JP7027624B1 - Hearth roll - Google Patents

Abstract

The hearth roll 100 of the present invention, which has a dense and durable film on the outer surface capable of suppressing build-up, has an upper layer portion 30 made of a ceramic sprayed coating and a ceramic and heat-resistant alloy in the lower layer of the upper layer portion 30. The surface of the ceramic sprayed coating is covered with a lower layer portion 20 made of a cermet sprayed coating composed of % Is contained.

Description

The present invention relates to a hearth roll for a heat treatment furnace for transporting a high-temperature stainless steel sheet or the like to be processed in a heat treatment line.

In the heat treatment furnace for heat-treating a metal plate such as a steel plate, a transport roll (hereinafter referred to as a hearth roll) for carrying in, transferring, and carrying out the steel plate is installed. Such a heat treatment furnace usually has a considerably high temperature as high as 1100 ° C., depending on the type of steel sheet. The hearth roll supports a heavy-weight steel sheet heated to a red-hot state, and is subject to intense dynamic friction, so that the surface is liable to have rough skin and scratches. As a result, the flaw is transferred to the steel sheet to be conveyed, and the surface of the steel sheet is scraped off to adhere to the roll, so-called “build-up” protrusions are generated. When build-up is generated on the roll, the surface shape of the conveyed steel sheet causes a larger flaw, which significantly deteriorates the product quality.

In Patent Document 1, for the purpose of preventing build-up, a nickel-chromium alloy is sprayed on the roll surface, and chrome carbide is sprayed on the outer layer so that the total film thickness with the nickel-chromium alloy is 0.03 to 2 mm. A hearth roll for a continuous heat treatment furnace is described.

In Patent Document 2, for the purpose of preventing build-up, a heat treatment furnace in which a plurality of thermal sprayed base layers in which the chromium content is sequentially changed is provided on the surface of the roll base, and a sprayed coating layer of chromium carbide is provided on the base layer. Hearth rolls for are listed.

In Patent Document 3, a ceramic sprayed coating layer is provided on the surface of a roll made of heat-resistant steel for the purpose of preventing metal transfer from the material to be conveyed, preventing wear of the roll surface, and preventing slipping of the steel plate. A heat treatment furnace roll is described in which the thermal spray coating layer is made of zirconia ceramic containing 1 to 10% by weight of chromium carbide.

In Patent Document 4, for the purpose of preventing build-up and improving oxidation resistance, Al is 3 to 8 mass%, Cr is 16 to 25 mass%, and Y is 0.1 to 1 mass with respect to the total amount of cermet powder. % And one or more selected from 1 to 5 mass% of boride and 5 to 10 mass% of carbide with respect to the total amount of cermet powder and alloy powder consisting of one or more selected from Co and Ni in the balance. Described is an in-furnace transfer roll of a steel strip heat treatment furnace in which a cermet powder for thermal spray coating composed of a ceramic powder composed of a ceramic powder is sprayed onto a roll surface.

Patent Document 5 contains 10 to 20 mass% of Cr ₂₃ C ₆ and _{10 to 20 mass% of Y2 O 3 with} respect to the total amount of cermet powder for the purpose of improving build-up resistance and oxidation resistance. The total amount of cermet powder is 30 mass% or less, and Al is 4 to 6 mass%, Cr is 12 to 16 mass%, and Y is 1 mass% or less with respect to the total amount of cermet powder, and the balance is from Co and / or Ni. Described is an in-furnace roll having excellent build-up resistance and oxidation resistance, in which a cermet powder composed of a mixed powder with a heat-resistant alloy powder is used to form a spray layer having a film thickness of 70 to 120 μm on the surface.

Patent Document 6 describes on a sprayed coating made of cermet or a heat-resistant alloy having a ceramic component content of 80 Vol% or less for the purpose of suppressing slipping, meandering, dusting on rolls, and build-up of metal plates during plate passing. It has an oxide layer consisting of one or more of one or more of sprayed metal, Cr, Si, Zr, and Al, and the surface of the oxide layer is set with the cutoff value as the initial value in accordance with JISB0633. The transfer roll for steel plate manufacturing has a ratio R / R'of 4 or more between the roughness parameter R measured in the process and the roughness parameter R'measured by setting the cutoff value to 1/10 of the initial value. Are listed.

