JP2022024337A - AUSTENITIC Fe-BASED HEAT RESISTANCE ALLOY - Google Patents

Abstract

To provide a novel Fe-based heat resistance alloy that can be processed and produced as a member by general methods such as melting, casting, forging, rolling, and has sufficient ductility at room temperature and sufficiently high strength at high temperatures.SOLUTION: An austenitic Fe-based heat resistance alloy contains, in atom%, Al: 10-21%, Ni: 25-40%, Cr: 5-16%, Nb: 2-5% with the balance being Fe and unavoidable impurities.SELECTED DRAWING: Figure 9

Description

The present invention relates to an austenitic Fe-based heat-resistant alloy having good room temperature ductility and high-temperature strength, which is suitable for use as high-temperature rotating parts such as various engines and turbines, and high-temperature corrosion-resistant members.

High-temperature rotating parts such as various engines and turbines are required to have higher temperatures and higher rotation speeds in response to requests for reduction of fuel consumption and carbon dioxide emissions. As a material suitable for such parts and devices, there is a demand for a material that has sufficient performance to withstand high temperatures and high rotation speeds and can be manufactured at a relatively low cost by a general-purpose manufacturing method.

Conventionally, 18-8 austenitic heat resistant steels such as SUS321H and SUS347H have been used as materials for various products used in a high temperature environment. However, in recent years, the conditions of use of parts and devices in a high temperature environment have become more severe, and along with this, the required performance such as high temperature strength for the materials used has become stricter. Therefore, the conventional 18-8. There is a need for superior heat-resistant steel to replace austenitic heat-resistant steel materials.

As a candidate for heat-resistant steel to replace the conventional 18-8 austenitic heat-resistant steel, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2001-011583) states that C: 0.01 to 0.10% and Si: ≦ by weight ratio. 1.50%, Mn: ≤1.50%, P: ≤0.030%, S: ≤0.015%, Ni: 25.00 to 35.00%, Cr: 19.00 to 29.00% , Mo + W: ≤3.0%, V: ≤0.5%, Co: ≤5.0%, Al: ≤0.15%, Ti: ≤0.15%, Nb + Ta: ≤1.0%, N : A heat-resistant alloy containing 0.1 to 0.35% and having a balance consisting of Fe and unavoidable impurities is disclosed.

According to Patent Document 2 (Japanese Patent Laid-Open No. 2003-041347), Cr: 12 to 15%, Ni: 20 to 30%, Ti: 0.20 to 0.50%, Nb: 0.10 to 0. Disclosed are austenitic heat-resistant steels characterized by 30%, P: 0.025 to 0.08%, V: 0.2 to 0.4%, and the balance consisting of Fe.

In Patent Document 3 (Japanese Patent Laid-Open No. 2012-001749), C: 0.01 to 0.12%, Si: 0.2 to 1.0%, Mn: 1.0 to 2.5%, in mass%, Ni: 10.0 to 28.0%, Cr: 18.0 to 26.0%, Al: 0.001 to 0.050%, P: 0.040% or less, S: 0.010% or less, N : 0.09 to 0.30%, Nb + V: 0.25 to 0.70%, Mo + 0.5W: 1.5 to 4.0%, W / Mo: 3 to 16, the balance Fe and inevitable There is disclosed an austenite-based heat-resistant steel which is composed of impurities and is characterized by being solidified at 1180 to 1250 ° C.

However, the heat-resistant steels described in any of the above documents have room for further improvement in improving high-temperature strength, and also have other properties required in an environment near room temperature, such as room temperature ductility. It was not always clear whether or not it was.

Japanese Unexamined Patent Publication No. 2001-011583 Japanese Patent Application Laid-Open No. 2003-041347 Japanese Unexamined Patent Publication No. 2012-001749

The present invention has been made to solve the conventional problems described in the above background technology section, and is processed or manufactured as a member by a general-purpose method such as melting, casting or forging, or rolling method. It is an object of the present invention to provide a novel Fe-based heat-resistant alloy having sufficient ductility at room temperature and sufficiently high strength at high temperature.

