BORIDE DISPERSION TYPE 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 forming method, or the like. Wear resistance against resin is required for parts of molding machines used in these methods. Corrosion resistance against corrosive gases generated by melting of the resin is also required for these parts.

[0003] Ni-based alloys are used in applications where wear resistance and corrosion resistance are required. Various improvements related to this Ni-based alloy, which are intended for use in a more severe environment, 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. This boride is hard. This boride 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 screw of the forming machine has a complex shape. The toughness of the conventional boride-dispersed Ni-based alloy is insufficient. This alloy is not suitable for processing products with complex shapes (such as screws).

[0008] An object of the present invention is to provide a boride-dispersed Ni-based alloy excellent in the balance of wear resistance, corrosion resistance, and toughness.

Means for Solving the Problems

[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 and contains. The balance is 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 is excellent in wear resistance, corrosion resistance, and toughness. This alloy is suitable for products with complex shapes.

Brief Description of the Drawings

[0012]

Figure 1

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% 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 and is a Ni alloy. 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. A typical chemical formula of the 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 mathematical formula (1). 34.0 ≦ Hr ≦ Hn - 2.0 (1) In this mathematical formula (1), Hn represents the standard hardness. The standard hardness Hn refers to the hardness as a calculated value as described later.

[0019] In general alloys, the 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 smaller than "Hn - 2.0". In other words, the hardness difference (Hr - Hn) between the hardness Hr and the standard hardness Hn is -2.0 or less. As described above, the hardness Hr has a negative correlation with toughness. Since the hardness Hr is small, this alloy is excellent in toughness. Despite the small hardness Hr, this alloy has sufficient wear resistance. The reason is not clear in detail, but it is considered that the matrix contributes to the low hardness and excellent toughness, and the boride contributes to the excellent wear resistance. Even if the matrix has a low hardness, if the state (quantity, hardness) of the boride is sufficient, it is considered that the inhibition of wear resistance by the low-hardness matrix is suppressed by the boride. Furthermore, the low hardness of the matrix does not inhibit the wear resistance of the alloy. An alloy with a difference (Hr - Hn) of -2.0 or less is excellent in the balance of wear resistance, corrosion resistance, and toughness.

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

[0021] In the present invention, the standard hardness Hn is calculated by the following regression formula. 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 inventor. Conventional boride-dispersed Ni-based alloys can be obtained by hot working and subsequent slow cooling. By performing multiple regression analysis on the hardness of this alloy without subsequent heat history based on the content of components excluding Cr, the inventor discovered this regression equation. The reason Cr is excluded in the analysis is that its contribution to hardness is small.

[0022] [Chromium (Cr)] Cr dissolves in Ni in the matrix. This matrix has corrosion resistance to various acids. In particular, this matrix has strong corrosion resistance to nitric acid. Cr further combines with B to precipitate borides. Borides containing Cr are of high hardness. This boride can contribute to the wear resistance of the alloy. However, as described above, Cr has a smaller contribution to hardness compared to Mo and B.

[0023] The content of Cr is preferably 18.0 mass% or more and 26.0 mass% or less. In an alloy with a content of 18.0 mass% or more, the toughness improvement effect by satisfying formula (1) is high, and in the matrix, sufficient Cr required for excellent corrosion resistance can be present. From this perspective, the content of Cr is more preferably 20.0 mass% or more, and particularly preferably 21.0 mass% or more. An alloy with a content of 26.0 mass% or less is excellent in toughness. From this perspective, the content of Cr is more preferably 24.0 mass% or less, and particularly preferably 23.0 mass% or less.

[0024] [Molybdenum (Mo)] Mo dissolves in Ni in the matrix. This matrix has corrosion resistance to various acids. In particular, this matrix has strong corrosion resistance to hydrofluoric acid and hydrochloric acid. Mo further combines with B to precipitate borides. Borides containing Mo are of high hardness. This boride can contribute to the wear resistance of the alloy.

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

[0026] [Boron (B)] B combines with one or more of Ni, Cr, and Mo to precipitate borides. A large number of borides are dispersed in the matrix. This alloy is excellent in wear resistance.

[0027] The B content is preferably 1.05 mass% or more and 1.75 mass% or less. An alloy with this B content of 1.05 mass% or more is excellent in wear resistance. From this viewpoint, the B content is more preferably 1.20 mass% or more, and particularly preferably 1.25 mass% or more. Excessive B precipitates excessive borides. The precipitation of excessive borides consumes excessive Mo and causes a shortage of Mo in the matrix. An alloy with insufficient Mo in the matrix is inferior in corrosion resistance. The precipitation of excessive borides further inhibits the toughness of the alloy. From the viewpoints of corrosion resistance and toughness, the B content is more preferably 1.60 mass% or less, and particularly preferably 1.55 mass% or less.