Patent Document 7 contains an alloy containing 30 to 50% by mass of chromium carbide in order to obtain build-up resistance and thermal impact resistance, and the balance is composed of an alloy containing at least one of cobalt and nickel, chromium, aluminum and ittrium. Described is a hearth roll provided with a thermal spray coating obtained by high-speed flame spraying of a thermal spraying powder having an average particle size of 20 to 60 μm.

In Patent Document 8, Cr ₃ C ₂ is more than 50 to 90 Vol%, Al ₂ O ₃ is 1 to 40 Vol%, and Y ₂ O ₃ is 0 to 0 for the purpose of suppressing build-up on the roll surface during plate passing. Ceramics containing 3 Vol% and ZrB ₂ in an amount of 0 to 40 Vol% and having unavoidable residues and pores in the balance, Cr in an amount of 5 to 20% by mass, Al in an amount of 5 to 20% by mass, and Y and Si in any one of 1 It has a cermet film on the surface, which contains 0.1 to 6% by mass of seeds or 2 types, and the balance is a heat-resistant alloy composed of any 1 or 2 types of Co and Ni and unavoidable impurities. A hearth roll for a continuous quenching furnace is described in which 50 to 90 Vol% of the cermet film is the ceramics and the balance is the heat-resistant alloy.

Japanese Unexamined Patent Publication No. 56-069321 Japanese Unexamined Patent Publication No. 62-10313 Japanese Unexamined Patent Publication No. 07-011323 International Publication No. 01/034866 Japanese Unexamined Patent Publication No. 2005-206863 Japanese Unexamined Patent Publication No. 2008-001927 Japanese Patent No. 2008-240072 International Publication No. 2009/069829

In the construction methods described in Patent Documents 1 and 2, since the chromium carbide is easily decomposed, the film is not formed unless the thermal spraying conditions are sufficiently selected, or even if the film is formed, the film is dense and has sufficient adhesion. It is difficult to form a film with. The thermal spray coating layer described in Patent Document 3 contains zirconia and is a relatively porous film, so that it is not sufficient as a build-up measure. In Patent Documents 4 to 8, a cermet material is used as a thermal spraying material, and since the binder metal is exposed on the surface layer, the effect of suppressing build-up is low.

In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a Haas roll having a dense and durable film on the outer surface, which can sufficiently suppress build-up.

The outer surface of the hearth roll of the present invention is covered with a ceramic sprayed coating, and the ceramic sprayed coating contains chromium carbide as a main component, chromium oxide is dispersed and contained, and oxygen is contained in an amount of 5 to 35 wt%. It is a feature.

In the present invention, the outer surface of the hearth roll is covered with a ceramic sprayed coating, and the metal component is not exposed on the surface layer, so that the effect of suppressing build-up is high. Further, such a ceramic sprayed coating exhibits high hardness even at high temperatures due to the action of chromium carbide contained as a main component. Furthermore, since chromium oxide is appropriately dispersed and present in such a sprayed coating containing chromium carbide as a main component, this chromium oxide acts as a binder for connecting chromium carbide particles, and chromium carbide is used. A dense film can be obtained while improving the interparticle bonding force of the particles. As a result, the outer surface of the hearth roll has excellent wear resistance.

In the present invention, "mainly composed of chromium carbide" means that among the constituent components of the sprayed coating, chromium carbide is the most abundant in terms of mass. As for the abundance ratio of chromium oxide, it is necessary that the entire sprayed coating contains 5 to 35 wt% of oxygen. If it is less than 5 wt%, the function of chromium oxide as a binder is impaired, and if it exceeds 35 wt%, chromium carbide is used. The function as is not fully exhibited. By setting the oxygen content as described above, the characteristics of chromium carbide and the characteristics of chromium oxide can be brought out in a well-balanced manner. From the viewpoint of maximizing the characteristics of chromium carbide, the ceramic sprayed coating is preferably composed of chromium carbide, chromium oxide, and unavoidable impurities, and preferably contains 5 to 35 wt% of oxygen. The abundance ratio of chromium oxide is preferably 10 wt% or more from the viewpoint of improving the fineness of the sprayed coating. The abundance ratio of chromium oxide is preferably less than 30 wt%, more preferably less than 20 wt%. The smaller the amount of chromium oxide, the more remarkable the characteristics of chromium carbide, which exhibits high hardness even at high temperatures.

