Heat-resistant castings

Abstract

A heat-resistant casting having an axial portion, wherein the structure in the plastically processed region of the axial portion contains dendrites, wherein the average value of the angle between the vertical direction of the central axis of the axial portion and the main axis of the dendrite is within 20°.

Description

[0001] This application is a divisional application with application date of July 29, 2016, application number 201680002437.6, and invention name “Heat-resistant casting”. Technical Field

[0002] The present invention relates to a heat-resistant casting having a shaft-shaped portion excellent in plastic workability. Background Art

[0003] Among the turbochargers installed in automobile engines, there is a vortex turbocharger called a variable nozzle turbocharger. The variable nozzle turbocharger is sometimes called a variable capacity turbine, a VG turbine, a variable nozzle vane turbine, a variable vane turbine, or a VGS turbine depending on the manufacturer.

[0004] The variable nozzle turbocharger opens and closes the nozzle vanes in the gas exhaust passage in the exhaust-side turbine housing, thereby changing the opening area of ​​the gas exhaust passage, and controls the flow rate and flow of the gas discharged to the exhaust-side turbine impeller in accordance with the engine speed to improve the supercharging effect.

[0005] A large number of nozzle vanes are incorporated in a variable nozzle turbocharger. In addition, since a variable nozzle turbocharger utilizes high-temperature exhaust gas, it is required to have high heat resistance.

[0006] Heat-resistant castings made of heat-resistant steel or heat-resistant alloy such as nozzle vanes are incorporated into the variable nozzle turbocharger body by plastic working such as welding or riveting.

[0007] When a heat-resistant casting is incorporated into a main body by welding, strain may be generated due to local heating and cooling, or the heat-resistant casting or the main body may be affected by heat, or post-processing may be required due to welding spatter.

[0008] On the other hand, when mounting is performed by plastic working such as riveting, the influence on the heat-resistant casting or the main body properties is small as described above. However, generally, heat-resistant castings have low plastic deformability, and therefore, sometimes they do not deform in a uniform state, causing undesirable deformation or cracking.

[0009] Therefore, a heat-resistant casting having excellent heat resistance and excellent plastic workability is eagerly desired.

[0010] As a method for manufacturing a nozzle vane, there is disclosed a method of molding the nozzle vane by pressing a shaft portion in the axial direction and pressing a rear vane portion thereafter after a casting process such as die casting or metal injection molding (for example, see Patent Document 1).

[0011] As a method for manufacturing a variable vane in a VGS type turbocharger, there is disclosed a method of making the solidified structure of a raw material finer during casting, then rolling the shaft portion, and then performing finish machining (for example, see Patent Document 2).

[0012] Patent Document 1: Japanese Patent Application Publication No. 2010-196583

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2003-49655 Summary of the invention

[0014] Problem that the invention aims to solve

[0015] However, in the technology disclosed in Patent Document 1, since the solidified structure is not intentionally controlled, it is difficult to perform plastic working with a large deformation amount.

[0016] In addition, in the technology disclosed in Patent Document 2, since the structure is merely refined, it is difficult to perform plastic working with a large deformation amount.

[0017] An object of one embodiment of the present invention is to provide a heat-resistant casting having excellent plastic workability and capable of suppressing the occurrence of unintended deformation and cracks when performing processing with a large amount of plastic deformation such as caulking.

[0018] Solutions for solving problems

[0019] Means for solving the problem include the following embodiments.

[0020] <1> A heat-resistant casting having an axial portion, wherein the structure in the area of ​​the axial portion that can be plastically processed contains dendrites, wherein the average value of the angle between the vertical direction of the central axis of the axial portion and the main axis of the dendrite is within 20°.

[0021] A dendrite is a branch-like crystal having a main axis and secondary dendrites branching from the main axis, and the main axis is a portion equivalent to a trunk.

[0022] In this specification, a heat-resistant casting refers to a casting formed of heat-resistant steel or heat-resistant alloy. Since the heat-resistant casting of the present embodiment has a portion with excellent plastic workability, it can be appropriately used in applications that require engagement with other components. That is, it can be considered that when the heat-resistant casting of the present embodiment is subjected to processing with a large amount of plastic deformation, such as riveting, the amount of deformation in the region with excellent plastic workability is larger than that of the existing heat-resistant casting, so the filling property of the groove of the component fixed by riveting is further improved, thereby further improving the bonding force.

