JPH07150368A - Cast iron parts having heat insulating covering layer - Google Patents

Abstract

PURPOSE:To provide cast iron parts having heat insulating covering layers which decrease the pores in sintered layers of metallic powder in particular and are improved in oxidation resistance as the covering layers to be formed on the surfaces of ferrous members. CONSTITUTION:The sintered layers 1 consisting of the ferrous alloy powder contg. 10 to 90wt.% Fe are formed on the surfaces of the cast iron embers 4 of the cast iron parts having the heat insulating covering layers. The pores 2 of the sintered layers 1 are internally impregnated with a glassy material 3 having a m.p. of 700 to 850 deg.C at >=50% of the entire part of the pores. Further, ceramic hollow bodies are dispersed in the sintered layers. The sintered layers have the heat insulating covering layers which form closed holes in the sintered layers by packing of the oxide of metallic powder formed by mixing metallic powders of at least >=1 kinds among Cr, Zr, Ti, Si, Mn, Nb and V and heating the mixture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating layer formed on the surface of an iron-based member, and particularly to cast iron having a heat-insulating coating layer with reduced porosity in the sintered layer of metal powder and improved oxidation resistance. Regarding parts.

[0002]

2. Description of the Related Art Iron-based members are surface-treated to provide heat insulation and oxidation resistance when they are repeatedly used at high temperatures. Of these, most of the coating treatments are mainly ceramics. However, the bonding strength between metal and this ceramic is not sufficient, and especially for members used for a long time in a high temperature environment such as automobile parts, the underlayer oxidation generated between the surface coating layer and the base material. This phenomenon causes a decrease in the bonding strength at the interface and eventually leads to peeling of the coating layer.

Generally, in the joining of a metal base material and a ceramic, since the joining strength is a problem due to the porosity of the ceramic, stress is applied at the time of melting by a mechanical method, and the sealing action is utilized to form the interface. It has been made to improve strength. Even in this method, it is difficult to obtain sufficient strength because the wettability of both is limited. Further, even if an attempt is made to improve the wettability by another chemical method, it is difficult to sufficiently increase the contribution to the bonding strength in the relationship between the base material and the gas accompanying the chemical reaction. (For example, Material Engineering Dictionary, p2463, vol. 4, 198
6)

Further, JP-A-61-163282 discloses a method of forming a ceramic coating by applying a slurry of ceramic and water glass as a binder and applying the slurry to a metal member. In addition, Japanese Patent Laid-Open No. 3-1
Japanese Patent No. 6969 discloses a method of forming a coating layer of iron oxide on the surface in advance, but this also has a problem that sufficient bonding strength cannot be obtained.

The present inventors have filed a patent application for Japanese Patent Application No. 4-28.
No. 1600 proposed a method of forming a sintered layer made of iron-based alloy powder and forming a ceramic coating layer on the surface thereof. As a result, sufficient bonding strength can be obtained,
Oxidation occurs on the surface of the base material due to the presence of pores. Further, depending on the operating environment, when a ceramic coating is formed on the sintered layer at a high temperature, there is a stress action due to the difference in the coefficient of thermal expansion between the sintered layer and the ceramic coating. The occurrence of stress may lead to peeling of the coating film, and it cannot be said that sufficient bonding strength is maintained. Furthermore, a coating layer that prevents oxidation at the interface between the iron-based member and the surface coating layer to improve the bonding strength thereof, and that exhibits sufficient heat insulation and oxidation resistance without necessarily forming a ceramic coating. Forming technology is desired.

[0006]

An object of the present invention is to provide a process for forming a powder layer of iron-based alloy powder containing Fe on the surface of the iron-based member, particularly a cast iron part, and heating and baking the powder layer. In the method of forming a ceramic coating layer constituted by the process of forming a bonding layer, the pores of the sintered layer, which is a porous body, are sealed in order to prevent a decrease in bonding strength with the ceramic due to oxidation on the surface of the member. And to provide a cast iron part provided with a heat-insulating coating layer that makes it possible to suppress the progress of oxidation of the base material surface without forming a blocking hole. Another object of the present invention is to provide a coating layer that exhibits sufficient heat insulation and oxidation resistance by preventing the above-mentioned oxidation and without necessarily forming a ceramic coating.

