JP2018040022A - Member for in-bath apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress increase of an abrasion loss and friction force that accompanies aging.SOLUTION: The invention relates to members for an in-bath apparatus to be used in a metal melting bath in continuous production equipment of a melting metal plating material. The members for an in-bath apparatus have a coating layer attached to at least a part of its surface, the coating layer being composed of hard particles and a matrix holding the hard particles. The matrix is a cobalt base alloy having Co as the main component. The hard particles are at least one simple substance selected from the group consisting of tungsten carbide, ditungsten carbide, chromium carbide, titanium carbide, and niobium carbide, or a granulated body formed by granulating the simple substance using a binder. The hard particles has an average shape factor of 1.55 or less, wherein the shape factor is obtained by dividing an area of a minimum circle enclosing a projection shape of the hard particles by an area corresponding to the projection shape of the hard particles.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a member for equipment in a bath.

  When the surface of a metal material such as a steel plate is plated using a metal such as zinc, a manufacturing method is used in which the metal material is continuously transferred in a tensioned state in a bath in which the metal used for plating is melted. There are many cases. In this case, a process is often employed in which a metal material is put into the molten metal bathtub from the snout and is pulled up from the bathtub by the support roll while being transported around the sink roll in the bath.

  The sink roll and support roll shafts and bearings are slid in a state where they are always exposed to molten metal. Therefore, excellent wear resistance is required for members in bath equipment such as sink rolls and support roll shafts and bearings. Therefore, conventionally, various techniques have been developed in order to improve the wear resistance of the in-bath equipment member.

  For example, in Patent Document 1 below, a coating layer containing a cobalt (Co) -based alloy and at least one of tungsten carbide, chromium carbide, titanium carbide, and niobium carbide is applied to the surface of a metal material with hot isostatic pressure ( A technique of forming by hot isostatic pressing (HIP) processing is disclosed.

  Also, in Patent Document 2 below, tungsten carbide composite lining for centrifugal casting, which uses spherical tungsten carbide hard particles having a specific particle size and reduces the opponent aggression by adopting a lining method by centrifugal casting. A material is disclosed.

  Further, in Patent Document 3 below, a corrosion-resistant wear-resistant sliding member that uses a Ni-based self-fluxing alloy as a tungsten carbide matrix and has improved corrosion resistance and wear resistance by covering the member with hot isostatic pressure treatment is disclosed. It is disclosed.

JP-A-7-268648 JP 7-290186 A JP 2000-266055 A

  However, the centrifugal casting method described in Patent Document 2 still has room for improvement in the characteristics of the manufactured member.

  Moreover, since the HIP processing material used by the said patent document 1 and the patent document 3 has a dense and homogeneous structure, while showing the outstanding abrasion resistance with respect to a thermal-spraying film or overlaying, it leads to generation | occurrence | production of a space | gap. Therefore, there is a limit to the amount of hard particles added such as various carbides. For this reason, as the continuous use period for the purpose of improving productivity is prolonged, the problem that the wear amount and the frictional force rapidly increase due to the dropping of the hard particles and the protrusion due to the matrix erosion occurred.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a member for equipment in a bath capable of suppressing an increase in wear amount and frictional force accompanying a change with time. Is to provide.

  In order to solve the above-mentioned problem, according to a certain aspect of the present invention, there is provided a member for an apparatus in a bath used for an apparatus in a molten metal bath in a continuous molten metal plating material manufacturing apparatus, wherein the member for an apparatus in a bath is: A coating layer provided on at least a part of the surface of the in-bath device member, wherein the coating layer includes hard particles and a matrix that holds the hard particles, and the matrix mainly includes Co. A cobalt-based alloy as a component, and the hard particles are at least one simple substance selected from the group consisting of tungsten carbide, ditungsten carbide, chromium carbide, titanium carbide and niobium carbide, or the simple substance using a binder. It is a granulated product, and the hard particles correspond to the projected shape of the hard particles with the area of the smallest circle including the projected shape of the hard particles That the average value of the shape coefficient expressed as divided by the area, 1.55 in a bath member equipment below is provided.

  The hard particles preferably have a particle size of 0.001 mm to 1 mm, and more preferably 0.02 mm to 0.5 mm.