[0023] <2> exist <1> The heat-resistant casting described in contains iron, more than 0 mass % and 1.4 mass % or less of carbon, more than 0 mass % and 69 mass % or less of nickel, and more than 6 mass % and 52 mass % or less of chromium.

[0024] <3> exist <1> The heat-resistant casting described in the specification is a nozzle vane of a turbocharger.

[0025] Effects of the Invention

[0026] According to one embodiment of the present invention, it is possible to provide a heat-resistant casting which can suppress the occurrence of unintended deformation and cracks when performing processing with a large amount of plastic deformation such as caulking and has excellent plastic workability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of a cross section obtained by cutting the heat-resistant castings of the embodiment and the comparative example using a plane including the central axis of the shaft-shaped portion, schematically showing an angle α formed by the main axis of the dendrite represented by the grid lines and the perpendicular direction to the central axis of the shaft-shaped portion.

[0028] Figure 2A This is a microscopic photograph of a cross section obtained by cutting the first sample of the heat-resistant casting of Example 1 along a plane including the central axis of the shaft-shaped portion.

[0029] Figure 2B is Figure 2A A partial enlarged photograph of the area for plastic processing shown in the box.

[0030] Figure 3A This is a microscopic photograph of a cross section obtained by cutting the second sample of the heat-resistant casting of Example 1 along a plane including the central axis of the shaft-shaped portion.

[0031] Figure 3B is Figure 3A A partial enlarged photograph of the area for plastic processing shown in the box.

[0032] Figure 4A This is a microscopic photograph of a cross section obtained by cutting the third sample of the heat-resistant casting of Example 1 along a plane including the central axis of the shaft-shaped portion.

[0033] Figure 4B is Figure 4A A partial enlarged photograph of the area for plastic processing shown in the box.

[0034] Figure 5A This is a microscopic photograph of a cross section obtained by cutting the fourth sample of the heat-resistant casting of Example 1 along a plane including the central axis of the shaft-shaped portion.

[0035] Figure 5B is Figure 5A A partial enlarged photograph of the area for plastic processing shown in the box.

[0036] Fig. 6A This is a microscopic photograph of a cross section of the fifth sample of the heat-resistant casting of Example 1 cut along a direction perpendicular to the central axis of the shaft-shaped portion.

[0037] Figure 6B is Fig. 6A The left box shows a partial magnified photograph of the area.

[0038] Figure 6C is Fig. 6A The box on the right is a partial magnified photograph of the area indicated.

[0039] Fig. 7A This is a microscopic photograph of a cross section obtained by cutting the heat-resistant casting of Comparative Example 1 along a plane including the central axis of the shaft-shaped portion.

[0040] Figure 7B is Fig. 7A A partial enlarged photograph of the area for plastic processing shown in the box.

[0041] Figure 8 This is a schematic partial side view of a heat-resistant casting used as a rivet member.

[0042] Fig. 9A is with Figure 8 A schematic partial top view of a plate-shaped rivet joint part (hereinafter simply referred to as a joint part) joined by rivet members.

[0043] Fig. 9B is with Figure 8 A schematic partial cross-sectional view of a plate-shaped joining part joined by a riveting member.

[0044] Fig. 10A It is a schematic partial plan view showing a state in which a caulking member is inserted into an opening of a joining component.

[0045] Fig. 10B It is a schematic partial cross-sectional view showing a state in which a caulking member is inserted into an opening of a joining component.

[0046] Fig.11A This is a schematic partial plan view showing a state after a caulking member is inserted into an opening of a joining component and caulking is performed.

[0047] Fig. 11B This is a schematic partial cross-sectional view showing a state after a caulking member is inserted into an opening of a joining component and caulking is performed.

[0048] Fig.12 This is a microscopic photograph of a cross section obtained by cutting the heat-resistant casting of Comparative Example 2 along a plane including the central axis of the shaft-shaped portion.

[0049] Fig.13 This is a top view photograph of the heat-resistant casting of Example 1 after the caulking process, viewed from above.

