Boride-dispersed Ni-based alloy

Abstract

To provide a boride dispersion type Ni-based alloy having excellent balance of abrasion resistance, corrosion resistance, and toughness.SOLUTION: A boride dispersion type Ni-based alloy contains Cr of 18 mass% or more and 26 mass% or less, Mo of 22 mass% or more and 30 mass% or less, and B of 1.05 mass% or more and 1.75 mass% or less. The balance is Ni and inevitable impurities. The alloy has a Rockwell hardness Hr satisfying the following expression (1): 34.0≤Hr≤Hn-2.0 (1), wherein Hn indicates a standard hardness and is calculated in the following equation: Hn=23.44+0.48*Mo%+5.08*B%, wherein Mo% indicates a mass content of Mo and B% indicates a mass% of B.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a boride-dispersed Ni-based alloy. Specifically, the present invention relates to a boride-dispersed Ni-based alloy containing Cr, Mo, and B.

Background Art

[0002] Resin molded products can be obtained by an injection molding method, an extrusion molding method, or the like. Parts of molding machines used in these methods are required to have wear resistance against resins. These parts are also required to have corrosion resistance against corrosive gases generated by melting of resins.

[0003] Ni-based alloys are used in applications where wear resistance and corrosion resistance are required. Various improvements regarding this Ni-based alloy, which are intended for use in more severe environments, have been proposed.

[0004] Japanese Patent Application Laid-Open No. 2004-137570 discloses a Ni-Cr-Mo 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 Application Laid-Open No. 2012-246517 discloses a boride-dispersed Ni-based alloy in which an appropriate amount of Cr and Mo are contained in a matrix. This alloy is excellent in corrosion resistance.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The screws of molding machines have complex shapes. Conventional boride-dispersed Ni-based alloys have insufficient toughness. These alloys are not suitable for processing products with complex shapes (e.g., screws).

[0008] The objective of the present invention is to provide a boride-dispersed Ni-based alloy that exhibits an excellent balance of wear resistance, corrosion resistance, and toughness. [Means for solving the problem]

[0009] The boride-dispersed Ni-based alloy according to the present invention is Cr: 18% by mass or more and 26% by mass or less, Mo: 22% by mass or more and 30% by mass or less and B: 1.05% by mass or more and 1.75% by mass or less It contains [component name]. The remainder consists of Ni and unavoidable impurities. The Rockwell hardness Hr of this alloy satisfies the following formula (1). 34.0 ≤ Hr ≤ Hn - 2.0 (1) In this formula (1), Hn represents the standard hardness and is calculated by the following formula. Hn = 23.44 + 0.48 * Mo% + 5.08 * B% In this formula, Mo% represents the mass content of Mo, and B% represents the mass content of B.

[0010] Preferably, in this boride-dispersed Ni-based alloy, the Rockwell hardness Hr satisfies the following formula (2). 34.0 ≤ Hr ≤ Hn - 3.2 (2) [Effects of the Invention]

[0011] The boride-dispersed Ni-based alloy according to the present invention exhibits excellent wear resistance, corrosion resistance, and toughness. This alloy is suitable for products with complex shapes. [Brief explanation of the drawing]

[0012] [Figure 1]Figure 1 is a graph showing the experimental results of the examples and comparative examples of the present invention.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the present invention will be described in detail based on preferred embodiments.

[0014] [Composition] The boride-dispersed Ni-based alloy according to the present invention is Cr: 18 mass% or more and 26 mass% or less, Mo: 22 mass% or more and 30 mass% or less and B: 1.05 mass% or more and 1.75 mass% or less is a Ni alloy containing. Preferably, the balance of Cr, Mo and B is Ni and unavoidable impurities.

[0015] [Metallographic Structure] The metallographic structure of this alloy contains a matrix and a large number of borides. These borides are dispersed in the matrix. These borides are uniformly dispersed in the matrix. Each boride is fine.

