Nickel-based alloy and projection material for wet shot peening

Abstract

In wet shot peening, to provide a projectile for wet shot peening that can impart sufficient compressive residual stress to a workpiece while suppressing the surface roughness of the workpiece to a small level, further has an adsorptivity to a magnet, and can suppress the occurrence of rust, and an alloy for this projectile. 【Solution means】The nickel-based alloy and the projectile for wet shot peening of the present invention contain 8.7 mass% or more of Ni, 18 mass% or more and 26 mass% or less of Cr, 1.1 mass% or more and 2.3 mass% or less of C, 3 mass% or more and 5.5 mass% or less of Si, 3 mass% or more and 5.5 mass% or less of B, and 10 mass% or more and 40 mass% or less of Fe.

Description

Technical Field

[0001] The present invention relates to nickel-based alloys and projection materials for wet shot peening.

Background Art

[0002] As a processing method of projecting particles called projection materials (also referred to as "shots", "shot materials", "media", "abrasives", etc.) onto the surface of a workpiece, there are shot blasting for forming a friction surface, deburring, and removing a film, and shot peening for imparting compressive residual stress.

[0003] In these processing methods, a dry method of injecting only dry projection materials onto a workpiece to be processed is common. However, in recent years, due to the improvement of the working environment by reducing the amount of dust generation and for the purpose of finer processing, the number of cases where a wet blasting method of injecting a slurry in which a projection material and a liquid are mixed has been applied is increasing. In this wet shot peening (sometimes referred to as wet peening) by the wet blasting method, the projection material is conveyed and injected using a liquid as a medium. Therefore, not only can a projection material having a smaller particle diameter than the dry method be used, but also the cooling effect of the processed surface by the liquid is high, and it is possible to effectively increase the hardness of the surface layer of the workpiece to be processed and impart compressive residual stress, which is the action of peening.

[0004] Regardless of the dry or wet method, generally, in the peening process, the higher the hardness of the projection material used, the more effective the peening action (hardness increase, compressive residual stress imparting) tends to be obtained. Under such a tendency, various studies have been made on the projection materials used in the peening process, focusing on their hardness. For example, new projection materials as described in Patent Documents 1 to 6 have been proposed. However, these projection materials are designed on the premise of being used in the conventional dry method, and do not necessarily have characteristics suitable for wet shot peening. There is a need to develop a projection material suitable for wet shot peening and an alloy for obtaining this projection material.

[0005] By the way, when focusing on enhancing the imparting of compressive residual stress and using a projection material with high hardness as the projection material used in wet shot peening, a new problem arises in that the surface roughness of the workpiece after wet shot peening increases. In this case, an additional post-processing step is required to reduce the surface roughness of the workpiece. That is, in wet shot peening, it can be said that improving the compressive residual stress and suppressing the surface roughness of the workpiece are in a trade-off relationship.

[0006] In wet shot peening, a method of injecting a slurry in which a projection material and a liquid are mixed is used, and water (for example, tap water) may be used as the liquid. In that case, the projection material is required to have corrosion resistance so that rust does not occur.

[0007] In addition, by performing wet shot peening, cracks and wear will occur in the projection material. In a wet blasting apparatus, the cracked projection material and wear powder are configured to be recovered as sludge, and a magnet separator using a magnet is utilized as a method for efficiently separating the cracked projection material and wear powder from this sludge. Therefore, the projection material is required to have characteristics that are adsorbed by a magnet.

[0008] Although the projection materials described in Patent Documents 1 and 2 have sufficient hardness, rust may occur when water is used as the liquid of the slurry. The projection materials described in Patent Documents 3 and 4 can enhance the corrosion resistance. However, there is a problem that the hardness of the projection material is very high and the surface roughness of the workpiece after treatment increases. The projection material described in Patent Document 5 can enhance the corrosion resistance, but the hardness of the projection material is not sufficient and the performance of imparting compressive residual stress is inferior. In addition, the projection material described in Patent Document 6 introduces a Co-based alloy projection material, which has the characteristic of adjustable hardness, but does not have sufficient magnetism and thus cannot be separated by a magnet separator.

