Ni-Cr-Mo precipitation-hardening alloys

Abstract

To provide a Ni-Cr-Mo type precipitation hardened type alloy which is excellent in wear resistance, corrosion resistance and machineability.SOLUTION: An Ni-Cr-Mo type precipitation hardened type alloy comprises: 18.0 mass% or greater and 26.0 mass% or smaller of Cr; 16.0 mass% or greater and 30.0 mass% or smaller of Mo; 0.10 mass% or greater and 1.0 mass% or smaller of C; 0.10 mass% or greater and 3.0 mass% or smaller of Al; and 2.0 mass% or smaller of Nb. A remainder of the alloy is formed of Ni and inevitable impurities. The alloy preferably has a metallographic structure comprising a matrix, and a γ' phase and a carbide dispersed in the matrix.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a precipitation hardened alloy containing Ni, Cr and Mo. [Background technology]

[0002] Engineering plastics generally have excellent mechanical strength and heat resistance. They are used in automobile parts, machine parts, electrical and electronic parts, etc. Products made of engineering plastics can be obtained by injection molding, extrusion molding, etc. Molding machine parts such as screws and cylinders require wear resistance against engineering plastics. These parts also require corrosion resistance against corrosive gases generated by melting engineering plastics.

[0003] Ni-based alloys are used in applications requiring wear resistance and corrosion resistance, and various improvements have been proposed for these Ni-based alloys intended for use in more severe environments.

[0004] Japanese Patent Publication No. 3983644 proposes an alloy in which borides are dispersed in a matrix mainly composed of Ni. These borides are hard and can contribute to the wear resistance of the alloy.

[0005] Japanese Patent No. 4816950 proposes a Ni-Cr-Mo alloy in which intermetallic compounds are dispersed in a matrix mainly composed of Ni. These intermetallic compounds contribute to the wear resistance of the alloy. In this alloy, Mo contributes to the corrosion resistance. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3983644 [Patent Document 2] Patent No. 4816950 Summary of the Invention [Problem to be solved by the invention]

[0007] In the alloy disclosed in Japanese Patent No. 3983644, borides precipitate during solidification. Even if this alloy is subjected to solution treatment, these borides are difficult to redissolve. Therefore, the hardness of this alloy before aging treatment is high. However, this alloy has poor machinability.

[0008] In the alloy disclosed in Japanese Patent No. 4816950, the intermetallic compounds contain a large amount of Mo. Therefore, the amount of Mo in the matrix of this alloy is insufficient. There is room for improvement in the corrosion resistance of this alloy.

[0009] An object of the present invention is to provide a Ni-Cr-Mo precipitation hardened alloy having excellent wear resistance, corrosion resistance and machinability. [Means for solving the problem]

[0010] The Ni-Cr-Mo precipitation hardened alloy according to the present invention has the following properties: Cr: 18.0 mass% or more and 26.0 mass% or less, Mo: 16.0% by mass or more and 30.0% by mass or less, C: 0.10% by mass or more and 1.0% by mass or less, Al: 0.10% by mass or more and 3.0% by mass or less, and Nb: 2.0% by mass or less The remainder is Ni and unavoidable impurities.

[0011] Preferably, the alloy has a metal structure including a matrix and γ' phase and carbides dispersed in the matrix. The matrix may contain Ni, Cr, and Mo. Preferably, the ratio of Cr in the matrix is ​​18.0% by mass or more and 26.0% by mass or less. Preferably, the ratio of Mo in the matrix is ​​14.0% by mass or more and 18.0% by mass or less.

[0012] The carbide may contain C, Cr, and Mo. Preferably, the Cr content in the carbide is 16.0 mass% or more and 23.0 mass% or less. Preferably, the Mo content in the carbide is 50.0 mass% or more and 58.0 mass% or less.

