JP4488840B2 - Method for forming hard nitride layer, and roller chain and silent chain obtained by this method - Google Patents

Description

  The present invention relates to a method for forming a hard nitride layer, and a roller chain and a silent chain obtained by this method, and in particular, prevents chain elongation due to wear caused by components of various chains, thereby making it durable. The present invention relates to a manufacturing technology for various chains with improved performance.

  Various chains are used in automobiles and industrial machines. Examples of these chains include a camshaft drive chain, an oil pump drive chain, a balancer shaft drive chain, and the like, and technical developments related to various characteristic improvements have been made.

  Among various improvements related to the properties of the chain, many techniques for improving durability by suppressing wear between components have been reported. For example, in order to realize excellent wear resistance even under high surface pressure, a technique for shaving a pin hole of a link plate is disclosed for a silent chain (see Patent Document 1). Also, for the same purpose, a technique is disclosed in which a carbide layer mainly composed of vanadium carbide and containing a small amount of chromium carbide is formed on the outermost surface portion of steel which is a base material of a chain connecting pin (patent) Reference 2). In addition, the pin hole of the joint row is formed and connected so that the inner surface of the pin hole is shaved to improve the surface roughness, surface accuracy, and perpendicularity to the plate surface. A silent chain is disclosed in which a hardened layer made of at least one metal carbide of Cr, Ti, V, and Nb having a small affinity with the inner surface of the pin hole is formed on the surface of the pin (see Patent Document 3). In addition, a silent chain is disclosed in which shaving is applied to the meshing surface and the back surface over a range of 70% or more of the plate thickness to improve the distance accuracy between the meshing surface and the back surface (see Patent Document 4). ).

JP 2002-195355 A (abstract) JP 2002-195356 A (Abstract) Japanese Patent No. 3199225 (Claims) Japanese Patent No. 3199241 (Claims)

  In recent years, in the manufacturing process of various chains, among such conventional techniques, metal carbides such as VC and CrC, particularly as shown in Patent Document 2, with carburizing quenching performed on the chain connecting pins. A so-called powder pack method is often used for coating the coating. However, when the chain obtained only by the powder pack method is applied to an automobile or the like equipped with a diesel engine having severe use environment conditions, sufficient wear resistance of the chain cannot be obtained due to the flaw or the like. For this reason, there has been a demand for the development of a chain with more wear resistance. Incidentally, the surface hardness of the connecting pin obtained by the powder pack method is about 1500, 2200, 2500, 2700 (HV), respectively, when the coating material is CrC, VC, NbC, TiC. Then, under the severe environment as described above, the current situation is that sufficient durability of the chain cannot be realized.

  Further, as described above, the chain connecting pin is generally manufactured by a powder pack method. The connecting pin coated by this method uses a coating material (NbC, TiC) that is not yet in mass production, even when a coating material (CrC, VC) that can already be mass-produced is used. Even in this case, there is no great difference in hardness as described above. For this reason, no matter which coating material is used, there is no great difference in the results of the durability test, and it is not preferable to use these coating materials by the conventional method.

  Therefore, an attempt has been made to develop a technique for coating carbides other than Cr, V, Nb, and Ti on the connecting pin material that has been conventionally used. However, for example, when the surface of the connecting pin material is coated with a carbide of W or Ta, a significant improvement in surface hardness cannot be expected. Therefore, in recent years, development of means for coating the connecting pin material with a layer harder than the carbide layer has been particularly demanded due to such circumstances.

  The present invention has been made in view of the above circumstances, and even when applied to an automobile or the like equipped with a diesel engine having severe use environment conditions, the constituent members of various chains exhibit sufficient wear resistance. It is an object of the present invention to provide a method for forming a hard nitride layer, and a roller chain and a silent chain obtained by this method.

  In consideration of the above circumstances, the present inventors have conducted extensive research on a suitable method for coating the hard layer on the constituent members of the chain, centering on the connecting pins, in order to produce various highly durable chains. As a result, the material forged into a predetermined shape is sequentially subjected to nitriding treatment and diffusion penetration treatment by the powder pack method, thereby forming a hard nitride layer on the material surface as compared with the conventional carbide layer. The knowledge that it can be obtained. The present invention has been made in view of such knowledge.

