WO2018221561A1 - Ni BASE ALLOY, FUEL INJECTION PART USING SAME, AND METHOD FOR PRODUCING Ni BASE ALLOY - Google Patents

Abstract

Provided are: an Ni base alloy having wear resistance equivalent to or greater than that of existing high-carbon martensitic stainless steel, without detriment to the superior corrosion resistance and non-magnetic properties which are characteristic of Ni base alloys; and a method for producing Ni base alloy, with which it is possible to efficiently produce the Ni base alloy. The Ni base alloy contains, in % by mass, 30-45% Cr, 2-5% Al, and more than 0.1% but no more than 1% B, with the remainder being made up of Ni and impurities. The Ni base alloy is preferably characterized by the Cr boride having a field of view surface area ratio of 5-30% in a field of view of 200000 µm2.

Description

Ni-based alloy, fuel injection component using the same, and method for producing Ni-based alloy

The present invention relates to a Ni-based alloy, a fuel injection component using the same, and a Ni-based alloy manufacturing method.

Conventionally, high carbon martensitic stainless steel has been used for fuel injection parts, bearing parts and molding dies that require high hardness and high corrosion resistance. Since this material has Fe as a main component, it cannot be used due to insufficient corrosion resistance in a corrosive environment. A Ni-based precipitation hardening alloy has been proposed as an alloy that further enhances corrosion resistance and provides high hardness. For example, in Patent Documents 1 to 3, by performing an aging treatment, a gamma prime phase (hereinafter referred to as γ ′ phase) of Ni ₃ (Al, Ti, Nb) and an α phase mainly composed of Cr are precipitated. High hardness can be obtained. Further, this alloy is non-magnetic and does not interfere with an external magnetic field.

JP 2002-69557 A JP 2005-82885 A JP 2001-62594 A

The above-described Ni-based precipitation hardening type alloy has the highest hardness among non-magnetic materials and excellent corrosion resistance, but has a problem of insufficient wear resistance compared to martensitic stainless steel and the like. was there. For this reason, when the sliding counterpart material has high hardness or contains hard particles, the wear progresses quickly, resulting in a short life, and this is a serious problem in putting parts and molds into practical use. Further, since the aging treatment temperature is usually about 700 ° C. for a long time, there is a problem that heat treatment deformation and manufacturing man-hours are required. Furthermore, the hot workability is poor and the processing yield is low.
An object of the present invention is to provide a Ni-based alloy having a wear resistance equivalent to or higher than that of an existing high-carbon martensitic stainless steel without deteriorating the excellent characteristics such as corrosion resistance and non-magnetism, which are characteristics of the Ni-based alloy, and the Ni-based alloy. It is to provide a fuel injection component using a base alloy and a method for producing a Ni-base alloy capable of efficiently producing the Ni-base alloy.

The present inventor examined the problem that the conventional Ni-based precipitation hardening type alloy has insufficient wear resistance, and increased the wear resistance by adjusting to a chemical composition capable of dispersing particles with high hardness in the alloy. We have found that it can be improved and have reached the present invention.
That is, the present invention is a Ni-based alloy consisting of Cr: 30 to 45%, Al: 2 to 5%, B: more than 0.10% and 1% or less with the balance being Ni and impurities.
Preferably, the Ni-based alloy includes Cr boride.
More preferably, the visual field area ratio of the Cr boride in the visual field of 200,000 μm ² is 5 to 30%.
More preferably, the hardness of the Ni-based alloy is 700 HV or more.
The present invention is also a fuel injection component using the Ni-based alloy.

Further, the present invention provides, in mass%, Cr: 30 to 45%, Al: 2 to 5%, B: more than 0.10% and 1% or less, the balance being Ni-based alloy composed of Ni and impurities, 1100 to A method for producing a Ni-based alloy comprising a solution treatment step for performing a solution treatment at 1250 ° C. and an aging treatment step for carrying out an aging treatment at 500 to 650 ° C. after the solution treatment step.
Preferably, the aging treatment time is 2 to 5 hours.
In the present invention, it is preferable to further include a hot working step of hot working at 800 to 1000 ° C. after the aging treatment step.

