JPH0483855A - Fe-cr-ni-al ferritic alloy - Google Patents

Abstract

PURPOSE:To obtain an Fe-Cr-Ni-Al ferritic alloy excellent in strength and hardness and having superior workability by specifying a composition consisting of Cr, Ni, Al, Ti, Zr, Y, Hf, Ce, La, Nd, Gd, and Fe and compositional relations among them, respectively. CONSTITUTION:An Fe-Cr-Ni-Al ferritic alloy has a composition which consists of, by weight, 25-35% Cr, 15-25% Ni, 4-8% Al, 0-0.5% Ti, 0.05-1.0% of one or >=2 elements among Zr, Y, Hf, Ce, La, Nd, and Gd, and the balance Fe and in which a relationship represented by [Ni content + 14] < [Cr content + Al content] < [Ni content + 17] exists among respective contents (by weight) of Cr, Ni, and Al, and further, a part of the structure of this ferritic alloy is composed of austenite phase. It is preferable to regulate the percentage of the above austenite phase to <=20vol.%, particularly about 5-15vol.%. By this method, the ferritic alloy excellent in strength and hardness, having superior workability, and capable of forming dense Al2O3 film on the surface uniformly can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is directed to the production of uniform A1803 (alumina) that is dense on the alloy surface and has excellent adhesion to the alloy in a high-temperature oxidizing atmosphere.

The same applies below), and the tensile strength is 0.
Extremely excellent in 2% yield strength, elongation, and hardness, and
The present invention relates to a Fe-Cr-Ni-Al ferrite alloy with good workability.

[Conventional technology]

Uniform Al z 0 due to high temperature oxidation! Examples of high-temperature oxidation-resistant alloys that form films include Fe-Cr-Aj2 alloys, as disclosed in JP-A-54-141314 and JP-A-60-262943. These alloys do not contain Ni. Also, JP-A-52-7
No. 8612 and Japanese Unexamined Patent Publication No. 174352/1986 propose an austenite phase alloy whose main component is l''e-Cr-Ni-Al.

[Problem to be solved by the invention]

The strength of the Fe-Cr-A1 alloy is approximately the same as that of ferritic stainless steel, and even if it is subjected to some heat treatment, the above-mentioned mechanical properties cannot be significantly improved. Furthermore, in order to produce an A1*Os film with a thickness of several cm or more, it must be exposed to high temperatures of 1100°C or more for several hours or more, during which time the crystal grains of the alloy grow significantly and the mechanical properties deteriorate. bring about. On the other hand, the above F
e-Ni-Cr-Al alloy has AI! on the surface! , 0,
When a film is formed, there is a problem that a uniform film is not formed and peels off.

On the other hand, in the case of alloys, they also need to have good workability from the viewpoint of practicality.

An object of the present invention is to provide an alloy that has significantly superior strength and hardness to conventional high-temperature oxidation-resistant alloys, and also has good workability.

[Means to solve the problem]

In order to solve the above problems, the Fe-Cr-
N1-Aj! based ferrite alloy Cr: 25 to 35% by weight, Ni: 15 to 25% by weight, An: 4 to 81% by weight,
Ti: 0 to 0.5jii amount%, Zr, Y% Hf, Ce
, any one or two of La, Nd and Gd
70.05 to 1.0% by weight of species or more, Fe: the balance, and between each content (in weight%) of Cr, Ni and Al, [Ni content + 14) < CCr content + A1 content ] [Ni content + 17], and a part of it is an austenite phase.

Fe-Cr-N1-A7 of this invention! In the case of a ferrite alloy, the proportion of the austenite phase is 20% by volume or less, preferably 5 to 15% by volume.

Hereinafter, the rFe-Cr-Ni-AA'-based ferrite alloy will be simply referred to as "ferrite alloy."

The ferrite alloy according to the present invention is characterized by having a ferrite phase as its base, and is also an alloy that can finely and uniformly disperse and precipitate NiAl-based intermetallic compounds, which are said to play a major role in toughening. be.

Therefore, the strength is significantly improved compared to ordinary ferritic stainless steel or FeCr-Al alloy that does not contain Ni.

