JP2014043597A - Ni-BASED ALLOY HAVING EXCELLENT HYDROGEN EMBRITTLEMENT RESISTANCE AND METHOD OF MANUFACTURING Ni-BASED ALLOY MATERIAL HAVING EXCELLENT HYDROGEN EMBRITTLEMENT RESISTANCE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material having excellent hydrogen embrittlement properties at a high temperature and usable for a pressure container of ammonothermal and the like.SOLUTION: A material contains, by mass%, Fe:30 to 40%, Cr:14 to 16%, Ti:1.2 to 1.7%, Al:1.1 to 1.5%, Nb:1.9 to 2.7%, by mass ppm, P:40 to 150 pp, and the remainder Ni with inevitable impurities, and as desired, Mg:0.01% or less and Zr:0.1% or less, and has excellent hydrogen embrittlement resistance with a hydrogen embrittlement index EI defined by EI=(RA-RA)/RA, where RAand RAare contractions in a tensile test of a hydrogen charge material and a non-hydrogen charge material respectively, of 0.1 or less at 625°C, and excellent high temperature creep properties with a creep fracture time at 700°C and 333 MPa of 1,500 hours or longer and a minimum creep speed of 1×10sor less.

Description

  The present invention relates to a Ni-base alloy having excellent hydrogen embrittlement resistance and a method for producing a Ni-base alloy material.

An ammonothermal method is known as a kind of single crystal growth method, and the ammonothermal method is applied to, for example, single crystal growth of gallium nitride which is a nitride semiconductor for blue light-emitting diodes.
Gallium nitride is expected to be used as an optical device such as a high-brightness LED or a semiconductor laser, or an electronic device used in a transistor for an electric vehicle or an amplifier for a mobile phone base station. In order to apply to these devices, it is necessary to increase the size of the gallium nitride single crystal, and a size of 2 inches or more to 6 inches or more and further larger is required.
Conventionally, vapor phase epitaxy has been the mainstream for growing gallium nitride single crystals. However, in order to cope with the above-mentioned enlargement, mass production, and cost reduction of crystals, it can be performed in high-temperature and high-pressure ammonia. It is being replaced by the ammonothermal method of growing crystals. Since the synthesis conditions in the ammonothermal method are generally a temperature of 600 to 650 ° C. and a pressure of 200 to 250 MPa, the application of a Ni-Fe based alloy as a pressure vessel material having high strength in a high temperature environment has been attempted. Yes.
Since the ammonothermal method operates at high temperature and high pressure, the raw material ammonia is decomposed and a large amount of high-pressure hydrogen is generated. Therefore, as a characteristic required for the pressure vessel material, firstly, it has excellent hydrogen embrittlement resistance at a high temperature. Moreover, since it is in a high temperature environment, creep characteristics are also required.

Conventionally, several technologies related to Ni-Fe base alloys having high strength and excellent hydrogen embrittlement resistance have been developed. For example, Patent Document 1 discloses a technique related to a Fe—Ni-based alloy having high strength and excellent hydrogen embrittlement resistance used as a high-pressure hydrogen piping material for a hydrogen station. In this document, a pipe material having a two-layer structure composed of an outer layer imparted with high strength by aging and an inner layer imparted with hydrogen embrittlement resistance is presented.
Patent Document 2 discloses a Ni—Fe alloy in which the particle size of the γ ′ phase and the fraction of each precipitated phase are controlled to exhibit high strength and hydrogen embrittlement resistance.
Further, Patent Document 3 is disclosed as a technique dealing with hydrogen embrittlement characteristics at high temperatures.

JP 2010-174360 A JP 2009-68031 A JP-A-5-255788

However, in Patent Documents 1 and 2, the temperature considered to be excellent in high strength and hydrogen embrittlement resistance is room temperature, and it is unclear whether these characteristics can be guaranteed under high temperature and high pressure.
Further, Patent Document 3 deals with a high Ni-base alloy having high strength and excellent hydrogen embrittlement resistance that can be used at 200 to 500 ° C., but the characteristics at 600 to 650 ° C., which is the subject of the present invention, cannot be guaranteed. In addition, the characteristics under high pressure cannot be guaranteed at all.
As described above, several Ni-Fe based alloys having high strength and excellent hydrogen embrittlement resistance have been developed so far, but none of them can guarantee the characteristics under the conditions handled by the present invention. .

  The present invention has been made against the background of the above circumstances, and Ni-base alloys and Ni-bases having high strength and excellent hydrogen embrittlement resistance even in high-temperature and high-pressure environments such as 600 to 650 ° C. and 200 to 250 MPa. It aims at providing the manufacturing method of an alloy material.

