JP2008115443A - Ni-BASED SELF-FLUXING ALLOY POWDER FOR THERMAL SPRAYING, ITS PRODUCTION METHOD, AND SELF-FLUXING ALLOY SPRAYED COATING OBTAINED USING THE POWDER - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide Ni-based self-fluxing alloy powder having hardness at high temperature as the index of heat resistance (high temperature hardness) as well as hardness at room temperature (room temperature hardness), wear resistance and thermal impact resistance (thermal cycle resistance), to provide its production method, and to provide a self-fluxing alloy sprayed coating. <P>SOLUTION: The Ni-based self-fluxing alloy powder for thermal spraying is composed of an Ni-based self-fluxing alloy comprising Cr, C and Co, and in which chromium carbides with a particle diameter of ≤5 μm are uniformly precipitated into the particles. The alloy powder contains, by mass, 30.0 to 65.0% Cr, 1.0 to 4.5% C, 5.0 to 20.0% Co, 0.5 to 4.0% Si, 0.5 to 4.0% B and 0.5 to 4.0% Mo, selectively comprises 0 to 5.0% Fe, and the balance Ni with inevitable impurities. Further, the powder is sorted in a grain size range of 45 to 106 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a Ni-based self-fluxing alloy powder used for thermal spraying, in particular, a Ni-based self-fluxing alloy powder obtained by an atomizing method, a manufacturing method thereof, and a self-fluxing alloy spray coating obtained using the powder.

  Thermal spraying is, for example, a kind of surface treatment method in which a metal powder in a semi-molten state is sprayed on a predetermined part of an object and a film is formed on the surface of the part, and since the formation of a hard film can be easily and easily performed, It is often used as one of the most effective measures for damage prevention. In order to prevent damage by thermal spraying, a method of preventing damage by forming a hard sprayed coating in advance and a method of recovering the damaged part by forming a sprayed coating after damage has occurred There is.

  In recent years, thermal spraying has been applied to prevent damage and recover damaged parts even in fields where heat resistance, corrosion resistance, and wear resistance are required, such as boiler tubes of power generation equipment.

  Boiler tubes are used for waste heat recovery in thermal power plants, garbage incinerators, and coke dry fire extinguishing equipment at steelworks. Specifically, by exposing the high-temperature combustion gas to the outside of the boiler tube and passing the circulating water inside the boiler tube, the heat of the combustion gas is transferred to the circulating water, and the circulating water is heated to high temperature and high pressure. The steam of the generator is turned as steam. The outside of the boiler tube is subject to erosion wear due to heated dust in addition to corrosion due to high-temperature combustion gas, so heat resistance, wear resistance, and thermal shock resistance as well as corrosion resistance are required. A film is formed.

Examples of the material sprayed on the outer surface of the boiler tube include chromium carbide / nickel chromium (Cr ₃ C ₂ —NiCr) cermet, Ni-based self-fluxing alloy (JIS SFNi type 4 or type 5), or powder such as 50Ni50Cr. used.

Among these, cermet powders such as Cr ₃ C ₂ —NiCr and tungsten carbide / cobalt (WC—Co) have high hardness and melting point, and primary particles composed of fine Cr ₃ C ₂ or WC and such primary particles. It is composed of Ni—Cr alloy or Co, which plays a role of particle binder. For the production of cermet powder, a granulation-sintering method is frequently used. In the granulation-sintering method, primary particles such as Cr ₃ C ₂ or WC or less and powder (binder) such as Co or Ni—Cr alloy are kneaded in a solvent to obtain a slurry. The resulting slurry is sprayed with a spray dryer to form a spherical shape, and then the solvent is vaporized and sintered to obtain a cermet powder.

  The obtained cermet powder is sized in a fine particle size range of about 15 μm to 53 μm, and is sprayed onto the base material at high speed using a spraying method such as a high-speed gas flame spraying method or a plasma spraying method. Get. The cermet powder is composed of porous secondary particles in which primary particles are aggregated and bonded, and can be sprayed at a temperature at which the binder melts. Therefore, a high melting point element can be added in a large amount as primary particles. Therefore, it is possible to form a sprayed coating that is dense and excellent in wear resistance and heat resistance.

  However, the obtained sprayed coating is non-uniform due to the interspersed primary particles in the matrix binder. In addition, because the thermal spray coating is mainly formed by mechanical bonding between the cermet powder and the base material due to the impact pressure during thermal spraying, the interparticle bonding force is lower than the coating obtained using the self-fluxing alloy powder. Since the thermal shock resistance (thermal cycle characteristics) is inferior, there is a problem that cracking and peeling are likely to occur due to thermal shock.

