Atomized powder, sprayed film, hearth roller, and method for manufacturing hearth roller

Abstract

An atomized powder, a sprayed film, a hearth roller, and a method for manufacturing a hearth roller, from which a film having high-temperature hardness, oxidation resistance, toughness, and heat shock resistance is obtained. The atomized powder has a heat-resistant alloy phase and a Cr7C3 phase dispersed in the heat-resistant alloy phase, and contains, in mass units, 20 to 46% of Ni, 22 to 43% of Cr, 4 to 13% of Al, 0.1 to 1.0% of Y, and 0.3 to 4.2% of C, with the remainder including Co and inevitable impurities.

Description

[0001] This application claims priority based on Japanese Application No. 2021-122668, filed on July 27, 2021, and incorporates all the contents of that Japanese application. Technical Field

[0002] This invention relates to a method for manufacturing atomized powder, sprayed film, furnace bottom roller, and furnace bottom roller. Background Technology

[0003] In heat treatment furnaces such as continuous annealing furnaces for steel plates, there are rollers called furnace bottom rollers used for conveying steel plates. The steel plates are heat treated in the furnace, but at this time, a substance called build-up forms on the surface of the furnace bottom rollers, which is produced by the reaction with the steel plates.

[0004] If a layer forms, it will cause pressing defects and other imperfections on the surface of the steel plate being transported on the furnace bottom rollers, resulting in poor steel plate quality. Therefore, in the event of a layer formation, operations must be stopped immediately to clean the roller surface, significantly reducing production efficiency.

[0005] Therefore, the occurrence of layering is prevented by providing a sprayed film on the surface of the furnace bottom roller (for example, see Patent Documents 1 to 3).

[0006] The spraying powder used in Patent Documents 1 to 3 contains chromium carbide and heat-resistant metal.

[0007] In addition, in Patent Document 4, a chromium carbide-based spraying powder is proposed as a spraying powder for forming a high-hardness sprayed film at high temperatures. The powder contains chromium carbide and a metal phase. The metal phase is formed by dispersing and strengthening a metal or alloy matrix with fine ceramic hard particles at a volume ratio of 0.5% to 15% relative to the metal phase.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 59-126772

[0011] Patent Document 2: Japanese Patent Application Publication No. 2008-240072

[0012] Patent Document 3: International Publication No. 2009 / 069829

[0013] Patent Document 4: Japanese Patent Application Publication No. 62-099449 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] The spraying powders proposed in Patent Documents 1 through 4 are all produced by a granulation-sintering method. In spraying powders produced by this method, the primary particles of chromium carbides and heat-resistant alloy powders are small, porous, and have a large specific surface area. Therefore, the sprayed film formed using these powders is easily oxidized. Furthermore, if the sprayed film is applied to the surface of the furnace bottom roller using these powders, the roller surface is prone to early oxidation, leading to problems such as foreign matter adhesion (growth on the roller surface) or foreign matter pick-up.

[0016] Furthermore, the sprayed films proposed in Patent Documents 1 to 4 have areas where the distribution or size of chromium carbides is uneven and the hardness is low in some areas, which also presents the problem that adhesion or over-layering is likely to occur.

[0017] Technical means to solve the problem

[0018] The inventors conducted extensive research to solve this problem and discovered that by using atomized powder with a specific composition as the spraying powder, the problem can be solved, thus completing the present invention.

[0019] (1) One embodiment of the atomized powder of the present invention is an atomized powder having a heat-resistant alloy phase and a Cr7C3 phase dispersed in the heat-resistant alloy phase, wherein

[0020] It contains 20%–46% Ni, 22%–43% Cr, 4%–13% Al, 0.1%–1.0% Y, and 0.3%–4.2% C by mass, with the remainder containing Co and unavoidable impurities.

[0021] Based on the atomized powder, a coating film with excellent high-temperature hardness, oxidation resistance, toughness, and thermal shock resistance can be obtained by using the atomized powder to form a sprayed film.

[0022] (2) Preferably, the heat-resistant alloy phase in the atomized powder of (1) is a Co-based alloy phase.

[0023] (3) Preferably, a portion of the Cr7C3 phase in the atomized powder of (1) or (2) is needle-like.

[0024] (4) Preferably, the proportion of Cr7C3 phase in the cross-sectional structure of any of the atomized powders in (1) to (3) is less than 50% of the area.

[0025] Atomized powder having one or more of the structures described in (2) to (4) is suitable as a spray powder for forming a spray coating film with high hardness and small hardness deviation in each region.

[0026] (5) In one aspect of the present invention, the sprayed film is a sprayed film formed using any of the atomized powders in (1) to (4).

