JP6534721B2 - Method of manufacturing a cast product having an alumina barrier layer - Google Patents

Description

  The present invention relates to a cast product having an alumina barrier layer, and more particularly to a cast product having an alumina barrier layer of stable structure.

  Heat-resistant cast steel products such as reaction tubes and decomposition tubes for ethylene production, hearth rolls of carburizing heat treatment furnaces, radiant tubes, metal dusting materials, etc. are exposed to high temperature atmosphere, so austenitic heat resistant alloys with excellent high temperature strength It is used.

  In this kind of austenitic heat-resistant alloy, a metal oxide layer is formed on the surface during use in a high temperature atmosphere, and this oxide layer serves as a barrier to protect the base material in a high temperature atmosphere.

On the other hand, if Cr oxides (mainly composed of Cr ₂ O ₃ ) are formed as these metal oxides, the denseness is low, and therefore the function of preventing intrusion of oxygen and carbon is not sufficient, and Oxidation occurs, causing the oxide film to enlarge. In addition, these Cr oxides are easily peeled off in repeated cycles of heating and cooling, and even if they do not come off, the function of preventing the infiltration of oxygen and carbon from the external atmosphere is not sufficient, so they pass through the film. There is a disadvantage that internal oxidation and carburization occur in the base material.

On the other hand, an oxide layer mainly composed of alumina (Al ₂ O ₃ ) which has high densification and is less likely to transmit oxygen and carbon by increasing the content of Al than a general austenitic heat-resistant alloy It is proposed to form on the surface of the material (for example, refer to Patent Document 1 and Patent Document 2).

However, since Al is a ferrite forming element, when the content is increased, the ductility of the material is deteriorated and the high temperature strength is reduced. This tendency to decrease the ductility is observed, in particular, when the content of Al exceeds 5%.
Therefore, the austenitic heat resistant alloys of the patent documents described above, even can be expected to improve the barrier function of the Al ₂ O _3, there is a disadvantage that lead to decrease in ductility of the matrix.

Therefore, in order to provide a cast product which can ensure the high temperature stability of Al ₂ O ₃ and can exhibit an excellent barrier function under a high temperature atmosphere without reducing the ductility of the material. In Patent Document 3, after the inner surface is processed so that the surface roughness (Ra) of the cast body is 0.05 to 2.5 μm, the heat treatment is performed in an oxidizing atmosphere to make the inner surface of the cast body Al. A cast product is proposed in which an alumina barrier layer containing ₂ O ₃ is formed, and Cr-based particles having a higher Cr concentration than the matrix are dispersed at the interface between the alumina barrier layer and the cast body (for example, Patent Document 3) reference).

  The cast product of Patent Document 3 can maintain excellent oxidation resistance, carburization resistance, nitriding resistance, corrosion resistance, etc. over a long period of time in use under a high temperature atmosphere by the presence of a stable alumina barrier layer. it can.

Japanese Patent Application Laid-Open No. 52-78612 Japanese Patent Application Laid-Open No. 57-39159 International Publication No. WO 2010/113830

  An object of the present invention is to provide a cast product which can further enhance the stability of the alumina barrier layer and can exhibit further excellent carburization resistance when used under a high temperature atmosphere.

The cast product according to the present invention is
A cast product having an alumina barrier layer comprising aluminum oxide on a base surface, comprising:
The aluminum oxide is (Al _(1-x) M _(x) ) ₂ O ₃ , where M: at least one of Cr, Ni, Si and Fe, and 0 <x <0.5.

In addition, the cast product according to the present invention is
A cast product having an alumina barrier layer comprising aluminum oxide on a base surface, comprising:
In the aluminum oxide, at least one of Cr, Ni, Si, and Fe is in solid solution, and at least one of Cr, Ni, Si, and Fe in solid solution with Al is Al / (Cr + Ni + Si + Fe) in atomic% ratio. ) ≧ 2.0.