[0007]

Means for Solving the Problems The above-mentioned object is a cast iron part having a heat-insulating coating layer, which has 10 to 10
A sintered layer composed of an iron-based alloy powder containing 90% by weight of Fe is formed, and the melting point is 70 in the pores of the sintered layer.
Vitreous substance at 0-850 ℃ is 50% of the total pores
This is achieved by a cast iron part having a heat insulating coating layer characterized by being impregnated as described above. Moreover, it is a cast iron part provided with a heat insulation coating layer, and the surface of the cast iron member is from 10 to 90.
A cast iron having a heat-insulating coating layer characterized in that a sintered layer made of an iron-based alloy powder containing wt% Fe is formed, and a hollow ceramic body is dispersed in the sintered layer. It is also achieved by parts.

Further, a cast iron part having a heat insulating coating layer, wherein a sintered layer made of an iron-based alloy powder containing 10 to 90% by weight of Fe is formed on the surface of the cast iron member,
The sintered layer is formed by mixing at least one metal powder of Cr, Zr, Ti, Si, Mn, Nb, and V and filling the oxide of the metal powder generated by heating. It is also achieved by a cast iron part provided with a heat-insulating coating layer characterized by forming closed holes.

The reasons for limitation of the present invention will be described in detail below. Fe in the composition of the iron-based metal powder of the present invention is limited to 10 to 90% by weight, but if Fe is less than 10%, the sinterability and bonding strength will be low, and if it exceeds 90%, the oxidation resistance will not be satisfied. This is because.

Further, in the present invention, the melting point of the vitreous substance impregnated in the metal layer (the vitreous substance does not have a definite melting point, but is used synonymously with the "softening point" at which the vitreous substance begins to soften). When the temperature is higher than 850 ° C., minute cracks occur between the vitreous substance present in the pores and the metal powder, and a sufficient oxygen blocking effect cannot be obtained. Further, if the melting point is lower than 700 ° C., the viscosity of the vitreous substance is lowered and the vitreous substance is washed away from the pores, and the effect is not exhibited. When the melting point is within the range of the first invention of the present invention, the vitreous substance is melted in the pores with an appropriate viscosity, and the effect of filling the gaps between the particles can be obtained.

Further, according to the present invention, the impregnation amount is set to 50 of the pore volume.
This is because the content is limited to at least%, but if it is less than this, the effect of filling the spaces between the particles and filling the gaps cannot be sufficiently obtained.
Further, the vitreous material of the present invention contains silicic acid and alkali (N
A two-component glass composed of a ₂ O, Li ₂ O, K ₂ O) is preferable. Note that the melting point of ordinary glass is 1000 ° C. or higher, which is outside the scope of the present invention. This is because the melting point can be adjusted to 700 to 850 ° C. by containing an alkali, and the two-component glass at room temperature exhibits water solubility when dried and can be easily impregnated.
Further, when a metal alloy or the like having a melting point of 700 to 850 ° C. having a similar degree is used, it tends to react with the metal layer and change the melting point of the glass, but the glass has a poor reactivity with the metal and is stable. This is because it can be maintained.

In the second invention of the present invention, for the same reason as in the first invention, the composition of the iron-based alloy powder is 10 to 9% Fe.
It is limited to 0% by weight. On the other hand, the composition of the ceramic hollow body is not limited as long as it is a sphere having a melting point of 1200 ° C. or higher, which is a use temperature, and a hollow inside, and the composition is not limited. Industrially, for example, Al ₂ O ₃ , SiO ₂ and Al ₂
It is a ceramic composed of O ₃ and SiO ₂ . The average particle size (outer diameter) is larger than that of iron-based alloy powder and is 2m
m or less is preferable.