[0009] Thus, among the projectiles proposed to date, the following trade-offs exist: (i) achieving good compressive residual stress, (ii) minimizing the surface roughness of the workpiece, (iii) having good corrosion resistance, and (iv) having magnet adsorption properties. At present, no projectile can satisfy all of these requirements simultaneously.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Summary of the Invention

Problems to be Solved by the Invention

[0011] The main problems of the present invention are to provide a projectile for wet shot peening that can impart sufficient compressive residual stress to a workpiece while suppressing the surface roughness of the workpiece, and further has magnet adsorption properties and can suppress the occurrence of rust, and to provide an alloy for this projectile.

Means for Solving the Problems

[0012] The nickel-based alloy according to the embodiment of the invention is A nickel-based alloy used as a shot peening projectile material,It contains 8.7 mass% or more of Ni, 18 mass% or more and 26 mass% or less of Cr, 1.1 mass% or more and 2.3 mass% or less of C, 3 mass% or more and 5.5 mass% or less of Si, 3 mass% or more and 5.5 mass% or less of B, and 10 mass% or more and 40 mass% or less of Fe. The above nickel-based alloy may contain 12 mass% or less of one or more selected from W, Mo, and Nb.

[0013] The projectile for wet shot peening according to an embodiment of the present invention contains 8.7 mass% or more of Ni, 18 mass% or more and 26 mass% or less of Cr, 1.1 mass% or more and 2.3 mass% or less of C, 3 mass% or more and 5.5 mass% or less of Si, 3 mass% or more and 5.5 mass% or less of B, and 10 mass% or more and 40 mass% or less of Fe. The above projectile for wet shot peening may contain 12 mass% or less of one or more selected from W, Mo, and Nb.

Advantages of the Invention

[0014] According to the projectile for wet shot peening of the present invention, in wet shot peening using the projectile, while suppressing the surface roughness of the workpiece to a small level, sufficient compressive residual stress can be imparted to the workpiece. Further, the projectile for wet shot peening of the present invention has an adsorptivity to a magnet and can suppress the generation of rust. Also, according to the nickel-based alloy of the present invention, this projectile for wet shot peening can be manufactured.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0016] (Projectile for wet shot peening) Hereinafter, a projectile for wet shot peening according to an embodiment of the present invention (hereinafter referred to as a projectile of one embodiment) will be specifically described. The projectile of one embodiment is a projectile used in the wet shot peening method. Wet shot peening as used in this specification means shot peening treatment using wet blasting. Wet blasting means a processing (treatment) method in which a slurry obtained by mixing a liquid and a projectile is sprayed onto a workpiece together with compressed air, and the projectile contained in the slurry is made to collide with the workpiece.

[0017] The projectile of one embodiment contains Ni, Cr, C, Si, B, and Fe as essential components. And the projectile of one embodiment contains Ni in an amount of 8.7% by mass or more, Cr in an amount of 18% by mass or more and 26% by mass or less, C in an amount of 1.1% by mass or more and 2.3% by mass or less, Si in an amount of 3% by mass or more and 5.5% by mass or less, B in an amount of 3% by mass or more and 5.5% by mass or less, and Fe in an amount of 10% by mass or more and 40% by mass or less, based on the total mass of the projectile.

[0018] According to the projectile of one embodiment, in wet shot peening, it is possible to impart sufficient compressive residual stress to the workpiece while suppressing the surface roughness of the workpiece to a small value. Specifically, by including the essential components within the above ranges, the Vickers hardness of the projectile can be made to be in the range of 750 HV or more and 1100 HV or less. The Vickers hardness of the projectile has a close relationship with the compressive residual stress imparted to the workpiece and the surface roughness of the workpiece after the treatment in wet shot peening using the projectile. When the Vickers hardness of the projectile is less than 750 HV, sufficient compressive residual stress cannot be imparted to the workpiece in wet shot peening. On the other hand, when the Vickers hardness of the projectile exceeds 1100 HV, although sufficient compressive residual stress can be imparted to the workpiece in wet shot peening, the surface roughness of the workpiece on which the treatment has been performed cannot be reduced.