  According to the cast product of the present invention, the alumina barrier layer formed on the base surface has a stable structure of the aluminum oxide phase by solid solution of at least one of Cr, Ni, Si and Fe. Can. This aluminum oxide can suppress the bond between the matrix and oxygen, and can suppress the formation of an oxide mainly composed of Cr, Ni, Si, Fe or the like on the matrix surface.

  Thereby, the cast product of the present invention can exhibit further excellent carburization resistance when used under high temperature atmosphere.

  Therefore, when the cast product of the present invention is employed, for example, in a reaction tube for producing ethylene, the occurrence of coking can be suppressed, and the decrease in yield due to the decrease in heat exchange coefficient and thermal conductivity due to the occurrence of coking is prevented. It is possible to extend the continuous operation time. Further, since coking hardly occurs, the number and time of the coking removal work can be shortened, and the operation efficiency can be improved.

FIG. 1 is a cross-sectional view of a cast product before heat treatment. FIG. 2: is sectional drawing which shows typically the state in which Al thinning layer is formed by low-temperature heat processing. FIG. 3 is a cross-sectional view schematically showing a state in which an Al-rich layer is formed between the Al thinning layer and the base by high-temperature heat treatment. FIG. 4 shows a coated TEM photograph of Example 2 and a graph of EDX analysis results. FIG. 5 shows a coated TEM photograph of Example 7 and a graph of EDX analysis results.

Hereinafter, embodiments of the present invention will be described in detail.
The cast product of the present invention has an alumina barrier layer containing aluminum oxide on the base surface.

The aluminum oxide of the alumina barrier layer is (Al _(1-x) M _(x) ) ₂ O ₃ , where M: at least one of Cr, Ni, Si and Fe, and 0 <x <0.5 Adjusted to

  Further, in the aluminum oxide of the alumina barrier layer, at least one of Cr, Ni, Si, and Fe is in solid solution, and at least one of Cr, Ni, Si, and Fe in solid solution with Al has an atomic percentage ratio Is adjusted to Al / (Cr + Ni + Si + Fe) ≧ 2.0.

<Description of the reasons for limiting ingredients>
The cast product of the present invention can obtain the effects of the present invention if it is a heat-resistant alloy containing 15% or more of Cr and 18% or more of Ni and 1 to 5% of Al in mass%. Ru. In the following description, “%” is all by mass unless otherwise indicated.

C: 0.05% to 0.7%
C has the effect of improving the castability and enhancing the high temperature creep rupture strength. For this reason, at least 0.05% is contained. However, if the content is too large, the primary carbide of Cr ₇ C ₃ is likely to be formed widely, and the movement of Al forming the alumina barrier layer is suppressed, so the supply shortage of Al to the surface portion of the cast body As a result, local disruption of the alumina barrier layer occurs and the continuity of the alumina barrier layer is lost. In addition, excessive precipitation of secondary carbides leads to a decrease in ductility and toughness. Therefore, the upper limit is 0.7%. The C content is more preferably 0.3% to 0.5%.

Si: more than 0% and 2.5% or less Si is contained as a deoxidizer for a molten metal alloy and to enhance the fluidity of the molten metal alloy, but if the content is too large, the high temperature creep rupture strength decreases. The upper limit is 2.5% because it causes The content of Si is more preferably 2.0% or less.

Mn: more than 0% and 3.0% or less Mn is contained as a deoxidizer for a molten alloy and to fix S in the molten metal, but if the content is too large, the high temperature creep rupture strength decreases. The upper limit is 3.0% because it will The content of Mn is more preferably 1.6% or less.

Cr: 15.0% to 50.0%
Cr is contained in an amount of 15.0% or more for the purpose of contributing to the improvement of the high temperature strength and the repeated oxidation resistance. However, if the content is too large, the high temperature creep rupture strength is reduced, so the upper limit is made 50.0%. The content of Cr is more preferably 23.0 to 35.0%.

