JP4843318B2 - Chrome plating material - Google Patents

Description

  The present invention relates to a chromium plated member in which an electrochrome plated layer is provided on the surface of a metal member.

  In order to increase the wear resistance of a metal member, the metal member is subjected to a chrome plating process to cover the surface of the metal member with a chrome plating layer. In chromium plating, a hard coating with a small friction coefficient (chromium plating layer) can be obtained at a relatively low cost, so that it is frequently used for protecting metal members. However, when the chromium plating layer is hardened by increasing the hardness, the wear resistance is improved, but the toughness is deteriorated. Therefore, cracks may occur when the chromium plated layer contracts due to the member subjected to chromium plating receiving tensile stress or thermal history. When a crack occurs in the chromium plating layer and the crack reaches the surface of the metal member, the corrosive medium enters from the surface of the chromium plating layer through the crack portion, and the metal member is corroded, resulting in poor corrosion resistance. There was a problem.

  Therefore, the technique of Patent Document 1 has been proposed as a chromium-plated part that does not deteriorate the corrosion resistance even if it receives a thermal history. In this technology, a chromium plating layer to which compressive residual stress is applied by plating is provided on the surface of the component, thereby preventing the occurrence of cracks when a thermal history of about 200 ° C. is received. This document discloses that if the crystallite size of the chromium plating layer is 9 nm or more, cracks do not occur even after the thermal history, and the crystallite size becomes too large. Since the crystal structure itself of the chromium layer itself starts to change, the upper limit of the crystallite may be less than 16 nm, and the occurrence of cracks in the chromium layer may depend on the residual stress of the chromium layer and the size of the crystallite. Are listed.

  By the way, the most widely used mold for continuous casting of steel is a mold made of Cu or a Cu alloy (hereinafter sometimes referred to as a Cu-based mold). Such a mold has a high thermal conductivity and an excellent cooling efficiency can be obtained.

  In continuous casting, flux is used to prevent oxidation of the molten steel, to prevent the molten steel or slab from coming into direct contact with the inner surface of the mold, and to provide lubricity between the inner surface of the mold and the solidified shell. Is used. However, since the thickness of the flux layer formed on the inner surface of the mold is not uniform, the molten steel or slab cannot be completely prevented from coming into direct contact with the inner surface of the mold, and the inner surface of the mold is damaged.

  Recently, scrap is sometimes used as a raw material for molten steel, but it has been confirmed that melting of the inner surface of the mold caused by zinc contained in the scrap is a major cause of shortening the mold life. Yes. That is, when zinc is mixed into the molten steel, it is condensed at the meniscus portion of the mold, and the inner surface of the Cu-based mold is eroded by the molten zinc and melts.

  Therefore, recently, the melting loss is reduced by forming a protective film on the surface of the Cu-based mold. The required properties required for such a protective coating are required to have heat resistance (crack resistance) and molten zinc resistance that can withstand the temperature of the molten steel because it contacts the molten steel on the meniscus side of the mold. On the other hand, wear resistance is required because it contacts the solidified shell on the exit side of the mold. Therefore, a chromium plating film is suitably provided as a protective film.

  However, when a continuous casting mold is used, the chromium plating layer is subjected to severe thermal cycles (thermal history) of rapid heating by contact with high-temperature molten steel and rapid cooling by water cooling when solidifying the molten steel. A large tensile stress acts on. Therefore, when the chrome plating layer receives a severe heat history, cracks occur in the chrome plating layer and the film peels off, or the molten zinc enters through the cracks and the mold is corroded.

In addition, as a chromium layer which does not generate | occur | produce a crack even if it receives the thermal history of 300 degreeC level, there exists a chromium layer obtained by the sputtering process. However, the hardness of the chromium layer obtained by the sputtering process is as low as Hv250, so it is not suitable for covering parts that require wear resistance, and it is easy to form voids, so it is resistant to melting. Inferior to zinc. Furthermore, sputtering does not have versatility due to restrictions on the shape of the metal member. Moreover, it becomes relatively expensive compared with a chromium plating layer obtained by electroplating.
JP 2000-199095 A ([Claims], [0006], [0008], [0036], [0047])

  The present invention has been made in view of such a situation, and an object of the present invention is to provide a chromium plated member provided with an electrochromic plating layer that is unlikely to crack even when subjected to a severe thermal history of 300 ° C. or higher. To do. Another object of the present invention is to provide a chromium plated member having excellent wear resistance.

