JP2006124757A - Method for manufacturing endless metallic belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an endless metallic belt by which the endless metallic belt having high strength can be obtained by preventing the generation of nitrogen compound on the surface after nitriding-treatment, when the endless metallic belt manufactured with a maraging steel as a base steel plate and used for power transmitting belt, such as non-stage transmission, is manufactured. <P>SOLUTION: After applying a solution-treatment to a ring-like member 12, with which the maraging steel is used as the base steel plate 11, the surface of the ring-like member 13 is polished or ground to about 0.5-3μm thickness with e.g. barrel-polishing, and an element condensed layer and an oxide layer formed at solution-treating time, are mechanically removed. In this way, in a nitriding-treatment thereafter, it can be avoided to generate the nitrogen compound on the front and the back surfaces and the endless metallic belt having high strength can be obtained. Desirably, the solution-treatment is applied by using a high frequency induction heating under inert gas atmosphere. In this way, the thickness of the surface layer to be removed can be thinned and the manufacturing cost can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an endless metal belt, and although not limited thereto, the present invention relates to an endless metal belt made of maraging steel used for a power transmission belt of a continuously variable transmission or the like as a raw steel plate.

  Since endless metal belts used for power transmission belts such as continuously variable transmissions are subjected to harsh usage environments, high strength steel such as maraging steel with sufficient toughness and fatigue strength is used as the material steel. . Maraging steel is a steel made by ultra-low carbon martensitic steel that has been toughened by aging precipitation after solution heat treatment. Alloy elements such as Co, Mo, Ti, and Al are contained in the base elements Fe and Ni. It is added in a large amount and has an excellent balance between strength and toughness as compared with other high-strength steels.

  Patent Document 1, Patent Document 2, and the like describe a method for producing an endless metal belt using maraging steel, and usually cuts a steel sheet of a desired size from a maraging steel sheet roll as a raw steel sheet, After the end portions are welded to form a ring shape, solution treatment is performed to homogenize the alloy composition of the welded portion, and further, cutting to a predetermined width and rolling. In order to remove the processing stress due to rolling or the like, a solution treatment is performed again, and then a nitriding treatment is performed to further improve the strength.

  In nitriding treatment, elements having strong affinity with nitrogen (Ti, Al, Co, Mo, etc.) are combined with nitrogen, and the nitrogen compounds (TiN, AlN, MON, etc.) are ultrafinely precipitated in the base element. This is a process for improving the strength by generating lattice strain. However, if Ti and Al are oxidized on the surface of the non-processed material before nitriding, the element that binds to nitrogen diffusing from the surface to the inside is scarce, while the base metal contains Since a large amount of nitrogen cannot be dissolved, when the nitrogen concentration exceeds a certain level, a nitride with a base element is formed on the surface. It is known that this nitride is brittle, and when it is formed, the strength is extremely reduced. FIG. 4 shows a case where an endless metal ring (steel plate: maraging steel) manufactured by a conventional method is polished by 0.5 μm from the surface after solution treatment (curve A) and polished to 3 μm (curve B). It is shown that a nitrogen compound (for example, Fe3N) is likely to be formed on the surface after nitriding treatment when the polishing amount after solution treatment is small.

  In the manufacture of the endless metal belt described above, oxides such as Ti and Al on the surface of maraging steel, which is an object to be processed, are generated during the solution treatment. For this purpose, it has been proposed to remove the oxide by pickling before the nitriding treatment, or to perform the solution treatment under a specific nitrogen atmosphere or in a vacuum furnace. Further, Patent Document 1 describes that the solution treatment immediately before the nitriding treatment is performed in a humidified atmosphere (mixed gas of nitrogen and hydrogen) having a dew point of 0 to 15 ° C. By performing such treatment, it is possible to suppress the formation of a nitride with a base element (Fe, Ni) on the surface, and to obtain a high-strength endless metal belt.