The hardness HV of the ceramic sprayed coating at 800 ° C. is preferably 200 or more. Since the hearth roll is generally used at a high temperature of 800 ° C. or higher, if the outer surface has such a high hardness, the durability as the hearth roll is high.

It is preferable to provide a cermet sprayed coating made of ceramics and a heat-resistant alloy under the ceramic sprayed coating. The presence of such a lower layer dramatically improves the thermal impact resistance and makes it difficult for the film to peel off. It is conceivable to form a film made of a heat-resistant alloy as the lower layer, but if a composite film of ceramics and a heat-resistant alloy is used, the difference in the coefficient of thermal expansion between the ceramic film and the ceramic film on the composite film will be smaller, so the film will be peeled off. Is less likely to occur.

Since the outer surface of the hearth roll of the present invention is covered with a ceramic sprayed coating containing chromium carbide as a main component, chromium oxide dispersedly contained, and oxygen in an amount of 5 to 35 wt%, it has an effect of suppressing build-up. High and highly durable in high temperature environments.

It is the perspective view and the surface layer enlarged sectional view of the hearth roll of this embodiment. It is a schematic diagram of the main part which shows an example of the thermal spraying apparatus for carrying out a suspension high-speed frame thermal spraying method. Test piece No. 1 to No. It is a table summarizing the appearance photograph of each film of No. 4, the cross-section observation photograph by a scanning electron microscope (SEM), the numerical value of each cross-sectional hardness HV, the oxygen content (wt%), and the porosity (%). Test piece No. 1 to No. It is a graph which shows the result of each wear resistance test of 5. Before the test, after the thermal cycle test at 900 ° C, and after the thermal cycle test at 1000 ° C, the test piece No. 1, No. 4, No. 5, No. It is a table which shows the appearance photograph of 6 and the evaluation result of the state after a test. Test piece No. before and after the test for examining the reactivity with the steel sheet component. 1, No. 4, No. It is a table summarizing the appearance photograph of 5 and the weight change.

An embodiment of the present invention will be described below. FIG. 1 is a perspective view and a surface layer enlarged sectional view of the Hearth Roll 100 of the present embodiment. The hearth roll 100 includes a base material 10, a lower layer portion 20 formed on the surface of the base material 10, and an upper layer portion 30 formed on the surface of the lower layer portion 20. Examples of the base material 10 include those made of steel.

The lower layer portion 20 formed between the upper layer portion 30 and the base material 10 is selected according to the required characteristics, and a cermet sprayed coating made of ceramics and a heat-resistant alloy is suitable. Examples of the ceramics include carbide ceramics such as TiC, NbC, WC, Cr ₃ C ₂ , B ₄ C, TaC, BiC, ZrC, HfC, and VC, TiB, ZrB ₂ , HfB ₂ , VB ₂ , TaB ₂ , and NiB. _2. Boroned ceramics such as W ₂ B ₅ and Cr B ₂ can be mentioned. Examples of the heat-resistant alloy include those containing at least one of Co and Ni, and preferably further containing at least one selected from Cr, Al, Y, and Si. As a result, the thermal impact resistance of the surface of the hearth roll 100 when the upper layer portion 30 described later is formed can be remarkably improved. Although it is conceivable to form a film made of a heat-resistant alloy as the lower layer portion 20, a composite film of ceramics and a heat-resistant alloy has a smaller difference in thermal expansion coefficient from the upper layer portion 30 made of a ceramic film, which will be described later. Therefore, the film peeling is less likely to occur.

The upper layer portion 30, which is formed on the surface of the lower layer portion 20 and constitutes the outer surface of the hearth roll, is a ceramic sprayed coating containing chromium carbide as a main component and chromium oxide dispersed therein. Oxygen contained in this sprayed coating is 5 to 35 wt% of the entire coating.

