Self-fluxing alloy spray coating film

Abstract

In order to provide a self-fluxing alloy spray coating film having both a wear resistant property and a thermal shock resistant property, the self-fluxing alloy spray coating film according to the present invention has: a first phase containing Ni at 50 mass% or more and W at less than 5 mass%; a second phase containing carbides or borides of W, and containing Ni at less than 50 mass% and W at 30 mass% or more; and a third phase containing carbides or borides of W, Cr, or Mo. The self-fluxing alloy spray coating film satisfies at least one of (1) including W at 5 mass% or more but less than 30 mass%, (2) including Cr at 30 mass% or more, and (3) including Mo at 20 mass% or more. The Vickers hardness of the first phase is 180 or more but less than 400 (Hv0.05), the Vickers hardness of the second phase is 900 or more but less than 2200 (Hv0.05), and the Vickers hardness of the third phase is 400 or more but less than 2200 (Hv0.05).

Description

Self-fluxing alloy spray coating

[0001] The present invention relates to a self-fluxing alloy thermal spray coating.

[0002] In the continuous casting process, molten steel is poured into a water-cooled copper mold, and the cast piece is drawn out with only the surface solidified. The cast piece is supported by rolls and cooled with water sprays to gradually solidify it. Continuous casting rolls used in such continuous casting equipment are used in harsh environments where rapid heating and cooling are repeated, and are subject to wear damage during the transport of the cast piece. Therefore, thermal shock resistance and wear resistance are required for such continuous casting rolls.

[0003] For example, Patent Document 1 proposes a breakage-resistant and wear-resistant roll for continuous casting, which is formed by spraying a Ni-based or Co-based self-fluxing alloy onto the barrel surface of a stainless steel roll and then subjecting the roll to a melting heat treatment.

[0004] Furthermore, Patent Document 2 mentions a drawback of the conventional technology of forming a thermal spray coating layer on the surface of a roll substrate using a self-fluxing alloy material with a high C content as a wear-resistant material, in that although the high C content makes the coating hard, the coating layer is brittle, and a carburized layer is formed due to interdiffusion between the coating layer and the substrate during fusing treatment, causing cracks to propagate within the carburized layer and making it prone to peeling. In response to this drawback, Patent Document 2 describes that by extremely reducing the C content of the thermal spray coating layer formed on the surface of the roll substrate to 0.02 to 0.25 wt %, the brittleness of the thermal spray coating layer is improved and the generation of a carburized layer is suppressed, making it possible to form a thermal spray coating layer with excellent peeling resistance, and that by adding a carbide such as tungsten carbide, excellent wear resistance can also be obtained.

[0005] JP 57-203765 ​​A JP 2006-263807 A

[0006] However, as a result of research by the present inventors, it has been found that even a thermal spray coating layer containing a Ni-based or Co-based self-fluxing alloy and a carbide such as tungsten carbide, as in Patent Document 2, does not have sufficient thermal shock resistance.

[0007] The present invention has been made in view of the above problems, and an object of the present invention is to provide a self-fluxing alloy sprayed coating that has both wear resistance and thermal shock resistance.

[0008] The self-fluxing alloy thermal spray coating of the present invention has a first phase containing 50 mass% or more of Ni and less than 5 mass% of W; a second phase containing less than 50 mass% of Ni and 30 mass% or more of W and containing a carbide or boride of W; and a third phase containing a carbide or boride of W, Cr, or Mo and satisfying at least one of the following (1) to (3): (1) containing 5 mass% or more but less than 30 mass% of W; (2) containing 30 mass% or more of Cr; or (3) containing 20 mass% or more of Mo. The Vickers hardness of the first phase is 180 or more and less than 400 (Hv 0.05), the Vickers hardness of the second phase is 900 or more and less than 2200 (Hv 0.05), and the Vickers hardness of the third phase is 400 or more and less than 2200 (Hv 0.05).

[0009] In addition, it is preferable that the area of ​​the cross section of the self-fluxing alloy thermal spray coating be occupied by the first phase at least 40% and the area of ​​the second phase at least 10%.

[0010] Furthermore, it is preferable that the area of ​​the cross section of the self-fluxing alloy thermal spray coating be occupied by the first phase is 40% or more, the area of ​​the third phase is 10% or more, and the Vickers hardness of the third phase is 900 or more (Hv 0.05).

