JP2016044340A - Endless metal belt production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an endless metal belt production method by which such a problem that a surface of it becomes too hard can be suppressed.SOLUTION: The endless metal belt production method comprises: a solution treatment step of applying solution treatment to a ring-shaped member obtained by a welding step; a removal step of polishing or grinding a surface of the ring-shaped member to which the solution treatment has been applied, thereby removing a chemical element concentrated layer and oxide layer formed during the solution treatment; and a nitration step of applying nitration to the ring-shaped member which has been subjected to the removal step. In the solution treatment step, a Ti-depletion layer having Ti concentration lower than that of the ring-shaped member before being subjected to the solution treatment, is formed. To the surface of the ring-shaped member subjected to the removal step, the Ti-depletion layer is exposed by removing the chemical element concentrated layer and oxide layer.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a method of manufacturing an endless metal belt that can be used for a power transmission belt or the like.

  The endless metal belt is provided in a continuously variable transmission or the like and can function as a power transmission belt. Endless metal belts are typically made from high strength steels with sufficient toughness and fatigue strength, such as maraging steels. The manufacturing method is as follows, for example. First, one steel plate is cut out from a steel plate roll, and both ends of the steel plate are welded to form a ring shape. Thereafter, a solution treatment is performed. After cutting and rolling, solution treatment is performed again. Thereafter, nitriding is performed.

  High-strength steel such as maraging steel contains elements (Ti, Al, etc.) having a strong affinity for nitrogen. During the nitriding treatment, these elements are combined with nitrogen. Nitrogen compounds (TiN, AlN, etc.) are precipitated very finely in the base element, thereby forming lattice strain and improving the strength of the object to be processed (endless metal belt).

  Here, when the solution treatment is performed, a part of Ti, Al, etc. present on the surface of the object to be processed is oxidized. It is assumed that nitriding is performed in a state where most of Ti and Al are oxidized. In this case, during nitriding (when nitrogen diffuses inward from the surface of the object to be processed), the number of elements that can be combined with nitrogen is reduced, and nitrogen is less likely to be dissolved in the base metal. When nitrogen diffuses, nitrides composed of nitrogen and base elements are also easily formed on the surface of the object to be processed. This nitride can cause a reduction in the strength of the workpiece.

  The manufacturing method of an endless metal belt disclosed in Japanese Patent Laid-Open No. 2006-124757 (Patent Document 1) includes a step of removing the element concentrated layer and the oxide layer formed during the solution treatment. . According to the publication, it is possible to completely remove the element concentrated layer and the oxide layer through the removal step, and as a result, the formation of nitride on the surface of the object to be processed is prevented after nitriding. It states that an endless metal belt with high strength can be obtained.

JP 2006-124757 A

  As described above, during the solution treatment, a part of Ti, Al, etc. present on the surface of the object to be processed is oxidized. Through the solution treatment, a Ti concentrated layer (element concentrated layer) and an oxide layer are formed on the surface of the object to be processed. At this time, a Ti-deficient layer is also formed as much as Ti is concentrated. The Ti-deficient layer is a layer having a Ti concentration lower than the Ti concentration of the object to be processed before the solution treatment is performed. The Ti deficient layer is formed at a deeper position than the Ti concentrated layer.

  The manufacturing method of an endless metal belt disclosed in Japanese Patent Laid-Open No. 2006-124757 (Patent Document 1) states that the element concentrated layer and the oxide layer formed during the solution treatment are completely removed. The publication does not specifically mention the Ti-deficient layer. If the Ti-deficient layer generated during the solution treatment is too small, or if the entire Ti-deficient layer is removed in the removal process and then nitriding is performed, a large amount of nitrogen and Ti are bonded. As a result, a nitride layer that is harder than necessary may be generated. When a hard nitrided layer is formed, the surface of the endless metal belt becomes too hard, and as a result, the endless metal belt may become brittle. In addition, an excessive compressive residual stress is applied to the surface, and the internal residual stress becomes larger on the tension side, and fatigue failure is likely to occur from the inside.