  The content of the hard particles is preferably 15% by volume to 70% by volume with respect to the total volume of the coating layer, and 25% by volume to 55% by volume with respect to the total volume of the coating layer. It is more preferable that

  It is preferable that the thickness of the coating layer is 1 mm or more to (thickness dimension of the member for equipment in bath) -7 mm or less.

  The cobalt-based alloy is, in mass%, Cr: 11% to 34%, C: 0.05% to 3.5%, W: 2% to 25%, Ni: 0.5% Inclusive of the above, 30 to 30%, Si: 0.5% to 4%, B: 0.5% to 4%, and the balance may be Co and impurities.

  As described above, according to the present invention, by increasing the shape of the hard particles to a spherical shape having a specific shape factor, it is possible to suppress an increase in the amount of wear and frictional force accompanying a change with time. .

It is explanatory drawing which showed typically the structure of the continuous hot-dip galvanized steel plate manufacturing apparatus. It is explanatory drawing which showed typically the structure of the member for apparatus in bath which concerns on the 1st Embodiment of this invention. It is explanatory drawing which showed an example of the cross-sectional captured image of the coating layer which concerns on the embodiment. It is explanatory drawing for demonstrating the shape factor of the hard particle which concerns on the same embodiment. It is explanatory drawing for demonstrating the calculation method of the shape factor of the hard particle which concerns on the same embodiment. It is the graph which showed an example of the relationship between the average value of a shape factor, a specific wear amount, and a friction coefficient. It is explanatory drawing which showed an example of the HIP apparatus typically. It is explanatory drawing which showed an example of the HIP apparatus typically.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

(First embodiment)
Below, the member for apparatus in a bath which concerns on the 1st Embodiment of this invention is demonstrated in detail. The in-bath apparatus member according to the present embodiment is used for an in-molten bath apparatus in a continuous molten metal plating material manufacturing apparatus.

  In the following description, attention is given to a hot dip galvanized steel sheet as an example of the hot dip galvanized material, and an explanation will be given by taking as an example a device in a hot dip galvanized bath in a continuous hot dip galvanized material manufacturing apparatus. However, the in-bath apparatus member according to the embodiment of the present invention is not limited to the in-bath apparatus member disposed in the molten zinc bath.

<About continuous hot-dip galvanized steel sheet manufacturing equipment>
Prior to the description of the in-bath apparatus member according to the present embodiment, the entire configuration of the continuous hot-dip galvanized steel sheet manufacturing apparatus in which the in-bath apparatus member is used will be briefly described with reference to FIG. FIG. 1 is an explanatory view schematically showing a configuration of a continuous hot-dip galvanized steel sheet manufacturing apparatus.

  As schematically shown in FIG. 1, the continuous hot-dip galvanized steel sheet manufacturing apparatus mainly includes a hot-dip zinc bath 1, a snout 2, a sink roll 3, and a pair of support rolls 4.

  In the molten zinc bath 1, zinc, which is a molten metal for plating the surface of the steel sheet S to be passed, is held in a molten state. The snout 2 is a facility for continuously feeding the steel sheet S to the molten zinc bath 1 and is filled with an inert gas such as nitrogen. The sink roll 3 and the support roll 4 have support shafts 5 and 6, respectively. The support shaft 6 is connected to a drive source (not shown) such as a motor, and has a constant speed in the direction of the arrow in the figure. Is driven to rotate.

  In addition, the continuous hot-dip galvanized steel sheet manufacturing apparatus as shown in FIG. 1 is provided with various other equipment (not shown) such as an ingot charging device, a dross recovery device, and a roll mount.

  The in-bath apparatus member according to the present embodiment is an in-bath apparatus disposed inside the molten zinc bath 1 such as the support shafts 5 and 6 of the sink roll 3 and the support roll 4 and a bearing (not shown). It is used as a member.

<About equipment for bath equipment>
Next, the in-bath apparatus member according to the present embodiment will be described in detail with reference to FIGS. FIG. 2 is an explanatory view schematically showing the configuration of the in-bath apparatus member according to the present embodiment. FIG. 3 is an explanatory diagram showing an example of a cross-sectional captured image of the coating layer according to the present embodiment. FIG. 4 is an explanatory diagram for explaining the shape factor of the hard particles according to the present embodiment, and FIG. 5 is an explanatory diagram for explaining a calculation method of the shape factor.

