JP2018162503A - Machine part and surface treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface treatment method capable of solid-dissolving oxygen on a member surface, while suppressing scale formation on the member surface.SOLUTION: A surface treatment method in one embodiment includes an acid-treatment step for solid-dissolving oxygen on a member surface by keeping the member at a heating temperature, in atmosphere gas containing inert gas and oxygen. The member is constituted of pure titanium or a titanium alloy. The concentration of oxygen in the atmosphere gas is 100 ppm or more and 500 ppm or less.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a machine part and a surface treatment method thereof. More specifically, the present invention relates to a surface treatment method for a member made of pure titanium or a titanium alloy.

  Pure titanium or a titanium alloy has a lower hardness than steel. For this reason, when a mechanical component composed of pure titanium or a titanium alloy is used for an application requiring wear resistance, it is necessary to perform a surface treatment.

  Conventionally, a surface treatment method described in International Publication No. 97/36018 (Patent Document 1) is known. In the surface treatment method described in Patent Document 1, a titanium alloy member is held at a heating temperature for a predetermined time in a nitrogen-based mixed atmosphere gas containing a small amount of oxygen. According to the surface treatment method described in Patent Document 1, nitrogen and oxygen are dissolved in the surface of the titanium alloy member.

International Publication No. 97/36018

  A titanium alloy in which nitrogen is solid solution has improved toughness but low toughness. For this reason, the wear resistance of the titanium alloy member subjected to the surface treatment according to the surface treatment method described in Patent Document 1 is not sufficient.

  On the other hand, the hardness of the titanium alloy can also be improved by dissolving oxygen in a solid solution. A titanium alloy in which oxygen is dissolved has higher toughness than a titanium alloy in which nitrogen is dissolved. However, since the surface treatment for dissolving oxygen on the surface of the titanium alloy member is performed in an atmosphere containing oxygen, a scale (a film composed of titanium oxide) is formed on the surface of the member.

  The present invention has been made in view of such problems of the prior art. More specifically, the present invention provides a mechanical component capable of dissolving oxygen on the surface while suppressing the formation of scale on the surface, and a surface treatment method thereof.

  The surface treatment method according to one aspect of the present invention includes an acid soaking process in which oxygen is dissolved in the surface of a member by holding the member at a heating temperature in an atmosphere gas containing an inert gas and oxygen. The member is made of pure titanium or a titanium alloy. The oxygen concentration in the atmospheric gas is 100 ppm or more and 500 ppm or less.

  According to the surface treatment method of one embodiment of the present invention, oxygen can be dissolved in the member surface while suppressing the formation of scale on the member surface.

  In the above surface treatment method, the member may be held at the heating temperature for 4 hours or more in the acid immersion step. In this case, the hardness of the member surface can be improved by increasing the amount of oxygen dissolved in the member surface.

  In the above surface treatment method, the heating temperature may be 900 ° C. or higher and may be equal to or lower than β transus of the member. In this case, the coarsening of the crystal grains constituting the member can be suppressed.

  In the above surface treatment method, the member may be made of 64 titanium alloy, and the heating temperature may be 900 ° C. or higher and 995 ° C. or lower. In this case, oxygen can be dissolved in the member surface while suppressing the formation of scale on the member surface.

  In the above surface treatment method, the member may be held at the heating temperature for 4 hours or more in the acid immersion step. In this case, the hardness of the member surface can be improved by increasing the amount of oxygen dissolved in the member surface.

  The above surface treatment method may further include an atmospheric gas recovery step of recovering the atmospheric gas after the immersion step and removing impurities from the recovered atmospheric gas. In this case, the processing cost can be reduced by reusing the atmospheric gas.

  The mechanical component according to one embodiment of the present invention is a mechanical component made of pure titanium or a titanium alloy. The mechanical part which concerns on 1 aspect of this invention has the scale comprised with a titanium oxide on the surface, and the diffusion layer which oxygen dissolved. The thickness of the scale is 0.015 mm or less. The concentration of oxygen in the diffusion layer is 2.2 mass percent or more at a position where the distance from the surface is 0.05 mm.

  According to the mechanical component according to one aspect of the present invention, oxygen can be dissolved in the surface of the machine component while suppressing the formation of scale on the surface of the machine component, and the hardness and wear resistance of the surface of the machine component can be improved. Can do.

