JP2020521051A - Ferrite alloy - Google Patents

Abstract

The following elements C0.01 to 0.1; N: 0.001 to 0.1; O: ≤ 0.2; Cr4 to 15; Al2 to 6; Si0.5 to 3; Mn in wt% [wt%] :≦0.4; Mo+W≦4; Y≦1.0; Sc, Ce, La and/or Yb≦0.2; Zr≦0.40; RE≦3.0; balance Fe and impurities usually generated And also satisfy the following equation: a ferrite alloy. [Selection diagram] None

Description

The present disclosure relates to a ferrite alloy according to the preamble of claim 1. The present disclosure further relates to the use of ferrite alloys and the objects or coatings produced therefrom.

Ferrite alloys, such as FeCrAl alloys containing 15 to 25 wt% levels of chromium (Cr) and 3 to 6 wt% levels of aluminum (Al), protect alpha-alumina when exposed to temperatures of 900 to 1300°C. (Al ₂ O ₃ ), aluminum oxide, known for its ability to form scales. The lower limit of Al content for forming and maintaining the alumina scale depends on the exposure conditions. However, if the Al level is too low at elevated temperatures, selective oxidation of Al is not achieved and chromium and iron based scales that are not stable and have poor protection are formed.

It is generally accepted that FeCrAl alloys usually do not form a protective α-alumina layer when exposed to temperatures below about 900°C. Attempts have been made to optimize the composition of the FeCrAl alloy to form protective α-alumina at temperatures below about 900°C. However, in general, these attempts have been less successful because the diffusion of oxygen and aluminum into the oxide-metal interface is relatively slow at low temperatures, which slows the rate of alumina scale formation, i.e. , Because of the risk of severe corrosion attack and the formation of less stable oxides.

Another problem that occurs at low temperatures, i.e. below 900°C, is the long-term embrittlement reduction caused by the low temperature solubility gap of Cr in the FeCrAl alloy system. There is a solubility gap at Cr levels above about 12 wt% at 550°C. Recently, lower Cr level alloys of about 10 to 12 wt% Cr have been developed to avoid this phenomenon. This group of alloys has been found to work very well in molten lead with controlled and low pressure O ₂ .

EP0475420 relates to a rapidly solidified ferrite alloy foil consisting essentially of about 1.5 to 3 wt% Cr, Al, Si, and REM (Y, Ce, La, Pr, Nd, balance Fe and impurities). The foil may further contain about 0.001 to 0.5 wt% of at least one element selected from the group consisting of Ti, Nb, Zr and V. This foil has a particle size of up to about 10 μm. EP075420 discusses Si additions to improve the flow properties of alloy melts, but its success was limited by reduced ductility.

EP0091526 relates to alloys that are oxidative to thermal cycling and are hot workable, and more specifically to rare earth added iron-chromium-aluminum alloys. Upon oxidation, the alloy produces an oxide of the desired whisker structure on the surface of the catalytic converter. However, the resulting alloy did not provide high temperature resistance.

Therefore, it is necessary to further improve the corrosion resistance of the ferrite alloy so that it can be used in a corrosive environment under high temperature conditions. An aspect of the disclosure is to solve or at least reduce the above problems.

フェライト合金に関する。 Accordingly, the present disclosure provides the following composition in wt% to provide a combination of good oxidation resistance and excellent ductility:

Regarding ferritic alloys.

Therefore, there is a relationship between the contents of Cr and Si and Al in alloys according to the present disclosure, and when this relationship is satisfied, reduced brittleness combined with excellent oxidation resistance and ductility and increased hot corrosion resistance. An alloy having is provided.

The present disclosure also relates to objects and/or coatings comprising the ferrite alloy according to the present disclosure. In addition, the present disclosure also relates to the use of the above or below ferrite alloys for manufacturing objects and/or coatings.