JP 2004-162134 A JP 2004-141877 A

  In the production of an endless metal belt, a treatment method for pickling oxides such as Ti and Al generated by solution treatment requires a treatment facility for that purpose and is not easy to remove to a uniform depth. When solution treatment is performed in a vacuum furnace, oxide generation can be suppressed to a considerable extent, but the vacuum furnace is expensive and it is not easy to completely eliminate air, and oxide generation is completely suppressed. It is not possible. Further, as the vacuum is increased, the concentration of Ti and Al on the surface becomes more intense, and this element-enriched layer also becomes a factor that inhibits nitriding. Even if the solution treatment is performed under a specific nitrogen atmosphere, oxide formation can be suppressed to a considerable extent, but there is a limit as long as it is a chemical treatment. For this reason, in the production of an endless metal belt using maraging steel or the like as the raw steel plate, there is still a problem regarding performing nitriding treatment in a state where there is no nitride with the base element on the surface.

  The present invention has been made in view of the circumstances as described above, and a nitrogen compound is formed on the surface after nitriding by completely removing the oxide layer or the element concentrated layer generated by the solution treatment. An object of the present invention is to provide a method for producing an endless metal belt that can eliminate the problem and obtain an endless metal belt having high strength.

  The method of manufacturing an endless metal belt according to the present invention includes a step of welding end portions of a raw steel plate to form a ring, a step of solution-treating the ring-shaped member, and a nitriding treatment of the ring-shaped member after solution treatment An element-enriched layer formed by a solution treatment by polishing or grinding the surface of a ring-shaped member between a solution treatment and a nitriding treatment. The method further includes a step of removing the physical layer.

  Basically, in the present invention, it is inevitable that the element-enriched layer and the oxide layer are chemically formed by the solution treatment, and the formed element-enriched layer and the oxide are formed before the nitriding treatment. The layer is removed from the surface of the ring-shaped member physically (mechanically), that is, by polishing or grinding. According to the present invention, by adjusting the removal depth from the surface, it is possible to completely remove the formed element concentrated layer and oxide layer, and as a result, a nitrogen compound is formed on the surface after nitriding. Can be prevented, and an endless metal belt having high strength can be obtained.

  In the method for producing an endless metal belt according to the present invention, there is no limitation on a specific method for the solution treatment, and a solution treatment method employed in a conventional method for producing an endless metal belt is arbitrarily employed. be able to. However, it is possible to completely remove the formed element concentrated layer and oxide layer without performing solution treatment in a vacuum furnace or solution treatment in a specific nitrogen atmosphere. Low cost and simplification can be achieved.

  If the element enriched layer and the oxide layer formed by the solution treatment are thin, the depth to be removed by polishing or grinding becomes smaller, and the removal work is facilitated. Therefore, the solution treatment is performed using high-frequency induction heating in an inert gas (eg, nitrogen, argon, etc.) atmosphere, or the solution treatment is performed using a tunnel-type heating furnace equipped with a mesh belt. Is a desirable embodiment. In the former case, it is possible to heat in a very short time compared to atmospheric heating or vacuum heat treatment, so that solution treatment can be performed with the minimum necessary holding time, and element concentration and oxidation on the surface are extremely low. Can be small. In the latter case, heating of the base tray can be omitted compared to the normal case where heat treatment is performed by arranging the objects to be processed on a heavy base tray, so that the temperature of the object to be processed increases. Thus, solution treatment can be performed in a short time. Therefore, the element concentration and oxidation on the surface can be extremely reduced.

  In our experiments, when the material steel plate is maraging steel, the solution treatment is performed by high-frequency induction heating or by using a tunnel-type heating furnace equipped with a mesh belt to remove the film thickness to be removed. Can be made extremely thin. When a normal solution treatment is performed, the removal thickness from the surface is set to 1.5 μm or more, more preferably about 3 μm or more, so that a nitrogen compound is not generated on the surface after nitriding. An endless metal belt with high strength can be obtained, but a high strength belt with a removal thickness of 0.5 to 1 mm is obtained by high-frequency induction heating or solution treatment in a short time in a tunnel-type heating furnace. I was able to.