  Studies were repeated to provide a chromium-plated member provided with an electrochrome-plated layer that is unlikely to crack even under severe heat history of 300 ° C. or higher. As a result, it has been found that if the crystallites of the electrochromic plating layer are enlarged and the crystal orientation is controlled to be uneven, even if a severe thermal history is received, thermal contraction does not occur and cracking can be prevented. Was completed.

  That is, the chromium plating member according to the present invention is a chromium plating member in which an electrochromic plating layer is provided on the surface of a metal member, and the average diameter of crystallites in the electrochromic plating layer is 16.0 nm or more. In addition, the point is that the peak intensity ratio ({211} / {222}) between {211} and {222} by X-ray diffraction is 0.10 or more.

  In order to increase toughness, the electrochromic plating layer preferably has a hardness of Hv 600 or less. In order to prevent the occurrence of cracks when receiving a thermal history of 450 ° C., the electrochrome plating layer preferably has a thickness of 5 μm or more.

  In order to further improve the wear resistance, it is preferable that a hard layer having a hardness higher than that of the electrochromic plating layer and exceeding a hardness of Hv600 is provided on the electrochromic plating layer.

  The present invention also includes a continuous casting mold composed of the chrome plated member.

  ADVANTAGE OF THE INVENTION According to this invention, the chromium plating member which provided the electrochromic plating layer which is hard to generate | occur | produce a crack even if it receives the severe thermal history of 300 degreeC or more, without degrading abrasion resistance can be provided. Since the electrochrome plating layer is unlikely to crack even when subjected to severe thermal history, for example, a medium that causes corrosion does not enter through the crack portion from the surface of the chromium plating layer, and corrosion of the member can be prevented. If a hard layer is provided above the electrochrome plating layer, the wear resistance of the chromium plating member can be improved.

  In the present invention, the chromium plating layer is formed by electroplating. By adopting electroplating, it is possible to make the hardness higher than that of the chromium plating layer obtained by the sputtering process, and to ensure wear resistance. Cost reduction can also be realized. However, since the chromium plating layer obtained by electroplating has a higher hardness than the chromium layer obtained by sputtering, it is generally difficult to suppress the occurrence of cracks when subjected to a thermal history. When the thermal history is applied, cracks occur in the electrochromic plating layer because the electrochromic plating layer shrinks, and this shrinkage affects the amount of lattice defects present at the grain boundaries of the electrochromic plating layer. Receive. The amount of lattice defects increases as the number of crystal grain boundaries increases, and cracks tend to occur when subjected to a thermal history. Therefore, if the number of crystal grain boundaries is reduced, the amount of lattice defects is reduced, thermal shrinkage can be suppressed even when subjected to a thermal history, and the occurrence of cracks can be prevented even in a chromium plating layer obtained by electroplating. In order to reduce the crystal grain boundaries, the crystallites should be enlarged.

  However, even if the crystallites are enlarged, cracks may occur when a severe thermal history of 300 ° C. or higher is received. Therefore, the present inventors have further studied to prevent the occurrence of cracks even when a severe thermal history is received. As a result, it was found that the crystal orientation of the chromium plating layer should be controlled in an uneven direction. Specifically, it was found that the crystal orientation should be varied in the {211} direction and the {222} direction.

  Therefore, the chromium plating member according to the present invention is a chromium plating member in which an electrochromic plating layer is provided on the surface of a metal member, and the crystallites of the electrochromic plating layer are large, and the electrochromic plating layer The crystal orientation is controlled in an uneven direction.