Disclosed are Fe-10% Cr-5% Al to Si level phases (FIG. 1a) and Fe-20% Cr-5% Al to Si level phases (FIG. 1b). This figure was generated using Databasebase TCFE7 and Thermocalc software. Polished parts of two alloys according to the present disclosure after 50 cycles of exposure to ash of biomass (wood pellets) containing large amounts of potassium at 850° C. for 1 hour are disclosed in comparison with three reference alloys.

フェライト合金を提供する。 As already mentioned above, the present disclosure is in weight percent (wt %):

Provide a ferrite alloy.

が満たされる（元素の全ての数字は重量分率で表される）ことを、発明者は驚くべきことに発見し、得られた合金は、本開示のＣｒ範囲内の優れた酸化耐性及び加工性及び成形性の組み合わせを有することになる。一実施態様によれば、

、例えば

である。 Alloys above or below, ie alloys containing alloying elements and within the ranges referred to herein, anticipate protective surface layers containing aluminum-rich oxides even at chromium levels as low as 4 wt %. It was surprisingly found to form without. This is very important for both the workability and the long-term stability of the alloy, as the undesired brittle σ-phase is reduced or even avoided after prolonged exposure in the temperature range mentioned herein. Is important to. Therefore, the interaction between Si, Al, and Cr enhances the formation of a stable and continuous protective surface layer containing an aluminum-rich oxide, and by using the above equation, Si It becomes possible to obtain ferritic alloys which can be added and both produce and form different bodies. If the amounts of Si and Al and Cr are balanced, the following conditions:

The inventors have surprisingly found that all of the numbers are expressed in weight fractions, and the resulting alloys have excellent oxidation resistance and workability within the Cr range of the present disclosure. Will have a combination of moldability and moldability. According to one embodiment,

, For example

Is.

The ferrite alloys of the present disclosure are particularly useful at temperatures below about 900° C., as they provide a protective surface layer containing an aluminum-rich oxide formed on an object and/or coating made of said alloy. This will prevent corrosion, oxidation and embrittlement of the object and/or coating. In addition, the present ferrite alloys have a protective surface layer containing an oxide rich in aluminum formed on the surface of objects and/or coatings produced from the ferrite alloys, which results in corrosion, oxidation and oxidation at low temperatures of 400°C. It may provide protection against embrittlement. Moreover, alloys according to the present disclosure will also perform well at temperatures up to about 1100° C. and will exhibit a reduced tendency for long-term embrittlement in the temperature range 400-600° C.

The alloy can be used to form a coating. In addition, the body may also include the present alloy. According to the present disclosure, the term “coating” is intended to refer to the embodiment in which the ferritic alloy according to the present disclosure is present in the form of a contact layer with a substrate, which is exposed to a corrosive environment and achieves it. It does not matter what means and method therefor, nor the relative thickness relationship between the layers and the substrate. As such, this example is, but not limited to, a PVD coating, cladding or compound or composite material. The purpose of the alloy is to protect the material from both corrosion and oxidation. Examples of suitable objects include, but are not limited to, compound tubes, tubes, boilers, gas turbine components and steam turbine components. Other examples include superheaters, water cooling walls of power plants, components of vessels or heat exchangers (for example for reforming or other treatment of hydrocarbons or gases containing CO/CO ₂ ), steel. And parts used in connection with industrial heat treatment of aluminum, powder metallurgy, gas and electric heating elements.

Moreover, the alloys according to the present disclosure are suitable for use in environments with corrosive conditions. Examples of such environments include, but are not limited to, exposure to salts, liquid lead, and other metals, exposure to ash or high carbon content deposits, combustion atmosphere, low pO ₂ and/or high N _2. And/or high carbon active environments.

Further, the present ferrite alloys can be manufactured using the solidification rates normally present (ranging from conventional metallurgy to quench solidification). The alloy will also be suitable for the manufacture of all types of forged and extruded objects such as wires, strips, bars and plates. The amount of hot and cold plastic deformation as well as the grain structure and grain size will vary between the morphology of the body and the manufacturing route, as is known to those skilled in the art.