[0011] In addition, in the cross section of the self-fluxing alloy sprayed coating, the area occupied by the second phase and the area occupied by the third phase are both preferably 2.0% or more, and more preferably 3.0% or more.

[0012] Furthermore, it is preferable that the self-fluxing alloy sprayed coating does not contain Mo or contains less than 3 mass% Mo, and that in a cross section of the self-fluxing alloy sprayed coating, the area occupied by the first phase is 65 to 85%, the area occupied by the second phase is 10 to 30%, and the area occupied by the third phase is more than 0% but not more than 15%.

[0013] Furthermore, it is preferable that the self-fluxing alloy sprayed coating contains 3 mass% or more of Mo, and that in a cross section of the self-fluxing alloy sprayed coating, the area occupied by the first phase is 40 to 65%, the area occupied by the second phase is 1 to 15%, and the area occupied by the third phase is 25 to 55%.

[0014] According to the present invention, the self-fluxing alloy sprayed coating can have both wear resistance and thermal shock resistance.

[0015] FIG. 1 is an SEM image of a cross section of the coating of Example 5. FIG. 2 is an SEM image of a cross section of the coating of Example 8. FIG. 3 is an SEM image of a cross section of the coating of Comparative Example 2.

[0016] <Self-fluxing alloy sprayed coating> Hereinafter, one embodiment of the self-fluxing alloy sprayed coating of the present invention will be described.

[0017] The self-fluxing alloy thermal spray coating according to this embodiment has a first phase, a second phase, and a third phase, the first phase containing 50 mass% or more of Ni and less than 5 mass% of W, the second phase containing less than 50 mass% of Ni and 30 mass% or more of W and including carbides or borides of W, and the third phase containing carbides or borides of W, Cr, or Mo. The third phase also satisfies at least one of the following (1) to (3): (1) Contains 5% by mass or more and less than 30% by mass of W, (2) Contains 30% by mass or more of Cr, and (3) Contains 20% by mass or more of Mo. The Vickers hardness of the first phase is 180 or more and less than 400 (Hv 0.05), the Vickers hardness of the second phase is 900 or more and less than 2200 (Hv 0.05), and the Vickers hardness of the third phase is 400 or more and less than 2200 (Hv 0.05). The Vickers hardness of the first phase is preferably 200 to 380 (Hv 0.05), the Vickers hardness of the second phase is preferably 1000 to 2000 (Hv 0.05), and the Vickers hardness of the third phase is preferably 500 to 2000 (Hv 0.05).

[0018] In a self-fluxing alloy sprayed coating having such a structure, the second and third phases have high hardness, so that wear of the self-fluxing alloy sprayed coating can be suppressed.

[0019] Furthermore, the first phase is softer than the other two phases and is less likely to crack. The first phase functions as a binder connecting the second and third phases, thereby suppressing coating peeling due to thermal shock. Even if cracks do occur in the coating due to strong thermal shock, the self-fluxing alloy sprayed coating contains different phases, which stops the crack propagation at the phase interface and makes it less likely for large cracks to occur. This effect is particularly enhanced by containing three different phases. As such, the self-fluxing alloy sprayed coating of this embodiment can achieve extremely high thermal shock resistance.

[0020] The lower limit of the W content in the first phase is not particularly limited and may be 0%. A low W content in the first phase reduces the hardness of the first phase. The lower limit of the Ni content in the second phase is also not particularly limited and may be 0%.

[0021] The hardness of each phase depends on the type and proportion of metal atoms that mainly constitute each phase, such as Ni, W, Cr, and Mo, as well as the type and proportion of other atoms, such as B and C. For example, the higher the B or C content, i.e., the higher the carbide or boride content, the higher the hardness.

[0022] Furthermore, when the area of ​​the cross section of the self-fluxing alloy thermal spray coating is occupied by the first phase, which is a relatively soft phase, of 40% or more, higher thermal shock resistance can be obtained.

[0023] Furthermore, when the area of ​​the second phase, which has high hardness, is 10% or more, higher wear resistance can be obtained. In particular, when the area of ​​the first phase is 40% or more and the area of ​​the second phase is 10% or more, both the thermal shock resistance and the wear resistance are improved, which is preferable.