[0050] Fig.14A This is a top view photograph of the appearance of the defective heat-resistant casting of Comparative Example 1 as viewed from above after the caulking process.

[0051] Fig. 14B This is a top view photograph of the appearance of the defective heat-resistant casting of Comparative Example 2 as viewed from above after the caulking process. DETAILED DESCRIPTION

[0052] Next, one embodiment of the present invention is described in detail.

[0053] The inventors have made the following discovery with respect to a heat-resistant casting having an axial portion: the structure of the plastically processed region of the axial portion contains dendrites, wherein the average value of the angle between the perpendicular direction of the central axis of the axial portion and the main axis of the dendrite is within 20°, and at this time, the plastic deformability of the dendrite in the main axis direction is improved.

[0054] The mechanism of action is not clear yet, but it can be considered that the reason is that due to the existence of dendrites whose average angle between the vertical direction of the central axis of the shaft-shaped part and the main axis of the dendrite is within 20°, the dendrite slides along the main axis during processing, thereby improving plastic deformability.

[0055] As described above, the heat-resistant casting of this embodiment can suppress the occurrence of undesired deformation and cracks when performing processing with a large amount of plastic deformation such as caulking, and is therefore useful as a heat-resistant casting that can be engaged with other members by plastic working.

[0056] In addition, this embodiment is not limited by the above-mentioned estimation mechanism.

[0057] From the viewpoint of having an effect, the heat-resistant casting of this embodiment achieves the effect of this embodiment by making the average value of the angle between the vertical direction of the central axis of the shaft-shaped portion and the main axis of the dendrite within 20 degrees. This angle is more preferably within 15 degrees, and further preferably within 10 degrees.

[0058] As a method for confirming the main axis of the dendrite, there is a method of corroding a mirror-polished heat-resistant casting sample with an appropriate liquid containing an acid, and observing and confirming the corroded surface at a magnification of 20 to 80 times using a stereo microscope.

[0059] In addition, in this specification, the average value of the angle formed by the perpendicular direction of the central axis of the axial portion and the main axis of the dendrite is the value obtained by the following method, that is, for one sample, the angle formed by the perpendicular direction of the main axis of the dendrite and the central axis of the axial portion that can be clearly confirmed in the cross section is measured at multiple positions, and the average value of the measured values ​​is calculated.

[0060] use Figure 1 , the angle formed by the perpendicular direction of the central axis of the shaft-shaped portion of the heat-resistant casting and the main axis of the dendrite is described. Figure 1 This is a schematic diagram of a cross section obtained by cutting a heat-resistant casting along a plane including the central axis of the shaft-shaped portion, and the main axis of the dendrite is schematically shown by grid lines.

[0061] Reference symbol A denotes the central axis of the shaft-shaped portion, reference symbol B denotes a line perpendicular to the central axis of the shaft-shaped portion, and reference symbol C denotes the direction of the main axis of the dendrite schematically shown with grid lines.

[0062] The angle between the vertical direction of the central axis of the shaft-shaped portion of the heat-resistant casting and the main axis of the dendrite in this specification means: Figure 1 The angle α formed by a line B perpendicular to the central axis of the shaft-shaped portion and a line C indicating the main axis direction of the dendrite is shown.

[0063] Figure 2A to Figure 5B The samples shown are four samples, namely, first to fourth samples, randomly selected from a plurality of samples obtained in Example 1 described later, and each of the selected samples was used as an observation object.

[0064] For example, for the average value of the angle between the vertical direction of the central axis of the shaft-shaped portion and the main axis of the dendrite, Figure 2B In the first sample shown, it is 18.4°. Figure 3B The second sample shown is 10.3°. Figure 4B The third sample shown is 12.1°. Figure 5B The fourth sample shown is 3.4°.

[0065] Fig. 6A The sample shown is the fifth sample randomly selected from a plurality of samples obtained using Example 1 described later. Fig. 6A The striped pattern represented by white is the main axis of the dendrite. It can be seen that the main axis of the dendrite is oriented toward the axis of the axial part. Fig. 6A The center axis of the paper plane exists perpendicularly at the intersection of line A and line B, and extends radially.