Since the Ni-base alloy of the present invention has improved wear resistance to the same level or higher than that of existing high carbon martensitic stainless steel, fuel injection parts, bearing parts and molding dies made using this have corrosive environments. Even under, it exhibits excellent corrosion resistance and wear resistance, and is effective in improving the life. In addition, since the Ni-based alloy of the present invention is not affected by a magnetic field, troubles caused by magnetization of parts and molds can be prevented. Further, since an efficient manufacturing method is provided for the aging treatment and the hot working method, the production cost can be reduced.

It is a microscope picture of Example 1 of this invention alloy.

As mentioned above, an important feature of the present invention is the chemical composition that allows the hard particles to be dispersed in the alloy to improve wear resistance. According to the invention described in the aforementioned patent document, a high hardness of about 650 HV can be obtained by aging treatment, which is due to the combined precipitation of the γ ′ phase and the α phase mainly composed of Cr. If any precipitate is fine and the hardness of the α phase itself is about 800 to 900 HV, and the hard material of the sliding partner is hard or contains hard particles, the wear due to the abrasive wear by the sliding partner material proceed.
In the present invention, in order to suppress this wear, the chemical composition is adjusted so that particles harder than the α phase and having a size of about several μm can be dispersed. For example, borides can be considered as the hard particles. In particular, Cr boride has a hardness of 1200 to 2000 HV, and has the effect of dramatically improving the wear resistance.
By crystallizing these borides during the solidification process, borides having a certain size can be distributed. Preferably, the amount of alloy is adjusted in the vicinity of the eutectic composition of boride and austenite in order to prevent crystallization of coarse borides.

In the Ni-based alloy of the present invention, the reasons for defining each element to be contained and the content thereof are as follows. Unless otherwise specified, the mass% is indicated.
<Cr: 30-45%>
Cr is an important element constituting the present invention. Cr is a boride-forming element, and is an element that can be dissolved in a matrix (matrix), precipitate an α phase mainly composed of Cr by aging treatment, and increase matrix hardness. The reason why the Cr content is 30 to 45% is to adjust the boride amount and aging hardness appropriately. If the Cr content is less than 30%, the amount of Cr dissolved in the matrix is small and the aging hardness is low. On the other hand, when Cr exceeds 45%, the α phase is stable, and even at temperatures around 1200 ° C., it becomes a three-phase structure of α phase, γ phase and Cr boride, and cracks occur at the interface between α phase and γ phase during hot working. It tends to occur. In order to dissolve the α phase at a high temperature, the upper limit of Cr is made 45%. In addition, the minimum with preferable Cr content is 33%, More preferably, it is 36%. Moreover, the upper limit with preferable Cr content is 43%, More preferably, it is 41%.
<Al: 2 to 5%>
Al is precipitated as an intermetallic compound γ ′ phase based on Ni ₃ Al by aging treatment. The γ 'phase is coherently precipitated from the austenite of the matrix. Since the amount of precipitation of the γ ′ phase increases as the Al content increases, a high hardness can be obtained. If Al is less than 2%, precipitation of the γ 'phase is small and the hardness is low, so Al is made 2% or more. On the other hand, if there is too much Al, the α phase becomes stable, and even at high temperatures, the α phase does not completely dissolve, resulting in poor hot workability. Therefore, the upper limit of Al is 5%. In addition, the minimum with preferable Al content is 3.2%, More preferably, it is 3.5%. Moreover, the upper limit with preferable Al content is 4.2%, More preferably, it is 4.0%.