[0024] Furthermore, higher wear resistance can be obtained when the area occupied by the third phase is 10% or more and the Vickers hardness of the third phase is 900 or more. In particular, it is preferable that the area of ​​the first phase is 40% or more and the area of ​​the third phase having a Vickers hardness of 900 or more is 10% or more, since this improves both thermal shock resistance and wear resistance.

[0025] In the cross section of the self-fluxing alloy thermal spray coating, the area occupied by the second phase and the area occupied by the third phase are both preferably 2.0% or more. By having the second phase and the third phase have a certain area, the propagation of cracks is suppressed, resulting in high thermal shock resistance.

[0026] Preferably, the self-fluxing alloy sprayed coating contains no Mo or less than 3 mass% Mo, and in the cross section of this coating, the area occupied by the first phase is 65 to 85%, the area occupied by the second phase is 10 to 30%, and the area occupied by the third phase is more than 0% but not more than 15%. In a self-fluxing alloy sprayed coating in which the Mo content of the entire coating is less than 3 mass%, by ensuring that the area ratio of each phase satisfies the above ranges, both thermal shock resistance and wear resistance are improved.

[0027] Furthermore, it is preferable that the self-fluxing alloy sprayed coating contains 3 mass% or more of Mo, and that in the cross section of this coating, the area occupied by the first phase is 40 to 65%, the area occupied by the second phase is 1 to 15%, and the area occupied by the third phase is 25 to 55%. In a self-fluxing alloy sprayed coating in which the Mo content of the entire coating is 3 mass% or more, by having the area ratio of each phase in the above ranges, both thermal shock resistance and wear resistance are improved.

[0028] The area ratio and hardness of each phase are measured as follows: First, the cross section of the sample is observed with a scanning electron microscope (SEM). In the backscattered electron image of the SEM, phases composed of different elements are observed as regions with different color tones. The components contained in each phase are identified by energy dispersive spectroscopy (EDS) analysis. The backscattered electron image of the SEM is analyzed, and the area ratio of each phase is calculated. Furthermore, while observing the enlarged image of the Vickers hardness tester, the indenter of the Vickers hardness tester is adjusted to a desired phase, and the hardness of each phase is measured. The position adjustment of the backscattered electron image of the SEM and the enlarged image of the Vickers hardness tester can be easily performed by marking the cross section of the sample.

[0029] Furthermore, examples of methods for forming a self-fluxing alloy sprayed coating include a method including the following steps: (a) spraying a powder material obtained by mixing a first powder, a second powder, and a third powder onto a substrate to form a sprayed coating on the substrate; and (b) fusing the sprayed coating to form a self-fluxing alloy sprayed coating. In step (a), the powder material obtained by mixing the first powder, the second powder, and the third powder is sprayed onto the substrate to form a sprayed coating on the substrate. The substrate may be, for example, a metal substrate, and is not particularly limited and may be any material. Furthermore, the metal substrate may be, for example, a stainless steel substrate. Furthermore, the substrate in the present invention may also include a substrate having a coating applied to its surface. Examples of such coatings include an iron-chromium-based hardfacing layer.

[0030] The powder material is a mixture of the first powder, the second powder, and the third powder, and is a material for self-fluxing alloy thermal spraying. The powder material may contain powder components other than the first powder, the second powder, and the third powder, but preferably the total amount of the first powder, the second powder, and the third powder is 80 mass% or more of the entire powder, more preferably 90 mass% or more, and even more preferably 95 mass% or more, and particularly preferably the powder material is composed only of the first powder, the second powder, the third powder, and inevitable impurities.

[0031] The first powder is a Ni-based self-fluxing alloy, which contains 0.8 to 4.5 mass% B and 1.5 to 5.0 mass% Si. When the B and Si contents satisfy the above ranges, the melting temperature of the alloy is lowered, self-fluxing properties are imparted, and the workability of the fusing treatment in step (b) is improved. More preferably, the self-fluxing alloy contains 2.5 to 4.0 mass% B and 3.0 to 5.0 mass% Si. When the B and Si contents satisfy these ranges, the above-mentioned effects are more easily achieved.

