JP2004300522A - Chromium-plated component and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a chromium-plated component which is excellent in corrosion resistance, even when subjected to an extensive thermal history, and to provide a manufacturing method which easily and stably yields the chromium-plated component. <P>SOLUTION: Plating treatment is performed by adjusting the maximum and minimum current densities of a pulsed current, the retention time of the maximum and minimum current densities, the temperature of a plating bath, etc. to deposit a crack-free chromium layer having a compressive residual stress, preferably of ≥100 MPa, on the work surface. Here, the microscopic lattice distortion of the chromium layer is adjusted to 0-3×10<SP>-3</SP>, preferably 0-1×10<SP>-3</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a chromium-plated component having a hard chromium layer deposited on a surface and a method for producing the same.
[0002]
[Prior art]
According to the general-purpose hard chromium plating process of depositing a hard chromium layer on the work surface, there are many cracks reaching the metal base in the obtained chromium layer, and as it is, the medium causing corrosion reaches the metal base. Inferior in corrosion resistance. Conventionally, for components used in corrosive environments, nickel plating or copper plating is generally applied as a pretreatment to form an underlayer with a thickness similar to that of the chromium plating layer. Was to be applied. However, according to such a countermeasure, the plating process must be performed twice by changing the process, so that an increase in manufacturing cost due to an increase in the number of processes is inevitable.
[0003]
On the other hand, it has been already confirmed that a so-called pulse plating process using a pulse current can form a chromium layer without cracks (for example, see Patent Documents 1 and 2). If this is the case, a chromium-plated part having excellent corrosion resistance can be obtained by one-step processing. However, according to the pulse plating process, there is a problem that large cracks (macrocracks) are likely to occur in the chromium layer when subjected to a heat history, and the application to components subjected to the heat history must be abandoned. Had become.
Therefore, the present inventors have conducted intensive studies on the occurrence of macrocracks and found that by applying a compressive residual stress of 100 MPa or more to the chromium layer, cracks can be prevented even at a heat history of 200 ° C. × 2 hours. This has already been disclosed in Patent Document 3.
[0004]
[Patent Document 1]
JP-B-43-20082 [Patent Document 2]
Japanese Patent Application Laid-Open No. 3-207888 [Patent Document 3]
Japanese Patent Application No. 2000-199095
[Problems to be solved by the invention]
However, when the chromium-plated part to which the compressive residual stress is applied is further subjected to additional experiments, it is found that the chromium-plated part has a compressive residual stress of less than 100 MPa (for example, −10 MPa residual stress). It was found that macrocracks did not occur even at a heat history of 200 ° C. × 2 hours depending on the processing conditions.
The present invention has been made in view of the above technical background, and an object of the present invention is to provide a chromium-plated part that exhibits excellent corrosion resistance even after extensive heat histories, An object of the present invention is to provide a manufacturing method capable of easily and stably obtaining parts.
[0006]
[Means for Solving the Problems]
Cracks occur when the thermal history is given, because the chromium layer shrinks, and this shrinkage is caused by the total amount of lattice defects and microscopic lattice strain that are often present at the crystal grain boundaries of the chromium layer. Affected. The present inventors have paid attention to the microscopic lattice distortion of the chromium layer, and have found that shrinking of the chromium layer due to thermal history can be suppressed by reducing the microscopic lattice distortion.
Therefore, a chromium-plated component according to the present invention for achieving the above object has a compressive residual stress, and in a chromium-plated component having a chrome layer without cracks, a microscopic lattice strain of the chromium layer is 0 to 1; It is characterized by being in the range of × 10 ^-3 .
Further, the chromium-plated component according to the present invention is a chromium-plated component having a crack-free chromium layer having a compressive residual stress of 100 MPa or more, wherein the chromium layer has a microscopic lattice strain of 0 to 3 × 10 ^−3. In the range.
In the chrome-plated component configured as described above, since the microscopic lattice distortion of the chromium layer is small, even if a thermal history is given, the chrome layer contraction caused by the release of the strain is suppressed, and as a result, the heat The occurrence of cracks due to the history is prevented.