Ni: 18.0% to 70.0%
Ni is an element necessary to secure the repeated oxidation resistance and the stability of the metal structure. In addition, when the content of Ni is small, the content of Fe becomes relatively large, and as a result, Cr-Fe-Mn oxide is easily generated on the surface of the cast body, so the formation of the alumina barrier layer is inhibited. . For this reason, at least 18.0% or more should be contained. If the content exceeds 70.0%, the effect corresponding to the increase can not be obtained, so the upper limit is 70.0%. The content of Ni is more preferably 28.0% to 45.0%.

Al: 1.0% to 5.0%
Al is an element effective for improving the carburization resistance and the coking resistance. In the present invention, it is an essential element to form an alumina barrier layer on the surface of a cast body. For this reason, it is contained at least 1.0% or more. However, if the content exceeds 5%, the ductility deteriorates, so in the present invention, the upper limit is specified as 5.0%. The Al content is more preferably 2.5% to 3.8%.

Rare earth elements: 0.005% to 0.4%
The rare earth elements mean 17 kinds of elements in which Y and Sc are added to 15 kinds of lanthanum series from La to Lu in the periodic table, but the rare earth elements to be contained in the heat-resistant alloy of the present invention are Ce, It is preferable that at least one or more of the group consisting of La and Nd be included. The rare earth elements contribute to promoting the formation and stabilization of the alumina barrier layer.
When the formation of the alumina barrier layer is carried out by heat treatment in a high temperature oxidizing atmosphere, the inclusion of 0.005% or more of the rare earth element effectively contributes to the formation of the alumina barrier layer.
On the other hand, if the content is too large, the ductility and toughness deteriorate, so the upper limit is made 0.4%.

W: 0.5% to 10.0% and / or Mo: 0.1% to 5.0%
W and Mo dissolve in the matrix and strengthen the austenite phase of the matrix to improve the creep rupture strength. In order to exert this effect, at least one of W and Mo is contained, and in the case of W, 0.5% or more, and in the case of Mo, 0.1% or more.
However, if the content of W and Mo is too large, the ductility decreases and the carburization resistance deteriorates. Further, as in the case where there is a large amount of C, the primary carbide of (Cr, W, Mo) ₇ C ₃ is likely to be formed widely, and the movement of Al forming the alumina barrier layer is suppressed. Undersupply of Al to the part occurs, local breakage of the alumina barrier layer occurs, and the continuity of the alumina barrier layer tends to be lost. Further, since W and Mo have a large atomic radius, solid solution in the matrix has the effect of suppressing the movement of Al and Cr and preventing the formation of the alumina barrier layer.
For this reason, W is 10.0% or less and Mo is 5.0% or less. Even when both elements are contained, the total content is preferably 10.0% or less.

  Moreover, the following components can be further included.

Ti: at least one selected from the group consisting of 0.01% to 0.6%, Zr: 0.01% to 0.6%, and Nb: 0.1% to 1.8% Since it is an element that easily forms carbides and does not form a solid solution in the matrix as W or Mo, no particular action is observed in the formation of the alumina barrier layer, but it has the action of improving the creep rupture strength. If necessary, at least one of Ti, Zr and Nb can be contained. The content is 0.01% or more of Ti and Zr, and 0.1% or more of Nb.
However, if it is added excessively, the ductility is reduced. Nb further reduces the peel resistance of the alumina barrier layer. Therefore, the upper limit is 0.6% for Ti and Zr, and 1.8% for Nb.

B: more than 0% and 0.1% or less B has an effect of strengthening grain boundaries of the cast body, and can be contained as necessary. In addition, in order to cause the fall of creep rupture strength when content increases, even when it adds, it makes it 0.1% or less.

  The heat-resistant alloy constituting the cast body of the present invention contains the above-mentioned components, and the balance is Fe, but P, S and other impurities which are inevitably mixed at the time of melting of the alloy are generally tolerated in this kind of alloy material It may be within the range of

<Casting products>
The cast product of the present invention melts the molten metal of the above-mentioned composition, and is cast to the above-mentioned composition by centrifugal casting, stationary casting, etc.