[0016] The matrix contains Ni, Cr and Mo. In this matrix, Cr and Mo are dissolved in Ni. The structure of the matrix is a Ni-based γ phase. Cr and Mo in the matrix can contribute to the corrosion resistance of the alloy.

[0017] The boride is a compound of a metal element and B. The chemical formula of a typical boride is "M3B2". In this chemical formula, M represents a metal element. The metal element M is Ni, Cr or Mo. The boride may contain two or more metal elements. The boride can contribute to the wear resistance of the alloy.

[0018] [Hardness] The Rockwell hardness Hr of the alloy is the value of the hardness symbol HRC measured with a conical diamond at room temperature and satisfies the following formula (1). 34.0 ≤ Hr ≤ Hn - 2.0 (1) In this formula (1), Hn represents the standard hardness. The standard hardness Hn refers to the hardness as a calculated value, as will be explained later.

[0019] In general alloys, hardness has a positive correlation with wear resistance and a negative correlation with toughness. The hardness Hr of the boride-dispersed Ni-based alloy according to the present invention is the same as or less than "Hn-2.0". In other words, the difference in hardness between hardness Hr and standard hardness Hn (Hr-Hn) is -2.0 or less. As mentioned above, hardness Hr has a negative correlation with toughness. Because hardness Hr is low, this alloy has excellent toughness. Despite the low hardness Hr, this alloy has sufficient wear resistance. The reason for this is not fully understood, but it is thought that the matrix contributes to the low hardness and excellent toughness, and the borides contribute to the excellent wear resistance. Even if the matrix has low hardness, if the state (amount, hardness) of the borides is sufficient, it is thought that the inhibition of wear resistance by the low-hardness matrix is ​​suppressed by the borides. Furthermore, the low hardness of the matrix does not impair the wear resistance of the alloy. Alloys with a difference (Hr-Hn) of -2.0 or less exhibit an excellent balance of wear resistance, corrosion resistance, and toughness.

[0020] From the standpoint of toughness, a difference (Hr-Hn) of -3.2 or less is more preferable. In other words, it is preferable that the Rockwell hardness Hr of the alloy satisfies the following formula (2). 34.0 ≤ Hr ≤ Hn - 3.2 (2) From the viewpoint of toughness, a difference (Hr-Hn) of -3.6 or less is particularly preferable. In other words, it is preferable that the Rockwell hardness Hr of the alloy satisfies the following formula (3). 34.0 ≤ Hr ≤ Hn - 3.6 (3) From the viewpoint of wear resistance, a hardness Hr of 34.0 or higher is preferred, 35.0 or higher is more preferred, and 36.0 or higher is particularly preferred.

[0021] In this invention, the standard hardness Hn is calculated by the following regression equation. Hn = 23.44 + 0.48 * Mo% + 5.08 * B% In this regression equation, Mo% represents the mass content of Mo, and B% represents the mass content of B. This regression equation was discovered by the inventors. Conventional boride-dispersed Ni-based alloys can be obtained by hot working followed by slow cooling. The inventors discovered this regression equation by performing a multiple regression analysis on the hardness of this alloy, excluding subsequent thermal history, based on the content of components other than Cr. The reason Cr is excluded from the analysis is that its contribution to hardness is small.

[0022] [Chromium (Cr)] Cr dissolves in Ni in the matrix. This matrix is ​​corrosion-resistant to various acids, particularly nitric acid. Cr further combines with B to precipitate borides. Cr-containing borides are highly hard. These borides can contribute to the wear resistance of the alloy. However, as mentioned above, Cr contributes less to hardness compared to Mo and B.