  According to the surface treatment method of one embodiment of the present invention, oxygen can be dissolved in the member surface while suppressing the formation of scale on the member surface. According to the machine component according to one aspect of the present invention, the hardness and wear resistance of the machine component surface can be improved by dissolving oxygen on the machine component surface while suppressing the formation of scale on the machine component surface. it can.

It is a top view of the machine part concerning an embodiment. It is sectional drawing in II-II of FIG. It is an enlarged view in the area | region III of FIG. It is process drawing which shows the surface treatment method of the machine component which concerns on embodiment. It is a typical graph which shows the relationship between the hardness of the test piece 1, and the distance from the surface. It is a typical graph which shows the relationship between the hardness of the test piece 2, and the distance from the surface. 3 is a schematic graph showing the relationship between the oxygen concentration in the test piece 1 and the distance from the surface. 3 is a schematic graph showing a relationship between an oxygen concentration in a test piece 2 and a distance from a surface.

  Embodiments will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

(Configuration of mechanical parts according to the embodiment)
Below, the structure of the machine component which concerns on embodiment is demonstrated with reference to FIGS. 1-3. FIG. 1 is a top view of a mechanical component according to the embodiment. 2 is a cross-sectional view taken along the line II-II in FIG. As shown in FIGS. 1 and 2, the mechanical component according to the embodiment is an inner ring 10 used for, for example, a rolling bearing. However, the machine component according to the embodiment is not limited to this.

  The inner ring 10 is made of pure titanium (Ti) or a titanium alloy. Pure titanium is a metal material composed of titanium and inevitable impurities. The titanium alloy constituting the inner ring 10 is ASTM standard B348-13GR. 5 is preferably a Ti-6Al (aluminum) -4V (vanadium) alloy. In the following, this Ti-6Al-V alloy is referred to as a 64 titanium alloy.

  The inner ring 10 is composed of a ring-shaped member. The inner ring 10 has an upper surface 10a, a bottom surface 10b, an inner peripheral surface 10c, and an outer peripheral surface 10d (surface). The bottom surface 10b is a surface opposite to the top surface 10a. The outer peripheral surface 10d is a surface opposite to the inner peripheral surface 10c. The upper surface 10 a and the bottom surface 10 b are surfaces of the inner ring 10 that are orthogonal to the central axis of the inner ring 10. The inner peripheral surface 10c and the outer peripheral surface 10d are connected to the upper surface 10a and the bottom surface 10b. The distance between the inner peripheral surface 10c and the central axis is larger than the distance between the outer peripheral surface 10d and the central axis. The outer peripheral surface 10 d constitutes the raceway surface of the inner ring 10.

  FIG. 3 is an enlarged view of region III in FIG. The inner ring 10 has a diffusion layer 10f. The inner ring 10 may have a scale 10e. The scale 10e may be removed as described later. The scale 10 e and the diffusion layer 10 f are on the outer peripheral surface 10 d of the inner ring 10. The diffusion layer 10f is on the inner side of the inner ring 10 than the scale 10e.

  The scale 10e has a thickness T1. The diffusion layer 10f has a thickness T2. The thickness T1 and the thickness T2 are the thicknesses of the scale 10e and the diffusion layer 10f in the direction orthogonal to the outer peripheral surface 10d. Preferably, the thickness T1 is 0.015 mm or less. Particularly preferably, the thickness T1 is 0.005 mm or less. The thickness T2 is preferably 0.15 mm or more.

The scale 10e is made of a titanium oxide. The titanium oxide constituting the scale 10e is, for example, TiO or TiO ₂ . Oxygen is dissolved in the diffusion layer 10f. The diffusion layer 10f preferably includes crystal grains composed of an α phase of titanium. The α-phase crystal grains contained in the diffusion layer 10f are preferably arranged in an equiaxed manner.

  The oxygen concentration in the diffusion layer 10f is preferably 2.2 mass percent or more at a position where the distance from the outer peripheral surface 10d is 0.05 mm. The concentration of oxygen in the diffusion layer 10f is preferably 0.99 mass percent or more at a position where the distance from the outer peripheral surface 10d is 0.1 mm. The oxygen concentration in the diffusion layer 10f is more preferably 3.47 mass percent or more at a position that is 0.05 mm from the outer peripheral surface 10d. The oxygen concentration in the diffusion layer 10f is more preferably 1.46% by mass or more at a position where the distance from the outer peripheral surface 10d is 0.1 mm.