[0013] The matrix, γ' phase, and carbides may each contain Al and / or Nb. Preferably, the sum (P1+P2+P3+P4) of the ratio P1 of Al in the matrix, the ratio P2 of Nb in the matrix, the ratio P3 of Al in the γ' phase, and the ratio P4 of Nb in the γ' phase is greater than the sum (P5+P6) of the ratio P5 of Al in the carbides and the ratio P6 of Nb in the carbides. [Effects of the Invention]

[0014] In the Ni-Cr-Mo precipitation-hardened alloy according to the present invention, Al and Nb can be dissolved in Ni by solution treatment. Therefore, the metal structure after this solution treatment contains few Al compounds and Nb compounds. This alloy has excellent machinability. In this alloy, Al or Nb bonds with Ni by aging treatment, resulting in the precipitation of a γ' phase. Therefore, the alloy after this aging treatment has high hardness. This γ' phase contributes to the wear resistance of the alloy. Since this alloy contains C, carbides precipitate in the metal structure by solidification and aging treatment. These carbides contribute to the wear resistance of the alloy. Since this alloy contains sufficient amounts of Cr and Mo, even if Cr or Mo is consumed by carbide precipitation, sufficient amounts of Cr and Mo remain in the matrix. This alloy has excellent corrosion resistance. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an SEM image showing a cross section of a precipitation hardened alloy according to one embodiment of the present invention. [Figure 2] FIG. 2 is a photograph showing the results of electron diffraction of the material for the precipitation hardened alloy of FIG. [Figure 3] FIG. 3 is a photograph showing the results of electron beam diffraction of the precipitation hardened alloy of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below based on preferred embodiments.

[0017] [composition] The Ni-Cr-Mo precipitation hardened alloy according to the present invention has the following properties: Cr: 18.0 mass% or more and 26.0 mass% or less, Mo: 16.0% by mass or more and 30.0% by mass or less, C: 0.1% by mass or more and 1.0% by mass or less Al: 0.1 mass% or more and 3.0 mass% or less and Nb: 0.0 mass% or more and 2.0 mass% or less Preferably, the balance is Ni and unavoidable impurities.

[0018] [Metal structure] As shown in the SEM image in Figure 1, the metal structure of this alloy contains a matrix and numerous carbides. These carbides are dispersed in the matrix. Each carbide precipitates during solidification, solution treatment, aging treatment, etc. The metal structure of this alloy also contains numerous γ' phases. These γ' phases are fine and dispersed in the matrix. Each γ' phase can precipitate during aging treatment, etc.

[0019] Figure 2 is a photograph showing the results of electron diffraction of a material after solution treatment but before aging treatment. All visible light spots in Figure 2 are diffractions of γNi. Figure 3 is a photograph showing the results of electron diffraction of a precipitation hardened alloy immediately after aging treatment. The bright light spots in Figure 3 are diffractions of γNi. The faint light spot sandwiched between two adjacent bright light spots is diffraction of the γ' phase. As is clear from a comparison of Figures 2 and 3, no γ' phase is present in the material after solution treatment but before aging treatment.

[0020] The matrix contains Ni, Cr, and Mo. The matrix may contain C, Al, and Nb. The main components of the matrix are Ni, Cr, and Mo. In this matrix, Cr or Mo is solid-solved in Ni. Cr and Mo can contribute to the corrosion resistance of the alloy.

[0021] Carbides contain C, Cr, and Mo. Carbides may contain Ni, Al, and Nb. The main components of carbides are C, Cr, and Mo. Carbides are compounds of C with metals such as Cr and Mo. A typical carbide is MC (M is a metal element). Carbides can contribute to the wear resistance of the alloy.

[0022] The γ' phase is a Ni-Al compound or a Ni-Al-Nb compound. A typical Ni-Al compound is Ni3Al. A typical Ni-Al-Nb compound is Ni3(Al,Nb). The γ' phase can contribute to the hardness and wear resistance of the alloy. As described below, this γ' phase precipitates by aging treatment. The alloy before aging treatment contains almost no γ' phase. The hardness of the alloy before aging treatment is low. The alloy before aging treatment can be easily subjected to cutting processing, plastic processing, etc. This alloy has excellent machinability.

[0023] Chromium Cr dissolves in Ni in the matrix. This matrix has strong corrosion resistance against various acids. Cr combines with C during solidification of the alloy, precipitating carbides. Cr also combines with C during aging treatment, precipitating carbides. Carbides containing C and Cr have high hardness. These carbides can contribute to the wear resistance of the alloy.