[0027] (6) Another sprayed film of one aspect of the present invention is a sprayed film comprising a heat-resistant alloy phase and a Cr7C3 phase dispersed in the heat-resistant alloy phase, the heat-resistant alloy phase comprising Co, Ni, Cr, Al, Y and unavoidable impurities, and the sprayed film comprising 5% by mass and more but less than 30% by mass of Cr7C3.

[0028] (7) The heat-resistant alloy phase in the sprayed film of (6) is preferably a Co-based alloy phase.

[0029] (8) Preferably, a portion of the Cr7C3 phase in the sprayed film of (6) or (7) is needle-like.

[0030] These sprayed coatings exhibit excellent high-temperature hardness, oxidation resistance, toughness, and thermal shock resistance.

[0031] (9) In one aspect of the present invention, the bottom roller is a bottom roller comprising a roller body and a sprayed film and the sprayed film is disposed on the surface, and the sprayed film is any of the sprayed films in (5) to (8).

[0032] The surface of the furnace bottom roller has excellent high-temperature hardness, oxidation resistance, toughness, and thermal shock resistance due to the sprayed coating.

[0033] Therefore, it can suppress the formation of adhesion or thickening on the surface of the furnace bottom roller (the contact surface with the steel plate).

[0034] (10) One aspect of the present invention is a method for manufacturing a furnace bottom roller comprising a roller body and a sprayed film having the sprayed film disposed on its surface, wherein in the manufacturing method,

[0035] Using any of the atomized powders described in (1) to (4), a sprayed film is formed on the surface of the roller body, and then the sprayed film is heat-treated to harden it.

[0036] According to the manufacturing method of the furnace bottom roller, since the formed sprayed film is subjected to heat treatment, fine chromium carbides are further precipitated in the heat-resistant alloy phase, which can further improve the hardness of the film and further improve the wear resistance in the manufactured furnace bottom roller.

[0037] (11) In the manufacturing method of the furnace bottom roller, it is preferable to further irradiate the surface of the heat-treated sprayed film with a laser beam after heat treatment, thereby melting / solidifying the surface of the heat-treated sprayed film and reducing the hardness of the heat-treated sprayed film.

[0038] In this case, laser treatment results in a smooth surface and a dense outer layer of the sprayed film. This further suppresses the possibility of adhesion or overlay.

[0039] Furthermore, if the sprayed film formed using the atomized powder is heat-treated and then laser-treated on the surface, the fine chromium carbide structure on the surface disappears, the hardness of the sprayed film decreases, and the toughness of the sprayed film increases, resulting in a film structure with excellent thermal shock resistance.

[0040] In addition, through the laser treatment, the heat-resistant alloy phase and chromium carbide melt, and the surface layer of the sprayed film becomes a uniform composition, eliminating the unevenness of oxidation resistance, thereby improving the oxidation resistance of the sprayed film.

[0041] The effects of the invention

[0042] According to the present invention, a sprayed coating film with excellent high-temperature hardness, oxidation resistance, toughness and thermal shock resistance, a sprayed powder for obtaining such a sprayed coating film, and a furnace bottom roller including the sprayed coating film can be provided. Attached Figure Description

[0043] Figure 1 This is a cross-sectional SEM image of an example of the atomized powder according to an embodiment of the present invention.

[0044] Figure 2 This is a cross-sectional SEM image of an example of granulated sintered powder.

[0045] Figure 3 This is a diagram illustrating an example of a furnace bottom roller according to an embodiment of the present invention.

[0046] Figure 4 This is a diagram showing the observation results of a cross-section of the atomized powder of Example 1.

[0047] Figure 5 (a)~ Figure 5 (c) is a graph showing the XRD results of the atomized powder and sprayed film manufactured in Example 1.

[0048] Figure 6 This is a graph showing the results of the evaluation (1) of the hardness of the sprayed film in the embodiment.

[0049] Figure 7 This is a graph showing the results of the evaluation (2) of the hardness of the sprayed film in the embodiment.

[0050] Figure 8 These are SEM-BEI images of cross-sections of the sprayed films of Example 1 and Comparative Example 1.

[0051] Figure 9This is a graph showing the results of the evaluation (3) of the hardness of the sprayed film in the embodiment.

[0052] Explanation of symbols

[0053] 10 Furnace bottom rollers

[0054] 11 Roller Body

[0055] 12 rollers

[0056] 13-roll substrate

[0057] 14 spray coating Detailed Implementation

[0058] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0059] <Atomized Powder>

[0060] The atomized powder in the embodiments of the present invention is an atomized powder having a heat-resistant alloy phase and a Cr7C3 phase. The heat-resistant alloy phase is preferably a Co-based alloy phase.