  The nitrogen concentration and the oxygen concentration in the diffusion layer 10f are measured by, for example, EPMA (electron beam microanalyzer).

  The hardness of the diffusion layer 10f decreases as the distance from the outer peripheral surface 10d increases. The hardness of the diffusion layer 10f is preferably 630 Hv or more at a position where the distance from the outer peripheral surface 10d is 0.05 mm and 500 Hv or more at a position where the distance from the outer peripheral surface 10d is 0.1 mm. The hardness of the diffusion layer 10f is more preferably 690 Hv or more at a position where the distance from the outer peripheral surface 10d is 0.05 mm, and more preferably 520 Hv or more at a position where the distance from the outer peripheral surface 10d is 0.1 mm.

  The hardness of the diffusion layer 10f is measured according to the Vickers hardness test method defined in JIS Z 2244: 2009.

(Surface treatment method for machine parts according to an embodiment)
Below, the surface treatment method of the machine component which concerns on embodiment is demonstrated with reference to FIG. FIG. 4 is a process diagram illustrating a surface treatment method for a machine part according to the embodiment. As shown in FIG. 4, the method for manufacturing a machine part according to the embodiment includes a preparation step S1, an acid immersion step S2, a cooling step S3, and a post-processing step S4.

  In the preparation step S1, a member to be processed is prepared. This member to be processed is a ring-shaped member made of pure titanium or a titanium alloy when the machine part according to the embodiment is the inner ring 10. The member to be processed has an outer peripheral surface. The outer peripheral surface of the member to be processed is a surface that eventually becomes the outer peripheral surface 10d of the inner ring 10.

  In the soaking step S2, soaking treatment is performed on the surface of the workpiece. More specifically, the acid treatment is performed on the outer peripheral surface of the workpiece. In the immersion treatment, heat treatment is performed using a heat treatment furnace in an atmosphere gas containing an inert gas and oxygen. The pressure of the atmospheric gas is, for example, normal pressure (atmospheric pressure). This heat treatment furnace may have an atmospheric gas recovery facility.

  The inert gas contained in the atmospheric gas is, for example, argon (Ar). The heating temperature in the heat treatment is preferably 900 ° C. or higher. The heating temperature in the heat treatment is preferably equal to or lower than β transus of pure titanium or titanium alloy constituting the workpiece. Here, β transus is the temperature at which the α phase in pure titanium or a titanium alloy starts to transform into the β phase. For example, the β transus of 64 titanium alloy is 995 ° C. The holding time in the heat treatment is preferably 4 hours or longer. The holding time in the heat treatment is more preferably 8 hours or longer.

  The partial pressure of oxygen in the atmospheric gas is set so that the growth of the oxide of the member to be processed (that is, the oxide of titanium) is suppressed at the heating temperature. More specifically, the concentration of oxygen in the atmospheric gas is 100 ppm or more and 500 ppm or less.

  In the soaking step S2, oxygen in the atmospheric gas enters and diffuses from the surface of the workpiece to be processed into the workpiece to form the diffusion layer 10f. Further, in the immersion step S2, the scale 10e is formed on the surface of the workpiece. The scale 10e may be removed, for example, in the post-processing step S4.

  As shown in FIG. 4, the surface treatment method for mechanical parts according to the embodiment may further include an atmospheric gas recovery step S5. The atmospheric gas recovery step S5 is performed using an atmospheric gas recovery facility provided in the heat treatment furnace. In the atmospheric gas recovery step S5, the atmospheric gas used in the immersion acid step S2 is recovered and impurities are removed from the atmospheric gas. The atmospheric gas that has been recovered and removed impurities in the atmospheric gas recovery step S5 is used again in the immersion acid step S2.

  In the cooling step S3, the workpiece is removed from the heat treatment furnace and cooled. The processing target member is cooled by water-cooling the processing target member taken out from the heat treatment furnace with, for example, a saline solution.

