Co-BASED ALLOY AND POWDER THEREOF

Abstract

To provide a Co-based alloy that exhibits a superior balance of corrosion resistance, wear resistance, and hardness.SOLUTION: A Co-based alloy comprising: C: 1.50 mass% or more and 3.00 mass% or less, Cr: 25.0 mass% or more and 34.0 mass% or less, W: 10.0 mass% or more and 15.0 mass% or less, Si: 0.01 mass% or more and 2.00 mass% or less, Mn: 0.01 mass% or more and 1.00 mass% or less, Ni: more than 15.0 mass% and 35.0 mass% or less, Fe: 0 mass% or more and 10.00 mass% or less, and Mo: 0 mass% or more and 15.00 mass% or less, the remainder being Co and unavoidable impurities. The Co-based alloy has a metal structure including a matrix and carbides dispersed in the matrix.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This specification discloses a Co-based alloy suitable for methods such as ingot manufacturing, powder metallurgy, powder cladding, laser cladding, and powder extrusion. [Background technology]

[0002] Co-based alloys generally have excellent corrosion resistance, and various improvements to these Co-based alloys have been proposed.

[0003] Japanese Patent Application Laid-Open Publication No. 2001-288521 discloses a Co-based alloy containing C, Si, Cr, W, Fe, Ni, Mo, and W. The metal microstructure of this Co-based alloy contains eutectic carbides dispersed in a matrix. The eutectic carbides are granular or lumpy. The grain size of the eutectic carbides is 30 μm or less. This metal microstructure is achieved by plastic working. This Co-based alloy has excellent corrosion resistance.

[0004] JP 2016-7632 A discloses a Co-based alloy containing Ni, Mn, Fe, C, Si, Cr, and Mo. These elements can contribute to cavitation erosion resistance and further to toughness. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2001-288521 A [Patent Document 2] JP 2016-7632 A Summary of the Invention [Problem to be solved by the invention]

[0006] The Co-based alloy disclosed in JP 2001-288521 A leaves room for improvement in wear resistance, while the Co-based alloy disclosed in JP 2016-7632 A has insufficient hardness.

[0007] The present applicant intends to provide a Co-based alloy that has an excellent balance of corrosion resistance, wear resistance, and hardness. [Means for solving the problem]

[0008] The Co-based alloy disclosed in this specification is C: 1.50% by mass or more and 3.00% by mass or less, Cr: 25.0% by mass or more and 34.0% by mass or less, W: 10.0% by mass or more and 15.0% by mass or less, Si: 0.01 mass% or more and 2.00 mass% or less, Mn: 0.01% by mass or more and 1.00% by mass or less, Ni: more than 15.0 mass% and 35.0 mass% or less, Fe: 0% by mass or more and 10.00% by mass or less, and Mo: 0 mass% or more and 15.00 mass% or less, The remainder is Co and unavoidable impurities. This Co-based alloy has a metal structure including a matrix and carbides dispersed in the matrix. Preferably, the volume fraction Pc of these carbides is 12.0% or more and 50.0% or less.

[0009] The powder material disclosed in this specification is a Co-based alloy. C: 1.50% by mass or more and 3.00% by mass or less, Cr: 25.0% by mass or more and 34.0% by mass or less, W: 10.0% by mass or more and 15.0% by mass or less, Si: 0.01 mass% or more and 2.00 mass% or less, Mn: 0.01% by mass or more and 1.00% by mass or less, Ni: more than 15.0 mass% and 35.0 mass% or less, Fe: 0% by mass or more and 10.00% by mass or less, and Mo: 0 mass% or more and 15.00 mass% or less, The remainder of the Co-based alloy is Co and unavoidable impurities. The Co-based alloy has a metal structure including a matrix and carbides dispersed in the matrix. Preferably, the volume fraction Pc of these carbides is 12.0% or more and 50.0% or less. [Effects of the Invention]

[0010] This Co-based alloy has sufficient hardness and toughness, and also has excellent corrosion resistance. DETAILED DESCRIPTION OF THE INVENTION

[0011] The Co-based alloy disclosed herein contains C, Cr, W, Si, Mn, and Ni. The alloy may further contain Fe or Mo. The alloy may contain both Fe and Mo. The balance is Co and unavoidable impurities. The metal structure of the Co-based alloy contains a matrix and carbides dispersed in the matrix. The role of each element in the alloy will be explained in detail below.

[0012] [Cobalt (Co)] Co is the main component of the matrix. At room temperature, the stable crystal structure of Co alone is a hexagonal close-packed (hcp) structure. At temperatures of 690 K or higher, the stable crystal structure of Co alone is a face-centered cubic (fcc) structure. In the Co-based alloy according to this embodiment, the matrix has a γ phase and may also have an ε phase. The crystal structure of the γ phase is fcc. The crystal structure of the ε phase is hcp.

