Plated member and method for manufacturing the same

Abstract

This plated member has a plating film, which contains at least chromium, carbon and oxygen, while having chromium that is precipitated from a trivalent chromium bath as a main component, on the outer surface; the plating film contains 60 at% to 80 at% of chromium and 16.5 at% to 30 at% of carbon; the indentation hardness of the outer surface is 7 GPa or more; and the crystallinity, which is calculated from the peak integrated intensity ratio of the measurement values in the X-ray diffractometry and formula (1), is 4% or less.　Formula (1): Crystallinity (peak integrated intensity ratio) = ((crystalline) / (crystalline + amorphous)) × 100% Meanwhile, the indentation hardness is the measurement value of instrumented indentation hardness obtained by a nanoindentation method; and the integrated intensity ratio of formula (1) is a value obtained by XRD analysis wherein 2θ is 30° to 60°, the half width of crystalline is less than 3, and the half width of amorphous is 3 or more.

Description

Technical Field

[0001] The present invention relates to a plating member and a method for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2022-142218 filed in Japan on September 7, 2022, and incorporates its content herein.

Background Art

[0002] A technique using a chromium plating layer deposited from a trivalent chromium bath, which has no problems in terms of toxicity and pollution generation compared to a hexavalent chromium bath, for a plating roll is described in Patent Document 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a chromium plating film formed on a rod with which a sliding part is slidably contacted, as an alternative to a plating film deposited from a hexavalent chromium bath, a plating film deposited from a trivalent chromium bath is regarded as promising. However, according to the research of the present inventor, it has been found that when a rod formed with a plating film deposited from a conventional trivalent chromium bath is polished, brittle fracture (peeling fracture) of the plating film occurs.

[0005] The problem to be solved by the present invention is to provide a plating member such as a rod provided with a plating film deposited from a trivalent chromium bath that is less likely to cause peeling fracture during polishing, and a method for manufacturing the same.

Means for Solving the Problems

[0006] The plated member of the present invention has a plating film on its outer surface that is mainly composed of chromium deposited from a trivalent chromium bath containing at least chromium, carbon, and oxygen, wherein the plating film is composed of chromium: 60-80 at%, carbon: 16.5-30 at%. Oxygen: 2-6 at%, chlorine or iron: 5 at% or less, the remainder being components derived from complexing agents (carboxylates), pH buffers, and conductive salts. It contains and has an indentation hardness of 7 GPa or more on its outer surface. A plated material in which the crystallinity calculated from the peak integral intensity ratio of the measured value of X-ray diffraction and the following equation (1) is 4% or less. Crystallinity (peak integral intensity ratio) = {(crystalline) / (crystalline + amorphous)} × 100% ... (1) However, the indentation hardness mentioned above refers to the value obtained by instrumented indentation hardness measurement using the nanoindentation method (ISO 14577), and the integrated intensity ratio in equation (1) refers to the value obtained by XRD (X-ray diffraction) analysis with 2θ: 30~60°, crystalline full width at half maximum: <3, and amorphous full width at half maximum: ≥3. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a plated member having a chromium-based plating film mainly composed of chromium deposited from a trivalent chromium bath, which does not cause environmental problems compared to hexavalent chromium, and which is less prone to tearing and fracture during polishing. Furthermore, the invention provides a technology for manufacturing this plated member. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing the overall configuration of a shock absorber equipped with a piston rod as a first embodiment of the plated member according to the present invention. [Figure 2] This is a front view showing the general shape of the piston rod. [Figure 3] This is a diagram showing the upper structure of the shock absorber, and is an enlarged partial cross-sectional view of part A in Figure 1. [Figure 4] This figure shows the tip structure of the piston rod, and is an enlarged cross-sectional view of part B in Figure 1. [Figure 5]It is a flowchart showing an example of the manufacturing process of the piston rod. [Figure 6] It is a perspective view of a main part showing an example of a polishing apparatus used for outer diameter polishing of the piston rod. [Figure 7] It is a graph showing the relationship between the deposition rate and the crystallinity of the plating film formed in the example. [Figure 8A] It is a graph showing the relationship between the deposition rate and the carbon concentration of the plating film formed in the example. [Figure 8B] It is a graph showing the relationship between the deposition rate and the oxygen concentration of the plating film formed in the example. [Figure 8C] It is a graph showing the relationship between the deposition rate and the chromium concentration of the plating film formed in the example. [Figure 9] It is a table showing the physical property values of the plating film formed in the example. [Figure 10] It shows the polishing marks of the brittle mode formed on the plating film of the comparative example sample. (A) is a magnified photograph at a magnification of 500 times, and (B) is a magnified photograph at a magnification of 5000 times. [Figure 11] It shows the polishing marks of the ductile mode formed on the plating film of the example sample. (A) is a magnified photograph at a magnification of 500 times, and (B) is a magnified photograph at a magnification of 5000 times. [Figure 12] It is a graph showing the relationship between the film hardness of the example sample and the comparative example sample and the number of polishing marks with a width of 8 μm or more. [Figure 13] It is a graph showing the relationship between the film carbon content of the example sample and the comparative example sample and the number of polishing marks with a width of 8 μm or more. [Figure 14] It is a graph showing the relationship between the film hardness and the film carbon content of the example sample and the comparative example sample. [Figure 15] (A) shows the analysis result by X-ray diffraction of the comparative example sample, and (B) is a surface photograph showing the polishing marks of the sample. [Figure 16] (A) shows the analysis result by X-ray diffraction of the example sample, and (B) is a surface photograph showing the polishing marks of the sample. [Figure 17]It is a graph showing the relationship between the deposition rate (film formation rate) of the plating film formed in the embodiment and the size of chromium crystal grains having orientation. [Figure 18] It is a figure showing a TEM image of a film cross section in a ductile mode with respect to Example 2 of Bath Type A1. [Figure 19] (A) is a figure showing a TEM image of a film cross section in a brittle mode with respect to Comparative Example 1 of Bath Type A1, and (B) is a figure showing a TEM image of a film cross section in a brittle mode with respect to Comparative Example 4 of Bath Type A1. [Figure 20] It is a figure showing a TEM image of a film cross section in a ductile mode with respect to Example 5 of Bath Type A2. [Figure 21] (A) is a figure showing a TEM image of a film cross section in a brittle mode with respect to Comparative Example 9 of Bath Type A2, and (B) is a figure showing a TEM image of a film cross section in a brittle mode with respect to Comparative Example 12 of Bath Type A2. [Figure 22] It is a figure showing an electron diffraction pattern of a film cross section in a ductile mode with respect to Example 2 of Bath Type A1. [Figure 23] (A) is a figure showing an electron diffraction pattern of a film cross section in a brittle mode with respect to Comparative Example 1 of Bath Type A1, and (B) is a figure showing an electron diffraction pattern of a film cross section in a brittle mode with respect to Comparative Example 4 of Bath Type A1. [Figure 24] It is a figure showing an electron diffraction pattern of a film cross section in a ductile mode with respect to Example 5 of Bath Type A2. [Figure 25] (A) is a figure showing an electron diffraction pattern of a film cross section in a brittle mode with respect to Comparative Example 9 of Bath Type A2, and (B) is a figure showing an electron diffraction pattern of a film cross section in a brittle mode with respect to Comparative Example 12 of Bath Type A2.