When the ferrite alloy according to the present invention is heated in a high-temperature oxidizing atmosphere, it forms an oxide film mainly composed of Altos, which is dense and has excellent adhesion to the alloy, and has high-temperature oxidation resistance. is very good. The temperature of the high temperature oxidizing atmosphere is preferably 800°C or higher and 1200°C or lower. If the temperature is below 800℃, AI will be uniform over the entire surface! gos
The film may not form and the base material may become brittle if the temperature exceeds 1200°C. Moreover, the heating time is preferably 0.5 hours or more. If the time is shorter than 0.5 hours, Al will be uniform on the entire surface.
A TOS film may not be formed. The thickness of the Al, 03 film is not particularly limited.

While Fe-Cr-Al alloys, which are conventional high-temperature oxidation-resistant alloys, have the disadvantage of low strength inherent to ferritic systems, the ferritic alloys of this invention are comparable to austenitic heat-resistant steels. It has strength.

In addition, when high-temperature heat treatment is applied to form a uniform Al x Oz film on the surface, coarsening of crystal grains is observed in general alloys, but in the ferrite alloy of the present invention, coarsening of crystal grains is observed in the alloy matrix. Due to the presence of NiA1 finely and uniformly dispersed and precipitated, coarsening of crystal grains is suppressed.

Therefore, in the ferrite alloy of the present invention, the mechanical properties of the alloy matrix hardly deteriorate due to high-temperature heat treatment.
It becomes possible to manufacture highly strong alloys.

That is, the alloy of the present invention exhibits excellent high-temperature oxidation resistance comparable to that of Fe-Cr-Al alloys, and improves its strength, which is a drawback thereof, and furthermore, the alloy is heat-treated in an oxidizing atmosphere. By doing so, it is possible to form an Autos film on the alloy surface, and due to the dispersed precipitation of NiAl, the A1. O, it is possible to prevent deterioration of the mechanical properties of the alloy due to the heat treatment of forming a film.

The content of the elements contained in the alloy of the present invention and the reason for limiting the content will be explained below. The alloy of this invention is an Fe-based alloy containing large amounts of ferrite-forming elements Cr and Al and austenite-forming element Ni, and the amounts of each element are adjusted so that the alloy is mainly composed of a ferrite phase. I have to choose. The reason why the alloy of this invention is mainly made of ferrite phase is as follows. Ferrite phase alloys tend to form a thick Adz O3 film on the surface that is dense and has good adhesion to the substrate through oxidation heat treatment, but austenite phase alloys tend to form a thick Adz O3 film on the surface with good adhesion to the substrate, but austenite phase alloys tend to form a thick Adz O3 film on the surface with good adhesion to the substrate.
This is because the film is not formed uniformly and peels off. When the alloy is made into a ferrite phase, increasing the amount of Ni causes [Cr+
A1) The amount also needs to be increased. Note that if the content is 20% by volume or less, even if the austenite phase is present, the excellent properties of the ferrite alloy described above are appropriately maintained without being significantly impaired.

In the alloy of this invention, Cr is 25 to 35% by weight of the total
occupies In the Fe-Cr-Aβ alloy, Cr is
It is necessary to form a dense and uniform AEZ O8 film on the alloy surface, but since the alloy of this invention contains a large amount of Ni, it is necessary to add N to form a ferrite phase in the alloy.
Even when i is the lower limit and Ae is the upper limit, 25% by weight or more of Cr is required. In an alloy in which the Ni content is at the lower limit, the Al content is near the upper limit, and the Cr content is 25% by weight, the formation of the A#zCh film is incomplete. Therefore, the lower limit of Cr is 25% by weight. Further, as the Cr content in the alloy increases, the tendency towards embrittlement becomes stronger, so the upper limit of Cr is 35% by weight.