[0013] [Carbon (C)] C combines with Cr and W to form carbides. These carbides can contribute to the high hardness of Co-based alloys. From this viewpoint, the C content is preferably 1.50% by mass or more, more preferably 1.75% by mass or more, and particularly preferably 2.00% by mass or more. Excess C impairs the toughness of this alloy. From the viewpoint of excellent toughness, the C content is preferably 3.00% by mass or less, more preferably 2.90% by mass or less, and particularly preferably 2.80% by mass or less.

[0014] Chromium Cr combines with C to form carbides. These carbides can contribute to the room temperature hardness, high temperature hardness, wear resistance, and corrosion resistance of the Co-based alloy. From these viewpoints, the Cr content is preferably 25.0 mass% or more, more preferably 26.0 mass% or more, and particularly preferably 27.0 mass% or more. Excess Cr impairs the toughness of this alloy. From the viewpoint of toughness, the Cr content is preferably 34.0 mass% or less, more preferably 32.0 mass% or less, and particularly preferably 31.0 mass% or less.

[0015] [Tungsten (W)] W combines with C to form carbides. These carbides can contribute to the high-temperature hardness and wear resistance of Co-based alloys. From these viewpoints, the W content is preferably 10.0% by mass or more, more preferably 10.5% by mass or more, and particularly preferably 11.0% by mass or more. Excess W impairs the toughness of this alloy. From the viewpoint of toughness, the W content is preferably 15.0% by mass or less, more preferably 14.5% by mass or less, and particularly preferably 14.0% by mass or less.

[0016] [Silicon (Si)] Silicon contributes to the corrosion resistance and machinability of Co-based alloys. From this viewpoint, the Si content is preferably 0.01% by mass or more, more preferably 0.50% by mass or more, and particularly preferably 0.90% by mass or more. Excessive silicon impairs the toughness of the alloy. From the viewpoint of toughness, the Si content is preferably 2.00% by mass or less, more preferably 1.50% by mass or less, and particularly preferably 1.30% by mass or less.

[0017] [Manganese (Mn)] Mn can contribute to the toughness of Co-based alloys. From this viewpoint, the Mn content is preferably 0.01% by mass or more, more preferably 0.15% by mass or more, and particularly preferably 0.20% by mass or more. Excess Mn reduces the strength of this alloy. From the viewpoint of strength, the Mn content is preferably 1.00% by mass or less, more preferably 0.80% by mass or less, and particularly preferably 0.50% by mass or less.

[0018] [Nickel (Ni)] Ni is an extremely important element in this Co-based alloy. Ni dissolves in the matrix and contributes to the corrosion resistance of this alloy. In particular, Ni contributes to corrosion resistance to hydrochloric acid and hydrofluoric acid. According to the findings of the present inventors, Ni can also dissolve in the matrix and contribute to the wear resistance of this alloy. From these perspectives, the Ni content is preferably greater than 15.0 mass%, more preferably 16.0 mass% or more, and particularly preferably 17.0 mass% or more. Excess Ni cannot overcome the effect of improving hardness due to carbide formation, resulting in low hardness of the Co-based alloy. From the perspective of high hardness of the alloy, the Ni content is preferably 35.0 mass% or less, more preferably 34.0 mass% or less, and particularly preferably 33.0 mass% or less.

[0019] [Iron (Fe)] Fe can contribute to the workability of Co-based alloys. From this viewpoint, the Fe content is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and particularly preferably 0.05% by mass or more. Excess Fe impairs the corrosion resistance of this alloy. From the viewpoint of corrosion resistance, the Fe content is preferably 10.0% by mass or less, more preferably 5.0% by mass or less, and particularly preferably 2.0% by mass or less. The Co-based alloy may have a composition that is substantially free of Fe. In other words, the preferred Fe content is 0% by mass or more and 10.0% by mass or less.

[0020] [Molybdenum (Mo)] Mo dissolves in the matrix. Mo further combines with C to form carbides. According to the findings of the present inventors, Mo dissolved in the matrix suppresses matrix elution in hydrochloric acid and hydrofluoric acid environments. According to the findings of the present inventors, Mo carbides contribute to the high hardness, wear resistance, and corrosion resistance of Co-based alloys. From these viewpoints, the Mo content is preferably 0.01% by mass or more, more preferably 0.50% by mass or more, and particularly preferably 1.00% by mass or more. Excess Mo impairs the toughness of the alloy. From the viewpoint of toughness, the Mo content is preferably 15.00% by mass or less, more preferably 10.00% by mass or less, and particularly preferably 6.00% by mass or less. The Co-based alloy may have a composition that is substantially free of Mo. In other words, the Mo content is preferably 0% by mass or more and 15.0% by mass or less.