  As illustrated schematically in FIG. 2, the in-bath apparatus member 10 according to the present embodiment includes a base material 11 and a coating layer 13 formed on at least a part of the surface of the base material 11.

  The base material 11 is not particularly limited, and is appropriately selected from known steel materials according to characteristics such as strength required for the sink roll 3 and the support roll 4. Examples of the base material 11 include various stainless steel plates such as SUS316L.

  The covering layer 13 is formed at least on a portion of the base material 11 where corrosion resistance and wear resistance are required as the in-bath apparatus member 10 such as a sliding portion of a shaft or a bearing. The covering layer 13 may be formed on the entire surface of the base material 11. The covering layer 13 is formed on a desired portion of the base material 11 by a known method such as HIP processing.

  As illustrated in FIG. 3, the coating layer 13 includes (a) a cobalt base alloy 15 mainly composed of cobalt (Co), and (b) hard particles 17 contained in the cobalt base alloy 15. Including.

  The covering layer 13 as described in detail below is preferably formed on the surface of the base material 11 by HIP treatment with a thickness of 1 mm or more to (thickness dimension of the member for equipment in bath) -7 mm or less. When the thickness of the coating layer 13 (thickness d shown in FIG. 2) is less than 1 mm, the durability of the coating layer 13 may be insufficient and sufficient reliability may not be obtained. . Moreover, when the thickness of the coating layer 13 exceeds (thickness dimension of the member for equipment in a bath) −7 mm, the base material 11 may be deformed or broken due to internal stress generated during the HIP process. It is not preferable.

  Hereinafter, the coating layer 13 will be described in detail.

[Cobalt-based alloy 15]
The cobalt-based alloy 15 containing Co as a main component is an alloy that functions as a matrix that holds the hard particles 17. The cobalt-based alloy 15 includes the following components. In addition, in the following component description,% means the metal conversion amount represented by the mass%.

Cr: 11% to 34% C: 0.05% to 3.5% W: 2% to 25% Ni: 0.5% to 30% Si: 0.5% to 4% or less B: 0.5% to 4%

  In the cobalt base alloy 15, the balance of the above components is Co and inevitable impurities.

○ Cr: 11% to 34% Chromium (Cr) is an element used for improving the corrosion resistance of the coating layer 13. By setting the Cr amount (Cr equivalent amount) to 11 mass% or more, it is possible to improve the corrosion resistance of the coating layer 13 and to effectively precipitate chromium carbide. On the other hand, when the amount of Cr exceeds 34% by mass, the toughness of the coating layer 13 decreases, and cracking may occur during the HIP treatment, which is not preferable.

C: 0.05% to 3.5% Carbon (C) is an element used for improving the resistance to melting of the coating layer 13. By setting the amount of C to 0.05 to 3.5% by mass, it becomes possible to effectively precipitate carbide, improve the corrosion resistance of the coating layer 13, and improve the corrosion resistance. On the other hand, when the amount of C is less than 0.05% by mass, the effect of improving the resistance to melting as described above cannot be sufficiently obtained, which is not preferable. In addition, when the amount of C exceeds 3.5% by mass, the coating layer 13 may become brittle, which is not preferable.

○ W: 2% to 25% Tungsten (W) is an element used for improving the strength of the coating layer 13. By setting the amount of W to 2 to 25% by mass, tungsten carbide can be effectively precipitated, the wear resistance of the coating layer 13 can be improved, and the corrosion resistance can be improved. On the other hand, when the amount of W is less than 2% by mass, the effect of improving the wear resistance as described above cannot be obtained sufficiently, which is not preferable. On the other hand, when the amount of W exceeds 25% by mass, the toughness of the coating layer 13 is lowered, and cracking may occur during the HIP treatment, which is not preferable.