If the particle size is more than the iron-based alloy powder, the sinterability and the bonding strength are low, and if the particle size is 2 mm or more, the upper limit of the film thickness is 2 mm, and the film is exposed and cannot be formed. The mixing ratio of the ceramic hollow body is iron-based alloy powder / (iron-based alloy powder + ceramic hollow body) in a volume ratio of 20 to 70%.
Is an appropriate range. If it is less than 20%, the sinterability and bonding strength are low, and if it exceeds 70%, the heat insulating property is insufficient.
Further, as a method for obtaining a film, a cast iron member may be coated with a slurry composed of an iron-based alloy powder, a ceramic hollow body, and an organic solvent such as butanol, and fired. At this time, since the slurry solvent does not contribute to the sintering at all, either alcohols or water may be used.

However, butanol is preferable in consideration of workability. The sintering condition of the present invention is that the sintering temperature is 700 to 12
The temperature is 00 ° C., which is lower than 700 ° C., the sinterability and the bonding strength are low, and the temperature higher than 1200 ° C. causes thermal strain in the metal base material, so that the film cannot be formed. The sintering atmosphere condition is preferably an oxygen concentration of 5% or less, and when the oxygen concentration is 5% or more, the iron-based alloy powder is oxidized and the sinterability and the bonding strength are reduced. In addition, a film thickness of 0.3 to 2.0 mm is appropriate,
If it is less than 0.3 mm, the heat insulating property is low, and if it exceeds 2.0 mm, the sinterability and the bonding strength are low.

Also in the third invention of the present invention, Fe is limited to 10 to 90% by weight as the composition of the iron-based alloy powder.
This is because if it is less than 10% by weight, the sinterability and the bonding strength are lowered, and if it exceeds 90% by weight, the oxidation resistance is lowered. That is, the voids in the metal layer can be prevented by the effect of Cr, but the oxidation resistance of the metal powder itself is reduced, oxygen is moved through grain boundaries and the like in this powder, and as a result, the base material is oxidized. Further, it is appropriate that the average particle diameter is 50 μm or less. If the particle size exceeds 50 μm, the sinterability and the bonding strength will decrease.
Next, as a requirement for the fine metal powder, it is necessary to be preferentially oxidized over the iron-based alloy powder, and the oxide of the fine metal powder should be a dense body. It is a necessary requirement that the melting point be 1000 ° C or higher.

It is also necessary that the average particle size is smaller than the average particle size of the iron-based alloy powder, that is, less than 50 μm. If it is larger than the average particle size of the iron-based alloy powder, the sinterability and bondability of the iron-based alloy powder are impaired. In the case of Cr, the mixing ratio is the total volume of Cr powder / (the total volume of Cr powder +
The total volume of iron-based alloy powder) is required to be 20 to 50%. If it is less than 20%, the oxidation resistance of the coating is insufficient due to its low air barrier property, and if it exceeds 50%, it impairs the sinterability and bondability of the iron-based alloy powder.

[0017]

The present invention has a melting point of 700 to 850 ° C. in the metal layer.
The first feature is to impregnate the glass material. Generally, a cast iron member has a feature that the oxidation amount increases at a temperature of 700 ° C. or higher, and in particular, it is significantly oxidized from 800 ° C. Taking this temperature condition into consideration, by impregnating a glassy substance having a specific melting point in the pores of the sintered layer,
Under the condition that the amount of oxidation increases, the vitreous substance has an appropriate viscosity and fills the pore gaps, so that the oxidation can be prevented, and the existence of the pores also provides the heat insulating property.

The reason why this is limited to the vitreous substance is that it has good wettability with respect to the sintered layer, and if this wettability is poor, a gap is created and oxidation is insufficiently prevented. Further, a ceramic coating may be formed to improve heat insulation. Further, according to the present invention, it is possible to impart a heat insulating property by dispersing the ceramic hollow body in the sintered layer, the formation of the ceramic coating layer is not necessarily required, and the internal due to the difference in the coefficient of thermal expansion is increased. It is possible to prevent peeling of the coating layer without generating stress.

Furthermore, by mixing the powder made of the above-mentioned specific metal in the sintered layer, the metal powder is oxidized into an oxide by the use of the cast iron member or by an additional oxidation treatment, and during this oxidation reaction. Due to the volume change (expansion), the sintered layer is sealed, and the cast iron can be prevented from being oxidized.

