Plated member and production method thereof

Abstract

To provide a plated member and a production method thereof.SOLUTION: A plated member relating to the present invention includes a plating film on the outer surface of the plated member. The film is composed of chromium as a primary component using a trivalent chromium bath including at least chromium, carbon, and oxygen. In the plating film, chromium: 60at% or more and carbon: 1at%-30at% are included. In addition, the indentation hardness of the outer surface is 11.1 GPa or more. In the TEM image taken by scanning transmission electron microscopy, the grain diameter of a chromium crystal grain with orientation, which is crystallized in the chromium base metal of microcrystals without orientation, is 15 nm or larger. The ratio of the chromium crystal grain occupied in the base metal is 3% or more. In the electron diffraction pattern by scanning transmission electron microscopy, the film has a diffraction spot at a position where the lattice plane distance d value is 2.0-2.3Å.SELECTED DRAWING: Figure 23

Description

[Technical Field]

[0001] The present invention relates to a plated member and a method for producing the same. [Background technology]

[0002] Patent Document 1 below describes a technology in which a chrome plating layer of trivalent chromium, which is less toxic and less likely to cause pollution than hexavalent chromium, is used on a plate-making roll. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-143169 Summary of the Invention [Problem to be solved by the invention]

[0004] In the chrome plating film formed on the rods that sliding parts slide against, chrome plating film using a trivalent chrome bath is considered promising as an alternative to hexavalent chrome plating film. However, research by the present inventors has revealed that when a rod on which a chromium plating film is formed using a conventional trivalent chromium bath is polished, brittle fracture (pulling fracture) of the plating film occurs.

[0005] The problem to be solved by the present invention is to provide a plated member such as a rod having a chromium plating film formed using a trivalent chromium bath that is less susceptible to tearing damage during polishing, and a method for producing the same. [Means for solving the problem]

[0006] The plated member according to the present invention has, on its outer surface, a plating coating whose main component is chromium, which is formed using a trivalent chromium bath containing at least chromium, carbon, and oxygen. The plating coating contains 60 at% or more chromium and 1 at% to 30 at% carbon, and has an outer surface indentation hardness of 11.1 GPa or more. In a TEM image obtained by scanning transmission electron microscopy, oriented chromium crystal grains precipitated in a non-oriented microcrystalline chromium matrix have a grain size of 15 nm or more and account for 3% or more of the matrix. The electron diffraction pattern obtained by scanning transmission electron microscopy has a diffraction spot at a position where the lattice plane distance d value is 2.0 to 2.3 Å. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a plated member having a chromium plating film that is mainly composed of chromium deposited from a trivalent chromium bath, which is environmentally friendly compared to hexavalent chromium, and that is less susceptible to damage by peeling during polishing. Also, it is possible to provide a technique for producing such a plated member. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing the overall configuration of a shock absorber equipped with a piston rod as a first embodiment of a plated member according to the present invention, taken along a cross section including a center line CL. [Figure 2] FIG. 2 is a side view showing the general shape of the piston rod. [Figure 3] FIG. 2 is a diagram showing the upper structure of the shock absorber, and is an enlarged partial cross-sectional view of part A in FIG. [Figure 4] 2 is a diagram showing the structure of the tip end of the piston rod, and is an enlarged partial cross-sectional view of part B in FIG. 1. FIG. [Figure 5] FIG. 4 is a flow chart showing an example of a manufacturing process of the piston rod. [Figure 6] FIG. 2 is a perspective view showing a main part of an example of a polishing device used to polish the outer diameter of the piston rod. [Figure 7]1 is a graph showing the relationship between the film formation rate and the crystallinity of the plating films formed in the examples. [Figure 8] 1 is a graph showing the relationship between the film formation rate and the impurity element concentration of the plating film formed in the examples. [Figure 9] 1 is a table showing physical property values ​​of plating films formed in Examples. [Figure 10] 1 is a table showing the relationship between the physical property values ​​of the plating films formed in the examples and the heat treatment temperature. [Figure 11] 1A and 1B show brittle-mode polishing marks formed on the plating film of the comparative sample, where (A) is an enlarged photograph at a magnification of 500 times, and (B) is an enlarged photograph at a magnification of 5000 times. [Figure 12] 1A and 1B show ductile-mode polishing marks formed on the plating film of the example sample, where (A) is an enlarged photograph at a magnification of 500 times, and (B) is an enlarged photograph at a magnification of 5000 times. [Figure 13] 1A is a diagram showing the results of X-ray diffraction analysis of a comparative sample, and FIG. 1B is a surface photograph showing polishing marks on the same sample. [Figure 14] 1A is a diagram showing the results of X-ray diffraction analysis of an example sample heat-treated at 250° C., and FIG. 1B is a surface photograph showing polishing marks on the same sample. [Figure 15] 1A is a diagram showing the results of X-ray diffraction analysis of an example sample heat-treated at 300° C., and FIG. 1B is a surface photograph showing polishing marks on the same sample. [Figure 16] 1 is a graph showing the relationship between the heat treatment temperature (baking temperature) and the maximum polishing mark width in the example samples and the comparative example samples. [Figure 17] 1 is a graph showing the relationship between the heat treatment temperature (baking temperature) and the number of polishing marks with a width of 8 μm or more in the example samples and the comparative sample. [Figure 18] 1 is a graph showing the relationship between the heat treatment temperature (baking temperature) and the coating hardness for example samples and comparative example samples. [Figure 19] 1 is a graph showing the relationship between the heat treatment temperature (baking temperature) and the crystallinity in the example samples and the comparative sample. [Figure 20] 1 is a graph showing the relationship between the coating hardness and the number of polishing marks with a width of 8 μm or more for example samples and comparative example samples. [Figure 21] 1 is a graph showing the relationship between the degree of crystallinity and the number of polishing marks with a width of 8 μm or more in the example samples and the comparative sample. [Figure 22] 1 is a graph showing the relationship between the coating hardness and the crystallinity of example samples and comparative sample samples. [Figure 23] FIG. 10 is a diagram showing a TEM image of a cross section of a coating in brittle mode for a comparative example sample. [Figure 24] FIG. 10 is a diagram showing a TEM image of a cross section of a coating in a ductile mode for an example sample. [Figure 25] FIG. 1 is a diagram showing an electron diffraction pattern of chromium crystal grains in a TEM image of an example sample. [Figure 26] 1 is a graph showing the relationship between the chromium crystal ratio and the number of polishing marks of 8 μm or more for example samples and comparative sample. [Figure 27] 1 is a graph showing the relationship between chromium crystal grains and the number of polishing marks of 8 μm or more for example samples and comparative sample. [Figure 28] 1 is a graph showing the relationship between the chromium crystal ratio and chromium crystal grains as determined by TEM for an example sample and a comparative example sample. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, a shock absorber (cylinder device) equipped with a piston rod as one embodiment of the plated member according to the present invention will be described. The embodiments described below are specifically described to provide a better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified. Furthermore, the scale of the drawings used to explain the embodiments below has been changed appropriately to make each part easier to see.