The present inventors have been diligently studying alloys having a composition ratio different from that of the conventional austenite-based Fe-based heat-resistant alloys described in the above documents, while constructing a hypothesis focusing on B2-type intermetallic compounds. As a result of advancing, surprisingly, when the Al content ratio is contained in a specific composition range, Ni, Cr and Nb are each in a specific composition range, and the balance is an alloy composed of Fe and unavoidable impurities. We have found that both high ductility at room temperature and high strength at high temperature can achieve both seemingly contradictory important characteristics, and have completed the present invention as a means for solving the above problems.

That is, the gist of the present invention is as follows.
[1] Austenitic Fe containing 10 to 21% Al, 25 to 40% Ni, 5 to 16% Cr, and 2 to 5% Nb in atomic%, with the balance being Fe and unavoidable impurities. Basic heat resistant alloy.
[2] The austenitic Fe-based heat-resistant alloy according to the above [1], which further contains W: 1 to 3% in atomic% and the balance is Fe and unavoidable impurities.
[3] In atomic%, Al: 11 to 19%, Ni: 26 to 38%, Cr: 5 to 15%, Nb: 2 to 5%, W: 1 to 3%, and the balance is Fe and unavoidable. Austenitic Fe-based heat-resistant alloy composed of impurities.
[4] The alloy according to any one of the above [1] to [3], which has a ductility of 5% or more in a tensile test at room temperature.
[5] The alloy according to any one of [1] to [4], which has a high-temperature strength of 450 MPa or more in a tensile test at 700 ° C.

The austenitic Fe-based heat-resistant alloy of the present invention can be processed and manufactured as a member by a general-purpose method such as conventional melting, casting or forging, and rolling method, has sufficient ductility at room temperature, and has sufficient ductility. It is possible to achieve both the excellent effect that the strength at high temperature is sufficiently high.

It is a figure which shows the appearance of the ingot produced in an Example. It is a figure which shows the appearance of the groove roll rolled material produced in an Example. It is a figure which shows the tensile test piece shape in an Example. It is a backscattered electron image photograph of alloy 1 (comparative alloy). It is a backscattered electron image photograph of alloy 5 (comparative alloy). It is a backscattered electron image photograph of alloy 20 (comparative alloy). It is a backscattered electron image photograph of alloy 25 (reference alloy). It is a backscattered electron image photograph of alloy 7 (invention alloy). It is a backscattered electron image photograph of alloy 17 (invention alloy).

Hereinafter, an example of a preferred embodiment of the present invention will be described. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to the following embodiments.

[Each component of austenitic Fe-based alloy]
Each component of the austenite-based Fe-based alloy of the present invention will be described.
<Al>
The austenitic Fe substrate alloy of the present invention contains Al as an essential component. Al is a component that can react with iron (Fe), which is a basic constituent element of an alloy, to form a B2 type intermetallic compound. It is considered that the appropriate precipitation of the B2 phase in the Fe-based alloy of the present invention has the effect of improving the high-temperature strength of the alloy, and this point is one of the important features of the present invention. ..
The compounding ratio of Al at the time of alloy production is preferably 10% or more, more preferably 11% or more, preferably 21% or less, and preferably 19% or less in atomic%. Is more preferable. If it is below the above lower limit, the effect of Al may be insufficient, and if it exceeds the upper limit, the ductility of the alloy at room temperature is lowered, and it is considered that the cause of this is that the amount of B2 phase precipitation is too large.

<Ni>
The austenitic Fe substrate alloy of the present invention contains Ni as an essential component. Ni is a component that contributes to the stabilization of the austenite phase of the alloy, thereby exhibiting the effect of increasing the ductility of the alloy at room temperature.
The compounding ratio of Ni at the time of alloy production is preferably 25% or more, more preferably 26% or more, preferably 40% or less, and 38% or less in atomic%. Is more preferable. Below the above lower limit, the ductility of the alloy at room temperature decreases, and above the upper limit, the high temperature strength of the alloy decreases.

<Cr>
The austenitic Fe substrate alloy of the present invention contains Cr as an essential component. Cr is a component that contributes to the solid solution strengthening of the matrix phase, thereby exhibiting the effect of improving the strength of the alloy at high temperatures.
The Cr compounding ratio at the time of alloy production is preferably 5% or more, preferably 16% or less, and more preferably 15% or less in atomic%. Below the above lower limit, the effect of Cr may be insufficient, and above the upper limit, the ductility of the alloy at room temperature decreases, which is caused by an excessive amount of brittle phase such as Laves phase. Can be considered.

