JP2005200771A - Method for producing chrome plated component and plating bath used for applying the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method capable of stably obtaining a chrome plated component maintaining excellent corrosion resistance even in the case it undergoes heat history, with high efficiency. <P>SOLUTION: Using a chrome plating bath containing organic sulfonic acid, plating is conducted by application of a pulse current to thereby form a crack-free lower chrome layer S<SB>1</SB>on a steel substrate M. The lower chrome layer has a compressive residual stress of 100 MPa or more, desirably, 150 MPa or more. Subsequently, in the same plating bath by application of a direct current, electroplating is performed to form a cracked upper chrome layer S<SB>2</SB>on the lower chrome layer S<SB>1</SB>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a production method for obtaining a chromium-plated part by applying industrial chromium plating to a surface and a plating bath used for carrying out the production method.

  Chromium plating, particularly hard chrome plating, is often used as industrial chrome plating for parts that require wear resistance because it provides a hard and low-coefficient metal film (chromium layer).

  By the way, according to general-purpose hard chromium plating, there are many cracks that reach the metal base in the obtained chromium layer, so-called channel cracks, and as it is, the medium causing the corrosion reaches the metal base and corrosion occurs, When steel is used as the metal substrate, so-called red rust is unavoidable. On the other hand, the chrome-plated parts are usually used after the plating process by polishing such as buffing to make the surface smooth, but during this polishing process, plastic flow occurs on the surface of the chrome layer and the cracks occur. Is known to be occluded. For this reason, conventional chrome-plated parts have been used after being polished without special anti-corrosion measures.

  However, according to the crack closure due to the plastic flow of the chromium layer, the crack opens due to the shrinkage of the chromium layer due to the subsequent thermal history, and in parts that are used in a high temperature environment of room temperature or higher, the corrosion resistance There was a problem that the decline of the inevitable.

In some cases, as a pretreatment, nickel plating or copper plating is applied to form a base with a film thickness comparable to that of the chromium layer, and hard chromium plating is applied on this base. According to this, there is a problem that the plating process has to be performed twice while changing the process, and a decrease in productivity and an increase in process cost due to an increase in the process are inevitable.
Others adopt a measure to prevent the cracks from penetrating into the substrate by changing the plating bath and applying chrome plating to stack two chrome layers with different crystal orientations. (For example, Japanese Patent Laid-Open No. 4-350193), even in this case, the two-step process is not changed, and a fundamental solution is not achieved.

  In others, a pulse current is supplied and so-called pulse plating is performed to obtain a crack-free chromium layer (for example, Japanese Patent Laid-Open No. 3-207884), but pulse plating is simply performed. However, the tensile stress remains in the chromium layer, and there is a drawback that a large crack is easily generated by receiving heat, so that the fundamental solution cannot be achieved.

  Furthermore, in others, a surge bath is used and an irregular pulse current is supplied to obtain a low-stress (non-stress) decorative chromium layer without cracks (for example, Japanese Patent Publication No. 43-20082). No.), and the stress has a gradient (in the case of compressive stress, the stress value shifts to the tension side as the plating thickness increases), and the average compressive stress is not sufficient (small), so the low When a stress chromium layer is used as the base and a nickel plating layer or a chromium layer with general cracks is laminated as the upper layer plating, there is a problem that the crack is propagated due to the tensile stress of the upper layer chromium layer. It does not lead to a solution. In the chromium plating bath disclosed in Japanese Patent Publication No. 43-20082, the average compressive residual stress is limited to about 100 MPa, no matter how the pulse current waveform, bath temperature, and current density are adjusted.

  The present invention has been made in view of the above-described conventional problems, and its object is to obtain a highly efficient and stable chrome-plated part that maintains excellent corrosion resistance even when it undergoes a thermal history. It is another object of the present invention to provide a plating method suitable for use in carrying out the manufacturing method.

  In order to achieve the above object, one of the methods for producing a chrome-plated part according to the present invention is to perform electroplating using a pulse current in a chrome plating bath, and there is no crack on the surface and is 100 MPa or more, preferably 150 MPa or more. A chromium layer having the following compressive residual stress is deposited.

  Another method of the present invention is to perform electroplating using a pulsed current in a chromium plating bath, and to provide an underlying chromium layer having no cracks on the surface and having a compressive residual stress of 100 MPa or more, preferably 150 MPa or more. Then, electroplating is performed in a chromium plating bath to deposit an upper chromium layer having cracks on the underlying chromium layer.

  Further, another method of the present invention is that the underlying chromium having a compressive residual stress which is not cracked on the surface and has a compressive residual stress of 100 MPa or more, preferably 150 MPa or more, which is electroplated using a pulse current in a chromium plating bath. After depositing the layer, electroplating is performed in a chromium plating bath, and an intermediate chromium layer is deposited on the underlying chromium layer. Thereafter, electroplating is performed in the chromium plating bath, and the intermediate chromium layer is deposited on the intermediate chromium layer. And an upper chromium layer having cracks is deposited.