[0061] The atomized powder is a powder manufactured using an atomization method, having a structure in which fine chromium carbides are uniformly dispersed / precipitated in the heat-resistant alloy phase.

[0062] The atomized powder differs from powders made by granulating / sintering chromium carbides and heat-resistant alloys, having a microstructure in which fine chromium carbides (Cr7C3) are uniformly dispersed / precipitated in the heat-resistant alloy phase.

[0063] Therefore, by using the atomized powder as the spraying powder to form the sprayed film, the obtained sprayed film has high overall hardness and small hardness deviation in each region.

[0064] The atomized powder differs from powder produced by granulation and sintering (hereinafter also referred to as granulated sintered powder) in that it is a solid powder, and therefore has a smaller specific surface area. Consequently, the atomized powder exhibits higher oxidation resistance than granulated sintered powder. Furthermore, the sprayed coating formed using the atomized powder demonstrates better oxidation resistance compared to the sprayed coating formed using the granulated sintered powder.

[0065] The chromium carbide in the atomized powder is Cr7C3.

[0066] Compared to Cr3C2, Cr7C3 is more stable at high temperatures. Therefore, the Cr7C3-coated film formed using the atomized powder is less prone to change over time even when exposed to high temperatures.

[0067] If a sprayed film formed using sprayed powder containing Cr3C2 and a heat-resistant alloy is exposed to a high-temperature environment, the Cr3C2 will change to Cr7C3. If this change occurs, the Cr content in the heat-resistant alloy phase will be insufficient, leading to a decrease in the oxidation resistance of the sprayed film. Furthermore, if the Cr3C2 in the sprayed film changes to Cr7C3, the dispersion of chromium carbides may be impaired, resulting in deviations in the hardness of the sprayed film.

[0068] In contrast, the Cr7C3-containing sprayed film formed using the atomized powder maintains a uniform dispersion of the chromium carbide phase (Cr7C3 phase) even at high temperatures. Therefore, hardness is maintained even if the chromium carbide content in the sprayed film is less than 30% by mass. Furthermore, since the Cr content in the heat-resistant alloy phase is not reduced, the oxidation resistance and toughness of the sprayed film are not compromised. Moreover, the sprayed film can sufficiently contain the heat-resistant alloy phase (e.g., 70% by mass or more), thus exhibiting excellent thermal shock resistance.

[0069] The atomized powder contains, by weight, 20%–46% Ni, 22%–43% Cr, 4%–13% Al, 0.1%–1.0% Y, and 0.3%–4.2% C, with the remainder containing Co and unavoidable impurities.

[0070] The atomized powder of this composition is designed to contain 5% by mass but less than 30% by mass of Cr7C3.

[0071] When the Cr7C3 content in the atomizing powder is less than 5% by mass, the amount of chromium carbide precipitated is insufficient, and sometimes sufficient hardness cannot be obtained.

[0072] On the other hand, if the Cr7C3 content in the atomized powder is 30% by mass or more, the content of the heat-resistant alloy phase in the atomized powder becomes less, and the thermal shock resistance of the sprayed film formed using the atomized powder sometimes becomes insufficient. In addition, powders containing both the heat-resistant alloy phase and the Cr7C3 phase, with a Cr7C3 content of 30% by mass or more, are difficult to manufacture by the atomization method.

[0073] Examples of heat-resistant alloys include those containing Co, Ni, Cr, Al, and Y. Specifically, examples include CoNiCrAlY alloys and NiCoCrAlY alloys.

[0074] The atomized powder contains specified amounts of Ni, Cr, Al, Y, and C as constituent elements. The reasons are as follows.

[0075] Ni: 20%–46% by mass

[0076] In the atomized powder, Ni is a basic constituent element alongside Co, and is included to impart heat resistance and oxidation resistance.

[0077] If the Ni content is less than 20% by mass, the toughness decreases and the oxidation resistance is poor. On the other hand, if the Ni content exceeds 46% by mass, the Cr or Al content decreases, thus resulting in poor oxidation resistance.

[0078] Cr: 22%–43% by mass

[0079] In the atomized powder, Cr is included to allow chromium carbide to precipitate and to form a protective oxide film.

[0080] If the Cr content is less than 22% by mass, the amount of chromium carbide precipitated will be insufficient, and adequate film hardness cannot be obtained. In addition, the oxidation resistance is also poor.

[0081] On the other hand, if the Cr content exceeds 43% by mass, the toughness is compromised. Furthermore, it easily causes nozzle clogging during atomization manufacturing, making production difficult.