The high-speed frame thermal spraying method is preferably used for forming the thermal spray coating forming the lower layer portion 20 and the upper layer portion 30. The high-speed flame spraying method is a thermal spraying method that uses the combustion energy of the combustion gas as a heat source. It generates a supersonic frame by increasing the pressure in the combustion chamber, and supplies the thermal spray powder to the center of the supersonic frame jet flow for acceleration. It is a thermal spraying method in which the material is melted or semi-melted and continuously sprayed at a high speed.

Since the molten sprayed particles collide with the base material at a supersonic velocity, it is possible to form a sprayed coating having a dense and high adhesion force, and in particular, the sprayed coating is continuously formed, so that a uniform sprayed coating can be obtained. Can be done. As the combustion gas used as a heat source, hydrogen, flammable gas such as acetylene, ethylene and propane containing carbon and hydrogen as main components, and combustible gas containing oxygen are used. A liquid fuel such as kerosene may be used instead of the flammable gas.

Specifically, for example, a mixed gas such as oxygen / propane, oxygen / propylene, oxygen / natural gas, oxygen / ethylene, and oxygen / hydrogen is used as the combustion gas, the frame speed is 900 to 2500 m / sec, and the frame temperature is high. A supersonic frame of 1800 to 3800 ° C. is generated, the thermal spraying distance is maintained at 100 to 350 mm, and the temperature of the base material during thermal spraying is controlled to 200 ° C. or lower to perform thermal spraying.

A suspension high-speed frame is particularly suitable for forming a ceramic sprayed coating containing chromium carbide as a main component, chromium oxide dispersed and containing 5 to 35 wt% of oxygen, which constitutes the upper layer 30 which is the outer surface of the hearth roll 100. The thermal spraying method is preferably used. The reason is that it is important to use chromium carbide particles having a relatively small particle size in order to obtain a sprayed coating in which chromium oxide is appropriately dispersed while the main component is chromium carbide. The smaller the particle size of the material, the more likely it is that chromium carbide becomes chromium oxide during thermal spraying, which acts as a binder for anchoring each particle of chromium carbide that constitutes the thermal spray coating. However, on the other hand, when the sprayed material of fine particles is used, there is a drawback that the materials are aggregated during transportation until the sprayed material reaches the sprayed frame.

On the other hand, in the suspension high-speed frame spraying method, the chromium carbide particles are conveyed as a suspension dispersed in a solvent, so that the particles can be charged into the frame while maintaining the state of the fine particles. In addition, the film formed in this way is not only a film of a material having a small particle size to be a dense film, but also a state in which oxides are dispersed in an appropriate amount, and the particles of the particles constituting the film are formed. It improves the interbonding and leads to the improvement of the adhesion with the base material.

As another thermal spraying method using a thermal spray material as a suspension, there is a suspension plasma thermal spraying method. However, since the suspension plasma spraying method generally uses a very high temperature plasma frame, the amount of oxide produced is too large, or the material is sublimated, which tends to significantly reduce the yield. .. Therefore, it can be said that the suspension high-speed frame thermal spraying method is more desirable if the purpose is to form a thermal spray coating containing chromium carbide as a main component.

FIG. 2 is a schematic diagram of a main part showing an example of a thermal spraying device 1 for carrying out a suspension high-speed frame thermal spraying method. This thermal spraying device 1 is configured as a device for thermal spraying of a suspension high-speed frame in which a thermal spraying material is supplied from the outside as a slurry (suspension). The thermal spraying device 1 is an external supply type slurry in which the thermal spray powder is dispersed in a solvent and is supplied from the outside, and includes a thermal spray gun 2 and a slurry supply nozzle 3.

The thermal spray gun 2 has a combustion container portion 5 forming a combustion chamber 4, a thermal spray nozzle 6 continuous with the combustion vessel portion 5, and an ignition device 7. A gas containing high-pressure oxygen and fuel is supplied to the combustion chamber 4, and the gas is ignited by the ignition device 7. Then, the frame 12 generated in the combustion chamber 4 is once throttled by the thermal spray nozzle 6, then expanded to form a supersonic frame, and is ejected from the tip of the thermal spray nozzle 6 at high speed. The slurry 11 is supplied from the slurry supply nozzle 3 to the injected frame 12. The sprayed powder in the slurry 11 is in a molten or semi-melted state, and is accelerated by the frame 12 and collides with the base material 10 or the lower layer portion 20 formed on the base material 10 at high speed to cause the base material. A thermal spray coating as a lower layer portion 20 is formed on the lower layer portion 20, and a thermal spray coating as an upper layer portion 30 is formed on the lower layer portion 20.