The lattice strain of the chromium layer described above is greatly affected by the conditions of the pulse current and the temperature of the plating bath when performing the plating process.
Therefore, one of the methods of manufacturing a chromium-plated component according to the present invention for achieving the above object is to perform a plating process by adjusting a pulse current, to provide a crack-free chromium layer having a compressive residual stress on the work surface. In the method of manufacturing a chromium-plated component to be deposited, the pulse current is adjusted such that the microscopic lattice strain of the chromium layer is in the range of 0 to 1 × 10 ⁻³ .
Another one of the production methods is a method for producing a chromium-plated component in which a plating process is performed by adjusting a pulse current, and a chromium layer without a crack having a compressive residual stress of 100 MPa or more is deposited on a work surface. The pulse current is adjusted so that the microscopic lattice distortion of the chromium layer is in the range of 0 to 3 × 10 ⁻³ .
Furthermore, another one of the present manufacturing methods is a method of manufacturing a chromium-plated component in which a plating process is performed by adjusting a pulse current to deposit a chromium layer having no compressive residual stress of 100 MPa or more on a work surface and having no crack. The temperature of the plating bath is adjusted so that the microscopic lattice strain of the chromium layer is in the range of 0 to 3 × 10 ⁻³ .
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0008]
In order to obtain the chromium-plated component according to the present invention, a so-called pulse plating process using a pulse current is performed. In this pulse plating process, a plating bath containing an organic sulfonic acid as shown in FIG. 1 is used. It is desirable to use. This plating bath has the same composition as that described in JP-B-63-32874, and contains 1 to 18 g / L of organic sulfonic acid based on chromic acid and sulfate group. It contains 5 to 12 g / L.
Incidentally, no organic sulfonic acid, chromic acid - may be used mixed catalyst bath containing sulfuric acid bath (Sargent bath) and silicofluoric product (SiF _6).
[0009]
As the waveform of the pulse current applied during pulse plating process, alternating between a maximum current density I _U and the minimum current density I _L as shown in FIG. 2, and the maximum current density I _U and the minimum current density I _L and the predetermined time T ₁ and T _{2 are} held. Although the minimum current density _IL is set to zero (off) here, it is needless to say that the minimum current density IL may be set to any value between the maximum current density IU and zero. Further, the holding time T ₁ and T ₂ may be set to be set to the same value different values.
[0010]
Here, the stress change of the chromium layer due to the temperature rise is a phenomenon caused by the thermal shrinkage of the chromium layer, and the amount of the stress change is correlated with the microscopic lattice strain ε of the chromium layer and the ambient temperature as shown in FIG. I do. The microscopic lattice strain ε can be obtained from the following Hall equation (1) by measuring the spread of the X-ray diffraction profile obtained by the X-ray diffraction method as a half width.
β · cos θ / λ = 1 / D + ε · sin θ / λ (1)
In this equation (1), β is the half width, D is the size of the crystallite, λ is the wavelength of the X-ray, and the half width β is measured by measuring the lattice planes {110} and ｛in the same direction. Perform at 220 °.
From the results shown in FIG. 3, the amount of change in the stress of the chromium layer due to heating is smaller as the microscopic strain ε is smaller, and is thermally stable. Further, the amount of change in stress changes with time, and the change gradually becomes smaller as time elapses. It stabilizes in about one month at room temperature, about one day at 150 ° C, and about 2 hours at 200 ° C.
[0011]
In the chromium-plated component manufactured in this manner, a compressive residual stress is applied to a crack-free chromium layer, and the microscopic lattice strain of the chromium layer is small. Is prevented and, as a result, excellent corrosion resistance is maintained.
