JPWO2009107594A1 - Connection method between cemented carbide and stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of connecting stainless steel and a cemented carbide such as tungsten carbide in a short time. SOLUTION: One end face of a rod-shaped member 12 made of a cemented carbide obtained by sintering tungsten carbide powder with cobalt is planarly finished so that the cobalt particles are exposed on the surface, and the planar finish is performed. A step of rotating at least one of the cemented carbide rod-shaped material 12 or the stainless steel rod-shaped material 11 while pressing one end surface of the stainless steel rod-shaped material 11 against the end surface; When the end of the material is softened, the rotation is stopped and the pressing force is increased to join the stainless steel rod 11 to the cemented carbide rod 12. [Selection] Figure 1

Description

  The present invention relates to a method of connecting a cemented carbide obtained by sintering tungsten carbide and stainless steel.

  Cemented carbides mainly composed of tungsten carbide are tough and excellent in heat resistance, and are therefore widely used as cutting tools for cutting metals and the like. Tungsten carbide is also used as a dental cutting tool. By using such a cemented carbide, it is possible to easily make a hole even with a hard tooth.

  When using cemented carbide as a cutting tool, insert a chip molded to the specified shape and dimensions to a base metal such as steel by brazing, or as a solid type with cemented carbide up to the base metal part. I use it.

  However, cemented carbide such as tungsten carbide is expensive, and if it is a solid type, the cost increases. In the case of the solid type, the chuck of the handpiece that holds the cutting tool is worn, easily damaged, and easily removed. On the other hand, brazing has problems such as time consuming and weak bonding strength.

  As a method for connecting tungsten carbide and carbon steel, there is Patent Document 1 (Japanese Patent Laid-Open No. 2003-53558). This is because a round bar-shaped carbon steel and a round bar-shaped tungsten carbide are pressed against each other, and one of them is rotated to generate frictional heat. , To be joined.

  However, this method has a problem that residual stress due to heat is likely to remain in the joint, and the strength of the joint is insufficient due to cracks.

  With respect to this problem, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2004-216410), connection is made by rotational friction as in Patent Document 1, but residual iron-nickel-cobalt-based alloy is interposed in the middle, thereby remaining due to thermal stress. A method for reducing stress is proposed.

  However, since the said patent document 2 joins an intermediate material, there exists a problem that the man-hour of joining increases and it takes time and effort.

  As a method of connecting stainless steel and tungsten carbide, Patent Document 3 (Japanese Patent Laid-Open No. 6-199580) is known. Here, it is proposed that tungsten carbide and stainless steel are joined together with a predetermined pressing force in a low oxygen atmosphere, and the butt portion is raised to a predetermined temperature. As a heating method for raising the temperature to a predetermined temperature, there is a method using a laser beam or a plasma beam in addition to energization.

The low oxygen atmosphere is used for the following reason. When butt welding is performed in the atmosphere, the growth of the decarburized layer is promoted by oxygen in the atmosphere. This is because the stainless steel has almost no carbon, so the carbon of the tungsten carbide is decarburized, the composition of the tungsten carbide at the joining site changes, and the joint becomes brittle.
JP 2003-53558 A JP-A-2004-216410 JP-A-6-199580

  However, since the method described in Patent Document 3 is performed in a low-oxygen atmosphere, batch processing is performed, continuous processing cannot be performed, and it is necessary to provide a room or the like that maintains a low-oxygen atmosphere for bonding. Therefore, there is a problem that the time required for joining becomes long.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide a method capable of connecting stainless steel and a cemented carbide such as tungsten carbide in a short time.

  In order to achieve the above object, the joining method of the stainless steel and the cemented carbide of the present invention is a step of finishing one end surface of a rod-shaped material made of cemented carbide obtained by sintering tungsten carbide powder with cobalt to a smooth surface. And rotating the at least one of the cemented carbide rod-shaped material or the stainless steel rod-shaped material while pressing the end surface finished to the smooth surface and one end surface of the stainless steel rod-shaped material, and rotating When the end of the stainless steel rod is softened by the frictional heat generated by the step, the step of joining the stainless steel rod to the carbide rod by increasing the pressing force just before the end of the rotation or stopping the rotation It is characterized by having.

  In the step of rotating the cemented carbide rod or stainless steel rod pressed against each other, both the cemented carbide rod and the stainless steel rod are rotated in opposite directions, In addition to rotational friction, the stainless steel rod-shaped material is heated by energization, the surface roughness (Rmax) of the end face of the cemented carbide is 0.8 to 5.0 μm, the stainless steel The surface roughness (Rmax) of the end face of the steel may be 0.8 to 5.0 μm. A smooth surface refers to a smooth surface with no irregularities on the surface, and includes both flat and curved surfaces. In the case of a curved surface, the end surface of the cemented carbide and the end surface of the rod-shaped material of stainless steel overlap each other. . Further, the smooth surface includes a mirror surface. The smoothness of the smooth surface may be the same as that polished with a # 140 diamond grindstone or sandpaper.