  Specifically, the average diameter of the crystallites is 16.0 nm or more. When the average diameter of the crystallites is less than 16.0 nm, the number of crystal grain boundaries increases, resulting in an increase in lattice defects. As a result, the shrinkage when receiving a thermal history is increased, and cracks are likely to occur in the chromium plating layer. Therefore, in the present invention, the diameter of the crystallite is increased. The average diameter is preferably 16.5 nm or more, more preferably 17 nm or more, and particularly preferably 17.5 nm or more. The upper limit of the average diameter of the crystallite is not limited and is preferably as large as possible. Most ideally, the electrochrome plating layer itself may be a single crystal. The upper limit of the crystallite calculated by the X-ray diffractometer (XRD) is about several tens of μm (for example, about 20 to 30 μm).

  The crystallite means a microcrystal that can be regarded as a single crystal. Generally, the average diameter of crystallites in an electrochrome plating layer obtained by electroplating is about 5 to 10 nm.

The diameter of the crystallite is measured on a Cr (222) diffraction surface using characteristic X-ray Cu-Kα by an X-ray diffractometer, and the measurement result of the spread (integration width) of the diffraction profile is included in the Scherrer equation below. Asked. Note that a value corrected by the Cauchy function was used as the integral width. The wavelength of the Kα ray is 1.54 mm.
D = K · λ / βcos θ
Where D is the crystallite diameter (Å), K is a constant (1.05), λ is the measured X-ray wavelength (Å), β is the broadening of the diffraction line due to the crystallite diameter (integral width; unit is radians) ), Θ represents the black angle of the diffraction line.

  The measurement position of the crystallite is the surface of the electrochrome plating layer, the measurement place is five places, and the average diameter is calculated by averaging the measurement results.

  Enlarging the crystallites of the electrochromic plating layer is effective in reducing the occurrence of cracks in the electrochromic plating layer, but it is not sufficient by itself. Therefore, in the present invention, as described above, the chrome plating layer is controlled so that the crystal orientation is not uniform. The degree of crystal orientation irregularity can be evaluated by X-ray diffraction. That is, the electrochromic plating layer of the present invention has a peak intensity ratio ({211} / {222}) by an X-ray diffraction method (XRD diffraction) of 0.10 or more. When the peak intensity ratio is less than 0.10, the degree of orientation in the {222} direction becomes too strong. In particular, when the thermal history is 300 ° C. or higher, shrinkage increases and cracks are likely to occur. The peak intensity ratio is preferably 0.2 or more, more preferably 0.4 or more. In particular, when the peak intensity ratio is 0.4 or more, cracks are hardly generated even when a thermal history of 400 to 500 ° C. or more is received. The upper limit of the peak intensity ratio is not particularly limited, but is about 0.5, for example.

  In addition, about the electrochromic plating layer formed in the Sargent bath generally used as an industrial chromium plating bath, when the said peak intensity ratio is measured with a X ray diffraction method, it is about 0.01-0.1, {222} Strong degree of orientation in the direction.

  The peak intensity ratio ({211} / {222}) is determined from {211] from the obtained X-ray diffraction chart using characteristic X-ray Cu-Kα (Kα-ray wavelength is 1.54Å) using an X-ray diffractometer. } And {222} peak intensities are calculated respectively, and the values obtained from these ratios ({211} peak intensity / {222} peak intensity).

  The peak intensity ratio is calculated by averaging the measurement results with the measurement position of the peak intensity being the surface of the electrochrome plating layer and the measurement place being five. The baseline was obtained by averaging three points with no peak.

  Although the said electrochromic plating layer should just be provided at least 1 layer on the surface of metal members, you may provide two or more electrochromic plating layers which satisfy the said requirements. For example, when two layers are provided, is the average diameter of the crystallites of the chromium plating layer provided on the surface side of the metal member equal to the average diameter of the crystals of the second chromium plating layer provided on the surface of the chromium plating layer? Or it is preferable to make it larger than the average diameter of the crystallites of the second chromium plating layer. Moreover, it is preferable that the peak intensity ratio of the chromium plating layer is the same as the peak intensity ratio of the second chromium plating layer or is larger than the peak intensity ratio of the second chromium plating layer. The case of providing three or more layers is the same as the case of two layers.