  In post-processing process S4, the post-processing with respect to a process target member is performed. In the post-processing step S4, for example, cleaning of the processing target member, machining such as grinding and polishing of the processing target member, and the like are performed. Thereby, the inner ring | wheel 10 is manufactured from a process target member.

(Relationship between scale thickness and diffusion layer hardness and oxygen concentration in diffusion layer)
Below, the evaluation test about the relationship between the thickness of the scale 10e, the hardness of the diffusion layer 10f, and the oxygen concentration in the diffusion layer 10f and the results thereof will be described.

<Specimen>
First, the test piece used for said test is demonstrated. Table 1 shows the composition of the titanium alloy used for each test piece. As shown in Table 1, the titanium alloy used for the test piece is a 64 titanium alloy. In addition, the dimension of a test piece is 20 mm x 10 mm x 10 mm.

<Heat treatment conditions>
The test piece was subjected to the immersion step S2 and the cooling step S3. Table 2 shows the heating temperature, holding time, and atmospheric gas in the soaking step S2. As shown in Table 2, in both the test piece 1 and the test piece 2, the heating temperature was 920 ° C. and the holding time was 8 hours. In both the test piece 1 and the test piece 2, the heat treatment was performed in an atmospheric gas containing oxygen and argon. However, the oxygen concentration in the atmospheric gas used for the test piece 1 was 100 ppm, and the oxygen concentration in the atmospheric gas used for the test piece 2 was 500 ppm. The cooling step S3 was performed by water cooling with 5% saline.

<Scale thickness>
When the cross section of the test piece 1 and the test piece 2 was polished and observed with a microscope, the thickness of the scale 10e formed on the surface of the test piece 1 was 0.005 mm and was formed on the surface of the test piece 2. The thickness of the scale 10e was 0.015 mm. The thickness of the scale 10e was 0.35 mm when the same member as that of the test piece 1 and the test piece 2 was subjected to an acid treatment in the atmosphere with a heating time of 850 ° C. and a holding time of 24 hours. .

<Hardness evaluation test>
FIG. 5 is a schematic graph showing the relationship between the hardness of the test piece 1 and the distance from the surface. FIG. 6 is a schematic graph showing the relationship between the hardness of the test piece 2 and the distance from the surface. As shown in FIGS. 5 and 6, the hardness of the test piece 1 and the test piece 2 decreased as the distance from the surface increased.

  As shown in FIG. 5, the hardness of the test piece 1 was 630 Hv at a position at a distance of 0.05 mm from the surface and 520 Hv at a position at a distance of 0.1 mm from the surface. The hardness of the test piece 1 was almost constant at a position where the distance from the surface was 0.15 mm or more. Therefore, in the test piece 1, it became clear that the diffusion layer 10f of about 0.15 mm was formed.

  As shown in FIG. 6, the hardness of the test piece 2 was 690 Hv at a position at a distance of 0.05 mm from the surface, and 500 Hv at a position at a distance of 0.1 mm from the surface. The hardness of the test piece 2 was almost constant at a position where the distance from the surface was 0.15 mm or more. Therefore, in the test piece 2, it became clear that the diffusion layer 10f of about 0.15 mm was formed.

  FIG. 7 is a schematic graph showing the relationship between the oxygen concentration in the test piece 1 and the distance from the surface. FIG. 8 is a schematic graph showing the relationship between the oxygen concentration in the test piece 2 and the distance from the surface. As shown in FIG.7 and FIG.8, the oxygen concentration in the test piece 1 and the test piece 2 became small as the distance from the surface became large.

  As shown in FIG. 7, the oxygen concentration in the test piece 1 is 2.2 mass percent at a position at a distance of 0.05 mm from the surface, and 0.99 mass at a position at a distance of 0.1 mm from the surface. It was a percentage. The oxygen concentration in the test piece 1 was substantially constant at a position where the distance from the surface was 0.15 mm or more. Therefore, in the test piece 1, it was also clarified from this test result that the diffusion layer 10f of about 0.15 mm was formed.

  As shown in FIG. 8, the oxygen concentration in the test piece 2 is 3.47 mass percent at a position at a distance of 0.05 mm from the surface, and 1.46 mass at a position at a distance of 0.1 mm from the surface. It was a percentage. The oxygen concentration in the test piece 2 was substantially constant at a position where the distance from the surface was 0.15 mm or more. Therefore, it was also clarified from this test result that the diffusion layer 10f of about 0.15 mm was formed in the test piece 2.