In the alloy of this invention, Ni is 15 to 25% by weight of the total
occupies In this invention, the mechanical properties are improved by precipitating fine NiAl into the alloy, but in the coexistence with A1, N1A7! N to precipitate
i is an essential element. In order to be sufficiently effective in improving mechanical properties, approximately 15% by weight or more of Ni is required, so the lower limit of Ni is 15% by weight. If the amount of Ni increases, NiA1! The alloy of the present invention preferably has a ferrite phase of about 80% by volume, and increasing the content of Ni, an austenite-forming element, increases the content of Cr and Al. It is necessary to increase the amount. However, if the amount of Ni exceeds 25% by weight, the amount of Cr must be increased, which makes it easier to read the mold, so the upper limit of Ni is 25% by weight.

In the alloy of this invention, A1 accounts for 4 to 8% by weight of the total. The amount of Al causes NiA# to precipitate in the alloy, and furthermore,
It is an essential element for forming an AA20 film on the alloy surface by high-temperature oxidation treatment. In particular, in order to form a dense and uniform film, it is necessary to contain 4% by weight or more of /l. The increase in Aβ content is due to the increase in Aβ content.
However, if it exceeds 8% by weight, the workability of the alloy decreases.
The upper limit of l is 8% by weight.

In the alloy of this invention, Zr, Y, Hf, Ce, La, N
Titanium group elements and rare earth elements such as d and Gd are mixed into the Autos film to improve the brittleness of the film, and are also dispersed as internal oxide particles within the alloy directly under the film, significantly improving the adhesion of the film. . In order to exhibit these effects, at least 0.05% by weight of one or more of Zr, Y, Hf, Ce, La, Nd and Gd is required. On the other hand, if the content exceeds 1.0% by weight, the workability of the alloy decreases rapidly, so the upper limit is 1.0% by weight.

When Ti is contained in the alloy at about 0.5% by weight,
Appropriate heat treatment forms fine intermetallic compounds that help strengthen the alloy. Although the alloy of the present invention may not contain Ti, for these reasons, it may not contain Ti.
May contain.

However, if the Ti content exceeds 0.5% by weight, At2
The content is preferably 0.5% by weight or less since it may impair the adhesion and density of the zoz film.

In the alloy of this invention, the balance other than the above components is Fe. However, this is not limited to the case where the remainder is entirely Fe; for example, the case where the remainder also contains impurities that are unavoidably present in addition to FeJ) is also included. Note that among the impurities, it is preferable that the three elements Si and C1N fall within the following ranges for the following reasons.

Si becomes SiOt during high-temperature oxidation treatment, and becomes Al, 0
8. Since there is a risk that it may be mixed into the film and impair the denseness of the film, it is desirable that the content be 0.3% by weight or less. It may be 0% by weight.

C reacts with Cr at high temperatures to form Cr carbides and embrittle the alloy. Also, CO becomes CO□ gas, and A 1
t 01 Destroy the film. Furthermore, it easily reacts with rare earth elements and reduces the effect of rare earth elements on improving the adhesion of the film. For these reasons, C is desirably 0.01% by weight or less. It may be 0% by weight.

N reduces the toughness of the alloy, and also reacts with Cr during high-temperature heating to form Cr-based nitrides, which can cause embrittlement of the alloy. Therefore, the content is preferably 0.015% by weight or less. 0
It may be expressed in percent by weight.

As stated above in the reasons for limiting the components, the ferrite alloy of the present invention is basically a ferrite phase, but contains an austenite phase mixed therein in an amount of 20% by volume or less, more preferably in the range of 5 to 15% by volume. It is possible to form a homogeneous film without impairing the properties of the alloy, and at the same time, the presence of the austenite phase improves workability (hot working/cold working). The alloy of this invention is a high-temperature oxidation-resistant alloy with improved strength by dispersing fine N1AA-based intermetallic compounds, and furthermore, it can be kept in an oxidizing atmosphere at a high temperature of 800°C or higher and 1200°C or lower for 0.5 hours or more. Heat treatment produces a dense and uniform Aj with excellent adhesion! z O! Forms a film. As a result, AA, 0! It is a high-strength material with a coating that is oxidation-resistant and serves as a protective film.

In the ferrite alloy of this invention, Cr,
In addition to adjusting Aj2 and Ni to the above numerical range, C
Between each content (wt%) of r, Ni and AN, [
Ni content + 14) < [Cr content + A1 content]
It is necessary to satisfy the following relationship: Ni content + 17].