[0019] Also, according to the projectile of one embodiment, even when water is used as the liquid of the slurry, rusting of the projectile can be suppressed. Further, according to the projectile of one embodiment, it can be adsorbed by a magnet, and the projectile can be easily recovered using the magnet.

[0020] (Ni (Nickel)) The content of Ni in the projectile of one embodiment is 8.7% by mass or more. There is no limitation on the upper limit value of the content of Ni, and it may be appropriately determined according to the content of other essential components. An example of the upper limit value of the content of Ni is the amount obtained by subtracting the total mass (% by mass) of the essential components other than Ni from the total mass (% by mass). An example of the upper limit value of the Ni content is 67.9% by mass. By setting the content of Ni to 8.7% by mass or more and setting the content of other essential components within the above range, the Vickers hardness of the projectile can be in the range of 750 HV or more and 1100 HV or less. As a result, in wet shot peening using the projectile of one embodiment, sufficient compressive residual stress can be imparted to the workpiece, and the surface roughness of the workpiece after processing can be reduced. Furthermore, the projectile can be imparted with adsorbability to a magnet, and rusting of the projectile can be suppressed.

[0021] (Cr (Chromium)) Cr has the effect of improving the corrosion resistance of the alloy by dissolving in the Ni solid solution. However, if the content is less than 18% by mass, the corrosion resistance cannot be made sufficiently high. Also, if it exceeds 26% by mass, the hardness of the Ni solid solution decreases, and in wet shot peening, sufficient compressive residual stress cannot be imparted to the workpiece. That is, the Vickers hardness of the projectile cannot be made 750 HV or more. Considering this point, the projectile of one embodiment defines the content of Cr to be 18% by mass or more and 26% by mass or less. The content of Cr is more preferably 20% by mass or more and 24% by mass or less. According to the projectile of one embodiment with the content of Cr being the preferred content, in wet shot peening, the surface roughness of the workpiece can be suppressed to be smaller.

[0022] (C (Carbon)) C forms a compound with Cr and contributes to increasing the hardness, that is, enhancing the performance of imparting compressive residual stress to the material to be treated. However, if it is less than 1.1% by mass, the hardness will be low and the effect will be insufficient. That is, the Vickers hardness of the projection material cannot reach 750 HV or more. Also, if it exceeds 2.3% by mass, the hardness will be excessive and the surface roughness of the workpiece after wet shot peening cannot be suppressed to a small value. That is, the Vickers hardness of the projection material cannot reach 1100 HV or less. Further, if it exceeds 2.3% by mass, the toughness of the projection material will decrease. Considering this point, the projection material of one embodiment defines the content of C to be 1.1% by mass or more and 2.3% by mass or less. The content of C is more preferably 1.2% by mass or more and 1.9% by mass or less, and particularly preferably 1.3% by mass or more and 1.7% by mass or less. According to the projection material of one embodiment with the content of C being the preferred content, in wet shot peening, the surface roughness of the workpiece can be suppressed to a smaller value.

[0023] (Si (Silicon)) Si dissolves in the Ni solid solution and contributes to increasing the corrosion resistance and hardness of the alloy, that is, enhancing the performance of imparting compressive residual stress. However, if it is less than 3% by mass, the hardness will be low and the effect will be insufficient. That is, the Vickers hardness of the projection material cannot reach 750 HV or more. Also, if it exceeds 5.5% by mass, the hardness will be excessive and the surface roughness of the workpiece after wet shot peening cannot be suppressed to a small value. That is, the Vickers hardness of the projection material cannot reach 1100 HV or less. Further, if it exceeds 5.5% by mass, the toughness of the projection material will decrease. Considering this point, the projection material of one embodiment defines the content of Si to be 3% by mass or more and 5.5% by mass or less. The content of Si is more preferably 3.8% by mass or more and 5.1% by mass or less, and particularly preferably 4.1% by mass or more and 4.9% by mass or less. According to the projection material of one embodiment with the content of Si being the preferred content, in wet shot peening, the surface roughness of the workpiece can be suppressed to a smaller value.