Mode for Carrying Out the Invention

[0009] Hereinafter, a shock absorber (cylinder device) provided with a piston rod as one embodiment of a plating member according to the present invention will be described. The embodiments described below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified. Furthermore, the drawings used in the description of the embodiments below have been scaled appropriately to make each part easier to see.

[0010] Figure 1 is a partial cross-sectional view showing the overall structure of a shock absorber (cylinder device) 1 equipped with a piston rod 21, which is an example of a plated member according to the present invention. The outer surface of the piston rod 21 has a plating coating, which will be described later. Before describing the plating coating, let's describe the overall structure of the shock absorber 1.

[0011] "Cylinder device" The cylinder device 1 shown in Figure 1 is a shock absorber used in the suspension systems of automobiles and railway vehicles, and specifically in the strut-type suspension systems of automobiles. This cylinder device 1 has a cylindrical inner cylinder 2 in which a working fluid is sealed, and a bottomed cylindrical outer cylinder 3 which has a larger diameter than the inner cylinder 2 and is located on the outer circumference of the inner cylinder 2, forming a reservoir chamber R between the inner cylinder 2 and the outer cylinder 3 in which working fluid and working gas are sealed. This cylinder device 1 is a twin-cylinder type shock absorber in which the inner cylinder 2 is installed inside the outer cylinder 3. In Figure 1, CL indicates the centerlines of the inner cylinder 2 and the outer cylinder 3.

[0012] The outer cylinder 3 has a cylindrical side wall portion 7 and a bottom portion 8 that closes one axial end of the side wall portion 7. The inner cylinder 2 is cylindrical. The inner cylinder 2 is engaged with the bottom portion 8 of the outer cylinder 3 via an annular base valve 13 attached to one axial end of the inner cylinder 2. The inner cylinder 2 is engaged with the other axial end of the side wall portion 7 via an annular rod guide 11 attached to the other axial end of the inner cylinder 2. The base valve 13 is positioned coaxially with the outer cylinder 3, and the rod guide 11 fits into the inner cylinder 2 and the outer cylinder 3, thereby supporting the other end of the inner cylinder 2 coaxially with the outer cylinder 3. In the rod guide 11, an oil seal 15 is positioned on the side opposite to the bottom portion 8. A locking portion 16 is formed on the other axial end of the side wall portion 7, and the oil seal 15 is supported by the locking portion 16.

[0013] A piston 25 is slidably fitted inside the inner cylinder 2. This piston 25 divides the inside of the inner cylinder 2 into a first chamber 22 and a second chamber 23. The first chamber 22 is formed between the piston 25 and the rod guide 11, and the second chamber 23 is formed between the piston 25 and the base valve 13. The second chamber 23 is separated from the reservoir chamber R by the base valve 13, which is provided on one end of the inner cylinder 2. A metal piston rod 21 is connected to the piston 25 by a nut 26. The piston rod 21 has a cylindrical large-diameter portion 21a and protrudes to the outside from one end of the inner cylinder 2 and outer cylinder 3, passing through the rod guide 11 and the oil seal 15. The large-diameter portion 21a of the piston rod 21 is slidably inserted into the inside of the rod guide 11 and the inside of the oil seal 15.

[0014] A small-diameter portion 21b is formed at the tip of the piston rod 21, and the piston 25 is inserted through this small-diameter portion 21b. The piston 25 is attached to the piston rod 21 by screwing a nut 26 onto the threaded portion at the tip of the small-diameter portion. An annular groove 21c is formed in the large-diameter portion 21a of the piston rod 21, near the small-diameter portion 21b, and a ring-shaped internal stopper 24 is mounted to engage with this annular groove 21c. A ring-shaped rebound rubber 19 is positioned on top of the internal stopper 24.

[0015] As shown in Figure 2, the sliding range A is defined as the portion of the large-diameter portion 21a of the piston rod 21 between a position P1 spaced apart from the annular groove 21c and the connecting portion P2 with the bolt portion 21d that serves as the mounting portion to the vehicle body. A plating film mainly composed of chromium deposited from a trivalent chromium bath, which will be described in detail later, is formed on the outer circumferential surface of the piston rod 21, including the sliding range A.

[0016] The piston rod 21 moves axially together with the piston 25. The oil seal 15, through which the large-diameter portion 21a of the piston rod 21 passes, closes the space between the inner cylinder 2 and the outer cylinder 3 and the piston rod 21, preventing leakage of the working fluid in the inner cylinder 2 and the working gas and working fluid in the reservoir chamber R to the outside. As shown in Figure 4, the piston 25 has passages 27 and 28 that penetrate in the axial direction. As shown in Figure 1, the passages 27 and 28 allow the first chamber 22 and the second chamber 23 to communicate with each other. The piston 25 has an annular disc valve 28a that can close the passage 28 by contacting the upper surface of the piston 25. The piston 25 also has an annular disc valve 27a that can close the passage 27 by contacting the lower surface of the piston 25.

[0017] When the piston rod 21 moves in the compression direction (downward in Figure 1), increasing the amount it penetrates into the inner cylinder 2 and the outer cylinder 3, the piston 25 moves in a direction that narrows the second chamber 23. When the pressure in the second chamber 23 becomes higher than the pressure in the first chamber 22 by a predetermined value or more, the disc valve 28a opens the passage 28, generating a damping force at that time. When the upper end of the piston rod 21 moves in the extension direction (rising in Figure 1), increasing the amount it protrudes from the inner cylinder 2 and outer cylinder 3, the piston 25 moves in a direction that narrows the first chamber 22. As a result, when the pressure in the first chamber 22 becomes higher than the pressure in the second chamber 23 by a predetermined value or more, the disc valve 27a opens the passage 27, and exerts a damping force at that time.