  In the method of manufacturing a chrome-plated part performed as described above, a crack-free chromium layer (underlying chromium layer) having a large compressive residual stress is deposited, so that the generation of new cracks is suppressed and obtained by the compressive residual stress. Chrome plated parts maintain excellent corrosion resistance even after a thermal history. In addition, when depositing an upper chromium layer having cracks on the underlying chromium layer, the hardness of the upper chromium layer can be maximized, which contributes to an improvement in wear resistance. The cracks present in the upper chrome layer function as a sump for retaining the lubricating oil, contributing to a reduction in sliding resistance. Furthermore, when an intermediate chromium layer is deposited between the underlying chromium layer and the upper chromium layer, direct crack propagation from the upper chromium layer to the underlying chromium layer is suppressed, greatly contributing to the stable maintenance of corrosion resistance. It will be a thing.

  By the way, the crack is generated when the thermal history is given because the chromium layer shrinks, and this shrinkage is influenced by the amount of lattice defects present in the crystal grain boundaries of the chromium layer. Therefore, by increasing the crystallite and shortening the grain boundary length, the number of lattice defects is reduced (the grain boundary length is inversely proportional to the size of the crystallite), and the shrinkage of the chromium layer due to thermal history can be suppressed. Become. In the manufacturing method of other chrome-plated parts according to the present invention, focusing on this point, electroplating is performed under a pulse condition in which the crystallite size of the crack-free chrome layer having the compressive residual stress is 9 nm or more. It is characterized by performing.

  The crystallite size of the chromium layer obtained by the general-purpose hard chromium plating process is about 6 nm, and the crystallite of the chromium layer according to the present invention is considerably larger than this. And when it is set as a chromium layer with such a big crystallite, a crack does not arise in the state after passing through heat history as well as the state which performed plating processing, and desired corrosion resistance is secured. . However, if the crystallite size becomes too large, the crystal structure itself of the chromium layer starts to change, so it is desirable to control this crystallite to be less than 16 nm.

  In the present manufacturing method, when electroplating is performed using the pulse current, the plating condition is such that a chromium layer having a compressive residual stress of almost the same magnitude is deposited regardless of the plating thickness, or a plating thickness of 1 μm. In this case, the electroplating is preferably performed under pulse conditions for depositing a chromium layer having a compressive residual stress of 100 MPa or more, preferably 150 MPa or more.

  When using the pulse current described above, the minimum current density of the pulse current is set to an arbitrary value between the maximum current density and zero. At this time, the holding time at the maximum current density of the pulse current can be arbitrarily set in the range of 100 μS to 1400 μS, and the holding time at the minimum current density can be arbitrarily set in the range of 100 μS to 600 μS.

  In this manufacturing method, when performing electroplating for depositing the upper chromium layer described above, a pulse current having a pulse waveform different from the pulse waveform of the pulse current used when depositing the underlying chromium layer is used, or a direct current Can be used. In addition, when performing electroplating for depositing the intermediate chromium described above, a pulse current or a direct current having another different pulse waveform can be used.

  The method of plating treatment in this manufacturing method is arbitrary, and the workpiece may be moved continuously in the plating bath for continuous treatment, or the workpiece may be immersed in the plating bath for batch treatment. . Moreover, when depositing a plurality of chromium layers, they may be deposited in the same plating bath.

  In the manufacturing method, when another chromium layer is laminated on the underlying chromium layer, the outermost chromium layer may be polished. By polishing in this way, the cracks existing on the outermost surface are closed by the plastic flow of the chromium layer, and the corrosion resistance is improved. However, the crack closed by this plastic flow is reopened by the subsequent heat oxidation treatment, but since there is a chromium layer with no crack in the base, the obtained chrome plated part has sufficient corrosion resistance against the occurrence of red rust. Have

In this manufacturing method, a heat oxidation treatment may be performed to form an oxide film mainly composed of Cr ₂ O ₃ on the outermost surface, thereby improving the corrosion resistance of the chromium layer itself and preventing the occurrence of so-called white rust. Be done. In this case, the method of heat oxidation treatment is arbitrary. For example, it can be performed under the same conditions as general-purpose baking treatment or using high-frequency heating. In the US Federal Specification QQ-C-320B, the baking process requires 191 ± 14 ° C. for 3 hours or more when the hardness of the steel base material is HRC 40 or more. Thus, an oxide film mainly composed of Cr ₂ O ₃ can be formed on the surface. In addition, in the case of performing high-frequency heating, for example, the processing can be completed by holding at a high temperature of about 400 ° C. for a short time of about several seconds to several tens of seconds.

  In order to achieve the above object, a plating bath according to the present invention is used for carrying out the above-described method for producing a chromium-plated part, and includes an organic sulfonic acid. In this case, the composition of the plating bath may include chromic acid 100 to 450 g / L, sulfuric acid 1 to 5 g / L, and organic sulfonic acid 1 to 18 g / L.

According to the method for producing a chrome-plated component according to the present invention, a crack-free chrome layer having a large compressive residual stress (underlying chrome layer) is deposited, so that excellent corrosion resistance is maintained even when a thermal history is passed, A chromium-plated part suitable for products used in corrosive and thermal environments can be obtained. Moreover, according to this manufacturing method, by adjusting the pulse conditions, the compressive residual stress and the size of the crystallite can be easily controlled, and a chromium-plated part having desired characteristics can be obtained efficiently. . Moreover, when the upper chromium layer having cracks is deposited on the lower chromium layer without cracks, a chromium plated part having excellent wear resistance and sliding properties can be obtained. When an intermediate chromium layer is deposited between the upper chromium layer, a chromium-plated part with stable corrosion resistance for a long period can be obtained. In addition, when forming an oxide film mainly composed of Cr ₂ O ₃ on the outermost surface, it is possible to reliably prevent the occurrence of white rust caused by corrosion of the chromium layer itself as well as red rust caused by corrosion of the metal substrate. .