  On the other hand, the self-fluxing alloy powder is a powder made of an Ni-based or Co-based alloy characterized by containing a flux component such as B or Si. Self-fluxing alloy powder is mainly made by bringing molten metal obtained by melting raw materials in a melting furnace into contact with high-pressure water or inert gas via a tundish while adjusting the flow rate and flow rate, and crushing and rapid solidification. The powder is produced by an atomizing method.

  The self-fluxing alloy powder is sized in the same manner as the cermet powder, sprayed by a high-speed gas flame spraying method and a plasma spraying method, and then reheated by applying heat. As a result, the bonding force between particles is improved, a diffusion layer is formed at the interface between the base material and the sprayed coating, the coating density of the resulting sprayed coating is increased, and the hardness and adhesion strength at high temperatures that are indicators of heat resistance. A sprayed coating having excellent (peeling resistance) and thermal shock resistance (heat cycle characteristics) can be obtained.

  As is clear from the fact that the remelting process is performed, the thermal spray coating using a known self-fluxing alloy has a problem that the heat resistance (high temperature hardness) is low unless the remelting process is performed. A self-fluxing alloy made of a Ni-based alloy such as Ni-16Cr-4Si-4B-4Fe-2.4Cu-2.4Mo-2.4W-0.5C is known as an object for improving the heat resistance. However, if the remelting treatment is not performed, the thermal shock resistance is not improved, so that the remelting treatment is still necessary.

  However, even in the case of a sprayed coating that has been remelted using such a self-fluxing alloy, as part of environmental measures in recent years, in order to improve power generation efficiency and suppress dioxin generation, Under the circumstances where higher temperatures and higher pressures are required, the high-temperature hardness of the sprayed coating becomes insufficient, and this requirement cannot be met.

  On the other hand, as a material for improving the self-fluxing alloy for thermal spraying, for example, there is a material in which WC is mixed with Ni-based self-fluxing alloy powder described in JP-A-08-31630. WC is mixed in a cermet such as WC-Co or WC-NiCr with a particle size close to that of the self-fluxing alloy powder so as not to have a non-uniform distribution due to the difference in specific gravity with the Ni-based self-fluxing alloy powder. The The thermal spray coating formed using the obtained mixed powder is in a state where WC cermet particles are scattered in the self-fluxing alloy matrix. Due to the presence of WC cermet particles, the wear resistance is improved compared to the sprayed coating using ordinary self-fluxing alloys, and good results are obtained in both the corrosion resistance and wear resistance characteristics that have been considered to be contradictory. It is done.

However, reflecting the characteristics of the self-fluxing alloy that is a matrix, there is a problem that it has poor heat resistance and is insufficient for use in a high temperature environment.
JP 08-31630 A

  In the present invention, hardness at room temperature (room temperature hardness), wear resistance, thermal shock resistance (heat cycle characteristics), and high temperature hardness (high temperature), which is an index of heat resistance, can be used without performing remelting treatment. An object is to provide a thermal spray coating using a Ni-based self-fluxing alloy having excellent hardness.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have incorporated Cr, C, and Co into the Ni-based self-fluxing alloy obtained by using the atomizing method, thereby reducing the particle size. Ni-based self-fluxing alloy powder in which chromium carbide such as fine Cr ₃ C ₂ or Cr ₇ C _{3 of} 5 μm or less is uniformly deposited inside the particles is obtained, and thermal spraying using the Ni-based self-fluxing alloy powder In order to complete the present invention, it is found that the film exhibits room temperature hardness, high temperature hardness, abrasion resistance, and thermal shock resistance equal to or higher than those of known thermal sprayed coatings without remelting treatment. It came.

  That is, the Ni-based self-fluxing alloy powder for thermal spraying of the present invention is characterized in that chromium carbide containing at least Cr, C, and Co and having a particle size of 5 μm or less is uniformly precipitated inside the particles.

  The specific composition of the Ni article alloy powder for thermal spraying is 30.0 mass% to 65.0 mass% Cr, 1.0 mass% to 4.5 mass% C, and 5.0 mass%. ~ 20.0 wt% Co, 0.5 wt% to 4.0 wt% Si, 0.5 wt% to 4.0 wt% B, 0.5 wt% to 4.0 wt% % Of Mo and the balance being Ni and inevitable impurities.

  Alternatively, 30.0 mass% to 65.0 mass% Cr, 1.0 mass% to 4.5 mass% C, 5.0 mass% to 20.0 mass% Co, 0.5 % By mass to 4.0% by mass of Si, 0.5% by mass to 4.0% by mass of B, 0.5% by mass to 4.0% by mass of Mo, and Fe of 5.0% by mass or less It is desirable that the balance be Ni and inevitable impurities.