[0018] As shown in Figure 1, the base valve 13 has passages 29, 29 that penetrate the base valve 13 in the axial direction. The passages 29 allow the second chamber 23 and the reservoir chamber R to communicate. An annular disc valve 30 is positioned on the bottom side of the base valve 13, which can close one of the passages 29 by contacting the bottom side of the base valve 13. An annular disc valve 31 is positioned on the top side of the base valve 13, which can close the other passage 29 by contacting the top side of the base valve 13.

[0019] The disc valve 30 is a check valve that allows the flow of working fluid from the second chamber 23 to the reservoir chamber R side via one passage 29, while restricting the flow of working fluid through the passage 29 in the opposite direction. The disc valve 30 is a valve that opens the passage 29 when the piston rod 21 moves to the compression side and the pressure in the second chamber 23 becomes higher than the pressure in the reservoir chamber R by a predetermined value or more. The disc valve 31 is a check valve that allows the flow of working fluid from the reservoir chamber R to the second chamber 23 through the other passage 29, while restricting the flow of working fluid through the passage 29 in the opposite direction. The disc valve 31 is a valve that opens the passage 29 when the piston rod 21 moves in the extension direction and the pressure in the second chamber 23 becomes lower than the pressure in the reservoir chamber R by a predetermined value or more.

[0020] As shown in Figure 1, a mounting eye 33 is attached to the outside of the bottom portion 8. The cylinder device 1 is used by attaching the outer portion of the piston rod 21 and the mounting eye 33 between the relative moving members to which it is attached. The cylinder device 1 is used by connecting, for example, the outer end of the piston rod 21 to the vehicle body and the mounting eye 33 to the vehicle's wheel side. In the cylinder device 1, the piston rod 21 and piston 25 slide together within the inner cylinder 2, changing the volume of the first chamber 22 and the second chamber 23. At that time, a damping force can be generated by the flow resistance of the liquid acting on the piston 25 and the base valve 13.

[0021] As shown in Figure 3, the rod guide 11 is a roughly stepped annular shape, with a large diameter portion 11a formed on one axial side and a small diameter portion formed on the other side. The large diameter portion 11a is fitted to the inner circumferential surface of the outer cylinder 3, and the small diameter portion is fitted to the inner circumferential surface of the inner cylinder 2. An annular projection 11c is formed at the end of the large-diameter portion 11a of the rod guide 11, projecting in the axial direction. A communication hole 11d is formed corresponding to the portion of the annular projection 11c, penetrating the rod guide 11 in the axial direction. In the communication hole 11d, the side of the rod guide 11 opposite the annular projection in the axial direction opens into the reservoir chamber R.

[0022] The oil seal 15 has a seal member body 37 which is an integrally molded product in which a metal annular member 36 is fitted into a seal material 35 made of synthetic rubber, and a metal annular spring 38. The annular member 36 maintains the shape of the seal material 35 and provides the seal member body 37 with the strength to fix it to the target part. The seal member body 37 is attached to the end side of the outer cylinder 3 by sandwiching the annular member 36 between the locking portion 16 and the annular projection 11c. The sealing material 35 has a dust lip portion 35a, an oil lip portion 35b, a seal ring portion 35c, and a check lip portion 35d, and surrounds the piston rod 21 to perform a sealing function.

[0023] During vehicle operation, the cylinder device 1 is configured such that the piston rod 21 or the outer cylinder 3 repeatedly receives external impact forces in their respective axial directions. Each time an impact force is received, the piston rod 21 moves in the compression or extension direction, and a damping force acts at that time. In this way, the cylinder device 1 functions as a shock absorber used in the strut-type suspension of an automobile. Furthermore, a plating film deposited from a trivalent chromium bath, as described below, is provided on the outer circumferential surface of the piston rod 21. This plating film is less prone to brittle fracture (tear fracture) when the outer circumferential surface of the piston rod 21 is polished to the desired surface roughness during manufacturing. If the outer circumferential surface is polished to the desired surface roughness and the piston rod 21 has the plating film described in detail later, then even if the large diameter portion 21a of the piston rod 21 repeatedly slides against the sealing material 35, it will exhibit excellent sliding characteristics and excellent wear resistance.

[0024] Figure 5 is a flow chart showing an example of the manufacturing process for the piston rod 21. As shown in step S1 of Figure 5, rod materials such as steel rods made of the type of steel necessary to construct the piston rod 21 are prepared. In step S2, this rod material is subjected to heat treatment such as high-frequency induction hardening and tempering to provide a surface hardening treatment suitable for piston rods. Next, the material is machined in step S3 to achieve the general shape shown in Figures 1-4, and then the outer diameter is ground in step S4. Next, the piston rod, which has been roughly shaped as shown in Figures 1-4, is subjected to a base plating treatment such as nickel plating in step S5, followed by a chromium plating treatment mainly consisting of chromium deposited from a trivalent chromium bath in step S6. Note that in step S5, where the base plating treatment is performed, other base plating treatments may be performed instead of nickel plating, or step S5 may be omitted, and the base plating may be omitted altogether. Next, in step S7, the outer diameter of the piston rod is polished and precision finished to obtain a piston rod with the final surface shape.

[0025] This embodiment is characterized by the plating treatment performed in step S6 and the chromium plating film mainly composed of chromium deposited from a trivalent chromium bath that is formed on the piston rod. The chromium plating film deposited from the trivalent chromium bath used in this embodiment is mainly composed of chromium and contains one or more impurity elements selected from carbon (C) and oxygen (O). For example, the chromium plating film preferably contains 60-80 at% chromium and 16.5-30 at% carbon, and has a surface indentation hardness of 7 GPa or higher. However, the aforementioned indentation hardness refers to the value measured by instrumented indentation hardness measurement using the nanoindentation method (ISO 14577). For example, an indentation load of 20 mN can be applied.

[0026] In the chromium plating film, oxygen may be present in an amount of approximately 2 to 6 at% from the elements mentioned above. Furthermore, in addition to the elements mentioned above, either chlorine (Cl) or iron (Fe) may be present in the chromium plating film as an impurity element in an amount of approximately 5 at% or less. Furthermore, the carbon content is more preferably around 18-25 at%, and the oxygen content is more preferably around 2-5 at%.

[0027] The main component of the plating film is chromium, and it is desirable that it be present in as high a quantity as possible. The carbon contained in the plating film is thought to originate from the organic components that make up the plating bath, as will be described later. However, if the carbon content is less than 16.5 at%, there is a high risk of brittle mode tearing marks occurring during outer diameter polishing. Based on the upper limit of the concentration of organic salts added to the plating bath, the maximum carbon content that can be contained in the plating film is considered to be 30 at%. The oxygen content in the plating film is in the range of 2 to 6 at%. When the oxygen content is less than 2 at%, there is a problem that the likelihood of developing brittle mode tear marks increases, and when the oxygen content exceeds 6 at%, there is a similar problem that the likelihood of developing brittle mode tear marks increases.