  One or both of the cemented carbide rod and stainless steel rods are pressed against each other and rotated, but at this time, the end surface of the cemented carbide is finished to a smooth surface, so contact The surface becomes large and a lot of frictional heat is generated. When the stainless steel is softened by frictional heat, if the rotation is stopped or a further pressing force is applied just before the end of the rotation, the cemented carbide rod and the stainless steel rod are joined. At this time, cobalt and stainless steel contained in the cemented carbide side enter each other's region to form an interdiffusion layer. Thereby, the residual stress can be reduced and the bonding strength can be increased. Further, when the stainless steel is in a semi-molten state due to rotational friction in a close contact state, the surroundings are sealed, so that a low oxygen state occurs and decarburization does not occur. In addition, bonding at a short time can provide sufficient strength at the bonded portion, suppress generation of microcracks on the carbide side, and suppress breakage.

BEST MODE FOR CARRYING OUT THE INVENTION

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a diagram showing an example of an embodiment for carrying out a method for connecting a cemented carbide and stainless steel according to the present invention. Here, a carbide bar will be described as an example of a dental cutting tool. In FIG. 1, a rod-shaped material 11 made of a stainless steel round bar is firmly held by a claw 23 of a chuck 22 attached to the tip of a rotating shaft 21. The rod-shaped member 12 made of the other cemented carbide round rod is also firmly held by the holding portion 25 of the clamp base 24.

  With regard to the lower end surface 12a serving as the bonding surface of the cemented carbide rod-shaped member 12, Patent Document 2 describes that a rough surface of 10 μm or more is desirable in order to easily generate frictional heat. This idea seems common to the connection between stainless steel and tungsten carbide. However, even if stainless steel and tungsten carbide are connected by this method, they cannot be joined well.

  As a result of intensive studies, the inventors of the present invention have found that it is important to form an interdiffusion layer on the joint surface in a short time when connecting stainless steel and tungsten carbide. When stainless steel and tungsten carbide are frictionally contacted and melt-bonded, if the surface is smooth, cobalt bonding tungsten carbide diffuses into stainless steel and stainless steel diffuses into cobalt of tungsten carbide By doing so, an interdiffusion layer can be formed and strongly bonded.

  Therefore, in the present invention, the lower end surface 12a of the cemented carbide rod-like material 12 is finished to be a smooth surface (a flat surface or a mirror surface). In order to obtain a flat or mirror surface, in the embodiment, polishing is performed with No. 140 abrasive grains. When the lower end surface is polished with abrasive grains coarser than No. 140, the frictional heat is generated excessively and more time and distance are required, so that the thermal influence is large and microcracks are easily generated. In addition, if it is carried out in a short time, the formation of the interdiffusion layer is insufficient and the bonding force is reduced.

  When the stainless steel rod-like material 11 and the cemented carbide rod-like material 12 are connected to each other, the strength of the joint increases as the axial length (thickness) of the interdiffusion layer becomes longer (thick). Also, the residual stress is reduced. Conversely, if the interdiffusion layer is short or absent, the joint becomes weak. Therefore, the lower end surface 12a of the cemented carbide rod-like material 12 is made flat or mirror surface to facilitate the formation of the interdiffusion layer.

  In order to increase the length of the interdiffusion layer, brazing can be considered. In the case of brazing, the thickness of the interdiffusion layer is 5 to 40 μm. However, in the case of brazing, the length of the interdiffusion layer could not be controlled, and when the bending strength of 50 pieces was examined, the standard deviation was 9.9, which showed a large variation between products, resulting in stability. It will be lacking. The bending strength test method referred to here follows ISO 8325: 2004.

  On the other hand, in the case of the above friction connection, although the thickness of the interdiffusion layer is 1 to 5 μm, it can be controlled, and when 50 bending strengths are examined, the standard deviation varies as 5.2. Therefore, a stable bonding strength can be obtained.

  When the joining surface is polished at about 140 and the surface roughness (Rmax) is set to 0.8 to 5 μm, it becomes easy to form an interdiffusion layer when frictionally connected, and the joining becomes strong. Desirably, it is 0.8-1.5 micrometers. If the surface roughness (Rmax) is 0.8 μm or less, the polishing process takes too much time and the manufacturing cost increases, which is not desirable. When the surface roughness (Rmax) is 10 μm or more, the strength of the joint portion decreases.

  Here, in order to investigate the bending strength of the joint, a bending test was performed using the above method. When the surface roughness (Rmax) was 1.4 μm, the bending strength was 55 N on an average of 100 tests. When the surface roughness (Rmax) was 0.8 μm, the bending strength was 63 N on average in 100 tests, and it was found that the smoother the surface, the stronger the joint.