The slurry 11 is obtained by dispersing the sprayed powder in a solvent containing a dispersion medium composed of water or alcohol and optionally an organic dispersant. The slurry 11 contains particles of the sprayed powder in a mass ratio of 5 to 40%. The slurry 11 is supplied to the frame 12 to be ejected from the tip of the thermal spray nozzle 6.

If the internal supply method is used in which the slurry is supplied inside the spraying nozzle, the sprayed material may be deposited in the nozzle tube, and the spraying material may be agglomerated and discharged. On the other hand, in the present embodiment, as shown in FIG. 2, the slurry 11 is supplied from the outside to the frame 12, and the occurrence of spitting can be prevented.

The sprayed powder may be only chromium carbide powder or a mixed powder containing chromium carbide powder and chromium oxide powder. When only the chromium carbide powder is used, the average particle size of the powder is preferably 0.1 to 5.0 μm, and the particle size distribution of the chromium carbide powder is at least in the range of 0.1 μm or more and less than 1.0 μm. , 1.0 μm or more and less than 10.0 μm are more preferable. In the present specification, the average particle size of the powder is defined as the particle size (median diameter) at which the cumulative value is 50% when the particle size distribution is measured by the laser diffraction / scattering method (microtrack method).

The thickness of the thermal spray coating forming the lower layer portion 20 is preferably in the range of 50 to 500 μm, and the thickness is appropriately set according to the purpose of use. When the thickness is 50 μm or more, the effect of thermostable impact resistance is remarkably exhibited, and when it is 500 μm or less, the decrease in mechanical strength due to the influence of the residual stress inside the film can be prevented.

The thickness of the thermal spray coating forming the upper layer portion 30 is preferably in the range of 15 to 500 μm, and the thickness is appropriately set according to the purpose of use. When the thickness is 15 μm or more, the wear resistance is excellent, and when the thickness is 500 μm or less, it is possible to prevent a decrease in mechanical strength due to the influence of residual stress inside the film.

The porosity of the sprayed coating constituting the lower layer 20 and the upper layer 30 may be about 0.1 to 5%, but the porosity of both the lower layer 20 and the upper layer 30 is 0.1 to 2%. It is preferable that the upper layer portion 30 has a porosity of 0.1 to 1%. By using the suspension high-speed frame thermal spraying method, the porosity can be reduced to 1% or less. In the present specification, the porosity is calculated by regarding the black part in the film of the cross-sectional film photograph (SEM-BEI image) of the scanning electron microscope as a pore and binarizing the black part to calculate the total area of the pore. , The value calculated by dividing the total area of the pores by the total area of the film within the observation range.

To give an example of a process for obtaining the lower layer portion 20 and the upper layer portion 30, following the cleaning treatment of the outer surface of the base material 10 and the roughening treatment by blasting, thermal spraying is performed on the base material 10 to perform thermal spraying. A lower layer portion 20 made of a film is formed, and further spraying is performed on the lower layer portion 20 to form an upper layer portion 30 made of a thermal spray coating. In addition, other steps such as preheating and surface polishing may be included.

In the case of the hearth roll 100 of the present embodiment, the outer surface of the hearth roll 100 is covered with the upper layer portion 30 made of a ceramic sprayed coating, and the metal component is not exposed on the surface layer, so that the build-up suppressing effect is high. .. Further, such a ceramic sprayed coating exhibits high hardness even at high temperatures due to the action of chromium carbide contained as a main component. Furthermore, since chromium oxide is appropriately dispersed and present in such a sprayed coating containing chromium carbide as a main component, this chromium oxide acts as a binder for connecting chromium carbide particles, and chromium carbide is used. A dense film can be obtained while improving the interparticle bonding force of the particles. As a result, the outer surface of the hearth roll 100 has excellent wear resistance. As a result, the effect of suppressing build-up is improved, and high durability in a high temperature environment can be obtained.

When the hardness HV of the ceramic sprayed coating at 800 ° C. is 200 or more, the durability as a hearth roll in a high temperature environment can be improved.