[0021] Oxygen In this Co-based alloy, O is an unavoidable impurity. From the viewpoint of the corrosion resistance of the alloy, the mass content of O is preferably 200 ppm or less, more preferably 150 ppm or less, and particularly preferably 100 ppm or less.

[0022] [Aluminum (Al)] In this Co-based alloy, Al is an unavoidable impurity. Al can combine with Ni or Ti to form an intermetallic compound. This intermetallic compound impairs the toughness of the alloy. From the viewpoint of toughness, the Al content is preferably 0.50 mass% or less, more preferably 0.40 mass% or less, and particularly preferably 0.35 mass% or less.

[0023] [Titanium (Ti)] In this Co-based alloy, Ti is an unavoidable impurity. Ti can combine with Ni or Al to form an intermetallic compound. This intermetallic compound impairs the toughness of the alloy. From the viewpoint of toughness, the Ti content is preferably 0.50 mass% or less, more preferably 0.40 mass% or less, and particularly preferably 0.35 mass% or less.

[0024] [carbide] Examples of carbides that can be contained in the metallographic structure of this Co-based alloy include M6C-based carbides, M7C3-based carbides, and M23C6-based carbides. Examples of M6C-based carbides include Co3W3C. Examples of M7C3-based carbides include Cr7C3. Examples of M23C6-based carbides include Cr23C6. The metallographic structure may include all of M6C-based carbides, M7C3-based carbides, and M23C6-based carbides, or may include any two or any one of them.

[0025] As described above, this Co-based alloy contains an appropriate amount of Ni. This Ni can contribute to the corrosion resistance of the Co-based alloy. On the other hand, Ni can cause the Co-based alloy to have low hardness. In this embodiment, carbides can compensate for the decrease in hardness caused by Ni.

[0026] M6C-based carbides, M7C3-based carbides, and M23C6-based carbides are resistant to elution in hydrochloric acid and hydrofluoric acid. Co-based alloys containing appropriate amounts of these carbides have excellent corrosion resistance. From the viewpoint of corrosion resistance, the total volume fraction Pc of M6C-based carbides, M7C3-based carbides, and M23C6-based carbides relative to the entire metal structure is preferably 12.0% or more, more preferably 15.0% or more, and particularly preferably 20.0% or more. Excessive carbides impair the toughness of the alloy. From the viewpoint of toughness, the volume fraction Pc is preferably 50.0% or less, more preferably 40.0% or less, and particularly preferably 30.0% or less. The volume fraction Pc (%) is calculated using the following formula: Pc = Xc 100 In this formula, Xc is the volume ratio of carbide. The volume ratio Xc is calculated from an image obtained by taking a backscattered electron image of the cross-sectional structure of the compact (sintered compact). Image analysis software is used for this calculation. The volume ratio Xc is calculated within the crystal grains, avoiding the grain boundaries.

[0027] [Alloy manufacturing] This Co-based alloy can be produced by melting, casting, or powder metallurgy. From the viewpoint of toughness of this alloy, powder metallurgy is preferred. Powders used in powder metallurgy can be obtained by atomization, pulverization, or the like. The atomization method is preferred.

[0028] [Powder] The present specification also relates to powders, and the material of the powders according to the present invention is the Co-based alloy described above. [Example]

[0029] The effects of the present invention will be clarified below by examples, but the present invention should not be construed as being limited based on the descriptions of these examples.

[0030] [Example 1] A raw metal having the composition shown in Table 1 was melted to obtain a molten metal. This molten metal was then melted in an inert gas atmosphere and subjected to nitrogen gas atomization to obtain a powder. This powder was then classified to adjust the particle size to 500 μm or less. This powder was then filled into a capsule, and the capsule was sealed. This powder was then subjected to hot isostatic pressing (HIP) at 1170°C to obtain the bulk of Example 1.

[0031] [Examples 2-13 and Comparative Examples 1-12] Bulks of Examples 2-13 and Comparative Examples 1-12 were obtained in the same manner as in Example 1, except that raw metals having the compositions shown in Tables 1 and 3 were used.

[0032] [Example 14] The raw metals were subjected to an arc melting process to obtain bulks having the compositions shown in Table 2.

[0033] [Examples 15-17] The bulks of Examples 15 to 17 were obtained in the same manner as in Example 14, except that different raw metals were used, and the compositions of these bulks are shown in Table 2 below.

