JPH073433A - Iron-base material excellent in high temperature oxidation resistance and production there of - Google Patents

Abstract

PURPOSE:To obtain the iron-base material having a dense insulating film vapor- deposition Al onto the surface of an iron-base alloy while regulating partial pressure of oxygen in an atmospheric gas and forming an Al-O film having lower oxygen concentration than Al2O3. CONSTITUTION:Al is vapor-deposited onto the surface of an iron-base alloy while regulating partial pressure of oxygen in an atmospheric gas to form a film containing, in Al, oxygen by the amount lower than the oxygen of the stoichiometric amount of Al2O3. The above iron-base alloy contains, by mass, 8-35% Cr, 0.4-8% Al, or 0.6-6% Si and further <=0.2% rare earth elements or U. Moreover, oxygen is contained by 1-50mo.% in Al in the above film, and an Al2O3 layer is formed on the outermost surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an iron-based material having an insulating film and excellent in high temperature oxidation resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Electric heating materials for heaters and the like must often have their surfaces insulated. One of the methods for obtaining a metal material whose surface is insulated is to form an insulating oxide film on the surface of the heating element. For example, high alloy steel
When (stainless steel) is used as a heating element material, a method is known in which Al-containing steel or Al-coated steel is heated in an air atmosphere or an oxidizing atmosphere to form an Al ₂ O ₃ layer on the surface.

By this heating, in the case of Al-containing steel, Al in the steel is oxidized to form an Al ₂ O ₃ layer on the surface, and in the case of Al-coated steel, the coating Al is oxidized to Al ₂ O ₃ as well. The remaining A
l diffuses into the steel and forms an insulating Al ₂ O ₃ layer on the surface.

The material produced in this manner, even if used at high temperature, undergoes oxidation of Al in the steel to maintain or increase the insulating property. It is also used as an insulating material. In particular, this material has a useful application as a sheet heating element.

[0005]

When an insulating layer made of Al ₂ O ₃ is formed on the surface of an iron base material such as high alloy steel, the insulating layer must be dense and free from cracks and the like. This is because if a crack occurs or peels off, the insulating property will be impaired.

However, on the surface of the iron base material, a dense A having a high insulating property is used.
To form the l ₂ O ₃ layer, high temperature heating or long time heating is required. For example, in steel containing 5% Al, the thickness is
Heating at 1100 ° C. for 5 hours is required to form a 0.5 μm Al ₂ O ₃ layer. Therefore, there are problems that this heating and oxidation treatment is costly, the productivity is low, and the life of the heating furnace is shortened.

On the other hand, when the iron base material is a thin plate such as a foil, since the volume of the iron base material is small relative to the surface area, a large proportion of Al is consumed by the first thermal oxidation treatment,
There is a problem that the amount of Al in the iron base material decreases. Therefore, the amount of Al in the iron base material required to maintain the Al ₂ O ₃ layer during use is reduced, and the surface insulation life and high temperature oxidation life of the iron base material are shortened. Also, when used as a heater material, the electrical resistivity changes due to a decrease in the amount of Al in the foil, and the expected heat generation is often not obtained. If the Al ₂ O ₃ layer peels off during use at higher temperatures, the Al consumption will increase further and the life will be very short.

The same problem occurs when an Al coating is formed on the surface of an iron base material and then heated in an oxygen atmosphere. To oxidize the Al coating into a dense Al ₂ O ₃ layer, a high temperature is required. Requires long-term heating. There is also a problem that abnormal oxidation occurs due to heating for a long time and the coating film cracks or peels off due to volume expansion, which shortens the useful life.

An object of the present invention is to solve the above-mentioned problems when forming an Al ₂ O ₃ -based insulating layer on the surface of an iron base material.

[0010]

The present invention is directed to an Al-O-based coating having a lower oxygen concentration than Al ₂ O ₃ , that is, a smaller amount of oxygen than the stoichiometric amount of Al ₂ O ₃ in Al. The present invention provides an iron-based material in which the coating contained in 1) is formed on the surface of an iron-based alloy, and further, an Al ₂ O ₃ layer is formed on at least the outermost surface of the coating.