○ Ni: 0.5% to 30% Nickel (Ni) is an element used for improving the toughness of the coating layer 13. By making the amount of Ni 0.5% by mass or more, the toughness of the coating layer 13 can be improved. On the other hand, when the amount of Ni is less than 2% by mass, the effect of improving toughness as described above cannot be sufficiently obtained, which is not preferable. On the other hand, when the amount of Ni is more than 30% by mass, the corrosion resistance of the coating layer 13 to the molten metal (molten zinc) is remarkably lowered, which is not preferable.

B and Si: 0.5% or more to 4% or less Boron (B) and silicon (Si) are added by 0.5 to 4% by mass of these elements, respectively, thereby melting the cobalt-based alloy 15 Is an element that can be lowered to 1100 ° C. or lower, for example. By adding these elements to lower the melting point, it is possible to further improve the denseness of the coating layer 13 during the HIP process. As for B, it is possible to improve the corrosion resistance by effectively precipitating the boride, and the wear resistance of the coating layer 13 can be improved. On the other hand, when the amount of B or Si is less than 0.5%, the above-described melting point lowering effect cannot be sufficiently obtained, which is not preferable. Further, when the amount of B or Si is more than 4% by mass, the toughness of the coating layer 13 is lowered, and cracking may occur during the HIP treatment, which is not preferable.

  Heretofore, the cobalt-based alloy 15 according to the present embodiment has been described in detail.

<About hard particles 17>
Hard particles 17 are added to the cobalt-based alloy 15 that is a matrix and is held by the cobalt-based alloy 15. The hard particles 17 are formed by granulating at least one simple substance selected from the group consisting of tungsten carbide, ditungsten carbide, chromium carbide, titanium carbide and niobium carbide, or a binder such as Ni or Co. It is a thing.

Among the hard particles 17, tungsten carbide (WC), ditungsten carbide (W ₂ C), and titanium carbide (TiC) are hard particles that improve the wear resistance of the coating layer 13, and chromium carbide (Cr ₂₃ C _6, Cr ₇ C _{3, and} Cr ₃ C ₂ ) are hard particles that relieve internal stress of the coating layer 13. Of the hard particles 17, niobium carbide (NbC) is a hard particle that improves the lubricity of the coating layer 13. The hard particles 17 having such characteristics can be used alone, but when used in combination, these characteristics are superimposed on each other.

  In the present embodiment, the hard particles 17 are spherical particles having an average shape factor as described below of 1.55 or less (see, for example, FIG. 3). Here, the shape factor is expressed as a value obtained by dividing the area of the minimum circle including the projected shape of one hard particle of interest by the area corresponding to the projected shape, as schematically shown in FIG. It is what is done. In the example shown in FIG. 4, the case where the projection shape of a certain hard particle 17 is schematically represented by a hexagon is shown. The minimum circle including such hard particles 17 is the minimum circumscribed circle circumscribing the projected shape of the hard particles as shown in FIG.

Hereinafter, the calculation method of the shape factor will be specifically described with reference to FIG.
In order to calculate the shape factor, first, a tissue image (cross-sectional image) of the tissue of interest is imaged using an electron microscope, an optical microscope, or the like. At this time, the size of the imaging field of view is about 10 times the average particle diameter of the hard particles 17. Further, out of the plurality of hard particles 17 existing in the field of view, hard particles at least part of which are in contact with the boundary of the field of view are excluded from the calculation process. Such tissue images are taken for 10 fields of view.

  Next, each obtained tissue image is binarized by a predetermined binarization threshold, and a portion corresponding to the hard particles 17 is separated. Thereafter, the hard particles 17 satisfying the above criteria are used as the calculation target of the shape factor.

  Subsequently, a known image processing or the like is applied to measure the projected area of each hard particle and the area of the minimum circle including the hard particle. By dividing the obtained projected area by the area of the corresponding inclusion minimum circle, the shape factor of the hard particle of interest can be calculated.

  By calculating the average value of the shape factors of the target particles included in the ten tissue images taken, it is possible to specify the average value of the shape factors.

  In the example shown in FIG. 5, it can be seen that there are 25 target hard particles in one cross-sectional tissue image. The average value of the hard particles corresponding to this cross-sectional structure image was 1.13.

  By using the hard particles 17 having such an average value of the trait coefficient, even if the cobalt-based alloy 15 as the matrix is melted and the hard particles 17 protrude, the hard particles 17 are separated from the mating surface. Since the contact portion has a specific spherical shape with a large curvature, it is possible to reduce the surface pressure at the contact point and extremely effectively suppress an increase in frictional force.