[0082] Al: 4%–13% by mass

[0083] In the atomized powder, Al is contained to form a protective oxide film.

[0084] If the Al content is less than 4% by mass, it is difficult to form a dense Al2O3 layer on the film surface. On the other hand, if the Al content exceeds 13% by mass, the film becomes brittle and has poor thermal shock resistance.

[0085] Y: 0.1% by mass to 1.0% by mass

[0086] In the atomized powder, Y is contained to stabilize the formation of a protective oxide film and prevent peeling.

[0087] If the content of Y is less than 0.1% by mass, the added effect will not be apparent. On the other hand, if the content of Y exceeds 1.0% by mass, the film will become brittle and have poor oxidation resistance.

[0088] C: 0.3% to 4.2% by mass

[0089] In the atomized powder, C is included to allow chromium carbide to precipitate.

[0090] If the C content is less than 0.3% by mass, the amount of chromium carbide precipitated will be insufficient, and sufficient film hardness cannot be obtained.

[0091] On the other hand, if the carbon content exceeds 4.2% by mass, the toughness is compromised. Furthermore, it easily causes nozzle clogging during atomization manufacturing, making production difficult.

[0092] The atomized powder differs from the granulated sintered powder in that the chromium carbide is uniformly dispersed in the powder.

[0093] Figure 1 This is a cross-sectional scanning electron microscope (SEM) image of an example of the atomized powder of the present invention (20wt% Cr7C3-CoNiCrAlY / Ref. Example 1).

[0094] Figure 2 This is a cross-sectional SEM image of granulated sintered powder (40wt% Cr3C2-CoNiCrAlY / Comparative Example 1).

[0095] The atomized powder is as follows: Figure 1 As clearly shown in the cross-sectional SEM images, fine Cr7C3 phases as chromium carbide phases are dispersed in each powder within the heat-resistant alloy phase (Co-based alloy phase).

[0096] On the other hand, such as Figure 2 As shown, coarse chromium carbides (Cr3C2 particles) separated from the heat-resistant alloy phase were observed in the granulated sintered powder; no other phases were observed. Figure 1 Such fine Cr7C3 phase dispersed in the heat-resistant alloy phase.

[0097] In the atomized powder, a portion of the Cr7C3 phase dispersed in the heat-resistant alloy phase (Co-based alloy phase) as observed by SEM is preferably acicular.

[0098] The atomized powder is preferably composed of a plurality of needle-like structures with an aspect ratio of 2 or more and 100 or less. Here, the aspect ratio of the needle-like structures is the ratio of the length of the long axis portion to the length of the short axis portion of each needle-like structure.

[0099] Atomized powder with needle-like structure of Cr7C3 phase having the aforementioned aspect ratio dispersed in powder is suitable as a spray powder for forming a spray coating film with high hardness and small hardness deviation in each region.

[0100] The short axis length of the acicular structure of the Cr7C3 phase is, in one example, 8 μm or less, preferably 3 μm or less. On the other hand, the short axis length of the acicular structure is, in another example, 0.1 μm or more. In this case, the Cr7C3 phase can be considered a fine structure.

[0101] In one example, the distance between adjacent needle-like structures of the Cr7C3 phase (the distance between the closest parts) is 5 μm or less. On the other hand, in another example, the distance between adjacent needle-like structures of the Cr7C3 phase (the distance between the closest parts) is 0.1 μm or more. In this case, the uniform dispersion of the Cr7C3 phase can be considered excellent.

[0102] Preferably, the proportion of the Cr7C3 phase in the cross-sectional structure of each powder in the atomized powder is 50% or less by area. If it exceeds 50% by area, the uniform dispersion of Cr7C3 is poor. On the other hand, the proportion of the Cr7C3 phase in the cross-sectional structure of each powder is preferably 20% or more by area. If it is less than 20% by area, it is difficult to obtain sufficient film hardness.

[0103] The proportion of the Cr7C3 phase in the cross-sectional microstructure of each powder can be calculated based on the cross-sectional SEM image of the atomized powder.

[0104] Examples of atomization methods include gas atomization, water atomization, and disc atomization.

[0105] In the atomization method, the particle size of the powder produced can also be adjusted by sieving.

[0106] In gas atomization, the raw metal is heated and melted to obtain molten metal. The molten metal flows out from a nozzle. A gas (argon, nitrogen, etc.) is then sprayed onto the molten metal.

[0107] Using the energy of the gas, the molten metal is pulverized into droplets, which are cooled as they fall. The droplets then solidify to form particles.

[0108] Water atomization is a method in which water is sprayed instead of gas in gas atomization.