It can be said that the film is a layer in which Al ₂ O ₃ is mixed in the metal Al. Such a coating can be formed by adjusting the oxygen partial pressure of the atmospheric gas when Al is vapor-deposited on the surface of the iron-based alloy.

[0012]

The function of the present invention is to form on the surface of an iron-based alloy,
Al ₂ O ₃ concentration of oxygen is low Al-O-based coatings than, since it can be said that the Al ₂ O ₃ in the Al is a layer mixed and heated at the high temperature heating in the air (e.g., 1000 to 1200 ° C. ) Al in the surface layer oxidizes early to form an Al ₂ O ₃ layer, but while the Al ₂ O ₃ layer on the outermost surface acts as a barrier and the oxidation of Al inside the film does not proceed, Al
Diffuses into the iron-based alloy and Al ₂ O ₃ inside the coating is concentrated. The diffusion of Al into the iron-based alloy increases the high temperature oxidation resistance of the iron-based alloy itself. Oxygen concentration in the film is 1
If it is less than mol%, the effect of early formation of the Al ₂ O ₃ layer on the surface layer cannot be expected. On the other hand, if the oxygen concentration exceeds 50 mol%, the diffusion of Al ₂ O _{3 into} the iron-based alloy is hindered and the Al concentration in the iron-based alloy does not increase. Therefore, the oxygen concentration in the film is preferably 1 mol% or more and 50 mol% or less.

The situation in which a dense Al ₂ O ₃ layer is formed on the surface of the iron-based alloy in a short time will be described below in detail with reference to the drawings.

FIG. 1 shows that Al ₂ is formed on both sides of a plate-shaped iron-based alloy 1.
The state in which the Al—O type coatings 2A and 2B having a lower oxygen concentration than O ₃ are applied is schematically shown. It can be said that the coating films 2A and 2B are layers in which Al ₂ O ₃ fine particles are mixed in the metal Al.

When the material of FIG. 1 is heated to, for example, 1100 ° C. in an air atmosphere as shown in Examples described later, (a) of FIG.
→ through the steps of (b) → (c), the coating of dense the Al ₂ O ₃ layer is produced early. In the initial stage (a), a thin Al ₂ O ₃ layer 3 is formed on the outermost surface of the film 2. Then, Al starts to diffuse from the inside of the coating 2 into the iron-based alloy base material. In the step (b), the Al ₂ O ₃ layer 3 on the outermost surface serves as a barrier to prevent oxidation of the inside, and the diffusion of Al inside the film proceeds to promote the film 2
When the total thickness of Al ₂ O ₃ is reduced and Al ₂ O ₃ in the film is concentrated, and Al is depleted, the stage (c) is reached, and the film 2 is Al ₂ O _3.
Only the O ₃ layer 3 is formed, and the iron-based alloy is covered with the dense Al ₂ O ₃ layer 3.

[0016] Since the early can dense the Al ₂ O ₃ layer 3, also become dense Al ₂ O ₃ produced in the subsequent high temperature heating, the oxidation increase is reduced. Decrease in oxidation weight increase means that high temperature oxidation life and insulating life are prolonged.

Therefore, the iron-based material of the present invention has the effect that the surface is insulative at an early stage and the insulating property is not lost even if high temperature heating is repeated. That is, according to the present invention, it is possible to provide an iron-based material having an insulating surface having high high temperature oxidation resistance. The material of the present invention is particularly suitable as a heat generating material for heaters, and is suitable as a planar heat generating element having a plate shape.

The material of the present invention has the state of FIG. 1, that is, Al ₂ O.
_Although it can be used for high temperature applications with the Al-O based coating 2 having an oxygen concentration lower than that of ₃ , it is actually shown in FIG.
As in steps (a), (b), and (c), it is preferable to use it in a state in which a dense Al ₂ O ₃ layer is formed on at least the outermost surface layer. When used in the state of Fig. 1 or the state of (a) or (b) of Fig. 2, it may be in the state of (c) during high temperature use, but in the sense of ensuring insulation, It is preferable to preheat up to step (c) to form a dense Al ₂ O ₃ layer on the surface of the iron-based alloy.