[0023] The Cr content is preferably between 18.0% by mass and 26.0% by mass. In alloys with a Cr content of 18.0% by mass or more, the toughness improvement effect due to satisfying formula (1) is high, and sufficient Cr necessary for excellent corrosion resistance can be present in the matrix. From this viewpoint, a Cr content of 20.0% by mass or more is more preferable, and 21.0% by mass or more is particularly preferable. Alloys with a Cr content of 26.0% by mass or less have excellent toughness. From this viewpoint, a Cr content of 24.0% by mass or less is more preferable, and 23.0% by mass or less is particularly preferable.

[0024] [Molybdenum (Mo)] Mo dissolves in Ni within the matrix. This matrix exhibits corrosion resistance to various acids, particularly strong resistance to hydrofluoric acid and hydrochloric acid. Mo further combines with B to precipitate borides. These borides, containing Mo, are highly hard. These borides can contribute to the wear resistance of the alloy.

[0025] The Mo content is preferably between 22.0% by mass and 30.0% by mass. In alloys with a Mo content of 22.0% by mass or more, the toughness improvement effect due to satisfying formula (1) is high, and sufficient Mo necessary for excellent corrosion resistance can be present in the matrix. From this viewpoint, a Mo content of 24.0% by mass or more is more preferable, and 25.0% by mass or more is particularly preferable. Alloys with a Mo content of 30.0% by mass or less have excellent toughness. From this viewpoint, a Mo content of 28.0% by mass or less is more preferable, and 27.0% by mass or less is particularly preferable.

[0026] [Boron (B)] B bonds with one or more of Ni, Cr, and Mo, causing borides to precipitate. Numerous borides are dispersed in the matrix. This alloy exhibits excellent wear resistance.

[0027] The B content is preferably 1.05% by mass or more and 1.75% by mass or less. Alloys with a B content of 1.05% by mass or more exhibit excellent wear resistance. From this viewpoint, a B content of 1.20% by mass or more is more preferable, and 1.25% by mass or more is particularly preferable. Excess B causes the precipitation of excess boride. The precipitation of excess boride consumes excess Mo, leading to a deficiency of Mo in the matrix. Alloys with insufficient Mo in the matrix have poor corrosion resistance. The precipitation of excess boride further inhibits the toughness of the alloy. From the viewpoint of corrosion resistance and toughness, a B content of 1.60% by mass or less is more preferable, and 1.55% by mass or less is particularly preferable.

[0028] [Nickel (Ni)] Ni is the main component of the matrix. Ni forms the γ phase in the matrix. In this matrix, as mentioned above, Cr and Mo are solid-solved in Ni. This matrix can contribute to the corrosion resistance and toughness of the alloy. The Ni content is preferably 35% by mass or more, more preferably 40% by mass or more, and particularly preferably 45% by mass or more. This content is preferably 60% by mass or less.

[0029] [Manufacturing method] An example of a manufacturing method for boride-dispersed Ni-based alloys according to the present invention is described below. In this manufacturing method, a powder having the aforementioned composition is prepared. This powder can be obtained by atomization. A preferred atomization method is gas atomization. In gas atomization, the raw material is placed in a container (quartz crucible) having pores at the bottom. This raw material is heated and melted in a high-frequency induction furnace in an argon or nitrogen gas atmosphere. Argon or nitrogen gas is injected into the raw material flowing out of the pores. The raw material is rapidly cooled and solidified to obtain powder.

[0030] This powder is classified as needed. The classified powder is subjected to hot extrusion molding. A molded body is obtained by this hot extrusion molding. This molded body is slowly cooled. This molded body is further subjected to heat treatment. In this heat treatment, the molded body is heated and then cooled. Cooling yields the alloy according to the present invention. Typical cooling methods are air cooling, water cooling, and oil cooling. The rate of cooling is relatively fast. This cooling imparts toughness to the matrix.

[0031] In this manufacturing method, a large amount of Cr and Mo are dissolved in Ni by atomization. This solid solution imparts corrosion resistance. In this manufacturing method, toughness is imparted by heat treatment. By combining atomization and heat treatment, a boride-dispersed Ni-based alloy with an excellent balance of wear resistance, corrosion resistance, and toughness can be obtained.