[0010] FIG. 1 is a partial cross-sectional view showing the overall structure of a shock absorber (cylinder device) 1 equipped with a piston rod 21 as an example of a plated member according to the present invention. A plated coating, which will be described later, is formed on the outer peripheral surface of the piston rod 21. Before describing the plated coating, the overall configuration of the shock absorber 1 will be described.

[0011] "Cylinder device" The cylinder device 1 shown in Fig. 1 is a shock absorber used in suspension devices for automobiles and railway vehicles, specifically in strut-type suspension devices for automobiles. This cylinder device 1 has a cylindrical inner tube (cylinder) 2 in which a working fluid is sealed, and a cylindrical outer tube 3 with a bottom that is larger in diameter than the inner tube 2 and is located on the outer periphery of the inner tube 2, forming a reservoir chamber R between the inner tube 2 and the outer tube 3 in which a working fluid and a working gas are sealed. This cylinder device 1 is a double-tube shock absorber in which the inner tube 2 is located inside the outer tube 3. In Fig. 1, CL indicates the center line of the inner tube 2 and the outer tube 3.

[0012] The outer cylinder 3 has a cylindrical side wall 7 and a bottom 8 that closes one axial end of the side wall 7. The inner cylinder 2 is cylindrical. The inner cylinder 2 is engaged with the bottom 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 7 via an annular rod guide 11 attached to the other axial end of the inner cylinder 2. The base valve 13 is disposed coaxially with the outer cylinder 3 , and the rod guide 11 is fitted to the inner cylinder 2 and the outer cylinder 3 to support the other end of the inner cylinder 2 coaxially with the outer cylinder 3 . An oil seal 15 is disposed on the rod guide 11 on the side opposite to the bottom 8. A locking portion 16 is formed on the other axial end of the side wall portion 7 by bending it inward, 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 interior 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 provided on one end side 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, which passes through the rod guide 11 and the oil seal 15 and protrudes to the outside from one end side of the inner cylinder 2 and the outer cylinder 3. The large-diameter portion 21a of the piston rod 21 is inserted slidably inside the rod guide 11 and inside the oil seal 15. Therefore, the oil seal 15 is a sliding part relative to the piston rod 21.

[0014] A small diameter portion 21b is formed on the tip side of the piston rod 21, and a piston 25 is inserted into 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 at a position close to the small diameter portion 21b, and a ring-shaped internal stopper 24 is attached so as to engage with this annular groove 21c. A ring-shaped rebound rubber 19 is disposed on the internal stopper 24.

[0015] As shown in FIG. 2, the sliding range A' is the portion of the large diameter portion 21a of the piston rod 21 between a position P1 that is farther away from the annular groove 21c and a connecting portion P2 with the bolt portion 21d that serves as the attachment portion to the vehicle body. The outer peripheral surface of the piston rod 21, including the sliding range A', is plated with a chromium-based plating film using a trivalent chromium bath, which will be described in detail later.

[0016] The piston rod 21 moves axially integrally with the piston 25. The oil seal 15, through which the large diameter portion 21a of the piston rod 21 is inserted, seals the gap 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 Fig. 4, passages 27 and 28 are formed in piston 25, penetrating in the axial direction. As shown in Fig. 1, passages 27 and 28 allow communication between first chamber 22 and second chamber 23. Piston 25 is formed with an annular disc valve 28a that can close passage 28 by abutting against the upper surface of piston 25. Piston 25 is formed with an annular disc valve 27a that can close passage 27 by abutting against the lower surface of piston 25.

[0017] When the piston rod 21 moves toward the compression side (downward in FIG. 1), increasing the amount of penetration into the inner cylinder 2 and the outer cylinder 3, the piston 25 moves in a direction narrowing 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. When the upper end of the piston rod 21 moves in the extension direction (upward in FIG. 1) to increase the amount of protrusion from the inner cylinder 2 and the outer cylinder 3, the piston 25 moves in the direction narrowing 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, thereby exerting a damping force.

[0018] 1, the base valve 13 is formed with passages 29, 29 that penetrate the base valve 13 in the axial direction. The passage 29 allows communication between the second chamber 23 and the reservoir chamber R. An annular disc valve 30 is disposed on the bottom side of the base valve 13, which is capable of closing one of the passages 29 by abutting against the bottom side of the base valve 13. An annular disc valve 31 is disposed on the top side of the base valve 13, which is capable of closing the other passage 29 by abutting against the top side of the base valve 13.

