speed tool steel having a small diameter portion and a large diameter portion formed continuously with the small diameter portion is configured such that the hardness decreases from the small diameter portion to the large diameter portion. The hardness of the small diameter portion may be set to 65HRC or more on the rockwell C scale, and the hardness of the large diameter portion may be set to 60HRC or less on the rockwell C scale.)

1. A friction stir welding tool made of a high-speed tool steel having a small diameter portion and a large diameter portion formed continuously with the small diameter portion, characterized in that the hardness thereof is continuously decreased from the small diameter portion toward the large diameter portion.

2. The friction stir welding tool according to claim 1, wherein the hardness of the small diameter portion is 65HRC or more on the rockwell C scale, and the hardness of the large diameter portion is 60HRC or less on the rockwell C scale.

3. The friction stir welding tool according to claim 1 or 2, wherein the high-speed tool steel comprises, in terms of weight%, 1.20 to 1.35% of carbon, 0.5% or less of silicon, 0.5% or less of manganese, 3.5 to 4.5% of chromium, 4.5 to 5.5% of molybdenum, 5.5 to 7.0% of tungsten, 2.5 to 3.5% of vanadium, 7.7 to 8.8% of cobalt, 60ppm or less of nitrogen, and 20ppm or less of oxygen, and the balance is iron and unavoidable impurities.

4. The friction stir welding tool according to any one of claims 1 to 3, wherein in any cross section of the high speed tool steel perpendicular to the forging direction or the rolling direction, the MC type carbide in the structure has an equivalent circle diameter in the range of 4 to 20 μm, and the MC type carbide accounts for 3 to 10% of the structure.

Technical Field

The present invention relates to a tool for friction stir welding (friction stir welding tool) used when metal materials are welded to each other by frictional heat generated by frictional force of the metal materials and a rotating tool.

Background

In order to join the same metal materials to each other, Friction Stir Welding (FSW) is known as a technique for temporarily melting the metal materials by inserting a rod-shaped tool rotating at a high speed into a joint portion of the metal materials, instead of Welding or the like. Rotary tools (friction stir welding tools) used for friction stir welding have been widely used in various forms, and relatively hard materials such as high-speed tool steel (high-speed steel) and nickel-based alloys have been used in many cases as materials (see, for example, patent documents 1 and 2).

In general, even a friction stir welding tool made of die steel (alloy steel) typified by SKD 61 can be used for friction stir welding of aluminum alloys. However, when dissimilar metals of an aluminum alloy and an iron-based alloy are joined to each other, it is necessary to consider selecting a material having a higher hardness for the material of the friction stir welding tool.

Prior art documents

Patent document

Patent document 1: japanese laid-open patent publication No. 2002-

Patent document 2: international publication WO2013/027474 pamphlet

Disclosure of Invention

Problems to be solved by the invention

In particular, when one of the bonding metals is an iron-based alloy, the hardness of the aggregate adhering to the tip of the friction stir bonding tool during bonding is higher than that in the case where aluminum alloys are bonded to each other, and depending on the bonding conditions, the tip of the friction stir bonding tool may be worn or chipped early.

Accordingly, the present invention has an object to provide a tool for friction stir welding that can suppress early wear and chipping even when a high-hardness aggregate adheres to a tip portion of the tool for friction stir welding when dissimilar metal materials such as an iron-based alloy and an aluminum alloy are friction stir welded to each other.

Means for solving the problems

The friction stir welding tool of the present invention is a friction stir welding tool made of high-speed steel having a small diameter portion and a large diameter portion, and has a structure in which the hardness is gradually reduced from the small diameter portion to the large diameter portion. As for the specific hardness, the hardness of the small diameter portion is set to 65HRC or more on the Rockwell hardness C scale, and the hardness of the large diameter portion is set to 60HRC or less on the Rockwell hardness C scale.

The high-speed tool steel (high-speed steel) comprises, by weight, 1.20 to 1.35% of carbon, 0.5% or less of silicon, 0.5% or less of manganese, 3.5 to 4.5% of chromium, 4.5 to 5.5% of molybdenum, 5.5 to 7.0% of tungsten, 2.5 to 3.5% of vanadium, 7.7 to 8.8% of cobalt, 60ppm or less of nitrogen, 20ppm or less of oxygen, and the balance of iron and unavoidable impurities.

Further, in any cross section perpendicular to the forging direction or the rolling direction of the high-speed tool steel, there is no problem in that the equivalent circle diameter of the MC type carbide in the structure is in the range of 4 to 20 μm and the ratio of the MC type carbide in the structure is in the range of 3 to 10%.

ADVANTAGEOUS EFFECTS OF INVENTION

The friction stir welding tool made of high-speed tool steel according to the present invention has a two-stage structure of a small diameter portion and a large diameter portion, and is inclined so-called to have a hardness which gradually decreases from the small diameter portion to the large diameter portion. As a result, even when the high-hardness aggregate generated at the time of friction stir welding of the iron-based alloy and the aluminum alloy adheres to the small diameter portion, the aggregate can be easily removed from the small diameter portion of the tool, and therefore, the damage of the tip portion (small diameter portion) can be prevented while maintaining the toughness of the tool.