  That is, among the Ni-based alloys excellent in hydrogen embrittlement resistance of the present invention, the first present invention is in mass%, Fe: 30-40%, Cr: 14-16%, Ti: 1.2- 1.7%, Al: 1.1 to 1.5%, Nb: 1.9 to 2.7%, mass ppm, P: 40 to 150 ppm, the balance from Ni and inevitable impurities It is characterized by becoming.

  The Ni-based alloy having excellent hydrogen embrittlement resistance according to the second aspect of the present invention is the same as that of the first aspect of the present invention, which is 1% by mass, Mg: 0.01% or less, and Zr: 0.1% or less. Or it contains 2 types, It is characterized by the above-mentioned.

Third Ni-based alloy having excellent hydrogen embrittlement resistance of the present invention, in any one of the first or second invention, respectively an aperture in a tensile test of a hydrogen-charged material and a non-hydrogen-charged material RA _H And RA _A , the hydrogen embrittlement index EI defined by EI = (RA _A −RA _H ) / RA _A is characterized by 0.1 or less at 625 ° C.

  The Ni-based alloy having excellent hydrogen embrittlement resistance according to the fourth aspect of the present invention has a creep rupture time of 1,500 hours or more at 700 ° C. and 333 MPa in any of the first to third aspects of the present invention. It is characterized by.

The Ni-based alloy having excellent hydrogen embrittlement resistance according to the fifth aspect of the present invention has a minimum creep rate of 1 × 10 ⁻⁸ s ^{−1 at} 700 ° C. and 333 MPa in any of the first to fourth aspects of the present invention. It is characterized by the following.

  The Ni-based alloy having excellent hydrogen embrittlement resistance according to the sixth aspect of the present invention is characterized by being used for an ammonothermal pressure vessel material in any of the first to fifth aspects of the present invention.

  The invention of the manufacturing method of the Ni-based alloy material having excellent hydrogen embrittlement resistance according to the seventh aspect of the present invention includes a temperature of 825 to 855 ° C. and 710 after the solution treatment of the Ni-based alloy in the first or second invention. An aging treatment is performed twice at a temperature of ˜740 ° C.

  The reason for determining the alloy composition of the present invention will be described below. Hereinafter, the content of each element other than P is indicated by mass%, and P is indicated by mass ppm.

Fe: 30-40%
Increasing the content of Fe is effective in reducing the cost of the alloy. However, if Fe is contained excessively together with Nb, a Laves phase is generated, which leads to deterioration of material properties such as increased hydrogen embrittlement sensitivity. Therefore, the content of Fe is set to 30 to 40%. For the same reason, it is desirable to set the lower limit to 33% and the upper limit to 38%.

Cr: 14-16%
Cr is an element necessary for increasing the oxidation resistance, corrosion resistance, and strength of the alloy. Moreover, it combines with C to form carbides and increase the high temperature strength. However, when the content is too large, the matrix is destabilized, and the generation of harmful TCP phases such as σ phase and α-Cr is promoted to adversely affect ductility and toughness. In addition, the σ phase may act as a hydrogen accumulation site in the alloy and may increase hydrogen embrittlement sensitivity. Therefore, the Cr content is limited to 14 to 16%.

Ti: 1.2-1.7%
Ti mainly forms MC carbides to suppress the grain coarsening of the alloy, and combines with Ni to precipitate a γ ′ phase, contributing to the precipitation strengthening of the alloy. However, if it is contained excessively, the stability of the γ ′ phase at high temperature is lowered, and further, the η phase is generated, and the strength, ductility, toughness, and structure stability at high temperature for a long time are impaired. In addition, the η phase also acts as a hydrogen accumulation site in the alloy and may increase the sensitivity to hydrogen embrittlement. Therefore, the Ti content is limited to the range of 1.2 to 1.7%.

Al: 1.1 to 1.5%
Al combines with Ni to precipitate a γ ′ phase, contributing to precipitation strengthening of the alloy. However, if the content is too large, the γ 'phase aggregates and becomes coarse at the grain boundaries, which significantly impairs the mechanical properties at high temperatures and also reduces hot workability. Therefore, the Al content is limited to 1.1 to 1.5%.

Nb: 1.9 to 2.7%
Nb is an element that stabilizes the γ ′ phase and contributes to an increase in strength. However, if excessively contained, the precipitation of harmful η phase, σ phase, and Laves phase is promoted, and the structural stability is remarkably reduced, resulting in hydrogen. Increases embrittlement susceptibility. Therefore, the Nb content is limited to 1.9 to 1.7%.

P: 40 to 150 ppm
P is included because it is considered to have an effect of suppressing the excessive accumulation of hydrogen at the grain boundary and increasing the hydrogen embrittlement sensitivity by increasing the consistency of the grain boundary. To obtain the above effect, a P content of 40 ppm or more is required. It also has the effect of increasing the creep rupture time and reducing the minimum creep rate. However, if it is contained in excess, the grain boundary segregation of P becomes excessive, and on the contrary, the consistency of grain boundaries is lowered, and there is a possibility that the effect of reducing the sensitivity to hydrogen embrittlement is lost. Therefore, the P content is limited to 40 to 150 ppm. For the same reason, it is desirable that the lower limit is 45 ppm and the upper limit is 140 ppm.

