JP2013198917A - Cast product having alumina barrier layer, and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cast product in which an alumina barrier layer is formed even in a welded spot, and a method for manufacturing the same.SOLUTION: A manufacturing method of a cast product used in a high-temperature atmosphere, obtained by welding a first casting body and a second casting body of heat resistant alloy containing, by mass, 15-18% Cr and 2-4% Al, includes steps of: joining the first casting body and the second casting body by welding; applying a surface treatment to the welded spot joined; and applying a heat treatment to the welded spot surface-treated.

Description

  The present invention relates to a cast product having an alumina barrier layer and a method for producing the same, and more specifically to a cast product having an alumina barrier layer formed by joining cast bodies by welding and a method for producing the same. is there.

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

In this kind of austenitic thermal 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 oxide (mainly composed of Cr ₂ C ₃ ) is formed as these metal oxides, the denseness is low, so that the function of preventing intrusion of oxygen and carbon is not sufficient, and the inside of the metal oxide in a high temperature atmosphere Oxidation occurs and the oxide film becomes enlarged. In addition, these Cr oxides are easy to peel off in repeated heating and cooling cycles, and even when they do not come off, they do not have sufficient functions to prevent oxygen and carbon from entering from the outside atmosphere, so they pass through the film. This has the disadvantage of causing internal oxidation and carburization of the base metal.

On the other hand, by increasing the Al content over a general austenitic heat-resistant alloy, an oxide layer mainly composed of alumina (Al ₂ O ₃ ), which has high density and hardly permeates oxygen and carbon, is used as a base. It has been proposed to form on the surface of a material (for example, see Patent Document 1 and Patent Document 2).

However, since Al is a ferrite-forming element, if the content increases, the ductility of the material deteriorates and the high-temperature strength decreases. This tendency of decreasing ductility is observed especially when the Al content exceeds 4%.
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, high temperature stability of Al ₂ O ₃ can be ensured without increasing the Al content to more than 4%, and an excellent barrier function is exhibited in a high temperature atmosphere without reducing the ductility of the material. In order to provide a cast product that can be processed, in Patent Document 3, after the inner surface is processed so that the surface roughness (Ra) of the cast body becomes 0.05 to 2.5 μm, heat treatment is performed in an oxidizing atmosphere. The cast product in which an alumina barrier layer containing Al ₂ O ₃ is formed on the inner surface of the cast body, and Cr-based particles having a higher Cr concentration than the base metal base are dispersed at the interface between the alumina barrier layer and the cast body. (See, for example, Patent Document 3).

  The casting product of Patent Document 3 can maintain excellent oxidation resistance, carburization resistance, nitridation resistance, corrosion resistance, etc. over a long period of time when used in a high temperature atmosphere due to the presence of a stable alumina barrier layer. it can.

JP-A-51-78612 JP-A-57-39159 International Publication No. WO2010 / 113830

  However, when a cast product in which an alumina barrier layer is formed is produced and the obtained cast products are joined together by welding, residual stress and distortion are generated in a so-called heat-affected zone that is easily affected by heat during welding. As a result, the previously formed alumina barrier layer may be partially peeled off.

  It is also conceivable to form an alumina barrier layer by performing heat treatment after welding the surface-treated cast products, but in this case, a metal oxide mainly composed of Cr oxide is formed especially in the welded portion. As a result, an alumina barrier layer having sufficient carburization resistance cannot be formed.

  In the prior art, compared to a cast body with an alumina barrier layer formed, a welded part without an alumina barrier layer allows oxygen, carbon, nitrogen, etc. to enter from the outside atmosphere and oxidizes, carbonizes, nitrides, etc. for a long time. Could not be prevented over.

  An object of the present invention is to provide a cast product in which an alumina barrier layer is formed on the entire surface of a cast body including a welded portion and a method for producing the same in order to solve the above problems.