Drawings

Fig. 1 is a schematic perspective view of a friction stir welding tool 1 (first embodiment) of the present invention.

Fig. 2 is a schematic perspective view of a friction stir welding tool 11 (second embodiment) of the present invention.

Fig. 3 is a schematic perspective view of a friction stir welding tool 21 (third embodiment) of the present invention.

Fig. 4 is a graph relating to the surface hardness of the friction stir welding tool of the present invention.

Detailed Description

In order to implement the mode of the invention

Embodiments of a friction stir welding tool according to the present invention will be described with reference to the drawings. Fig. 1 is a schematic perspective view of a friction stir welding tool 1 according to a first embodiment of the present invention as viewed from a distal end portion (small diameter portion) side thereof, fig. 2 is a schematic perspective view of a friction stir welding tool 11 according to a second embodiment, and fig. 3 is a schematic perspective view of a friction stir welding tool 21 according to a third embodiment.

A friction stir welding tool 1 (hereinafter, referred to as a "tool") according to a first embodiment of the present invention is generally configured by respective portions of a small diameter portion 2 and a large diameter portion 3 as shown in fig. 1, the small diameter portion 2 is also referred to as a probe, and the large diameter portion 3 is formed continuously with the small diameter portion 2 and is located in the vicinity of a rotation axis side connected to the tool 1. The same applies to the tools 11 and 21 according to the second and third embodiments shown in fig. 2 and 3. The details of the small diameter portion and the large diameter portion constituting the tool will be described below for each part.

The small diameter portion 2 of the tool 1 shown in fig. 1 is formed as a portion which is partially or entirely buried in the materials to be joined at the time of friction stir welding and contributes to actual friction stir welding. The overall shape may be a cylindrical small diameter portion 2 as shown in fig. 1, a truncated cone-shaped small diameter portion 12 as shown in fig. 2, or a conical small diameter portion 22 as shown in fig. 3.

When dissimilar metal materials such as an iron-based alloy and an aluminum alloy are joined to each other, the materials are joined while pressing the surface of one of the materials to be joined, and a large compressive stress is generated at the tip of the small diameter portion. Therefore, the tip of the small diameter portion 2 is desirably a smooth surface having a predetermined size (area), that is, the form shown in fig. 1 and 2.

The large diameter portion 3 and the small diameter portion 2 forming the tool 1 shown in fig. 1 are formed continuously, and are located in the vicinity of the rotation axis side of the tool 1. When the tool 1 is attached to the friction stir welding apparatus, as shown in fig. 2, a fastening portion 50 attached to another component such as a rotating shaft (shaft) of the friction stir welding apparatus may be provided by providing a screw or a recess-projection (fitting shape) on one end side of the large diameter portion 13 (on the opposite side of the small diameter portion 12).

The shoulder portion, which is the boundary portion between the large diameter portion and the small diameter portion, has no problem in a shape inclined toward the axial center side or the outer peripheral surface side (tapered shape or mortar shape) other than the flat shape as shown in fig. 1 to 3. In addition, when the fastening portion is provided at one end side of the large diameter portion 3 or 23 shown in fig. 1 or 3, a male screw process may be performed on the outer peripheral surface thereof or a screw hole (female screw) may be provided at the center.

Next, the material and the like of the tool will be described. The tool of the present invention is made of the same material for both the small diameter portion and the large diameter portion, and in order to make the tool suitable as a tool, high-speed tool steel limited to the following components or the like is used. Specifically, the steel is a high-speed tool steel comprising: in% by weight, comprising carbon (C): 1.20 to 1.35%, silicon (Si): 0.5% or less, manganese (Mn): 0.5% or less, chromium (Cr): 3.5 to 4.5% of molybdenum (Mo): 4.5-5.5%, tungsten (W): 5.5 to 7.0%, vanadium (V): 2.5-3.5%, cobalt (Co): 7.7-8.8%, nitrogen (N): 60ppm or less of oxygen (O): 20ppm or less, and the balance of Fe and inevitable impurities, and is preferably a material corresponding to SKH40 defined in JIS G4403.

In any cross section perpendicular to the forging direction or the rolling direction, the equivalent circle diameter of the largest carbide (MC type carbide) in the structure is in the range of 4 to 20 μm, and the ratio (area ratio) of the MC carbide in the structure is in the range of 3 to 10%. Here, the "equivalent circle diameter" refers to the diameter of a circle in the case where the area of the cross section of the measured particle (in the present application, MC type carbide) is replaced with the area of a circle, and can be obtained by image analysis software or the like performed by a computer.

The components contained in the high-speed tool steel are defined in the above-described composition ranges, which is effective in achieving high hardness of the tool (for example, 65HRC or more on the rockwell C scale). Further, the MC type carbide is defined in the above-described distribution state, which is effective in suppressing the defect of the tool while reducing the wear of the tool and the material to be joined.