  Furthermore, the particle size range of the Ni-based self-fluxing powder for thermal spraying is desirably 45 μm to 106 μm.

  The Ni-based self-fluxing alloy powder of the present invention is manufactured by mixing raw materials at a predetermined ratio, melting the obtained mixture, and forming the powder by an atomizing method.

  By spraying the Ni-based alloy powder for thermal spraying by a known thermal spraying method, the self-fluxing alloy spray coating of the present invention can be obtained using any of the above-mentioned Ni-based self-fluxing alloy powders for thermal spraying.

  The self-fluxing alloy spray coating obtained by spraying the Ni-based self-fluxing alloy powder for thermal spraying of the present invention includes a spray coating obtained by using a known self-fluxing alloy powder and cermet powder without performing remelting treatment. In comparison, all of the hardness at room temperature (room temperature hardness), high temperature hardness, wear resistance, and thermal shock resistance (heat resistance cycle characteristics) are equivalent or equivalent, and have high high temperature hardness. Therefore, it has excellent high temperature erosion wear resistance.

  Regarding the constituent components in the Ni-based self-fluxing alloy powder for thermal spraying of the present invention, the reasons for limitation will be described below.

  Cr combines with C to form double carbides, and further combines with B to form double borides, increasing the hardness of the resulting sprayed coating and significantly improving heat resistance, corrosion resistance and wear resistance. It is an element that has an effect to make.

  The content of Cr is preferably 30.0 mass% to 65.0 mass%. If the Cr content is less than 30.0% by mass, the formation of double carbides and double borides becomes insufficient, and the above-mentioned characteristics cannot be obtained sufficiently. On the other hand, if it exceeds 65.0% by mass, the toughness of the resulting sprayed coating will decrease, the melting point will increase, and defects such as blow holes will easily be caused on the processed surface.

  C is an element which contributes to the improvement of the hardness and wear resistance of the sprayed coating obtained by mainly combining with Cr or Mo to form double carbides.

  As for the content rate of C, 1.0 mass%-4.5 mass% are preferable. When the C content is less than 1.0% by mass, the melting point of the powder becomes high, the powder adhesion yield at the time of thermal spraying decreases, and the working efficiency decreases. In addition, the resulting sprayed coating becomes porous, and the amount of double carbides crystallized in the sprayed coating decreases, so that sufficient wear resistance cannot be obtained. Moreover, when it exceeds 4.5 mass%, while hardness will become high too much, toughness will fall and it will become easy to generate | occur | produce a crack at the time of a process or use.

  Co is an element having an effect of improving the hardness, high temperature hardness and heat resistance of the thermal spray coating by forming an alloy with Cr, Mo, Fe and Ni.

  The content of Co is preferably 5.0% by mass to 20.0% by mass. When the Co content is less than 5.0% by mass, the formed alloy phase becomes insufficient, and the above-mentioned characteristics cannot be obtained sufficiently. Moreover, when it exceeds 20.0 mass%, toughness will fall and it will become easy to generate | occur | produce a crack at the time of a process or use.

  Si, together with B described later, is an important element as a self-fluxing alloy material for thermal spraying, and as a deoxidizer, it reduces oxides and pores in the thermal spray coating, thereby improving thermal shock resistance and melting point of the powder. Has the effect of lowering. In addition, it contributes to improving the hardness and wear resistance of the resulting sprayed coating by dissolving in the matrix.

  The content of Si is preferably 0.5% by mass to 4.0% by mass. If the Si content is less than 0.5% by mass, the above-described effects cannot be obtained sufficiently. On the other hand, if it exceeds 4.0% by mass, it becomes too hard and brittle, and cracks are likely to occur during processing and use.

  B, like Si, is an important element as a self-fluxing alloy material for thermal spraying, and lowers the melting point of the powder. In addition, it combines with Cr and Mo to form a Cr—Mo—B double boride, which increases the hardness of the resulting sprayed coating and contributes to improved wear resistance.

  The content of B is preferably 0.5% by mass to 4.0% by mass. When the B content is less than 0.5% by mass, a sufficient amount of Cr—Mo—B double boride is not formed, so that a sufficient effect cannot be obtained. Moreover, when it exceeds 4.0 mass%, the formation amount of Cr-Mo-B type double boride becomes excessive, and the toughness of the sprayed coating obtained will fall.

  Mo, like Cr, combines with C to form double carbides, and combines with B to form double borides, thereby greatly improving the wear resistance of the resulting sprayed coating. It is an element with Some of them are dissolved in Ni and Co matrices to improve the corrosion resistance against sulfides and chlorides.