The method for producing a cast product according to the present invention includes:
A cast product to be used in a high temperature atmosphere, wherein the first cast body and the second cast body of a heat-resistant alloy containing 15% or more of Cr and 18% or more of Ni and 2 to 4% of Al are welded by mass%. A method for producing a cast product obtained by:
Joining the first cast body and the second cast body by welding;
Applying a surface treatment to the welded joint;
Applying a heat treatment to the surface-treated weld,
Is included.

Further, the casting product having the alumina barrier layer of the present invention,
It is a cast product formed by welding a first cast body and a second cast body of a heat-resistant alloy which is used in a high temperature atmosphere and contains Cr 15% or more Ni 18% or more and Al 2 to 4% by mass%. And
The welds of the first cast body and the second cast body are covered with an alumina barrier layer containing Al ₂ O ₃ .

According to the method for producing a cast product of the present invention, the surface roughness of the welded portion is adjusted by performing a surface treatment after joining the first cast body and the second cast body by welding. At this time, the surface roughness of the surfaces of the first cast body and the second cast body as well as the welded portion including the heat affected zone and the molten metal portion generated by welding may be adjusted.
Thus, the alumina barrier layer containing Al ₂ O ₃ can be formed on the welded portion including the heat affected zone and the molten metal portion by performing the heat treatment after adjusting the surface roughness of the welded portion. At this time, the first cast body, the second cast body and the welded portion subjected to the surface treatment can be heat-treated at the same time.
Accordingly, in the obtained cast product, an alumina barrier layer containing Al ₂ O ₃ is formed not only on the first cast body and the second cast body but also on the entire continuous surface over the welded portion. In use in an atmosphere, it is possible to effectively prevent oxygen, carbon, nitrogen and the like from entering not only the cast body surface but also the welded portion.

  In addition, since the Al content of the heat-resistant alloy of the cast body does not exceed 4%, a decrease in ductility is suppressed and an excellent high-temperature strength is provided.

As described above, the cast product of the present invention has an alumina barrier layer containing stable Al ₂ O ₃ not only on the surface of the cast body but also on the welded portion. Oxidation resistance, carburization resistance, nitridation resistance, corrosion resistance, etc. can be maintained over a long period of time.

1 shows a test tube No. 1 of the invention example. 4 is a cross-sectional photograph taken by cutting 4 in the axial direction. FIG. 2 shows a test tube No. 1 as a comparative example. 13 is a cross-sectional photograph taken by cutting 13 in the axial direction. FIG. 3 shows the test tube No. of the invention example. 4 is a cross-sectional photograph of the specimen obtained from 4 perpendicular to the weld. 4 shows the test tube No. of the comparative example. 13 is a cross-sectional photograph of the specimen obtained from No. 13 perpendicular to the weld. FIG. 5 shows a test tube No. of the invention example. 4 is a photograph by cross-sectional SEM analysis of No. 4; 6 shows a test tube No. 1 as a comparative example. 13 is a photograph by 13 cross-sectional SEM analysis.

Hereinafter, embodiments of the present invention will be described in detail.
The present invention welds a first cast body and a second cast body of a heat-resistant alloy containing Cr 15% or more, Ni 18% or more, and containing Al 2 to 4%, and joined to form a first cast body and a second cast body. By subjecting the welded part to surface treatment and then subjecting the welded part to heat treatment, a cast product in which the welded part is formed of a so-called “alumina barrier layer” containing Al ₂ O ₃ is obtained. In the present specification, “%” is all mass% unless otherwise indicated.

<Description of reasons for limiting ingredients>

Cr: 15% or more Cr is contained in an amount of 15% or more for the purpose of contributing to improvement in high temperature strength and repeated oxidation resistance. However, if the content is too high, the high temperature creep rupture strength is lowered, so the upper limit is made 50%. The Cr content is more preferably 23 to 35%.

Ni: 18% or more Ni is an element necessary for ensuring repeated oxidation resistance and stability of the metal structure. In addition, when the Ni content is small, the Fe content is relatively increased, and as a result, Cr-Fe-Mn oxide is easily generated on the surface of the cast body, so that the formation of the alumina barrier layer is hindered. . For this reason, it shall contain at least 18% or more. Since even if it contains exceeding 70%, the effect corresponding to the increase cannot be obtained, the upper limit is made 70%. The Ni content is more preferably 28 to 45%.