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

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

[0030] This powder is classified as necessary. The classified powder is subjected to hot extrusion molding. By this hot extrusion molding, a molded body is obtained. This molded body is slowly cooled. Further heat treatment is performed on this molded body. In this heat treatment, the molded body is heated and cooled. By cooling, the alloy according to the present invention is obtained. Typical cooling is air cooling, water cooling, and oil cooling. The cooling rate 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. By this solid solution, corrosion resistance is imparted. In this manufacturing method, toughness is imparted by heat treatment. By combining atomization and heat treatment, a boride-dispersed Ni-based alloy excellent in the balance of wear resistance, corrosion resistance, and toughness can be obtained.

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

[0033] The present invention is also directed to parts of a molding apparatus for resin molded products. The material of the parts according to the present invention is a boride-dispersed Ni-based alloy. This alloy 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 and the balance 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 to a screw of a 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 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 and the balance 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] Hereinafter, the effects of the present invention will be clarified by examples, but the present invention should not be construed in a limited manner based on the description of these examples.

[0036] [Experiment 1] [Example 1] The raw materials were heated by high-frequency induction heating method in an alumina crucible under an argon gas atmosphere. By this heating, the raw materials were melted to obtain a molten metal. The molten metal was dropped from a nozzle with a diameter of 5 mm located under the crucible. Argon gas was sprayed onto this 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 a material of carbon steel. The inside of this capsule was vacuum degassed. This capsule was sealed to obtain a billet. This billet was heated to 1170 °C and held at this temperature for 2 hours. Extrusion processing was performed on this billet to obtain a molded body with a diameter of 60 mm. This molded body was slowly cooled. This slow cooling took 168 hours. After heating this molded body to 1000 °C and holding for 4 hours, it was air-cooled to obtain the alloy of Example 1. When the microstructure of this alloy was observed by SEM and analyzed by EPMA, its metal structure had a matrix and a large number of precipitates. In the matrix, Cr and Mo were dissolved in Ni. The precipitates were compounds of Cr, Mo, Ni, and B.

[0037] [Examples 2-11 and Comparative Examples 1-10] Alloys of Examples 2-11 and Comparative Examples 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] Test pieces were fabricated from the molded body (boride-dispersed Ni-based alloy) by machining. The size of this test piece was 7 mm × 25 mm × 50 mm. This test piece was subjected to a test using a Ogoshi-type rapid wear tester. The conditions were as follows. Counter material: SCM420 (86 HRC) Wear rate in the high-speed range: 1.36 m / sec Final load: 61.8 N Lubrication: None Temperature: Room temperature The wear scar width obtained in 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] Test pieces with a size of 10 mm × 10 mm × 55 mm were prepared. These test pieces had notches. The size of the notch was "10R-C". A Charpy impact test was performed on these test pieces 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 pieces were fabricated from the compact by machining. The size of this test piece was 10 mm × 10 mm × 15 mm. The mass of this test piece was measured. Two test pieces were prepared and these test pieces were immersed in a 10% aqueous solution of nitric acid and a 10% aqueous solution of hydrofluoric acid for 10 hours, respectively. The temperature of these aqueous solutions was 40°C. Further, the mass of the test pieces was measured and the mass reduction amount 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] Alloys of 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, except that the composition, extrusion conditions and heat treatment conditions were as shown in Tables 3 and 4 below.

[0044] [Example 13] Billet was obtained from the powder having the composition shown in Table 3 below in the same manner as in Example 1 of Experiment 1. HIP treatment was performed on this billet to obtain a compact. In this HIP process, the billet was held at a temperature of 1120 °C and a pressure of 150 MPa for 5 hours. After the HIP process, this compact was furnace cooled. This compact was heated up to 1150 °C, and hot forging was performed on this compact to obtain a forged product having a diameter of 25 mm. This 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 of the HIP process were as shown in Table 3 below.

[0046] [Evaluation] In the same manner as in Experiment 1, the specific wear rate, impact value, and corrosion rate of the alloy were measured. 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 of Fig. 1. As shown in Tables 1 - 4 and Fig. 1, the alloys of each example are excellent in various properties. From this evaluation result, the superiority of the present invention is clear. [Industrial Applicability]

[0050] The boride dispersion type Ni - based alloy described above is 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 containing, the balance being Ni and unavoidable impurities, a boride dispersion type Ni-based alloy having a Rockwell hardness Hr (value of the hardness symbol HRC measured with a conical diamond at room temperature) satisfying 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 dispersion type 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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