<Nb>
The austenitic Fe substrate alloy of the present invention contains a small amount of Nb as an essential component. Nb is a component that contributes to strengthening precipitation, which has the effect of improving the strength of the alloy at high temperatures.
The compounding ratio of Nb at the time of alloy production is preferably 2% or more in atomic%, and preferably 5% or less. Below the above lower limit, the effect of Nb may be inadequate, and above the upper limit, the ductility of the alloy at room temperature decreases, which is caused by an excessive amount of brittle phase such as Laves phase. Can be considered.

<W>
The austenitic Fe substrate alloy of the present invention preferably contains a small amount of W. Like Nb, W is a component that contributes to strengthening precipitation, thereby exhibiting the effect of improving the strength of the alloy at high temperatures.
The compounding ratio of W at the time of alloy production is preferably 2% or more in atomic%, and preferably 5% or less. Below the above lower limit, the effect of W may be inadequate, and above the upper limit, the ductility of the alloy at room temperature will decrease, which is due to the excessive amount of brittle phases such as the Laves phase. Can be considered.

[Characteristics of austenitic Fe-based alloy]
The characteristics of the austenitic Fe-based alloy of the present invention will be described.

<Room temperature ductility>
The austenitic Fe substrate alloy of the present invention preferably has a ductility of 4.3% or more, more preferably a ductility of 5.0% or more, and more preferably an elongation in a tensile test at room temperature. It has a ductility of 5.5% or more, and most preferably an elongation of 6.0% or more. The above lower limit of ductility can be set as a guide for ensuring stability during use.

<High temperature strength>
The austenite-based Fe substrate alloy of the present invention preferably has a high-temperature strength of 435 MPa or more in a tensile test at 700 ° C., more preferably has a high-temperature strength of 450 MPa or more, and more preferably a tensile strength. It has a high temperature strength of 460 MPa or more, and most preferably a high temperature strength of 465 MPa or more. The lower limit of the tensile strength at 700 ° C. can be set with a strength equal to or higher than that of known ordinary austenitic heat-resistant steel as a guide.

[Manufacturing method of austenitic Fe-based alloy]

The austenite-based Fe-based alloy of the present invention can be produced by using a general-purpose method such as melting, casting or forging, rolling method, etc. of the raw materials of each component element, and other known and well-known methods in the art. It may be manufactured by appropriately combining the technologies related to the above. Further, ingots may be produced by high frequency melting using an alumina crucible, groove roll rolling using heating at 1100 ° C., and / or heat treatment at 900 ° C. for 50 hours in sequence according to the procedure of Examples described later. ..
The heat treatment temperature is set to strengthen the solid solution and precipitation of the Fe-based alloy by dissolving and precipitating Al, Ni, Cr, Nb, which are essential elemental components of the present invention, and optionally W in the austenite structure. , 800 to 1300 ° C., more preferably 850 to 1200 ° C., most preferably 900 to 1100 ° C., and the heat treatment time is preferably 1 to 100 hours. It is more preferably about 70 hours, and most preferably 10 to 50 hours. The production conditions of the Fe-based alloy of the present invention can be appropriately selected from the viewpoint of preventing oxidation loss of the steel material in the heat treatment and reducing the cost of the heat treatment as long as the alloy can exert the effect of the present invention.