[0032] The Ni-based self-fluxing alloy can be selected from the group consisting of types 1, 2, 3, 4, 5, 6, 7, 8, and 9 of Ni-based self-fluxing alloys, for example, as shown in Table 1 below. Such first powders play a particular role in improving the thermal shock resistance of the self-fluxing alloy thermal spray coating. Note that in Table 1, the words "below" may not necessarily include the element in question.

[0033]

[0034] The second powder is one or more selected from the group consisting of carbide ceramics and carbide cermets. Examples of carbide ceramics include tungsten carbide (WC), and examples of carbide cermets include carbide ceramics combined with metals. Tungsten carbide cermets are particularly preferred for the second powder. Any tungsten carbide cermet commonly used in the relevant technical field can be used as appropriate. For example, WC-Co, WC-Co-Cr, or WC-Ni can be used as the tungsten carbide cermet. Furthermore, the tungsten carbide cermet preferably has a total W and C content of 70% by mass or more relative to the entire tungsten carbide cermet.

[0035] The third powder is at least one selected from the group consisting of Cr, Mo, Fe, Ni, Co, and alloys containing any of these as a primary component. However, alloys containing Ni as a primary component (hereinafter also referred to as "Ni-based alloys") are materials other than the Ni-based self-fluxing alloys defined for the first powder. In this specification, the term "primary component" refers to the component with the highest content among all components. The primary component preferably accounts for 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more of all components. Examples of Ni-based alloys that can be used as the third powder include those selected from the group consisting of Monel K500, Monel 400, Hastelloy B, Hastelloy C276, Hastelloy C22, Inconel 600, Inconel 625, Incoloy 800, and Incoloy 825. Furthermore, the Co-based alloy that can be used as the third powder can be selected from the group consisting of, for example, Stellite 6, Stellite 12, Stellite 21, Stellite 31, Tribaloy T-400, and Tribaloy T-800. The Fe-based alloy that can be used as the third powder can be selected from the group consisting of, for example, SUS316L, SUS304, SUS310S, SUS430, SUS420J2, and S45C. The Mo-based alloy that can be used as the third powder can be selected from the group consisting of, for example, MoSi ２ and Mo-Ti-Zr-C (TZM alloy). The third powder preferably contains 10 to 30 mass% of Cr or 5 to 20 mass% of Mo. The Cr or Mo in the third powder combines with the B contained in the first powder to form an intermetallic compound. The Cr, Mo, Fe, Ni, or Co used as the third powder may contain one or more other metal components as impurities in addition to these metal components.

[0036] When the element most abundant in the third powder is Cr, Fe, Ni, or Co, the powder material contains 45 to 65 mass% of the first powder, 5 to 35 mass% of the second powder, and 5 to 50 mass% of the third powder. When each powder contains multiple materials, the total content of each is defined as the total content of each. For example, Inconel 625 and Stellite 21 are both classified as the third powder, but when the powder material contains both, the total content of these materials may be 5 to 50 mass% of the entire powder material.

[0037] When the element contained most abundantly in the third powder is Mo, the powder material contains 70 to 85 mass% of the first powder, 5 to 25 mass% of the second powder, and 5 to 25 mass% of the third powder. When each powder contains multiple types of materials, the total content of each is defined as the total content of each. For example, Mo and MoSi ２ are all classified as third powders, and when the powder material contains both of these, the total of these may account for 5 to 25 mass % of the entire powder material.

[0038] As described above, the components contained in each powder also diffuse into the phases primarily formed by the other powders. For example, the first powder primarily forms the first phase, but atoms contained in the first powder also diffuse into the second and third phases. The same applies to the components of the second and third powders. The area proportions of the first to third phases can be adjusted, for example, by adjusting the ratios of the first to third powders used.

[0039] The thermal spraying in step (a) can be carried out by any thermal spraying method, such as powder flame spraying, plasma spraying, preferably atmospheric plasma spraying.

[0040] The shape and dimensions of the substrate in step (a) are not particularly limited and may be any. The thickness of the thermal spray coating formed on the substrate in step (a) is, for example, 500 to 5000 μm.

[0041] In step (b), the thermal spray coating formed in step (a) is subjected to a fusing treatment (remelting treatment) to form a self-fluxing alloy thermal spray coating.