[0012]
【Example】
Example 1
A steel rod (diameter 20 mm) made of JIS S45C was used as a test material, and a plating bath having a composition of chromic acid 252 g / L, sulfate group 3.1 g / L, and organic sulfonic acid 3.5 g / L was used. Bath temperature 61 ° C., maximum current density (peak current density) I _U = 60, 80, 100, 120, 140, 160, 180, ²⁰⁰ A / dm ² , minimum current density I _L = 0 A / dm ² ( 1), pulse plating under the conditions of holding time (on time) T ₁ = 1.0 ms at maximum current density I _{U and} holding time (off time) T ₂ = 0.5 ms at minimum current density I _L By performing the treatment, eight types of samples having a chromium layer having a thickness of about 10 μm on the work surface and having different initial residual stresses were obtained.
Then, for each sample obtained as described above, an X-ray diffraction test is performed to determine the half-value width β and the crystallite size D, and these values are substituted into the above-mentioned Hall equation (1) to substitute for the chromium layer. And the residual stress of the chromium layer was determined by performing an X-ray stress measurement test. The measurement of the initial residual stress was performed by using the “X-ray stress measurement method” described in “Non-Destructive Inspection”, Vol. Hereinafter, the present method was used for measuring the residual stress of the chromium layer.
FIG. 4 shows the results of the X-ray diffraction test and the X-ray stress measurement test. From the results shown in the figure, the residual stress of the chromium layer increases toward the compression side as the peak current density increases, and the microscopic lattice strain ε increases as the peak current density increases. Note that no crack was observed in the chromium layer in any of the samples.
[0013]
Example 2
Using the same test material and plating bath as in Example 1, bath temperature 56, 59, 61, 63, 65.5 ° C., maximum current density I _U = 120 A / dm ² , minimum current density I _L = 0 A / dm ² (pattern of FIG. 1), the pulse plating with a maximum current density _{I U} on time _T 1 = 1.0 ms at a minimum current density _{I L} off time _T 2 = 0.5 ms of conditions in, Five types of samples having a chromium layer having a thickness of about 10 μm on the work surface and having different initial residual stress were obtained. Then, an X-ray diffraction test and an X-ray stress measurement test were performed on each sample obtained as described above in the same manner as in Example 1, and the microscopic lattice strain ε and residual stress of the chromium layer were determined.
FIG. 5 shows the results of the X-ray diffraction test and the X-ray stress measurement test. From the results shown in the figure, the residual stress of the chromium layer increases toward the compression side as the bath temperature increases, and the microscopic lattice strain ε decreases as the bath temperature increases. Note that no crack was observed in the chromium layer in any of the samples.
[0014]
Example 3
Using the same test material and plating bath as in Example 1, bath temperature 61 ° C., maximum current density I _U = 120 A / dm ² , minimum current density I _L = 0 A / dm ² (pattern of FIG. 1), On time T ₁ = 0.8, 1.2, 1.6 ms at the maximum current density I _{U and} off time T ₂ = 0.2, 0.3, 0.4, 0.5 at the minimum current density I _L , 0.6, 0.7, and 0.8 ms, and 19 types of samples having a chromium layer having a thickness of about 10 μm on the surface of the work and having different initial residual stresses were obtained.
Then, an X-ray stress measurement test was performed on each of the samples obtained as described above in the same manner as in Example 1 to determine the residual stress of the chromium layer.
FIG. 6 shows the results of the X-ray stress measurement test. From the results shown in the figure, the residual stress of the chromium layer has a minimum (maximum compressive stress) at a certain off-time, and the minimum off-time shifts to the long off-time side with the extension of the on-time. Note that □ and Δ in FIG. 6 indicate that chromium hydride (CrH) was mixed in the chromium layer.
[0015]
Example 4
Each sample obtained in Example 1 and Example 2 was subjected to a heat treatment at 200 ° C. × 2 h, and after the heat treatment, each sample was subjected to the X-ray stress measurement test to determine the residual stress. As a result, it was confirmed that the residual stress of the chromium layer was changed in the tensile direction by the heat treatment in each of the samples. Next, the residual stress before the heat treatment is subtracted from the residual stress after the heat treatment, and the resulting value is regarded as the amount of change in the residual stress value due to the heat treatment. The correlation with the visual lattice strain was investigated. Note that no crack was observed in the chromium layer in any of the samples.
