JPS61210171A - Wear-resistant treatment of metallic material - Google Patents

Abstract

PURPOSE:To form a treated layer having excellent wear resistance on a metallic material by coating or impregnating liquids contg. carbon on or in a thermally sprayed layer formed on the surface of the metallic material by using a thermally spraying material contg. a metal then subjecting the material to a heat treatment in an inert atmosphere. CONSTITUTION:The thermally sprayed layer is formed by the thermally spraying material contg. the metal on the surface of the metallic material. After >=1 kinds of the liquids contg. inorg. carbon or inorg. compd. contg. carbon or org. material are coated on or impregnated in the thermally sprayed layer, the material is subjected to the heat treatment in the inert atmosphere. The carbide having high hardness is thus formed in the pores in the thermally sprayed layer, by which the density of the thermally sprayed layer is increased and the wear resistance of the metallic material is improved. The above- mentioned thermal spraying is executed dividedly at least twice so that the porosity of the finally sprayed layer is preferably made 10-30%. The cermet powder consisting of the alloy contg. carbide and the elements constituting the carbide or the alloy powder, etc., contg. the carbide forming elements are preferable as the thermally spraying material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for treating metal materials for wear resistance, and more particularly to an improvement in a treatment method for improving wear resistance by forming a sprayed layer on the surface of a metal material.

[Cost of invention]

In boilers that use coal or a mixture of heavy oil and coal as fuel, when the ash in the coal turns into fly ash and scatters in the boiler along with the flow of combustion gas, it collides with the tube group of the boiler heat exchanger tubes, causing the tubes to explode. A phenomenon that causes wear and thinning of the outer surface,
That is, it is known that ash erosion occurs. As shown in FIG. 4, this ash erosion mainly occurs near the boiler wall of the primary superheater (-next week's heater upper bank 8, -next week's heater interrupted bank 9, and primary superheater lower bank 10) and the energy saver 11. The combustion gas flow is concentrated,
Alternatively, the problem occurs at a location where the combustion gas drifts and the gas flow velocity becomes high (particularly at the location indicated by reference numeral 17 in FIG. 4).

The rate of thinning due to ash erosion depends on the properties of the coal used (shape and density of fly ash, etc.), metal temperature,
Although it varies depending on the material of the heat transfer tube (usually carbon steel or low alloy steel) and the gas flow rate, in severe cases, the amount of thinning can reach several millimeters per year, which is an important problem in boiler operation.

One way to prevent such thinning of the heat exchanger tube due to ash erosion is to install a protector made of a material with excellent wear resistance on the outside of the heat exchanger tube. The problem with this method is that a gap is created between the protector and the heat exchanger tube, which may significantly reduce the heat absorption of the heat exchanger tube, and furthermore, the heat exchanger tube may cause ash erosion over a wide area. There are technical and economical problems in applying this method in this case.

Another method to prevent heat exchanger tube wall thinning due to ash erosion is to use a double-walled tube in which the outer layer is made of a metal material with excellent wear resistance and the inner layer is made of a normal heat exchanger tube material. However, double pipes are very expensive, and when used in large quantities, there is a problem in that the overall material cost increases significantly.

Furthermore, although the protector method and double pipe method can reduce the wall thinning rate to some extent in boilers that use low-grade coal with high ash content or in locations where the gas flow rate is extremely high,
It cannot be a permanent solution.

Furthermore, as another method to prevent thinning of heat exchanger tubes due to ash erosion, there is a method of creating an alloy layer by diffusing and penetrating metals such as chromium or aluminum into the surface of the metal material, or after carburizing the surface layer of the metal material. There is a method of diffusing metals such as chromium and vanadium to create a carbide layer on the surface of the metal material.

In the former case, the hardness of the treated layer is at most 400H.

Since the thickness of the treated layer is approximately 100 μm at maximum, it is not expected that the wear resistance will improve much in areas where wear is severe. On the other hand, in the case of the latter, the hardness of the treated layer is over 1000Hv and the wear resistance is very good.
Since the processing is complicated, the material cost increases significantly when used in large quantities.

Furthermore, since the latter method involves carburizing the material to be treated, there is a risk that the material to be treated will become brittle, making it difficult to apply this method to boiler heat exchanger tubes that require high strength.

Compared to the above-mentioned methods, a relatively inexpensive and reliable method for preventing ash erosion is a method of thermally spraying a material with excellent wear resistance on the outer surface of the heat transfer tube.

Thermal spray materials can be roughly divided into: (1) metal-based materials (for example, Fe-
(Cr-based, Ni-Cr-based, etc.) (2) Cermet-based (chromium carbide, tungsten carbide, etc. produced by mixed spraying of carbide and metal) (3) Pure ceramic-based (alumina, zirconia, etc.) . The properties of the sprayed layer that affect wear resistance include its hardness, dense porosity), and bonding strength between particles.

