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 a molding machine used in these methods are required to have wear resistance against the resin. These parts are also required to have corrosion resistance against corrosive gases generated by melting of the resin.

[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 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 containing an appropriate amount of Cr and Mo 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 having an excellent 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 being Ni and inevitable impurities. The Rockwell hardness Hr of this alloy satisfies the following formula (1).

[0010] 34.0 ≦ Hr ≦ Hn - 2.0 (1) In this formula (1), Hn represents the standard hardness and is calculated by the following formula.

[0011] 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.

[0012] Preferably, in this boride-dispersed Ni-based alloy, the Rockwell hardness Hr satisfies the following formula (2).

[0013] 34.0 ≦ Hr ≦ Hn - 3.2 (2)

Effects of the Invention

[0014] 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 having complex shapes.

Brief Description of the Drawings

[0015]

Figure 1

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the present invention will be described in detail based on preferred embodiments. [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 and is a Ni alloy. Preferably, the balance of Cr, Mo, and B is Ni and unavoidable impurities. [Metallographic Structure] The metallographic structure of this alloy includes 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.

[0017] 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.

[0018] 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. [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).

[0019] 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.

[0020] 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 low hardness and excellent toughness, and the boride contributes to excellent wear resistance. Even if the matrix has a low hardness, if the state (amount, 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.

[0021] 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).

[0022] 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).

[0023] 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.

[0024] In the present invention, the standard hardness Hn is calculated by the following regression equation.

[0025] 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 of the present invention. 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 the subsequent heat history based on the content of components excluding Cr, the inventor discovered this regression equation. The reason why Cr is excluded in the analysis is that the contribution of Cr to hardness is small. [Chromium (Cr)] Cr dissolves in Ni in the matrix. This matrix has corrosion resistance against various acids. In particular, this matrix has strong corrosion resistance against nitric acid. Cr further combines with B to precipitate borides. Borides containing Cr have high hardness. This boride can contribute to the wear resistance of the alloy. However, as described above, the contribution of Cr to hardness is small compared to Mo and B.

[0026] The content of Cr is preferably 18.0 mass% or more and 26.0 mass% or less. In an alloy with a content of Cr of 18.0 mass% or more, the toughness improvement effect by satisfying formula (1) is high, and sufficient Cr required for excellent corrosion resistance can exist in the matrix. 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 Cr 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. [Molybdenum (Mo)] Mo dissolves in Ni in the matrix. This matrix has corrosion resistance against various acids. In particular, this matrix has strong corrosion resistance against hydrofluoric acid and hydrochloric acid. Mo further combines with B to precipitate borides. Borides containing Mo have high hardness. This boride can contribute to the wear resistance of the alloy.

[0027] The content rate of Mo is preferably 22.0 mass% or more and 30.0 mass% or less. In the alloy with the content rate of Mo being 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 exist. From this viewpoint, the content rate of Mo is more preferably 24.0 mass% or more, and particularly preferably 25.0 mass% or more. The alloy with the content rate of Mo being 30.0 mass% or less is excellent in toughness. From this viewpoint, the content rate of Mo is more preferably 28.0 mass% or less, and particularly preferably 27.0 mass% or less. [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.

[0028] The content rate of B is preferably 1.05 mass% or more and 1.75 mass% or less. The alloy with the content rate of B being 1.05 mass% or more is excellent in wear resistance. From this viewpoint, the content rate of B 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. The 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 content rate of B is more preferably 1.60 mass% or less, and particularly preferably 1.55 mass% or less. [Nickel (Ni)] Ni is the 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 content rate of Ni is preferably 35 mass% or more, more preferably 40 mass% or more, and particularly preferably 45 mass% or more. This content rate is preferably 60 mass% or less. [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 above-described composition is prepared. This powder can be obtained by atomization. Preferred atomization is gas atomization. In gas atomization, raw materials are charged into a container (quartz crucible) having pores at the bottom. The raw materials are heated by a high-frequency induction furnace and melted in an atmosphere of argon gas or nitrogen gas. Argon gas or nitrogen gas is injected into the raw materials flowing out of the pores. The raw materials are rapidly cooled and solidified to obtain powder.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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 contains the balance being Ni and inevitable impurities. The Rockwell hardness Hr of this component satisfies the following formula (1).

[0033] 34.0 ≦ Hr ≦ Hn - 2.0 (1) In this formula (1), Hn represents the standard hardness and is calculated by the following formula.

[0034] 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.

[0035] 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 contains the balance being Ni and inevitable impurities. The Rockwell hardness Hr of this screw satisfies the following formula (1).

[0036] 34.0 ≦ Hr ≦ Hn - 2.0 (1) In this formula (1), Hn represents the standard hardness and is calculated by the following formula.

[0037] 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

[0038] The effects of the present invention will be clarified by the following examples, but the present invention should not be construed in a limited manner based on the description of these examples. [Experiment 1] [Example 1] The raw materials were heated by high-frequency induction heating in an alumina crucible in 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 a 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. This billet was subjected to extrusion processing 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. [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. [Specific wear rate] Test pieces were produced 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.

[0039] 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. [Impact value] Test pieces with a size of 10 mm × 10 mm × 55 mm were prepared. These test pieces have notches. The size of the notch is "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. [Corrosion amount] Test pieces were manufactured from the formed body 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 piece was measured and the mass reduction amount was calculated. The results are shown in Tables 1 and 2 below.

[0040]

Table 1

[0041]

Table 2

[0042]

Table 3

[0043]

Table 4

Industrial Applicability

[0044] The boride-dispersed Ni-based alloy described above is suitable for various products obtained through machining.

Claims

1. The material is a boride-dispersed Ni-based alloy, and the boride-dispersed Ni-based alloy contains 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 the balance of the boride-dispersed Ni-based alloy is Ni and unavoidable impurities, and a component of a molding apparatus for resin molded products, wherein the Rockwell hardness Hr (value of the hardness symbol HRC measured with a conical diamond at room temperature) of the boride-dispersed Ni-based 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.)

2. The material is a boride-dispersed Ni-based alloy, and the boride-dispersed Ni-based alloy contains 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 the balance of the boride-dispersed Ni-based alloy is Ni and unavoidable impurities, and a screw of a molding apparatus for resin molded products, wherein the Rockwell hardness Hr (value of the hardness symbol HRC measured with a conical diamond at room temperature) of the boride-dispersed Ni-based 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.)

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