The functions and effects of the essential alloying elements of the alloys mentioned above and below are given in the following paragraphs. The list of functions and effects of each alloying element should not be considered complete, as further functions and effects of said alloying elements may exist.

Carbon (C)
Carbon can be present as an unavoidable impurity resulting from the manufacturing process. Carbon may be included in the ferrite alloys above or below to increase strength by precipitation hardening. Carbon should be present in an amount of at least 0.01 wt% in order to significantly affect the strength of the alloy. If the content is too high, carbon becomes an obstacle to the formation of the material and can also have a negative effect on the corrosion resistance. Therefore, the maximum amount of carbon is 0.1 wt %. For example, the carbon content is 0.02 to 0.09 wt%, for example 0.02 to 0.08 wt%, for example 0.02 to 0.07 wt%, for example 0.02 to 0.06 wt%, for example 0. It is from 02 to 0.05 wt%, for example from 0.01 to 0.04 wt%.

Nitrogen (N)
Nitrogen can be present as an unavoidable impurity resulting from the manufacturing process. Nitrogen may be included in the ferrite alloys above or below to enhance strength by precipitation hardening, especially when powder metallurgy process routes are applied. If the content is too high, nitrogen becomes an obstacle to the formation of alloys and may also have a negative effect on corrosion resistance. Therefore, the maximum amount of nitrogen is 0.1 wt %. Suitable ranges of nitrogen are, for example, 0.001 to 0.08 wt%, such as 0.001 to 0.05 wt%, such as 0.001 to 0.04 wt%, such as 0.001 to 0.03 wt%, such as 0. 0.001 to 0.02 wt %.

Oxygen (O)
Oxygen may be present in the alloys above or below as an impurity produced by the manufacturing process. In that case, the amount of oxygen may be up to 0.02 wt%, for example up to 0.005 wt%. When oxygen is intentionally added to provide strength by dispersion strengthening, such as when the alloy is manufactured through the powder metallurgy process route, the alloys above or below contain up to 0.2 wt% oxygen. ..

Chrome (Cr)
Chromium is present in the alloy mainly as a matrix solid solution element. Chromium promotes the formation of an aluminum oxide layer on the alloy by the so-called "third element effect", i.e. by forming chromium oxide in a temporary oxidation step. To meet this purpose, chromium is preferably present in the above or below alloys in an amount of at least 4 wt %. In the alloys of the present invention, Cr also enhances susceptibility to form brittle σ phase and Cr ₃ Si. This effect appears at approximately 12 wt% and is enhanced at levels above 15 wt%, so the Cr limit is 15 wt%. From an oxidative point of view, levels above 15 wt% also result in an undesired contribution of Cr to the protective oxide scale. According to one embodiment, the content of Cr is 5 to 13 wt %, eg 5 to 12 wt %, eg 6 to 12 wt %, eg 7 to 11 wt %, eg 8 to 10 wt %.

Aluminum (Al)
Aluminum is an important element in the above or below alloys. Aluminum forms a dense and thin oxide, Al ₂ O ₃ , through selective oxidation when exposed to oxygen at high temperatures, which protects the potential alloy surface from further oxidation. .. The amount of aluminum is such that sufficient aluminum is present to ensure that a protective surface layer containing an aluminum-rich oxide is formed and for repairing if the protective surface layer is damaged. Should be at least 2 wt %. However, aluminum has a negative effect on formability and large amounts of aluminum can lead to its crack formation during machining of the alloy. Therefore, the amount of aluminum should not exceed 6 wt %. For example, aluminum can be 3 to 5 wt%, such as 2.5 to 4.5 wt%, such as 3 to 4 wt%.

Silicon (Si)
In commercial FeCrAl alloys, silicon is often present at levels up to 0.4 wt %. In the ferrite alloys mentioned above or below, Si plays an important role, since Si has a great influence on the improvement of oxidation and corrosion resistance. The upper limit of Si is set workability loss at high and low temperature conditions, and the increased susceptibility to formation of long-term brittle Cr 3 _Si and σ phase during exposure. Therefore, the addition of Si has to be carried out in relation to the content of Al and Cr. Therefore, the amount of Si is 0.5 to 3 wt %, for example 1 to 3 wt %, for example 1 to 2.5 wt %, for example 1.5 to 2.5 wt %.