In particular, it is very effective to suppress coarsening of carbide (MC type carbide) formed in the structure and to ensure toughness as a tool by defining the content of nitrogen (N) as a gas component contained in high-speed tool steel to be 60ppm or less and the content of oxygen (O) to be 20ppm or less. Accordingly, it is possible to impart a characteristic of being less likely to be broken while having high wear resistance in addition to the inclination of the surface hardness described later, and therefore it is possible to obtain a tool suitable for friction stir welding of dissimilar metal materials.

Further, high-speed tool steel is manufactured by melting (casting), and as a method for reducing the gas component in the steel material at this time, a vacuum casting method such as melting or casting in a reduced pressure atmosphere, a method such as ESR method for remelting (remelting) a primarily cast steel material, or the like can be singly applied or a combination thereof can be applied. The final form of the tool can be finished by press forming using a die or cutting (cutting) with a milling cutter at the time of the above-described melting (casting).

The tip end portion (small diameter portion) of the tool is actually used for friction stir welding, and therefore, is exposed to a high-temperature and high-pressure environment, and therefore, is required to have higher hardness than the large diameter portion. On the other hand, the large diameter portion is also a portion directly or indirectly connected to the friction stir welding device as described above. Therefore, if the hardness is high as in the small diameter portion, a high pressure (bending stress) is applied during friction stir welding, and the shaft portion may be broken. In particular, when the hardness is changed greatly between the small diameter portion and the large diameter portion of the tool, the tendency thereof is remarkably exhibited in terms of the change in the hardness of the tool in the axial direction.

Therefore, the large diameter portion needs to maintain toughness in advance in accordance with the bending stress generated at the time of joining. Therefore, the tool of the present invention is provided with a region in which the hardness is changed so as to be inclined, the hardness of which is continuously reduced from the small diameter portion to the large diameter portion. Fig. 4 shows an embodiment in which the surface hardness changes in the axial direction (longitudinal direction) of the tool of the present invention.

In the case of a tool in which the fastening portion 50 is provided on one end side of the large diameter portion 13 shown in fig. 2, the surface hardness of the small diameter portion at the center position in the axial direction (position a in fig. 4) is 65HRC (corresponding to a vickers hardness 830Hv) as shown in fig. 4. The small diameter portion of the tool is a portion that is submerged in the materials to be joined during friction stir welding, and receives both a rotational force and a pressing force (pressing force) from the friction stir welding device, and therefore, the small diameter portion of the tool has the highest hardness.

Next, the surface hardness at a position (position B in fig. 4) shifted from the shoulder portion (boundary portion between the large diameter portion and the small diameter portion) of the tool by about 1/4 length was 59HRC (corresponding to a vickers hardness of 670Hv), and the surface hardness at the center position (position C in fig. 4) of the large diameter portion in the longitudinal direction was 54HRC (corresponding to a vickers hardness of 580 Hv).

Further, the surface hardness at the end of the large diameter portion (the boundary portion with the fastening portion: at the position D in FIG. 4) was 48HRC (corresponding to a Vickers hardness of 480 Hv). The surface hardness of the fastening portion (at position E in fig. 4) was 40HRC (corresponding to a vickers hardness of 390 Hv). Thus, the tool of the present invention has a so-called hardness gradient region in which the surface hardness in the axial direction is continuously reduced from the small diameter portion to the large diameter portion.

In friction stir welding, not only the materials to be welded but also surrounding oxygen and nitrogen are involved by the rotation of the tool, and oxides and nitrides are generated between the tool and the materials to be welded, so that the aggregate adhering to the tip end portion of the tool generally has a higher hardness than the hardness of the materials to be welded. In addition, if the material to be joined is an iron-based alloy, the hardness of the aggregate becomes at least higher than that in the case of a light metal such as an aluminum alloy or a copper alloy.

In the case where at least one of the materials to be joined is an iron-based alloy, the hardness of the aggregates produced by friction stir welding is at least about 62HRC on the rockwell C scale (corresponding to 750Hv on the vickers hardness), and therefore the hardness of the small diameter portion of the present invention is set to a hardness higher than the hardness of the aggregates and is 65HRC or higher on the rockwell C scale. On the other hand, if the hardness of the large diameter portion is made high as the hardness of the small diameter portion, there is a possibility that the connection portion with the friction stir welding device will be broken at the time of friction stir welding.

Therefore, in order to maintain flexibility (to ensure toughness) capable of withstanding bending stress generated when the tool itself moves on a flat surface or a curved surface while rotating at a high speed, the hardness of the large diameter portion is set to 60HRC or less on the rockwell C scale.

Further, the tip portion (small diameter portion) of the tool is assumed to be used repeatedly, and from the viewpoint of prolonging the life of the tool, it is more preferable that the rockwell C scale is 67HRC or more (equivalent to 900Hv in terms of vickers hardness).

Description of the symbols

1. 11, 21: a friction stir welding tool; 2. 12, 22: a small diameter part; 3. 13 and 23: a large diameter portion; 50: and fastening the connecting part.