[0020]

EXAMPLES The present invention will be described in detail below with reference to the accompanying drawings by way of example embodiments and comparative examples of the present invention.

Example 1 The first invention of the present invention was carried out on an exhaust manifold made of cast iron for automobiles (hereinafter abbreviated as Ex manifold). First, Ex
The inner surface of the manifold was roughened by shot blasting and FeNi
(Fe-50 wt% Ni) alloy powder (particle size 10 to 20μ
Distilled water is added to m) and stirred to form a slurry. The clay at this time is adjusted to 1000 to 4000 cps. The slurry was poured into a cast iron Ex manifold to obtain a film thickness of 10
Apply so that the thickness becomes 0 μm. After coating, this is dried at 200 ° C., and this is heated in vacuum or in an inert gas,
Hold at 900 ° C. for 5 hours.

Then, the metal layer is formed by furnace cooling. SiO ₂ of silicate glass as a glassy substance
Using Na ₂ O (water glass), distilled water is added to a commercially available water glass No. 3 solution (75% SiO ₂ -25% Na ₂ O) to dilute the concentration to 25% by weight. The treated Ex-manifold is dipped in this solution and placed in a vacuum to impregnate the metal layer with water glass. Then, it is dried at 300 ° C., the weight is measured, the degree of impregnation is examined with respect to the pore volume (preliminarily measured), and the glassy impregnation step is repeated to impregnate up to 50% or more of the total pore volume. It was In the case of Ex manifold, the impregnation can be performed up to 60% of the pore volume by repeating the impregnation step 5 times. Then ZrO ₂
Apply ceramic slurry using the above as an aggregate, 500 ℃
Was fired to form a heat insulating coating. FIG. 1 and FIG. 2 are schematic views after the film formation of this embodiment. In FIG. 1, a metal layer 1 obtained by sintering an iron-based alloy powder is formed on the surface of a cast iron member 4, and the vitreous substance 3 is impregnated in the pores 2 of the metal layer 1. Figure 2
FIG. 1 shows a structure in which a heat insulating coating having a ceramic 5 coated thereon is further formed.

The Ex manifold manufactured in the above process and the conventional product without the impregnation process were held in the atmosphere at 850 ° C., and the oxidation state between the metal layer and the base material was cut and observed. The result is shown in Fig. 7.
Shown in. As shown in FIG. 7, it can be seen that the base material of the conventional product is remarkably oxidized, whereas the product of the present invention prevents the base material from being oxidized. Table 1 collectively shows the oxidation resistance performance when the glass component, the impregnation amount and the glass melting point were changed. Here, as an index of oxidation resistance, the oxide scale thickness of the base material interface portion after holding at 850 ° C. in the atmosphere for 200 hours is shown. It can be seen from Table 1 that the oxidation resistance is excellent within the range of the present invention.

[0024]

[Table 1]

Embodiment 2 In this embodiment, the second invention is applied to an Ex manifold. The manufacturing process is 50 wt.% Fe-50 wt.% N
i powder (average particle size 10 μm) and alumina hollow body (average particle size 50 μm) metal powder / (metal powder + alumina hollow body)
Was mixed so as to be 50 vol.%. To 1 part of this mixed powder, 1 part of butanol was added and sufficiently stirred to obtain a raw material slurry. This slurry was applied to the inner surface of the Ex manifold, the excess slurry was removed, and then dried in a dryer at 80 ° C. for 2 hours.

After that, the film was formed by holding it at 900 ° C. for 5 hours in an argon atmosphere. A schematic diagram of the cross-sectional structure after film formation is shown in FIG. Further, for comparison, a schematic diagram after the conventional ceramic coating is formed is shown in FIG. In FIG. 4, the ceramic powder 8 and the ceramic hollow body 6 did not contribute to the bonding at all, and the coating and the base metal were bonded with the inorganic binder 9. Therefore, the bonding strength is low, and the coating may peel off when a cooling / heating cycle occurs. As shown in FIG. 3, in this embodiment, the iron-based metal powder is sintered to form the sintered metal layer 7, and the ceramic hollow body 6 is solidified, and at the same time, the cast iron member 4 is formed.
Since both are diffusion bonded, higher bonding strength can be obtained as compared with the conventional ceramic coating.