[0028] In the plated film of this embodiment, elemental analysis can be performed using an electron probe microanalyzer (EPMA), and conditions such as acceleration voltage: 10kV and irradiation current: 100nA can be used. In this specification, when specifying a numerical range, if the upper and lower limits are indicated with a "~", unless otherwise specified, the concept includes both the upper and lower limits. Therefore, the aforementioned 60~80at% means the range of 60at% or more and 80at% or less.

[0029] The impurity elements other than chromium mentioned above are presumed to originate from organic components in the plating bath, such as carboxylates, pH buffers, and conductivity salts, which are described below. In the chromium plating film according to this embodiment, the amount of impurities contained in the plating film varies depending on the plating treatment conditions, and it is thought that current density, bath temperature, and pH conditions contribute to this. These phenomena are presumed to be caused by the fact that the incorporation of additives during chromium precipitation is affected by the current density (reduction rate), bath temperature (reduction rate), and pH (complex formation, reduction rate).

[0030] [Temperature analysis of hard trivalent chromium plating film to determine its structure] In this embodiment, the microstructure of the plated film is preferably such that the oriented chromium crystal grain size is less than 10 nm, and the base material is a non-oriented microcrystal. Furthermore, it is desirable that there are no chromium diffraction spots in the electron diffraction pattern at positions with interlattice plane distance d values ​​of 2.0 to 2.2 Å (d value of chromium: 2.04 Å). The structure of the plated film varies depending on the plating conditions, and it can be confirmed in the examples described later that current density, bath temperature, and pH conditions contribute significantly to this. This is presumed to be because the ability of additives to be incorporated during chromium deposition affects the current density (reduction rate), bath temperature (reduction rate), and pH (complex formation). In this embodiment, a transmission electron microscope (STEM) can be used to observe the structure of the plated film, and the acceleration voltage can be selected to conditions such as 200kV. Furthermore, when obtaining an electron diffraction pattern, measurement conditions such as an acceleration voltage of 200kV, an electron beam wavelength λ of 0.00251nm at 200kV, and a camera length of 399.4mm can be used.

[0031] In this embodiment, the plating bath used for chromium plating can be a plating bath containing trivalent chromium salt, and additives such as a complexing agent, a pH buffer, and a conductivity salt. While trivalent chromium salts such as chromium chloride, chromium sulfate, and basic chromium sulfate can be used, chromium chloride is preferable among these. As a complexing agent, carboxylate salts such as glycine, formic acid, oxalic acid, and acetic acid can be used, but among these, glycine is preferred. Boric acid and citric acid can be used as pH buffering agents, but boric acid is preferred among these. Ammonium chloride, ammonium sulfate, and ammonium sulfonate can be used as conductivity salts, but ammonium chloride is preferred among these.

[0032] When using a strongly acidic trivalent chromium bath as a plating bath, it is desirable to select a strongly acidic solution with a pH weaker than 0.1, for example, a strongly acidic solution in the range of pH 0.1 to pH 0.6, and more preferably a strongly acidic solution in the range of pH 0.2 to pH 0.5. If the pH is strongly acidic, below 0.1, it becomes difficult to obtain a chromium-based plating film deposited from a trivalent chromium bath, which is the target of this application. If the pH exceeds 0.6, the gloss of the plating film deteriorates, and the ability of impurity elements to be incorporated during chromium deposition changes due to the rate of film formation. For these reasons, it is not possible to obtain a chromium-based plating film deposited from a trivalent chromium bath, which is the target of this application. When using a weakly acidic trivalent chromium bath as the plating bath, one example of a commercially available product is Blue Chromium (product name manufactured by Atotech). When using Blue Chromium, a pH range of 5.2 to 5.8 can be selected as an example. A pH range of 5.4 to 5.6 is more preferable.

[0033] In this embodiment, when using Atotec's trivalent chromium plating solution Blue Chromium, the plating bath used for the chromium plating process can be a plating bath containing trivalent chromium salt and additives such as a complexing agent, a pH buffer, and a conductivity salt. While trivalent chromium salts such as chromium chloride, chromium sulfate, and basic chromium sulfate can be used, chromium sulfate is preferable among these. As a complexing agent, carboxylate salts such as glycine, formic acid, oxalic acid, and acetic acid can be used, but among these, formic acid is preferred. Ammonia, boric acid, citric acid, etc., can be used as pH buffering agents, but ammonia is preferred among these. Ammonium chloride, ammonium sulfate, and ammonium sulfonate can be used as conductive salts, but ammonium sulfate is preferred among these.

[0034] The pH of the plating bath should ideally be acidic, and it is desirable to select an acidity weaker than pH 6.0, for example, in the range of pH 5.3 to pH 5.7. If the pH is acidic (below 5.3), it is not possible to obtain the chromium-based plating film deposited from the trivalent chromium bath that is the target of this application. If the pH is above 5.7, it is possible that the chromium-based plating film deposited from the trivalent chromium bath that is the target of this application may not be obtainable due to reasons such as poor gloss of the plating film and changes in the incorporation of impurity elements during chromium deposition due to the rate of film formation. During the plating process, a higher current density results in a faster film deposition rate and better productivity. However, to achieve the above composition, the current density should be 45-100 A / dm². 2 A range can be selected. Under conditions of high current density and high concentration of trivalent chromium salt, the film deposition rate increases, but the incorporation of impurity elements during chromium deposition changes depending on the film deposition rate. It is desirable to set a film deposition rate suitable for obtaining the desired chromium and carbon content in the resulting plated film. Furthermore, a higher plating bath temperature is preferable; for example, a range of 55 to 80°C can be selected. For the plating bath, a gentle stirring method is preferable, such as allowing the plating solution to flow near the surface to be plated. For the anode material, materials with good insolubility, such as Pt, Ti, Ir, and graphite, can be used.

[0035] During the plating process, a higher current density results in a faster film deposition rate and better productivity. However, to achieve the above composition, the current density should be 45-100 A / dm². 2 A range can be selected. Under conditions of high current density and high concentration of trivalent chromium salt, the film deposition rate increases, but the incorporation of impurity elements during chromium deposition changes depending on the film deposition rate. It is desirable to set a film deposition rate suitable for obtaining the desired chromium and carbon content in the resulting plated film. Furthermore, a higher plating bath temperature is preferable; for example, a range of 55 to 80°C can be selected. For the plating bath, a gentle stirring method is preferable, such as allowing the plating solution to flow near the surface to be plated. For the anode material, materials with good insolubility, such as Pt, Ti, Ir, and graphite, can be used.