[0066] like Figure 2B , Figure 3B , Figure 4B , Figure 5B As shown, since the average value of the angle between the vertical direction of the central axis of the shaft-shaped portion and the main axis of the dendrite is within the range specified in this embodiment, which is within 20°, the dendrite slides in the main axis direction of the adjacent dendrite when the rivet is pressed, and the plastic deformability can be improved. As a result, the filling property of the groove of the component fixed by rivet is improved, the generation of strain, deformation, and cracks in the heat-resistant casting can be effectively suppressed, and the bonding force achieved by rivet is further improved.

[0067] Figure 7B The average value of the angle between the perpendicular direction of the central axis of the shaft-shaped portion of the plastically workable region of the heat-resistant casting of Comparative Example 1 and the main axis of the dendrite is 26.7°, which is outside the range of the present embodiment.

[0068] In the heat-resistant casting of the present embodiment, from the viewpoint of facilitating plastic working such as caulking, the shaft diameter of the shaft-shaped portion subjected to plastic working is preferably 15 mm or less, more preferably 10 mm or less, and even more preferably 7 mm or less.

[0069] Although the lower limit of the shaft diameter is not particularly limited, it is preferably 2 mm or more from the viewpoint of having strength sufficient to withstand plastic working.

[0070] The heat-resistant casting of the present embodiment preferably contains iron, more than 0 mass % and 1.4 mass % or less of carbon, more than 0 mass % and 69 mass % or less of nickel, and 6 mass % or more and 52 mass % or less of chromium.

[0071] Examples of heat-resistant alloys suitable for production include SCH21 and SCH22 among the alloys described in JIS G5122 (2003) "Heat-resistant steel and heat-resistant alloy castings".

[0072] For example, SCH21 is an alloy containing iron, 0.25 mass% to 0.35 mass% of carbon, 19.00 mass% to 22.00 mass% of nickel, 23.00 mass% to 27.00 mass% of chromium, 1.75 mass% or less of silicon, 0.040 mass% or less of phosphorus, 0.040 mass% or less of sulfur, and 1.50 mass% or less of manganese.

[0073] There is no particular limitation on the method for controlling the main axis direction of the dendrite of the heat-resistant casting of the present embodiment. For example, a method of directly controlling the temperature conditions of the mold, a method of using a crystallization refiner, etc., can be cited, and one or more of these methods can be appropriately selected for use according to the purpose. As the crystallization refiner, for example, cobalt aluminate, cobalt oxide, etc. can be cited.

[0074] Conditions during casting, such as the temperature and fluidity of the molten metal, the position of the main inlet of the molten metal, the injection speed, and the mold temperature, can be optimized according to the purpose.

[0075] After the heat-resistant alloy injected into the mold is cooled and solidified, it is taken out of the mold to produce a casting that is a prototype of the heat-resistant casting of the present embodiment.

[0076] After that, the final product can be obtained by performing processing such as cutting and surface grinding.

[0077] For example, after forming a casting that becomes a prototype, a portion having a structure having a preferred form including a large number of dendrites can be cut to form a heat-resistant casting.

[0078] The obtained shaft-shaped portion of the heat-resistant casting can be joined to a mounting target part by combining them and performing caulking.

[0079] In the riveting process, a tool called an insert is used and riveting is performed with the center of the tip positioned on the central axis of the shaft-shaped portion.

[0080] The structure of the area that can be plastically processed of the heat-resistant casting of this embodiment includes dendrites, and the average value of the angle between the vertical direction of the central axis of the shaft-like portion and the main axis of the dendrite is within 20°. Therefore, the riveted portion is plastically deformed and extended uniformly in the same way. The top end of the shaft-like portion is formed as a riveted portion that is close to a circle when viewed from above, thereby achieving stable fixation and being able to suppress the occurrence of cracks, strains, etc. after riveting.

[0081] The heat-resistant casting of the present embodiment has a portion excellent in plastic deformability.

[0082] Therefore, it can be applied to parts involving joining such as engine parts and boiler parts used under high temperature conditions, and its application range is wide.

[0083] In particular, the present invention can be suitably used for nozzle vanes of a variable geometry turbocharger which require heat resistance.