The higher the ratio of [Cr content+A1 content], the easier it is to form an excellent A12tO* film. However, if the ratio of [Cr content + A1 content] is too high, the alloy will become a single ferrite layer and the workability will decrease, so the upper limit should be set as [Ni
content + 17] [Cr content 10 Al content]
The smaller the ratio, the better the workability. However, [C
If the ratio of [r content + Al content] is too low, the austenite phase will be too large (for example, more than 20% by volume), and the mechanical strength will not be sufficient, and the excellent AI
! , it becomes difficult to form an O1 film, so the lower limit is set to exceed [Ni content +14].

Since the ferrite alloy of the present invention has an aluminum oxide film formed on its surface and exhibits high oxidation resistance, it is suitable for electric heating materials, automobile exhaust gas purification materials, boiler pipes, and exhaust valves for internal combustion engines. It can also be applied to interior and exterior building materials. However, the uses are not limited to these.

〔Example〕

Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following examples.

1. Examples 1 to 5, Comparative Examples 1 to 6, and Conventional Example 1.2 - Alloys having the compositions shown in the columns of Examples 1 to 5, Comparative Examples 1 to 6, and Conventional Example 1 in Table 1 were heated by high-frequency induction. It was melted in a type vacuum melting furnace and rolled into two crane plate shapes by hot and cold working.

That is, in a high vacuum of 5 x 10-'Torr or more, electrolytic iron, electrolytic chromium, and Ni pellets are placed in an aluminum crucible and melted, and in the melt, aluminum-iron alloy, FeZr alloy, FeTi alloy, and Hf and rare earth element pieces were added. The alloy was then cast into an iron or copper mold in a furnace in the same vacuum to obtain an alloy ingot. The obtained ingot was heated to 800° C. to 1100° C., forged with a hammer, and further cold rolled at the same temperature. Conventional Example 2 used commercially available materials. The alloys of Examples, Comparative Examples, and Conventional Examples were cut into sizes of 2 mm x 15 m x 20 m, the surfaces were finished with No. 600 emery paper, and heat treatment (oxidation treatment) was performed at 1150°C for 15 hours in the air to give a surface finish. An oxide film was formed.

(Test 1) The workability (
Rollability), hardness before and after forming the Al film, 0°2% proof stress, tensile strength, elongation, and austenite phase occupancy (before forming the film) were investigated. In addition, the composition of the oxide film, that is, AAz
An Os film (○) or a mixed oxide film of Fe1Cr, Ni and A6 (x) was also investigated. The results of the investigation are shown in Table 2.

Regarding the rolling properties, ○: easy workability, ×: difficult workability (cracking occurred during rolling).

The alloy of the example has an A1tos film formed on the surface and also has sufficient Vickers hardness and tensile strength. On the other hand, each alloy of Comparative Example and Conventional Example 2 has Aρ203 on the surface.
No film is formed, and Fe-Cr-A of Conventional Example 1
# alloy is AI! 20. Even if a film is formed, it is completely inadequate in terms of hardness and tensile strength.

It was confirmed by X-ray diffraction that each of the alloys of Examples 1 to 5 had a ferrite phase with an austenite phase of 20% by volume or less, and that the main component of the formed film was AAzOs. It was also confirmed by X-ray diffraction that each alloy of Comparative Example 1.2 was a single ferrite layer. The alloy surfaces of Examples 1 to 5 and Comparative Example 1.2 after the AltO film formation were observed using a secondary electron image (SE image) using a scanning electron microscope, and it was found that a dense and uniform surface film was formed. I confirmed that Exactly similar results were obtained for any of the alloy sizes mentioned above. Furthermore, when the film cross sections of each alloy of all Examples and Comparative Example 1.2 were similarly examined, it was found that Fe-
As with the Cr--Al alloy, as shown in FIG. 1, the boundary between the alloy matrix 2 and the Al2O8 film 1 was found to be complex, and the adhesion was extremely excellent.