  According to the present invention, a strong endless metal belt suitable for use in a power transmission belt such as a continuously variable transmission can be manufactured.

  Hereinafter, an endless metal belt manufacturing method according to the present invention will be described based on one embodiment. FIG. 1 shows the main steps until an endless metal belt is manufactured according to the present invention. In this example, the material is maraging steel, and general maraging steel is Ni: 17-19%, Co: 7-13%, Mo: 4-5%, Ti: 0.3-1%, Al: 0.05 to 0.15%, C: 0.03% or less, the rest: Fe.

  A steel plate 11 having a required size is cut from a roll 10 of a maraging steel plate (FIG. 1a), and ends thereof are welded to form a cylindrical drum 12 (FIG. 1b). The drum 12 is subjected to a primary solution treatment in order to homogenize the alloy composition of the welded portion (FIG. 1c), and the drum 11 after the solution treatment is cut into a predetermined width to form the ring-shaped member 13 and the drum 12. (FIG. 1d). For the reasons described above, an oxide layer such as Ti or Al and an element concentrated layer (hereinafter simply referred to as an oxide layer) are formed on the surface (front and back surfaces) of the drum 12 during the solution treatment. Moreover, although it is trace amount, the diffused layer of nitrogen may be formed. FIG. 2 shows a surface state when a drum 12 made of a maraging steel plate is subjected to a solution treatment under a nitrogen atmosphere, and a diffusion layer of nitrogen (N) to a depth of about 3 μm together with an oxide layer of Ti and Al. It can be seen that is formed.

  In the manufacturing method according to the present invention, a step of polishing or grinding the surface of the drum 12 or the ring-shaped member 13 cut to a predetermined width and removing it to a predetermined depth is performed. In the example shown in FIG. 1, necessary surface removal is performed by barrel polishing (FIG. 1e). The barrel polishing itself is a conventional method, and detailed description thereof is omitted. A method of grinding the surface using a rod-shaped grindstone or the like instead of barrel polishing can also be employed.

  If necessary, the ring-shaped member 13 whose surface (front and back surfaces) is polished or ground to a degree slightly exceeding 1.5 μm to 3 μm to remove the surface layer is subjected to rolling (FIG. 1 f), rolling, etc. In order to remove the processing stress due to, secondary solution treatment is performed (FIG. 1g). Also in the secondary solution treatment, if necessary, a surface removal step by polishing or grinding is performed. As described above, by removing the front surface (front and back surfaces) as an example at a depth of 1.5 μm to 3 μm, an oxide layer or 3 μm formed by solution treatment as shown in FIG. 2 as an example. The diffusion layer of nitrogen (N) is almost completely removed to a certain depth. Of course, when the oxide layer or the like is formed deeper, the removal thickness is made thicker.

  Thereafter, the ring-shaped member 13 that has been subjected to processing such as super-adjustment (FIG. 1h) is subjected to aging and nitriding treatment (FIG. 1i) in the same manner as in the prior art to complete an endless metal ring. As described above, since no oxide layer is present on the surface of the ring-shaped member 13 when the nitriding treatment is performed, generation of nitrogen compounds on the surface after nitriding can be avoided, which is high. An endless metal belt having strength can be obtained.

  FIG. 3 shows one embodiment of the solution treatment preferably used in the method of the present invention. In FIG. 3, 12 is a cylindrical drum formed by welding end portions of the maraging steel plate 11, and the cylindrical drum 12 is placed in a chamber (not shown) in an inert gas atmosphere such as nitrogen, for example. It arrange | positions and the upper and lower ends are fixed with the fixing tools 21 and 22 which rotationally drive. The annular high-frequency coil 23 moves vertically with respect to the rotating cylindrical drum 12, and the cylindrical drum 12 is heated to, for example, 840 ° C. to 880 ° C. by high-frequency induction heating. After heating, for example, the same gas as the atmosphere gas is cooled by means such as spraying from a nozzle at a high pressure, and after being reduced to about 200 ° C. or lower, the gas is taken out from the inert gas atmosphere to the atmosphere. It is desirable to put in and out the atmosphere by a method such as evacuating the chamber and replacing with an inert gas.