  According to the plating bath according to the present invention, the above-described electroplating process using the pulse current can be stably performed.

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

FIG. 1 shows a state of a surface layer portion of a chromium plated part obtained by the first embodiment of the manufacturing method according to the present invention. The chromium layer S ₁ and the upper chromium layer S ₂ having many cracks F are provided in two layers. Here, the underlying chromium layer S ₁ is formed so as to have a compressive residual stress of 100 MPa or more and a crystallite size within a range of 9 nm or more and less than 16 nm. Here, the upper chromium layer S ₂ is formed so as to have a compressive residual stress or a tensile residual stress of less than 100 MPa and a crystallite size of less than 9 nm.

Since the above-described chromium-plated component is provided with the base chromium layer S ₁ having no cracks as a lower layer, even if cracks F are present in the upper chromium layer S ₂ , the medium that causes corrosion is the metal of the steel base material M. The desired corrosion resistance is ensured without reaching the substrate. In addition, since the underlying chromium layer S ₁ has a predetermined compressive residual stress and crystallite size, no new cracks are generated even after a thermal history, and excellent corrosion resistance is maintained. The In addition, since the upper chromium layer S ₂ may have cracks F, it is possible to impart a sufficiently high hardness (900 HV or higher) and sufficient wear resistance. In addition, the large number of cracks F present in the chromium layer S ₂ functions as an oil sump for retaining the lubricating oil, thereby contributing to the improvement of the sliding characteristics.

Here, the two chromium layers S ₁ and S ₂ used a plating process using a pulse current (hereinafter referred to as a pulse plating process) and a direct current in a chromium plating bath containing an organic sulfonic acid. It is formed by performing a two-stage process including a plating process (hereinafter referred to as a general-purpose plating process), and the current density pattern at this time is set as shown in FIG. 2 as an example. In addition, as a chromium plating bath containing organic sulfonic acid, it is desirable to use the component composition shown in Table 1 described in Japanese Patent Publication No. 63-32874.

In FIG. 2, zone A represents the range of the first-stage pulse plating process, zone B represents the range of the second-stage general-purpose plating process, and the pulse current waveform in zone A is the maximum current density I _U. alternating between a minimum current density I _L, and has a maximum current density I _U and the minimum current density I _L and the predetermined time T _1, T ₂ holds to form. Here, the minimum current density I _L is set to zero (off), but may be set to any value between the maximum current density I _U and zero. Also, the holding times T ₁ and T ₂ may be set to the same value or different values. In the present embodiment, the maximum current density I _U and the minimum current density I _L (here, I _L = 0) and the holding times T ₁ and T ₂ held at those current densities are set to appropriate values. Then, a pulse plating process is performed to obtain a base chromium layer S ₁ (FIG. 1) having the above-described predetermined compressive residual stress and crystallite size.

FIG. 3 shows one embodiment of an apparatus for obtaining a chrome-plated part having the _two chrome layers S ₁ and S _{2. The} work (eg, piston rod) W is suspended and supported endlessly. A mounting station 2, an alkaline electrolytic degreasing tank 3, a plating tank 4, a washing tank 5 and a detaching station 6 are arranged in this order under the moving line of the moving hanger 1. The plating tank 4 is divided into an etching treatment tank 4A on the alkaline electrolytic degreasing tank 3 side and a plating treatment tank 4B following this, and the plating tank 4B contains the chromium plating bath containing the organic sulfonic acid described above. Has been.

  Further, the bus bars 7, 8, and 9 are divided and arranged along the alkaline electrolytic degreasing tank 3, the etching processing tank 4A, and the plating processing tank 4B, respectively, and the bus bar 9 along the plating processing tank 4B is further connected to the etching processing tank 4A side. The front bus bar 9A and the rear bus bar 9B on the flush tank 5 side are divided. Among these bus bars, DC power sources 10, 11 and 13 are connected to the bus bar 7 corresponding to the alkaline electrolytic degreasing tank 3, the bus bar 8 corresponding to the etching process tank 4A, and the rear bus bar 9B corresponding to the plating process tank 4B, respectively. Further, a pulse power source 12 is connected to the pre-stage bus bar 9A corresponding to the plating tank 4B.

  On the other hand, the power supply brush 14 provided in the hanger 1 is slidably contacted with each bus bar 7, 8, 9 </ b> A, 9 </ b> B. It has become so. Further, in the alkaline electrolytic degreasing tank 3 and the etching treatment tank 4A, a plurality of cathodes 15 and 16 connected in parallel for each tank are disposed, respectively, and in the plating treatment tank 4B, the previous bus bar 9A and A plurality of anodes 17 and 18 connected in parallel in the rear bus bar 9B unit are arranged, and currents are supplied to the cathodes 15 and 16 and the anodes 17 and 18 from the corresponding power sources 10, 11, 12, and 13, respectively. It is like that. In addition, ammeters 19a and 19b are interposed between the anodes 17 and 18 in the plating tank 4B and the power supplies 12 and 13, respectively.