<B: more than 0.10% and 1% or less>
B is one of the important elements constituting the present invention. B forms Cr boride. B needs to exceed 0.10% in order to form a boride. As the amount of B increases, Cr boride increases and wear resistance is improved. On the other hand, if there is too much B, a coarse Cr boride crystallizes out as an initial crystal during solidification, which becomes a starting point for early breakage and the like. In addition, the amount of Cr dissolved in the matrix is reduced, the α-phase precipitation amount after the aging treatment is reduced, and the hardness is lowered. Therefore, the upper limit of B is set to 1%. In addition, the minimum with preferable B content is 0.15%, More preferably, it is 0.20%. Moreover, the upper limit with preferable B content is 0.80%, More preferably, it is 0.65%.
<Balance: Ni and impurities>
The balance is substantially Ni, but impurities that are inevitably mixed in the manufacture are included. Although it is preferable that the impurity content is small, it may be within the following range.
C ≦ 0.1%, Mn ≦ 2%, Si ≦ 1%, P ≦ 0.05%, S ≦ 0.05%, N ≦ 0.05%, Mg ≦ 0.01%

<Cr boride>
The presence of the hard boride effectively prevents the abrasive wear caused by the sliding material and improves the wear resistance. In order to reliably obtain this effect, it is preferable that the visual field area ratio of Cr boride (hereinafter also simply referred to as area ratio) in a visual field of 200,000 μm ² is 5 to 30%. When the viewing area ratio of Cr boride is less than 5%, the effect of preventing abrasive wear becomes low. On the other hand, the greater the amount of Cr boride, the more effective the wear resistance is improved. However, if there is too much Cr boride, the workability is lowered and breakage tends to occur. %. In addition, the minimum with the preferable visual field area ratio of Cr boride is 8%, More preferably, it is 10%. Moreover, the upper limit with preferable visual field area ratio of Cr boride is 25%, More preferably, it is 22%.
Whether or not the boride is a Cr boride containing Cr is determined by, for example, comparing a scanning electron microscope (SEM) / energy dispersive X-ray analysis (EDX) with an optical micrograph to obtain a Cr boron in an optical micrograph. The compound can be identified and the area ratio can be calculated.
The measurement of the visual field area ratio of the Cr boride can be performed, for example, by performing image processing on visual field data of an optical microscope observed at 500 times. Although it is possible to measure Cr boride by observation with an electron microscope, for example, a Cr boride having a maximum diameter of less than 0.5 μm, which has a low effect of effectively preventing abrasive wear, is also an object of measurement. There is a case. Therefore, observation with an optical microscope capable of efficiently confirming the Cr boride that can be confirmed by observing at 500 times is preferable.
In addition, the field area for measuring Cr boride is set to 200000 μm ² because if the field area is excessively narrow, there is a possibility that the field area ratio of Cr boride increases, and the field area exceeding 200000 μm ² This is because the measurement result hardly changes even when the area ratio is measured.

<Hardness>
The higher the hardness of the Ni-based alloy of the present invention, the higher the wear resistance. In order to improve the wear resistance more reliably, it is desirable that the temperature be 700 HV or higher. In this alloy, a high hardness of 700 HV or more can be obtained by applying appropriate heat treatment conditions. The condition will be described later. In addition, about hardness, 730HV or more is preferable, More preferably, it is 750 or more. The upper limit of the hardness is not particularly limited, but a hardness of up to about 800 HV can be obtained by a combination of an appropriate alloy composition and heat treatment conditions.
<Fuel injection parts>
The fuel injection component is preferably made of a non-magnetic material that does not interfere with the magnetic field as much as possible for controlling the solenoid valve. The Ni alloy of the present invention is non-magnetic, and is required to have high corrosion resistance and high wear resistance to cope with high fuel injection pressure and poor fuel. Therefore, the application of the Ni-based alloy of the present invention that satisfies these requirements is optimal.