[0032] A molded body may be obtained by applying HIP (hot isostatic pressing) to the powder. This molded body is then furnace-cooled (slowly cooled). Hot working is then performed on this molded body. Hot forging is a specific example of hot working. The forged product obtained by this process is then cooled. Cooling yields the alloy according to the present invention. Typical cooling methods include air cooling, water cooling, and oil cooling. The rate of this cooling is relatively fast. This cooling imparts toughness to the matrix.

[0033] The present invention is also directed toward components of molding apparatus for resin molded products. The material of the component according to the present invention is a boride-dispersed Ni-based alloy. This alloy is Cr: 18% by mass or more and 26% by mass or less, Mo: 22% by mass or more and 30% by mass or less and B: 1.05% by mass or more and 1.75% by mass or less It contains [component name]. The remainder consists of Ni and unavoidable impurities. The Rockwell hardness Hr of this component satisfies the following formula (1). 34.0 ≤ Hr ≤ Hn - 2.0 (1) In this formula (1), Hn represents the standard hardness and is calculated by the following formula. Hn = 23.44 + 0.48 * Mo% + 5.08 * B% In this formula, Mo% represents the mass content of Mo, and B% represents the mass content of B.

[0034] The present invention is also directed toward screws in molding apparatus for resin molded products. The material of the screw according to the present invention is a boride-dispersed Ni-based alloy. This alloy is Cr: 18% by mass or more and 26% by mass or less, Mo: 22% by mass or more and 30% by mass or less and B: 1.05% by mass or more and 1.75% by mass or less It contains [component name]. The remainder consists of Ni and unavoidable impurities. The Rockwell hardness Hr of this screw satisfies the following formula (1). 34.0 ≤ Hr ≤ Hn - 2.0 (1) In this formula (1), Hn represents the standard hardness and is calculated by the following formula. Hn = 23.44 + 0.48 * Mo% + 5.08 * B% In this formula, Mo% represents the mass content of Mo, and B% represents the mass content of B. [Examples]

[0035] The effects of the present invention will be demonstrated below by the examples, but the present invention should not be interpreted restrictively based on the description in these examples.

[0036] [Experiment 1] [Example 1] The raw materials were heated in an alumina crucible in an argon gas atmosphere using high-frequency induction heating. This heating melted the raw materials, yielding molten metal. The molten metal was dropped from a nozzle with a diameter of 5 mm below the crucible. Argon gas was sprayed onto the molten metal to obtain powder. This powder was classified to adjust the particle size to 500 μm or less. The composition of this powder is shown in Table 1 below. This powder was filled into a capsule with a diameter of 155 mm, a height of 400 mm, and made of carbon steel. The inside of the capsule was degassed under vacuum. The capsule was sealed to obtain a billet. This billet was heated to 1170°C and held at this temperature for 2 hours. This billet was extruded to obtain a molded body with a diameter of 60 mm. This molded body was slowly cooled. This slow cooling took 168 hours. This molded body was heated to 1000°C and held for 4 hours, then air-cooled to obtain the alloy of Example 1. Microstructural analysis of this alloy using SEM and EPMA revealed that its structure consisted of a matrix and numerous precipitates. In the matrix, Ni was in solid solution with Cr and Mo. The precipitates were compounds of Cr, Mo, Ni, and B.

[0037] [Examples 2-11 and Comparative Examples 1-10] Alloys for Example 2-11 and Comparative Example 1-10 were obtained in the same manner as in Example 1, except that the composition, extrusion conditions, and heat treatment conditions were as shown in Tables 1 and 2 below.

