Fe-based alloy for sintering

Abstract

To provide a powder that can give a sintered body having excellent meltability and high hardness.SOLUTION: A powder is made from an Fe-based alloy. The Fe-based alloy contains B: 4.0 mass% or more and 7.0 mass% or less, C: 0.01 mass% or more and 0.80 mass% or less, and Cr: 0 mass% or more and 20.0 mass% or less, with the balance being Fe and inevitable impurities. From the powder, various sintered bodies can be obtained.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an Fe-based alloy suitable for sintering, and further to a powder made from this alloy. [Background technology]

[0002] Examples of methods for obtaining a compact from powder include thermal spraying, three-dimensional additive manufacturing, and sintering. In thermal spraying and three-dimensional additive manufacturing, a compact is obtained by a liquid-phase reaction. On the other hand, in sintering, a compact (sintered body) is obtained by a solid-phase reaction. Examples of sintering methods include spark plasma sintering, hot pressing, hot isostatic pressing, and metal injection molding. Japanese Patent Application Laid-Open Publication No. 2006-131952 discloses an Fe-based alloy powder suitable for sintering. A highly hard sintered body can be obtained from this Fe-based alloy powder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-131952 A Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional Fe-based alloys generally have high melting points. To obtain a sintered body from this alloy, the powder must be heated at high temperatures. This heating requires a large amount of energy. Furthermore, this heating requires equipment (such as a furnace) that can withstand high temperatures. Therefore, there is a demand for Fe-based alloys that can be sintered at relatively low temperatures.

[0005] An object of the present invention is to provide an alloy powder that can be easily sintered and that can give a sintered body with high hardness. [Means for solving the problem]

[0006] The Fe-based alloy for sintering according to the present invention is B: 4.0% by mass or more and 7.0% by mass or less, C: 0.01% by mass or more and 0.80% by mass or less, and Cr: 0 mass% or more and 20.0 mass% or less The remainder is Fe and unavoidable impurities.

[0007] In another aspect, the present invention relates to a powder for sintering. The powder is made of an Fe-based alloy. The Fe-based alloy comprises: B: 4.0% by mass or more and 7.0% by mass or less, C: 0.01% by mass or more and 0.80% by mass or less, and Cr: 0 mass% or more and 20.0 mass% or less The remainder is Fe and unavoidable impurities.

[0008] According to yet another aspect, the present invention relates to a sintered body. The material of this sintered body is an Fe-based alloy. This Fe-based alloy is B: 4.0% by mass or more and 7.0% by mass or less, C: 0.01% by mass or more and 0.80% by mass or less, and Cr: 0 mass% or more and 20.0 mass% or less The remainder is Fe and unavoidable impurities. [Effects of the Invention]

[0009] The Fe-based alloy according to the present invention has a low solidus temperature, and a highly hard compact can be obtained from powder made of this Fe-based alloy. DETAILED DESCRIPTION OF THE INVENTION

[0010] The sintering powder according to the present invention is an aggregate of a large number of particles. The material of these particles is an Fe-based alloy. This Fe-based alloy is B: 4.0% by mass or more and 7.0% by mass or less, C: 0.01% by mass or more and 0.8% by mass or less, and Cr: 0 mass% or more and 20.0 mass% or less The remainder is Fe and unavoidable impurities.

[0011] [Metal structure] In the Fe-based alloy according to the present invention, a large number of FeB compounds are dispersed in a matrix of a eutectic structure of "FeB + αFe." This Fe-based alloy has a low solidus temperature. This Fe-based alloy is easily sinterable. A sintered body can be obtained from this powder at a relatively low temperature. This sintered body can be obtained with low energy. This sintering can be performed in a relatively simple furnace.

[0012] The particle size of the dispersed Fe2B compound is approximately 5 μm. The particle size of the Fe2B in the eutectic structure is 1 μm or less. The dispersed Fe2B compound is hard. The Fe2B in the eutectic structure is also hard. Because the alloy contains two types of Fe2B that are different in size and both hard, a hard sintered body can be obtained from this alloy. In this structure, C is also dissolved in αFe. This solid solution also allows the sintered body to achieve high hardness. The hardness of this sintered body is extremely high compared to the hardness of general steel materials. This sintered body has excellent wear resistance. The composition of this Fe-based alloy is described in detail below.

[0013] [Boron (B)] An Fe-based alloy containing a sufficient amount of B can have a eutectic structure rather than an excessive hypoeutectic structure. An Fe-based alloy with a eutectic structure has a low melting point. In other words, an Fe-based alloy containing a sufficient amount of B has excellent melting properties. Furthermore, B combines with Fe to form Fe2B. This Fe2B is hard. An Fe-based alloy containing a sufficient amount of B can produce a sintered body containing a sufficient amount of Fe2B. This sintered body has excellent wear resistance. From the viewpoints of the melting properties of the Fe-based alloy and the wear resistance of the sintered body, the B content is preferably 4.0 mass% or more, more preferably 4.5 mass% or more, and particularly preferably 4.8 mass% or more.