FIG. 7 shows the results of the above investigation, in which the change in the residual stress value due to the heat treatment is closely correlated with the microscopic lattice strain ε, and the change in the residual stress value due to the heat treatment is It increases linearly with the strain ε. This means that the smaller the microscopic lattice strain ε is, the more stable it is thermally. In order to sufficiently withstand the heat history of 200 ° C. × 2 h, the microscopic lattice strain must be reduced. It was found that the range was preferably 3 × 10 ^{−3, more} preferably 1 × 10 ⁻³ .
[0016]
【The invention's effect】
As described above, according to the chromium-plated component and the method of manufacturing the same according to the present invention, it is possible to stably obtain a chromium-plated component exhibiting excellent corrosion resistance not only at around normal temperature but also after extensive heat history. Can be.
[Brief description of the drawings]
FIG. 1 is a chart showing an example of a component composition of a plating bath used for a pulse plating process.
FIG. 2 is a graph showing an example of a pulse waveform in a pulse plating process.
FIG. 3 is a graph showing the effects of microscopic lattice strain and heating temperature on the amount of stress change due to heating.
FIG. 4 is a graph showing the results of an X-ray diffraction test and an X-ray stress measurement test in Example 1 of the present invention, and is a graph showing an influence of a peak current density of a pulse on a residual stress and a microscopic lattice strain. is there.
FIG. 5 is a graph showing the results of an X-ray diffraction test and an X-ray stress measurement test in Example 2 of the present invention, and is a graph showing the effect of plating bath temperature on residual stress and microscopic lattice strain. .
FIG. 6 is a graph showing the results of an X-ray stress measurement test in Example 3 of the present invention, and is a graph showing the influence of the on-time and off-time of the pulse current on the residual stress.
FIG. 7 is a graph showing the results of a thermal hysteresis test in Example 4 of the present invention, and is a graph showing the effect of microscopic lattice strain on the amount of change in residual stress value due to heat treatment.

Claims (8)

A chromium-plated component having a crack-free chromium layer having a compressive residual stress, wherein the microscopic lattice strain of the chromium layer is in a range of 0 to 1 × 10 ⁻³ . A chromium-plated component having a crack-free chromium layer having a compressive residual stress of 100 MPa or more, wherein the chromium layer has a microscopic lattice strain in the range of 0 to 3 × 10 ^−3. parts. In a method of manufacturing a chromium-plated component in which a plating process is performed by adjusting a pulse current and a crack-free chromium layer having a compressive residual stress on a work surface is deposited, the chromium layer has a microscopic lattice strain of 0 to 1; A method for manufacturing a chrome-plated component, comprising adjusting a pulse current so as to be in a range of × 10 ⁻³ . In a method of manufacturing a chrome-plated component that performs a plating process by adjusting a pulse current and has a compressive residual stress of 100 MPa or more on a work surface and deposits a chromium layer without cracks, the microscopic lattice strain of the chromium layer is A method for producing a chrome-plated component, comprising adjusting a pulse current so as to fall within a range of 0 to 3 × 10 ⁻³ . 5. The method for producing a chromium-plated component according to claim 3, wherein the maximum current density and the minimum current density of the pulse current are adjusted. The method for manufacturing a chrome-plated component according to any one of claims 3 to 5, wherein the holding time of the maximum current density and the minimum current density of the pulse current is adjusted. In a method of manufacturing a chromium-plated component in which a plating process is performed by adjusting a pulse current and a crack-free chromium layer having a compressive residual stress on a work surface is deposited, the chromium layer has a microscopic lattice strain of 0 to 1; A method for producing a chromium-plated part, comprising adjusting the temperature of a plating bath so as to be in the range of ^10-3 . In a method of manufacturing a chrome-plated component that performs a plating process by adjusting a pulse current and has a compressive residual stress of 100 MPa or more on a work surface and deposits a chromium layer without cracks, the microscopic lattice strain of the chromium layer is A method for producing a chromium-plated part, comprising adjusting the temperature of a plating bath so as to fall within a range of 0 to 3 × 10 ⁻³ .

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