[0019] The disc valve 30 is a check valve that allows the flow of hydraulic fluid from the second chamber 23 to the reservoir chamber R through one passage 29, while restricting the flow of hydraulic fluid in the opposite direction through the passage 29. The disc valve 30 is a valve that opens the passage 29 when the piston rod 21 moves toward 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 hydraulic fluid from the reservoir chamber R to the second chamber 23 via the other passage 29, while restricting the flow of hydraulic fluid in the opposite direction via the passage 29. The disc valve 31 is a valve that opens the passage 29 when the piston rod 21 moves to the extension side 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] 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 a relative moving member that is the mounting target. The cylinder device 1 is used by, for example, connecting the outer end of the piston rod 21 to the body side of the vehicle and connecting the mounting eye 33 to the wheel side of the vehicle. In the cylinder device 1, the piston rod 21 and the piston 25 slide integrally within the inner cylinder 2, changing the volumes 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] 3, the rod guide 11 is substantially stepped and annular, with a large diameter portion 11a formed on one axial side and a small diameter portion formed on the other axial side. The large diameter portion 11a is fitted to the inner peripheral surface of the outer cylinder 3, and the small diameter portion is fitted to the inner peripheral surface of the inner cylinder 2. An annular protrusion 11c having a circular ring shape that protrudes in the axial direction is formed at the end of the large diameter portion 11a of the rod guide 11, and a communication hole 11d that axially penetrates the rod guide 11 is formed corresponding to the portion of the annular protrusion 11c. The communication hole 11d opens to the reservoir chamber R on the side opposite to the annular protrusion side in the axial direction of the rod guide 11.

[0022] The oil seal 15 has a seal member main body 37, which is an integrally molded product in which a metal annular member 36 is fitted into a synthetic rubber sealing material 35, and a metal annular spring 38. The annular member 36 maintains the shape of the sealing material 35 and provides the seal member main body 37 with the strength necessary to fix it to the target portion. The seal member main 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 protrusion 11c. The seal member 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 provide a sealing function.

[0023] When the vehicle is running, the cylinder device 1 is configured so that the piston rod 21 or the outer cylinder 3 is repeatedly subjected to external impact forces in the axial direction. Each time an impact force is received, the piston rod 21 moves toward the contraction side or the extension side, and a damping force is applied at that time. In this way, the cylinder device 1 functions as a shock absorber used in the strut-type suspension of an automobile. In addition, the outer peripheral surface of the piston rod 21 is provided with a plated coating, which is a hard layer made of chromium using a trivalent chromium bath, as described below. This plated coating is less likely to cause brittle fracture (plucking fracture) when the outer peripheral surface of the piston rod 21 is polished to a desired surface roughness during manufacture. If the outer peripheral surface of the piston rod 21 is polished to a desired surface roughness and has a plated coating, as described in detail below, the piston rod 21 will exhibit excellent sliding characteristics and obtain excellent wear resistance, even if the large diameter portion 21a of the piston rod 21 repeatedly slides against the seal material 35.

[0024] FIG. 5 is a process flow diagram showing an example of a method for manufacturing the piston rod 21. As shown in step S1 of FIG. 5, a rod material such as a steel bar made of a type of steel required to form the piston rod 21 is prepared. In step S2, this rod material is subjected to heat treatment such as induction hardening and tempering, and is subjected to a surface hardening treatment suitable for a piston rod. Next, in step S3, cutting is performed to obtain the general shape shown in FIGS. 1 to 4, and in step S4, outer diameter grinding is performed. Next, the piston rod having the general shape shown in Figures 1 to 4 is subjected to a base plating treatment such as nickel plating in step S5, and then to a chromium plating treatment mainly containing chromium using a trivalent chromium bath in step S6 (plating step). Note that in step S5 where the base plating treatment is performed, other base plating treatments may be performed instead of nickel plating, or the base plating may be omitted by omitting step S5 where the plating treatment is performed. After plating in step S6, heat treatment is performed in step S7. The heat treatment can be performed at 250°C to 400°C for several hours. Note that after plating, baking can also be performed to remove hydrogen, and this baking treatment can also be used as heat treatment. Next, in step S7, the outer diameter of the piston rod is polished and precision-finished to obtain a piston rod having a final surface shape.

[0025] This embodiment is characterized by the plating treatment performed in step S6, the heat treatment performed in step S7, and the chromium plating coating, which is a hard layer mainly composed of chromium and formed on the piston rod using a trivalent chromium bath. The chromium plating film used in this embodiment is mainly composed of chromium, and contains, as other elements, one or more impurity elements selected from carbon (C) and oxygen (O). For example, it is preferable that the chromium plating film contains 60 at % or more of chromium and 1 at % to 30 at % of carbon, and that the surface indentation hardness is 11.1 GPa or more. The indentation hardness is a 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] The chrome plating film may contain, among the above elements, an oxygen concentration of about 2 at% to 6 at%.Furthermore, in addition to the above elements, the chrome plating film may contain, as an impurity element, either chlorine (Cl) or iron (Fe) at a concentration of about 5 at% or less. Furthermore, the carbon content is more preferably about 8 at % to 25 at %, and the oxygen content is more preferably about 2 at % to 5 at %.

[0027] Chromium, the main component of the trivalent chromium bath that forms the plating film, is desirable to contain as much as possible. The carbon contained in the plating film is thought to be derived from the organic components that make up the plating bath, as described below. If the carbon content is less than 8 at%, it is thought that there is a high risk of brittle-mode ripping 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 thought to be 30 at%. The oxygen content (oxygen concentration) in the plating film is in the range of 2 at% to 6 at%. If the oxygen content is less than 2 at%, there is a problem that the likelihood of occurrence of brittle mode ripping marks increases, and if the oxygen content exceeds 6 at%, there is a problem that the likelihood of occurrence of brittle mode ripping marks increases similarly to the above.

[0028] In the plating film of this embodiment, elemental analysis can be performed using an electron probe micro analyzer (EPMA), and conditions such as an acceleration voltage of 10 kV and a probe current of 100 nA can be used. In this specification, when specifying a numerical range, if the upper and lower limit values ​​are indicated with "to" then the concept includes both the upper and lower limit values ​​unless otherwise specified. Therefore, the above-mentioned 1 at% to 30 at% means a range of 1 at% or more and 30 at% or less.