[0042] The fusing treatment is performed on the thermal spray coating formed on the substrate in step (a). The fusing treatment is not particularly limited, but can be performed under conditions commonly used in the field of self-fluxing alloy thermal spraying. For example, the temperature of the coating is raised to 950°C to 1200°C in air or a non-oxidizing atmosphere. This fusing treatment reduces porosity within the thermal spray coating, making it possible to densify the thermal spray coating. Furthermore, a diffusion layer is formed between the substrate and the thermal spray coating, resulting in a self-fluxing alloy thermal spray coating with high adhesion. In the self-fluxing alloy thermal spray coating formed in step (b), the diffusion layer formed between the substrate and the thermal spray coating has a thickness of, for example, 50 to 500 μm. Furthermore, the diffusion layer contains components of the substrate in addition to the components of the first to third powders. The content of such a substrate component is preferably 10 mass% or less.

[0043] An example of a method for producing a self-fluxing alloy thermal spray coating is described below. First, the first, second, and third powders described above are weighed and transferred to containers, and then mixed to prepare a powder material. The prepared powder material is then sprayed onto the surface of a substrate to form a thermal spray coating on the substrate. For example, in the case of atmospheric plasma spraying, a voltage is applied between a cathode and an anode to generate a DC arc. A working gas, such as argon gas, is then supplied to the DC arc to ionize the working gas, generating a high-temperature, high-velocity plasma jet. The powder material is then supplied into the generated plasma jet using argon gas or the like, and sprayed onto the substrate to form a thermal spray coating (step (a)). Finally, the thermal spray coating formed on the substrate is heated, for example, in an atmosphere using a flame at approximately 3000°C to raise the coating temperature to approximately 1000°C, thereby fusing the coating to form a self-fluxing alloy thermal spray coating (step (b)). In this way, a self-fluxing alloy sprayed coating that has both wear resistance and thermal shock resistance can be manufactured. However, the method for manufacturing a self-fluxing alloy sprayed coating in this embodiment is not limited to the example described above.

[0044] Examples of the present invention and comparative examples will be described below. These examples are intended to illustrate the present invention and are not intended to limit the scope of the invention.

[0045] <Sample Preparation> [First Powder] As the first powder, a powder of a Ni-based self-fluxing alloy (manufactured by Fukuda Metal Foil & Powder Co., Ltd.) containing 3.10 mass% B, 0.03 mass% C, 4.75 mass% Si, and the remainder Ni (i.e., Ni is 92.12 mass%) was used.

[0046] [Second Powder] As the second powder, a tungsten carbide cermet powder (manufactured by Sumitomo Metal Mining Co., Ltd.) containing 5.40 mass % of C, 12.30 mass % of Co, and the remainder W (i.e., 82.30 mass % W) was used.

[0047] [Third Powder] The following four types of materials were used as the third powder: Inconel 625: Ni-based alloy powder (manufactured by Höganäs) containing 0.02 mass% C, 0.11 mass% N, 0.05 mass% O, 0.42 mass% Si, 21.30 mass% Cr, 0.37 mass% Fe, 3.52 mass% Nb, 9.10 mass% Mo, 0.41 mass% Mn, 0.03 mass% Al, and the balance being Ni (i.e., 64.67 mass% Ni). SUS316L: Powder of an Fe-based alloy (hereinafter also referred to as "SUS316L") containing 0.01 mass% C, 0.84 mass% Si, 0.01 mass% P, 17.38 mass% Cr, 12.51 mass% Ni, 2.13 mass% Mo, 0.70 mass% Mn, and the balance being Fe (i.e., 66.42 mass% Fe) (manufactured by Sanyo Special Steel Co., Ltd.). Stellite 21: Powder of a Co-based alloy (hereinafter also referred to as "Stellite 21") containing 0.24 mass% C, 1.22 mass% Si, 26.97 mass% Cr, 0.44 mass% Fe, 3.04 mass% Ni, 6.13 mass% Mo, 0.33 mass% Mn, and the balance being Co (i.e., 61.64 mass% Co) (manufactured by Sanyo Special Steel Co., Ltd.) Pure Mo: Powder of Mo containing 0.29 mass% C, 0.09 mass% O, 0.03 mass% Fe, and the balance being Mo (i.e., 99.59 mass% Mo) (manufactured by Powrex Corporation)