[0034] [Hardness] The bulk Rockwell hardness (HRC) was measured, and the results are shown in Tables 1-3 below. Co-based alloys with a hardness of 45 HRC or greater are preferred.

[0035] [Wear resistance] A test piece was cut out from the bulk. The size of this test piece was 19 mm x 41 mm x 6 mm. This test piece was set in an Ohkoshi type abrasion tester, and the specific wear rate was measured. The measurement conditions were as follows: Ring: SCM420 Wear rate: 0.78m / sec Wear distance: 200m Load: 61.8N Lubrication: None Temperature: room temperature The results are shown in Table 1-3 below. The specific wear rate was 5.0 x 10 -7 mm 2 / kg or less is preferred.

[0036] [Shock Value] Test pieces (10R2mmC notch) were obtained from the bulk. These test pieces were subjected to a Charpy impact test to measure the impact value. The results are shown in Table 1-3 below. The impact value was 5J / cm 2 The Co-based alloy having the above properties is excellent in toughness.

[0037] [Corrosion resistance] Test pieces (10 mm x 10 mm x 14 mm) were obtained from the bulk. These test pieces were subjected to a corrosion resistance test under the following test conditions. Solution: 10% hydrofluoric acid aqueous solution Temperature: 40℃ Duration: 10 hours The corrosion rate was calculated by dividing the corrosion weight loss by the surface area of ​​the test piece before the test and the time. The results are shown in Table 1-3 below. 2 A Co-based alloy having a melting point of 0.1 .mu.m or less is preferred.

[0038] [Table 1]

[0039] [Table 2]

[0040] [Table 3]

[0041] The alloy of Comparative Example 1 had too little C, resulting in a small carbide volume fraction Pc and insufficient hardness. The alloy of Comparative Example 2 had too much C, resulting in a large carbide volume fraction Pc and insufficient toughness. The alloy of Comparative Example 3 had too little Cr, resulting in insufficient hardness. The alloy of Comparative Example 3 also had insufficient corrosion resistance. The alloy of Comparative Example 4 had too much Cr, resulting in insufficient toughness. The alloy of Comparative Example 5 had too little W, resulting in insufficient hardness. The alloy of Comparative Example 6 had too much W, resulting in insufficient toughness. The alloy of Comparative Example 7 had too much Si, resulting in insufficient toughness. The alloy of Comparative Example 8 had too much Mn, resulting in insufficient toughness. The alloy of Comparative Example 9 had too little Ni, resulting in insufficient wear resistance. The alloy of Comparative Example 9 also had insufficient corrosion resistance. The alloy of Comparative Example 10 had too much Ni, resulting in insufficient hardness. The alloy of Comparative Example 11 contained an excess of Fe, and therefore did not have sufficient corrosion resistance. The alloy of Comparative Example 12 contained an excess of Mo, and therefore had a large carbide volume fraction Pc, and therefore did not have sufficient toughness.

[0042] The alloys according to Examples 1-17 have an excellent balance of various properties.

[0043] From these results, the superiority of the present invention is clear. [Industrial Applicability]

[0044] The Co-based alloys described above are suitable for a variety of applications requiring corrosion resistance.

Claims

1. C: 1.50% by mass or more and 3.00% by mass or less, Cr: 25.0% by mass or more and 34.0% by mass or less, W: 10.0% by mass or more and 15.0% by mass or less, Si: 0.01% by mass or more and 2.00% by mass or less, Mn: 0.01% by mass or more and 1.00% by mass or less, Ni: more than 15.0% by mass and not more than 35.0% by mass, Fe: 0% by mass or more and 10.00% by mass or less, and Mo: 0% by mass or more and 15.00% by mass or less, It contains The balance is Co and unavoidable impurities, A Co-based alloy having a metal structure including a matrix and carbides dispersed in the matrix.

2. The Co-based alloy according to claim 1, wherein the volume fraction Pc of the carbides is 12.0% or more and 50.0% or less.

3. The material is a Co-based alloy, The Co-based alloy is C: 1.50% by mass or more and 3.00% by mass or less, Cr: 25.0% by mass or more and 34.0% by mass or less, W: 10.0% by mass or more and 15.0% by mass or less, Si: 0.01% by mass or more and 2.00% by mass or less, Mn: 0.01% by mass or more and 1.00% by mass or less, Ni: more than 15.0% by mass and not more than 35.0% by mass, Fe: 0% by mass or more and 10.00% by mass or less, and Mo: 0% by mass or more and 15.00% by mass or less, It contains The balance is Co and unavoidable impurities, The powder is a Co-based alloy having a metal structure including a matrix and carbides dispersed in the matrix.

4. The powder according to claim 3, wherein the volume fraction Pc of the carbide is 12.0% or more and 50.0% or less.

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