Manganese (Mn)
Manganese may be present as an impurity in the above or below alloys up to 0.4 wt%, for example 0 to 0.3 wt%.

Yttrium (Y)
In melt metallurgy, yttrium may be added in amounts up to 0.3 wt% to improve the adhesion of the protective surface layer. Furthermore, in powder metallurgy, when yttrium is added to form a dispersion with oxygen and/or nitrogen, the yttrium content is increased to achieve the desired dispersion hardening effect of the oxides and/or nitrides. Present in an amount of at least 0.04 wt %. The maximum amount of yttrium in a dispersion hardened alloy in the form of an oxygen-containing Y compound can be up to 1.0 wt %.

Scandium (Sc), cerium (Ce), and lanthanum (La), ytterbium (Yb)
Scandium, cerium, lanthanum, and ytterbium are exchangeable elements to improve oxidation properties, self-repair of aluminum oxide (Al ₂ O ₃ ) layers, or adhesion between alloys and Al ₂ O ₃ layers. Can be added individually or in combination in a total amount of up to 0.2 wt %.

Molybdenum (Mo) and tungsten (W)
Both molybdenum and tungsten have a positive effect on the hot strength of the above or below alloys. Mo can also have a positive effect on wettability properties. They can be added individually or in combination in amounts of up to 4.0 wt%, for example 0 to 2.0 wt%.

Reactive element (RE)
By definition, reactive elements are highly reactive with carbon, nitrogen, and oxygen. Titanium (Ti), niobium (Nb), vanadium (V), hafnium (Hf), tantalum (Ta), and thorium (Th) are reactive elements in the sense that they have a high affinity for carbon, It is therefore a strong carbide-forming element. These elements are added to improve the oxidative properties of the alloy. The total amount of elements is at most 3.0 wt %, eg more than 1.0 wt %, eg 1.5 to 2.5 wt %.

The maximum amount of each reactive element is mainly dependent on the tendency of the elements to form harmful intermetallic phases.

Zirconium (Zr)
Zirconium is often referred to as a reactive element because it is highly reactive with oxygen, nitrogen and carbon. In this alloy, Zr may have a dual role because it is present in the protective surface layer containing the oxide rich in aluminum, thereby improving the oxidation resistance and also forming carbides and nitrides. It's been found. Therefore, it is advantageous to include Zr in the alloy in order to achieve the best properties of the protective surface layer containing an aluminum-rich oxide.

However, Zr levels above 0.40 wt% affect the oxidation due to the formation of Zr-rich intermetallic inclusions, and levels below 0.05 wt% are independent of the two C and N contents. Too small for the purpose. Thus, if Zr is present, its range is 0.05 to 0.40 wt%, eg 0.10 to 0.35.

、例えば

、例えば

が満たされる場合、得られる合金は、良好な耐酸化性を達成することを、驚くべきことに発見した。 Furthermore, it has been discovered that the relationship between Zr, N and C can be important in order to achieve better oxidation resistance of the protective surface layer, i.e. alumina scale. Therefore, the inventor has found that when Zr is added to the alloy and the alloy also contains N and C, and the following conditions:

, For example

, For example

It has been surprisingly found that the resulting alloy achieves good oxidation resistance if

The balance of the above or below ferrite alloy is Fe and inevitable impurities. Examples of unavoidable impurities include, for example, elements and compounds that have not been intentionally added, but cannot be completely prevented because they usually occur as impurities in materials used for manufacturing ferrite alloys. ..

1a and 1b show that a large amount of Cr in the Si-containing ferrite alloy easily forms Si ₃ Cr inclusions, and when Cr is 20%, an undesired brittleness σ is exhibited after long-time exposure in a focus temperature region. It is shown to promote the phase. Although these figures show only two levels of Cr, 10% and 20%, a clear demonstration of the tendency for higher Cr to increase the embrittlement phase. Note that at 10% Cr, the σ phase is absent and the higher Si content at both Cr levels increases the amount of Cr ₃ Si phase. Therefore, these figures show that there is a problem when using approximately 20% Cr levels.