  By this method, the thickness of the oxide layer of Ti and Al on the surface of the cylindrical drum 12 subjected to the solution treatment should be much thinner than that performed by normal atmospheric heat treatment, and should be 0.5 μm or less. it can. Further, even when the treatment is performed in a nitrogen atmosphere as described above, the above-described nitrogen diffusion layer can be 1 μm or less. Therefore, the margin of the surface in the subsequent process (thickness from the surface to be removed by polishing or grinding) can be reduced, and the manufacturing cost can be greatly reduced.

[Example]
As a material, maraging steel (Ni: 17 to 19%, Co: 7-13%, Mo: 4 to 5%, Ti: 0.3 to 1%, Al: 0.05 to 0.15%, C: 0.03% or less, the remainder: Fe) was used. The primary solution treatment of the drum 12 described in FIG. 1c was performed by holding at 880 ° C. for 10 minutes in a nitrogen + hydrogen (5 to 10%) atmosphere. A Ti oxide layer having a thickness of about 1 μm and an Al oxide layer having a thickness of about 0.5 μm were formed on the surface. Further, a nitrogen diffusion layer was formed to a depth of about 3 μm from the surface though it was a small amount.

  The drum 12 after the solution treatment is cut into a ring-shaped member 13 and barrel burrs are used to remove end surface burrs at the time of cutting and apply R to the end surface. Removed by thickness. (2) In order to remove the nitrogen diffusion layer, it was removed to a degree exceeding 3 μm. After rolling them, the secondary solution treatment was performed again. The ring-shaped members (1) and (2) were subjected to nitriding treatment by a usual method. There was no formation of nitrogen compounds on the surface after nitriding, and a high-strength endless metal belt was obtained.

[Comparative example]
(1) Except for the fact that the end surface burrs were removed by barrel polishing and the end surface was just rounded, and the front and back surfaces were not actively ground. An endless metal belt was produced in the same manner. Further, (2) end face burrs at the time of cutting were removed by barrel polishing or a grindstone, and endless metal belts were manufactured in the same manner as in the examples except that the front and back surfaces were not ground. When these were subjected to a strength test in the same manner as in the Examples, the fatigue test life was 1/10 or less, and sufficient strength was not obtained.

The figure which shows the main processes until an endless metal belt is manufactured by this invention. The graph which shows the surface state when solution-treating the drum which consists of a maraging steel plate in nitrogen atmosphere. The figure explaining the aspect which carries out solution treatment using the high frequency coil used preferably in the method of this invention. The graph which shows an example when the endless metal ring (material steel plate: maraging steel) manufactured by the conventional method is grind | polished from the surface by 0.5 micrometer (curve A), and when grind | polished to 3 micrometers (curve B).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Maraging steel plate roll, 11 ... Steel plate of required size, 12 ... Cylindrical drum obtained by welding end part, 13 ... Obtained by cutting the drum after solution treatment to predetermined width Ring-shaped member, 21, 22 ... Fixing jig, 23 ... Annular high-frequency coil

Claims (4)

  Manufacture of an endless metal belt having at least a step of welding end portions of a raw steel plate into a ring shape, a step of solution-treating the ring-shaped member, and a step of nitriding the ring-shaped member after solution treatment The method further includes a step of polishing or grinding the surface of the ring-shaped member between the solution treatment and the nitriding treatment to remove the element concentrated layer and the oxide layer formed by the solution treatment. A method for producing an endless metal belt, which is characterized.   The method for producing an endless metal belt according to claim 1, wherein the solution treatment is performed using high-frequency induction heating in an inert gas atmosphere.   The method for producing an endless metal belt according to claim 1, wherein the solution treatment is performed using a tunnel-type heating furnace provided with a mesh belt.   The method for producing an endless metal belt according to claim 2 or 3, wherein the material steel plate is maraging steel and the thickness for removing the surface is 1.5 µm or more, more preferably 3 µm or more.

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