[0024] (B (Boron)) B forms a compound with Cr and contributes to increasing the hardness, that is, enhancing the performance of imparting compressive residual stress to the workpiece. However, if it is less than 3% by mass, the hardness will be low and the effect will be insufficient. That is, the Vickers hardness of the projectile cannot reach 750 HV or more. Also, if it exceeds 5.5% by mass, the hardness will be excessive and the surface roughness of the workpiece after wet shot peening cannot be suppressed to a small value. That is, the Vickers hardness of the projectile cannot reach 1100 HV or less. Further, if it exceeds 5.5% by mass, the ductility of the projectile decreases. Considering this point, the projectile of one embodiment defines the content of B to be 3% by mass or more and 5.5% by mass or less. The content of B is more preferably 3.8% by mass or more and 5.1% by mass or less, and particularly preferably 4.1% by mass or more and 4.9% by mass or less. According to the projectile of one embodiment with the content of B being the preferred content, in wet shot peening, the surface roughness of the workpiece can be suppressed to a smaller value.

[0025] (Fe (Iron)) Fe contributes to exhibiting the property of dissolving in the Ni solid solution and adsorbing to the magnet. However, if it is less than 10% by mass, the effect is insufficient, and if it exceeds 40% by mass, the corrosion resistance of the material decreases. Considering this point, the projectile of one embodiment defines the content of Fe to be 10% by mass or more and 40% by mass or less. The content of Fe is more preferably 13% by mass or more and 30% by mass or less, and particularly preferably 17% by mass or more and 23% by mass or less. According to the projectile of one embodiment with the content of Fe being the preferred content, the property of adsorbing to the magnet and the corrosion resistance of the projectile can be made better.

[0026] (Optional component) In the projectiles of one embodiment, within a range not departing from the gist of the present invention, that is, within a range where the Vickers hardness of the projectiles can be 750 HV or more and 1100 HV or less, other components than those described above can be included. The projectiles of one embodiment as an example have the total mass of the essential components being 95% by mass or more, 99% by mass or more, or 99.5% by mass or more with respect to the total mass of the projectiles. The projectiles of one embodiment as an example have the total mass of the essential components and the optional components exemplified below being 95% by mass or more, 99% by mass or more, or 99.5% by mass or more with respect to the total mass of the projectiles.

[0027] A preferred form of the projectiles of one embodiment includes one or more selected from W (tungsten), Mo (molybdenum), and Nb (niobium) together with the components described above. According to the projectiles for wet shot peening of this form, while maintaining corrosion resistance and magnetism, sufficient compressive residual stress can be imparted to the workpiece in wet shot peening using the projectiles.

[0028] More preferably, the mass of one or more selected from W, Mo, and Nb (in the case of two or more, their total mass) is 12% by mass or less with respect to the total mass of the projectiles. According to this form, the surface roughness of the workpiece after wet shot peening can be suppressed to be smaller.

[0029] There is no limitation on the shape of the projectiles of one embodiment, and spherical, irregular shape, polygonal shape, etc. can be exemplified. Other shapes may also be possible.

[0030] There is no limitation on the particle size of the projectiles of one embodiment, and as an example, the particle size is 30 μm (range value: about 10 μm to about 50 μm) or more and 250 μm or less (range value: about 180 μm to about 320 μm) in median diameter. The median diameter means the particle diameter at which the cumulative frequency of the particle diameter is 50% in the particle size distribution, and the lower limit and the upper limit of the range value roughly mean the cumulative frequency 10% diameter and the cumulative frequency 90% diameter in the particle size distribution.

[0031] The manufacturing method of the projectile of one embodiment is not limited. For example, the ingot in which the essential components described above are adjusted and blended by mass% and an optional component is added in a predetermined amount as necessary is completely melted in the crucible of the melting furnace, and then the molten alloy is atomized or melted and pulverized. The projectile of one embodiment can be manufactured in powder form.

[0032] Furthermore, the alloy powder produced by the atomization method can be adjusted to a particle size suitable for the intended construction method and then applied to wet shot peening. By performing wet shot peening with this powder, it is possible to achieve both high residual stress application performance and the characteristic of reducing the surface roughness of the material to be treated. Also, it is possible to separate cracked projectiles and worn powders from the sludge using a magnetic separator.