  In order to perform chrome plating using the above apparatus, first, a work W is mounted on the hanger 1 at the mounting station 6, and the alkaline electrolysis degreasing tank 3 and the etching treatment tank 4 </ b> A are suspended while the work W is suspended on the hanger 1. Are sequentially transferred. Then, the degreasing process using the workpiece W as an anode in the alkaline electrolytic degreasing tank 3 is performed, and the etching process using the work W as an anode is performed in the etching process tank 4A. Subsequently, the work W is transferred to the plating process tank 4B. Here, a chromium plating process using the workpiece W as a cathode is performed.

In the chrome plating process, first, a pulse current having a pulse waveform shown in the A zone of FIG. 2 is supplied from the pulse power supply 12 to the work W through the front bus bar 9A and the anode 17 to perform the pulse plating process. . This pulse plating process is continued while the power supply brush 14 of the hanger 1 that supports the work W in a suspended state is in contact with the front bus bar 9A. Layer S ₁ (FIG. 1) is formed. Thereafter, the power supply brush 14 of the hanger 1 that suspends and supports the work W is transferred onto the rear bus bar 9B, and a direct current is supplied from the DC power source 13 to the work W via the rear bus bar 9B and the anode 18, thereby performing general-purpose plating. Done. The universal plating process, while the power supply brush 14 of the hanger 1 for suspended supporting the workpiece W is in contact with the subsequent bus bar 9B, is continued, thereby on the underlying chrome layer S _1, like in FIG. 1 As shown, an upper chromium layer S ₂ having a large number of cracks F is laminated. The workpiece W is then washed in the washing tank 5 to the separation station 6 where it is removed from the hanger 1.

According to the above apparatus and method, since the two chromium layers S ₁ and S ₂ can be formed while continuously moving the workpiece W in the same chromium plating bath, it is possible to efficiently produce a chromium plated part having excellent corrosion resistance and heat resistance. Can be manufactured.

In the above embodiment, the hard chromium plating process is performed in two stages to form the two underlying chromium layers S ₁ and S _2. However, the present invention omits the upper chromium layer S _2. Thus, only the underlying base chromium layer S ₁ may be formed. In this case, since the underlying chromium layer S ₁ having no cracks is exposed on the surface, it cannot be expected to serve as an oil reservoir as in the above embodiment, but it is sufficient in terms of corrosion resistance.

In the above-described embodiment, the two chromium layers S ₁ and S ₂ are laminated by continuous processing using the apparatus shown in FIG. 3, but one independent unit containing a chromium plating bath is provided. Using the plating tank, the two chromium layers S ₁ and S ₂ may be laminated and formed by batch processing. In this case, a separate controller may be provided to control the power output so that, for example, the current density pattern shown in FIG. 2 is obtained.

Furthermore, in the batch processing, a plating tank for forming the chromium layer S ₁ and a plating tank for forming the chromium layer S ₂ are provided independently, and a pulse current is supplied to the plating tank for forming the chromium layer S ₁ . A direct current may be supplied to the plating tank in which the chromium layer S ₂ is formed, and the two chromium layers S ₁ and S ₂ may be laminated.

FIG. 4 shows the state of the surface layer portion of the chrome-plated part obtained by the second embodiment of the manufacturing method according to the present invention. The feature of the second embodiment is that two intermediate chromium layers S ₃ and S ₄ are provided between the base chromium layer S ₁ and the upper chromium layer S _{2 in the first} embodiment. It is in the point. These intermediate chromium layers S ₃ and S ₄ are not particularly limited in their properties, but the lower intermediate chromium layer S ₃ is closer to the underlying chromium layer S ₁ , and the upper intermediate chromium layer S ₄ is It is desirable to have the properties closer to the upper chromium layer S ₂ . Therefore, it may be present some of the cracks F is the intermediate chrome layer S ₄ on the upper layer side. By providing the intermediate chromium layers S ₃ and S ₄ in this way, direct crack propagation from the upper chromium layer S ₂ to the underlying chromium layer S ₁ is suppressed, which greatly contributes to the stable maintenance of corrosion resistance. The intermediate chromium layer is not limited to the two layers S ₃ and S _4, and may be one layer or three or more layers.

In the second embodiment, for example, as shown in FIG. 5, and sets the zone C _1, C ₂ in the middle of the by the zone A was a B (Fig. 2), each zone C _1, C ₂ The plating process is performed by setting the waveform of the pulse current in the pattern different from the waveform of the pulse current in the first-stage zone A described above. Further, as the apparatus for performing the plating process, the same apparatus as shown in FIG. 3 can be used. In this case, the previous bus bar 9A (FIG. 3) corresponding to the plating process layer 4B is further subdivided, Different pulse power sources 12 may be connected to each of them.