  An object of this invention is to provide the manufacturing method of the endless metal belt which can suppress that the surface becomes hard too much and can suppress that an internal residual stress becomes large too much to a tension | pulling side.

  The manufacturing method of the endless metal belt includes a welding process in which ends of steel plates bent into a cylindrical shape are welded together to form a ring-shaped member, and a solution for subjecting the ring-shaped member obtained by the welding process to a solution treatment And a removal step of removing the element concentrated layer and the oxide layer formed during the solution treatment by polishing or grinding the surface of the ring-shaped member subjected to the solution treatment. And a nitriding treatment step for nitriding the ring-shaped member that has undergone the removing step, and in the solution treatment step, the ring-shaped member before the solution treatment is provided has A Ti-deficient layer having a Ti concentration lower than the Ti concentration is formed, and the Ti-deficient layer is removed by removing the element-enriched layer and the oxide layer on the surface of the ring-shaped member after the removal step. Layer is dew It is.

  According to said structure, Ti deficient layer formed in the case of solution treatment is exposed to the surface of a ring-shaped member through a removal process. Since the presence of the Ti-deficient layer can suppress a large amount of binding of nitrogen and Ti during nitriding treatment, the surface of the endless metal belt is hardly hardened more than necessary. There is little possibility of becoming brittle, and the surface is not nitrided more than necessary, so that the tensile residual stress generated inside can be reduced.

It is a perspective view which shows the preparation process of the manufacturing method of the endless metal belt in embodiment. It is a perspective view which shows the welding process of the manufacturing method of the endless metal belt in embodiment. It is a perspective view which shows the solution treatment process (primary solution treatment) of the manufacturing method of the endless metal belt in embodiment. It is a schematic diagram which shows the solution treatment process (primary solution treatment) of the manufacturing method of the endless metal belt in embodiment. It is a graph which shows Ti concentration distribution of the ring-shaped member obtained by the solution treatment performed on specific process conditions. It is a perspective view which shows the cutting process of the manufacturing method of the endless metal belt in embodiment. It is a perspective view which shows the rolling process of the manufacturing method of the endless metal belt in embodiment. It is a perspective view which shows the circumference adjustment process of the manufacturing method of the endless metal belt in embodiment. It is a graph which shows distribution of the nitrogen concentration after the nitriding process regarding an Example and a comparative example. It is a graph which shows distribution of the residual stress after the nitriding process regarding an Example and a comparative example.

  Hereinafter, a method for manufacturing an endless metal belt in the embodiment will be described with reference to FIGS. In the following description, the same parts and corresponding parts are denoted by the same reference numerals, and redundant description may not be repeated. FIGS. 1-8 has shown the main processes of the manufacturing method of an endless metal belt.

  With reference to FIG. 1, first, a roll 10 made of a maraging steel plate is prepared. The material of the roll 10 is maraging steel, and its composition is, for example, Ni: 17-19%, Co: 7-13%, Mo: 4-5%, Ti: 0.3-1%, Al: 0.00. 05-0.15%, C: 0.03% or less, the rest: Fe. The steel plate 11 is cut from the roll 10. Next, referring to FIG. 2, the steel plate 11 is bent into a cylindrical shape (see the arrow in the figure). The ends of the steel plate 11 bent into a cylindrical shape are welded together to form the ring-shaped member 12 (welding process).

  Referring to FIGS. 3 and 4, ring-shaped members 12 obtained by the above welding process are arranged on tray 20 and arranged in reaction chamber 21 (FIG. 4). In the reaction chamber 21, the ring-shaped member 12 is subjected to a primary solution treatment (solution treatment step). The processing temperature is set to about 820 ° C to 900 ° C. The treatment atmosphere may be set to a reduced pressure (vacuum) or an atmosphere containing an inert gas such as nitrogen as a main component.