Since the lower layer portion 30 made of the ceramic sprayed coating is provided with the lower layer portion 20 made of the cermet sprayed coating made of ceramics and a heat-resistant alloy, the thermal impact resistance is dramatically improved and the film peeling can be prevented from occurring. ..

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

(Preparation of test pieces)
As a base material for forming a thermal spray coating, a flat plate made of steel (SUS310S) having a length of 50 mm, a width of 50 mm, and a thickness of 10 mm was prepared, and different spraying methods or materials were used on the surface of the base material. 1 to No. 6 test pieces were prepared. No. In the test piece No. 1, a slurry material obtained by adjusting Cr ₃ C ₂ powder having an average particle diameter (D50) of 3 μm to 20 wt% of the whole with purified water was used, and a substrate was subjected to high-speed flame spraying (HVOF) in the atmosphere. A 50 μm sprayed coating was formed on the surface. No. For the test piece No. 2, Cr _{3C 2} powder having a particle size of 5 to 20 μm was prepared, and a 50 μm sprayed coating was formed on the surface of the substrate by high-speed flame spraying in the atmosphere.

No. For the test piece No. ₃ , Cr 3C ₂ powder having a particle size of 5 to 20 μm was prepared, and a 50 μm thermal spray coating was formed on the surface of the substrate by atmospheric pressure plasma spraying (APS). No. For the test piece No. ₄ , a Cr ₃ C ₂ cermet (Cr ₃ C 2-60 mass% CoNiCrAlY) powder having a particle size of 20 to 53 μm was prepared, and a 150 μm sprayed coating was applied to the surface of the substrate by high-speed frame spraying in the atmosphere. Formed. No. In the test piece No. 5, 8YZ (ZrO _2-8 mass% Y ₂ O ₃ ) powder having a particle size of 10 to 45 μm was prepared, and a 150 μm sprayed coating was formed on the surface of the substrate by atmospheric pressure plasma spraying. .. No. In the test piece of No. 6, on the surface of the base material, No. A thermal spray coating as an lower layer was formed under the condition of 4, and then No. A thermal spray coating as an upper layer was formed under the condition of 1.

(Film observation, hardness measurement, component analysis)
Test piece No. 1 to No. No. 4 was cut, and the cross-sectional structure of each film was observed using a scanning electron microscope (SEM). Further, the hardness (HV) of each film was measured by a Vickers hardness tester under two conditions of normal temperature (RT) and 800 ° C. Furthermore, the oxygen content and porosity within the range were investigated from the cross-sectional observation photographs of each film. An energy dispersive X-ray analyzer (EDX) was used to measure the oxygen content. FIG. 3 shows the test piece No. 1 to No. It is a table summarizing the appearance photograph of each film of No. 4, the cross-section observation photograph by a scanning electron microscope (SEM), the numerical value of each cross-sectional hardness HV, the oxygen content (wt%), and the porosity (%).

When the cross-sectional structure was observed, the test pieces (No. 1 and No. 2) on which the thermal spray coating was formed by high-speed frame spraying were more precise than the test pieces (No. 3) on which the thermal spray coating was formed by atmospheric pressure plasma spraying. It became a thing. However, even with the same high-speed flame spraying, the test pieces (No. 1 and No. 2) on which the sprayed coating was formed using Cr ₃ C ₂ powder formed the sprayed coating using Cr ₃ C ₂ cermet powder. The result was that the hardness was much higher than that of the test piece (No. 4). Further, even in the case of high-speed flame spraying using the same Cr ₃ C ₂ powder, a test piece in which a thermal spray coating was formed using a slurry material rather than a test piece (No. 2) in which a thermal spray coating was formed using a powder material. (No. 1) had a smaller oxygen content in the sprayed coating and became denser.

(Abrasion resistance)
Test piece No. 1 to No. No. 5 was used to perform a wear resistance test using a Suga type wear tester. FIG. 4 shows the test piece No. 1 to No. It is a graph which shows the result of each wear resistance test of 5. The horizontal axis of FIG. 4 represents the number of slides, and the vertical axis represents the wear loss (mg).