FIG. 6 shows the state of the surface layer portion of the chrome-plated part obtained by the third embodiment of the manufacturing method according to the present invention. The feature of the third embodiment is that an oxide film S ₅ mainly composed of Cr ₂ O ₃ is provided on the outermost surface of the chromium plated component obtained in the first embodiment. The oxide film S ₅ is formed by polishing (buffing) the surface of the workpiece W that has been subjected to the above-described plating process, and then performing a thermal oxidation process. Thus, the presence of the oxide film S ₅ mainly composed of Cr ₂ O ₃ improves the corrosion resistance of the upper chromium layer S ₂ itself and prevents the occurrence of white rust due to the corrosion of the chromium layer. The

Here, in order to perform the polishing process and the heat oxidation treatment, for example, an apparatus as shown in FIG. 7 can be used. The apparatus centerless grinding machine 20 to the primary production line L _1, the secondary production line L ₂ is set in parallel with the primary production line L _1, the pusher 21, by placing a high-frequency coil 22 and the cooling coil 23, both The production lines L ₁ and L ₂ are connected by an inclined stand 24, and the workpiece W after the chrome plating process is polished by a centerless polishing machine 20, and this is passed through the inclined stand 24. Te transferred to the secondary production line L _2, the extension of the rod 21a of the pusher 21 by sending continuously the workpiece W to the high frequency coil 21 and the cooling coil 22, by performing the polishing and heat oxidation treatment effectively Can do.

JIS S25C steel rod (diameter 12.5mm, length 200mm) was used as the test material, and chromic acid plating bath of chromic acid 250g / L, sulfuric acid 2.5g / L, organic sulfonic acid 8g / L, boric acid 10g / L The component composition is used. First, the bath temperature is 60 ° C., the maximum current density I _U = 120 A / dm ² , the minimum current density I _L = 0 A / dm ² (pattern in FIG. 2), and the maximum current density I _U is maintained. time performs pulse plating with (on-time) T ₁ = 100 ~800 μs, the minimum current density I retention time in the _L (off-time) T ₂ = 100 ~500 μs, a frequency 0.8 to 5.0 kHz conditions, test materials A base chromium layer S ₁ (FIG. 1) having a thickness of about 3 μm was formed on the surface. Next, in the same chrome plating bath, general-purpose plating treatment is performed under constant conditions of a bath temperature of 60 ° C. and a current density of 60 A / dm ² , and an upper chrome layer S ₂ having a thickness of about 10 μm is formed on the base chrome layer S _1. (FIG. 1) was formed, and samples 2 to 18 shown in Table 2 were obtained. For reference, the same specimen and plating bath are used, and a general-purpose hard chromium plating treatment is performed under constant conditions of a bath temperature of 60 ° C. and a current density of 60 A / dm ² , and the thickness of the specimen is about 20 μm. Sample 1 having a chromium layer was obtained.

Then, for these samples 1 to 18, together with measuring the surface hardness was observed for the presence of cracks in the underlying chrome layer S ₁ and the upper chrome layer S ₂ Metropolitan by microscopic observation, furthermore, the underlying chrome layer S ₁ is Residual stress and crystallite size were measured by the methods described below. In addition, a salt spray test according to JIS Z2371 was conducted to observe the presence or absence of rusting. For samples where rusting was not observed, this was subjected to heat treatment at 200 ° C for 2 hours, and after the heat treatment, the same as above. The presence or absence of cracks in the base chrome layer S ₁ and the upper chrome layer S ₂ was observed, and a salt spray test according to JIS Z2371 was performed again to observe the presence or absence of rusting. Note that the samples 2-18 was carried out a two-stage plating process, at the time of completion of the plating process in the first stage (formation of the underlying chrome layer S _1), and observed skin color of the surface.

Here, the residual stress of the chromium layer was measured using “X-ray stress measurement method” disclosed in “Non-destructive inspection”, Volume 37, No. 8, pp. 636-642 edited by Japan Nondestructive Inspection Association. .
The size of the crystallites in the chromium layer is measured on the Cr (222) diffraction surface using characteristic X-ray Cu-Kα (wavelength: 1.5405620 angstroms) with an X-ray diffractometer, and the diffraction profile spread (integral width). ) Was obtained by calculating into the following Scherrer equation. For the integral width, a value corrected by the Cauchy function was used.
D _hkl = K ・ λ / β ₁ cosθ
D _hkl : crystallite size (angstrom, crystallite size perpendicular to hkl)
λ: Measurement X-ray wavelength (angstrom)
β ₁ : Broadening of diffraction line due to crystallite size: Integral width (radian)
θ: Black angle of diffraction line K: Constant (1.05)
Table 2 collectively shows the above measurement results.

From the results shown in Table 2, sample 1 (comparative material) subjected to general-purpose hard chromium plating treatment has many cracks in the chromium layer and is very early (2 hours) by the salt spray test after plating treatment. The entire surface rusted.
Among the samples 2 to 15 was performed a two-stage plating process, samples 2-4 and 16-18 (comparative material), in a state in which plated, numerous cracks both in the upper chromium layer S ₂ And cracks were also observed in the underlying chrome layer S ₁ . Moreover, it turned out that these samples 2-4 and 16-18 rust comparatively early (24 to 96 hours) by the salt spray test after a plating process. In addition, about these samples, since rusting was recognized in the state which performed the plating process as mentioned above, the subsequent heat processing was stopped.
In contrast, the samples 5-15 was subjected to the same two-step plating process, in a state in which plated, although both a large number of cracks were observed on the chromium layer S _2, the underlying chrome layer S ₁ No cracks were observed. Moreover, about these samples 5-15, rusting was not recognized to 300 hours in the salt spray test after a plating process.