As shown in FIG. 1, a material in which an Al-O coating 2 having a lower oxygen concentration than Al ₂ O ₃ is applied to the surface of an iron-based alloy is manufactured by a vapor deposition method such as PVD method or CVD method. can do. That is, when Al is vapor-deposited on the surface of an iron-based alloy by such a vapor deposition method, the iron-based alloy is coated with a film containing oxygen less than Al ₂ O ₃ by adjusting the oxygen partial pressure of atmospheric gas. It may be vapor-deposited on the surface of.

At that time, in order to adjust the partial pressure of oxygen gas in the atmosphere, not only oxygen gas but also oxygen-containing gas such as H ₂
It can be performed by adjusting the partial pressure of O, CO ₂ , CH ₃ OH gas or the like. In addition to the oxygen-containing gas, an inert gas such as Ar may be present when it is advantageous to maintain the predetermined pressure inside the vapor deposition device.

When the iron-based alloy as the base material for forming the coating film 2 is used as a heat-generating material for heating the material of the present invention by energization, it is necessary to adjust the electric resistance to an intended value by the alloy component. However, in any case, stainless steel is preferable because it is used at high temperature. Specifically, iron-based alloys contain 8 to 35 mass% Cr and 0.4 to 8 mass%.
A stainless steel containing% Al is preferred.

In such an Al-containing stainless steel, if Si is contained in an amount of 0.6 to 6 mass%, the high temperature oxidation resistance is further improved. Similarly, 0.2 mass% of rare earth element or Y
%, The high temperature oxidation resistance can be improved.

The action of Cr, Al, Si, rare earth elements or Y in the iron-based alloy will be described below.

Regarding Cr. When the iron-based alloy is foil, etc., it is contained due to repeated cracking and self-repairing during the heating / cooling cycle.
l may be exhausted. In this case, the conductive Fe
The oxide grows rapidly, the Al ₂ O ₃ film peels off, and the insulating property is lost. The growth of Fe oxide can be prevented by including 8 mass% or more of Cr in the iron base material. This is because when Al is exhausted, Cr ₂ O ₃ and FeO.Cr
_{This is because 2} O ₃ can be made dense and the subsequent growth of oxide is suppressed. In addition, the inclusion of Cr enhances the toughness and workability of the material. However, the upper limit of Cr content is 3
Up to 5 mass%. When the content exceeds 35 mass%, the base material is 30
Below 0 ° C, it becomes extremely brittle and cannot be processed.

Regarding Al. When Al is contained in the base steel, when the Al ₂ O ₃ coating film is cracked or peeled off for some reason, it serves to restore it during use at high temperature. In the material of the present invention, Al in the original coating is diffused into the base material and Al exists in the base material. However, if the base material itself contains Al from the beginning, it is sufficient as an Al supplement source. Becomes For this reason,
It is preferable to use an iron-based alloy containing 0.5 mass% or more of Al. However, since steel containing Al exceeding 8 mass% is vulnerable to thermal shock, iron-based alloys contain 0.5-8 mass% of A.
Those containing l are preferable.

Regarding Si. Si is the high temperature resistance of the material of the present invention, as shown in Examples below.
It has the effect of improving the oxidation life. That is, the same as Cr
When Al is exhausted like₂Or Fe₂ SiO₂Is precise
It becomes dense and has a protective effect, and suppresses subsequent oxidation. This
In order to obtain the effect of Si, the amount of Si in the iron-based alloy is 0.6m.
More than ass% is required, but if more than 6mass% is included
The effect is saturated, and the manufacturability and workability of steel are
Since it will worsen, it is better to add 0.6-6 mass% Si.
Yes.

Regarding the rare earth element or Y. The rare earth element or Y also has the effect of improving the high temperature oxidation resistance as shown in the examples described later, and has the effect of increasing the adhesion of the Al ₂ O ₃ layer. However, if the total amount of rare earth elements and Y exceeds 0.2 mass%, the Al ₂ O ₃ film is likely to be peeled off by depositing as inclusions in the iron base material. Therefore, the total content of rare earth elements or Y should be 0.2 mass% or less.

[0028]

【Example】

[Example 1] Two kinds of stainless steel No. 1 and No. 2 having the chemical composition values shown in Table 1 (both having a thickness of 1 mm and 200 x 200 mm) were prepared by using a vacuum evaporation apparatus equipped with an electron beam evaporation apparatus. ) Was used as a substrate, and pure Al was used as the electron beam target to form Al vapor deposition films having different oxygen concentrations on both surfaces of the substrate while adjusting the oxygen partial pressure in the atmosphere.