  In the reaction chamber 21, an element having a strong affinity for nitrogen (oxygen) such as Ti, Al, and Cr is concentrated on the surface of the ring-shaped member 12 (an element concentrated layer is formed by oxidation). If the oxygen partial pressure is too high, oxygen diffuses into the metal and Ti, Al, and Cr are difficult to concentrate on the surface. Therefore, the treatment atmosphere in the reaction chamber 21 is such that Ti, Al, and Cr are ring-shaped members 12. An appropriate oxygen partial pressure is set so as to concentrate on the surface layer. In order to remove the element enriched layer (oxide layer of Ti, Al, Cr, etc.) in a removal process performed later, the element enriched layer formed in this solution treatment process has a thickness of about 2 μm or less. It is desirable to have.

  With reference to FIG. 4 and FIG. 5, an example regarding the process temperature and process atmosphere in the reaction chamber 21 in a solution treatment process is demonstrated. The atmosphere in the reaction chamber 21 may be 100% nitrogen, but in that case, a small amount of oxygen may be introduced in order to keep the quality constant. On the other hand, if a dew point is controlled by introducing a small amount (less than 3%) of hydrogen and introducing wet nitrogen (for example, a dew point of −40 ° C. or less in which liquid nitrogen is vaporized), Quality can be controlled to a certain level.

  When the processing temperature in the reaction chamber 21 is set to 880 ° C., the processing time is set to 60 minutes, the processing atmosphere is set to 98% nitrogen and 2% hydrogen, and the dew point is set to −20 ° C. A Ti concentration distribution as shown in FIG. 5 is formed. A line CA in FIG. 5 indicates the Ti concentration of the workpiece before the solution treatment is performed.

  As shown in FIG. 5, in the ring-shaped member 12 that has undergone the solution treatment, Ti is concentrated in the vicinity of the surface layer on both the front surface and the back surface, and the Ti concentration sharply decreases in a portion slightly deeper than that. (FIG. 5 shows only the Ti concentration distribution on the front surface side and does not describe the back surface side). A Ti-deficient layer is formed in the vicinity of a depth of about 2.5 μm (the depth indicated by the line DA), and the Ti concentration of the Ti-deficient layer decreases between the depth DA and the depth of about 5 μm. It is substantially constant between about 5 μm and 10 μm, and gradually increases between about 10 μm and 20 μm in depth. Although details will be described later, when the ring-shaped member 12 having a Ti concentration distribution as shown in FIG. 5 is obtained, the portion between the depth 0 and the depth DA is removed in a later removal step. The

  Referring to FIG. 6, the ring-shaped member 12 that has undergone the solution treatment is divided into a plurality of ring-shaped members 13 by cutting. Here, the surface layer portion of the ring-shaped member 13 obtained by cutting is polished or ground to remove the element concentrated layer and the oxide layer formed during the solution treatment (removal step). At this time, barrel polishing is preferably performed. A method of grinding the surface using a rod-shaped grindstone or the like instead of barrel polishing can also be employed.

  The degree of removal of the element enriched layer and the oxide layer is such that the Ti enriched layer (Ti is exposed to the surface (surface layer portion) of the ring-shaped member 13 when the removal step is completed). Concentrated layer) and oxide layer are removed. That is, the Ti-deficient layer is exposed on the surface (surface layer) of the ring-shaped member 13 that has been subjected to the removing step, by removing the element concentrated layer and the oxide layer. As described above, when the ring-shaped member 12 having the Ti concentration distribution as shown in FIG. 5 is obtained, the portion between the depth 0 and the depth DA is removed in the removal step. For example, when a Ti-deficient layer having a depth of 10 μm to 15 μm is formed, the Ti concentrated layer on the surface layer is removed by polishing about 3 μm from the surface, and Ti having a depth of 7 μm to 12 μm. It becomes possible to leave a deficient layer. In the present embodiment, the removing step is performed on the ring-shaped member 13 obtained by cutting. However, the removing step is performed on the ring-shaped member 12 (after the solution treatment is completed) before cutting. May be implemented.