Samples 5 to 15 in which rusting was not observed in the state where the plating treatment was performed were then subjected to heat treatment (200 ° C. × 2 hours) as described above, and the presence of cracks and rusting were again performed. The sample 5 (comparative material) was found to have cracks in the underlying chromium layer S ₁ and rusted relatively early (24 hours) in the salt spray test. In contrast, Samples 6 to 15 (materials of the present invention) showed no cracks in the underlying chromium layer S ₁ even after heat treatment, and no rusting was observed up to 300 hours in the salt spray test. It was.

On the other hand, when the residual stresses of the base chromium layer S ₁ (sample 1 is only one layer) in each sample are compared, the samples 1 to 4 and 16 to 18 (comparative material) all have tensile residual stress. On the other hand, Samples 5 to 15 all have compressive residual stress, and Samples 6 to 15 (material of the present invention) have a large compressive residual stress of 150 MPa or more. Further, comparing the size of the crystallites of the underlying chromium layer S ₁ (sample 1 is only one layer) in each sample, samples 1 to 5 (comparative material) are all less than 9 nm, whereas sample 6 .About.18 are all 9 nm or more. Particularly, the samples 16 to 18 are large crystallites of 16 nm or more.

The surface hardness of sample 1 subjected to general-purpose hard chrome plating treatment is the highest, and in other samples, the larger the crystallite size, the lower the surface hardness. In addition, as for the skin color of the surface of the base chrome layer S ₁ (sample 1 is only one layer), samples 1 to 15 were all found to have a gloss specific to the chrome plating layer, but samples 16 to 18 were milky white. It was presenting.

From this, it is clear that the occurrence of cracks in the chromium layer depends on the residual stress and crystallite size of the chromium layer. to ensure corrosion resistance performs chromium plating process as 150MPa or more compressive residual stress in the underlying chrome layer S ₁ is generated, and more preferably, a size of 9nm or more crystallites underlying chrome layer S ₁ Thus, it can be said that it is necessary to perform chrome plating. However, with regard to the compressive residual stress, there is a limit in increasing the compression residual stress only by adjusting the pulse waveform as described above. Therefore, it can be said that an appropriate pulse waveform may be selected in consideration of practicality. On the other hand, it can be said that it is desirable to suppress the crystallite size to less than 16 nm because the samples 16 to 18 having a size of 16 nm or more generate tensile residual stress.

The same test material and chromium plating bath as in Example 1 were used. First, the bath temperature was 60 ° C., the maximum current density I _U = 120 A / dm ² , the minimum current density I _L = 0 A / dm ² , and the maximum current density I _U. Pulse plating is performed under the conditions of holding time (on time) T ₁ = 1400 μs, minimum current density I _L holding time (off time) T ₂ = 600 μs, frequency 500 Hz, and the surface thickness of the specimen is about A 2 μm-base chromium layer S ₁ (FIG. 4) was formed. Next, in the same chromium plating bath, bath temperature 60 ° C., maximum current density I _U = 120 A / dm ² , minimum current density I _L = 0 A / dm ² , on-time T ₁ = 1400 μs, off-time T ₂ = Pulse plating was performed under the conditions of 400 μs and frequency of 625 Hz to form an intermediate chromium layer S ₃ (FIG. 4) having a thickness of about 2 μm on the underlying chromium layer S ₁ . Next, in the same chromium plating bath, bath temperature 60 ° C., maximum current density I _U = 120 A / dm ² , minimum current density I _L = 0 A / dm ² , on-time T ₁ = 200 μs, off-time T ₂ = 100 .mu.s, performs pulse plating process at a frequency of 3333Hz, the formation of the intermediate chrome layer S ₃ having a thickness of about 2μm on the intermediate chrome layer S ₄ (FIG. 4). Further, in the same chromium plating bath, general-purpose plating is performed under a constant condition of a bath temperature of 60 ° C. and a current density of 60 A / dm ² , and an upper chromium layer S ₂ having a thickness of about 5 μm is formed on the intermediate chromium layer S _5. Formed.

Then, the samples obtained as described above, the underlying chrome layer S ₁ by microscopic observation, to observe the presence or absence of cracks in the intermediate chrome layer S _3, S ₄ and the upper chromium layer S _2, similarly to Example 1 together with The residual stress and crystallite size in each layer were measured by this method, and a salt spray test according to JIS Z2371 was conducted to observe the presence or absence of rusting. In addition, after these tests, the sample was subjected to heat treatment at 200 ° C. for 2 hours, and a salt spray test according to JIS Z2371 was performed to observe the presence or absence of rusting. The results are collectively shown in Table 3.

From the results shown in Table 3, no cracks were observed in the lower chrome layer S ₁ and the intermediate chrome layer S ₃ , but slight cracks were observed in the upper intermediate chrome layer S _4. Many cracks were observed in the upper chrome layer S ₂ in the upper layer. In terms of residual stress, the underlying chromium layer S ₁ and intermediate chromium layer S ₃ on the lower layer side have large compressive residual stress exceeding 150 MPa, but the intermediate chromium layer S ₄ and upper chromium layer on the upper layer side. S ₂ has a tensile residual stress. Further, when looking at the size of the crystallite, the lower chromium layer S ₁ and the intermediate chromium layer S ₃ are larger than 9 nm, whereas the upper chromium intermediate chromium layer S ₄ and the upper chromium layer are larger than 9 nm. Layer S ₂ is much smaller than 9 nm. On the other hand, as a result of the salt spray test, rusting was not observed in either the state of the plating treatment or the state after the heat treatment, and it was confirmed that it had sufficient corrosion resistance.