  The content of Mo is preferably 0.5% by mass to 4.0% by mass. If the Mo content is less than 0.5% by mass, the above-mentioned double carbide and double boride are not sufficiently formed, and the effect cannot be sufficiently obtained. Moreover, even if it exceeds 4.0 mass%, the further improvement of an effect cannot be anticipated greatly, and on the contrary, the toughness of the sprayed coating obtained and the fall of the self-flux of the powder are caused.

  Ni is an element that forms a matrix of the Ni-based self-fluxing alloy powder for thermal spraying according to the present invention.

  In order to further improve the characteristics of the Ni-based self-fluxing alloy powder for thermal spraying of the present invention, it is possible to further add Fe. Fe is an element that is solid-dissolved in the Ni matrix and further improves the strength of the resulting sprayed coating, and can be added for the purpose of such an effect.

  The content rate of Fe shall be 5.0 mass% or less. When the Fe content exceeds 5.0% by mass, the hardness and corrosion resistance of the resulting sprayed coating are lowered, leading to deterioration of wear resistance and corrosion resistance.

  As described above, the mixture obtained by mixing within the composition range of the present invention is once melted into a melt. And it is set as powder by the gas atomization method or the water atomization method, for example. In these atomization methods, it is possible to adjust the particle size of the obtained powder by changing the ratio of the melt to gas or liquid among the atomization conditions.

  The classification particle size range of the Ni-based self-fluxing alloy powder for thermal spraying varies depending on the type of thermal spray gun used, but when using a powder gun and a plasma spray gun, 45 μm to 125 μm, 45 μm to 106 μm, 45 μm to 90 μm, 20 μm -75 micrometers and 10 micrometers-53 micrometers are suitable, and 45 micrometers-106 micrometers are especially preferable. When a high-speed gas flame spray gun is used, 5 μm to 30 μm, 5 μm to 38 μm, 5 μm to 45 μm, 10 μm to 45 μm, 15 μm to 45 μm, and 20 μm to 53 μm are appropriate.

  When the particle size of the obtained powder is coarser than the respective particle size ranges, it is difficult to form a dense sprayed coating by thermal spraying, and only a sprayed coating with low hardness can be obtained. In addition, when the particle size is finer than the respective particle size ranges, the flowability of the powder is lowered, and the fine powder with high heat receiving efficiency is melted and deposited on the inner surface of the nozzle of the spray gun. Is significantly impaired.

  The raw material is melted and homogenized at a high temperature of 1550 to 1700 ° C., and then rapidly cooled by an atomizing method to produce a powder. As a result, strong affinity Cr and C are combined, and chromium carbide particles having a particle size of 5 μm or less crystallize. Are uniformly dispersed and precipitated in the matrix alloy phase. Co is combined with Ni or Cr to form a NiCoCr matrix alloy phase. If the particle size of the chromium carbide inside the powder particles is larger than 5 μm, the sprayed coating becomes brittle and wear resistance, thermal shock resistance and the like are deteriorated. In addition, even if it deposits unevenly inside, variation in hardness occurs, which is not preferable because it reduces wear resistance, thermal shock resistance, and heat resistance.

  Examples of the present invention will be described below in comparison with comparative examples, but the present invention is not limited to the following examples.

[Example 1]
First, the raw materials blended so as to have the composition shown in Table 1 were melted using a high frequency induction vacuum melting furnace. The obtained molten metal at about 1650 ° C. was powdered by a gas-water atomization method. The obtained powder was dried with hot air and then classified into 45 μm to 106 μm with a vibration classifier to prepare a Ni-based self-fluxing alloy powder for thermal spraying of this example. The chemical composition and the classified particle size range of the obtained Ni-based self-fluxing alloy powder for thermal spraying were the same as those shown in Table 1.

When the cross section of the obtained Ni-based self-fluxing alloy powder for thermal spraying was etched with Murakami reagent (etching solution containing ferrocyanide and caustic potash) and observed with an electron microscope, Cr ₃ C _{2 having} a particle size of 5 μm or less, Chromium carbide particles composed of Cr ₇ C ₃ and Cr ₂₃ C ₆ were uniformly dispersed and precipitated inside the NiCoCr matrix alloy phase.

  Next, the obtained Ni-based self-fluxing alloy powder for thermal spraying was sprayed onto an SS400 mild steel plate with a plasma spray gun to obtain a thermal sprayed coating having a thickness of 450 μm. Furthermore, the surface of the obtained thermal spray coating was smoothed by cutting and polishing, and room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance were measured as follows.