(Effects of machine parts and surface treatment method according to embodiment)
The effects of the surface treatment method for machine parts according to the embodiment will be described below. In the surface treatment method for mechanical parts according to the embodiment, the immersion step S2 is performed using an atmospheric gas having a small amount of oxygen, and thus the thickness of the scale 10e formed on the surface of the member to be processed. The surface of the member to be processed can be hardened by solid solution strengthening of oxygen while suppressing the above.

  In the mechanical component surface treatment method according to the embodiment, when the holding time is 4 hours or more, more oxygen diffuses on the surface of the workpiece. Therefore, in this case, the hardness of the diffusion layer 10f can be improved by increasing the amount of dissolved oxygen in the diffusion layer 10f.

  In the mechanical component surface treatment method according to the embodiment, when the oxygen concentration in the atmospheric gas is 100 ppm or less and 500 ppm or more, the thickness of the scale 10e formed on the surface of the workpiece is suppressed and the workpiece is processed. Can be hardened by solid solution strengthening of oxygen.

  In the heat treatment of pure titanium and titanium alloy, the crystal grains tend to be coarsened by the transformation of the α phase into the β phase during the heat treatment. Therefore, in the surface treatment method for mechanical parts according to the embodiment, when the heating temperature is 900 ° C. or higher and β transus or lower, the crystal grains constituting the workpiece to be processed are coarsened during the acid treatment. Can be suppressed.

  In the surface treatment method for a machine part according to the embodiment, when the workpiece is a 64 titanium alloy, the surface of the workpiece is oxygen-suppressed while suppressing the thickness of the scale 10e formed on the surface of the workpiece. It can be cured by solid solution strengthening.

  When the surface treatment method for mechanical parts according to the embodiment includes the atmospheric gas recovery step S5, the processing cost can be reduced by reusing the atmospheric gas.

  According to the mechanical component according to the embodiment, the surface of the mechanical component can be hardened by solid solution strengthening of oxygen while suppressing the thickness of the scale 10e formed on the surface of the mechanical component.

  Although the embodiment of the present invention has been described above, the above-described embodiment can be variously modified. Further, the scope of the present invention is not limited to the above-described embodiment. The 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.

  The above embodiment is advantageously applied to a mechanical component made of pure titanium or a titanium alloy and a surface treatment method thereof.

  S1 preparation step, S2 acid soaking step, S3 cooling step, S4 post-treatment step, S5 atmosphere gas recovery step, 10 inner ring, 10a top surface, 10b bottom surface, 10c inner peripheral surface, 10d outer peripheral surface, 10e scale, 10f diffusion layer, T1 Thickness, T2 thickness.

Claims (7)

In an atmospheric gas containing an inert gas and oxygen, an immersion process is provided in which the oxygen is dissolved in the surface of the member by maintaining the member at a heating temperature,
The member is made of pure titanium or a titanium alloy,
The surface treatment method, wherein a concentration of the oxygen in the atmospheric gas is 100 ppm or more and 500 ppm or less.   The surface treatment method according to claim 1, wherein, in the acid immersion step, the member is held at the heating temperature for 4 hours or more.   The surface treatment method according to claim 1, wherein the heating temperature is 900 ° C. or higher and is β transus or lower of the member. The member is made of a 64 titanium alloy,
The surface treatment method according to claim 1, wherein the heating temperature is 900 ° C. or higher and 995 ° C. or lower.   5. The surface treatment method according to claim 4, wherein in the immersion step, the member is held at the heating temperature for 4 hours or more.   The surface treatment method according to claim 1, further comprising an atmospheric gas recovery step of recovering the atmospheric gas after the immersion step and removing impurities from the recovered atmospheric gas. Machine parts made of pure titanium or titanium alloy,
The mechanical component has a scale composed of titanium oxide and a diffusion layer in which oxygen is dissolved in the surface,
The thickness of the scale is 0.015 mm or less,
The mechanical component, wherein the oxygen concentration in the diffusion layer is 2.2 mass percent or more at a position where the distance from the surface is 0.05 mm.

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