The same test material and chromium plating bath as in Example 1 were used. First, the bath temperature was 60 ° C., the maximum current density I _U = 120 A / dm ² , the minimum current density I _L = 0 A / dm ² , and the maximum current density I _U. retention time (on-time) T ₁ = 300 μs, the minimum current density I retention time in the _L (off-time) T ₂ = 300 μs, performs pulse plating process at a frequency of 1.7 kHz, thick test piece surface of the An underlying chromium layer S ₁ (FIG. 1) having no cracks of about 3 μm was formed. Next, in the same chrome plating bath, general-purpose plating treatment is performed under the constant conditions of a bath temperature of 60 ° C. and a current density of 60 A / dm ² , and the upper chrome with cracks having a thickness of about 10 μm is formed on the base chrome layer S _1. Layer S ₂ (FIG. 1) was formed. After the plating treatment, the surface is buffed to finish the surface to a surface roughness Ra = 0.08 μm. After that, a part of the sample 31 is baked at 210 ° C. for 4 hours to obtain the upper chromium layer S _2. An oxide (mainly Cr ₂ O ₃ ) is formed on the upper part, and the other chrome sample 32 is subjected to high-frequency heating that is held at a maximum heating temperature of 400 ° C. for a short time (about 10 seconds), and the upper chromium layer S _An oxide (mainly Cr ₂ O ₃ ) was formed on ₂ .

For comparison, the same test material and chromium plating bath as in Example 1 were used. First, the bath temperature was 60 ° C., the maximum current density I _U = 120 A / dm ² , and the minimum current density I _L = 0 A / dm ^2. Then, pulse plating is performed under the conditions of on-time T ₁ = 200 μs, off-time T ₂ = 200 μs, and frequency of 2.5 kHz, and a base chromium layer S ₁ having a crack of about 3 μm is formed on the surface of the test material. Next, general-purpose plating is performed in the same chromium plating bath under constant conditions of a bath temperature of 60 ° C. and a current density of 60 A / dm ² , and a crack having a thickness of about 10 μm is formed on the underlying chromium layer S _1. The upper chrome layer S ₂ was formed, and this was used as a sample 33, which was subjected to the buffing and high-frequency heat treatment described above. Further, for comparison, a sample 34 was obtained by reversing the final step of the sample 31, that is, by performing a buffing process after performing a baking process.

Then, the samples 31 to 34 obtained in the manner as described above, as well as measuring the magnitude of the compressive stress and the crystallite in the underlying chrome layer S ₁ in the same manner as in Example 1, subjected to salt spray test according to JIS Z2371 The occurrence of red rust and white rust was observed. The results are collectively shown in Table 4.

From the results shown in Table 4, Samples 31 and 32 have a sufficiently large compressive residual stress in the underlying chromium layer S ₁ and a sufficiently large crystallite size. On the other hand, in Samples 31 and 32, although the underlying chrome layer S ₁ is a compressive residual stress, the value is not sufficient, also has a magnitude also smaller crystallite.

As a result of the salt spray test, in Samples 31 and 32 (invention material), red rust due to corrosion of the metal substrate and white rust due to corrosion of the plating layer were not observed, but in Sample 33 (comparative material) And red rust were observed in Sample 34 (comparative material). The reason why red rust was observed in sample 33 was that cracks existed in both base chrome layer S ₁ and upper chrome layer S _2, and the reason why white rust was observed in sample 34 was formed by heat oxidation. This is because the oxide film was removed by the final buffing. FIG. 8 is an electron micrograph showing the occurrence of white rust. The reason why no red rust was observed in the sample 34 was that the final buffing caused plastic flow in the chromium layer and closed the cracks.

  Plating was performed under the same pulse current conditions as in Sample No. 12 in Example 1, and the plating stress was variously changed, and the residual stress was measured for each. FIG. 9 shows the relationship between the plating thickness obtained as described above and the residual stress. As shown in Japanese Patent Publication No. 43-20082 of the prior art, there is almost no stress gradient with respect to the plating thickness. It can be seen that the average compressive residual stress is stable at 100 MPa or more. Further, a compressive residual stress close to 300 MPa is obtained even at a plating thickness of 1 μm.

It is a schematic diagram which shows the state of the surface layer part of the chromium plating component obtained in the 1st Embodiment of this invention. It is a graph which shows an example of the waveform of the pulse current employ | adopted by the chromium plating process in the 1st embodiment. It is a top view which shows typically the structure of one plating apparatus for enforcing the method of this invention. It is a schematic diagram which shows the state of the surface layer part of the chromium plating component obtained by the 2nd Embodiment of this invention. It is a graph which shows an example of the waveform of the pulse current employ | adopted by the chromium plating process in the 2nd embodiment. It is a schematic diagram which shows the state of the surface layer part of the chromium plating component as the 3rd Embodiment of this invention. It is a top view which shows typically an example of the structure of the grinding | polishing and heating apparatus used by the 3rd Embodiment. It is a microscope picture which shows the state of the white rust generate | occur | produced in the Example of this invention. It is a graph which shows the relationship between the plating thickness and the residual stress in the Example of this invention.

