JP2009007612A - Method for manufacturing nitrided component, and endless metal belt - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply and surely detect a poorly nitrided part while relying on a color of the surface. <P>SOLUTION: This detection method includes adding an oxidation treatment step of heating an endless hoop material (W) made from a maraging steel to 300 to 400°C in atmospheric air to a process of manufacturing an endless metal belt by the steps of solution-heat-treating the hoop material, controlling a peripheral length of the hoop material, and then subjecting the hoop material to aging treatment and nitriding treatment to impart a compressive residual stress to the surface of the hoop material; and simply and surely determining whether the nitriding treatment has been adequate or not, according to a color difference between a normally nitrided portion which shows a blue color and a poorly nitrided portion which shows other colors except the blue color. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a nitrided part subjected to nitriding treatment and an endless metal belt manufactured by the manufacturing method.

  For example, in a belt used in a continuously variable transmission (CVT), as indicated by reference numeral 1 in FIG. 3, a number of elements 2 that engage with a pulley P whose V-groove interval can be changed are arranged through a laminated ring 3. It has a structure that is bundled in an annular shape. In such a CVT belt 1, the laminated ring 3 has a structure in which a large number of endless metal belts 4 having different circumferential lengths are closely adhered to each other (for example, 9 pieces), and in the illustrated example, The saddle surfaces 2b on both sides of the neck 2a of each element 2 are arranged in two rows. There is a CVT belt having a structure in which laminated rings are arranged in two rows in a recess between hook portions provided on both sides of a saddle surface of each element.

  By the way, since a high bending load repeatedly acts on the laminated ring 3, the endless metal belt 4 constituting the laminated ring 3 is required to have high fatigue strength. Therefore, conventionally, maraging steel having high strength and toughness is selected as the material of the endless metal belt 4, and as shown in FIG. 4, it is solutionized in an endless hoop material W made of the maraging steel. After the treatment, the perimeter was adjusted, and then an aging treatment and a nitriding treatment were performed to impart compressive residual stress to the surface.

  However, the nitriding treatment for the endless metal belt 4 described above is performed at a low temperature (410 to 450 ° C.) unlike the general nitriding treatment for various parts, and the thickness of the nitride layer formed thereby is also common. It is considerably thinner than the thickness of the nitrided layer (for example, about 25 to 40 μm). For this reason, if even a slight amount of nitriding inhibitor adheres to the surface before nitriding, a nitriding layer will not be formed or a thin nitriding defect will occur, and a reduction in the strength of the resulting endless metal belt can be avoided. It will not be.

  For this reason, in the manufacture of the endless metal belt described above, it is indispensable to finally inspect for the presence of nitriding defects. However, in general, the inspection is made visually by relying on slight discoloration of the surface. Therefore, there is a problem that the inspection requires a lot of skill and time, and the reliability of the inspection result is still poor.

Note that, for example, in the one described in Patent Document 1, the surface unevenness is measured using a surface roughness meter, and if the amount of dents is equal to or greater than the target amount of dents, the compressive residual stress is not sufficient, and it is determined that the nitriding is defective. However, even in this case, it is assumed that the discolored portion is specified by visual inspection, and the above-described problem cannot be solved.
JP 2005-248978 A

  The present invention has been made in view of the above-described conventional problems, and the problem is that the nitriding failure can be easily and reliably grasped by relying on the surface color, and the reliability of quality assurance can be improved. An object of the present invention is to provide a method of manufacturing a nitrided part that greatly contributes to improvement, and to provide an endless metal belt manufactured by the manufacturing method.

In order to solve the above-described problems, the method for manufacturing a nitrided part according to the present invention is characterized in that after nitriding, heating is performed in the air, and the quality of nitriding is determined from the difference in the color of the oxide film on the surface. In general, when heated in the air after nitriding, the color of the oxide film on the surface changes from brown to purple to blue as the heating temperature rises. However, if there is a defective nitriding portion on the surface, the color of the defective portion is different from the surrounding color. Therefore, the quality of nitriding can be easily and reliably determined from this color difference.
Hereinafter, some aspects of the present invention will be illustrated and described in terms of items.

  (1) A method for producing a nitrided part, characterized in that after the nitriding treatment, an oxidation treatment is performed by heating to 300 to 400 ° C. in the air, and the quality of nitriding is judged from the difference in surface color.

  When heated to 300-400 ° C. in the atmosphere after nitriding, the color of the oxide film on the surface becomes blue. However, in a portion where the nitrided layer is thin or where there is no nitrided layer, the color is completely different from blue. Become. Therefore, the quality of nitriding can be easily and reliably determined from the difference from blue.

  In the present manufacturing method, the above-described color difference can be visually determined, but an image obtained by imaging the surface may be automatically determined by image processing. In the latter case, labor can be saved by automation. And productivity can be improved.

  (2) The method for producing a nitrided part according to (1), wherein the nitrided part is an endless metal belt for a continuously variable transmission and is made of maraging steel.