Among the above-mentioned thermal spray materials, pure ceramic materials have extremely high hardness, but they have the drawbacks that a large number of pores are generated in normal thermal spraying and that the bonding force between particles in the thermal spray layer is weak. Furthermore, in the case of metal-based materials, the porosity and interparticle bonding force of the sprayed layer are good, but they have the disadvantage of low hardness. On the other hand, cermet-based materials have the highest hardness among the three types, but have the disadvantage that the bonding force between carbide and metal is weaker than that of metal-based materials.

When these thermal spray materials are applied to actual equipment, they exhibit excellent wear resistance in areas where the gas flow rate is relatively low.

However, in areas where the gas flow rate is high and the collision force of ash is strong, the bonding force between particles of the pure ceramic type and the Sarno-7 type is weak, while the hardness of the metal type is low, so both can be used for a short time. The problem is that wear progresses and the intended purpose cannot be achieved.

[Purpose of the invention]

The purpose of the present invention is to solve the problems of the prior art described above,
An object of the present invention is to provide a method for treating a metal material with improved wear resistance by improving the wear resistance of a sprayed layer formed on the surface of the metal material.

[Summary of the invention]

The present invention was achieved as a result of research into overcoming the problems of improving the hardness of the sprayed layer, improving the bonding force between particles, and reducing the porosity when a sprayed layer is employed as a countermeasure against ash erosion. After spraying a thermal spray material containing metal onto the surface of the metal material, a liquid containing inorganic carbon, an inorganic compound containing carbon, or an organic substance is interposed in the pores of the sprayed layer, and then heat treatment is performed in an inert atmosphere to complete the thermal spraying process. The sprayed layer is made denser by forming carbides in the pores in the layer.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram showing the state in which the surface treatment according to the present invention has been carried out, FIG.
FIG. 3 is an enlarged explanatory diagram showing step-by-step the method of the present invention in FIG.

An inner sprayed layer 2 and a final sprayed layer 3 are provided on the surface of the metal to be processed 1 which has been roughened. After thermal spraying, a coating liquid containing inorganic carbon or an organic substance having a carbon skeleton is applied or impregnated to be interposed in the pores of the final thermal sprayed layer 3, and then heated at 900 to 1200°C for several hours in an inert atmosphere. As shown in FIG. 2(B), carbides 6 (for example, chromium carbide) are formed in the pores 5 formed in the sprayed material 4 of the final sprayed layer 3 to form a dense sprayed layer.

As for the thermal spraying method, thermal spraying is performed in two steps, and the porosity of the inner thermal sprayed layer 2 is 5% or less, and the porosity of the final thermal sprayed layer 3 is 10 to 30%. The reason why the porosity of the inner sprayed layer 2 is set to 5% or less is to strengthen the bonding force between the metal to be treated and the inner sprayed layer 2 and to prevent a decrease in thermal conductivity of the inner sprayed layer 2. Setting the porosity to 5% is very easy if plasma spraying is used, and there is no particular problem in construction. On the other hand, the reason why the porosity of the final thermal sprayed layer 3 is set to 10 to 30% is that if the porosity is small, it will be difficult for the coating liquid to sufficiently penetrate into the final thermal sprayed layer 3, making it difficult to seal the pores. This is because it will be insufficient.

In other words, the porosity is approximately 10 when the pores in the sprayed layer begin to connect continuously, and where there are enough pores for the coating liquid to penetrate into the pores.
Corresponds to %. Further, the state in which particles in the sprayed layer begin to come into point contact corresponds to approximately 30% porosity.

In order to control the porosity using a normal thermal spraying method, it is sufficient to control the amount of welding. In reality, since the welding speed of thermal spraying is very fast, it is difficult to accurately control the porosity, but it is easy to control the porosity in the range of 10 to 30%.

In addition, considering peeling resistance, thermal conductivity, and economic efficiency, the thickness of the thermal sprayed layer is 1.
00 to 200 .mu.m, preferably around 300 .mu.m for the entire sprayed layer, but this is not particularly limited in the present invention. Further, in this embodiment, thermal spraying is performed in two steps, but multilayer thermal spraying may be performed if necessary. Further, in the case of a multi-layer thermal sprayed layer, it is desirable to adjust the porosity so that it increases from the thermal sprayed layer on the side of the metal to be treated to the outer thermal sprayed layer.

The thermal spraying material is preferably a metal or cermet material that has good wettability and is firmly bonded to the carbide formed in the pores by the pore sealing treatment described below.

An alloy powder containing carbide-forming elements such as chromium, tungsten, and boron is suitable as the metallic thermal spray material. On the other hand, as the cermet-based thermal spray material, a mixture of carbides such as chromium, tungsten, boron, etc. and the above-mentioned metal-based thermal spray materials is suitable.

Next, the sealing treatment performed after thermal spraying will be explained.