  Although the film thickness of the said electrochromic plating layer is not specifically limited, It is good to set it as 1-50 micrometers. If the film thickness is less than 1 μm, it is difficult to sufficiently improve the corrosion resistance because it penetrates the plated layer even if fine cracks occur in the electrochrome plated layer. The film thickness is more preferably 2 μm or more, further preferably 5 μm or more, and particularly preferably 10 μm or more. In particular, in order to prevent the occurrence of cracks when subjected to a thermal history of 450 ° C., it is recommended that the thickness of the electrochrome plating layer be 5 μm or more. However, if the film thickness exceeds 50 μm, the electrochrome plating layer becomes too thick and cracks are likely to occur, and the corrosion resistance deteriorates. The film thickness is more preferably 45 μm or less, further preferably 40 μm or less, and particularly preferably 35 μm or less.

  According to the electrochrome plating layer, it is possible to achieve both reduction of crack generation and securing of appropriate hardness. The hardness of the electrochrome plating layer is, for example, Hv 350 or higher, preferably Hv 380 or higher, more preferably Hv 400 or higher. In addition, when the hardness of a general electrochrome plating layer is measured, it is Hv 900 or higher, but if the hardness is increased to this level too much, as described above, even if the average diameter and crystal orientation of the crystallites of the electrochrome plating layer are controlled, Cracks are likely to occur when receiving a thermal history. Therefore, it is recommended that the hardness of the electrochrome plating layer is, for example, Hv 600 or less, more preferably Hv 590 or less.

  The hardness of the electrochrome plating layer may be determined by measuring the cross section of the electrochrome plating layer with a micro Vickers hardness meter. The load during measurement is 0.49 N (50 gf). The hardness is measured at five locations, and the hardness is calculated by averaging three points of the measurement results excluding the maximum and minimum values.

  In this invention, it is preferable to provide the hard layer whose hardness is higher than this electrochromic plating layer on the surface of the said electrochromic plating layer. By providing the hard layer, the wear resistance of the chromium plating member can be further improved. The hard layer only needs to have a hardness higher than that of the electrochrome plating layer and higher than Hv600 in order to ensure wear resistance. The hardness of the hard layer is more preferably Hv800 or higher, and still more preferably Hv900 or higher. The upper limit of the hardness of the hard layer is not particularly limited, but if the hardness is too high, the toughness becomes too low and the hard layer is peeled off.

  The kind of hard layer is not specifically limited, For example, a hard chromium layer, a hard Ni-P plating layer, a CrN layer, a TiN layer etc. are mentioned. In particular, it is preferable to provide a hard chromium layer because the adhesion with the electrochrome plating layer is improved.

  The hard chromium layer has an average diameter of crystallites of 16.0 nm or more and a peak intensity ratio ({211} / {222}) of {211} and {222} by X-ray diffraction method of 0.10 or more. Preferably there is. This is because if the average diameter of the crystallites and the peak intensity ratio satisfy these ranges, cracks hardly occur even when subjected to a severe thermal history of 300 ° C. or higher.

  The hard layer may be provided by being laminated on the surface of the electrochrome plating layer, but an intermediate layer may be provided between the electrochrome plating layer and the hard layer.

  Although the film thickness of a hard layer is not specifically limited, What is necessary is just to be about 10-50 micrometers. When the thickness is less than 10 μm, the wear resistance cannot be sufficiently improved even if a hard layer is provided. However, if it exceeds 50 μm, the film thickness becomes too large and a large amount of cracks are likely to occur.

  When the hard chrome layer is laminated on the surface of the electrochrome plating layer, the total film thickness of the electrochrome plating layer and the hard chromium layer is preferably 100 μm or less.