  Referring to FIG. 7, if necessary, the ring-shaped member 13 from which the surface layer is removed so that the Ti-deficient layer is exposed is subjected to a rolling process. The ring-shaped member 13A is obtained through the rolling process. In order to remove processing stress due to rolling or the like, a secondary solution treatment is performed (solution treatment step). Also in the secondary solution treatment, if necessary, a removal step by polishing or grinding is performed.

  With reference to FIG. 8, thereafter, circumferential length adjustment processing using a roller 22 or the like is performed, and aging and nitriding processing are performed on the ring-shaped member 13 </ b> A. Thereby, the endless metal belt 13B is completed. In the present embodiment, the Ti-deficient layer formed during the solution treatment is exposed on the surface of the ring-shaped member through the removal process. When the Ti-deficient layer does not exist on the surface, a large amount of nitrogen is bonded to Ti in the nitriding step, and as a result, a hard nitrided layer is generated and the nitrided layer may become brittle.

  In the present embodiment, the presence of the Ti-deficient layer can suppress a large amount of nitrogen and Ti from being bonded during the nitriding process, so that the surface of the endless metal belt 13B may become excessively hard. There is almost no possibility that the endless metal belt 13B becomes brittle. Therefore, endless metal belt 13B having high strength can be obtained.

[Examples and Comparative Examples]
With reference to FIGS. 9 and 10, the relationship between the nitrogen concentration distribution after nitriding (FIG. 9) and the residual stress distribution (FIG. 10) will be described. The graph shown as “Example” in FIGS. 9 and 10 is obtained by the endless metal belt manufacturing method based on the above-described embodiment. The graph shown as “Comparative Example” is obtained by a known method for producing an endless metal belt. The nitrogen concentration shown in FIG. 9 is a value analyzed by a glow discharge emission spectrometer. The residual stress shown in FIG. 10 is a value measured with an X-ray residual stress measuring apparatus.

  As shown in FIG. 9, in the case of the example, the nitrogen concentration in the range from the surface (depth = 0 μm) to about 10 μm is lower than in the case of the comparative example. As shown in FIG. 10, in the case of the example, it can be seen that the internal stress (residual stress) remaining near the surface of the endless metal belt is also smaller in absolute value than in the case of the comparative example. . Therefore, according to the configuration of the above-described embodiment, the residual stress at the weakest part can be reduced, and the tensile residual stress generated inside can be reduced, so that the residual stress at the weakest part is shifted in the compression direction. (Ie, it is possible to reduce tension and increase compression). The surface of the endless metal belt 13B does not become excessively hard, and the endless metal belt 13B is less likely to become brittle. Therefore, it can be said that an endless metal belt 13B having high strength can be obtained.

  Although the embodiments and examples have been described above, the above disclosure is illustrative in all respects and not restrictive. The technical scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  10 rolls, 11 steel plates, 12, 13, 13A ring-shaped members, 13B endless metal belts, 20 trays, 21 reaction chambers, 22 rollers.

Claims (1)

A welding process in which ends of steel plates bent into a cylindrical shape are welded together to form a ring-shaped member;
A solution treatment step for subjecting the ring-shaped member obtained by the welding step to a solution treatment;
Removing the element-concentrated layer and the oxide layer formed during the solution treatment by polishing or grinding the surface of the ring-shaped member subjected to the solution treatment;
A nitriding treatment step of nitriding the ring-shaped member that has undergone the removing step,
In the solution treatment step, a Ti-deficient layer having a Ti concentration lower than the Ti concentration of the ring-shaped member before the solution treatment is performed is formed,
The Ti-deficient layer is exposed by removing the element concentrated layer and the oxide layer on the surface of the ring-shaped member that has undergone the removing step,
A method for producing an endless metal belt.

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