[0024] The Cr content is preferably 18.0% by mass or more and 26.0% by mass or less. In an alloy with a Cr content of 18.0% by mass or more, Cr-containing carbides are sufficiently precipitated, and sufficient Cr is present in the matrix. From this perspective, the Cr content is more preferably 19.0% by mass or more, and particularly preferably 20.0% by mass or more. An alloy with a Cr content of 26.0% by mass or less can be obtained at low cost. From this perspective, the Cr content is more preferably 24.0% by mass or less, and particularly preferably 23.0% by mass or less.

[0025] [Molybdenum (Mo)] Mo dissolves in Ni in the matrix. This matrix has strong corrosion resistance against non-oxidizing acids. Mo combines with C during solidification of the alloy to precipitate carbides. Mo also combines with C through aging treatment to precipitate carbides. Carbides containing C and Mo have high hardness. These carbides can contribute to the wear resistance of the alloy. The carbides may contain C, Cr, and Mo.

[0026] The Mo content is preferably 16.0% by mass or more and 30.0% by mass or less. In an alloy with a content of 16.0% by mass or more, Mo-containing carbides are sufficiently precipitated, and sufficient Mo is present in the matrix. From this perspective, the Mo content is more preferably 17.0% by mass or more, and particularly preferably 18.0% by mass or more. An alloy with a content of 30.0% by mass or less can be obtained at low cost. From this perspective, the Mo content is more preferably 28.0% by mass or less, and particularly preferably 24.0% by mass or less.

[0027] [Carbon (C)] C combines with Cr and / or Mo during solidification of the alloy, causing carbide precipitation. C also combines with Cr and / or Mo during aging treatment, causing carbide precipitation. A large number of carbides are dispersed in the matrix. This alloy has high hardness. This alloy has excellent wear resistance.

[0028] The C content is preferably 0.10% by mass or more and 1.0% by mass or less. Alloys with a C content of 0.10% by mass or more have high hardness and excellent wear resistance. From this perspective, the C content is more preferably 0.15% by mass or more, and particularly preferably 0.20% by mass or more. Excess C precipitates excess carbides. The precipitation of excess carbides consumes excess Mo, resulting in a Mo deficiency in the matrix. Alloys with insufficient Mo in the matrix have poor corrosion resistance. The precipitation of excess carbides further impairs the toughness of the alloy. Products made of alloys with poor toughness are prone to chipping. From the perspectives of corrosion resistance and toughness, the C content is specified to be 1.0% by mass or less in the present invention. This content is more preferably 0.8% by mass or less, and particularly preferably 0.7% by mass or less.

[0029] [Aluminum (Al)] Al exists in alloys as both a solute atom and a compound. Solution treatment causes much Al to dissolve in Ni, and many Al compounds disappear. Alloys with fewer Al compounds have low hardness. These alloys are easy to cut. They are also easy to plastically work. When alloys are aged, Al precipitates numerous γ' phases. A typical γ' phase is Ni3Al. Numerous γ' phases are dispersed in the matrix. Alloys with these γ' phases have high hardness. These γ' phases contribute to the alloy's wear resistance. This alloy offers both machinability before aging and wear resistance after aging.

[0030] The Al content is preferably 0.10% by mass or more and 3.0% by mass or less. In an alloy with an Al content of 0.10% by mass or more, sufficient γ' phase can be precipitated. From this viewpoint, the Al content is more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more. From the viewpoint of corrosion resistance and toughness, the Al content is more preferably 2.7% by mass or less, and particularly preferably 2.3% by mass or less.

[0031] [Niobium (Nb)] Nb exists in alloys as both a solute atom and a compound. By solution treatment, much of the Nb dissolves in Ni, and many of the Nb compounds disappear. Alloys with fewer Nb compounds have low hardness. These alloys are easy to cut. They are also easy to plastically work. When alloys are aged, Nb precipitates numerous γ' phases. A typical γ' phase is Ni3(Al,Nb). Numerous γ' phases are dispersed in the matrix. Alloys with these γ' phases have high hardness. These γ' phases contribute to the wear resistance of the alloy. This alloy offers both good machinability before aging and good wear resistance after aging.