[0109] In the disc atomization method, the raw material metal is heated and melted to obtain molten metal. The molten metal flows out from the nozzle and falls onto a high-speed rotating disc. The molten metal is rapidly cooled and solidified to obtain powder.

[0110] The preferred atomization method is gas atomization.

[0111] In gas atomization, molten metal is instantaneously dropletized and simultaneously cooled, thus obtaining a uniform, fine microstructure. Furthermore, because droplets are formed continuously, the compositional differences between particles are extremely small. This is one of the reasons why gas atomization is preferred.

[0112] <Spray coating>

[0113] The sprayed film of the present invention comprises a heat-resistant alloy phase and a Cr7C3 phase dispersed in the heat-resistant alloy phase, the heat-resistant alloy phase comprising Co, Ni, Cr, Al, Y and unavoidable impurities, and the sprayed film comprises 5% by mass and more but less than 30% by mass of Cr7C3.

[0114] Compared to Cr3C2, Cr7C3 is more stable at high temperatures. Therefore, the sprayed coating is less prone to change over time even when exposed to high temperatures.

[0115] Furthermore, the sprayed coating containing Cr7C3 as a chromium carbide maintains a uniform dispersion of the chromium carbide phase even at high temperatures. Therefore, even if the chromium carbide content in the coating is less than 30% by mass, the coating can maintain its hardness. Additionally, since the Cr content in the heat-resistant alloy phase does not decrease even at high temperatures, the coating's oxidation resistance and toughness are not compromised. Moreover, the sprayed coating can contain more than 70% by mass of the heat-resistant alloy phase, thus exhibiting excellent thermal shock resistance.

[0116] The sprayed coating contains 5% to 30% by mass of Cr7C3.

[0117] When the Cr7C3 content is less than 5% by mass, the hardness or heat resistance of the sprayed film may sometimes become insufficient.

[0118] On the other hand, if the content of Cr7C3 is 30% by mass or more, the amount of heat-resistant alloy phase in the sprayed film becomes less, and the thermal shock resistance of the sprayed film may sometimes become insufficient.

[0119] The composition of the sprayed film is preferably 20% to 46% Ni, 22% to 43% Cr, 4% to 13% Al, 0.1% to 1.0% Y, and 0.3% to 4.2% C by mass, with the remainder containing Co and unavoidable impurities.

[0120] This composition is suitable for producing spray-coated films with excellent high-temperature hardness, oxidation resistance, toughness, and thermal shock resistance.

[0121] The spray-coated film can be manufactured by spraying the atomized powder as the spray-coating powder.

[0122] The spray-coated film formed using the atomized powder is also an aspect of the present invention.

[0123] The spraying method used to form the sprayed film is not particularly limited; for example, high-speed flame spraying (high-velocity oxygen fuel (HVOF)) can be used.

[0124] In the HVOF, kerosene, C3H8, C2H2, and C3H6 are typically used as fuel gases. The fuel gas pressure must be between 0.1 MPa and 1 MPa, and the flow rate between 10 L / min and 500 L / min. Similarly, the oxygen pressure must be between 0.1 MPa and 1 MPa, and the flow rate between 100 L / min and 1200 L / min.

[0125] <Furnace Bottom Roller and Its Manufacturing Method>

[0126] Figure 3 This is a diagram illustrating an example of a furnace bottom roller according to an embodiment of the present invention.

[0127] like Figure 3 As shown, the furnace bottom roller 10 of the embodiment of the present invention includes a roller body 11 and a sprayed coating film 14.

[0128] The roller body 11 includes a roller shaft 12 and a roller substrate 13 mounted on the roller shaft 12.

[0129] A spray-coated film 14 is disposed on the surface (circumferential surface) of the roller substrate 13.

[0130] The furnace bottom roller 10 functions as a steel plate conveying roller. While rotating around the roller shaft 12, the furnace bottom roller 10 contacts the steel plate with its circumferential surface (the surface of the sprayed coating 14), thereby conveying the steel plate.

[0131] The roller substrate 13 is formed of metal such as steel.

[0132] For example, stainless steel-based heat-resistant cast steel can be used as the metal.

[0133] Spray-coated film 14 is the spray-coated film of the embodiment of the present invention.

[0134] Therefore, the bottom roller 10 is not prone to adhesion or layering on its circumference.

[0135] The thickness of the sprayed film 14 is preferably 20 μm or more and 300 μm or less.

[0136] When the thickness of the sprayed film 14 is less than 20 μm, the effect of setting the sprayed film (suppressing the occurrence of overlay or thickening) cannot be fully obtained. On the other hand, if the thickness of the sprayed film 14 exceeds 300 μm, the sprayed film is prone to cracking due to the difference in thermal expansion between it and the roller substrate.