[0029] The impurity elements other than chromium mentioned above are presumed to originate from organic components contained in the plating bath, such as carboxylates, pH buffers, and conductivity salts, which will be explained below. In the chromium plating film according to this embodiment, the content of impurities contained in the plating film varies depending on the plating treatment conditions, and it is believed that the current density, bath temperature, and pH conditions contribute to this. The reason for this is thought to be that the ability of additives to be incorporated during chromium deposition is affected by the current density (reduction rate), bath temperature (reduction rate), and pH (complex formation, reduction rate).

[0030] [Coating structure by TEM analysis of hard trivalent chromium plating coating] The structure of the plating film of this embodiment is preferably such that, in a TEM image, the grain size of oriented chromium crystal grains precipitated in a non-oriented microcrystalline chromium base material is 23 nm or more, and the ratio of chromium crystal grains to the base material is 4% or more.Furthermore, in an electron diffraction pattern, it is preferable that a chromium diffraction spot is present at a position where the interplanar distance d value is 2.0 to 2.3 Å (chromium d value: 2.04 Å). In this embodiment, a scanning transmission electron microscope (STEM) can be used to observe the structure of the plated coating, and an acceleration voltage of 200 kV or the like can be selected. When obtaining an electron diffraction pattern, the measurement conditions may be an acceleration voltage of 200 kV, an electron beam wavelength λ at 200 kV of 0.00251 nm, and a camera length of 399.4 mm.

[0031] In this embodiment, the plating bath used in the chromium plating treatment may contain components such as a trivalent chromium salt, a complexing agent as an additive, a pH buffer, and a conductivity salt. As the trivalent chromium salt, chromium chloride, chromium sulfate, basic chromium sulfate, etc. can be used, but among these, it is preferable to use chromium chloride. As the complexing agent, carboxylates such as glycine, formic acid, oxalic acid and acetic acid can be used, with glycine being preferred among these. As the pH buffering agent, boric acid, citric acid, etc. can be used, with boric acid being preferred. As the conductive salt, ammonium chloride, ammonium sulfate, ammonium sulfonate, etc. can be used, but among these, ammonium chloride is preferably used.

[0032] When a strongly acidic trivalent plating bath is used, it is desirable to select a plating bath that is weakly acidic, such as a strongly acidic bath having a pH of less than 0.1, for example, a strongly acidic bath having a pH of 0.1 to 0.6, more preferably a strongly acidic bath having a pH of 0.2 to 0.5. If the pH is strong acidity of 0.1 or less, it is not possible to obtain the chromium-based plating film using a trivalent chromium bath as intended in this embodiment. If the pH exceeds 0.6, the gloss of the plating film will deteriorate, and the uptake of impurity elements during chromium deposition will change depending on the film formation rate, making it impossible to obtain the chromium-based plating film as intended in this embodiment. When a weakly acidic trivalent chromium bath is used as the plating bath, Blue Chrome (trade name, manufactured by Atotech) can be used as an example of a commercially available product. When Blue Chrome is used, the pH range can be selected from, for example, 5.2 to 5.8. The pH value is more preferably in the range of 5.4 to 5.6.

[0033] The higher the current density during plating, the faster the film formation rate and the better the productivity. However, to obtain the above composition, the current density should be 45 to 100 A / dm 2 The film formation rate can be selected from the range of 100 to 1500. Under conditions of high current density and high concentration of trivalent chromium salt, the film formation rate is increased, but the incorporation of impurity elements during chromium deposition varies depending on the film formation rate. It is desirable to select a film formation rate suitable for achieving the desired chromium and carbon contents described above in the resulting plated film. It is desirable that the plating bath temperature be high, and for example, a range of 55°C to 80°C can be selected. The plating bath should be stirred gently by moving the plating solution around the surface to be plated. Anode materials with good insolubility, such as Pt, Ti, Ir, and graphite, can be used.

[0034] The chromium plating film formed in the first step of the plating process described above has an amorphous structure when formed. In the second step, this amorphous plating film is preferably subjected to a heat treatment at a heating temperature of 250°C to 400°C to form a plating film with a crystallinity of 5% or more. The crystallinity is a value calculated from the peak integrated intensity ratio of the measured value of X-ray diffraction measurement and the following formula (1). Crystallinity (peak integrated intensity ratio) = {(crystalline) / (crystalline + amorphous)} × 100%...Equation (1) The integrated intensity ratio in equation (1) indicates a value determined in XRD (X-ray diffraction) analysis under the conditions of 2θ: 30° to 60°, half width of crystalline: <3, and half width of amorphous: ≧3. The heat treatment is performed to increase the crystallinity of the plated coating to 5% or more. The heat treatment time is preferably about 1.5 to 4.0 hours, for example, about 2 hours. Heat treatment at a temperature exceeding 400°C is not desirable because it changes the mechanical properties of the steel material that constitutes the piston rod 21. The crystallinity is more preferably in the range of 5% to 95%.

[0035] It is desirable that the plating film of this embodiment is less likely to produce polishing marks due to the brittle mode when polished. For example, the polishing marks produced when polishing is performed using the film polishing device shown in Figure 6 are observed. The film polishing device 40 shown in Figure 6 has drive rollers 41 and 42 arranged close to each other with parts of their peripheral surfaces close to each other and horizontally and rotatably about their respective axes, and 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. When the rod material 21A is placed on the boundary between the drive rollers 41 and 42 that are arranged close to each other, the supported rod material 21A can be rotated around its axis as the drive rollers 41 and 42 rotate.

[0036] A backup roller 43 that can rotate freely around the periphery is arranged horizontally above the rod material 21A, on the boundary between the drive rollers 41 and 42, and a polishing film 44 can be supplied to the bottom side of this backup roller 43 from a film supply device (not shown). The polishing film 44 is a strip-shaped film, and can be supplied to the bottom side of the backup roller 43 as indicated by arrow a from a film supply device (not shown) provided on one side in a direction perpendicular to the central axis of the backup roller 43. The film 44 can also be moved and taken up as indicated by arrow b onto a film take-up device (not shown) provided on the other side in a direction perpendicular to the central axis of the backup roller 43. The required length of polishing film 44 can be wound around the film supply device and continuously supplied to the bottom side of the backup roller 43.