[0084] Example

[0085] Hereinafter, this embodiment will be described in detail with reference to specific examples.

[0086] Example 1

[0087] (Making of casting mold)

[0088] First, a prototype mold having a concave shape corresponding to the heat-resistant casting is prepared, and wax is injected to produce a wax model.

[0089] In order to form the initial layer of the casting mold, a slurry containing zirconium sand as the main material and 0.5 mass % of cobalt aluminate relative to the total amount of the refractory material is used as the raw material of the refractory material. The refractory material for forming the initial layer is covered on the obtained wax model by an impregnation method and dried, thereby forming the initial layer of the casting mold.

[0090] The slurry contained a mixture of 80 mass % zircon sand and 20 mass % fused silica.

[0091] The thickness of the initial layer after drying is 0.05 mm to 0.50 mm.

[0092] After the initial layer is formed, the steps of coating with the slurry and drying are repeated to produce a wax model having a coating layer made of a refractory material having an appropriate strength.

[0093] In the present embodiment, the coating of the refractory material is performed by the dipping method, but it may also be performed by a coating method using a brush or the like, a spraying method using a spray or the like, or the like.

[0094] Next, the wax pattern having the coating layer formed of the refractory material is pressurized and heated in a heating furnace at a temperature range of 150° C. to 200° C. at a pressure of 490 kPa to 1642 kPa to melt and remove the wax pattern.

[0095] Then, drying is performed to prepare a casting mold (casting die) formed of a refractory material.

[0096] Furthermore, a firing step is performed in which the mold is fired at a temperature within a range of 1000° C. to 1200° C. to obtain a casting mold having a strength sufficient for casting.

[0097] (Casting)

[0098] Heat-resistant alloy SCH21 (JIS G5122 (2003)) was heated to 1650° C. to obtain a melt.

[0099] The temperature of the casting mold obtained as described above was set to 1000° C. to 1100° C., and the molten metal was poured into the casting mold under reduced pressure and at a casting temperature of 1650° C.

[0100] After confirming the solidification of the molten metal and leaving it in the air for 2 hours, the casting mold was broken to obtain the original shape of the heat-resistant casting.

[0101] Then, sandblasting and cutting were performed to obtain the heat-resistant casting of Example 1.

[0102] Figure 8 This is a schematic side view of a riveted shaft. The dimensions of each part are as follows.

[0103] H1: 4.0mm

[0104] H2: 1.6mm,

[0105] D1:

[0106] D2:

[0107] (Observe the cross-section structure)

[0108] Four heat-resistant castings of Example 1 were randomly selected from a plurality of manufacturing batches, and were cut using a plane including the central axis of each shaft-shaped portion. The cross-sections were etched using aqua regia, which is a mixture of hydrochloric acid and nitric acid in a volume ratio of 3:1. The etched cross-sections were washed with water to remove the aqua regia, and then the cross-sections were observed using a stereo microscope at a magnification of 20 times (e.g. Figure 2A ) and 80 times (e.g. Figure 2B ) was taken under the microscope. The obtained cross-section photo is as follows Figure 2B , Figure 3B , Figure 4B , Figure 5B As shown. The main axis of the dendrite is observed as a white stripe-like layer. In each figure, a dotted line is drawn on the main axis of the dendrite for easy observation.

[0109] like Figure 2B As shown in FIG. 1 , the average value of the angle between the vertical direction of the central axis of the shaft-shaped portion and the main axis of the dendrite is 18.4° in the first sample. Figure 3B As shown, in the second sample it is 10.3°, in Figure 4B The third sample shown is 12.1°. Figure 5B The fourth sample shown is 3.4°.

[0110] according to Figure 6A to Figure 6C From the cross-sectional photograph, we can see that the main axis of the dendrite is from the periphery to Fig. 6A The central axis of the shaft-shaped portion in FIG. 1 , which passes through the intersection of line A and line B and is perpendicular to the paper surface, is formed radially.

[0111] (Performance Evaluation)

[0112] The heat-resistant casting of Example 1 was used as the caulking member 10, which was inserted into the opening 14 of the joining part 12 and caulked.