  In addition, when an electrochrome plating layer and a hard chromium layer are laminated | stacked, if the cross section is observed with a microscope, it can be confirmed whether the hard chromium layer is provided. As the microscope, any of an optical microscope, a scanning electron microscope (SEM), and a transmission electron microscope (TEM) can be used. Moreover, simply, if the hardness of a laminated part is measured several places, it can be confirmed whether the hard chromium layer is provided.

  The metal member used as a base material such as the electrochrome plating layer is not particularly limited, and examples thereof include copper, copper alloy, iron, steel, aluminum, aluminum alloy, titanium alloy, and magnesium alloy. In addition, when using the chromium plating member of this invention as a raw material of the casting_mold | template for continuous casting, it is preferable to use copper or a copper alloy as said base material from a viewpoint of improving cooling efficiency.

  The chromium-plated member of the present invention is suitable as a material used on the meniscus side of a mold that comes into contact with molten steel. On the other hand, a member provided with a hard chromium layer as a hard layer on the upper layer of the electrochromic plating layer is also excellent in wear resistance, so that it is preferably used as a material used on the exit side of the mold in contact with the solidified shell. it can.

  The chrome-plated member according to the present invention satisfies the above requirements, and its manufacturing method is not particularly limited, but an example of the manufacturing method will be described below.

A chromium plated member satisfying the above requirements is obtained by electroplating with a bath temperature of 65 to 100 ° C. and a current density of 50 to 500 A / dm ^{2 during} electroplating.

  An electrochrome plating layer is provided on the surface of the metal member at a bath temperature of 65 to 100 ° C. When the bath temperature is less than 65 ° C., the crystallites are small, and the electrochrome plating layer has a strong degree of orientation in the {222} direction, so that the crystal orientation is not uneven. The bath temperature is preferably 70 ° C. or higher, more preferably 75 ° C. or higher. However, when the bath temperature exceeds 100 ° C., an internal pressure control container such as an autoclave is required, and the workability is deteriorated and the cost is increased. The bath temperature is preferably 95 ° C. or lower.

In manufacturing the chromium plating member of the present invention, the bath temperature is set higher than usual, but even if only the bath temperature is increased, the degree of unevenness of the crystallite diameter and crystal orientation in the electrochrome plating layer is sufficient. Cannot be controlled. So the bath in addition to the control of the temperature, the current density at the time of electric chromium plating and 50~500A / dm ^2. When the current density is less than 50 A / dm ² , the film formation rate is low, the growth of crystallites is impaired, and it is considered that the crystal orientation is easily adjusted during the adsorption of Cr grains. They are aligned in the {222} direction. Further, when the film formation rate is low, the amount of hydrogen taken into the film increases, and it is considered that a large amount of distortion occurs due to the presence of hydrogen, and as a result, the hardness of the electrochrome plating layer becomes too high. Furthermore, the film forming speed is reduced, and the cost is increased. The current density is preferably 100 A / dm ² or more, more preferably 150 A / dm ² or more. However, if the current density exceeds 500 A / dm ² , defective plating may occur at the end portions or convex portions of the member, and the plating layer may be peeled off. Therefore, the current density is set to 500 A / dm ² or less. The current density is preferably 450 A / dm ² or less, more preferably 400 A / dm ² or less, and particularly preferably 350 A / dm ² or less.

  The electrochromic plating may be pulsed electrochromic plating with a pulse current. When a pulse is applied, it is considered that electricity is cut off before the hydrogen generation reaction occurs at the time of adsorption of Cr particles, and the amount of hydrogen taken into the film decreases, and the amount of strain in the film decreases. As a result, the occurrence of cracks when receiving a thermal history can be further prevented.

When pulsed electrochromic plating is performed, the bath temperature is set to 65 to 100 ° C., the maximum current density of the pulse current is set to 50 to 500 A / dm ² , and the frequency is set to 100 to 1000 Hz. If the frequency is less than 100 Hz, even if the bath temperature and the maximum current density are appropriately controlled, the crystallites become smaller and the orientation of the crystal orientation in the {222} direction becomes stronger. On the other hand, if the frequency is small, the effect of applying the pulse is hardly obtained, and only the film forming speed is lowered. The frequency is preferably 150 Hz or more, more preferably 200 Hz or more. However, when the frequency exceeds 1000 Hz, the crystallites become small, and the hardness of the electrochrome plating layer becomes high. The frequency is preferably 900 Hz or less, and more preferably 800 Hz or less. The minimum current density may be 0 A / dm ² or less (including the case where the polarities are opposite).