The resulting cast product can be shaped according to the intended application.
For example, as a cast product, a tube, in particular a reaction tube used in a high temperature environment can be exemplified.

  The cast products of the invention are particularly preferably produced by centrifugal casting. By applying centrifugal casting, it is possible to obtain an alloy structure in which a fine metal structure grows with orientation in the radial direction by the progress of cooling by the mold, and Al is easy to move.

  Then, the cast product is subjected to a heat treatment described later. By this heat treatment, an alumina barrier layer having a stable phase structure is formed.

<Heat treatment>
The cast product of the present invention is heat-treated in an oxidizing atmosphere. The heat treatment can be divided into low temperature heat treatment and high temperature heat treatment. The low-temperature heat treatment and the high-temperature heat treatment can be performed in separate steps, or the high-temperature heat treatment may be performed after the low-temperature heat treatment.

<Low temperature heat treatment>
The low temperature heat treatment is a treatment of forming a layer of aluminum oxide on the surface of the base in an oxidizing atmosphere. Low temperature can illustrate below 1050 ° C. Desirably, it is 600 ° C-900 ° C. The low temperature heat treatment is preferably performed for 5 hours to 15 hours.

  By performing low temperature heat treatment, as shown in FIG. 1, base 10 is in contact with oxygen to oxidize Al, Cr, Ni, Si and Fe diffused from base 10 to the base surface, as shown in FIG. The oxide layer 22 is formed on the Since this heat treatment is performed at a low temperature, Al forms an oxide in preference to Cr, Ni, Si, and Fe. Therefore, the oxide layer is mainly composed of Al, and becomes a layer 22 of aluminum oxide in which at least one of Cr, Ni, Si, and Fe diffused from the base is dissolved as well.

In the aluminum oxide formed by the low-temperature heat treatment, at least one of Cr, Ni, Si, and Fe solid-solved in Al has an atomic percentage ratio of Al / (Cr + Ni + Si + Fe) ≧ 2.0. In addition, the composition thereof is (Al _(1-x) M _(x) ) ₂ O ₃ , where M: at least one of Cr, Ni, Si, and Fe, and 0 <x <0.5. Is desirable. Further, in the aluminum oxide, at least Cr is in solid solution, and Cr in solid solution with Al is more preferably Al / Cr ≧ 10 in atomic percent ratio, and Al / Cr ≧ 15. Is more preferred. Furthermore, it is more desirable that at least one of Ni, Si and Fe is solid-solved, and the total atomic percent of at least one of Ni, Si and Fe solid-soluted with Al is 10 atomic% or less.

  The aluminum oxide formed by the above-described low-temperature heat treatment has a metastable γ or θ alumina structure and a porous structure. Therefore, the strength is not sufficient.

<High temperature heat treatment>
The high-temperature heat treatment is a heat treatment carried out after the low-temperature heat treatment, and as described later, phase-transforms the aluminum oxide formed by the low-temperature heat treatment into an alpha alumina structure (corundum structure) An aluminum oxide layer having a high concentration of Al is formed between the object layer and the base.

  The high temperature heat treatment can be performed by heating the cast product on which the low temperature heat treatment is performed and on which the alumina barrier layer having the γ or θ alumina structure is formed at a high temperature under an oxidizing atmosphere. With high temperature, 1050 degreeC or more can be illustrated. It is desirable to carry out the high temperature heat treatment for 3 hours to 15 hours.

  By performing the high temperature heat treatment, the aluminum oxide having the γ or θ alumina structure formed first undergoes phase transformation to a stable α alumina structure (corundum structure). In the present invention, at least one of Cr, Ni, Si and Fe is solid-solved in the layer of aluminum oxide having the γ or θ alumina structure. Thereby, the phase transformation from the γ or θ alumina structure to the α alumina structure (corundum structure) can be accelerated compared to when the aluminum oxide layer has high purity of Al.