[0014] An Fe-based alloy containing a small amount of B can have a eutectic structure, rather than an excessive hypereutectic structure. An Fe-based alloy with a eutectic structure has a low melting point. In other words, an Fe-based alloy containing a small amount of B has excellent melting properties. A sintered body containing an appropriate amount of FeB can be obtained from an Fe-based alloy containing a small amount of B. This sintered body has excellent toughness. Furthermore, an Fe-based alloy containing a small amount of B suppresses the release of B from αFe. A sintered body with suppressed B release has high hardness and excellent wear resistance. From the viewpoints of the melting properties of the Fe-based alloy and the toughness and wear resistance of the sintered body, the B content is preferably 7.0% by mass or less, more preferably 6.5% by mass or less, and particularly preferably 6.2% by mass or less.

[0015] [Carbon (C)] C dissolves in the Fe matrix, contributing to solid-solution strengthening. Fe-based alloys containing sufficient C can produce sintered bodies with high hardness and excellent wear resistance.

[0016] According to the findings of the present inventors, it has been found that C unexpectedly contributes to the material yield during powder production. The reason for this is presumably that C deoxidizes the molten alloy, lowering its viscosity and reducing adhesion of the molten alloy to the refractories of the furnace wall.

[0017] During powder production, gas components dissolved in the molten alloy gasify during the solidification process. This gasification can cause pores to form inside the particles. In a sintered body obtained from a powder with pores, the gas from the pores remains. It is difficult to obtain a dense sintered body from this powder. According to the findings of the present inventors, C can surprisingly suppress these pores. This is presumably because C deoxidizes the molten alloy, removing the gas components from the molten alloy and resulting in a powder with fewer pores. A dense sintered body can be formed from a powder with fewer pores, that is, a powder that does not contain a large amount of gas.

[0018] From these viewpoints, the C 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.

[0019] A sintered body having an excess of C has poor toughness. From the viewpoint of toughness, the C content is preferably 0.80 mass % or less, more preferably 0.50 mass % or less, and particularly preferably 0.30 mass % or less.

[0020] The C content is affected by the raw materials selected. When an alloy is obtained using inexpensive raw materials containing a certain amount of C as an impurity, and the aforementioned content is achieved by the C contained in the raw materials alone, C does not need to be intentionally added. When the C contained in the raw materials alone does not reach the aforementioned lower limit, the aforementioned content can be achieved by intentionally adding C. Furthermore, even when raw materials containing almost no C (generally expensive raw materials) are used, the aforementioned content can be achieved by intentionally adding C. As long as the total C content is within the above range, the aforementioned effects can be achieved.

[0021] Chromium Cr contributes to the corrosion resistance of the sintered body. Cr is added to the alloy when corrosion resistance is required for the sintered body. Therefore, Cr is not an essential element. In other words, the chromium content may be zero. From the viewpoint of corrosion resistance, the Cr content is preferably 1.0 mass% or more, more preferably 3.0 mass% or more, and particularly preferably 5.0 mass% or more. Excess Cr impairs workability during powder production. Specifically, excessive Cr causes nozzle clogging during atomization. From the viewpoint of workability, the Cr content is preferably 20.0 mass% or less, more preferably 15.0 mass% or less, and particularly preferably 12.0 mass% or less.

[0022] [Iron (Fe)] The main component of the alloy according to the present invention is Fe. Fe with dissolved C can undergo martensitic transformation by heat treatment. The sintered body after this heat treatment has high hardness. Furthermore, in this sintered body, αFe can contribute to toughness. From the viewpoint of hardness and toughness, the Fe content in the Fe-based alloy is preferably 65% ​​by mass or more, more preferably 70% by mass or more, and particularly preferably 75% by mass or more. From the viewpoint that the Fe-based alloy can contain sufficient amounts of B, C, and Cr, the Fe content is preferably 95% by mass or less.

[0023] [Powder production] The powder can be preferably obtained by atomization. Gas atomization, disk atomization, water atomization, centrifugal atomization, etc. can be employed. Preferred atomization methods are gas atomization and disk atomization. The powder obtained by atomization may be subjected to mechanical milling, etc. Rapid cooling during atomization can produce a eutectic structure in the Fe-based alloy. An Fe-based alloy with a eutectic structure has a low solidus temperature and a low liquidus temperature.