[0113] Fig. 9A FIG. 1 is a schematic partial top view of a joining part 12 having an opening 14. Fig. 9B This is a schematic partial cross-sectional view of the vicinity of the portion where the riveting member is inserted. Fig. 9B The dimensions shown are shown below.

[0114] H3: 3.0mm

[0115] H4: 1.5mm,

[0116] D3:

[0117] D4:

[0118] Fig. 10A 1 is a schematic partial plan view showing a state in which the caulking member 10 is inserted into the opening 14 of the joining part 12. Fig. 10B yes Fig. 10A A schematic partial cross-sectional view of the riveted portion.

[0119] As a caulking device, US-36 manufactured by Yoshikawa Iron Works Co., Ltd. was used, and the top end of the caulking member 10 was plastically deformed to perform joining.

[0120] The caulking was performed with caulking allowances (reduction in the height direction of the shaft-shaped portion) of 0.95 mm, 1.05 mm, 1.15 mm, and 1.25 mm. The larger the reduction, the greater the deformation during caulking.

[0121] The insert of the riveting device was in a plate shape, and the riveting was performed under the conditions of a tip diameter of 4.5 mm, an angle of 5°, a load of 2300 N, and a rotation speed of 1460 rpm (times / minute).

[0122] Fig.11A This is a schematic top view of the rivet member 10 after being inserted into the joining part 12 and riveted. Fig. 11B yes Fig.11A A schematic partial cross-sectional view of the riveted portion. Fig. 11B As shown, the top end of the rivet member 10 is plastically deformed, and is deformed and fixed in a manner that matches the shape of the rivet portion of the joining part 12 .

[0123] <Required specifications for riveting test>

[0124] The condition that the caulking part deforms uniformly and does not crack is the requirement specification of the caulking test. Samples that meet this requirement specification are considered to be qualified.

[0125] 160 heat-resistant castings were selected from the heat-resistant castings of Example 1 manufactured in a plurality of manufacturing batches, and 40 heat-resistant castings were used to perform a riveting test under various conditions. The results are shown below.

[0126] (1) Riveting allowance: 0.95mm

[0127] All 40 heat-resistant castings passed the test.

[0128] (2) Riveting allowance: 1.05mm

[0129] All 40 heat-resistant castings passed the test.

[0130] (3) Riveting allowance: 1.15mm

[0131] All 40 heat-resistant castings passed the test.

[0132] (4) Riveting allowance: 1.25mm

[0133] All 40 heat-resistant castings passed the test.

[0134] That is, all 160 heat-resistant castings obtained in Example 1 were qualified products.

[0135] Comparative Example 1

[0136] In the manufacturing method of Example 1, the position of the main inlet of the molten metal was changed to produce a heat-resistant casting of Comparative Example 1 having an average angle of more than 20° between the vertical direction of the central axis of the shaft-shaped portion and the main axis of the dendrite.

[0137] (Observe the cross-section structure)

[0138] exist Fig. 7A 2 shows a microscopic photograph of a cross section obtained by cutting the heat-resistant casting of Comparative Example 1 along a plane including the central axis of the shaft-shaped portion. Figure 7B for Fig. 7A Enlarged photo in the frame.

[0139] like Figure 7B As shown, the average value of the angle between the vertical direction of the central axis of the shaft-shaped portion and the main axis of the dendrite is 26.7°, which is a heat-resistant casting whose average value falls outside the range of this embodiment. Figure 7B The main axis of the dendrite is observed as a white stripe-like layer. Figure 7B In the figure, a dotted line is drawn on the main axis of the dendrite for easy observation. Fig. 7A as well as Figure 7B The black spots observed in the figure are indentations produced when measuring the hardness of the heat-resistant casting and have nothing to do with the structure of the heat-resistant casting.

[0140] 160 heat-resistant castings were selected from the heat-resistant castings of Comparative Example 1, and 40 heat-resistant castings were used to perform a riveting test under each condition. The results are shown below.

[0141] (1) Riveting allowance 0.95mm

[0142] ·37 out of 40 heat-resistant castings were qualified.

[0143] (2) Riveting allowance 1.05mm

[0144] ·36 out of 40 heat-resistant castings were qualified.

[0145] (3) Riveting allowance 1.15mm

[0146] ·35 out of 40 heat-resistant castings were qualified.