Further, when an EPMA line analysis was performed on the bonded interface, diffusion of Fe and Ni elements was recognized. In the same process, the film formation was performed by changing the metal powder composition and particle diameter, the alumina hollow sphere particle diameter, the mixing ratio of both materials, and the sintering temperature as shown in Table 2. As a comparative example, Al ₂ O ₃ powder (particle size 2
0 μm) 10 parts, Al ₂ O ₃ hollow spheres (particle size 50 μm) 1
0 part and 20 parts of a water glass binder (water glass No. 2) were mixed, and after coating, a film having a thickness of 0.5 mm was formed at 500 ° C.

The performance of the exhaust pipe produced as described above was investigated by the following method. The results are summarized in Tables 2-4. The heat insulation was evaluated by incorporating the Ex manifold into a 2000 cc 4-cylinder gasoline engine and operating it at a rotational speed of 4000 rpm for 30 minutes. The temperature difference between the upper part of the coating and the lower part of the coating at that time was measured with a thermocouple, and this was used as the adiabatic temperature. Therefore,
It can be said that the higher this temperature is, the more excellent the heat insulating property is. Regarding the evaluation of adhesion (bondability), a test piece was cut out from the exhaust pipe and the bondability was evaluated by a shear adhesion measurement method. From Tables 2 to 4, it can be seen that the adhesion strength and the heat insulating property are excellent within the range of the present invention.

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

Embodiment 3 An embodiment in which the third invention of the present invention is applied to an Ex manifold will be described below. 50 wt.% Fe-50 wt.% Ni powder (average particle size 10 μm) and Cr powder with 95% purity (average particle size 2
μm) is the total volume of Cr powder / (total volume of Cr powder +
The iron-based alloy powder was mixed so that the total volume of the powder was 30%. (33 wt.% In weight ratio) 10 parts of butanol was mixed with 100 parts of this mixed powder and sufficiently stirred to obtain a raw material slurry. This slurry was applied to the inner surface of the Ex manifold, the excess slurry was removed, and then dried in a dryer at 80 ° C. for 2 hours. Then, it was baked by holding at 900 ° C. for 5 hours in an argon atmosphere. A schematic diagram of the cross-sectional structure after firing is shown in FIG. The iron-based alloy powders 10 are mutually sintered and firmly bonded to the cast iron member 4 of the base material by diffusion. In this embodiment, Cr powder is observed as the minute metal powder 11 in the voids (pores). The film thickness is 50
It was 0 μm. The Ex manifold is heated to 850 ° C. in the atmosphere.
Hold for 10 hours.

Thereafter, a test piece (50 × 50 × 5) was cut out and the cross-sectional structure was observed. A schematic diagram of the structure is shown in FIG. In this figure, the minute metal powder 11 existing in the sintered layer voids of the iron-based alloy powder 10 causes volume expansion to fill the sintered layer voids of the iron-based alloy powder 10. This blocks the passage of oxygen to the base material and prevents the base material from oxidizing. In this example, open pores (open pores) in the coating film
The Cr powder located at is oxidized and expands its volume to close the pores. On the other hand, the Cr powder located in the closed pores (close pores) remains as Cr without being oxidized. In this way, by blocking the open pores by the oxidation expansion of Cr, air (oxygen) is not supplied to the base material, and base material oxidation is prevented. The results are shown in Table 5 No.
39.

[0034]

[Table 5]

Example 4 50 wt.% Fe-50 wt.% Ni powder (average particle size 10 μm)
And Cr powder having a purity of 95% (average particle diameter 2 μm) were mixed so that the total volume of Cr powder / (total volume of Cr powder + total volume of iron-based alloy powder) was 30%. (33 wt.% In weight ratio) Al _{2 to the} total volume 50 of this mixed powder
The O ₃ hollow spheres (particle size 50 μm) were mixed so that the volume was 50. (Converted to 100 parts by weight of powder, A
l ₂ O ₃ hollow sphere 8 parts) 1 part to 100 parts of this mixture
0 part of butanol was mixed and sufficiently stirred to obtain a raw material slurry.