[0024] [Sintering method] The sintered body can be formed by spark plasma sintering, hot pressing, hot isostatic pressing, metal injection molding, or the like. A film-like sintered body may also be formed. In the production of a film-like sintered body, a large number of particles made of an Fe-based alloy are spread on a base. These particles are heated. When the particles reach a temperature higher than the solidus temperature of the Fe-based alloy, the Fe-based alloy enters a solid-liquid mixed state. The Fe-based alloy then solidifies, forming a sintered body. Since the Fe-based alloy according to the present invention contains a eutectic structure, its solidus temperature is low. Therefore, the sintering temperature can be low. This sintering method can suppress damage to the base due to heat. Furthermore, this sintering method allows for the formation of a sintered body at low cost.

[0025] [Remelting process] The sintered body may be subjected to a remelting treatment. In the remelting treatment, the sintered body is heated to a temperature equal to or higher than the solidus temperature. This heating generates a liquid phase in the sintered body. The sintered body is in a solid-liquid mixed state. This liquid phase solidifies, reforming the sintered body. The remelting treatment increases the density of the sintered body. Since the Fe-based alloy according to the present invention contains a eutectic structure, a liquid phase can be generated at a relatively low heating temperature. Therefore, damage to the base due to heat can be suppressed.

[0026] [Hardness of sintered body] From the Fe-based alloy according to this embodiment, a sintered body having a Vickers hardness (HV) of 900 or more can be obtained. The hardness of representative conventional steel materials is as follows. General structural rolled steel (SS400): 100HV to 160HV Austenitic stainless steel (SUS304): Approximately 200HV Mo-added austenitic stainless steel (SUS316): Approx. 200HV Powdered high-speed steel: 600HV to 850HV Compared with the hardness of these steel materials, the hardness (900 HV or more) of the sintered body obtained from the Fe-based alloy according to this embodiment is significantly greater.

[0027] The high hardness of the sintered body can be achieved by the martensite structure, and the reason for the existence of this martensite structure is presumed to be either or both of the following (1) and (2). (1) The structure formed by martensitic transformation during atomization remains in the sintered body. (2) Martensitic transformation occurs in the sintered body during slow cooling during sintering or remelting treatment. It is known to those skilled in the art that rapid cooling of conventional Fe-C alloys can induce martensitic transformation and achieve high hardness. In the present invention, high hardness can be achieved in sintered bodies without rapid cooling treatment such as quenching. This is a new finding made by the present inventors.

[0028] [Liquidus temperature of Fe-based alloys] The liquidus temperature of the Fe-based alloy is preferably 1250° C. or lower. The melting points of typical conventional steel materials are as follows: General structural rolled steel (SS400): Approximately 1500°C Austenitic stainless steel (SUS304): Approximately 1400°C Mo-added austenitic stainless steel (SUS316): Approximately 1370°C Powdered high-speed steel: approx. 1350°C The liquidus temperature of the Fe-based alloy according to this embodiment is lower than the melting points of these steel materials. The difference is 100°C or more. The coating 6 can be easily formed from this Fe-based alloy. From this perspective, the liquidus temperature of the Fe-based alloy is more preferably 1200°C or less, and particularly preferably 1180°C or less. The alloy according to the present invention combines the properties of conventional self-fluxing alloys and conventional steel materials, and exhibits a liquidus temperature of approximately 1100°C to 1200°C. The liquidus temperature of the Fe-based alloy may be 1100°C or less. The heat treatment temperature for an Fe-based alloy with a liquidus temperature of 1100°C or less is low. Therefore, the production cost of this Fe-based alloy is low.

[0029] As described above, the solidus and liquidus temperatures of the alloy according to the present invention are low. Furthermore, sintered bodies made of this alloy exhibit high hardness. This alloy can be utilized in fields requiring wear resistance and durability. For example, this alloy can be used as part of components for aircraft, automobiles, boilers, agricultural machinery, etc.

[0030] [Combined use with other materials] The Fe-based alloy powder according to the present invention may be mixed with other powders and subjected to a sintering method or the like. Appropriate other powders are selected so that the intended properties of the sintered body are obtained. For example, appropriate other powders are selected from the viewpoint of the toughness of the sintered body. Examples of other powders include flux powder, Ni-based alloy powder, Co-based alloy powder, and polymer material powder. When the Fe-based alloy powder according to the present invention is mixed with other powders, the mass ratio R1 between the two is preferably 40 / 60 or more and 95 / 5 or less. However, mixing with other powders is not essential. In other words, the mass ratio R1 may be 100 / 0. [Example]

[0031] 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.