Al: 2-4%
Al is an element effective for improving carburization resistance and coking resistance. Moreover, in this invention, it is an indispensable element in order to produce an alumina barrier layer on the surface of a casting. For this reason, it contains at least 2% or more. However, if the content exceeds 4%, the ductility deteriorates as described above, so the upper limit is defined as 4% in the present invention. The Al content is more preferably 2.5 to 3.8%.

  In addition, it is preferable to contain the following components.

C: 0.05-0.7%
C has the effect of improving castability and increasing 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 widely formed, and the movement of Al forming the alumina barrier layer is suppressed, so there is insufficient supply of Al to the surface portion of the cast body. As a result, local breakage of the alumina barrier layer occurs, and the continuity of the alumina barrier layer is impaired. Moreover, since secondary carbide precipitates excessively, it causes a reduction in ductility and toughness. For this reason, the upper limit is set to 0.7%. The C content is more preferably 0.3 to 0.5%.

Si: more than 0% and 2.5% or less Si is included as a deoxidizer for molten alloy and to increase the fluidity of the molten alloy. However, if the content is too high, the high temperature creep rupture strength is reduced. Therefore, the upper limit is 2.5%. The Si content is more preferably 2.0% or less.

Mn: more than 0% and 3.0% or less Mn is included as a deoxidizer for molten alloy and for fixing S in the molten metal, but if the content is too large, the high temperature creep rupture strength is reduced. Therefore, the upper limit is set to 3.0%. The Mn content is more preferably 1.6% or less.

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

W: 0.5 to 10% and / or Mo: 0.1 to 5%
W and Mo are dissolved in the matrix and strengthen the austenite phase of the matrix, thereby improving the creep rupture strength. In order to exert this effect, at least one of W and Mo is contained. In the case of W, 0.5% or more is contained, and in the case of Mo, 0.1% or more is contained.
However, if the content of W and Mo is too large, the ductility is lowered and the carburization resistance is deteriorated. In addition, as in the case where there is a large amount of C, primary carbides of (Cr, W, Mo) ₇ C ₃ are easily formed widely, and the movement of Al that forms the alumina barrier layer is suppressed. Insufficient supply of Al to the portion occurs, the local breakage of the alumina barrier layer occurs, and the continuity of the alumina barrier layer is easily impaired. In addition, since W and Mo have a large atomic radius, they dissolve in the matrix, thereby suppressing the movement of Al and Cr and preventing the formation of an alumina barrier layer.
For this reason, W is 10% or less, and Mo is 5% or less. Even when both elements are contained, the total content is preferably 10% or less.

At least one of Ti: 0.01 to 0.6%, Zr: 0.01 to 0.6% and Nb: 0.1 to 3.0% Ti, Zr and Nb are elements that easily form carbides. Since W and Mo do not dissolve in the base as much as possible, there is no particular effect on the formation of the alumina barrier layer, but it has the effect of improving the creep rupture strength. If necessary, at least one of Ti, Zr and Nb can be contained. The contents of Ti and Zr are 0.01% or more and Nb is 0.1% or more.
However, if added excessively, ductility is reduced. Nb further reduces the peel resistance of the alumina barrier layer. For this reason, the upper limits are 0.6% for Ti and Zr, and 3.0% for Nb.

B: 0.1% or less B has an effect of strengthening the grain boundary of the cast body, and can be contained as necessary. In addition, since the fall of creep rupture strength will be caused when content increases, even when adding, it shall be 0.1% or less.

  The heat-resistant alloy constituting the cast body of the present invention contains the above components and the balance is Fe, but P, S and other impurities inevitably mixed during the melting of the alloy are usually allowed in this type of alloy material. As long as it is within the range, it may be present.