Mg: 0.01% or less Mg is mainly combined with S to form a sulfide and enhance hot workability, so it is contained as desired. However, if the content is too large, the grain boundary becomes brittle and the hot workability is lowered, so the Mg content is 0.01% or less. In order to fully express the above effect, the lower limit of the Mg content is preferably 0.0005% or more.

Zr: 0.1% or less Zr is segregated at the grain boundaries and contributes to the improvement of high temperature characteristics. However, if excessively contained, the hot workability of the alloy is lowered, so that Zr contained if desired is made 0.1% or less. In order to acquire said effect, it is desirable to make it contain 0.01% or more.

  The Ni-based alloy of the present invention has excellent hydrogen embrittlement resistance and can be suitably used as a material exposed to a hydrogen environment. Moreover, it is excellent in high strength characteristics at high temperatures, and can be suitably used for ammonothermal pressure vessel materials.

  As a main effect of the present invention, it is possible to provide a Ni-based alloy having good hydrogen embrittlement resistance at a high temperature such as 625 ° C. and excellent creep properties at 700 ° C. As a further effect, by applying the alloy of the present invention to an ammonothermal pressure vessel material, it becomes possible to produce a pressure vessel that can cope with higher temperature and high pressure environments. For example, the gallium nitride single crystal is enlarged, It is expected that mass production and cost reduction will make great progress.

FIG. 1 shows the relationship between the hydrogen embrittlement index and the P content of the inventive material and the comparative material. FIG. 2 shows the relationship between the creep stress and the creep rupture time of the inventive material and the comparative material. FIG. 3 shows the creep stress and creep rate of the inventive material and the comparative material.

The Ni-based alloy of the present invention is in mass%, Fe: 30-40%, Cr: 14-16%, Ti: 1.2-1.7%, Al: 1.1-1.5%, Nb: 1.9 to 2.7% in mass, ppm: P: 40 to 150 ppm, further optionally Mg: 0.01% or less, Zr: 0.1% or less one or two of It is contained and the remainder is prepared into a component consisting of Ni and inevitable impurities.
The Ni-based alloy of the present invention can be melted by a conventional method, and the melting method is not particularly limited as the present invention.

The Ni-based alloy can be subjected to processing such as forging as desired, and can be subjected to solution treatment and heat treatment by aging.
The solution treatment can be performed, for example, at 1040 to 1140 ° C. for 4 to 10 hours. The aging treatment is desirably performed in at least two stages, and the aging treatment can be performed in two stages at a temperature of 825 to 855 ° C. and a temperature of 710 to 740 ° C.
By adopting the conditions, 1000 and 820 MPa can be secured for the tensile strength at room temperature and 625 ° C., respectively.
If the former temperature is less than 825 ° C. or more than 855 ° C., the γ ′ phase cannot be sufficiently grown and the above strength cannot be ensured.
Further, if the latter temperature is less than 710 ° C., M ₂₃ C ₆ type carbide is excessively precipitated, and if it exceeds 740 ° C., MC type carbide is coarsened, which may cause adverse effects such as a decrease in hot ductility. There is.

The Ni-based alloy obtained above is a hydrogen defined by EI = (RA _A −RA _H ) / RA _A when the drawing in the tensile test of the hydrogen charge material and the non-hydrogen charge material is RA _H and RA _A , respectively. Hydrogen embrittlement resistance with an embrittlement index EI of 0.1 or less at 625 ° C. can be obtained. The hydrogen charge simulates an intrusion of 50 ppm of hydrogen.

Moreover, the Ni-based alloy obtained as described above can obtain a high temperature creep characteristic in which a creep rupture time at 700 ° C. and 333 MPa is 1,500 hours or more.
Furthermore, the Ni-based alloy obtained as described above can obtain a high temperature creep characteristic in which the minimum creep rate at 700 ° C. and 333 MPa is 1 × 10 ⁻⁸ s ⁻¹ or less.

  The material using the Ni-based alloy can be used for a desired application capable of exhibiting hydrogen embrittlement resistance through plastic processing, machining, etc., and particularly preferably used for ammonothermal pressure vessel materials. For example, it is possible to realize enlargement, mass production, and cost reduction of a gallium nitride single crystal.

Examples of the present invention will be described below.
In order to obtain the composition shown in Table 1, 50 kg round steel ingot materials were melted by vacuum induction melting as 2 types of invention materials and 2 types of comparative materials, respectively. These materials were forged into plates.
A forged plate was cut into a suitable size and subjected to a solution treatment at 1040 ° C. for 4 hours and two-stage aging at 840 ° C. for 10 hours and 730 ° C. for 24 hours to obtain a test material. Subsequently, the test material was machined to obtain a tensile test piece and a creep test piece for evaluating hydrogen embrittlement characteristics.