  The room temperature hardness and the high temperature hardness were measured for the cross section and the surface using a Vickers hardness tester (load: 0.3 kgf). The high temperature hardness was measured by heating and holding at 200 ° C, 400 ° C, and 600 ° C.

  Abrasion resistance was measured using a suga type reciprocating wear tester, load: 3.25 kgf, number of reciprocations (DS): 1600 times, mating material: SiC # 320 abrasive paper, JIS H 8503 (plating wear resistance test) The amount of wear resistance (DS / mg) was measured according to the test method defined in Item 9 (Method of Reciprocating Wear Test).

  Thermal shock resistance was evaluated by a thermal cycle test. The thermal cycle test was held in an electric furnace at 600 ° C. for 30 minutes, and then the thermal cycle for forced air cooling was repeated 30 times, and at each time, the presence or absence of cracks and peeling occurring in the sprayed coating was visually and color-checked. Observed.

  Table 2 shows the measurement results of room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance.

[Examples 2 to 4]
A Ni-based self-fluxing alloy powder for thermal spraying was obtained in the same manner as in Example 1 except that the raw materials were blended so as to have the composition shown in Table 1. The chemical composition and the classified particle size range of the obtained Ni-based self-fluxing alloy powder for thermal spraying were the same as those shown in Table 1. Further, when the obtained powder was analyzed, as in Example 1, chromium carbide having a particle size of 5 μm or less was uniformly deposited inside the particles.

  Next, a thermal spray coating was obtained in the same manner as in Example 1, and the obtained thermal spray coating was measured for room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance in the same manner as in Example 1. Table 2 shows the measurement results of room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance.

[Comparative Example 1]
A powder in which only 50% of Cr was added and the balance was Ni was produced.

  Next, a thermal spray coating was obtained in the same manner as in Example 1, and the obtained thermal spray coating was measured for room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance in the same manner as in Example 1. Table 2 shows the measurement results of room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance.

[Comparative Example 2]
As a commonly used material, a Ni-based self-fluxing alloy powder for thermal spraying was obtained in the same manner as in Example 1 except that the raw materials were blended so as to have the composition shown in Table 1. The chemical composition and the classified particle size range of the obtained Ni-based self-fluxing alloy powder for thermal spraying were the same as those shown in Table 1.

  Next, a thermal spray coating was obtained in the same manner as in Example 1, and the obtained thermal spray coating was measured for room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance in the same manner as in Example 1. Table 2 shows the measurement results of room temperature hardness, high temperature hardness, wear resistance, and thermal shock resistance.

  From the above results, the thermal spray coating obtained by using the Ni-based self-fluxing alloy powder for thermal spraying obtained in Examples 1 to 4 of the present invention has been conventionally used without remelting treatment. It has the same or better room temperature hardness, high temperature hardness, wear resistance, thermal shock resistance (heat cycle resistance) as the known thermal spray coating, and also has high high temperature hardness, so it has high temperature erosion wear resistance. It is clear that

Claims (6)

  A Ni-based self-fluxing alloy powder for thermal spraying, characterized in that chromium carbide containing at least Cr, C, and Co and having a particle size of 5 μm or less is uniformly precipitated inside the particles.   30.0 mass% to 65.0 mass% Cr, 1.0 mass% to 4.5 mass% C, 5.0 mass% to 20.0 mass% Co, and 0.5 mass% -4.0% by mass of Si, 0.5% -4.0% by mass of B, 0.5% -4.0% by mass of Mo, the balance being Ni and inevitable impurities The Ni-based self-fluxing alloy powder for thermal spraying according to claim 1.   30.0 mass% to 65.0 mass% Cr, 1.0 mass% to 4.5 mass% C, 5.0 mass% to 20.0 mass% Co, and 0.5 mass% -4.0 mass% Si, 0.5 mass% -4.0 mass% B, 0.5 mass% -4.0 mass% Mo, and 5.0 mass% or less Fe are included. The Ni-based self-fluxing alloy powder for thermal spraying according to claim 1, wherein the balance is Ni and inevitable impurities.   4. The Ni-based self-fluxing alloy powder for thermal spraying according to claim 1, wherein a particle size range is 45 μm to 106 μm.   A method for producing a Ni-based self-fluxing alloy powder for thermal spraying according to any one of claims 1 to 4, wherein raw materials are mixed at a predetermined ratio, the obtained mixture is melted, and a powder is obtained by an atomizing method. A method for producing a Ni-based self-fluxing alloy powder characterized by the above.   A self-fluxing alloy spray coating obtained by using the Ni-based self-fluxing alloy powder for thermal spraying according to any one of claims 1 to 4.