<Cast body>
The first cast body and the second cast body constituting the cast product of the present invention are produced by melting the molten metal and casting the above composition by centrifugal casting, stationary casting, or the like.
The obtained 1st cast body and 2nd cast body can be made into the shape according to the intended use by performing welding joining.
In addition, before performing welding, groove processing etc. can also be given as needed.
In the present invention, the welding method and the composition of the welding rod used at the time of welding are not limited, and TIG welding, arc welding, and the like can be exemplified as methods capable of welding the cast body of the present invention.

Regardless of the presence or absence of prior surface treatment, a welded portion including a heat-affected zone and a molten metal portion is formed at the joined portion of the cast body joined by welding. Residual stress and strain are generated in the heat-affected zone, Cr moves along the strain line of the heat-affected zone, Cr oxide is given priority, and Al ₂ O ₃ is difficult to make.

Even if heat treatment is performed in a subsequent process, Al ₂ O ₃ constituting the alumina barrier layer cannot be sufficiently formed in such a weld.

  Therefore, in the present invention, after welding the casts, surface treatment is performed on the target portion that will be in contact with the high temperature atmosphere when the product is used, and after adjusting the surface roughness of the portion, in an oxidizing atmosphere Heat treatment is performed.

<Surface treatment>
The surface treatment can be exemplified by a polishing treatment. This surface treatment is desirably performed on the entire target portion that comes into contact with a high-temperature atmosphere when the product is used. However, it is not necessary to perform the entire target portion at the same time, and surface treatment or the like may be performed in advance except for the welded portion to adjust the surface roughness, and the surface treatment may be performed only on the welded portion or only the welded portion and the vicinity thereof.

  The surface treatment can be performed so that the surface roughness (Ra) of the target site is 0.05 to 2.5 μm. More desirably, the surface roughness (Ra) is 0.5 to 1.0 μm. When the surface roughness (Ra) is less than 0.05 μm, Cr oxidizes in preference to Al. However, when it is 0.05 μm or more, the generation of Cr oxide scale can be suppressed, and the subsequent heat treatment is more effective. An alumina barrier layer can be suitably formed. When the thickness is 2.5 μm or more, it is considered that a Cr oxide scale is likely to be generated due to processing distortion. At this time, by adjusting the surface roughness by the surface treatment, the residual stress and distortion of the heat affected zone can be removed at the same time.

  When the surface treatment is performed by a polishing process, it is desirable to perform paper polishing with a count of 12 to 220 and then finish polishing with a count of 240 to 1200.

  In the case of acid treatment, surface treatment can be performed by immersing the target site in a corrosive liquid for a predetermined time or applying a corrosive liquid. The acid used for the acid treatment may contain an alcohol in addition to the acid. It should be noted that after the acid treatment, the corrosive liquid adhering to the target site is desirably washed with water or the like.

<Heat treatment>
After the surface treatment is performed on the cast bodies joined by welding, heat treatment is performed under the following conditions.
The heat treatment is performed by performing a heat treatment in an oxidizing atmosphere.
An oxidizing atmosphere is an oxidizing gas containing 20% by volume or more of oxygen, or an oxidizing environment in which steam or CO ₂ is mixed. The heat treatment is performed at a temperature of 900 ° C. or higher, preferably 1000 ° C. or higher, more preferably 1050 ° C. or higher, and the heating time is 1 hour or longer.

<Casting products>
As described above, by sequentially performing welding, surface treatment and heat treatment on the welded portion, an alumina barrier layer is stably formed on the welded portion including the heat-affected zone and the molten metal portion of the cast body produced by welding. Casting products can be obtained.

<Alumina barrier layer>
The alumina barrier layer containing Al ₂ O ₃ formed in the cast product of the present invention has a high density and functions as a barrier for preventing oxygen, carbon, and nitrogen from entering the base material from the outside. In the present invention, as described above, after the castings are welded to the castings for the intended use, the surface treatment is performed on the part that will come into contact with the high temperature atmosphere when the product is used, and the surface roughness of the part is obtained. After that, by heat-treating the part in an oxidizing atmosphere, Al ₂ O ₃ is continuously formed as an alumina barrier layer on the surface continuous across the welded portion of the cast product. So that Thereby, not only the alumina barrier layer is formed on the surface of the cast body, but also the alumina barrier layer can be formed on the welded portion including the heat affected zone generated on the butt surface of the cast body by welding.