[0048] [Example 1] A first powder was mixed at 60 mass%, a second powder at 20 mass%, and a third powder (Inconel 625) at 20 mass%. Using the resulting mixture, atmospheric pressure plasma spraying was performed on a 50 mm x 50 mm x 30 mm S45C substrate under the following conditions to form a sprayed coating on the substrate. The temperature of the sprayed coating was then raised to approximately 1000°C and a fusing process was performed to form a self-fluxing alloy sprayed coating, and a test piece for Example 1 was produced. Current value: 400 A, Argon gas flow rate: 36 NLPM

[0049] [Example 2] A test piece of Example 2 was prepared in the same manner as in Example 1, except that the first powder was used in an amount of 60 mass%, the second powder in an amount of 20 mass%, and SUS316L was used as the third powder in an amount of 20 mass%.

[0050] [Example 3] A test piece of Example 3 was prepared in the same manner as in Example 1, except that the first powder was used in an amount of 60 mass%, the second powder in an amount of 30 mass%, and SUS316L was used as the third powder in an amount of 10 mass%.

[0051] [Example 4] A test piece of Example 4 was prepared in the same manner as in Example 1, except that the first powder was used in an amount of 60 mass%, the second powder in an amount of 10 mass%, and Stellite 21 was used as the third powder in an amount of 30 mass%.

[0052] [Example 5] A test piece of Example 5 was prepared in the same manner as in Example 1, except that the first powder was used in a proportion of 60 mass%, the second powder in a proportion of 15 mass%, and Stellite 21 in a proportion of 25 mass% as the third powder.

[0053] [Example 6] A test piece of Example 6 was prepared in the same manner as in Example 1, except that the first powder was used in an amount of 60 mass%, the second powder in an amount of 20 mass%, and Stellite 21 was used as the third powder in an amount of 20 mass%.

[0054] [Example 7] A test piece of Example 7 was prepared in the same manner as in Example 1, except that the first powder was used in an amount of 80 mass%, the second powder in an amount of 10 mass%, and Mo was used as the third powder in an amount of 10 mass%.

[0055] [Example 8] A test piece of Example 8 was prepared in the same manner as in Example 1, except that the first powder was used in an amount of 75 mass%, the second powder in an amount of 15 mass%, and Mo was used as the third powder in an amount of 10 mass%.

[0056] Comparative Example 1 A test piece of Comparative Example 1 was prepared in the same manner as in Example 1, except that only the first powder was used as the powder material.

[0057] Comparative Example 2 A test piece of Comparative Example 2 was prepared in the same manner as in Example 1, except that the first powder and the second powder were used in proportions of 65 mass % and 35 mass %, respectively.

[0058] <Evaluation> [Identification of phases and compositions, calculation of area ratios] The samples of each example and comparative example were cut in the thickness direction of the self-fluxing alloy thermal spray coating, and marks were placed on the cross sections for alignment. The cross sections were observed with an SEM, and composition analysis was further performed with EDS to identify each phase and calculate its area ratio. The results are shown in Table 2.

[0059] The method for identifying each phase will be described with reference to Figures 1 to 3. Figure 1 is an SEM image of the cross section of the coating of Example 5, Figure 2 is an SEM image of the cross section of the coating of Example 8, and Figure 3 is an SEM image of the cross section of the coating of Comparative Example 2.

[0060] As shown in Figure 1, the cross section of the coating of Example 5 contained phases of different brightnesses. The atomic composition ratios of each phase were confirmed by EDS. The relatively light gray phase R1 contained 67.1 mass% Ni and 2.4 mass% W, the brightest phase (white phase) R2 contained 1.9 mass% Ni and 89.7 mass% W, and the relatively dark gray phase R3 contained 3.1 mass% W, 67.1 mass% Cr, and 0.4 mass% Mo. Furthermore, the EDS analysis results confirmed that carbon and boron were distributed throughout the coating. From these results, for Example 5, the relatively light gray phase R1 was identified as the first phase, the brightest phase R2 as the second phase, and the relatively dark gray phase R3 as the third phase. Furthermore, SEM images were analyzed to measure the area of ​​each phase in the field of view, and the percentage (%) of the area occupied by each phase in the total field of view was calculated. Similarly, the percentage (%) of the area of ​​each phase relative to the total area of ​​the field of view was calculated for each of the five fields of view, and the average value was obtained. The results are shown in Table 2.