[0137] As a method for manufacturing the furnace bottom roller 10, for example, a manufacturing method can be adopted in which a sprayed film is formed on the surface of the roller body 11 using the atomized powder.

[0138] In the manufacturing method of the furnace bottom roller 10, it is preferable to harden the sprayed film by heat treatment after the sprayed film is formed. By heat treating the sprayed film, the hardness can be improved compared with the sprayed film before heat treatment.

[0139] The heat treatment can be carried out, for example, by heating at a temperature of 300°C or higher and 600°C or lower for 1 hour or more and 10 hours or less. More preferably, the heating temperature is 400°C or higher.

[0140] The heat treatment can be performed in an oxidizing atmosphere (e.g., in the atmosphere) or a non-oxidizing atmosphere. For example, a method involving placing a roller body with a sprayed coating in a furnace within an inert gas atmosphere such as nitrogen or argon can be described.

[0141] By performing the aforementioned heat treatment, fine chromium carbides (Cr7C3) are further precipitated in the heat-resistant alloy phase of the sprayed film. As a result, the hardness of the sprayed film is further improved, and its wear resistance is further enhanced.

[0142] In the manufacturing method of the furnace bottom roller 10, it is preferable to further irradiate the sprayed film with a laser beam after the heat treatment, thereby melting / solidifying the surface of the heat-treated sprayed film. This reduces the hardness of the heat-treated sprayed film.

[0143] If the aforementioned laser treatment is performed, the fine chromium carbide (Cr7C3) structure on the surface of the sprayed film disappears, and the hardness of the sprayed film decreases. On the other hand, the toughness of the laser-treated sprayed film is improved, thus becoming a film with excellent thermal shock resistance.

[0144] Furthermore, if the aforementioned laser treatment is performed, the surface of the sprayed film becomes smooth, and the surface layer becomes a dense structure. As a result, adhesion or thickening is less likely to occur.

[0145] Furthermore, if the laser treatment is performed, the heat-resistant alloy phase and chromium carbide melt and solidify, thus the temporarily molten portion of the sprayed film becomes a homogeneous composition. As a result, the oxidation resistance of the sprayed film is improved.

[0146] The conditions for laser processing are not particularly limited, as long as a portion of the sprayed film is melted.

[0147] Examples of lasers used in the laser processing include fiber lasers, neodymium-doped yttrium aluminum garnet (Nd / YAG) lasers, and disk lasers.

[0148] The depth of the sprayed film melted by the laser treatment can be set to, for example, 5 μm or more and 20 μm or less.

[0149] The embodiments disclosed herein are illustrative in all respects and are not limiting. The scope of the invention is not limited to the described embodiments, but includes all modifications within the range equivalent to the structures described in the claims.

[0150] Example

[0151] The embodiments of the present invention will be described in more detail below through examples, but the embodiments of the present invention are not limited to the following examples.

[0152] Here, a sprayed film is formed on the surface of a plate-shaped substrate (made of austenitic stainless steel (SUS304), 50mm long × 50mm wide × 5mm thick) using a high-speed flame (HVOF) spraying method to create a test piece. The obtained test piece is then subjected to heat treatment and laser treatment.

[0153] (Example 1)

[0154] 1. Preparation of Spray Coating Powder (Atomized Powder)

[0155] As an atomizing powder, 20wt% Cr7C3-CoNiCrAlY (particle size -38 / +10μm) powder was manufactured.

[0156] Raw materials, weighed according to the specified composition shown in Table 1 below, are induction melted in an argon atmosphere using a refractory crucible. Argon gas is sprayed onto the molten metal flowing from a nozzle at the bottom of the crucible. The molten metal is rapidly cooled and solidified, thereby obtaining a gas-atomized powder. The gas-atomized powder is graded to obtain a sprayed powder.

[0157] [Table 1]

[0158] Element Ni Cr Al Co Y C <![CDATA[20wt%Cr7C3-CoNiCrAlY]]> 25.6 34.1 6.4 30.7 0.48 2.67

[0159] 2. Observation of precipitated carbides in atomized powder

[0160] A cross-sectional SEM backscattered electron image (BEI) of the atomized powder was observed. Furthermore, image processing (binarization) was performed on the observed image to calculate the area fraction of precipitated carbides in the overall atomized powder.

[0161] Figure 4 The image shows a cross-sectional SEM-BEI image and a binarized image of the atomized powder, as well as the calculated area ratio of the precipitated carbides.