[0032] [Example 1] The raw material metal was placed in a refractory crucible. The raw material was melted in argon gas to obtain a molten metal. The molten metal was discharged from the nozzle of the crucible and sprayed with high-pressure nitrogen gas to obtain a large number of fine particles. These particles were classified using a sieve to adjust the particle size to 250 μm or less, thereby obtaining the powder of Example 1. The material of this powder was an Fe-based alloy. The composition of this Fe-based alloy is shown in Table 1 below. The remainder of this Fe-based alloy, other than the components shown in Table 1, was Fe and unavoidable impurities.

[0033] [Examples 2-11 and Comparative Examples 1-4 and 6] Powders of Examples 2-11 and Comparative Examples 1-4 and 6 were obtained in the same manner as in Example 1, except that the compositions were as shown in Tables 1 and 2 below.

[0034] [Example 12] An Fe-based alloy powder was obtained in the same manner as in Example 1, except that the composition was as shown in Table 1 below. A flux powder was added to this powder as another powder to obtain a mixed powder. The mass ratio R1 of the Fe-based alloy powder to the flux powder was 62 / 38.

[0035] [Examples 13-15 and Comparative Example 5] A mixed powder was obtained in the same manner as in Example 12, except that the types of other powders and the mass ratio R1 were as shown in Tables 1 and 2 below.

[0036] [Liquidus temperature] The liquidus temperature of the powder was measured using a thermal analyzer (DTA) under the following conditions. Powder amount: 20mg Atmosphere: After evacuation, argon gas was introduced at 200 cm 3 Flow in / min Heating rate: 20°C / min Starting temperature: room temperature Achieved temperature: 1500℃ (held for 5 minutes) The liquidus temperature is the highest temperature at which the endothermic heat absorption occurs among the exothermic peaks observed in the DTA signal during cooling. The results are shown in Tables 1 and 2 below.

[0037] [Hardness] The Fe-based alloy powder or mixed powder was packed closely into a glass tube with a diameter of 20 mm. The temperature of this glass tube was increased from room temperature at a rate of 10°C / min in an air atmosphere. After the temperature reached 1180°C, it was held for 20 minutes. Then, it was cooled to room temperature in the furnace to obtain a compact. A test piece was cut out from this compact, and the cross section was polished. The Vickers hardness of this cross section was measured at a load of 2.94 N. The average values ​​of the results of five measurements are shown in Tables 1 and 2 below.

[0038] [Density rate] A test piece was cut out from the compact obtained for hardness evaluation, and the cross section was polished. This cross section was observed using an SEM with a magnification of 200x. Five SEM images were taken at points 4mm to 5mm inward from the outermost periphery of the sintered body. Each image was square, with a side length of 600µm. This image was binarized into powder-filled areas and void areas using "ImageJ 1.45," a public domain image processing software. The area of ​​the void area in this image, AV (µm 2 ) was measured, and the density ratio P1 (%) was calculated according to the following formula. P1 = 100 · (360000- AV) / 360000 The average densities P1 of the five SEM images are shown in Tables 1 and 2 below.

[0039] [Toughness] Test pieces were cut out from the molded bodies obtained for hardness evaluation, and the cross sections were polished. A load of 4.9 N was applied to the test pieces. The test pieces were visually observed and ranked according to the following criteria. A: There are no cracks. B: There is a crack. The results are shown in Tables 1 and 2 below.

[0040] [Corrosion resistance] Test pieces were cut out from the molded body obtained for the hardness evaluation. The test pieces were cubic, with each side measuring 4 mm. The test pieces were subjected to a high-temperature, high-humidity test under the following conditions. Temperature: 70℃ Humidity: 95%RH Time: 96 hours After the test, the test pieces were visually inspected and rated according to the following criteria. A: No rust B: Rust is visible in some areas C: Rust is visible throughout The results are shown in Tables 1 and 2 below.

[0041] [Table 1]

[0042] [Table 2]

[0043] As shown in Tables 1 and 2, the Fe-based alloys according to the examples are excellent in various performances. These evaluation results clearly demonstrate the superiority of the present invention. [Industrial Applicability]

[0044] The Fe-based alloy according to the present invention is suitable for a variety of applications requiring easy melting.

Claims

[Claim 1] The sintered body is made of an Fe-based alloy, The Fe-based alloy is B: 4.0% by mass or more and 7.0% by mass or less, C: 0.01% by mass or more and 0.80% by mass or less, and Cr: 0 mass% or more and 20.0 mass% or less and the balance being Fe and unavoidable impurities, The sintered body has a metal structure formed by slow cooling martensitic transformation, The metal structure includes a matrix of a eutectic structure of "Fe 2 B + αFe" and an Fe 2 B compound dispersed in the matrix, The sintered body, wherein the particle size of Fe 2 B in the eutectic structure is 1 μm or less.

Images