[0061] As shown in FIG. 2 , the cross section of the coating of Example 8 also contained phases with different brightnesses. The relatively dark gray phase R4 contained 89.7 mass% Ni and 3.1 mass% W, the brightest phase (white phase) R5 contained 7.6 mass% Ni and 86.0 mass% W, and the relatively light gray phase R6 contained 15.2 mass% W, 0 mass% Cr, and 31.4 mass% Mo. Furthermore, EDS analysis confirmed that carbon and boron were distributed throughout the coating. From these results, for Example 8, the relatively dark gray phase R4 was identified as the first phase, the brightest phase R5 as the second phase, and the relatively light gray phase R6 as the third phase. Furthermore, SEM images were analyzed to measure the area of ​​each phase in the field of view, and the percentage (%) of the area occupied by each phase in the field of view was calculated. Similarly, the percentage (%) of the area of ​​each phase relative to the total area of ​​the field of view was calculated for each of the five fields of view, and the average value was obtained. The results are shown in Table 2.

[0062] In Comparative Example 2, two phases, a light phase and a dark phase, were observed. The dark phase R7 contained 77.9 mass% Ni and 8.4 mass% W, and the light phase R8 contained 3.6 mass% Ni and 88.1 mass% W. Boron and carbon were distributed throughout the coating. Although neither of these phases corresponds to the first phase, for convenience, the dark phase R7 was designated the first phase and the light phase R8 the second phase. Furthermore, the SEM image was analyzed to measure the area of ​​each phase in the field of view, and the percentage of the area of ​​the entire field of view was calculated. Similarly, the percentage of the area of ​​each phase in the entire field of view was calculated for each of the five fields of view, and the average value was obtained. The results are shown in Table 2.

[0063]

[0064] The Mo content (mass %) of the entire coating in Table 2 is the Mo content measured by observing the cross section of each sample with an SEM at 50x magnification and performing EDS analysis within an area of ​​1 mm length × 2 mm width of the self-fluxing alloy thermal spray coating.

[0065] [Hardness Test] The position of each phase was identified based on its positional relationship with the above-mentioned marks attached to the sample, and measurements were taken at ten points using a micro Vickers hardness tester under a load of 50 gf, and the average value was calculated.

[0066] [Suga Abrasion Test] In the Suga abrasion test of the self-fluxing alloy sprayed coating, the amount of wear was measured under conditions of a load of 3.25 kgf, a rotation speed of 60 rpm, 2000 reciprocations, and SiC#320 test paper, and the amount of wear was judged based on the following index: ◎: Less than 50 mg; ○: 50 mg or more but less than 100 mg; △: 100 mg or more but less than 200 mg.

[0067] [Thermal Shock Resistance Test] In the thermal shock resistance test of the self-fluxing alloy spray coating, one set of work was performed by heating the test piece in a high-temperature flame to a surface temperature of approximately 100 to 150°C and then cooling the test piece with water. This was repeated to check whether peeling of the coating occurred, and the thermal shock resistance was evaluated based on the following index: ◯: Peeling occurred after the fourth time or no peeling occurred. △: Peeling occurred on the third time. ×: Peeling occurred on the first or second time.

[0068]

[0069] Comparative Example 1 was a coating consisting only of the first phase, and was inferior in both abrasion resistance and impact resistance. Although the first powder used to prepare Comparative Example 1 was the same as the first powder used to prepare the other examples, the hardness of the first phase in Comparative Example 1 was higher than the hardness of the first phase in the other examples. This is thought to be because, while in the other examples, B in the first powder diffused into the second and third phases, in Comparative Example 1, all of the B in the first powder was contained in the first phase.

[0070] Comparative Example 2 was composed of two phases, a relatively soft phase and a hard phase, and had excellent wear resistance but poor thermal shock resistance. This is thought to be because Comparative Example 2 was composed of only two different phases, which was less effective in suppressing crack growth and resulted in large cracks occurring within the coating.