[0036] The plated film deposited from the trivalent chromium bath formed by the above-described plating process has an amorphous structure at the time of film formation. This amorphous plated film may be heat-treated at a heating temperature of 200°C or less to obtain an amorphous plated film with a crystallinity of, for example, 4% or less, preferably 2% or less, and more preferably 1% or less. The degree of crystallinity is a value calculated from the peak integral intensity ratio of the measured values ​​obtained by X-ray diffraction and the following equation (1). Crystallinity (peak integral intensity ratio) = {(crystalline) / (crystalline + amorphous)} × 100% ... (1) However, the integral intensity ratio in equation (1) is the value obtained in XRD (X-ray diffraction) analysis with 2θ: 30~60°, full width at half maximum for crystalline materials: <3, and full width at half maximum for amorphous materials: ≥3. In this specification, a plating film with a crystallinity of 0%, determined according to the following formula (1), is considered amorphous, and a plating film with a crystallinity of 4% or less is defined as a concept that includes a plating film with a crystallinity of 0%.

[0037] In this embodiment, it is desirable that the plated film is less prone to generating polishing marks due to the brittle mode when polished. For example, observe the polishing marks that occur when polished using the film polishing apparatus shown in Figure 6. The film polishing apparatus 40 shown in Figure 6 has drive rollers 41 and 42 that are arranged in close proximity to each other, with parts of their circumferential surfaces touching, and are individually rotatable horizontally and individually around their axes. The apparatus is configured so that the rod material 21A for the piston rod to be processed can be placed on the boundary between these adjacent drive rollers 41 and 42. By placing the rod material 21A on the boundary between the closely positioned drive rollers 41 and 42, the supported rod material 21A can be rotated around its axis in accordance with the rotation of the drive rollers 41 and 42.

[0038] A backup roller 43 is horizontally positioned above the rod material 21A, on the boundary between the drive rollers 41 and 42, and is circumferentially rotatable. Polishing film 44 can be supplied from a film supply device (not shown) to the bottom side of this backup roller 43. The polishing film 44 is a strip-shaped film, and can be supplied to the bottom side of the backup roller 43 from a film supply device (not shown) located on one side perpendicular to the central axis of the backup roller 43, as indicated by arrow a. This film 44 can also be moved and wound onto a film winding device (not shown) located on the other side perpendicular to the central axis of the backup roller 43, as indicated by arrow b. The required length of polishing film 44 can be wound onto the film supply device and continuously supplied to the bottom side of the backup roller 43.

[0039] The backup roller 43 is supported by a vertical movement mechanism (not shown) that allows it to rotate freely while maintaining a horizontal position, and the vertical movement mechanism also allows for fine adjustment of its own vertical position. Above the backup roller 43 is a pressure head 45 supported by a vertical-forward-backward movement mechanism (not shown). This pressure head 45 can press the backup roller 43 downward with a predetermined pressure while descending from slightly above the backup roller 43 as shown by arrow c. Furthermore, the pressure head 45 is supported by the aforementioned vertical-forward-backward movement mechanism so as to be movable in the axial direction of the backup roller 43 as shown by arrow d, and the pressure head 45 is supported so as to be able to reciprocate in the axial direction of the backup roller 43 while pressing the backup roller 43 downward with a predetermined force.

[0040] Using three film polishing devices as shown in Figure 6, for example, a #600 polishing film is loaded into the first film polishing device, a #400 polishing film into the second film polishing device, a #1000 polishing film into the third film polishing device, and a #2000 polishing film into the fourth film polishing device, and a polishing test of a piston rod is performed. These polishing conditions are equivalent to those applied to sample 1 shown in Figure 28 of International Publication No. 2021 / 193107. During polishing, the rotation speed of the drive rollers 41 and 42 was set to 1400 rpm, and the pressing force of the pressure head 45 was set to 0.15 to 0.3 MPa. The steel rod used for the test can have a diameter of 22 mm and a length of 200 mm.

[0041] When the above-described polishing process is performed, the sample will either produce polishing marks of the brittle mode as shown in Figures 10(A) and (B), as shown in the later examples and comparative examples, or produce polishing marks of the ductile mode as shown in Figures 11(A) and (B). The polishing marks shown in Figures 10(A) and (B) are, as is clear from the magnified photograph in Figure 10(B), samples exhibiting a brittle mode of polishing marks, which are caused by brittle fracture. The polishing marks shown in Figures 11(A) and (B) are, as is clear from the magnified photograph in Figure 11(B), samples exhibiting polishing marks of the ductile mode without tearing marks.

[0042] When the plating film that produces polishing marks as shown in Figures 10(A) and (B) is used as the plating film for the piston rod 21 shown in Figures 1 to 4, polishing the outer diameter in step S7 shown in Figure 5 results in brittle mode polishing marks showing tearing marks on the surface, making it impossible to finish to the desired surface roughness. The film polishing apparatus 40 shown in Figure 6 is a device for finishing the outer surface of a piston rod, and is an important device for polishing the outer surface of the piston rod to a desired surface roughness. If polishing marks of the brittle mode described above occur during this outer diameter polishing, it will adversely affect the finishing accuracy of the outer surface of the piston rod, making it impossible to obtain excellent sliding properties, wear resistance, and corrosion resistance.

[0043] Therefore, as the plating film to be applied to the piston rod 21 used in this embodiment, it is preferable to observe the polishing marks on the surface of the sample subjected to the above-described polishing test, for example, using a microscope at 200x magnification. Then, measure the number and width of the polishing marks within the same field of view, measure the number of polishing marks with a width of 8 μm or more, and evaluate the quality of the plating film based on the number of polishing marks generated, and then use the selected plating film. The reason for using polishing marks with a width of 8 μm or more as the criterion is that, in the examples described later, when polishing tests were conducted on multiple samples, the polishing marks in the brittle mode, which resulted in tearing marks, were predominantly 8 μm or wider. Based on the results of the examples described later, it is desirable to use a chromium plating film that contains one or more impurity elements selected from carbon and oxygen in addition to chromium, with a chromium content of 60-80 at%, carbon content of 16.5-30 at%, and an indentation hardness of 7 GPa or higher on the outer surface.