[0162] 3.Spray coating

[0163] Using the atomized powder as the spraying powder, a sprayed film is formed on the surface of the substrate by high-speed flame spraying, thereby obtaining a test piece.

[0164] As a high-speed flame spraying device, the JP-5000 (manufactured by Praxair / TAFA) is used.

[0165] The details of the spraying conditions in this embodiment are as follows.

[0166] Oxygen: 896 L / min

[0167] Kerosene: 0.32 L / min

[0168] Spraying distance: 380mm

[0169] Material supply rate: 50g / min

[0170] 4. Heat treatment of the sprayed coating

[0171] The test piece prepared in step 3 is placed in a heating furnace and subjected to heat treatment in the atmosphere.

[0172] Here, the heat treatment temperature is set to 400℃, 500℃ or 600℃, and the heat treatment time is set to 6 hours.

[0173] 5. Laser treatment

[0174] The test pieces that underwent heat treatment at 500℃ for 6 hours in section 4 were further subjected to laser treatment.

[0175] Here, laser processing is performed under the following conditions.

[0176] Laser type: Yb-series fiber laser

[0177] Laser wavelength: 1070nm

[0178] Power density: 1.4 × 10 6 W / cm 2

[0179] Output: 1000W

[0180] Laser spot diameter: 300μm

[0181] (Comparative Example 1)

[0182] 1. Powder coating

[0183] Prepare 40wt% Cr3C2-CoNiCrAlY (particle size -53 / +20μm) powder by granulation and sintering.

[0184] 2.Spray coating

[0185] Using the powder manufactured by the granulation and sintering method as the spraying powder, a sprayed film was formed on the surface of the substrate by high-speed flame spraying under the same conditions as in Example 1, thereby obtaining a test piece.

[0186] 3. Heat treatment of the sprayed coating

[0187] The test pieces were subjected to heat treatment under the same conditions as in Example 1.

[0188] 4. Laser treatment

[0189] The test pieces that underwent heat treatment in step 3, which were heat-treated at 500°C for 6 hours, were subjected to laser treatment under the same conditions as in Example 1.

[0190] <Physical Property Evaluation>

[0191] 1. Confirmation of structural phases based on X-ray diffraction (XRD) analysis

[0192] The atomized powder, the sprayed film (before heat treatment), and the sprayed film (after laser treatment) manufactured in Example 1 were measured by XRD.

[0193] The results are shown in Figure 5 (a)~ Figure 5 (c) Figure 5 The results of the atomized powder determination are shown in (a). Figure 5 (b) shows the measurement results for the sprayed film (before heat treatment). Figure 5 The measurement results for the sprayed coating (after laser treatment) are shown in (c). Furthermore, in Figure 5 (a)~ Figure 5 In (c), the downward arrow indicates the peak position of Cr3C2.

[0194] like Figure 5 (a)~ Figure 5 As shown in (c), the atomized powder and sprayed film in Example 1 contain Cr7C3 as chromium carbide, and Cr3C2 was not detected.

[0195] 2. Evaluation of the hardness of the sprayed coating (1)

[0196] For the test pieces of Example 1 and Comparative Example 1 after (i) formation of the sprayed film and (ii) after heat treatment at specified temperatures (400°C, 500°C, 600°C) for 6 hours following the formation of the sprayed film, the Vickers hardness of the surface layer of the sprayed film was measured. Measurements were performed at 10 locations, and the average value was taken as the film hardness. The results are shown below. Figure 6 .

[0197] Vickers hardness is determined using a micro Vickers hardness tester under a load of 25g.

[0198] like Figure 6 As shown in Example 1 (in the figure, it is represented as gas atomized powder), Figures 7-9 (The same applies) and Comparative Example 1 (described in the figure as granulated sintered powder, Figures 7-9 In either of the two methods (which are also the same), the hardness of the film increases by performing heat treatment after the formation of the sprayed film.

[0199] In addition, in Example 1, at any stage, the deviation in hardness of the sprayed film was small compared to Comparative Example 1.

[0200] 3. Evaluation of the hardness of the sprayed coating (2)

[0201] For the test pieces of Example 1 and Comparative Example 1 after (i) formation of the sprayed film, (ii) after heat treatment (500°C × 6 hours) following the formation of the sprayed film, and (iii) after laser treatment following the heat treatment, the Vickers hardness of the surface layer of the sprayed film was measured. Measurements were performed at 10 locations, and the average value was taken as the film hardness. The results are shown below. Figure 7 .

[0202] Vickers hardness is determined using a micro Vickers hardness tester under a load of 25g.

[0203] like Figure 7 As shown, in Example 1, the hardness of the sprayed film temporarily increased after heat treatment, but decreased after laser treatment. In contrast, in Comparative Example 1, the hardness of the sprayed film increased after heat treatment, and then increased further after laser treatment.