[0037] The backup roller 43 is supported by a vertical movement mechanism (not shown) so that it can rotate freely while maintaining a horizontal position, but the vertical movement mechanism also allows fine adjustment of its own vertical position. A pressure head 45, supported by a vertical / front-rear movement mechanism (not shown), is provided above the backup roller 43. This pressure head 45 can press the backup roller 43 downward with a predetermined pressure while descending from a position slightly above the backup roller 43, as indicated by arrow c. The pressure head 45 is also supported by the vertical / front-rear movement mechanism (not shown) so that it can move axially of the backup roller 43, as indicated by arrow d, and is supported so that it can move back and forth in the axial direction of the backup roller 43 while pressing the backup roller 43 downward with a predetermined force.

[0038] Three film polishing devices shown in Figure 6 are used, and a piston rod polishing test is performed by loading, for example, #600 polishing film into the first film polishing device, #400 polishing film into the second film polishing device, and #2000 polishing film into the third film polishing device. The polishing conditions were the same as those applied to Sample 2 shown in Figure 28 of WO 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 in the test had a diameter of 22 mm and a length of 200 mm.

[0039] When the above-mentioned polishing process is performed, for example, the sample will have brittle mode polishing marks as shown in Figures 11(A) and (B), as shown in the examples and comparative examples below, or the sample will have ductile mode polishing marks as shown in Figures 12(A) and (B). The polishing marks shown in Figures 11(A) and (B) are from a sample having brittle mode polishing marks that indicate ripping marks due to brittle fracture, as is clear from the enlarged photograph of Figure 11(B). The polishing marks shown in Figures 12(A) and (B) are from a sample having ductile-mode polishing marks without ripping marks, as is clear from the enlarged photograph of Figure 12(B).

[0040] If the plating coating that generates polishing marks shown in Figures 11(A) and (B) is used as the plating coating of the piston rod 21 shown in Figures 1 to 4, polishing of the outer diameter in step S8 shown in Figure 5 will result in brittle-mode polishing marks indicative of ripped marks on the surface, and the desired surface roughness cannot be achieved. The film polishing device 40 shown in Fig. 6 is a device that finishes 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 have a negative impact on the finishing accuracy of the outer surface of the piston rod, making it impossible to obtain excellent sliding properties, wear resistance, and corrosion resistance.

[0041] Therefore, for the plating coating to be provided on the piston rod 21 used in this embodiment, it is preferable to observe the polishing marks on the surface of the sample that has been subjected to the above-mentioned polishing test using a microscope at a magnification of 200 times, measure the number and width of the polishing marks within the same field of view, count the number of polishing marks with a width of 8 μm or more, and evaluate the quality of the plating coating based on the number of polishing marks. The reason why polishing marks of 8 μm or more in width were used as the evaluation criterion is that in the examples described below, polishing tests were conducted on multiple samples, and it was found that the majority of brittle mode polishing marks that produced ripped marks were 8 μm or more in width. From the results of the examples described later, it is desirable to use a chromium plating film that contains, in addition to chromium, one or more impurity elements selected from carbon and oxygen, and that contains chromium: 60 at% or more and carbon: 1 at% to 30 at% and has an outer surface indentation hardness of 11.1 GPa or more after heat treatment and a crystallinity of 5% or more.

[0042] The above-mentioned chromium plating film is formed, for example, using a plating bath containing the above-mentioned trivalent chromium salt, carboxylate salt, pH buffer and conductive salt, at a pH of 0.1 to 0.6, a bath temperature of 55°C to 80°C, and a cathode current density of 45 A / dm 2 ~100A / dm 2 The plating can be performed under the following conditions. The plated coating formed and heat-treated under the above conditions on the outer circumferential surface of the piston rod 21 has a hardness of 11.1 GPa or more and a crystallinity of 5% or more. The above plated coating with a hardness of 11.1 GPa or more and a crystallinity of 5% or more is unlikely to produce ripped marks (marks of fracture due to brittle mode) even when the outer diameter is polished under the above conditions using the film polishing device 40 shown in Figure 6. Therefore, even if the above-mentioned polishing process is performed, the piston rod 21 can be obtained without any ripping marks.

[0043] In the above-described embodiment, a plated member in which a chromium plating coating is formed on the piston rod (sliding contact member) 21 using a trivalent chromium bath has been described. However, the plating coating may also be applied to the sliding surfaces of various sliding contact members, such as automobile parts such as piston rings and brake pistons, shafts of hydraulic equipment, and gravure rolls of printing equipment. [Example]

[0044] Several low-carbon steel rods (22 mm in diameter, 200 mm in length) were prepared as test materials, and a trivalent chromium plating bath containing chromium chloride, glycine, boric acid, and ammonium chloride was used. The bath temperature was 65-75°C, and the current density was 45-100 A / dm 2 The plating treatment was carried out under the conditions of pH: 0.3 to 0.46, and a trivalent chromium plating film having a thickness of about 20 μm was formed on the surface of the test material.

[0045] Figure 7 shows the crystallinity (%) of each plating film calculated based on the above-mentioned formula (1) when plating films were formed on each test material at five different deposition rates by adjusting the current density. At each deposition rate, only a halo pattern was observed in the 2θ range of 30 to 60° in the XRD (X-ray diffraction) analysis, indicating that the as-deposited plating film was an amorphous film with a crystallinity of 0.0%.