[0044] The aforementioned chromium plating film, for example, when using a strongly acidic plating bath containing the aforementioned trivalent chromium salt, carboxylate, pH buffer, and conductive salt, has a pH of 0.1 to 0.6, a bath temperature of 55 to 80°C, and a cathode current density of 45 to 100 A / dm². 2 It can be obtained by plating under these conditions. Under the conditions described above, the plating film formed on the outer surface of the piston rod 21 has a hardness of 7 GPa or higher. With a plating film having a hardness of 7 GPa or higher, even when the outer diameter is polished using the film polishing apparatus 40 shown in Figure 6 under the conditions described above, tear marks (fracture marks due to the brittle mode) are unlikely to occur. Furthermore, if the plating film has the above-mentioned composition containing chromium: 60-80 at% and carbon: 16.5-30 at%, even when the outer diameter is polished using the film polishing apparatus 40 shown in Figure 6 under the aforementioned conditions, tear marks are less likely to occur. Therefore, even after the polishing process described above, a piston rod 21 can be obtained that does not show any tearing marks.

[0045] By the way, in the above-described embodiment, a plated member was described in which a plating film was deposited on the piston rod 21 from a trivalent chromium bath. However, the plating film may also be applied to the sliding surfaces of various sliding members, including automotive parts such as piston rings and brake pistons, as well as shafts of hydraulic equipment and gravure rolls of printing equipment. [Examples]

[0046] Several steel rods (22 mm in diameter, 200 mm in length) made of low-carbon steel were prepared as test materials, and a strongly acidic plating bath (hereinafter abbreviated as A1) containing chromium chloride, glycine, boric acid, and ammonium chloride was used as the trivalent chromium plating bath. For bath A1, the bath temperature is 65-75°C, and the current density is 50-90 A / dm². 2 Plating was performed under pH conditions of 0.3 to 0.46 to form a chromium plating film approximately 20 μm thick on the surface of the test material. When using a chromium plating bath consisting of weakly acidic blue chromium (product name of Atotech) (hereinafter abbreviated as A2) as the trivalent chromium plating bath, the bath temperature is 48-60°C and the current density is 40-90 A / dm². 2 Plating was performed under conditions of pH: 5.39 to 5.65 to form a chromium plating film with a thickness of approximately 20 μm on the surface of the test material.

[0047] Figure 7 shows the results of determining the degree of crystallinity (%) of each plated film based on equation (1) above, when forming the plated films of Examples 1-6 and Comparative Examples 1-12 shown in Figure 9 later, by adjusting the current density to form each plated film at various deposition rates (film formation rates). In all deposition rates, only a halo pattern was observed in the range of 2θ:30-60° in the XRD (X-ray diffraction) analysis results, indicating that the plated film as it was formed was an amorphous film with a degree of crystallinity of 0.0%.

[0048] Figures 8A to 8C show the component analysis results for each plating film of Examples 1 to 6 and Comparative Examples 1 to 12, which are shown in Figure 9 later. The component analysis was performed using an electron probe microanalyzer under the conditions of acceleration voltage: 10kV and irradiation current: 100nA. As shown in Figure 8A, the plated films deposited from trivalent chromium baths formed at various deposition rates contained carbon as an impurity element, oxygen as shown in Figure 8B, and approximately 80 at% chromium as shown in Figure 8C. Figure 9 shows the film components. In the film components of Examples 1 to 6, carbon, the most abundant impurity element, was present at approximately 18-23 at%, and oxygen, the second most abundant element, was present at approximately 1.5-5 at%. More specifically, carbon was present at 18.1-22.8 at%, and oxygen at 1.7-4.6 at%. Figures 8 and 9 show that the carbon content can be adjusted by adjusting the deposition rate (film formation rate) of the plated film. The deposition rate can be set to approximately 0.2-4 μm / min, or even faster, and can be adjusted by changing the amount of chromium chloride added to the chromium plating bath. Therefore, it can be seen that the carbon content can be adjusted within the range of 8-30 at% by adjusting the plating conditions.

[0049] Figure 9 shows the results of measuring the indentation hardness of these multiple plating films and analyzing the components of the samples for which hardness was measured. The indentation hardness values ​​shown are those measured using instrumented indentation hardness measurement by the nanoindentation method (ISO 14577). The indentation load was set to 20 mN. In Figure 9, samples with an indentation hardness of 7.5 GPa or higher on the outer surface and a carbon content of 16.5 at% or higher are labeled as examples, while samples that do not meet the above conditions are labeled as comparative examples. Furthermore, samples prepared using a strongly acidic plating bath are labeled as bath type A1, and samples prepared using a weakly acidic plating bath are labeled as bath type A2. Since all of these plating films were amorphous based on the XRD analysis results, the degree of crystallinity is indicated as 0.0%.

[0050] The samples of Examples 1 to 6 shown in Figure 9 had an indentation hardness of 7.5 GPa or higher. When the polishing test described below was performed, it was determined that the polishing marks were in the ductile mode, so in Figure 9, the ductile mode is indicated by the minus sign next to the polishing mark mode. The samples of Comparative Examples 1 to 12 shown in Figure 9 either have a hardness of less than 16 GPa or a carbon content outside the range of 16.5 to 30 at%. However, when the polishing tests described below were performed, it was determined that the polishing marks were in a brittle mode, and therefore, in Figure 9, "brittle mode" is indicated in the column for polishing mark mode.

[0051] "Polishing test" Using four film polishing devices as shown in Figure 6, a polishing test of a piston rod was performed by loading a #600 polishing film into the first film polishing device, a #400 polishing film into the second film polishing device, and a #2000 polishing film into the third film polishing device. These polishing conditions are the same as those applied to sample 2 shown in Figure 28 of International Publication No. 2021 / 193107. During polishing, the rotation speed of the drive rollers 41 and 42 was set to 1400 rpm, and the pressing force of the pressure head 45 was set to 0.15 to 0.3 MPa.

[0052] After the polishing test, Figure 10(A) shows an image of the surface of the piston rod of Comparative Example 1 taken with a scanning electron microscope at 500x magnification, and Figure 10(B) shows an image taken at 5000x magnification. After the polishing test, Figure 11(A) shows an image of the surface of the piston rod of Example 1 taken with a scanning electron microscope at 500x magnification, and Figure 11(B) shows an image taken at 5000x magnification. Vertical lines can be seen along the vertical direction in Figures 10 and 11, and these lines indicate that the polishing was performed by moving the polishing film along the direction of these vertical lines. As shown in the magnified view in Figure 10(B), the sample of Comparative Example 1 shows polishing marks (peel marks) that appear to be caused by tearing fracture resulting from brittle fracture, which are arranged along the direction of movement of the polishing film. In contrast, as shown in the enlarged view in Figure 11(B), the sample from Example 1 exhibits flow-shaped polishing marks along the direction of movement of the polishing film due to shear deformation.