[0204] In addition, in Example 1, at any stage, the deviation in hardness of the sprayed film was small compared to Comparative Example 1.

[0205] 4. Observation of the sprayed coating

[0206] The cross-sections of the sprayed films prepared in Example 1 and Comparative Example 1 were observed using a scanning electron microscope (SEM).

[0207] Figure 8 These are cross-sectional SEM-BEI images of the sprayed films prepared in Example 1 and Comparative Example 1 at various stages. Figure 8In this document, observation images of each sprayed film prepared in Example 1 and Comparative Example 1 are shown, including (i) after the formation of the sprayed film, (ii) after heat treatment (500°C × 6 hours) after the formation of the sprayed film, and (iii) after laser treatment following the heat treatment.

[0208] according to Figure 8 As shown in the observation images, at any stage, the chromium carbides in the sprayed film of Example 1 remained fine and the pores were fewer than those in the sprayed film of Comparative Example 1.

[0209] Furthermore, in Example 1, the surface of the sprayed film was melted / solidified and densified by laser treatment, and the surface became smooth. On the other hand, in Comparative Example 1, although the surface of the sprayed film was smooth after laser treatment, a uniform structure was not formed on the surface.

[0210] 5. Evaluation of the hardness of the sprayed coating (3)

[0211] For the test pieces that underwent heat treatment and laser treatment in Example 1 and Comparative Example 1, the Vickers hardness of the central part of the sprayed film (the part that did not melt during laser treatment) was measured at room temperature and high temperature.

[0212] Specifically, measurements were performed in an Ar atmosphere at temperatures of 23°C, 400°C, 600°C, and 800°C. Measurements were taken at five locations, and the average value was used as the Vickers hardness at room temperature or high temperature. The results are presented below. Figure 9 The Vickers hardness at both room temperature and high temperature is determined using a high-temperature microhardness tester under a load of 200g.

[0213] like Figure 9 As shown, the sprayed film prepared in Example 1 and the sprayed film prepared in Comparative Example 1 have no significant difference in hardness, and both maintain a certain hardness in a high-temperature environment.

Claims

1. An atomized powder comprising a heat-resistant alloy phase and a Cr7C3 phase dispersed within the heat-resistant alloy phase, wherein the heat-resistant alloy phase is a Co-based alloy phase, and wherein the atomized powder contains... Containing 5% or more but less than 30% by mass of Cr7C3, and It contains 20%–46% Ni, 22%–43% Cr, 4%–13% Al, 0.1%–1.0% Y, and 0.3%–4.2% C by mass, with the remainder containing Co and unavoidable impurities.

2. The atomized powder according to claim 1, wherein a portion of the Cr7C3 phase is needle-like.

3. The atomized powder according to claim 1 or 2, wherein the proportion of Cr7C3 phase in the cross-sectional microstructure of each powder is less than 50% by area.

4. A spray-coated film formed using atomized powder as described in any one of claims 1 to 3.

5. A sprayed coating comprising a heat-resistant alloy phase and a Cr7C3 phase dispersed in the heat-resistant alloy phase, the heat-resistant alloy phase comprising Co, Ni, Cr, Al, Y and unavoidable impurities, and the sprayed coating comprising 5% by mass and less than 30% by mass of Cr7C3. The sprayed coating contains, by weight, 20%–46% Ni, 22%–43% Cr, 4%–13% Al, 0.1%–1.0% Y, and 0.3%–4.2% C, with the remainder containing Co and unavoidable impurities.

6. The sprayed coating according to claim 5, wherein the heat-resistant alloy phase is a Co-based alloy phase.

7. The spray-coated film according to claim 5 or 6, wherein a portion of the Cr7C3 phase is needle-like.

8. A furnace bottom roller, comprising a roller body and a sprayed film having the sprayed film disposed on its surface, wherein the furnace bottom roller, The sprayed coating is the sprayed coating as described in any one of claims 4 to 7.

9. A method for manufacturing a furnace bottom roller, the furnace bottom roller comprising a roller body and a sprayed film having the sprayed film disposed on its surface, wherein in the method for manufacturing the furnace bottom roller, Using the atomized powder as described in any one of claims 1 to 3, a sprayed film is formed on the surface of the roller body, and then the sprayed film is heat-treated to harden it.

10. The method for manufacturing a furnace bottom roller according to claim 9, wherein after heat treatment, a laser beam is further irradiated, thereby melting and solidifying the surface of the heat-treated sprayed film, thereby reducing the hardness of the heat-treated sprayed film.

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