[0046] Figure 8 shows the results of component analysis of the plating films formed at five different deposition rates. The component analysis was performed using an electron probe microanalyzer under the conditions of an accelerating voltage of 10 kV and a probe current of 100 nA. As shown in Figure 8, it was confirmed that the chromium plating films formed using trivalent chromium baths at various deposition rates contained trace amounts of chlorine and iron as impurity elements in addition to carbon and oxygen. Of these impurity elements, carbon, which is the most abundant, is present at approximately 7 at% to 23 at% and oxygen, which is the second most abundant, is present at approximately 3 at% to 5 at%. In addition, it can be seen that chlorine and iron are present in trace amounts near the measurement limit. From Figure 8, it can be seen that the carbon content can be adjusted by adjusting the deposition rate of the plating film. It is also possible to select conditions for the deposition rate to exceed 2.0 μm / min, and this can also be adjusted by changing the amount of chromium chloride added to the chromium plating bath. Therefore, it can be recognized that the carbon content can be adjusted within the range of 5 at% to 30 at% by adjusting the plating conditions.

[0047] Three types of plating films were selected from these multiple plating films, and the indentation hardness of these samples was measured. The hardness-measured samples were then subjected to component analysis, and the crystallinity was calculated. The results are shown in Figure 9. Note that the indentation hardness is the value measured by instrumented indentation hardness measurement using the nanoindentation method (ISO 14577). An indentation load of 20 mN was used. The plating films of the test materials 1 to 3 shown in FIG. 9 had an indentation hardness of 8.5 GPa to 9.0 GPa, a crystallinity of 0% (amorphous) in XRD, a chromium content of 76% to 88%, and a carbon content of 8% to 16%.

[0048] The specimens 1 to 3 shown in Figure 9 were subjected to the polishing test described below, and it was determined that the polishing marks were of brittle mode, so "brittle mode" is indicated in the polishing mark mode column in Figure 9. The pH of the plating solution used to prepare the specimens is as shown in Figure 9. For specimens 1 to 3, the specimens were heat-treated at 200°C, 250°C, and 300°C for 2 hours each, and then the indentation hardness was measured, the crystallinity was calculated, and the coating composition was analyzed. The results are shown in Figure 10.

[0049] "Polishing test" The polishing test was carried out using four film polishing devices as shown in Figure 6. The first film polishing device was loaded with #600 polishing film, the second film polishing device was loaded with #400 polishing film, and the third film polishing device was loaded with #2000 polishing film. The polishing conditions were the same as those applied to Sample 2 shown in Figure 28 of WO 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 MPa to 0.3 MPa.

[0050] Among the samples subjected to the polishing test, for the sample of Comparative Example 1-1, which was heat-treated at 200°C for 2 hours with Test Material 1, an image of the surface of the piston rod taken with a scanning electron microscope at 500x magnification is shown in Figure 11(A), and an image taken at 5000x magnification is shown in Figure 11(B). Vertical lines running up and down in Figure 11 can be seen, and traces of polishing that were made by moving the polishing film along the direction of these vertical lines can be seen. As shown in the enlarged view of Figure 11(B), polishing marks (pick marks) that appear to be caused by brittle fracture appear along the direction of movement of the polishing film. These polishing marks can be described as brittle mode polishing marks. In addition, for the sample of Example 1-3, which was heat-treated at 300°C for 2 hours compared to Test Material 1, an image of the surface of the piston rod taken with a scanning electron microscope at a magnification of 500 times is shown in Figure 12(A), and an image taken at a magnification of 5000 times is shown in Figure 12(B). As shown in the enlarged view of Figure 12(B), flow-type polishing marks are generated along the direction of movement of the polishing film due to shear deformation. These polishing marks can be described as ductile mode polishing marks.

[0051] Figure 13(A) shows the results of X-ray diffraction analysis of Sample 3 (amorphous plating film), and Figure 13(B) is a 200x magnification photograph of the surface of the same sample showing the polishing marks. In the surface photograph shown in Figure 13(B), three polishing marks (accompanied by ripping fractures) with widths of 8 μm or more can be seen, as indicated by the arrows. Fig. 14 shows the results of X-ray diffraction analysis of Example 3-4, in which Sample 3 was subjected to a heat treatment (baking treatment) at 250°C for 2 hours. From the results of X-ray diffraction analysis shown in Fig. 14, it can be determined that the sample of Example 3-4, in which Sample 3 was subjected to a heat treatment at 250°C, is a sample with a high degree of crystallinity, with a sharpened peak. Figure 15(A) shows the results of X-ray diffraction analysis of a sample of Test Material 3 that was subjected to heat treatment (baking treatment) at 300°C for 2 hours, and Figure 15(B) is a surface photograph showing the polishing marks on the same sample.

[0052] The X-ray diffraction analysis results shown in Figure 13(A) indicate that Sample 3 is a 100% amorphous sample (crystallinity 0.0%) that shows only a halo pattern. In contrast, the X-ray diffraction analysis results shown in Figure 15(A) indicate that the sample of Example 3-5, which was obtained by heat-treating Sample 3 at 300°C, is a crystalline sample with a sharpened peak. The amorphous plating film shown in Figure 13(B) had three polishing marks with a width of 8 μm or more, whereas the crystalline plating film shown in Figure 15(B) did not have any polishing marks with a width of 8 μm or more.

[0053] According to the above-mentioned formula (1), crystallinity (peak integrated intensity ratio) = {(crystalline) / (crystalline + amorphous)} × 100%, the integrated intensity ratio of formula (1) is calculated in Figure 13(A) with 2θ: 30° to 60°, half width of crystalline: <3, and half width of amorphous: ≥ 3. From the analysis results by X-ray diffraction shown in FIG. 13(A), the crystallinity calculated based on formula (1) is 0%. From the X-ray diffraction analysis results shown in Figure 14(A), the crystallinity calculated based on formula (1) is 13.2%, and from the X-ray diffraction analysis results shown in Figure 15(A), the crystallinity calculated based on formula (1) is 12%.

[0054] For each sample shown in Figure 10 and several other piston rods fabricated under the same polishing conditions as these samples, the number and width of friction marks present within a 200x field of view were observed using a metallurgical microscope at three locations on each rod. As a result, multiple polishing marks with widths of 8 μm or more were confirmed in both the sample that had not been heat-treated and the sample that had been heat-treated at 200°C, and it was confirmed that damage due to ripping occurred in polishing marks with widths of 8 μm or more. Furthermore, no polishing marks with ripping marks were observed in the example sample shown in Figure 10. Based on the above results, it was determined that when the above-mentioned polishing test was performed on a plated film, counting the number of polishing marks with a width of 8 μm or more would provide an indication of whether the plated film would be in brittle mode or ductile mode in the above-mentioned polishing test.