[0033] The projectile according to another embodiment of the present disclosure contains, based on the total mass of the projectile, 18 mass% or more and 26 mass% or less of Cr, 1.1 mass% or more and 2.3 mass% or less of C, 3 mass% or more and 5.5 mass% or less of Si, 3 mass% or more and 5.5 mass% or less of B, 10 mass% or more and 40 mass% or less of Fe, and the balance is Ni and unavoidable impurities. As used herein, "unavoidable impurities" refers to impurities that are unavoidably mixed in during the manufacturing process of each raw material, etc., without being intentionally added, and the total of these is usually 0.5 mass% or less and does not affect the operation of the present invention. This form of projectile also exhibits the same effects as the projectile of the one embodiment described above.

[0034] The projectile according to another embodiment of the present disclosure contains, based on the total mass of the projectile, 18 mass% or more and 26 mass% or less of Cr, 1.1 mass% or more and 2.3 mass% or less of C, 3 mass% or more and 5.5 mass% or less of Si, 3 mass% or more and 5.5 mass% or less of B, 10 mass% or more and 40 mass% or less of Fe, one or more selected from W, Mo, and Nb of 12 mass% or less, and the balance is Ni and unavoidable impurities. This form of projectile also exhibits the same effects as the projectile of the one embodiment described above.

[0035] (Slurry) The projection materials in various forms described above can be applied to wet shot peening as a slurry mixed with a liquid. The concentration in the slurry as an example of the projection material in one embodiment is 3% by volume or more and 45% by volume or less. The concentration in the slurry as an example of the projection material in one embodiment is preferably 10% by mass or more and 75% by mass or less. As the liquid of the slurry, water can be preferably used. The projection material in one embodiment can suppress the generation of rust even when water is used as the liquid of the slurry.

[0036] (Nickel-based alloy) Next, the nickel-based alloy according to the embodiment of the present invention (hereinafter referred to as the alloy of one embodiment) will be specifically described.

[0037] The alloy of one embodiment contains Ni, Cr, C, Si, B, and Fe as essential components. And the projection material of one embodiment contains Ni at 8.7% by mass or more, Cr at 18% by mass or more and 26% by mass or less, C at 1.1% by mass or more and 2.3% by mass or less, Si at 3% by mass or more and 5.5% by mass or less, B at 3% by mass or more and 5.5% by mass or less, and Fe at 10% by mass or more and 40% by mass or less with respect to the total mass of the projection material.

[0038] According to the alloy of one embodiment, by processing the alloy by a conventionally known method, the projection materials for wet shot peening in various embodiments described above can be manufactured. That is, according to the alloy of one embodiment, in wet shot peening, it is possible to manufacture a projection material for wet shot peening that can suppress the surface roughness of the workpiece to a small level while applying sufficient compressive residual stress to the workpiece, and further has an adsorptivity to a magnet and can suppress the generation of rust. In other words, the alloy of one embodiment has a Vickers hardness of 750 HV or more and 1100 HV or less, has an adsorptivity to a magnet, and can suppress the generation of rust.

[0039] The alloy of one embodiment is different from the projection materials for wet shot peening of the various embodiments described above in that it is not limited in any way in its shape, but is otherwise the same. Therefore, a detailed description of the alloy of one embodiment will be omitted. The projection materials (projection materials for wet shot peening) of the various embodiments (one embodiment, another embodiment) described above may be read as the alloys of the various embodiments (one embodiment, another embodiment).

[0040] Therefore, the alloy in a preferred form contains, together with the essential components, one or more selected from W (tungsten), Mo (molybdenum), and Nb (niobium). More preferably, the mass of one or more selected from W, Mo, and Nb (in the case of two or more, their total mass) is 12% by mass or less based on the total mass of the alloy.

[0041] There is no limitation on the manufacturing method of the alloy of one embodiment. For example, it can be manufactured by adjusting and blending the essential components described above to mass%, and completely melting the ingot with a predetermined amount of optional components added as necessary in a melting furnace.