<Production conditions>
The Ni-based alloy of the present invention is formed into a predetermined shape by hot plastic working a melt-cast ingot. At this time, before hot plastic working, the hot plastic work material may be once heated to a region where the α phase is solid-solved to improve the hot workability. If the α phase is once heated to a region where the α phase is dissolved, approximately 1150 to 1250 ° C. is sufficient. Thus, after making it the shape applied to heat processing, predetermined heat processing is performed.
The heat treatment of the present invention includes a solution treatment process in which a solution treatment is performed at 1100 to 1250 ° C., and an aging treatment process in which an aging treatment is performed at 500 to 650 ° C. after the solution treatment process.
The reason for setting the temperature of the solution treatment step in the present invention to 1100 to 1250 ° C. is to obtain a high hardness by once solidifying the α phase into the γ phase and finely precipitating the α phase after the aging treatment. When the solution treatment temperature is less than 1100 ° C., the granular α phase remains undissolved even in the solution treatment, there are few α phases precipitated by aging, and the hardness is lowered. On the other hand, when the solution treatment temperature exceeds 1250 ° C., the crystal grains become coarse and the grain boundary decreases, so that the distribution unevenness of the precipitated phase increases due to aging, and the hardness decreases. Also, heat treatment deformation is increased. The minimum of the preferable temperature of a solution treatment is 1120 degreeC, More preferably, it is 1140 degreeC. The upper limit of preferable temperature is 1200 degreeC, More preferably, it is 1180 degreeC. It is sufficient that the solution treatment time is 0.5 to 1.5 hours.

The γ ′ precipitation hardening type alloy is usually treated at a temperature of around 700 ° C. because it requires a long-time treatment of several tens of hours when the aging temperature is treated at around 600 ° C. In contrast, in the aging treatment step for the Ni-based alloy of the present invention, the hardness can be increased in a short time at an aging temperature of 500 to 650 ° C. In addition, a short processing time of 2 to 5 hours is sufficient.
When the aging treatment temperature is less than 500 ° C., the precipitation reaction hardly occurs and the hardness does not increase. On the other hand, when the aging temperature exceeds 650 ° C., the precipitates become coarse and the hardness starts to decrease. The minimum of the preferable temperature of an aging treatment is 550 degreeC, More preferably, it is 570 degreeC. Moreover, the upper limit of preferable temperature is 630 degreeC, More preferably, it is 600 degreeC.
In the present invention, if the aging treatment time is less than 2 hours, the precipitation reaction may not proceed sufficiently and high hardness may not be obtained. On the other hand, when the aging treatment time exceeds 5 hours, the precipitation reaction is almost completed, and the hardness hardly changes even when the treatment is performed for a longer time.

In the present invention, the hot workability is further improved by performing a hot working step of hot working at 800 to 1000 ° C. after the aging treatment step. This is because the formation of a fine α-phase and γ-phase two-phase structure facilitates grain boundary sliding and facilitates plastic deformation. The temperature of the hot working process is set to 800 to 1000 ° C. When the temperature is less than 800 ° C, the strength is high and the softening does not occur. This is because it decreases and the ductility decreases. The minimum of the temperature of a preferable hot working process is 850 degreeC, More preferably, it is 880 degreeC. Moreover, the upper limit of preferable temperature is 980 degreeC, More preferably, it is 950 degreeC. Typical examples of hot working include hot rolling and hot extrusion.

The following examples further illustrate the present invention.
A 10 kg steel ingot was produced by vacuum melting, heated to 1150 to 1180 ° C., forged to a thickness of 20 mm and a width of 50 mm to obtain a forged material. The chemical composition is shown in Table 1. Samples for various tests were cut out from the forged material. Table 2 shows the heat treatment conditions performed on each sample.

After heat treatment shown in Table 2, boride quantitative measurement, hardness measurement, salt spray test, sulfuric acid corrosion resistance test, and earth and sand wear test were performed. The test conditions are as follows, and the evaluation results are shown in Table 3.
<Boride quantitative measurement>
The area ratio of a boride having a maximum diameter of 0.5 μm or more in a measurement visual field area of 200,000 μm ² observed with a 500 × optical microscope was measured with an image analyzer. In FIG. The microstructure after heat processing of 2 alloys is shown. The corrosive solution used was a mixture of aqua regia and cupric chloride. White particles are Cr boride. Cr boride was identified by SEM / EDX analysis.
<Hardness measurement>
Using a Vickers hardness tester, the measurement was performed with a measurement load of 30 kgf.
<Salt spray test>
A 10 mm square block was used as the test piece. A 5% salt spray test at 35 ° C. was conducted to evaluate the rusting state after 5 hours.
<Sulfuric acid corrosion test>
The size of the test piece was a cylindrical test piece having a diameter of 10 mm and a length of 20 mm, and the corrosion weight loss was measured before and after a 96-hour immersion test in 30 ° C. pH 3 sulfuric acid.
<Sediment wear test>
The test piece was 8 mm thick, 25 mm wide and 76 mm long, and the friction surface was polished with # 600. In accordance with ASTMG65, the abrasive grain was No. 6 sand, and a friction test was performed at a flow rate of 350 g / min and a load of 133 N. Wear loss before and after the test was measured.