  Then, by further continuing the high-temperature heat treatment on the cast product having the layer of aluminum oxide phase-transformed to the α-alumina structure (corundum structure), as shown in FIG. Pass through.

  The oxygen which has passed through the layer of aluminum oxide 22 oxidizes Al diffused from the matrix to form a layer 24 of aluminum oxide having a high concentration of Al.

  Here, as shown in FIG. 3, the layer of aluminum oxide in which at least one of Cr, Ni, Si and Fe, which is formed by low-temperature heat treatment, forms a solid solution is referred to as “Al thinned layer”, Al thinned layer, The layer of aluminum oxide with a high concentration of Al formed between it and the base surface is called "Al-rich layer". That is, the Al-rich layer 24 is a layer in which Al / (Cr + Ni + Si + Fe) is larger than that of the Al thinning layer 22.

  The following reasons can be considered as the reason why the concentration of Al in the Al-rich layer formed between the base and the Al-thinned layer is higher in the alumina barrier layer than in the Al-thinned layer on the surface.

The formed Al thinned layer 22 allows the passage of a small amount of oxygen in an oxidizing atmosphere.
Then, from the base 10 side, as shown in FIG. 3, Al, Cr, Ni, Si and Fe are diffused to the base surface side. However, Al has a lower energy required for bonding with oxygen than Cr, Ni, Si, and Fe, so Al preferentially bonds with oxygen, and the layer of aluminum oxide with a high concentration (Al This is because the layer 24) is formed between the base 10 and the Al thinning layer 22.

  The Al-rich layer 24 has a stable α-alumina structure (corundum structure) because it is generated by heat treatment at a high temperature. Desirably, as for the aluminum oxide of the Al thinning layer 22 and the Al concentration layer 24, the crystal structure of 80 volume% or more is an alpha alumina structure (corundum structure).

  Since the alumina barrier layer 20 composed of the Al thinned layer 22 and the Al enriched layer 24 formed between the base 10 and the Al thinned layer 22 has a stable α-alumina structure (corundum structure), A high-density, cast product equipped with these acts as a barrier to prevent oxygen, carbon and nitrogen from intruding into the base material from the outside when used in a high temperature atmosphere, and has excellent carburization resistance over a long period of time Can be maintained.

  It is preferable that the Al-rich layer 24 be formed to a thickness larger than that of the Al thinning layer 22, and the Al-rich layer 24 be formed to be 1⁄5 or more of the thickness of the alumina barrier layer 20. Is preferred.

  More desirably, the thickness of the Al thinning layer 22 is 0.04 μm to 8.0 μm, and the thickness of the Al concentrated layer 24 is 0.01 μm to 2.0 μm.

  In the low temperature heat treatment and the high temperature heat treatment described above, it is desirable to heat the cast product while rotating it in order to suitably form the layer of aluminum oxide. Thus, the cast product can be uniformly heated and can be in good contact with oxygen. And as a result, surface roughness (Ra) of the alumina barrier layer 20 produced | generated can be made small.

<Surface treatment>
If desired, the cast product can be surface treated with an alumina barrier layer. For example, polishing can be exemplified as surface treatment. For example, when a cast product is used in a reaction tube, the raw material hydrocarbon and the cast product Fe, Ni, etc. touch each other, and coke (carbon) easily adheres to the inner surface of the tube by the catalytic action of Fe or Ni. By performing the treatment to reduce the surface roughness (Ra) of the alumina barrier layer, adhesion of coke can be suppressed.

  The surface roughness (Ra) of the alumina barrier layer is desirably 15 μm or less. More desirably, the surface roughness (Ra) is 0.05 μm to 10 μm.

  The molten metal was melted by air melting of a high frequency induction melting furnace, and a tube having an alloy chemical composition listed in Table 1 below was cast by mold centrifugal casting. The tube had an inner diameter of 80 mm, an outer diameter of 100 mm, and a length of 250 mm.