These films did not peel off at all even when quenched in water from the oxidation temperature. In addition, in Fig. 1, 4 is the precipitated N1A.
It is A.

On the other hand, according to X-ray diffraction, each of the alloys of Comparative Examples 3 to 6 consists of two phases of ferrite decaustenite or austenite phase, and the oxide film is composed of a mixture of Cr%Ni, Fe oxides, and Altos. was. Also,
The adhesion of the film was poor, and peeling occurred when the film was cooled from the oxidation temperature to room temperature. This peeling occurred over the entire surface of the sample size mentioned above. Peeling occurred over the entire surface of the alloy (Test 2) The relationship between the state of the oxide film on the alloy surface and the content of Cr, Aj2, and Ni in Examples 1 to 5 and Comparative Examples 1 to 6 was investigated.

In Figure 2, the horizontal axis is [Ni content expressed in weight%] and the vertical axis is [Cr content expressed in weight%] + [Al content expressed in weight%]. The alloys of each example are plotted with ○, and l”e, Cr,
The alloys of each comparative example in which a mixed oxide film of Ni and A1 was formed are plotted with x. The alloy of Comparative Example 1.2, which has a single ferrite layer and has poor workability, was also plotted. As shown in FIG. 2, it can be seen that when the thickness is between the two straight lines, an Alto* film with excellent adhesion is formed, and also exhibits good workability with an austenite phase mixed therein.

Expressing this as a formula, [Ni content + 14) < [C
The relationship is as follows: r content + Al content) <, [Ni content + 17].

(Test 3) Fig. 3 shows the ferrite alloy of this invention (Example 2),
Fe-Cr-A1 alloy (conventional example 1) and 5UH660
An oxidation weight gain curve is shown when (Conventional Example 2) is heated to a temperature of 1000 to 1150°C in the atmosphere. In FIG. 3, the solid line curve is the oxidation weight gain curve of the alloy of Example 2, the - dotted line curve is the oxidation weight gain curve of the conventional example 10 alloy, and the broken line curve is the oxidation weight gain curve of the conventional example 2 alloy. The heating temperature is written next to the curve. As is clear from FIG. 3, the oxidation weight gain of the alloy of the example is approximately the same as that of the Fe-Cr-A# gold alloy, and the oxidation resistance is extremely excellent. Moreover, when compared with the oxidation weight gain of 5UH660 by heating at 1000° C. for 20 hours, it can be seen that the weight gain is about 1/9 of that.

In this way, the alloy of the example is an alloy that has both high temperature oxidation resistance and mechanical strength, and is also rich in workability.
Since the s film is formed, it is suitable for materials that require wear resistance and sliding properties. [Effects of the Invention] The ferrite alloy of the present invention has the composition as described above, and has excellent strength and hardness. Moreover, it is highly practical because it has good workability and can uniformly form a dense Al3O3 film on the surface.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the matrix and coating of the ferrite alloy of the present invention, and FIG. 2 is a cross-sectional view showing the amount of Ni and [Cr+A
1) A graph showing the relationship between the amount and the amount. FIG. 3 is a graph showing the relationship between the high temperature oxidation treatment time and the oxidation amount increase. 1...AzOs film 2...Matrix Ni amount % 3rd 8th grade (hr) Procedural amendment (voluntary November 9, 1990 Patent application No. 2-200742 2, title of the invention Fe-Cr-N1 3. Relationship with the person making the amendment Al-based ferrite alloy

Claims (1)

[Claims] 1 Cr: 25-35% by weight, Ni: 15-25% by weight
, Al: 4-8% by weight, Ti: 0-0.5% by weight, Zr
, Y, Hf, Ce, La, Nd and Gd: 0.05 to 1.0% by weight, F
e: consists of the remainder, each content of Cr, Ni and Al (
There is a relationship between [Ni content + 14] < [Cr content + Al content] < [Ni content + 17] (expressed in weight%), and a part of it is the austenite phase Fe-Cr-
Ni-Al ferrite alloy. 2 Claim 1 wherein the austenite phase is 20% by volume or less
Fe-Cr-Ni-Al based ferrite alloy as described.