The hydrogen embrittlement resistance was evaluated according to the following procedure.
First, test pieces having a parallel part diameter and length of 10 mm and 50 mm, respectively, were held for 72 hours in an atmosphere at a temperature of 450 ° C. and a hydrogen pressure of 25 MPa to charge hydrogen. This hydrogen charge condition is set so as to simulate 50 ppm which is the amount of hydrogen assumed to enter the material by the actual ammonothermal method. After hydrogen charging, a tensile test was performed at 625 ° C., and tensile strength and drawing were measured. The hydrogen embrittlement resistance was evaluated by calculating the hydrogen embrittlement index EI defined by the following equation using the tensile test result at 625 ° C. of the non-hydrogen charge material.
Hydrogen embrittlement index EI = (RA _A −RA _H ) / RA _A (1)
Here, RA _A is a restriction for a non-hydrogen charge material, and RA _H is a restriction for a hydrogen charge material.
The formula (1) shows that the smaller the hydrogen embrittlement index, the better the hydrogen embrittlement resistance.

Creep characteristics were evaluated by performing creep rupture test and creep plate test. In all the tests, the test temperature was 700 ° C., the test stress was 333 MPa and 275 MPa in the rupture test, and 333 MPa in the rate test.
Table 2 shows the tensile strength, drawing, and hydrogen embrittlement index at 625 ° C. for the hydrogen charge material and the non-hydrogen charge material. Although the hydrogen embrittlement index of the inventive material P1 is negative, in Table 2, this is displayed as 0 for convenience.

  FIG. 1 shows the relationship between the hydrogen embrittlement index and the P content at 625 ° C. for the inventive material and the comparative material. From the figure, it was found that the hydrogen embrittlement index of the inventive material is significantly smaller than that of the comparative material, and the inventive material is extremely excellent in hydrogen embrittlement resistance at high temperatures. As indicated by the shaded portion in the figure, when the P content is 40 ppm or more, the hydrogen embrittlement index becomes 0.1 or less, and the hydrogen embrittlement sensitivity is reduced until the influence of hydrogen can be almost ignored. From this, it was found that in order to improve the hydrogen embrittlement resistance by increasing the P content, a P content of 40 ppm or more is necessary.

  2 and 3 show the creep rupture test results and the creep plate test results, respectively. The break time of the inventive material is significantly longer than that of the comparative material, and the break time when the test stress is 333 MPa is at least 10 times that of the comparative material. In addition, the minimum creep rate of the inventive material is at least 1/4 or less than that of the comparative material, and it has been clarified that the inventive material has excellent creep characteristics.

  The present invention has been described based on the above-described embodiments and examples. However, the present invention is not limited to the contents of the above-described embodiments and examples, and is appropriate as long as it does not depart from the scope of the present invention. It can be changed.

Claims (7)

  In mass%, Fe: 30-40%, Cr: 14-16%, Ti: 1.2-1.7%, Al: 1.1-1.5%, Nb: 1.9-2.7% A Ni-based alloy having excellent hydrogen embrittlement resistance, characterized by containing, in mass ppm, P: 40 to 150 ppm, the balance being made of Ni and inevitable impurities.   The Ni group having excellent hydrogen embrittlement resistance according to claim 1, further comprising one or two of Mg: 0.01% or less and Zr: 0.1% or less. alloy. The hydrogen embrittlement index EI defined by EI = (RA _A −RA _H ) / RA _A is 625 ° C. when the drawing in the tensile test of the hydrogen charge material and the non-hydrogen charge material is RA _H and RA _A , respectively. The Ni-based alloy having excellent hydrogen embrittlement resistance according to claim 1 or 2, wherein the Ni-base alloy has a resistance to hydrogen embrittlement.   The Ni-based alloy having excellent hydrogen embrittlement resistance according to any one of claims 1 to 3, wherein a creep rupture time at 700 ° C and 333 MPa is 1,500 hours or more. 5. The Ni-based alloy having excellent hydrogen embrittlement resistance according to claim 1, wherein a minimum creep rate at 700 ° C. and 333 MPa is 1 × 10 ⁻⁸ s ⁻¹ or less.   The Ni-based alloy having excellent hydrogen embrittlement resistance according to any one of claims 1 to 5, which is used for an ammonothermal pressure vessel material.   The Ni-based alloy according to claim 1 is excellent in hydrogen embrittlement resistance, characterized by performing aging treatment twice at a temperature of 825 to 855 ° C and a temperature of 710 to 740 ° C after solution treatment. Manufacturing method of Ni-based alloy material.

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