  The pulse current waveform is not particularly limited, but the ratio of the time during which the plating film is formed to the electrochromic plating time (the time during which the plating film is formed / the total plating time) is 0.25 to 0.9. Preferably there is. If the ratio is less than 0.25, the film forming speed is too low, and it takes too much time to obtain a desired film thickness. On the other hand, when the ratio exceeds 0.9, it is difficult to cut off the hydrogen generation reaction.

  In addition, the treatment conditions (for example, bath temperature, current density, frequency, etc.) may be gradually changed during electrochromic plating so that the hardness is inclined. In addition, when electrochromic plating is performed, it is preferable to perform stirring (for example, air stirring or vibration), filtration of impurities, liquid circulation, and the like.

  As the electrochrome plating bath, a sergeant bath can be used. The Sargent bath is a plating bath containing chromic acid and sulfuric acid as main components, and when this plating bath is used, a relatively hard electrochrome plating layer can be formed industrially at high speed. The Sargent bath preferably contains 100 to 400 g / L of chromic anhydride, 1 to 20 g / L of trivalent chromium, and 1.0 to 5.0 g / L of sulfuric acid with respect to the plating solution.

  In particular, the chromic anhydride in the electrochromic plating bath is preferably 270 to 400 g / L. By increasing the chromic anhydride to 270 g / L or more, the deposition rate of the electrochromic plating layer can be increased, and thick plating with an appropriate film quality can be easily performed.

  An activator may be added to the electrochrome plating bath. Examples of the activator include organic sulfonic acid. When the activator is added, about 5 to 10 g / L of organic sulfonic acid may be added to the plating solution.

  Conditions for providing a hard layer having a hardness higher than that of the electrochrome plating layer on the surface of the electrochrome plating layer are not particularly limited, and a known method can be employed. When a hard chromium layer is provided as the hard layer, it is preferable to employ electroplating in consideration of cost. When electroplating, two types of chromium plating baths may be prepared, or the same chromium plating bath may be used to form a film by changing processing conditions during electroplating. In order to provide a hard chromium layer having a hardness higher than that of the electrochromic plating layer using the same chromium plating bath in the electrochromic plating method, when using a Sargent bath as the chromium plating bath, for example, lowering the bath temperature of the plating bath. The current density during electrochrome plating may be reduced. Further, in order to provide a hard chromium layer by a pulse applied electrochromic plating method with a pulse current, for example, a ratio of a time during which a plating film is formed with respect to a frequency or an electrochromic plating time (a time during which a plating film is formed / total time The plating time) may be controlled according to the composition of the plating bath so that the hardness of the hard chromium layer is increased. Note that a hard chromium layer may be provided by sputtering.

  When a hard chrome layer is provided on the surface of the electrochrome plating layer, the electrochrome plating layer and the hard chromium layer may be continuously formed so that the hardness is inclined.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the following experimental examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

Experimental example 1
The following test was performed using as a test piece what formed the electrochromic plating layer by carrying out the electrochromic plating using the Sargent bath on the surface of the round bar made from Cu obtained by deoxidation.

  The composition of the Sargent bath used was composed of chromic acid and sulfuric acid as main components and an organic sulfonic acid of 8 g / L added to the plating solution as an activator. The Sargent bath contains 300 g / L of chromic anhydride, 5.0 g / L of sulfuric acid, and 5 g / L of trivalent chromium.

  The electrochrome plating was performed at a constant current density shown in Table 1 with the bath temperature of the plating bath shown in Table 1. The thickness of the obtained electrochrome plating layer is 30 μm.