  The thickness of the alumina barrier layer formed on the cast body is preferably 0.05 μm or more and 3 μm or less in order to effectively exhibit the barrier function, and is preferably about 1 μm on average. More desirably, the thickness of the alumina barrier layer is not less than 0.5 μm and not more than 1.5 μm.

The cast body having the composition of the Cr—Ni—Al heat-resistant alloy is welded and then subjected to heat treatment in an oxidizing atmosphere without surface treatment. A layer is not formed. For this reason, it is affected by oxidation, carburization and the like from the weld.
In addition, a Cr oxide scale mainly composed of Cr ₂ C ₃ is formed on the outermost surface of the cast body, and as described above, it is easy to peel off. It may be peeled off.

  Therefore, in the present invention, as described above, after the castings are welded to each other, the surface roughness is adjusted by the surface treatment of the cast product before the formation of the alumina barrier layer by heat treatment, so that the heat-affected zone of the castings produced by welding is adjusted. An alumina barrier layer can be stably formed on the welded portion including

When the surface of the cast product of the present invention is examined by SEM / EDX, a part of the Cr oxide scale may be formed on the alumina barrier layer. This is because the Cr oxide scale formed inside the alumina barrier layer is pushed up to the product surface by Al ₂ O ₃ . However, it is preferable that the oxide scale is small, and it is preferable that Al ₂ O ₃ occupies 80 area% or more so that it is less than 20 area% on the product surface.

The molten metal is melted by melting in the air in a high-frequency induction melting furnace, and two tubes (outer diameter 59 mm, wall thickness 8 mm, length 3000 mm) of the alloy chemical composition listed in Table 1 are cast by mold centrifugal force casting. Casting was performed on one side of the pipe, and pipes having the same composition as a pair were joined to each other by butt welding.
In Table 1, “REM” represents a rare earth element.

  The obtained test tube was a test tube No. 1-No. 8 is an example of the present invention; 11-No. 13 is a comparative example. More specifically, the comparative example is a test tube No. No. 11 is a comparative example containing a large amount of Al with respect to the alloy chemical composition of the present invention, test tube No. 11 No. 12 is a comparative example containing a large amount of Ni with respect to the chemical composition of the alloy of the present invention, test tube no. Reference numeral 13 is a comparative example in which the chemical composition of the alloy is included in the present invention, but no surface treatment is applied to the welded portion.

<Surface treatment>
These test tubes were subjected to roughing skiving in the range of about 20 mm to 40 mm in the width direction around the welded portion on the inner surface side of the tube.
Furthermore, test tube No. 1-No. 8, no. 11 and no. 12 (that is, other than test tube No. 13) was subjected to surface treatment by paper polishing.
Table 1 shows the surface roughness (Ra) at the welded portion of each test tube.

<Visual observation before heat treatment>
Test tube No. which is an example of the invention. 4 and test tube No. which is a comparative example. The photograph which cut | disconnected the test tube to the axial direction about 13 is shown in FIG.1 and FIG.2, respectively.
When FIG. 1 is compared with FIG. 4 shows that the welded portion is glossy, and the unevenness of the welded portion is reduced by the surface treatment.

<Heat treatment>
After the surface treatment, all the test tubes were heated in air (approximately 21% oxygen) at 1000 ° C. for 10 hours, and then heated and cooled in the furnace.

<Surface measurement>
About each test tube after performing the said process, the test piece of width 20mm x length 30mm including a welding part is cut out, and the film thickness (micrometer) of the alumina barrier layer formed in the welding part inside a test piece ) And Al ₂ O ₃ area ratio (%). The measurement method is shown below, and these measurement results are shown in Table 2 as “film thickness” and “area ratio”.