  As described above, the endless metal belt for continuously variable transmission is subjected to nitriding treatment at a low temperature for the purpose of imparting compressive residual stress, and a thin nitride layer is formed. In this case, the difference in the color of the portion where the nitriding failure exists appears more clearly. Therefore, this manufacturing method is particularly useful for manufacturing such an endless metal belt for a continuously variable transmission.

  (3) An endless metal belt, which is subjected to an oxidation treatment which is heated to 300 to 400 ° C. in the air after the nitriding treatment.

  (4) The endless metal belt according to item (3), wherein the surface is blue.

  Since the endless metal belt according to the present invention is subjected to an oxidation treatment that is heated to 300 to 400 ° C. in the atmosphere and has a blue surface, the confirmation of the oxidation treatment at 300 to 400 ° C. described in (3) Or by confirming the blue color described in (4), it can be ascertained that the quality of nitriding by the surface inspection is reliably determined.

  According to the method for manufacturing a nitrided part according to the present invention, it is possible to easily and reliably grasp the nitriding defect by relying on the color of the surface, so that the reliability for quality assurance is remarkably high.

  In addition, the endless metal belt manufactured by the above-described manufacturing method can grasp whether the nitriding quality is reliably determined by confirming the oxidation treatment at 300 to 400 ° C. or confirming the blue color of the surface, thereby increasing the product value. .

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a manufacturing process of a nitrided part according to the present invention. The nitrided part manufactured here is an endless metal belt 4 for a continuously variable transmission (CVT) shown in FIG. 3, and after an endless hoop material W made of maraging steel is subjected to a solution treatment. The process from the adjustment of the circumference to the subsequent application of aging treatment and nitriding treatment to impart compressive residual stress to the surface is exactly the same as in the prior art (FIG. 4). The standard solution temperature of maraging steel is about 830 ° C, and the standard aging temperature is about 480 ° C. By performing solution treatment before adjusting the circumference, the workability necessary for adjusting the circumference can be obtained. On the other hand, high strength and toughness are imparted by performing an aging treatment after adjusting the circumference. Moreover, the nitriding treatment is performed at 410 to 450 ° C. which is lower than the aging temperature of the maraging steel. Therefore, the strength and toughness imparted by the aging treatment are not impaired by this nitriding treatment.

  In the present embodiment, after the above nitriding treatment, an oxidation treatment is performed by heating to 300 to 400 ° C. in the atmosphere. By this oxidation treatment in the atmosphere, a blue oxide film is formed on the surface of the endless metal belt 4. However, when there is a poorly nitrided portion where the nitrided layer is thin or the nitrided layer is not formed on the surface of the endless metal belt 4 after the nitriding treatment, the color of the poorly nitrided portion 4a is blue as shown in FIG. Will be different colors. The lower right figure in FIG. 2 shows a color photograph (enlarged photograph) of the actually captured surface converted into monochrome, and in the same figure, the white portion at the center is a real image that is light green to yellow green. The black part around it is blue in the real image.

  Thus, by performing the oxidation treatment finally heated to 300 to 400 ° C. in the atmosphere, the color is different from blue in a portion where nitridation is satisfactorily performed and blue in a portion where nitridation is poor. This color difference can be clearly determined by visual observation. Therefore, the quality of nitriding can be easily and reliably determined from this color difference.

  Since the surface color is the color of the oxide film, the performance is not adversely affected. Therefore, the obtained endless metal belt 4 can be commercialized with a blue color applied as it is. In this case, it is possible to ascertain whether nitriding quality is reliably determined by confirming the blue color on the surface, thereby increasing the product value.

  Here, in the above-described embodiment, the color difference between the defective nitriding portion and the normal nitriding portion is discriminated visually. However, in the present invention, this color difference is image-processed using the image pickup unit. Thus, it may be automatically determined. In this case, for example, the entire circumference of the endless metal belt 4 is imaged at a predetermined pitch by the imaging means, and image processing is performed on the captured image to determine whether the nitriding is good or bad for the entire circumference. As the image pickup means used at this time, it is desirable to use a CCD camera because data processing of the picked-up image becomes simple. Thus, when automatically distinguishing between the colors, it is possible to save labor and improve productivity.

It is a schematic diagram which shows the manufacturing process based on this invention in the case of manufacturing the endless metal belt as a nitrided component. It is a schematic diagram which shows the color state of the surface of the endless metal belt obtained by the manufacturing process of this invention. It is sectional drawing which shows the principal part structure of the continuously variable transmission to which the endless metal belt as a nitriding component is applied. It is a schematic diagram which shows the manufacturing process of the conventional endless metal belt.

Explanation of symbols

1 Belt for continuously variable transmission 2 Element 3 Laminated ring 4 Endless metal belt 4a

Claims (4)

  A method for producing a nitrided part, characterized in that after the nitriding treatment, an oxidation treatment is performed by heating to 300 to 400 ° C. in the atmosphere, and the quality of nitriding is determined from the difference in surface color.   The method for producing a nitrided part according to claim 1, wherein the nitrided part is an endless metal belt for a continuously variable transmission and is made of maraging steel.   An endless metal belt, which is subjected to an oxidation treatment after heating to 300 to 400 ° C. in the atmosphere after nitriding.   The endless metal belt according to claim 3, wherein the surface has a blue color.