In the test piece (No. 5) having a thermal spray coating containing 8YZ as a main component, the test piece (No. 1 to No. 4) having a thermal spray coating containing Cr ₃ C ₂ or Cr ₃ C ₂ cermet as a main component was formed. ), The result is that the wear resistance is significantly inferior. Further, even if the same Cr ₃ C ₂ is the main component of the thermal spray coating, the test pieces (No. 1 and No. 2) on which the thermal spray coating is formed by high-speed flame spraying form the thermal spray coating by atmospheric pressure plasma spraying. The wear resistance was better than that of the test piece (No. 3). Further, even if the test piece is produced by the same high-speed flame spraying, the test piece (No. 4) on which the sprayed coating containing Cr ₃ C ₂ cermet is the main component is sprayed containing Cr ₃ C ₂ as the main component. The result was that the wear resistance was inferior to that of the test pieces (No. 1 and No. 2) on which the film was formed.

(Heat-resistant impact resistance)
Test piece No. 1, No. 4, No. 5, No. A thermal shock test was performed using No. 6. The thermal shock test was carried out under two conditions: a cycle of heating to 900 ° C. and then water cooling was repeated 10 times, and a condition of repeating a cycle of heating to 1000 ° C. and then water cooling 10 times. FIG. 5 is a table showing an external photograph of each test piece and an evaluation result of the state after the test before the test, after the heat cycle test at 900 ° C., and after the heat cycle test at 1000 ° C.

In the thermal cycle test at 900 ° C., minute cracks were found in the test pieces (No. 1, No. 4, No. 6) on which the sprayed coating containing Cr ₃ C ₂ or Cr ₃ C ₂ cermet was the main component. No change was observed in the test piece (No. 5) on which a sprayed coating containing 8YZ as a main component was formed. In the thermal cycle test at 1000 ° C, a test piece (No. 4) having a sprayed coating containing Cr ₃ C ₂ cermet as the main component and Cr ₃ C ₂ with a lower layer (lower layer) made of Cr ₃ C ₂ cermet. The test piece (No. 6) on which the thermal spray coating was formed mainly of the above was retained in minute cracks, whereas the test piece (No. 6) on which the thermal spray coating of Cr ₃ C ₂ without underlay was formed was formed. Chipping was observed in the test pieces (No. 5) on which the sprayed coating containing No. 1) and 8YZ as the main components was formed, resulting in inferior thermal shock resistance.

(Reactivity with steel sheet components)
Test piece No. 1, No. 4, No. No. 5 was used to perform a test for examining the reactivity with the steel sheet component. As a test method, manganese oxide powder is sandwiched between the surface of each test piece and a flat plate of SS400, fired in a vacuum furnace adjusted to 1000 ° C. for 10 hours, and then the weight change of the test piece before and after the test is observed. I went by comparing. FIG. 6 is a table summarizing the appearance photographs and weight changes of each test piece before and after the test for examining the reactivity with the steel sheet component. A test piece (No. 1) on which a sprayed coating containing Cr ₃ C ₂ was the main component showed almost no change in weight, whereas a test on which a sprayed film containing Cr ₃ C ₂ cermet was formed was formed. A slight change in weight was observed in the piece (No. 4), and a large change in weight was observed in the test piece (No. 5) having a sprayed coating containing 8YZ as a main component.

The above embodiments and examples are illustrative and not restrictive. The hearth roll of the present invention can be changed as long as the effect of the present invention is not impaired, and the form of other configurations and processes provided as necessary is not limited.

1 Thermal spraying device 2 Thermal spraying gun 3 Slurry supply nozzle 4 Combustion chamber 5 Combustion chamber part 6 Thermal spraying nozzle 7 Ignition device 10 Base material 11 Slurry 12 Frame 20 Lower layer 30 Upper layer 100 Hearth roll

Claims (3)

A hearth roll whose outer surface is covered with a ceramic sprayed coating.
The ceramic sprayed coating is a hearth roll containing chromium carbide as a main component, chromium oxide dispersed and contained, and oxygen in an amount of 5 to 35 wt%. The hearth roll according to claim 1, wherein the ceramic sprayed coating has a hardness HV of 200 or more at 800 ° C. The hearth roll according to claim 1 or 2, wherein a cermet sprayed coating made of ceramics and a heat-resistant alloy is provided under the ceramic sprayed coating.

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