[0038] [Specific wear rate] A test specimen was fabricated from a molded body (boride-dispersed Ni-based alloy) by machining. The size of this test specimen was 7 mm × 25 mm × 50 mm. This test specimen was subjected to testing using an Okoshi-type rapid wear testing machine. The conditions were as follows: Countering material: SCM420 (86HRC) Wear rate at high speeds: 1.36 m / sec Final load: 61.8N Lubrication: None Temperature: room temperature The wear mark width obtained during the test was measured, and the wear volume was calculated. The specific wear rate was calculated by dividing this wear volume by the product of the wear distance and the final load. The results are shown in Tables 1 and 2 below.

[0039] [Impact value] A test specimen measuring 10 mm x 10 mm x 55 mm was prepared. This specimen had a notch, the size of which was "10R-C". A Charpy impact test was performed on this specimen in accordance with the provisions of "JIS Z 2242:2005", and the impact value was measured. The results are shown in Tables 1 and 2 below.

[0040] [Corrosion amount] Test specimens were fabricated from molded bodies by machining. The size of these specimens was 10mm × 10mm × 15mm. The mass of these specimens was measured. Two specimens were prepared and immersed for 10 hours in a 10% nitric acid aqueous solution and a 10% hydrofluoric acid aqueous solution, respectively. The temperature of these solutions was 40°C. Furthermore, the mass of the specimens was measured, and the mass loss was calculated. The results are shown in Tables 1 and 2 below.

[0041] [Table 1]

[0042] [Table 2]

[0043] [Experiment 2] [Examples 12, 14, 16, 18 and 20-25 and Comparative Examples 11-26] Except for the composition, extrusion conditions, and heat treatment conditions shown in Tables 3 and 4 below, alloys for Examples 12, 14, 16, 18, and 20-25, and Comparative Examples 11-26 were obtained in the same manner as in Example 1 of Experiment 1.

[0044] [Example 13] A billet was obtained from a powder having the composition shown in Table 3 below, in the same manner as in Example 1 of Experiment 1. A molded body was obtained by the HIP method on this billet. In this HIP method, the billet was held at a temperature of 1120°C and a pressure of 150 MPa for 5 hours. After the HIP method, the molded body was furnace-cooled. The molded body was heated to 1150°C and hot-forged to obtain a forged product with a diameter of 25 mm. The forged product was air-cooled to obtain the alloy of Example 13.

[0045] [Examples 15, 17, and 19] Alloys of Examples 15, 17, and 19 were obtained in the same manner as in Example 13, except that the conditions for the HIP method were as shown in Table 3 below.

[0046] [evaluation] The specific wear rate, impact value, and corrosion rate of the alloy were measured using the same method as in Experiment 1. The results are shown in Tables 3 and 4 below.

[0047] [Table 3]

[0048] [Table 4]

[0049] [Summary of Experiments 1 and 2] The results of Experiments 1 and 2 are shown in the graph in Figure 1. As shown in Table 1-4 and Figure 1, the alloys of each example exhibit excellent performance in various aspects. From these evaluation results, the superiority of the present invention is clear. [Industrial applicability]

[0050] The boride-dispersed Ni-based alloys described above are suitable for various products obtained through machining.

Claims

1. Cr: 18% by mass or more and 26% by mass or less, Mo: 22% by mass or more and 30% by mass or less and B: 1.05% by mass or more and 1.75% by mass or less It contains, The remainder consists of Ni and unavoidable impurities. A boride-dispersed Ni-based alloy whose Rockwell hardness Hr (the value of the hardness symbol HRC measured at room temperature using a conical diamond) satisfies the following formula (1). 34.0 ≦ Hr ≦ Hn - 2.0 (1) (In this formula (1), Hn represents the standard hardness and is calculated by the following formula.) Hn = 23.44 + 0.48 * Mo% + 5.08 * B% In this formula, Mo% represents the mass content of Mo, and B% represents the mass content of B.

2. The boride-dispersed Ni-based alloy according to claim 1, wherein the Rockwell hardness Hr satisfies the following formula (2). 34.0 ≦ Hr ≦ Hn - 3.2 (2)

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