[0032] From the viewpoint of corrosion resistance and toughness, the Nb content is preferably 2.0 mass % or less, more preferably 1.7 mass % or less, and particularly preferably 1.3 mass % or less.

[0033] Nb is not an essential element, so the Nb content may be substantially zero. In alloys that do not contain Nb, the γ' phase of Al precipitates upon aging treatment.

[0034] [Cr in matrix] The ratio of Cr in the matrix is ​​preferably 18.0 mass% or more and 26.0 mass% or less. An alloy with this ratio of 18.0 mass% or more has excellent corrosion resistance. From the viewpoint of corrosion resistance, this ratio is more preferably 19.0 mass% or more, and particularly preferably 20.0 mass% or more. An alloy with this ratio of 26.0 mass% or less has excellent toughness. Therefore, the flexural strength of this alloy is high. From the viewpoint of flexural strength, this ratio is more preferably 25.0 mass% or less, and particularly preferably 24.0 mass% or less. The Cr ratio in the matrix is ​​the percentage of the mass of Cr contained in the matrix relative to the total mass of the matrix.

[0035] [Mo in matrix] The ratio of Mo in the matrix is ​​preferably 14.0 mass% or more and 18.0 mass% or less. Alloys with this ratio of 14.0 mass% or more have excellent corrosion resistance. From the viewpoint of corrosion resistance, this ratio is particularly preferably 15.0 mass% or more. Alloys with this ratio of 18.0 mass% or less have excellent toughness. Therefore, the flexural strength of these alloys is high. From the viewpoint of flexural strength, this ratio is particularly preferably 17.0 mass% or less. The ratio of Mo in the matrix is ​​the percentage of the mass of Mo contained in the matrix relative to the total mass of the matrix.

[0036] [Cr and Mo in carbides] It is preferable that the Cr ratio in the carbide is 16.0 mass% or more and 23.0 mass% or less, and the Mo ratio in the carbide is 50.0 mass% or more and 58.0 mass% or less. In alloys with Cr and Mo ratios within these ranges, the matrix contributes to corrosion resistance, and the carbide contributes to wear resistance. The Cr ratio in the carbide is the percentage of the mass of Cr contained in the carbide relative to the total mass of the carbide. The Mo ratio in the carbide is the percentage of the mass of Mo contained in the carbide relative to the total mass of the carbide.

[0037] [Al and Nb] As mentioned above, Al and Nb are dissolved in the matrix and are also contained in the γ' phase. Furthermore, Al and Nb can also be contained in carbides. It is preferable that the alloy satisfies the following mathematical formula (I): P1 + P2 + P3 + P4 > P5 + P6 (I) P1: Ratio of Al in the matrix (mass%) P2: Ratio of Nb in the matrix (mass%) P3: Ratio of Al in the γ' phase (mass%) P4: Ratio of Nb in the γ' phase (mass%) P5: Ratio of Al in carbide (mass%) P6: Ratio of Nb in carbide (mass%) In alloys satisfying this formula (I), the matrix contributes to corrosion resistance, and the γ' phase contributes to wear resistance. The ratio of Al to the matrix is ​​the percentage of the mass of Al contained in the matrix relative to the total mass of the matrix. The ratio of Nb to the matrix is ​​the percentage of the mass of Nb contained in the matrix relative to the total mass of the matrix. The ratio of Al to the γ' phase is the percentage of the mass of Al contained in the γ' phase relative to the total mass of the γ' phase. The ratio of Nb to the γ' phase is the percentage of the mass of Nb contained in the γ' phase relative to the total mass of the γ' phase. The ratio of Al to the carbides is the percentage of the mass of Al contained in the carbides relative to the total mass of the carbides. The ratio of Nb to the carbides is the percentage of the mass of Nb contained in the carbides relative to the total mass of the carbides.