The operating procedure is as follows. First, the apparatus is evacuated to 1 × 10 ^-5 Torr, a mixed gas of O ₂ : Ar = 1: 1 is introduced into the apparatus until the set oxygen partial pressure is reached, and then Al is added. Evaporated with electron beam. Ar gas was introduced to prevent deterioration of pump oil. Vapor deposition rate on a steel plate substrate is 0.1 μm / s
The partial pressure of the mixed gas of O ₂ and Ar was adjusted so that the oxygen concentration in the Al vapor deposition film would be the target value.

In all cases, the pure Al equivalent is 5.5 g / m²Inclusion
Deposition at the time it is deposited on both sides of the substrate
Finished. Table 2 shows the vapor deposition film of each coated steel sheet obtained.
The oxygen concentration (mol%) is shown. Al₂O₃In case of film
Stoichiometric oxygen concentration is 3/5 x 100 mol% = 60 mol
%, The deposited film of each coated steel sheet obtained is Al₂O ₃
It is a substance with a much lower oxygen concentration. Therefore,
These are Al in Al₂O₃Think of it as a mixture
Good. In addition, the oxygen concentration in the vapor deposition film in the comparative example is 0%.
Is a pure Al film obtained by making the oxygen partial pressure extremely low.

[0031]

[Table 1]

[0032]

[Table 2]

Each coated steel sheet was heated at 1100 ° C. in the atmosphere. The resistance value is 1 × 10 ⁸ due to the formation of the Al ₂ O ₃ film.
The heating time until it became Ωm or more was examined. The results are also shown in Table 2.

From the results shown in Table 2, in the examples of the present invention, the higher the oxygen concentration in the vapor-deposited film, the shorter the heating time until the insulating property is obtained, and the extent thereof is independent of the chemical composition of the base stainless steel. It can be seen that it is. That is, according to the example of the present invention, a fine Al ₂ O ₃ film is formed through the steps (a) → (b) → (c) of FIG.
The formation time of layer 3 is short. On the other hand, in the case of pure Al coating or the case of oxidizing Al in steel as in the comparative example, it takes a very long time to form a similar Al ₂ O ₃ layer.

Example 2 In Table 1, the thickness was 0.05 μm.
Inventive Examples A and B of Table 3 were prepared in the same manner as in Example 1 except that No. 2 steel was used as the substrate and vapor deposition was performed on both sides of the substrate such that the pure Al equivalent was 4 g / m ^2. And three types of coated steel sheets of Comparative Example C were manufactured. Comparative Example C is a pure Al coating. Comparative Example D is the No. 1 raw material steel in Table 1 itself having a thickness of 0.05 μm.

[0036]

[Table 3] Inventive Examples A and B differ from each other in the oxygen concentration in the vapor-deposited film.
g / m ² is vapor-deposited on both sides, and Comparative Example D is A
It is a material without vapor deposition of stainless steel with a content of 5.01%, and the total amount of Al of A, B and C is equal.

Then, heat resistance tests of four kinds of materials were conducted. In the test, each sample was continuously heated at 1100 ° C in the atmosphere and the increase in oxidation was measured over time. The results are shown in Fig. 3.
The unit of time on the horizontal axis is the square root, and the actual time is its square.

From the results of FIG. 3, the invention samples A and B are
Up to 22 ^{2 to} 25 ² hours (480 to 630 h), the amount of oxidation increase gradually increased and abnormal oxidation did not occur, but in Comparative Examples C and D, Al in the steel was depleted early and about 12 ^{2 to} 14 ² Time (140-190
It can be seen that abnormal oxidation starts in h).

When the electric resistance of the surface of the sample after the abnormal oxidation of the comparative example was measured, it was 1 × 10 ⁸ Ωm or less, and the insulating property was deteriorated. This is because the coating film expanded in volume during abnormal oxidation, causing cracks and peeling.