As a sealing treatment, a colloidal solution prepared by mixing and suspending fine powder of inorganic carbon such as carbon or carbon-containing substances such as carbide in water or an organic solvent such as ethyl alcohol, or a liquid organic material with carbon as a skeleton is used. Compounds (e.g. oil, etc.)
A method is adopted in which the surface of the melt-resistant layer is coated with or impregnated with an emulsion, suspension, etc. of an organic compound having a carbon skeleton, and then heat-treated in an inert atmosphere.

This pore sealing process utilizes the carbide-forming reaction that occurs between the carbon impregnated into the pores 5 of the final sprayed layer 3 or the carbon generated by heat treatment and the carbide-forming elements in the sprayed layer. At the same time, the carbide in the pores 5 strengthens the bonds between the particles in the sprayed layer, thereby improving the wear resistance of the sprayed layer.

In this case, the higher the heat treatment temperature is, the faster the carbide production reaction will proceed, but from the economic point of view, a lower heat treatment temperature is more advantageous. In addition, by adding a reaction accelerator such as N''d4C1 to the coating liquid during heat treatment,
Heat treatment can be performed by heating at a relatively low temperature of 200°C. Since the heating temperature and heating time of the heat treatment can be determined thermodynamically, they are not particularly limited in the present invention.

The atmosphere during the heat treatment must be an inert atmosphere such as argon or nitrogen. If the heat treatment is performed in the atmosphere, oxides are generated along with carbides as the coating liquid is heat treated, resulting in insufficient interparticle bonding force in the sprayed layer.

Carbon in the coating liquid or carbon generated by heat treatment produces carbides through a carbide-forming reaction with carbide-forming elements such as chromium, tungsten, or boron in the sprayed layer as the heat treatment continues. By adding carbide-forming metals such as chromium, tungsten, and poron, it is possible to increase the amount of carbide generated in the pores and further enhance the pore sealing effect.

In this case, by adding a carbide-forming metal that is the same as the carbide-forming element contained in the sprayed layer to the coating liquid that is applied or impregnated onto the surface of the sprayed layer, it is possible to more effectively improve the interparticle bonding force of the sprayed layer. can be taken as a thing.

Next, for comparison, a coating treated with the above-described treatment of the present invention, a N1-Cr alloy powder sprayed coating, a chromium carbide-(Ni-
The wear resistance of four types of test pieces made of cermet sprayed Cr) and carbon steel was investigated. In addition, the wear test is approximately 10
5iO1 with particle size around 0 μm at 20 m/s
It was added to the ejected air of EC and sprayed onto the test piece for 2 hours. The results are shown in FIG. 3, and the material treated according to the present invention has about 10 times the wear resistance of other thermal sprayed materials.

〔Effect of the invention〕

As described above, according to the present invention, the sprayed layer is denser than the conventional sprayed layer, and the hardness of the surface layer is extremely high.
A treated layer having significantly superior wear resistance can be obtained. Furthermore, the method of the present invention can form a good treated layer without adverse effects such as embrittlement on the metal to be treated, and if the method of the present invention is applied to actual equipment, the life of the metal material can be significantly extended. , its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the present invention, and FIG. 2 (A
), (B) are schematic diagrams showing the processing steps of the embodiment of the present invention in the outer thermal sprayed layer of FIG. 1, and FIG. Figure 4 is a schematic diagram of the main parts of the boiler to show the locations where ash erosion occurs. ! ...Metal to be treated, 2...Inner sprayed layer, 3...Final (outer) sprayed layer, 4...
Thermal spray material, 5...pores, 6...carbide,
7... Reheater, 8... Primary superheater upper bank, 9... Primary superheater middle bank, 10.
... Flammable superheater lower bank, 11 ... Energy saver, 12 ... Cage front wall, 13 ... Cage rear wall, 14 ... Primary superheater inlet header, 1
5... Economizer outlet header, 16... Economizer inlet header, 17... Erosion occurrence position

Claims (6)

[Claims] (1) A sprayed layer is formed on the surface of a metal material using a thermal spray material containing metal to improve the wear resistance of the metal material, and the sprayed layer is coated with a liquid containing inorganic carbon, an inorganic compound containing carbon, or an organic substance. 1. A method for treating metal materials with wear resistance, which comprises applying or impregnating one or more kinds of materials and then heat-treating the material in an inert atmosphere. (2) Thermal spraying is carried out in at least two parts, and the porosity of the final sprayed layer is 10 to 30%.
Wear-resistant treatment method for metal materials described in section (3) The method for treating metal materials with wear resistance according to claim 1, wherein the thermal spraying material is a cermet-based powder made of a carbide and an alloy containing an element constituting the carbide. (4) The method for treating metal materials for wear resistance according to claim 1, wherein the thermal spray material is an alloy powder containing a carbide-forming element. (5) Wear-resistant treatment of the metal material according to claim 1, in which a fine powder of the same metal as the carbide-forming element contained in the sprayed layer is added to the liquid applied to or impregnated into the sprayed layer. Method. (6) The method for anti-wear treatment of metal materials according to any one of claims 3 to 5, wherein the carbide-forming element is selected from the group consisting of chromium, tungsten, and boron.