  On the other hand, the upper end surface 11a of the rod-shaped material 11 made of stainless steel may be finished with a surface roughness (Rmax) of 0.8 to 5.0 μm, but may be a rough surface that has been cut with a cutter. This is because stainless steel is softer and easier to melt than cemented carbide. Further, the upper end surface 11a of the rod-shaped material made of stainless steel and the lower end surface 12a of the rod-shaped material made of cemented carbide may not be flat. However, when the upper end surface 11a and the lower end surface 12a are overlapped, the entire shape needs to be overlapped.

  When the cemented carbide rod 12 and the stainless steel rod 11 are set in the state of FIG. 1, the rotating shaft 21 is rotated. At the same time, the clamp base 24 is pressed downward with a force f in FIG. 1, and the lower end surface 12 a of the cemented carbide rod 12 is pressed against the upper end surface 11 a of the stainless steel round bar 11. The contact surface becomes high temperature due to frictional heat, and eventually the upper end surface 11a of the stainless steel rod 11 and its vicinity are softened.

  FIG. 2 is a view showing a state in which a rod-shaped material 11 made of stainless steel and a rod-shaped material 12 made of cemented carbide are joined. When the vicinity of the upper end surface 11a of the stainless steel rod 11 is softened, the contact surface between the lower end surface 12a and the upper end surface 11a is covered with the stainless steel softened in a semi-molten state and is isolated from the surroundings. The rotation is stopped in this state, and the pressing force of the clamp base 24 is increased to the force F just before the end of the rotation or after the rotation is stopped. Then, the cemented carbide rod 12 and the stainless steel rod 11 are joined by the joint 13. Cobalt diffuses from the cemented carbide rod 12 to the stainless steel rod 11, and the stainless steel diffuses from the stainless steel rod 11 to the cemented carbide rod 12. 11b and 12b are formed to strengthen the bonding.

  As shown in FIG. 2, the joint portion 13 bulges outward and the stainless steel hangs slightly downward, and the joint portion 13 is sealed with semi-molten stainless steel and is in a low oxygen state. 11b and 12b are formed so as to expand above and below the joint portion 13.

  FIG. 3 is a view showing a state in which a cemented carbide rod-shaped material 12 and a stainless steel rod-shaped material 11 are joined. Thereafter, the carbide bar 16 having a carbide bar blade 15 at the tip of the stainless steel rod 11 as shown in FIG. 4 is completed by grinding the cemented carbide rod 12 into a predetermined shape. To do.

  The carbide bar 16 is used by gripping a portion of the stainless steel bar 11 with a chuck of a handpiece.

  In the above embodiment, the stainless steel rod 11 is rotated, but the cemented carbide rod 12 may be rotated. Although both may be rotated, in that case, if they are rotated in directions opposite to each other, the frictional force increases and the joining time can be shortened. In addition, the timing for increasing the pressing force may be after the rotation is completely stopped, or may be increased during the rotation, such as just before the end of the rotation.

It is a figure which shows an example of the form which implements the connection method of the cemented carbide alloy and stainless steel of this invention. It is a figure which shows the state which the stainless steel round bar and the cemented carbide round bar have joined. It is a figure which shows the state which the round bar of the cemented carbide and the round bar of stainless steel joined. It is a figure of a carbide bar.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Stainless steel rod-shaped material 11a Upper end surface 11b, 12b Mutual diffusion layer 12 Cemented carbide rod-shaped material 12a Lower end surface 13 Joint part 15 Blade part 16 Carbide bar 21 Rotating shaft 22 Chuck 23 Claw 24 Clamp base 25 Gripping part

Claims (5)

  A step of finishing one end face of a rod-shaped material made of cemented carbide obtained by sintering tungsten carbide powder with cobalt into a smooth surface, and an end surface finished to the smooth surface and one end surface of a stainless steel rod-shaped material are mutually connected. The step of rotating at least one of the cemented carbide rod or stainless steel rod while pressing, and when the end of the stainless steel rod is softened by the frictional heat generated by the rotation, A method of connecting the cemented carbide and the stainless steel, comprising the step of stopping the rotation and increasing the pressing force to join the rod-shaped material of stainless steel to the rod-shaped material of cemented carbide.   In the step of rotating the cemented carbide rods or stainless steel rods pressed against each other, both the cemented carbide rods and the stainless steel rods are rotated in opposite directions. A method of connecting the cemented carbide according to claim 1 and stainless steel.   2. The cemented carbide and stainless steel according to claim 1, wherein, in addition to the friction caused by the rotation, the end of the stainless steel rod is softened by energizing and heating the stainless steel rod. How to connect with.   4. The method of connecting a cemented carbide and a stainless steel according to claim 1, wherein the end surface of the cemented carbide has a surface roughness (Rmax) of 0.8 to 5.0 μm. 5. .   The method for connecting a cemented carbide and a stainless steel according to claim 4, wherein a surface roughness (Rmax) of an end face of the stainless steel is 0.8 to 5.0 µm.

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