  The crystallite diameter and peak intensity ratio of the obtained electrochrome plating layer were measured by the procedure described above using an X-ray diffractometer (X-ray diffractometer “RINT ULTIMA PC (device name)” manufactured by Rigaku Electric Co., Ltd.). did. The measurement position was the surface of the electrochromic plating layer at the center of the test piece, and the average was obtained by measuring five locations. The results are also shown in Table 1 below.

  Next, the hardness of the electrochrome plating layer in the cross section of the test piece was measured. For the measurement of hardness, a micro Vickers hardness meter (“Hardness Tester MVK-G2 (device name)” manufactured by Akashi Co., Ltd.) was used, and the load was 0.49N. Hardness was measured at five locations, and the hardness was calculated by averaging three points from the measurement results excluding the maximum and minimum values. The results are shown in Table 1 below.

  Next, the presence or absence of cracks in the case where the obtained electrochrome plating layer received a thermal history was evaluated by a hot dip immersion test. In the molten zinc immersion test, the test piece was immersed in molten zinc at 450 ° C. for 20 minutes, the test piece after immersion was cut vertically in the length direction, embedded in resin, mirror-polished, and a Cu substrate ( The interface between the round bar) and the electrochrome plating layer was observed at 400 times using an optical microscope. The observation position is the center and end of the test piece, and the ratio of the length of the portion where the Cu base and the electrochromic plating layer are in close contact with each other is calculated and averaged with respect to the surface length of the electrochromic plating layer. The thing is defined as the film soundness rate. The test piece provided with the above-mentioned electrochromic plating layer can be given a thermal history by immersing it in molten zinc at 450 ° C. Since zinc penetrates from the part and reaches the surface of the Cu base, the Cu base is corroded and peeling of the electrochrome plating layer is generated. Therefore, the degree of occurrence of cracks can be evaluated by calculating the film soundness rate. . The film soundness rate is determined to be acceptable when it is 60% or more, and unacceptable when it is less than 60%.

  From Table 1, it can be considered as follows. No. 1-3 are examples that satisfy the requirements defined in the present invention, and the crystallite size and peak intensity ratio of the electrochromic plating layer are appropriately controlled, so that the film soundness rate is high and severe at 300 ° C. or higher. The occurrence of cracks can be reduced even when subjected to a thermal history. On the other hand, no. Nos. 4 to 6 are examples that do not satisfy the requirements defined in the present invention, and the Cu base material is corroded because it cannot withstand a thermal history of 300 ° C. or higher and many cracks are generated.

Experimental example 2
In Experimental Example 1, instead of electrochromic plating, pulsed electrochromic plating was performed to form an electrochromic plating layer. Pulsing electric chromium plating is a bath temperature of the plating bath to a temperature shown in Table 2, the current density shown in Table 2 the maximum current density, the minimum current density was performed with 0A / dm ^2. The ratio of the plating film formation time to the electrochrome plating treatment time (plating film formation time / total plating time) was 0.5. The film was formed by applying a sine wave with a constant frequency. The thickness of the obtained electrochrome plating layer is 30 μm. In addition, No. For No. 15 and No. 21, the plating time was changed to control the thickness of the electrochrome plating layer. 15 is 3 μm. 21 was 5 μm.

  The crystallite diameter, peak intensity ratio, hardness, and film soundness rate of the obtained pulse applied electrochromic plating layer were measured by the same procedure as in Experimental Example 1. The results are also shown in Table 2 below.

  It can be considered from Table 2 as follows. No. 11 to 15 are examples satisfying the requirements defined in the present invention, and the crystallite size and the peak intensity ratio of the electrochromic plating layer are appropriately controlled, so that the film soundness rate is high and severe at 300 ° C. or higher. The occurrence of cracks can be reduced even when subjected to a thermal history. On the other hand, no. 16-19 is an example which does not satisfy the requirements prescribed | regulated by this invention, and since it cannot endure the heat history of 300 degreeC or more and many cracks generate | occur | produced, Cu base material is corroded.