[Action of austenitic Fe-based alloy of the present invention]
In the examples described later, the austenitic Fe-based alloy of the present invention could be produced and the excellent effect of the alloy could be demonstrated, although not exactly all the detailed reasons are clear. It is inferred as follows.
The most important point of the austenite-based Fe-based alloy of the present invention is that by adding a larger amount of Al than a normal austenite-based Fe-based heat-resistant alloy, a large amount of FeAl-based B2 type intermetallic compound is precipitated, and its effect. The purpose is to improve the high temperature strength of the alloy while ensuring sufficient room temperature ductility of the alloy.
Since the conventional austenite-based Fe-based heat-resistant alloy is a solid solution alloy, the mechanism of structural strengthening is basically the solid solution strengthening of the parent phase by the additive element, and further, the precipitation strengthening of fine precipitates by the additive component is intended. However, it is considered that there is a limit to the improvement of high temperature strength only by such a method.
On the other hand, the austenite-based Fe-based heat-resistant alloy of the present invention is capable of strengthening precipitation with a B2 type intermetallic compound based on FeAl, in addition to strengthening solid solution and strengthening precipitation of fine precipitates. There is a feature. By adopting such a complex structural strengthening method, the heat-resistant alloy of the present invention is expected to be used as a heat-resistant material in a high-temperature part such as an apparatus. In the present invention, the feature that the B2 type intermetallic compound itself based on FeAl is not easily deformed at a high temperature is utilized, and a strengthening mechanism by an interface effect can be exhibited at the interface between the intermetallic compound and the matrix. The feature is also utilized. The austenitic Fe-based alloy having these characteristics has not been described or suggested in the above-mentioned prior art documents, and has been discovered for the first time by the diligent studies of the present inventors.

Hereinafter, the production of the austenitic Fe-based heat-resistant alloy of the present invention and its characteristics will be described in more detail based on Examples. It should be noted that these descriptions are examples of embodiments of the present invention, and the present invention is not limited to these examples.

[Procedure 1: Ingot preparation]
FIG. 1 is a photograph showing the appearance of the ingot produced in this example. An ingot having the composition shown in Table 1 below was prepared by high frequency melting using an alumina crucible. As the raw material of the ingot, massive electrolytic iron and granular Al, Ni, Cr, Nb, and W were used, and the total weight was about 1.5 kg. The dissolution atmosphere was in argon gas. Casting was performed on a cast iron mold having an inner diameter of φ40 mm, cutting was performed at the position shown by the dotted line in FIG. 1, and the lower side (length of about 90 mm) was subjected to groove roll rolling described later.

[Procedure 2: Groove roll rolling]
An ingot having a diameter of 40 mm and a diameter of 90 mm obtained by cutting the pressed water was heated to 1100 ° C. and subjected to groove roll rolling. The shape of the grooves was square, and the cross-sectional area was gradually reduced by passing ingots in order between grooves of different sizes. Further, after rolling about 3 times, reheating was performed. The heating and holding time was about 10 minutes. An example of the groove roll rolling process is shown below using arrow symbols (the numbers are the length of one side of the groove (mm)):
<Start> → Heat retention → 38.2 → 35.0 → 31.7 → Reheat → 28.7 → 25.9 → 23.5 → Reheat → 21.3 → 19.3 → 17.5 → Re Heating → 15.8 → 14.3 → 12.9 → <End>
In this embodiment, the groove roll rolled material shown in FIG. 2 was obtained by the above steps.

[Procedure 3: Heat treatment and microstructure observation]
The groove roll rolled material was heat-treated at 900 ° C. for 50 hours, and then the structure was observed by a backscattered electron image. Pictures of the backscattered electron image structures of alloys 1, 5, 20, 25, 7 and 17, are shown in FIGS. 4 to 9, respectively.

[Procedure 4: Characteristic evaluation]
The test piece shown in FIG. 3 was processed from the rolled groove roll material after the heat treatment, and a tensile test at room temperature and a tensile test at 700 ° C. were performed. In the tensile test at room temperature, elongation was measured as an evaluation of room temperature ductility, and in the tensile test at 700 ° C., tensile strength was measured as an evaluation of high temperature strength.
The measurement results are shown in Table 1 below.

From Table 1, it was found that the groove roll rolled material of each ingot produced with a specific composition (component ratio) was as follows.