[0147] (4) Riveting allowance 1.25mm

[0148] ·31 out of 40 heat-resistant castings were qualified.

[0149] From the above results, it is understood that in the heat-resistant casting of Comparative Example 1, as the amount of plastic deformation during the caulking process increases, the yield rate of the heat-resistant casting decreases.

[0150] Comparative Example 2

[0151] In the same production method as in Example 1, a heat-resistant casting of Comparative Example 2 was produced and evaluated in the same manner as in Example 1 except that the crystal refining agent was not used.

[0152] (Cross-section structure observation)

[0153] exist Fig.12 ] A microscopic photograph of a cross section obtained by cutting the heat-resistant casting of Comparative Example 2 along a plane including the central axis of the shaft-shaped portion is shown in FIG.

[0154] like Fig.12 As shown, it is a heat-resistant casting in which no dendrites are formed in the left half, and in the right half, the average value of the angle between the vertical direction of the central axis of the axial portion and the main axis of the dendrite is 62.6°, which falls outside the range of this embodiment. Fig.12 In the figure, a dotted line is drawn on the main axis of the dendrite for easy observation.

[0155] 160 heat-resistant castings were selected from the heat-resistant castings of Comparative Example 2, and 40 heat-resistant castings were used to perform a riveting test under each condition. The results are shown below.

[0156] (1) Riveting allowance: 0.95mm

[0157] · 29 out of 40 heat-resistant castings were qualified.

[0158] (2) Riveting allowance: 1.05mm

[0159] · 23 out of 40 heat-resistant castings were qualified.

[0160] (3) Riveting allowance: 1.15mm

[0161] ·19 out of 40 heat-resistant castings were qualified.

[0162] (4) Riveting allowance: 1.25mm

[0163] · 18 out of 40 heat-resistant castings were qualified.

[0164] The results show that, in the heat-resistant casting of Comparative Example 2, when the amount of plastic deformation is small, the pass rate is also low, and the pass rate decreases significantly as the caulking allowance increases.

[0165] The appearance photo of the riveted part after the test is as follows Fig.13 , Fig.14A as well as Fig. 14B shown.

[0166] Fig.13 This is a photograph of the appearance of an example of the heat-resistant casting of Example 1, all of which were qualified products. The casting was uniformly plastic worked and no cracks were observed.

[0167] Fig.14A This is a photograph of the appearance of an example of a defective heat-resistant casting of Comparative Example 1. Since the deformation is non-uniform, white cracks are observed at the positions indicated by arrows.

[0168] Fig. 14B This is a photograph of the appearance of an example of a defective heat-resistant casting of Comparative Example 2. Since the deformation is non-uniform, white cracks are observed at the positions indicated by arrows.

[0169] As described above, the heat-resistant casting of the present embodiment has a region excellent in plastic workability, and therefore, even when subjected to processing with a large amount of plastic deformation such as caulking, non-uniform deformation and cracking do not occur.

[0170] For all documents, patent applications and technical specifications described in this specification, each document, patent application and technical specification is introduced by reference in this specification to the same extent as if it were specifically and individually described.

Claims

1. A method for manufacturing a heat-resistant casting, which is a method for manufacturing a heat-resistant casting having a shaft-shaped portion with a shaft diameter of 2 mm to 15 mm, wherein the structure in the area of ​​the shaft-shaped portion that can be plastically processed includes dendrites, and the dendrites are dendrites whose average value of the angle between the vertical direction of the central axis of the shaft-shaped portion and the main axis of the dendrite is within 20°, and the heat-resistant casting is formed using a casting mold containing a crystal refiner.

2. The method for producing a heat-resistant casting according to claim 1, wherein: The heat-resistant casting contains iron, more than 0 mass % and 1.4 mass % or less of carbon, more than 0 mass % and 69 mass % or less of nickel, and more than 6 mass % and 52 mass % or less of chromium.

3. The method for producing a heat-resistant casting according to claim 1, wherein: The heat-resistant casting is a nozzle blade of a turbocharger.

4. The method for producing a heat-resistant casting according to claim 1, wherein: The crystallization fine-refining agent is selected from cobalt aluminate and cobalt oxide.

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