[0042] As described above, the case where the alloy of one embodiment is applied to the projection materials for wet shot peening of the various embodiments has been described as an example. However, the alloy of one embodiment may be applied to projection materials for other uses, for example, projection materials for hard shot peening (projection materials for dry blasting).

Examples

[0043] Next, the present invention will be described more specifically with reference to examples and comparative examples. Hereinafter, unless otherwise specified, parts or % are based on mass.

[0044] Alloys were melted and compounded according to the compounding ratios shown in Tables 1 to 3 below, and were evaluated for Vickers hardness, presence or absence of rust, and presence or absence of adsorption to a magnet by the methods shown below. In the alloys shown in Table 2, (a) to (f) are the projectiles of prior art documents respectively described in "Japanese Patent Laid-Open No. 2-228448", "Japanese Patent Laid-Open No. 2014-213441", "Japanese Patent Laid-Open No. 2009-263756", "Japanese Patent Laid-Open No. 2020-40200", "Japanese Patent Laid-Open No. 2002-317203", and "Japanese Patent Laid-Open No. 2017-115177". "Bal." in the table means the balance excluding inevitable impurities.

[0045] (Measurement of Vickers hardness) Twenty grams of ingots having the compounding compositions shown in Tables 1 to 3 below were heated and melted to about 1600 °C in an argon stream using an electric furnace, and the molten metal was solidified on a water-cooled copper plate. The bottom surface (the surface in contact with the water-cooled copper plate) of the obtained solidification test piece was machined to a diameter of about 5 mm × length of about 7 mm so as to include it, and used as a test piece, with the bottom surface (the surface in contact with the water-cooled copper plate) as the test surface. This test piece was resin-embedded so that the test surface was exposed, the test surface was mirror-polished, and the Vickers hardness of the polished surface was measured with a test force of 1.96 N in accordance with JIS Z2244:2009. The measurement results are shown together in Tables 1 to 3.

[0046] (Rust evaluation) The polished resin-embedded test piece prepared by the same procedure as the measurement of the above Vickers hardness was put into a beaker containing 500 ml of tap water and taken out, and then left to dry naturally for 24 hours. After natural drying, the presence or absence of rust was visually confirmed, and the rust was evaluated based on the following evaluation criteria. The evaluation results are shown together in Tables 1 to 3.

[0047] A: No rust is seen. NG: Rust is seen.

[0048] (Adsorbability evaluation) The solidification test piece obtained by the same procedure as the measurement of the above Vickers hardness was machined into a test piece with a diameter of about 5 × length of 7 mm, brought into contact with a ferrite magnet of 20 mm × 10 mm × 5 mm and lifted, and it was confirmed whether the test piece was adsorbed. Based on the following evaluation criteria, the adsorption property evaluation was carried out. The evaluation results are shown together in Tables 1 to 3.

[0049] A: Adsorbs to the ferrite magnet. NG: Does not adsorb to the ferrite magnet.

[0050]

Table 1

[0051]

Table 2

[0052]

Table 3

[0053] As is clear from the above results, according to the alloy of the example in which the essential components are blended within the specified range (see Table 1), sufficient compressive residual stress can be imparted when the workpiece is treated by wet shot peening, and the Vickers hardness range (750 HV or more and 1100 HV or less) can reduce the surface roughness of the workpiece after treatment. Furthermore, it has been clarified that it has adsorption to the magnet and can suppress rusting.

[0054] On the other hand, according to the alloy in which the blending amount of at least one of the essential components does not satisfy the specified range (see Table 2) or the alloy that does not contain all of the essential components (see Table 3), it does not have adsorption to the magnet, or rusting cannot be suppressed, or even if it has adsorption to the magnet and can suppress rusting, it has been clarified that sufficient compressive residual stress cannot be imparted when the workpiece is treated by wet shot peening, and the Vickers hardness range (750 HV or more and 1100 HV or less) cannot reduce the surface roughness of the workpiece after treatment.

[0055] Next, the following evaluations were conducted on the relationship between the Vickers hardness of the projectile, the compressive residual stress, and the surface roughness of the workpiece.