[0038] [Carbide ratio] From the viewpoint of wear resistance, the area fraction PC of carbides in the metal structure is preferably 10% or more, more preferably 11% or more, and particularly preferably 12% or more. From the viewpoint of corrosion resistance and toughness, this area fraction PC is preferably 30% or less, more preferably 28% or less, and particularly preferably 26% or less. The area fraction PC is determined by the cross section (area of ​​13600 μm) of the alloy. 2 ) is observed under a microscope and calculated. Image processing software can be used for the calculation.

[0039] [Manufacturing method] An example of a manufacturing method for the precipitation-hardened alloy according to the present invention will be described below. In this manufacturing method, a raw material having a controlled composition is first prepared. The raw material may be obtained by melting or powder metallurgy.

[0040] In powder metallurgy, powder can be obtained by atomization. A preferred atomization method is gas atomization. In gas atomization, raw materials are placed in a container (quartz crucible) with a small hole at the bottom. The raw materials are heated and melted in a high-frequency induction furnace in an argon gas or nitrogen gas atmosphere. Argon gas or nitrogen gas is sprayed onto the raw materials flowing out of the small hole. The raw materials are rapidly cooled and solidified, yielding powder.

[0041] This powder is classified as necessary. The classified powder is filled into a capsule made of carbon steel. The inside of this capsule is evacuated and then sealed to obtain a billet. This billet is then subjected to HIP (hot isostatic pressing). The preferred pressure for HIP is 50 MPa or more and 300 MPa or less, and the preferred sintering temperature is 1000°C or more and 1350°C or less. A green body (raw material) is obtained by HIP.

[0042] Next, this material is subjected to solution treatment. In solution treatment, the material is held in an environment of 1000°C to 1250°C for 1 to 6 hours. The material is then cooled. Typical cooling methods are water cooling and air cooling. Solution treatment creates a grain boundary and a matrix. Carbide precipitates at the grain boundary. There is almost no γ' phase in this material. This material has low hardness. This material is then machined.

[0043] Next, this material is subjected to aging treatment. In aging treatment, the material is held in an environment of 600°C to 800°C for 2 to 40 hours. After that, the material is cooled. Typically, the cooling method is furnace cooling or air cooling. This aging treatment results in a precipitation hardened alloy. This alloy contains γ' phase dispersed in the matrix. This alloy has high hardness. [Example]

[0044] The effects of the present invention will be clarified by the following examples, but the present invention should not be construed as being limited based on the descriptions of these examples.

[0045] [Example 1] The raw materials were heated in an alumina crucible in an argon gas atmosphere by high-frequency induction heating. The raw materials were melted by this heating to obtain a molten metal. The molten metal was dropped from a nozzle with a diameter of 5 mm located below the crucible. Nitrogen gas was sprayed onto the molten metal to obtain a powder. The powder was classified to adjust the particle size to 500 μm or less. The composition of this powder is shown in Table 1 below. The powder was filled into a capsule made of carbon steel with a diameter of 100 mm and a height of 100 mm. The capsule was evacuated under vacuum. The capsule was sealed to obtain a billet. This billet was subjected to HIP molding. The HIP temperature was 1150°C. A rod-shaped compact was obtained by HIP. This compact was subjected to solution treatment and aging treatment to obtain the precipitation-hardened alloy of Example 1.

[0046] [Examples 2-18 and Comparative Examples 1-8] Except for changing the composition of the raw materials, the compacts (precipitation hardened alloys) according to Examples 2 to 18 and Comparative Examples 1 to 8 were obtained in the same manner as in Example 1. The compositions of the respective alloys are shown in Tables 1 and 2 below.

[0047] [Hardness] The compact (precipitation hardened alloy) was polished to obtain a test piece with parallel upper and lower surfaces. The Rockwell hardness H1 of this test piece was measured and rated according to the following criteria. A: Hardness is 40HRC or more. B: Hardness is less than 40HRC. The results are shown in Tables 1 and 2 below.

[0048] [Hardness increase] The Rockwell hardness H2 of the compact before aging treatment was measured, and the difference from the hardness H1 (ΔH=H1−H2) was calculated. The hardness was rated according to the following criteria. A: The difference ΔH is 6 or more. B: The difference ΔH is less than 6. The results are shown in Tables 1 and 2 below.