(1) Suitable component ratio of Al Alloys 1 to 5 are a group in which the Al component ratio is significantly changed. In this group, the component ratio excluding Al, Fe and unavoidable impurities is atomic%, Ni (25-40%): Cr (5-15%): Nb (2-5%): W (1-3%). ), When Al is 11.0%, 16.0%, and 19.0% (alloys 1, 2 and 3 respectively), both room temperature ductility and high temperature strength are good (◎). However, when Al is relatively low at 9.0% (alloy 1, comparative alloy), the high-temperature strength is poor (x), and when Al is relatively high at 22.0% (alloy 5, comparison). It was found that the alloy) had poor room temperature ductility (x).
In alloy 1, which is a comparative alloy, the Al component ratio is below the range of 10 to 20%, and as can be seen from the backscattered electron image photograph (FIG. 4), the amount of B2 phase (black phase) is small. Recognize. Therefore, it is probable that the alloy 1 did not have the effect of improving the high temperature strength by adding Al.
On the other hand, in the alloy 5 which is a comparative alloy, the Al component exceeds the range of 10 to 20%, and the amount of the B2 phase (black phase) is too large as observed from the backscattered electron image photograph (FIG. 5). Therefore, it is probable that this was the cause of the poor room temperature ductility.

(2) Suitable component ratio of Ni Alloys 6 to 10 are a group in which the Ni component ratio is significantly changed. In this group, the component ratio excluding Ni, Fe and unavoidable impurities is atomic%, Al (10 to 20%): Cr (5 to 15%): Nb (2 to 5%): W (1 to 3%). ), When Ni is 26.0%, 32.0%, and 38.0% (alloys 7, 8 and 9 respectively), both room temperature ductility and high temperature strength are good (◎). However, when Ni is relatively low at 24.0% (alloy 6, comparative alloy), the room temperature ductility is poor (x), and when Ni is relatively high at 41.0% (alloy 10, comparison). It was found that the high temperature strength of the alloy) was poor (x).
In the alloy 6 which is a comparative alloy, the Nl component ratio is below the range of 25 to 40%, and it is probable that the austenite phase is not stable and the room temperature ductility is poor.
On the other hand, in the alloy 10 which is a comparative alloy, the Ni component exceeds the range of 25 to 40%, and it is considered that the high temperature strength is lowered due to this.
In the alloy 7 which is the invention alloy, the Ni component ratio is in the range of 25 to 40%, and as can be observed from the backscattered electron image photograph (FIG. 8), the amount of the B2 phase (black phase) and the precipitate. It is probable that both the room temperature ductility and the high temperature strength were good because they existed in a good balance with the amount of (white phase) and were under suitable conditions.

(3) Suitable component ratio of Cr Alloys 11 to 15 are a group in which the Cr component ratio is significantly changed. In this group, the component ratio excluding Cr, Fe and unavoidable impurities is atomic%, Al (10 to 20%): Ni (25 to 40%): Nb (2 to 5%): W (1 to 3%). ), When Cr is 5.0%, 10.0%, and 15.0% (alloys 12, 13 and 14, respectively), both room temperature ductility and high temperature strength are good (◎). However, when Cr is relatively low at 4.0% (alloy 11, comparative alloy), the high-temperature strength is poor (x), and when Cr is relatively high at 17.0% (alloy 15, comparison). It was found that the alloy) had poor room temperature ductility (x).
In the alloy 11 which is a comparative alloy, the Cr component ratio is below the range of 5 to 15%, and it is probable that the effect of improving the high temperature strength by the solid solution strengthening was not observed.
On the other hand, in the alloy 15 which is a comparative alloy, the Cr component exceeds the range of 5 to 15%, and the amount of brittle phases such as the Laves phase becomes too large, which causes poor room temperature ductility. It is considered to be.

(4) Suitable component ratio of Nb Alloys 16 to 20 are a group in which the Nb component ratio is significantly changed. In this group, the component ratio excluding Nb, Fe and unavoidable impurities is atomic%, Al (10 to 20%): Ni (25 to 40%): Cr (5 to 15%): W (1 to 3%). ), When Nb is 2.0%, 3.0%, and 5.0% (alloys 17, 18 and 19 respectively), both room temperature ductility and high temperature strength are good (◎). However, when Nb is relatively low at 1.0% (alloy 16, comparative alloy), the high-temperature strength is poor (x), and when Nb is relatively high at 6.0% (alloy 20, comparison). It was found that the alloy) had poor room temperature ductility (x).
In the alloy 16 which is a comparative alloy, the Nb component ratio was below the range of 2 to 5%, and it is probable that the effect of improving the high temperature strength by strengthening precipitation was not observed.
On the other hand, in the alloy 20 which is a comparative alloy, the Nb component exceeds the range of 2 to 5%, and as can be seen from the backscattered electron image photograph (FIG. 6), the precipitate (white phase) associated with the addition of Nb It is probable that the room temperature ductility was poor due to this because the amount was too large.
In the alloy 17 which is the invention alloy, the Nb component ratio is in the range of 2 to 5%, and as can be observed from the backscattered electron image photograph (FIG. 9), the amount of the B2 phase (black phase) and the precipitate. It is probable that both the room temperature ductility and the high temperature strength were good because the balance with the amount of (white phase) was well present and the conditions were suitable.