  About Example 1 thru | or Example 8 which are the inventions obtained, and Comparative example 1 thru | or Comparative example 6, two-step heat processing from which a heating temperature differs was performed under oxidizing atmosphere, respectively. The heat treatment was performed first at low temperature and then at high temperature. The low temperature heat treatment is 5 hours, and the high temperature heat treatment is 5 hours.

  In the test tubes of Examples 1 to 8 and Comparative Examples 1 to 6 subjected to the heat treatment, elements (Al, Cr, Fe, Ni, Si, O) contained in the alumina barrier layer formed on the surface The atomic percent of) was determined by EDX analysis (energy dispersive X-ray spectroscopy). The results are shown in Table 3.

  Referring to Examples 1 to 8 which are invention examples, all satisfy the condition of Al / (Cr + Ni + Si + Fe) ≧ 2.0 in atomic% ratio. Also, Al / Cr ≧ 10. On the other hand, in the comparative example, since the base of the comparative example 1 does not contain Al, aluminum oxide is not generated, and both Al / (Cr + Ni + Si + Fe) and Al / Cr are zero.

  In addition, in each of Comparative Examples 2 to 6, Al / (Cr + Ni + Si + Fe) <2.0 and Al / Cr <10.

  Furthermore, the atomic percent of Fe + Ni + Si is 10 atomic% or less in Examples 1 to 4, Example 6, Example 7 and Comparative Example 3, and the other Examples and Comparative Examples exceed 10 atomic%. ing.

  Moreover, the thickness of the Al concentration layer with respect to the thickness of the produced | generated alumina barrier layer was measured about obtained Example 1 thru | or Example 8 and Comparative Example 1 thru | or Comparative example 6. FIG. The results are shown in Table 3 above.

  Referring to Table 3, in each of the examples, the thickness of the Al-enriched layer with respect to the thickness of the alumina barrier layer is 0.3 or more, that is, 1/5 or more, but the comparative example is 0.15 at maximum. Know that In addition, since the comparative example 1 does not contain Al in a base, the alumina barrier layer is not formed.

  This is because the example of the invention example was implemented at a low temperature heat treatment temperature of less than 1050 ° C. and a high temperature heat treatment temperature of 1050 ° C. or more, so an Al thinned layer was formed on the surface of the matrix by low temperature heat treatment. Thereafter, it is shown that an Al-rich layer can be formed between the Al thinning layer and the base by high-temperature heat treatment.

On the other hand, in Comparative Examples 2 to 6 in which the alumina barrier layer was formed, it is considered that the Al-rich layer remained at a maximum of 0.15 for the following reasons.
The comparative example 2 is because Al contained in a cast is as low as 0.9%, and Al for forming a film on the cast surface is insufficient. In Comparative Example 3, since the low temperature heat treatment temperature is as high as 1200 ° C., an oxide mainly composed of Cr, Ni, Si, Fe, etc. is formed before an alumina barrier layer having a γ or θ alumina structure is formed. It is. Comparative Example 4 is because the alumina barrier layer having the γ or θ alumina structure was not formed because the low temperature heat treatment temperature was as low as 500 ° C. The reason is that the temperature of the high temperature heat treatment is as low as 1000 ° C. in Comparative Examples 5 and 6. As a result, after the Al thinning layer is formed in the low temperature heat treatment, less oxygen passes through the Al thinning layer in the high temperature heat treatment, and the temperature is low, so that the incorporated oxygen and Al are sufficiently bonded. Energy was not obtained.

Next, a coking test was performed on the obtained test tube.
The coking test was performed by placing the test tube in an electric furnace, supplying hydrocarbons (ethane) to the test tube, and heating at high temperature (955 ° C.) for a predetermined time (12 to 24 hours). After completion of the test, the carburizing degree of the inner surface of the test tube was compared, and the weight ratio of coke (carbon) attached to the inner surface of the test tube was measured. The results are shown in Table 4.