[0053] For the piston rods of both the example and the comparative example, the number and width of friction marks present within a 200x field of view were observed at three locations each using an optical microscope. As a result, multiple polishing marks with a width of 8 μm or more were observed in all comparative examples, and it was confirmed that tearing fracture occurred in polishing marks with a width of 8 μm or more. In contrast, no polishing marks with tearing fracture were observed in the example samples. Based on these results, we determined that when the above-described polishing test is performed on the plated film, measuring the number of polishing marks with a width of 8 μm or more can serve as an indicator of whether the plated film enters the brittle mode or the ductile mode in the polishing test described above.

[0054] Figure 12 shows the results of measuring the film hardness (GPa) and the number of polishing marks (marks / mm) with a width of 8 μm or more for the samples from Examples 1 to 6 and Comparative Examples 1 to 12. Figure 13 shows the results of measuring the carbon content (at%) in the coating and the number of polishing marks (marks / mm) with a width of 8 μm or more for the samples of Examples 1 to 6 and Comparative Examples 1 to 12. Figure 14 shows the correlation between coating hardness and carbon content in the coating, based on the results shown in Figures 12 and 13.

[0055] As shown in Figure 12, it can be seen that the occurrence of brittle mode polishing marks decreases above a film hardness of 7.5 GPa, with the boundary being around 7.5 GPa. On the other hand, in the range of 5 to 7 GPa, only brittle mode polishing marks occur. As shown in Figure 13, it can be seen that the occurrence of brittle mode polishing marks disappears around 16.5 at% carbon content. On the other hand, in the range below 16 at%, mild brittle mode polishing marks and brittle mode polishing marks occurred. In light of these results, as shown in Figure 14, when polishing piston rods using the polishing test described above, it is desirable to use a plating film containing 16.5 at% or more carbon and with an indentation hardness of 7 GPa or higher on the outer surface. With these plating films, it can be determined that the plating film is deposited from a trivalent chromium bath, mainly consisting of ductile mode polishing marks, and does not produce tear marks. Furthermore, considering that the limit of carbon that can be incorporated into the plating film is approximately 30 at%, depending on the amount of organic components added to the plating bath, the effective carbon content of the plating film is considered to be 16.5 to 30 at%. With a carbon content within this range, the hardness of the plating film can be obtained in the range of 7 to 15 GPa, as shown in Figure 14.

[0056] On the other hand, in the range of plating film hardness 6.0 to 6.9 GPa and carbon content 10 to 16 at%, polishing marks of the brittle mode occur as described above. Furthermore, even with a film hardness of 6.9 GPa or higher, in the range of carbon content less than 15 at%, it is thought that the film exhibits either the brittle mode or an asymptotic form before changing to the ductile mode. Regarding the changes in each range, it is thought that different chromium carbide films are formed, and accordingly, the film hardness and carbon content shown in each range change. These results suggest that the properties of the coating originate from organic components in the plating bath, such as carboxylates, pH buffers, and conductive salts. Furthermore, it is believed that the amount of organic components incorporated into the coating changes depending on the pH, bath temperature, and current density conditions during plating.

[0057] Figure 15(A) shows the results of X-ray diffraction analysis of the sample of Comparative Example 1, and Figure 15(B) is a 200x magnification surface photograph showing the polishing marks of the same sample. In the surface photograph shown in Figure 15(B), three polishing marks (accompanied by tearing fracture) with a width of 8 μm or more, indicated in front of the arrows, can be seen. Figure 16(A) shows the results of X-ray diffraction analysis of the sample from Example 1, and Figure 16(B) is a surface photograph showing the polishing marks of the same sample. From the X-ray diffraction analysis results shown in Figure 15(A), it can be seen that the sample of Comparative Example 1 is a 100% amorphous sample (crystallinity 0.0%) showing only a halo pattern. In contrast, from the X-ray diffraction analysis results shown in Figure 16(A), it can be seen that the sample of Example 1 is a 100% amorphous sample (crystallinity 0.0%) showing only a halo pattern. This sample has a carbon content of 22.8 at%, which is higher than 16.5%, and a hardness of 12.7 GPa, which is higher than 7 GPa, thus exhibiting a ductile mode.

[0058] According to the aforementioned equation (1), crystallinity (peak integral intensity ratio) = {(crystalline) / (crystalline + amorphous)} × 100%, the integral intensity ratio in equation (1) is determined in Figure 16(A) with 2θ: 30~60°, crystalline full width at half maximum: <3, amorphous full width at half maximum: ≥3. Based on the X-ray diffraction analysis results shown in Figure 16(A), the degree of crystallinity calculated using equation (1) is 0.0%. The sample shown in Figure 16(B) shows a reduction in the wide polishing marks present in the structure shown in Figure 15(B). This demonstrates that even amorphous samples with a crystallinity of 0.0% can have fewer brittle polishing marks.

[0059] As shown in Figure 9 above, in Examples 1 to 6, a ductile mode plating film was obtained by setting the hardness to 7.5 to 12.7 GPa in a plating film having a composition of chromium content 72 to 80 at%, carbon content 19 to 23 at%, and oxygen content 1.7 to 4.6 at%.

[0060] Figure 17 is a graph showing the relationship between deposition rate (film formation rate) and the size of oriented chromium crystal grains for the plating films of Examples 2 and 5 and Comparative Examples 1, 4, 9, and 12. Figure 17 shows that the ductile mode coating has chromium grains smaller than 10 nm. It also shows that the chromium grain size increases as the deposition rate increases. The grain size shown here represents the length of at least one side of each particle.

[0061] Figure 18 shows a TEM image of the ductile mode cross-section of the plating film from Example 2. The presence of chromium crystal grains could not be confirmed from Figure 18. The microstructure of the plated film was observed using an operational transmission electron microscope (STEM), with an acceleration voltage of 200kV. Figure 19 shows TEM images of the brittle mode cross-section of the coating for Comparative Examples 1 and 4, which used bath type A1. Chromium crystal grains were confirmed to be present in both Comparative Example 1 and Comparative Example 4.

[0062] Figure 20 shows a TEM image of the cross-section of the coating in ductile mode for Example 5, which uses bath type A2. The presence of chromium crystal grains could not be confirmed from Figure 20. Figure 21 shows TEM images of the brittle mode cross-section of the coating for Comparative Examples 9 and 12, which used bath type A2. The presence of chromium crystal grains was confirmed in both Comparative Example 9 and Comparative Example 12.