(5) Suitable component ratio of W Alloys 21 to 25 are a group in which the W component ratio is significantly changed. In this group, the component ratio excluding W, Fe and unavoidable impurities is atomic%, Al (10 to 20%): Ni (25 to 40%): Cr (5 to 15%): Nb (2 to 5%). ), When W is 1.0%, 2.0%, and 3.0% (alloys 22, 23, and 24, respectively), both room temperature ductility and high temperature strength are good (◎). However, when W is relatively low at 0.7% (alloy 21, reference alloy), the evaluation of high temperature strength is limited to (〇), and when W is relatively high at 4.0% (alloy 25, reference alloy). For the reference alloy), it was found that the evaluation of room temperature ductility was limited to (○).
In the alloy 21 which is a reference alloy, the W component ratio is below the range of 1 to 3%, and it is considered that the effect of improving the high temperature strength by strengthening precipitation was relatively small.
On the other hand, in the alloy 25, which is a reference alloy, the W component exceeds the range of 1 to 3%, and as can be seen from the backscattered electron image photograph (FIG. 7), the precipitate (white phase) associated with the addition of W It is probable that the evaluation of room temperature ductility was limited to (○) due to this because the amount was a little too large.
(6) Summary As described above, from the measurement results and evaluation results in Table 1, the component ratio excluding Fe and unavoidable impurities is atomic%, Al (10 to 20%): Ni (25 to 40%): Cr ( 5 to 15%): It was shown that austenitic Fe-based alloys in the range of Nb (2 to 5%) have both excellent effects compared to alloys outside these composition ratios. ..
Further, from the measurement results and evaluation results in Table 1, the component ratio excluding Fe and unavoidable impurities is atomic%, and Al (10 to 20%): Ni (25 to 40%): Cr (5 to 15%) :. Austenitic Fe-based alloys in the range of Nb (2-5%): W (1-3%) may achieve even better effects than alloys outside the range of these composition ratios. Shown.

The austenitic Fe-based heat-resistant alloy of the present invention has sufficient ductility at room temperature and has sufficiently high strength at high temperatures, and is therefore used as a material for high-temperature rotating parts such as various engines and turbines, and high-temperature corrosion-resistant members. It is suitable for. Further, since the austenitic Fe-based heat-resistant alloy of the present invention can be processed and manufactured as a member by a general-purpose method such as melting, casting or forging, and rolling method, the superiority in terms of manufacturing cost is maintained. It can be put to practical use.

Claims (5)

At atomic percent,
Al: 10-21%,
Ni: 25-40%,
Cr: 5-16%,
Nb: 2-5%
Austenitic Fe-based heat-resistant alloy containing Fe and the balance consisting of Fe and unavoidable impurities. In addition, at atomic%,
W: 1-3%
The austenitic Fe-based heat-resistant alloy according to claim 1, wherein the austenitic Fe-based heat-resistant alloy contains Fe and the balance is composed of Fe and unavoidable impurities. At atomic percent,
Al: 11-19%,
Ni: 26-38%,
Cr: 5 to 15%,
Nb: 2-5%,
W: 1-3%
Austenitic Fe-based heat-resistant alloy containing Fe and the balance consisting of Fe and unavoidable impurities. The alloy according to any one of claims 1 to 3, which has a ductility of 5% or more in a tensile test at room temperature. The alloy according to any one of claims 1 to 4, which has a high-temperature strength of 450 MPa or more in a tensile test at 700 ° C.

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