Example 3 Al ₂ O ₃ -containing Al vapor-deposited film made of stainless steel No. 3 to No. 8 having chemical composition values shown in Table 4 and having an average oxygen concentration of 20 mol% on both surfaces having a thickness of 0.05 μm. A coated steel sheet was manufactured in the same manner as in Example 1 except that The vapor deposition of each coated steel sheet was adjusted so as to have an Al equivalent of 5.5 g / m ² . For comparison, No. 3, No. 4 and No. 7 steels (thickness 0.05 μm) were also vapor-deposited with pure Al.

Each coated steel sheet was heated to 1150 ° C., and the time until the oxidation started to proceed rapidly, that is, the time when the increase in the oxidation increased suddenly (high temperature oxidation life) was measured. The results are also shown in Table 4. In addition, in each case, the resistance became 1 × 10 ⁸ Ωm or less at the high temperature oxidation life, and the insulating property deteriorated.

[0042]

[Table 4]

The following can be seen from the results in Table 4. (1) Even with the same steel type, the Al ₂ O ₃ -containing Al vapor deposition film of the present invention has a higher high temperature oxidation life than the pure Al vapor deposition film of the comparative example. (2) Even with the same Al ₂ O ₃ -containing Al vapor-deposited film, the higher the Al content in the steel, the higher the high temperature oxidation life. (3) As seen in the comparison of steel No. 4 and No. 5,
The higher the value, the higher the high temperature oxidation life. (4) As can be seen from the comparison between Steel No. 6 and Steel No. 7, the inclusion of rare earth elements in steel increases the high temperature oxidation life.

[0044]

As explained above, according to the present invention, an iron-based material having a dense insulating coating on the surface of an iron-based alloy can be obtained. The material of the present invention is particularly useful when used as a heater material because its surface is insulated, and the insulating coating is stable for a long time. Further, even when the insulating coating is damaged, it has the ability to be self-repaired by receiving Al supplementation from the iron-based alloy. The material of the present invention also has an effect that the manufacturing cost is low because the insulating coating formed of the Al ₂ O ₃ layer is formed in a short time in terms of manufacturing.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a state of an intermediate product of the material of the present invention having an Al ₂ O ₃ -containing Al coating on the surface of an iron-based alloy.

FIG. 2 is a schematic cross-sectional view similar to FIG. 1, schematically showing a step of forming an Al ₂ O ₃ layer from the state of the intermediate product of FIG.

FIG. 3 is a diagram showing the results of Example 3 in the text, and is a diagram showing the results of heat resistance tests of the present invention materials A and B and the comparative materials C and D.

[Explanation of symbols]

1 Iron-based alloy 2 Al ₂ O ₃ containing Al coating 3 Al ₂ O ₃ layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Ando 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. (72) Inventor Minoru Saito 5 Ishizu Nishimachi, Sakai City, Osaka Nisshin Steel Co., Ltd. Steel Research Institute

Claims (7)

[Claims] 1. An iron-based material excellent in high-temperature oxidation resistance, wherein a coating containing a smaller amount of oxygen in Al than the stoichiometric amount of Al ₂ O ₃ is formed on the surface of an iron-based alloy. 2. A coating containing a smaller amount of oxygen in Al than the stoichiometric amount of Al ₂ O ₃ is formed on the surface of the iron-based alloy, and Al ₂ O ₃ is formed on at least the outermost surface of the coating. An iron-based material that has excellent resistance to high-temperature oxidation in which layers are formed. 3. The iron-based material according to claim 1, wherein 1 mol% or more and 50 mol% or less of oxygen is contained in Al of the coating film. 4. The iron-based alloy contains Cr of 8 to 35 mass% and
The iron-based material according to claim 1, containing 0.4 to 8 mass% of Al. 5. The iron-based material according to claim 4, wherein the iron-based alloy contains 0.6 to 6 mass% Si. 6. The iron-based material according to claim 4, wherein the iron-based alloy contains 0.2 mass% or less of a rare earth element or Y. 7. When depositing Al on the surface of an iron-based alloy, a film containing oxygen less than Al ₂ O _{3 in} Al is adjusted on the surface of the iron-based alloy by adjusting the oxygen partial pressure of atmospheric gas. A method for producing an iron-based material excellent in high-temperature oxidation resistance, characterized by vapor deposition.