In forming a hard nitride on the surface of a forged material, the present inventors perform a nitriding treatment on the material, and then perform a diffusion permeation treatment, quenching, and tempering sequentially to form a hard nitride layer. The various chains using the connecting pin provided with the nitride layer were studied. For chain components that have had the same hardness in the past, for example, roller chains (silent chains), there is a difference in hardness between the surface layers of the bush (link plate) and the connecting pin, thereby increasing the durability of the chain. The knowledge that it can improve remarkably was acquired. That is, when the two members contact and wear, the surface layer of the relatively uneven member is made relatively soft, while the surface layer of the relatively uneven member is made relatively hard, A relatively large number of members are polished, and the shapes of the two are gradually adapted to suppress wear after a certain period of use. In the case of a roller chain (silent chain), the inner surface of the bush (link plate) is less uneven than the inner surface of the bush (link plate). On the other hand, by using a relatively hard nitride layer on the surface of the connecting pin, sufficient wear resistance can be achieved even when applied to automobiles equipped with diesel engines with harsh environmental conditions. Thus, durability can be improved. The inventions related to the various chains shown below have been made in view of such knowledge.

That is, the roller chain of the present invention includes a pair of inner plates, a bush fixed to one of the pair of inner plates and having pin holes, and a pair of outer plates disposed on both outer sides of the pair of inner plates. A plurality of units formed by connecting pins fixed to one of the pair of outer plates and rotatably inserted into the pin holes of the bush, and at least the surface of the connecting pins has a hard nitride This hard nitride layer is a nitride layer that is formed by performing nitriding treatment on a forged material, then sequentially performing diffusion penetration treatment, quenching, and tempering, and containing Ti. It is characterized by that.

The silent chain of the present invention is fixed to one of the plurality of link plates having pin holes, a pair of guide plates disposed on both outer sides of the plurality of link plates, and the plurality of guide plates. A plurality of units formed by connecting pins that are rotatably inserted into the pin holes of the link plate are connected to each other, and a hard nitride layer is provided at least on the surface of the connecting pins. The nitrided layer is formed by performing a nitriding treatment on the forged material, then sequentially performing a diffusion permeation treatment, quenching, and tempering, and is a nitride layer containing Ti .

For the roller chain and silent chain of the present invention, a hard layer of nitride or carbide can be appropriately formed on the inner surface of the bush or link plate in addition to the surface of the connecting pin. At that time, in order to make the member coated on the surface of the connecting pin harder than the member coated on the inner surface of the bush (link plate), a difference in hardness is provided in each surface layer of the connecting pin and the bush (link plate). is required.

  As described above, according to the present invention, at least the surface of the connecting pin among the constituent members of the various chains is subjected to nitriding treatment, and then diffusion diffusion treatment, quenching, and tempering are sequentially performed, so that the roller About a chain (silent chain), the hardness difference is provided in each surface layer of a bush (link plate) and a connection pin, and, thereby, the durability of a chain can be improved remarkably. In addition, when a hard nitride is formed on the surface of the connecting pin as in the present invention, sufficient wear resistance can be obtained even when applied to a vehicle or the like equipped with a diesel engine having severe use environment conditions. Can be realized. Incidentally, according to the present invention, for example, the hardness of the TiN layer formed on the surface of the connecting pin is 3800 (HV), which is extremely superior to the hardness of the conventional various carbide layers described above.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
First, the results of investigating the hardness in the vicinity of the surface layer of the connecting pin obtained by the method for forming a hard nitride layer of the present invention are shown below.
A high carbon chrome bearing steel SUJ2 was prepared as a material, and forged with a connecting pin shape of a roller chain by forging it. Next, the forged product was subjected to gas soft nitriding treatment at 600 ° C. for 90 minutes to form Fe _2-3 N (white layer) on the surface of the forged product. When the depth of the white layer was measured by a cross-sectional photograph taken with a microscope, it was about 24 μm as shown in FIG.

Next, a forging product having a white layer on the surface as described above was subjected to diffusion penetration treatment by a powder pack method, quenching, and tempering sequentially to obtain a connecting pin having TiN on the surface. Here, the diffusion permeation treatment is performed by using 50% by mass of Fe—Ti, 0.5% by mass of Cr, 49.5% by mass of Al ₂ O ₃ , and the above three components (Fe—Ti, Cr and relative to the total weight of al ₂ O _3), was carried out under the conditions of 980 ° C. × 10 hours using a of _NH 4 Cl 0.5% by weight. The quenching temperature was 860 ° C. and the tempering temperature was 280 ° C.

  FIG. 2 is a microscope cross-sectional structure photograph showing a connecting pin obtained by sequentially performing nitriding treatment, diffusion penetration treatment, quenching, and tempering on a forged product. As shown in the figure, a hard layer of about 20 μm is formed on the surface layer of the connecting pin. FIG. 3 is a graph showing the relationship between the hardness and the distance from the surface to the depth direction for the connecting pin shown in FIG. 2, and FIG. 4 shows the relationship between each element of the connecting pin by EPMA analysis. It is a graph which shows the relationship between content and the distance from the surface to a depth direction. 5 is a microscope cross-sectional structure photograph showing locally the surface layer portion of the same connecting pin as in FIG. 2, and FIG. 4 is a result of investigation along the dotted line portion (analysis position) in FIG.