[0049] [Corrosion resistance] Test pieces were cut from the compact (precipitation hardened alloy). The size of the test pieces was 10 mm x 10 mm x 15 mm. The mass of the test pieces was measured. Four test pieces were prepared and immersed in a 10% aqueous solution of hydrochloric acid, a 10% aqueous solution of nitric acid, a 10% aqueous solution of sulfuric acid, and a 10% aqueous solution of hydrofluoric acid for 10 hours, respectively. The temperature of these aqueous solutions was 40°C. Furthermore, the mass of the test pieces was measured and the mass loss was calculated. They were ranked according to the following criteria. A: The loss rate for all four test pieces is 1.0 g / m2 / h or less. B: The reduction in any of the four test pieces is greater than 1.0 g / m2 / h. The results are shown in Tables 1 and 2 below.

[0050] [Wear resistance] Test pieces were cut from the compact (precipitation hardened alloy). The size of the test pieces was 7 mm x 25 mm x 50 mm. The test pieces were subjected to a test using an Ohkoshi rapid wear tester. The test conditions were as follows: Mating material: SCM420 Wear rate in high speed range: 2.38 m / sec Final load: 6.3kgf Lubrication: None Temperature: room temperature The width of the wear scar obtained in the test was measured, and the wear volume was calculated. The specific wear amount was calculated by dividing this wear volume by the product of the wear distance and the final load. The results were rated according to the following criteria. A: Specific wear volume is 1.0 x 10 -7 mm 2 / kg or less. B: Specific wear volume is 1.0 x 10 -7 mm 2 / kg or greater.

[0051] [Transverse rupture strength] Test pieces were cut from the compact (precipitation hardened alloy). The size of the test pieces was 2 mm x 2 mm x 20 mm. The test pieces were subjected to a three-point bending test. The distance between the supports was 10 mm. The test pieces were graded according to the following criteria. A: Transverse rupture strength is 1.5 GPa or more. B: The transverse rupture strength is less than 1.5 GPa. The results are shown in Tables 1 and 2 below.

[0052] [Table 1]

[0053] [Table 2]

[0054] As shown in Tables 1 and 2, the precipitation hardened alloys of the examples are excellent in various performances. From these evaluation results, the superiority of the present invention is clear. [Industrial Applicability]

[0055] The Ni-Cr-Mo precipitation hardened alloys described above are suitable for a variety of products obtained through machining.

Claims

1. Cr: 18.0% by mass or more and 26.0% by mass or less, Mo: 16.0% by mass or more and 30.0% by mass or less, C: 0.10% by mass or more and 1.0% by mass or less, Al: 0.10% by mass or more and 3.0% by mass or less, and Nb: 2.0% by mass or less Contains A Ni-Cr-Mo precipitation hardening alloy with the balance being Ni and unavoidable impurities.

2. The alloy has a metal structure including a matrix and a γ' phase and carbides dispersed in the matrix, The matrix contains Ni, Cr, and Mo, The ratio of Cr in the matrix is ​​18.0 mass% or more and 26.0 mass% or less, 2. The precipitation hardened alloy according to claim 1, wherein the ratio of Mo in the matrix is ​​14.0 mass % or more and 18.0 mass % or less.

3. The carbide contains C, Cr, and Mo, The ratio of Cr in the carbide is 16.0 mass% or more and 23.0 mass% or less, 3. The precipitation hardened alloy according to claim 2, wherein the ratio of Mo in the carbides is 50.0 mass % or more and 58.0 mass % or less.

4. each of the matrix, the γ' phase, and the carbides contains Al and / or Nb; 4. The precipitation hardened alloy according to claim 2, wherein the sum (P1 + P2 + P3 + P4) of the ratio P1 of Al in the matrix, the ratio P2 of Nb in the matrix, the ratio P3 of Al in the γ' phase, and the ratio P4 of Nb in the γ' phase is greater than the sum (P5 + P6) of the ratio P5 of Al in the carbides and the ratio P6 of Nb in the carbides.

5. A steel sheet having a metal structure including a matrix and a γ' phase and carbides dispersed in the matrix, 2. The precipitation hardened alloy according to claim 1, wherein the area fraction PC of the carbides is 10% or more and 30% or less.

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