No. 1 to 5 are examples of the present invention. The hardness of the alloy of the present invention example after heat treatment is 700 HV or more. In the earth and sand abrasion test, all are in the range of 350 mm ³ or less. It can be seen that the alloy of the example of the present invention has less wear than the conventional example and is excellent in wear resistance.
As the boride area ratio increases, the wear resistance is further improved and the hardness is high. Five
Has the least amount of wear. In the evaluation of corrosion resistance, no. Compared with Fe (22) (conventional example) Fe-based martensitic stainless steel, it was remarkably superior and no corrosion was observed even when sprayed with salt water or immersed in sulfuric acid. In addition, it was confirmed that the alloys of the examples of the present invention did not show substantial magnetization by VSM measurement and were all non-magnetic. From these results, it can be seen that the alloys according to the examples of the present invention have excellent hardness, wear resistance and corrosion resistance, have a good balance between them, and are non-magnetic. Alloys having these characteristics are suitable for fuel injection parts such as fuel injection devices.

Next, Invention Example No. A high temperature tensile test was conducted using the alloy No. 2. A tensile test piece having a parallel part diameter of 6.35 mm was prepared, heated to a predetermined temperature, and then subjected to a tensile test at a strain rate of 0.0008S- ¹ . Table 4 shows the heat treatment conditions and high-temperature tensile test results of the test pieces.
No. in Table 4 As shown in A and B, when a tensile test was performed after the aging treatment, the ductility was remarkably improved, and an elongation of 120% or more and a drawing of 80% or more were obtained. This is presumably because the ferrite phase was finely precipitated by the aging treatment, and deformation was likely to occur due to grain boundary sliding due to the superplastic phenomenon by forming a fine two-phase structure of austenite and ferrite. It is possible to improve hot workability by utilizing this phenomenon.

Since the present invention is non-magnetic and excellent in corrosion resistance and wear resistance, it can be applied to an environment where wear resistance is indispensable in an environment where it is desired to avoid magnetization or in a corrosive environment. For example, application to bearing parts, molding dies, and garbage power plant members in addition to fuel injection parts is suitable.

Claims (8)

1. Ni-based alloy characterized in that Cr: 30 to 45%, Al: 2 to 5%, B: more than 0.10% and 1% or less, with the balance being Ni and impurities.
2. The Ni-based alloy according to claim 1, wherein the Ni-based alloy contains a Cr boride.
3. The Ni-based alloy according to claim 2, wherein a field area ratio of the Cr boride in a visual field of 200,000 μm ² is 5 to 30%.
4. The Ni-based alloy according to any one of claims 1 to 3, wherein the hardness of the Ni-based alloy is 700 HV or more.
5. A fuel injection part using the Ni-based alloy according to any one of claims 1 to 4.
6. In mass%, Cr: 30 to 45%, Al: 2 to 5%, B: more than 0.10% and 1% or less, the remainder is Ni-based alloy consisting of Ni and impurities at 1100 to 1250 ° C. A solution treatment process for performing
   An aging treatment step of performing an aging treatment at 500 to 650 ° C. after the solution treatment step;
   The manufacturing method of Ni base alloy characterized by including these.
7. The method for producing a Ni-based alloy according to claim 6, wherein the aging treatment time is 2 to 5 hours.
8. The method for producing a Ni-based alloy according to claim 6 or 7, further comprising a hot working step of hot working at 800 to 1000 ° C after the aging treatment step.
   
   

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