[0071] Examples 1 to 8 contain three phases: a relatively soft first phase (Vickers hardness of 180 or more and less than 400 (Hv 0.05)), a hard second phase (900 or more and less than 2200 (Hv 0.05)), and a hard third phase (400 or more and less than 2200 (Hv 0.05)), and showed excellent results in both wear resistance and thermal shock resistance.

[0072] In Examples 1 to 6, the area ratio of the third phase was less than 10%, but the area ratio of the second phase was 10% or more, so wear resistance of "good" or better was obtained. In Examples 7 and 8, the area ratio of the second phase was less than 10%, but the area ratio of the third phase, which had a Vickers hardness of 900 (Hv0.05) or more, was 10% or more, so wear resistance of "good" or better was obtained.

[0073] In particular, good wear resistance and thermal shock resistance were obtained in Examples 1, 4, 5, 7, and 8. This is thought to be because the area ratio of the second phase and the area ratio of the third phase were both 2.0% or more.

[0074] The self-fluxing alloy coating according to the present invention is a self-fluxing alloy coating on a substrate that has both wear resistance and thermal shock resistance, and therefore can be widely used in industrial fields such as steel and non-ferrous metals, etc. In particular, it can be suitably used in iron-making equipment, pig iron-making equipment, steel-making equipment, non-ferrous metal refining equipment, iron and steel or non-ferrous metal hot rolling equipment, continuous casting equipment, etc.

[0075] R1 First phase in the coating of Example 5 R2 Second phase in the coating of Example 5 R3 Third phase in the coating of Example 5 R4 First phase in the coating of Example 8 R5 Second phase in the coating of Example 8 R6 Third phase in the coating of Example 8 R7 First phase in the coating of Comparative Example 2 (referred to as the first phase for convenience) R8 Second phase in the coating of Comparative Example 2 (referred to as the second phase for convenience)

Claims

1. A steel sheet having a first phase containing 50 mass% or more of Ni and less than 5 mass% of W, a second phase containing less than 50 mass% of Ni and 30 mass% or more of W and containing a carbide or boride of W, and a third phase satisfying at least one of the following (1) to (3) and containing a carbide or boride of W, Cr, or Mo, wherein: (1) the steel sheet contains 5 mass% or more and less than 30 mass% of W, (2) the steel sheet contains 30 mass% or more of Cr, and (3) the steel sheet contains 20 mass% or more of Mo, the Vickers hardness of the first phase is 180 or more and less than 400 (Hv 0.05), the Vickers hardness of the second phase is 900 or more and less than 2200 (Hv 0.05), and the Vickers hardness of the third phase is 400 or more and less than 2200 (Hv 0.05), Self-fluxing alloy spray coating.

2. The self-fluxing alloy thermal sprayed coating according to claim 1, wherein the first phase occupies 40% or more of the cross section of the self-fluxing alloy thermal sprayed coating, and the second phase occupies 10% or more of the cross section.

3. A self-fluxing alloy thermal sprayed coating according to claim 1, wherein the area of ​​the cross section of the self-fluxing alloy thermal sprayed coating is occupied by the first phase at least 40% and the area of ​​the third phase at least 10%, and the Vickers hardness of the third phase is 900 or more (Hv 0.05).

4. The self-fluxing alloy sprayed coating according to claim 1, wherein the area occupied by the second phase and the area occupied by the third phase are both 2.0% or more in a cross section of the self-fluxing alloy sprayed coating.

5. The self-fluxing alloy sprayed coating according to claim 1, wherein the self-fluxing alloy sprayed coating does not contain Mo or contains less than 3 mass% Mo, and in a cross section of the self-fluxing alloy sprayed coating, the area occupied by the first phase is 65 to 85%, the area occupied by the second phase is 10 to 30%, and the area occupied by the third phase is more than 0% and 15% or less.

6. The self-fluxing alloy sprayed coating according to claim 1, wherein the self-fluxing alloy sprayed coating contains 3 mass% or more of Mo, and in a cross section of the self-fluxing alloy sprayed coating, the area occupied by the first phase is 40 to 65%, the area occupied by the second phase is 1 to 15%, and the area occupied by the third phase is 25 to 55%.

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