  From the result of the hardness distribution in FIG. 3 and the result of the EPMA analysis in FIG. 4, the outermost layer portion of the connecting pin is coated with an extremely hard TiN layer. As is apparent from FIGS. It was confirmed that the layer was present in the depth direction from the surface to about 17 to 20 μm.

  Next, the durability improvement based on suppression of chain | stretch elongation at the time of using the various connection pins obtained by the formation method of the hard nitride layer of this invention is demonstrated. That is, in recent years, there is a tendency for the engine to be mounted on the vehicle body and the engine itself to be lighter and more compact. Under such circumstances, the contact pressure between the connecting pin and the bush (or link plate) is increased, and the wear on the bush (or link plate) side made of an iron-based member having a low hardness and melting point is increased among the constituent members. . Below, the optimal combination pattern which suppresses abrasion with a connection pin and a bush about a roller chain is proposed. In this embodiment, no hard layer coating is applied to the surface layer of the bush.

  A high carbon chrome bearing steel SUJ2 was prepared as a raw material, and forged to obtain a roller chain connecting pin-shaped forged product and a bush-shaped forged product. Next, among these forged products, only the connecting pin-shaped forged products are formed under the same conditions as in Example 1, while TiN is formed on the outermost layer portion of the forged product, while all the steps except the nitriding treatment of Example 1 are performed. That is, diffusion penetration treatment, quenching, and tempering were performed to form CrC, VC, NbC, and TiC on the outermost layer portion of the forged product. Furthermore, a roller chain was manufactured by combining these connecting pins and the bush.

  About each roller chain obtained in this way, the elongation accompanying the driving time was measured. In the measurement, the chain was meshed around a sprocket with 18 teeth (8000 rpm) and a sprocket with 36 teeth (4000 rpm), the chain tension was set to 1860 N, and contamination oil was used as an oiling agent. Contaminant oil contains 16% carbon black, 2% ferritic oxide, 4% PV resin, and 78% straight mineral oil by a specified amount. Mixed. The reason why the contamination oil is used is to demonstrate that the chain of the present invention exhibits excellent durability even when a highly deteriorated lubricating oil having an extremely deteriorated degree of oxidation is used. In addition, the amount of oil required for actual chain driving was 1.0 L / min. The result is shown in FIG.

  As is clear from FIG. 6, the use of a connecting pin coated with a TiN layer shows better durability than the use of a connecting pin coated with any carbide layer in a forged product. I understand. Therefore, the effect regarding durability was demonstrated about the roller chain of this invention.

  As described above, according to the present invention, among the various chain components, at least the surface of the connecting pin is subjected to nitriding treatment, and diffusion diffusion treatment, quenching, and tempering are sequentially performed to form a roller chain (silent In the chain), a difference in hardness is provided between the surface layers of the bush (link plate) and the connecting pin, whereby the durability of the chain can be remarkably improved. Therefore, the present invention is useful for manufacturing various chains that require improved durability as the peripheral members become more complex and sophisticated in the future.

It is a cross-sectional structure | tissue photograph of the forging product of the connection pin shape which gave the nitriding process. It is a cross-sectional structure | tissue photograph about the connecting pin for roller chains of this invention. It is a graph which shows the relationship between the hardness and the distance from the surface to the depth direction about the connecting pin for roller chains of this invention. It is a graph which shows the relationship between content of each element and the distance to the depth direction from the surface about the connecting pin for roller chains of this invention. It is a cross-sectional structure | tissue photograph which shows the measurement location at the time of measuring content of each element about the connecting pin for roller chains of this invention. It is a graph which shows the relationship between chain elongation and durable time about each roller chain obtained using the connection pin which gave various coatings.

Claims (2)

A pair of inner plates, a bush fixed to one of the pair of inner plates and having pin holes, a pair of outer plates disposed on both outer sides of the pair of inner plates, and one of the pair of outer plates In a roller chain formed by connecting a plurality of units formed by connecting pins that are fixed and rotatably inserted into the pin holes of the bush,
A hard nitride layer is provided at least on the surface of the connecting pin, and the hard nitride layer is formed by performing nitriding treatment on a forged material, and then sequentially performing diffusion penetration treatment, quenching, and tempering. A roller chain characterized by being a nitride layer containing Ti . A plurality of link plates having pin holes, a pair of guide plates disposed on both outer sides of the plurality of link plates, and fixed to one of the pair of guide plates, and freely rotatable in the pin holes of the plurality of link plates In a silent chain formed by connecting a plurality of units formed by connecting pins inserted into
A hard nitride layer is provided at least on the surface of the connecting pin, and the hard nitride layer is formed by performing nitriding treatment on a forged material, and then sequentially performing diffusion penetration treatment, quenching, and tempering. And the silent chain characterized by being a nitride layer containing Ti .

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