<Measurement of film thickness>
The layer thickness of the alumina barrier layer with respect to the surface of the welded part of the test piece was measured by SEM (scanning electron microscope). In Table 2, “N” indicates that no alumina barrier layer was produced, and that the portion having a thickness of less than 0.05 μm (including zero thickness) intermittently exists in a part of the alumina barrier layer. The letter is attached.

<Measurement of coating area ratio>
The area ratio of Al ₂ O ₃ with respect to the weld surface of the test piece was measured using a SEM / EDX (scanning analytical electron microscope) measurement tester. The measurement was performed on a 1.35 mm × 1 mm region on the surface of the welded part of the test piece, and the distribution state of Al was subjected to surface analysis, and the distribution amount was converted into an area ratio.

<Ductility test>
A tensile test piece was prepared from the test tube according to JIS Z2201, and a ductility test was performed.
Specifically, the test piece was processed to have a parallel part diameter of 10 mm including the welded part and a parallel part length of 50 mm, and a ductility test was performed according to the metal material tensile test method of JIS Z2241. Note that the test was performed at room temperature because the difference appears more clearly than at high temperatures.

  Table 2 shows the results of the above tests. In Table 2, “-” indicates that measurement or test was not performed.

<Consideration of test results>
Referring to Table 2, test tube No. which is an example of the invention. 1-No. No. 8 is a test tube No. which is a comparative example. 11-No. It can be seen that the film thickness and area ratio of the alumina barrier layer are both better than 13.

Considering the inventive examples, it can be seen that the film thicknesses are all in the preferred range of 0.05 μm or more and 3 μm or less. It can also be seen that the tensile ductility is sufficient.
When the inventive examples were compared, the test tube No. 7 and no. 8 is inferior to other invention examples in terms of film thickness and area ratio. The surface roughness due to the surface treatment of No. 7 is rough. This is because the surface roughness in the surface treatment No. 8 is too fine. Therefore, it can be seen that the surface roughness (Ra) of 0.05 to 2.5 μm is suitable for the surface treatment applied to the welded portion so that the alumina barrier layer of the welded portion is 80 area% or more.

  On the other hand, for the comparative example, the test tube No. No. 11 is inferior in tensile ductility although a suitable alumina barrier layer is formed. This is because the Al content in the alloy chemical composition exceeds 4%. Therefore, it can be seen that the Al content is preferably 4% or less.

  In addition, test tube No. 12 and no. In No. 13, a sufficient alumina barrier layer is not formed. Test tube No. No. 12 is because the content of Ni in the alloy chemical composition is lower than 18%. As a result, the content of Fe is relatively increased, and a Cr—Fe—Mn oxide is generated on the surface of the cast body. This is because the formation of the alumina barrier layer is hindered. Test No. 13 is because the chemical composition of the alloy is within the scope of the present invention, but as a result of not performing the surface treatment, the surface roughness is rough and the formation of the alumina barrier layer is inhibited.

  From the above, it can be seen that the sample tube of the invention example has a suitable alumina barrier layer formed as compared to the sample tube of the comparative example.

<Cross-section analysis>
In addition, test tube No. which is an example of the present invention. 4 and test tube No. which is a comparative example. With respect to the specimen obtained from No. 13, a cross-sectional photograph perpendicular to the weld was taken and a cross-sectional SEM analysis was performed. In the cross-sectional SEM analysis, the specimen was plated with Ni, covered with a stainless steel sheet, and further coated with a resin.
Cross-sectional photographs of the obtained invention examples and comparative examples are shown in FIGS. 3 and 4, respectively, and enlarged photographs of the invention examples and comparative examples by cross-sectional SEM analysis are shown in FIGS. 5 and 6, respectively.
Referring to the figure, it can be seen that in the inventive example, an alumina barrier layer having a film thickness of 0.5 μm is uniformly formed on the surface of the substrate. On the other hand, it can be seen that the comparative example has large surface irregularities and the alumina barrier layer is not well formed.
The advantages of the present invention will be understood from these cross-sectional photographs.