[0063] Figure 22 shows the electron diffraction pattern in the cross-section of the coating in ductile mode for Example 2 using bath type A1. The measurement conditions for determining the electron diffraction pattern were an acceleration voltage of 200 kV, an electron beam wavelength λ of 0.00251 nm at 200 kV, and a camera length of 399.4 mm. Figure 22 shows that the presence of a first ring was confirmed at a d-value (interlattice plane distance) of 2.0 to 2.3 Å. This indicates the presence of chromium, which is a microcrystal without orientation, as the matrix material (d-value of chromium: 2.04 Å). On the other hand, since no diffraction spots indicating crystalline material were observed on the first ring, it is possible that it does not contain chromium crystal grains.

[0064] Figure 23 shows the electron diffraction patterns in the cross-section of the coating in the brittle mode for Comparative Example 1 (Figure 23(A)) and Comparative Example 4 (Figure 23(B)) using bath type A1. From Figure 23, in both (A) and (B), the first ring was observed at a d-value (interlattice plane distance) of 2.0 to 2.3 Å. This means that chromium, which is a microcrystal without orientation, is present as the matrix material (d-value of chromium: 2.04 Å). On the other hand, since diffraction spots indicating crystalline material can be observed on the first ring, it can be seen that oriented chromium crystal grains are present.

[0065] Figure 24 shows the electron diffraction pattern in the cross-section of the coating in ductile mode for Example 5, which uses bath type A2. Figure 24 shows that the presence of a first ring was confirmed at a d-value (interlattice plane distance) of 2.0 to 2.3 Å. This indicates the presence of chromium, which is a microcrystal without orientation, as the matrix material (d-value of chromium: 2.04 Å). On the other hand, since no diffraction spots indicating crystalline material were observed on the first ring, it is possible that it does not contain chromium crystal grains.

[0066] Figure 25 shows the electron diffraction patterns in the cross-section of the coating in the brittle mode for Comparative Example 9 (Figure 25(A)) and Comparative Example 12 (Figure 25(B)) using bath type A2. From Figure 25, in both (A) and (B), the presence of a first ring can be confirmed at positions with d-values ​​(interlattice plane distances) of 2.0 to 2.3 Å. This means that chromium, which is a microcrystal without orientation, is present as the matrix material (d-value of chromium: 2.04 Å). On the other hand, since diffraction spots indicating crystalline material can be confirmed on the first ring, it can be seen that oriented chromium crystal grains are present. [Explanation of Symbols]

[0067] 1…Shock absorber (cylinder device) 2…Inner cylinder 3…Outer cylinder 15… Oil seal 21… Piston rod 25... Piston A... Sliding range

Claims

1. A plated member having a plating film on its outer surface mainly composed of chromium deposited from a trivalent chromium bath containing at least chromium, carbon, and oxygen, wherein the plating film contains chromium: 60-80 at%, carbon: 16.5-30 at%, oxygen: 2-6 at%, chlorine or iron at 5 at% or less, and the remainder consists of components derived from complexing agents (carboxylates), pH buffers, and conductivity salts, and the indentation hardness of the outer surface is 7 GPa or higher. A plated material in which the crystallinity calculated from the peak integral intensity ratio of the measured value obtained by X-ray diffraction and the following equation (1) is 4% or less. Crystallinity (peak integral intensity ratio) = {(crystalline) / (crystalline + amorphous)} × 100% ... (1) However, the indentation hardness mentioned above refers to the value obtained by instrumented indentation hardness measurement using the nanoindentation method (ISO 14577), and the integrated intensity ratio in equation (1) refers to the value obtained by XRD (X-ray difference) analysis with 2θ: 30 to 60°, crystalline full width at half maximum: <3, and amorphous full width at half maximum: ≥3.

2. The plated member according to claim 1, wherein the plated film does not have diffraction spots at positions with interlattice plane distance d values ​​of 2.0 to 2.2 Å in a film inspection using electron diffraction.

3. The plated member according to claim 1 or claim 2, wherein the plated member is a sliding contact member that is slidably contacted by a sliding component.

4. A method for manufacturing a plated member having a plated coating formed by plating with chromium deposited from a trivalent chromium bath as the main component, comprising a plating step of forming a plated coating consisting of a hard layer with chromium deposited from a trivalent chromium bath as the main component on the surface of the plated member, wherein the plating step is performed in a plating bath containing a trivalent chromium salt, a carboxylate salt, a pH buffer, and a conductive salt, with a pH of 0.2 to 5.7 and a bath temperature of 55 to 80°C, and a cathode current density of 45 to 100 A / dm ２ The plating film is formed under the following conditions: The aforementioned plating film is a plating film mainly composed of chromium deposited from a trivalent chromium bath containing at least chromium, carbon, and oxygen, wherein the plating film contains chromium: 60-80 at%, carbon: 16.5-30 at%, oxygen: 2-6 at%, chlorine or iron at 5 at% or less, and the remainder consists of components derived from complexing agents (carboxylates), pH buffers, and conductivity salts, and the indentation hardness of the outer surface is 7 GPa or higher. A method for manufacturing plated components.

5. A method for manufacturing a plated member having a plated coating formed by plating with chromium deposited from a trivalent chromium bath as the main component, comprising a plating step of forming a plated coating consisting of a hard layer with chromium deposited from a trivalent chromium bath as the main component on the surface of the plated member, wherein the plating step is performed in a plating bath containing a trivalent chromium salt, a carboxylate salt, a pH buffer, and a conductive salt, with a pH of 0.2 to 5.7 and a bath temperature of 55 to 80°C, and a cathode current density of 45 to 100 A / dm ２ The plating film is formed under the following conditions: The aforementioned plating film is a plating film mainly composed of chromium deposited from a trivalent chromium bath containing at least chromium, carbon, and oxygen, wherein the plating film contains chromium: 60-80 at%, carbon: 16.5-30 at%, oxygen: 2-6 at%, chlorine or iron at 5 at% or less, and the remainder consists of components derived from complexing agents (carboxylates), pH buffers, and conductivity salts. The aforementioned plating film does not have diffraction spots at positions with interlattice plane distance d values ​​of 2.0 to 2.2 Å, as determined by film inspection using electron diffraction. A method for manufacturing plated components.

6. The method for manufacturing a plated member according to claim 4, wherein the plated member is a sliding contact member that is in sliding contact with a sliding component.

7. The method for manufacturing a plated member according to claim 4, wherein the crystallinity of the plated film, calculated from the peak integral intensity ratio of the measured value of the X-ray diffraction measurement and the following equation (1), is 4% or less. Crystallinity (peak integral intensity ratio) = {(crystalline) / (crystalline + amorphous)} × 100% ... (1) However, the integral intensity ratio in equation (1) above is the value obtained in XRD (X-ray difference) analysis with 2θ: 30 to 60°, crystalline full width at half maximum: <3, amorphous full width at half maximum: ≥3.

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