[0056] (Projectile of Example 1) 300 kg of ingot having the composition of Example No. 9 described in Table 1 was heated and melted at about 1600°C in an air atmosphere using a high-frequency melting furnace, pulverized by the gas atomization method, and the particle size was adjusted with a vibrating sieve machine to obtain the projectile of Example 1. The Vickers hardness of the projectile of Example 1 was 1034 HV as shown in Table 1, and the particle diameter (D50) was 45.8 μm.

[0057] (Projectile of Comparative Example 1 (zirconia projectile)) A zirconia projectile with a particle diameter (D50) of 50 μm was used as the projectile of Comparative Example 1. The Vickers hardness of the projectile of Comparative Example 1 was 1250 HV.

[0058] (Projectile of Comparative Example 2 (zirconia projectile)) A zirconia projectile with a particle diameter (D50) of 50 μm was used as the projectile of Comparative Example 2. The Vickers hardness of the projectile of Comparative Example 2 was 700 HV.

[0059] (Measurement of compressive residual stress) Slurries containing water and the projectile of Example 1 were prepared. Slurries containing water and the projectile of Comparative Example 1 were prepared. Slurries containing water and the projectile of Comparative Example 2 were prepared. The concentration of the projectile in each slurry was 5% by volume. As the workpiece, SCM415 (Vickers hardness of about 750 HV) subjected to carburizing and quenching treatment was used, and wet shot peening using each slurry prepared above was performed on this workpiece. For the wet shot peening, a wet blast apparatus manufactured by Marco Co., Ltd. was used. The conditions for the wet shot peening were a slurry projection pressure of 0.3 MPa and 0.4 MPa (Comparative Example 2 was 0.4 MPa only), and an area coverage of 600%. After the wet shot peening, the measurement of the compressive residual stress imparted to the workpiece was carried out. For the measurement of the compressive residual stress, an X-ray residual stress measuring device (μ-X360n) manufactured by Pulstec Industrial Co., Ltd. was used. The measurement results of the compressive residual stress using the projectile of Example 1 are shown in Fig. 1, the measurement results of the compressive residual stress using the projectile of Comparative Example 1 are shown in Fig. 2, and the measurement results of the compressive residual stress using the projectile of Comparative Example 2 are shown in Fig. 3.

[0060] (Measurement of surface roughness) After the wet shot peening, the surface roughness of the workpiece was measured with an objective lens magnification of ×50 using a shape analysis laser microscope "VK-X1000" (manufactured by Keyence Corporation). The surface roughness of the workpiece after the wet shot peening (slurry projection pressure of 0.4 MPa) using the projectile of Example 1 was Ra = 0.36 μm, and the surface roughness of the workpiece after the wet shot peening (slurry projection pressure of 0.4 MPa) using the projectile of Comparative Example 1 was Ra = 0.54 μm.

[0061] From the above results, it was confirmed that the Vickers hardness of the projectile has a relationship with the compressive residual stress imparted to the workpiece in wet shot peening and the surface roughness of the workpiece after the treatment. By using a projectile with a Vickers hardness of 750 HV or more and 1100 HV or less, it is possible to impart sufficient compressive residual stress to the workpiece in wet shot peening and to suppress the surface roughness of the workpiece to a small value.

Claims

1. A nickel-based alloy used as a projection material for shot peening, containing 8.7 mass% or more of Ni, 18 mass% or more and 26 mass% or less of Cr, 1.1 mass% or more and 2.3 mass% or less of C, 3 mass% or more and 5.5 mass% or less of Si, 3 mass% or more and 5.5 mass% or less of B, 10 mass% or more and 40 mass% or less of Fe, a nickel-based alloy.

2. Further containing 12 mass% or less of one or more selected from W, Mo, and Nb, the nickel-based alloy according to Claim 1.

3. containing 8.7 mass% or more of Ni, 18 mass% or more and 26 mass% or less of Cr, 1.1 mass% or more and 2.3 mass% or less of C, 3 mass% or more and 5.5 mass% or less of Si, 3 mass% or more and 5.5 mass% or less of B, 10 mass% or more and 40 mass% or less of Fe, a projection material for wet shot peening.

4. Further containing 12 mass% or less of one or more selected from W, Mo, and Nb, the projection material for wet shot peening according to Claim 3.

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