The slurry was applied to the inner surface of the Ex manifold,
After removing the excess slurry, it was dried in an oven at 80 ° C. for 2 hours. Then, it was baked by holding at 900 ° C. for 5 hours in an argon atmosphere. The Ex manifold was held at 850 ° C. for 10 hours in the air atmosphere. Then test piece (50x50x
5) was cut out and the cross-sectional structure was observed. as a result,
The Cr powder located in the open pores (open pores) in the coating film is oxidized and its volume expands to close the pores. At this time, the film thickness was 500 μm. 20 Ex Mani
Installed in a 00cc gasoline engine, 4000rp
It was operated for 30 minutes at a rotation speed of m. The temperature difference between the upper part of the coating and the lower part of the coating at that time was measured with a thermocouple, and this was used as the adiabatic temperature. For comparison, the Ex manifold (without hollow spheres) manufactured in Example 3 was also evaluated.

It was confirmed that both films had the same film thickness of 500 μm and were evaluated. As a result, the hollow sphere-free product (Example 3) had an adiabatic temperature of 5 ° C, whereas the hollow sphere-added product (Example 4) had an adiabatic temperature of 40 ° C. From this result, by adding hollow spheres,
It was confirmed that heat insulation can also be imparted. The results are shown in Table 5.
No. 40 of.

Example 5 50 wt.% Fe-50 wt.% Ni powder (average particle size 10 μm)
And Cr powder having a purity of 95% (average particle diameter 2 μm) were mixed so that the total volume of Cr powder / (total volume of Cr powder + total volume of iron-based alloy powder) was 30%. (Weight ratio: 33 wt.%) To 100 parts of this mixed powder, 20 parts of butanol was mixed and sufficiently stirred to obtain a raw material slurry.
This slurry was applied to the inner surface of the Ex manifold, the excess slurry was removed, and then dried in a dryer at 80 ° C. for 2 hours. Then, it was baked by holding at 900 ° C. for 5 hours in an argon atmosphere.

At that time, when the film thickness was measured after firing,
It was 100 μm. Ceramics is coated on the FeNi-Cr layer to provide heat insulation. Al ₂ O
_To 100 parts of ₃ powders (particle size 20 μm or less), 50 parts of water glass No. 1 (concentration 30 wt.%) Solution was added, and sufficiently stirred to obtain a raw material coating material. This paint (slurry) is poured onto the inner surface of the FeNi-coated Ex manifold manufactured in the above step,
After coating and removing the excess slurry, use a dryer at 80 ° C for 1
Allowed to dry for hours.

Then, it was baked by holding it at 300 ° C. for 5 hours in the air atmosphere. After firing, the film thickness was measured and found to be 500
μm (ceramic layer 400 μm, FeNiCr layer 100
μm). The Ex manifold is heated to 850 ° C. in the atmosphere.
Then, the FeNiCr layer was oxidized for 5 hours.
In this example, this oxidation treatment was performed last, but this has the effect of allowing the slurry to soak into the FeNiCr layer during coating of the ceramic slurry and improving the adhesion strength. If the oxidation treatment is performed before applying the ceramic slurry, Fe
This is because the NiCr layer may seal the pores and hinder this penetration.

Further, in this embodiment, an alkaline water glass solution was used as the ceramic slurry solvent, but in the case of an acidic solvent such as an alumina phosphate solution, this solvent penetrates through the pores of the FeNiCr layer, and the iron group May corrode the base material. In such a case, solvent corrosion can also be prevented by coating the ceramic layer after the oxidation treatment. The Ex manifold was installed in a 2000 cc gasoline engine and operated at a rotation speed of 4000 rpm for 30 minutes.

The temperature difference between the upper part of the coating and the lower part of the coating at that time was measured with a thermocouple to evaluate the heat insulating property. As a result, the adiabatic temperature was 40 ° C., and it was found that the adiabatic temperature was equivalent to that of the hollow sphere-added product (Example 4). This result is shown in Table 5.
No. 41 shows.