  No. 20 and no. 21 is a reference example. No. No. 20, because the current density at the time of pulse-applied electrochromic plating is out of the range recommended in the present invention, the film soundness rate of the electrochromic plating layer at the center of the test piece was good. Peeling was observed in the electrochrome plating layer at the end. No. No. 21 is an example in which the thickness of the electrochromic plating layer is too thin. When a thermal history of 450 ° C. is received, the generation of cracks cannot be sufficiently suppressed, and zinc penetrates from the cracks, and the corrosion resistance of the Cu base material is reduced. It has not improved.

Experimental example 3
On the surface of a Cu disk-shaped test piece (φ44 mm × 8 mm) obtained by deoxidation, No. 1 of Experimental Example 1 was applied. 3 or No. 3 in Experimental Example 2 above. After forming the electrochromic plating layer under the same conditions as shown in FIG. 14, a hard layer was provided on the surface of the electrochromic plating layer in the same plating bath without washing and drying. As the hard layer, No. 1 in Experimental Example 1 was used. 4, No. 1 in Experimental Example 1 above. 5 or No. 5 in Experimental Example 2 above. The electrochrome plating layer was provided under the same conditions as shown in FIG. However, as a hard layer, No. 1 in Experimental Example 1 above. When the electrochrome plating layer shown in FIG. 3 or No. 3 in Experimental Example 2 above. After the electrochrome plating layer shown in FIG. 14 was formed, the bath temperature was cooled to 50 ° C. over 10 minutes, and kept at this temperature for electroplating. Since the electroplating is performed while cooling the bath temperature, the hardness of the hard layer is inclined.

The wear resistance of a test piece provided with a hard layer on the surface of the electrochrome plating layer was evaluated by a sliding wear test. In the sliding wear test, a pin-on-disk type tester was used as a sliding wear tester. The sliding test conditions were dry using a round bar of φ5 mm made of Al ₂ O ₃ as the mating pin material, a sliding speed of 1 m / sec, a load of 98 N (10 kgf), and a sliding distance of 1 km. The amount of decrease due to wear of the test piece was measured, and the wear resistance was evaluated according to the following criteria. The results are shown in Table 3 below. In addition, the Al ₂ O ₃ round bar was used as the mating pin material because the continuous casting mold and the Al ₂ O ₃ inclusions in the solidified slab contacted to wear the surface of the continuous casting mold. Because it is possible.

[Evaluation criteria for wear resistance]
A: The amount of decrease in the test piece due to wear is less than 50 mg, and the wear resistance is particularly excellent.
A: The amount of decrease in the test piece due to wear is 50 to 100 mg, and the wear resistance is excellent.
X: The amount of decrease in the test piece due to wear exceeds 100 mg, and the wear resistance is poor.

  From Table 3, it can be considered as follows. No. 31 to 34 are examples that satisfy the requirements defined in the present invention, and since a hard layer having a hardness higher than that of the electrochromic plating layer and a hardness exceeding Hv600 is provided on the upper layer of the electrochromic plating layer, Excellent wear resistance. On the other hand, no. 35 and No. No. 36 is inferior in wear resistance because the hardness of the hard layer is smaller than the hardness of the electrochromic plating layer or larger than the hardness of the electrochromic plating layer but 600 Hv or less.

Claims (5)

A chromium plated member provided with an electrochrome plated layer on the surface of a metal member,
The average diameter of the crystallites in the electrochrome plating layer is 16.0 nm or more, and the peak intensity ratio ({211} / {222}) of {211} and {222} by the X-ray diffraction method is 0.10 or more. A chrome-plated member, wherein   The chrome plated member according to claim 1, wherein the electrochrome plated layer has a hardness of Hv 600 or less.   The chromium plating member according to claim 1 or 2, wherein the electrochrome plating layer has a thickness of 5 µm or more.   The chrome-plated member according to any one of claims 1 to 3, wherein a hard layer having a hardness higher than that of the electrochromic plating layer and exceeding a hardness of Hv600 is provided on the electrochromic plating layer.   A casting mold for continuous casting comprising the chrome-plated member according to any one of claims 1 to 4.