Explanation of symbols

F Crack M Steel base material S ₁ Base chromium layer S ₂ Upper chromium layer S ₃ Intermediate chromium layer S ₄ Intermediate chromium layer S ₅ Oxide film W Workpiece

Claims (23)

A method for producing a chromium-plated part, comprising performing electroplating using a pulsed current in a chromium plating bath to deposit a chromium layer having no cracks on the surface and having a compressive residual stress of 100 MPa or more. A method for producing a chromium-plated component, characterized in that electroplating is performed using a pulsed current in a chromium plating bath to deposit a chromium layer having no cracks on the surface and having a compressive residual stress of 150 MPa or more. Electroplating is performed using a pulse current in a chromium plating bath, and after depositing an underlying chromium layer having no cracks on the surface and having a compressive residual stress of 100 MPa or more, electroplating is performed in the chromium plating bath, A method for producing a chromium-plated component, comprising depositing an upper chromium layer having cracks on the underlying chromium layer. Electroplating is performed using a pulsed current in a chromium plating bath, and after depositing an underlying chromium layer having no cracks on the surface and having a compressive residual stress of 150 MPa or more, electroplating is performed in the chromium plating bath, A method for producing a chromium-plated component, comprising depositing an upper chromium layer having cracks on the underlying chromium layer. Electroplating is performed using a pulse current in a chromium plating bath, and after depositing an underlying chromium layer having no cracks on the surface and having a compressive residual stress of 100 MPa or more, electroplating is performed in the chromium plating bath, An intermediate chromium layer is deposited on the underlying chromium layer, and then electroplating is performed in a chromium plating bath to deposit an upper chromium layer having cracks on the intermediate chromium layer. Manufacturing method of parts. Electroplating is performed using a pulsed current in a chromium plating bath, and after depositing an underlying chromium layer having no cracks on the surface and having a compressive residual stress of 150 MPa or more, electroplating is performed in the chromium plating bath, An intermediate chromium layer is deposited on the underlying chromium layer, and then electroplating is performed in a chromium plating bath to deposit an upper chromium layer having cracks on the intermediate chromium layer. Manufacturing method of parts. The method for manufacturing a chromium-plated component according to any one of claims 1 to 6, wherein the electroplating is performed under a pulse condition in which a crystallite size of the chromium layer without cracks is 9 nm or more. The method for manufacturing a chromium-plated component according to claim 7, wherein the electroplating is performed under a pulse condition in which a crystallite size of the chromium layer having no crack is less than 16 nm. The method for manufacturing a chromium-plated component according to any one of claims 1 to 8, wherein electroplating is performed under a pulse condition in which a compressive residual stress of a chromium layer having no crack is substantially the same regardless of a plating thickness. The chrome-plated component according to any one of claims 1 to 9, wherein electroplating is performed under a pulse condition in which a compressive residual stress of a chromium layer having no crack is 100 MPa or more, preferably 150 MPa or more at a plating thickness of 1 µm. Production method. The method for manufacturing a chromium-plated component according to any one of claims 1 to 10, wherein the minimum current density of the pulse current is set to an arbitrary value between the maximum current density and zero. The manufacture of a chromium-plated part according to claim 11, wherein the holding time at the maximum current density of the pulse current is arbitrarily set in the range of 100 µS to 1400 µS, and the holding time at the minimum current density is arbitrarily set in the range of 100 µS to 600 µS. Method. The chromium plating according to any one of claims 3 to 12, wherein the upper chromium layer is deposited using a pulse current or a direct current having a pulse waveform different from the pulse waveform of the pulse current when the underlying chromium layer is deposited. Manufacturing method of parts. The intermediate chromium layer is deposited using a pulse current or direct current with a pulse waveform different from the pulse waveform of the pulse current used when depositing the underlying chromium layer, and another pulse current or direct current with a different pulse waveform is used. The method for producing a chromium-plated component according to any one of claims 5 to 12, wherein an upper chromium layer is deposited. The method for producing a chromium-plated part according to any one of claims 1 to 14, wherein the workpiece is continuously moved in the plating bath to perform continuous treatment. The method for producing a chromium-plated component according to any one of claims 1 to 14, wherein the workpiece is immersed in a plating bath and batch processing is performed. The method for producing a chromium-plated component according to any one of claims 3 to 16, wherein the plurality of chromium layers are deposited in the same plating bath. The method for manufacturing a chromium-plated component according to any one of claims 3 to 17, wherein an outermost chromium layer is polished. The method for manufacturing a chromium-plated part according to any one of claims 1 to 18, wherein a heat oxidation treatment is performed to form an oxide film mainly composed of Cr ₂ O ₃ on the outermost surface. The method for manufacturing a chromium-plated component according to claim 19, wherein the heat oxidation treatment is performed under the same conditions as the general-purpose baking treatment. The method for manufacturing a chromium-plated component according to claim 19, wherein the heat oxidation treatment is performed using high-frequency heating. A plating bath used for carrying out the method for producing a chromium-plated component according to any one of claims 1 to 21, comprising an organic sulfonic acid. The plating bath according to claim 22, comprising 100 to 450 g / L of chromic acid, 1 to 5 g / L of sulfuric acid, and 1 to 18 g / L of organic sulfonic acid.

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