  Referring to Table 4, it can be seen that all of the inventive examples 1 to 8 have good carburization resistance. On the other hand, in each of the comparative examples, carburization was performed to the inside of the test tube.

  Examples 1 to 8 are superior in carburization resistance by suitably forming an alumina barrier layer having a stable α-alumina structure (corundum structure) consisting of an Al-rich layer and an Al-thinned layer on the surface of a matrix. It is because In particular, the first embodiment, the third embodiment, the fourth embodiment, and the sixth to eighth embodiments have carburization resistance which is extremely superior to those of the other embodiments. It is considered that this is because Example 2 and Example 5 formed less Al-concentrated layers as compared to the other examples.

  Moreover, the surface roughness (Ra) of these test tubes was measured. The results are shown together in Table 4. Referring to Table 4, it can be seen that there is a substantially proportional relationship between the weight ratio of the produced coke and the surface roughness (Ra). From this, the surface roughness (Ra) is preferably 15 μm or less, more preferably 10 μm or less.

  The surface roughness (Ra) can be adjusted by heat treatment while rotating the cast product to adjust the surface roughness, and the surface roughness (Ra) of Comparative Example 3 and Comparative Example 6 exceeds 15 μm. It is considered that the heat treatment for film formation was not appropriate, and the surface roughness became rough due to peeling and regeneration of the film.

  About the invention example 2 and the invention example 7, coating TEM observation of the alumina barrier layer was performed using the transmission type microscope (TEM). In addition, EDX analysis was performed on each of the Al thinned layer and the Al enriched layer. The result of the invention example 2 is shown in FIG. 4 and the result of the invention example 7 is shown in FIG.

  Referring to FIG. 4, it can be seen that although the Al thinned layer 22 formed on the surface side of the invention example 2 is mainly an oxide of Al, small amounts of Cr, Fe, and Ni are observed. On the other hand, in the Al-rich layer 24, Cr, Fe, Ni and the like other than Al are not observed. Therefore, it can be seen that the Al-rich layer 24 is formed of aluminum oxide of very high purity.

  Referring to FIG. 5, it can be seen that, in the example 7 of the invention, the Al thinned layer 22 formed on the surface is mainly an oxide of Al, but a small amount of Cr is observed. On the other hand, Al concentrated layer 24 is not observed except Al. Therefore, it can be seen that the Al-rich layer 24 is formed of aluminum oxide of very high purity.

10 Base 20 Alumina Barrier Layer 22 Al Thinned Layer 24 Al Concentrated Layer

Claims (4)

A method of manufacturing a cast product having an alumina barrier layer containing aluminum oxide on a base surface, comprising:
Forming processing of the aluminum oxide, in facilities Succoth the low-temperature heat treatment for 5 hours to 15 hours under oxidizing atmosphere at 600 ° C. to 900 ° C., after forming the first aluminum oxide layer on the surface, 1050 ° C. in facilities Succoth temperature heat treatment for 3 hours to 15 hours under more oxidizing atmosphere, it comprises a steps of forming a second aluminum oxide layer between the first aluminum oxide layer and the base A method of producing a cast product characterized by In the first aluminum oxide, at least Cr is in solid solution, and Cr in solid solution with Al is Al / Cr ≧ 10 in atomic percent ratio.
A method of manufacturing a cast product according to claim 1 . In the first aluminum oxide, at least one of Ni, Si and Fe is solid-solved,
The total atomic percent of at least one of Ni, Si and Fe in solid solution with Al is 10 atomic percent or less
The manufacturing method of the cast product of Claim 1 or Claim 2 . The base is, by mass%, at least Si: 0% to 2.5% or less, Cr: 15.0% to 50.0%, Ni: 18.0% to 70.0%, Al: 1 Containing .0% to 5.0%,
A method of manufacturing a cast product according to any one of claims 1 to 3 .