[0055] Therefore, it can be seen that a crystalline plating film with a crystallinity of 5% or more as measured by XRD, such as a plating film with a crystallinity of 7% to 44% as shown in Figure 10, is less likely to produce problematic brittle-mode polishing marks. Furthermore, Figure 10 shows the particle size (nm) of oriented chromium crystal grains precipitated in a non-oriented microcrystalline chromium matrix in a TEM image obtained by scanning transmission electron microscopy, and the ratio of oriented chromium crystal grains to the chromium matrix. As shown in Figure 10, a TEM image obtained using a scanning transmission electron microscope (STEM) shows that a plating film in which the grain size of oriented chromium crystal grains precipitated in a non-oriented microcrystalline chromium base material is 15 nm or greater and the ratio of chromium crystal grains to the base material is 3% or greater is less likely to produce problematic brittle-mode polishing marks.

[0056] FIG. 16 is a graph showing the relationship between the heat treatment temperature (referred to as baking temperature in the figure) and the maximum width of polishing marks produced in the above-mentioned polishing test for plated films formed at various deposition rates (film formation rates). It can be seen that the sample with the heat treatment temperature set to 200°C has multiple polishing marks with a width of 8 μm or more, but when the heat treatment temperature is set to 250°C or 300°C, no polishing marks with a width of 8 μm or more are produced. FIG. 17 is a graph showing the relationship between the heat treatment temperature (baking temperature) and the number of polishing marks with a width of 8 μm or more generated in the above-mentioned polishing test for plated films formed at various deposition rates (film formation rates). It can be seen that the sample with the heat treatment temperature set to 200°C has multiple polishing marks with a width of 8 μm or more, but when the heat treatment temperature is set to 250°C or 300°C, no polishing marks with a width of 8 μm or more are produced.

[0057] FIG. 18 is a graph showing the relationship between the heat treatment temperature (baking temperature) and the film hardness for plated films formed at each (deposition rate) film formation rate. Among the samples that were not heat-treated and the samples that were heat-treated at a temperature of 200°C, there were samples with a hardness of less than 11.1 GPa, but it was found that when the heat treatment temperature was set to 250°C or 300°C, the hardness of the plated coating exceeded 11.1 GPa. FIG. 19 is a graph showing the relationship between the heat treatment temperature (baking temperature) and the degree of crystallinity for plated films formed at different film formation rates. It can be seen that when the heat treatment temperature exceeds 200°C, crystallization progresses, and when the heat treatment temperature exceeds 250°C, the degree of crystallinity increases, resulting in a plated coating with a crystallinity of 5% or more.

[0058] FIG. 20 shows the results of measuring the hardness (GPa) of the plated coating and the number of polishing marks (marks / mm) with a width of 8 μm or more for the plated coating formed at each (deposition rate) film formation rate. FIG. 21 shows the results of measuring the crystallinity (%) of the plated coating and the number of polishing marks (marks / mm) with a width of 8 μm or more for the example sample and the comparative sample. FIG. 22 shows the correlation between the hardness of the plated film and the crystallinity of the plated film, based on the results shown in FIGS. 20 and 21. As shown in Figure 21, it can be seen that there is a large difference in the number of brittle mode polishing marks at a crystallinity of 5% or higher. At crystallinity levels of less than 1%, the number of brittle mode polishing marks varies depending on the test material, but at levels of 5% or higher, the frequency of occurrence is low in all samples, which is desirable.

[0059] As shown in FIG. 22, it can be seen that samples with a plated film surface indentation hardness higher than the plated film hardness of approximately 11.1 GPa have a crystallinity of 5% or higher. A surface indentation hardness of 10.3 GPa or higher is preferable because it can suppress the number of polishing marks with a width of 8 μm or more, and a surface indentation hardness of 10.9 GPa or higher is desirable because the frequency of occurrence is even lower. For samples with a heat treatment temperature of 250°C or higher, all samples exceeded 11 GPa (11.1 GPa or higher), which was preferable.

[0060] 23 shows a TEM image and an electron diffraction pattern of Comparative Example 4-2. In the TEM image, it was confirmed that black precipitates were present in places in the uniformly spread base material. The electron diffraction pattern of the base material confirmed the presence of a first ring at a d value (distance between lattice planes) of 2.0 to 2.3 Å. The absence of a diffraction spot indicates the presence of chromium in the form of microcrystalline, non-oriented crystals (d value of chromium: 2.04 Å). On the other hand, the electron diffraction pattern of the black precipitates confirmed the presence of a faint first ring at a d value of 2.0 to 2.3 Å. Multiple diffraction spots were also observed on the ring pattern. This indicates that the black precipitates are oriented chromium crystal grains. TEM analysis can thus be used to confirm the crystalline state of the object. In the electron diffraction pattern, the non-oriented microcrystalline portion is referred to as the "chromium matrix," and the oriented crystalline black precipitates are referred to as "chromium crystal grains."

[0061] Figure 24 shows the results of TEM measurement of the cross section of the brittle mode plating coating of Comparative Example 4-1. The TEM image shows that the maximum size of the chromium crystal grains is 13 nm. Furthermore, the ratio of the base material to the chromium crystal grains was calculated by binarizing the image, and the chromium crystal grain ratio was found to be 0.24%. The measurement conditions for obtaining the electron diffraction pattern were an accelerating voltage of 200 kV, an electron beam wavelength λ of 0.00251 nm at 200 kV, and a camera length of 399.4 mm. The electron diffraction pattern confirmed the presence of a faint first ring at a d value of 2.0 to 2.3 Å. Multiple diffraction spots were also confirmed on the ring pattern. This confirmed the presence of oriented chromium crystal grains.