By using the hard particles 17 as described above, the specific wear amount of the coating layer 13 (for example, the total amount when the coating layer 13 is applied to both the shaft and the bearing) is 1 × 10 ^−6. mm ³ / m · N or less, and the friction coefficient is 0.2 or less. FIG. 6 shows the results of a laboratory test in which the specific wear amount and the friction coefficient were measured by changing the shape factor of the hard particles 17. As is apparent from FIG. 6, by setting the average value of the shape factor of the hard particles 17 to 1.55 or less, the specific wear amount becomes 1 × 10 ⁻⁶ mm ³ / m · N or less, and the friction coefficient becomes 0. It turns out that it is 2 or less.

  The average particle size of the hard particles 17 is preferably 0.001 mm to 1 mm. When the average particle size is less than 0.001 mm, the hard particles 17 are aggregated and may not be uniformly mixed with the cobalt-based alloy 15 as the matrix, which is not preferable. On the other hand, when the average particle diameter exceeds 1 mm, pores may remain inside the coating layer 13, which is not preferable.

  The average particle diameter of the hard particles 17 is more preferably 0.02 mm to 0.5 mm. By making the average particle diameter 0.02 mm or more and 0.5 mm or less, the dispersibility of the hard particles 17 in the matrix is maintained well, and the corrosion resistance and wear resistance of the coating layer 13 are exhibited well. It becomes possible.

  The average particle size of the hard particles 17 was measured by, for example, a laser diffraction particle size distribution measurement method after classification at the raw material stage.

  The hard particles 17 having such a shape and average particle diameter can be manufactured using a general method used for manufacturing a thermal spray material powder, such as a granulation sintering method or a gas atomization method. . At this time, the shape factor can be controlled by appropriately using the production conditions such as the use of primary particles sufficiently smaller than the target particle size, the rolling time and the gas temperature.

  For example, when the hard particles 17 are produced by the granulation sintering method, by increasing the rolling time, the irregularities of the primary particles are smoothed to make the particle shape closer to a sphere, and a hard material having a desired shape factor. Particles 17 can be obtained. Further, when the hard particles 17 are manufactured by the gas atomization method, the hard particles 17 can be manufactured by sufficiently increasing the gas temperature and the atmospheric temperature so that a desired shape factor can be obtained.

  Further, the content of such hard particles 17 is preferably 15% by volume to 70% by volume with respect to the total volume of the coating layer 13. When the content of the hard particles 17 is less than 15% by volume, the area ratio of the cobalt-based alloy 15 that is a matrix is increased, the corrosion resistance is lowered, and the wear resistance of the coating layer 13 is insufficient. Therefore, it is not preferable. Moreover, when content of the hard particle | grains 17 exceeds 70 volume%, since a crack may generate | occur | produce at the time of construction of the coating layer 13, it is unpreferable.

  The content of the hard particles 17 is more preferably 25% by volume to 55% by volume with respect to the total volume of the coating layer 13. Regarding the content of the hard particles 17, the crack resistance and the wear resistance are in a trade-off relationship such that the smaller the content, the better the crack resistance, and the higher the content, the better the wear resistance. By making the content of the hard particles 17 25 volume% or more and 55 volume% or less, it becomes possible to efficiently exhibit both crack resistance and wear resistance.

  In addition, when adding a multiple types of compound as the hard particle | grains 17, it is preferable that total content shall be in said range.

  The hard particles 17 according to this embodiment have been described in detail above.

<About the manufacturing method of the coating layer 13>
Next, a method for manufacturing the coating layer 13 as described above will be briefly described with reference to FIGS. 7A and 7B. 7A and 7B are explanatory diagrams schematically illustrating an example of the HIP device.

  The HIP process is performed using an apparatus (HIP apparatus) as shown in FIGS. 7A and 7B. As illustrated in FIG. 7A, the HIP apparatus is provided with a pressure vessel for storing an article to be processed and a Mo heater, and is configured as a heating furnace. Moreover, the HIP apparatus can make a pressure vessel and its inside into a predetermined pressure condition with the high-pressure cylinder provided in the apparatus. Furthermore, the HIP apparatus is provided with a vacuum pump for exhausting the gas in the pressure vessel and a gas supply pipe for introducing Ar gas, and HIP processing can be performed in an Ar gas atmosphere. .