Example 6 Composition of iron-based alloy powder, particle size and composition of fine metal powder,
Ex Manifolds were prepared in the same steps as in Example 3 while changing the particle size, and the oxidation resistance and the bonding strength were evaluated. These are shown collectively in Nos. 44 and after of Tables 6 to 7. In this table, the oxidation resistance evaluation method is that a test piece (50x50x5) is cut out from the Ex mani
And the state of oxidation of the base material was examined by cutting observation.

The holding time is 200 hours at the maximum, and 0 to 5
The investigation was conducted every 10 hours until 0 hour, and every 50 hours from 50 to 200 hours. The time when the vicinity of the base material interface is oxidized by 10 μm or more is used as an index of oxidation resistance, and it is considered that the longer this time is, the better the oxidation resistance is. The measuring method for the bonding strength is from the above-mentioned Ex manifold to a test piece (50x50x
5) was cut out and the joint strength was measured by shearing.

[0045]

[Table 6]

[0046]

[Table 7]

[0047]

INDUSTRIAL APPLICABILITY The present invention forms a sintered layer of an iron-based alloy having excellent oxidation resistance as a coating layer by impregnating a glassy substance on the surface of an iron-based member, and has a large coefficient of thermal expansion and Since the elastic modulus is small, the thermal stress generated during use at high temperature can be small. Further, it is possible to form a ceramic coating having excellent bonding properties on the outermost surface, and it is possible to significantly extend the coating life in a use environment of a cooling / heating cycle.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a cross-sectional structure of a coating layer obtained by impregnating a sintered metal layer with a glassy substance according to the present invention.

FIG. 2 is a schematic diagram of a cross-sectional structure in which the surface of a metal sintered layer according to the present invention is further coated with a ceramic layer.

FIG. 3 is a schematic view of a cross-sectional structure of a coating layer containing ceramic hollow spheres in a metal sintered layer according to the present invention.

FIG. 4 is a schematic diagram of a cross-sectional structure of a conventional ceramic coating layer.

FIG. 5 is a schematic view of a cross-sectional structure of a coating layer in which a metal powder and a fine metal powder are mixed in a metal sintered layer according to the present invention.

FIG. 6 is a schematic diagram of a cross-sectional structure of a coating layer in which oxidation has progressed by using a coating layer in which a metal powder and a minute metal powder are mixed in a metal sintered layer according to the present invention.

FIG. 7 is a diagram showing a comparison between the present invention and conventional oxidation resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sintered metal layer 2 ... Porosity 3 ... Vitreous substance 4 ... Cast iron base material 5 ... Ceramic layer 6 ... Ceramic hollow sphere 7 ... Sintered metal layer 8 ... Ceramic powder 9 ... Inorganic binder 10 ... Iron-based metal powder 11 ... fine metal powder 12 ... metal oxide 13 ... closed pores

Claims (3)

[Claims] 1. A cast iron part having a heat insulating coating layer, comprising a cast iron member having a surface on which a sintered layer made of an iron-based alloy powder containing 10 to 90% by weight of Fe is formed. A cast iron component provided with a heat-insulating coating layer characterized in that the vitreous substance having a melting point of 700 to 850 ° C. is impregnated in the pores of the layer by 50% or more with respect to the entire pores. 2. A cast iron part having a heat insulating coating layer, wherein a sintered layer made of an iron-based alloy powder containing 10 to 90% by weight of Fe is formed on the surface of the cast iron member, A cast iron part provided with a heat insulating coating layer, characterized in that a ceramic hollow body is dispersed in the tie layer. 3. A cast iron part provided with a heat insulation coating layer, wherein a sintered layer made of an iron-based alloy powder containing 10 to 90% by weight of Fe is formed on the surface of the cast iron member, and the sintered product The binder layer is a mixture of at least one metal powder of Cr, Zr, Ti, Si, Mn, Nb, and V, and is filled with an oxide of the metal powder generated by heating, thereby forming closed pores in the sintered layer. A cast iron part provided with a heat-insulating coating layer.