  As shown in the above examples, the cast body of the present invention has a uniform alumina barrier layer on the entire surface of the cast body including the welded part by performing a surface treatment on the welded part and then performing a heat treatment. Since it can be formed, intrusion of oxygen, carbon, nitrogen, etc. from the outside atmosphere is effectively prevented, and the entire cast body including the welded portion has excellent repeated oxidation resistance, carburization resistance, nitriding resistance, and corrosion resistance at high temperatures. Etc. can be maintained over a long period of time.

  INDUSTRIAL APPLICABILITY The present invention is useful as a cast product in which an alumina barrier layer is also formed in a welded part and a method for manufacturing the same.

Claims (15)

A cast product to be used in a high temperature atmosphere, wherein the first cast body and the second cast body of a heat-resistant alloy containing 15% or more of Cr and 18% or more of Ni and 2 to 4% of Al are welded by mass%. A method for producing a cast product obtained by:
Joining the first cast body and the second cast body by welding;
Applying a surface treatment to the welded joint;
Applying a heat treatment to the surface-treated weld,
The manufacturing method of the casting product characterized by including.   The method for producing a cast product according to claim 1, wherein the surface treatment is a polishing treatment.   2. The method for producing a cast product according to claim 1, wherein the surface treatment is acid treatment. The method for producing a cast product according to any one of claims 1 to ₃ , wherein an alumina barrier layer containing Al ₂ O ₃ having a thickness of 0.05 µm or more is formed on the surface of the cast body by heat treatment.   The first cast body and the second cast body are, in mass%, C: 0.05 to 0.7%, Si: more than 0% to 2.5% or less, Mn: more than 0% to 3.0% %: Cr: 15-50%, Ni: 18-70%, Al: 2-4%, Rare earth elements: 0.005-0.4%, and W: 0.5-10% and / or Mo The method for producing a cast product according to any one of claims 1 to 4, comprising 0.1 to 5%, and comprising the balance Fe and inevitable impurities.   Further, the first cast body and the second cast body are, in mass%, Ti: 0.01 to 0.6%, Zr: 0.01% to 0.6%, and Nb: 0.1 to 3.0. The manufacturing method of the cast product of Claim 5 containing at least 1 type of%.   The cast product according to claim 5 or 6, wherein the first cast product and the second cast product further contain, in mass%, B: more than 0.01% and 0.1% or less. Method.   The method for manufacturing a cast product according to any one of claims 1 to 7, wherein the first cast body and the second cast body are pipe bodies, and the joining is performed by butt welding. A cast product manufactured by the method for manufacturing a cast product according to any one of claims 1 to 8, wherein an alumina barrier layer containing Al ₂ O ₃ having a thickness of 0.05 µm or more is formed on the surface of the cast product. Casting product formed. It is a cast product formed by welding a first cast body and a second cast body of a heat-resistant alloy which is used in a high temperature atmosphere and contains Cr 15% or more Ni 18% or more and Al 2 to 4% by mass%. And
A welded product of the first cast body and the second cast body is coated with an alumina barrier layer containing Al ₂ O ₃ .   The cast product according to claim 10, wherein the alumina barrier layer is continuously connected by the first cast body, the welded portion, and the second cast body.   The cast product according to claim 10 or 11, wherein the alumina barrier layer covers 50% or more of the welded portion and has a thickness of 0.05 µm or more.   The first cast body and the second cast body are, in mass%, C: 0.05 to 0.7%, Si: more than 0% to 2.5% or less, Mn: more than 0% to 3.0% %: Cr: 15-50%, Ni: 18-70%, Al: 2-4%, Rare earth elements: 0.005-0.4%, and W: 0.5-10% and / or Mo The cast product according to any one of claims 10 to 12, comprising 0.1 to 5%, and comprising the balance Fe and inevitable impurities.   The first cast body and the second cast body are further, in mass%, Ti: 0.01 to 0.6%, Zr: 0.01% to 0.6%, and Nb: 0.1 to 3.0. The cast product according to claim 13, which contains at least one of%.   The cast product according to claim 13 or 14, wherein the first cast body and the second cast body further contain, in mass%, B: more than 0.01% and 0.1% or less.