In the HIP process, first, as illustrated in FIG. 7B, a cobalt-based alloy 15 and hard particles 17 that are a matrix with respect to a space formed between a base material 11 used as a base material and a metal capsule are formed. The material powder is enclosed and accommodated in a pressure vessel. Then, it is processed in an Ar gas atmosphere at a pressure of 1000 to 1500 kgf / cm ² and a temperature of 1050 to 1250 ° C. for 1 to 3 hours. In addition, 1 kgf is about 9.8N.

  By performing such a process, it is possible to manufacture the in-bath apparatus member according to the present embodiment.

  Below, the member for apparatus in bath which concerns on embodiment of this invention is demonstrated concretely, showing an Example and a comparative example. In addition, the Example shown below is only an example of the member for apparatus in bath which concerns on embodiment of this invention, Comprising: The member for apparatus in bath which concerns on embodiment of this invention is limited to the Example shown below. I don't mean.

(Experimental example)
In accordance with the above-described method for manufacturing an in-bath equipment member, a plurality of types of shaft sleeves are manufactured, and each of the shaft sleeves is used in a continuous molten metal plating apparatus to generate a steel sheet slip as the specific wear amount and friction coefficient increase. The presence or absence was evaluated. The Co-based alloy and hard particles used in this experimental example are as shown in the following table.

  In the table below, the particle size and primary particle size of the hard particles were measured by a laser diffraction particle size distribution measurement method after classification at the raw material stage. The specific wear amount was calculated from the change in the shaft diameter of the in-bath equipment member before and after use. Further, the average value of the shape factor was measured by the method described above.

  The obtained results are shown in Table 1 below.

  As is apparent from Table 1, in the comparative example of the present invention, the specific wear amount was large, the base material was deformed, cracks occurred during construction, and steel plate slip occurred. In the example, the specific wear amount was small, and no steel plate slip occurred. This result shows that in the examples of the present invention, the increase in the specific friction amount and the friction coefficient are extremely well suppressed.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

11 Base material 13 Coating layer 15 Cobalt base alloy 17 Hard particles

Claims (7)

A member for an in-bath apparatus used for an apparatus in a molten metal bath in a continuous molten metal plating material manufacturing apparatus,
The in-bath apparatus member has a coating layer provided on at least a part of the surface of the in-bath apparatus member,
The coating layer includes hard particles and a matrix that holds the hard particles,
The matrix is a cobalt-based alloy containing Co as a main component,
The hard particles are at least one simple substance selected from the group consisting of tungsten carbide, ditungsten carbide, chromium carbide, titanium carbide and niobium carbide, or a granulated product obtained by granulating the simple substance using a binder,
The hard particles have an average value of a shape factor represented by a value obtained by dividing the area of the minimum circle including the projected shape of the hard particles by the area corresponding to the projected shape of the hard particles, which is 1.55 or less. , Components for equipment in the bath.   The member for equipment in a bath according to claim 1 whose particle size of said hard particles is 0.001 mm or more-1 mm or less.   The member for apparatus in a bath of Claim 2 whose particle size of the said hard particle is 0.02 mm-0.5 mm.   4. The member for an in-bath apparatus according to claim 1, wherein the content of the hard particles is 15% by volume to 70% by volume with respect to the total volume of the coating layer.   5. The device member in a bath according to claim 4, wherein the content of the hard particles is 25% by volume to 55% by volume with respect to the total volume of the coating layer.   The member for apparatus in bath of any one of Claims 1-5 whose thickness of the said coating layer is 1 mm or more-(thickness dimension of the member for apparatus in bath) -7mm or less. The cobalt-based alloy is mass%,
Cr: 11% to 34%,
C: 0.05% to 3.5%,
W: 2% to 25%,
Ni: 0.5% to 30%,
Si: 0.5% to 4%,
B: 0.5% to 4%,
The member for equipment in a bath according to any one of claims 1 to 6, wherein the balance is Co and impurities.

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