[0062] Figure 25 shows the results of TEM measurement of the cross section of the plating coating of Example 4-3 in ductile mode. The TEM image shows that the maximum size of the chromium crystal grains is 25 nm. In addition, the ratio of the base material to the chromium crystal grains was calculated by binarizing the image, and the chromium crystal ratio was found to be 15.45%. The electron diffraction pattern confirmed the presence of a faint first ring at a d value of 2.0 to 2.3 Å. Multiple diffraction spots were also observed on the ring pattern, confirming the presence of oriented chromium crystal grains.

[0063] 24, 25, and 10, it can be seen that increasing the heat treatment temperature increases the chromium crystal grain size and also increases the chromium crystallinity.

[0064] Figure 26 shows the results of measuring the chromium crystal ratio (%) obtained from TEM images and the number of polishing marks (marks / mm) with a width of 8 μm or more for each sample of Test Material 3, Examples 3-1, 3-4, 4-3, and Comparative Examples 4-1 and 4-2. As shown in Figure 26, it can be seen that there is a large difference in the number of brittle mode polishing marks at a chromium crystal ratio of 3%. At 3% or more, the frequency of occurrence is low in all samples, which is desirable.

[0065] FIG. 27 shows the results of measuring the chromium crystal grain size (μm) and the number of polishing marks of 8 μm or more (numbers / mm) for each of the samples of Test Material 3, Examples 3-1, 3-4, 4-3, and Comparative Examples 4-1 and 4-2. As shown in Figure 27, it can be seen that there is a large difference in the number of brittle mode polishing marks that occur in samples with chromium crystal grains larger than 15 nm, with this being the dividing line. It can be seen that above 15 nm, the frequency of occurrence is low in all samples, which is desirable.

[0066] FIG. 28 shows the correlation between the chromium crystal ratio (%) obtained from the TEM image and the chromium crystal grain size, based on the results shown in FIGS. 26 and 27. As shown in Figure 28, the chromium crystal ratio in the TEM image reaches a threshold of 3%, and in samples with a higher chromium crystal ratio, the particle size of the chromium crystal grains is 15 nm or more. These results suggest that the physical properties of the coating are derived from organic components in the plating bath, such as carboxylates, pH buffers, and conductive salts. Furthermore, the amount of organic components incorporated into the coating is thought to change depending on the conditions of pH, bath temperature, and current density during plating. Furthermore, by performing heat treatment to produce a plating coating with a crystallinity of 5% or more as measured by XRD, or by measuring a chromium crystal ratio of 3% or more and a chromium crystal grain size of 15 nm or more as measured by image binarization in a TEM image, it is expected that a plating coating without ripping marks can be produced, even if it is finished by polishing. [Industrial Applicability]

[0067] According to the above-described aspects of the present invention, a plated member can be provided that includes a chromium plating film that is primarily made using a trivalent chromium bath, which is less environmentally problematic than hexavalent chromium, and that is less susceptible to damage by ripping during polishing. Furthermore, a method for producing this plated member can be provided. Therefore, the present invention has great industrial applicability. [Explanation of symbols]

[0068] 1...Shock absorber (cylinder device), 2...inner cylinder (cylinder), 3...outer cylinder, 15...Oil seal, 21... Piston rod (sliding contact member), 25...piston, A'...sliding range.

Claims

1. A plated member having, on its outer surface, a plating film containing chromium as a main component, which is formed using a trivalent chromium bath containing at least chromium, carbon, and oxygen, The plating film is chromium: 60 at% or more, carbon: 1 at% to 30 at%; and the indentation hardness of the outer surface is 11.1 GPa or more; In a TEM image obtained by scanning transmission electron microscopy, the grain size of oriented chromium crystal grains precipitated in a non-oriented microcrystalline chromium matrix is ​​15 nm or more, and the ratio of chromium crystal grains to the matrix is ​​3% or more, A plated member having a diffraction spot at a position where the interplanar distance d value is 2.0 to 2.3 Å in an electron diffraction pattern obtained by scanning transmission electron microscopy.

2. The plated member according to claim 1 , wherein the plated member is a sliding contact member that is in sliding contact with a sliding part.

3. 3. The plated member according to claim 1, wherein the oxygen concentration of the plated coating is 2 at % to 6 at %.

4. A plated member having, on its outer surface, a plating film containing chromium as a main component, which is formed using a trivalent chromium bath containing at least chromium, carbon, and oxygen, The plating film is chromium: 60 at% or more, carbon: 1 at% to 30 at%; and the indentation hardness of the outer surface is 11.1 GPa or more; In a TEM image obtained by scanning transmission electron microscopy, the grain size of oriented chromium crystal grains precipitated in a non-oriented microcrystalline chromium matrix is ​​15 nm or more, and the ratio of chromium crystal grains to the matrix is ​​3% or more, a method for producing a plated member in which an electron diffraction pattern obtained by scanning transmission electron microscopy has a diffraction spot at a position where the interplanar distance d value is 2.0 to 2.3 Å, a plating step of forming a plating film consisting of a hard layer containing chromium as a main component on the surface of the plated member, the plating step including a first step of forming an amorphous plating film in XRD analysis, and a second step of heating and crystallizing the amorphous plating film formed in the first step; A method for manufacturing plated members.

5. The plating step is carried out in a plating bath containing a trivalent chromium salt, a carboxylate salt, a pH buffer, and a conductivity salt, the bath temperature being 55°C to 80°C, and the cathode current density being 45 A / dm ２ ~100 A / dm ２ The plating film is formed under the following conditions: The method for producing a plated member according to claim 4 .

6. The method for producing a plated member according to claim 4 or 5, wherein the plated member is a sliding contact member that is in sliding contact with a sliding part.

7. 6. The method for producing a plated member according to claim 4, wherein the oxygen concentration of the plated film is set to 2 at % to 6 at %.

8. 6. The method for producing a plated member according to claim 4, wherein the heating temperature in the second step is 250°C to 400°C.

Images