When the term “≦” or “less than or equal to” is used in the context “element ≦ number” below, one of ordinary skill in the art will appreciate that the lower limit of the range is 0 wt% unless otherwise stated. know. Further, the indefinite article "a" does not exclude a plurality.

The present disclosure is further illustrated by the following non-limiting examples.

The test melt was produced in a vacuum melting furnace. The composition of the test melt is shown in Table 1.

The resulting sample was hot rolled and machined into a flat rod with a cross section of 2 x 10 mm. It was then cut into 20 mm long coupons, crushed to 800 mesh with SiC paper and exposed to air and combustion conditions. Several rods were cut into rods 200 mm x 3 x 12 mm long for tensile testing at room temperature on a Zwick/Roell Z100 tensile tester.

The results of the exposure and tensile tests are shown in Table 1.

The samples were tested for yield stress and breaking stress, and elongation at break on a standard tensile tester, and the results of breaking elongation >3% are indicated by "x" in the "Workability" column of the table. Thus, "x" represents an alloy that is easily hot rolled and exhibits ductile behavior at room temperature. In the "Oxidation" column, "x" indicates that the alloy forms a protective alumina-rich oxide scale in air at 950°C and by biomass ash deposits at 850°C.
Table 1-Melting composition and processability and oxidation test results (x) represent elongation values of 3 to 6%.

Thus, as can be seen from the table above, the alloys of the present disclosure exhibit good workability and good oxidation performance.

2a to e show the polished part of the sample of the present disclosure (FIGS. 2a4783 and 2b4779) after 50 cycles of exposure to ash of biomass (wood pellets) containing large amounts of potassium at 850° C. for 1 hour. It is disclosed in comparison with three comparative alloys. Micrographs were taken with a JEOL FEG SEM at 1000X magnification, which shows a clear advantage in the behavior between the alloys of the present disclosure and the reference material. Thus, the alloys of the present disclosure form a protective alumina scale (aluminum oxide layer) that is as thin as 3-4 μm, whereas a thinner, less protective scale that is rich in chromia (chromium oxide). Made of stainless steel (2c-11Ni, 21Cr, N, Ce, Fe bal.) and Ni alloy (2e-Inconel 625: 58Ni, 21Cr, 0.4Al, 0.5Si, Mo, Nb, Fe) for comparison. A porous scale and less protective alumina scale is formed with a comparative FeCrAl alloy (alloy 4776) (FIGS. 2d-20Cr, 5Al, 0.04 Si, Fe bal).

As can be seen from FIGS. 2a-2e, the addition of Si, Al and Cr according to the ranges according to the present disclosure results in the formation of alumina scale at Al levels as low as about 2 wt% and chromium levels as low as about 5 wt %. Facilitate.

Claims (17)

The following elements in wt% [wt%]

Ferrite alloy.

The ferrite alloy according to claim 1, wherein the element is represented by a weight fraction. The ferrite alloy according to claim 1 or 2, wherein Zr is 0.05 to 0.40% by weight. The ferrite alloy according to any one of claims 1 to 3, wherein Cr is 5 to 13% by weight. The ferrite alloy according to any one of claims 1 to 4, wherein RE is more than 1.0 to 3.0% by weight. Ferrite alloy according to any one of claims 1 to 5, wherein Al is 2.5 to 4.5% by weight or 3 to 5% by weight. The ferrite alloy according to any one of claims 1 to 6, wherein Al is 3 to 4% by weight. The ferrite alloy according to any one of claims 1 to 7, wherein Si is 1.0 to 3% by weight. The ferrite alloy according to claim 1, wherein Si is 1.5 to 2.5% by weight. The ferrite alloy according to claim 1, wherein Zr is 0.10 to 0.35% by weight. The amount of C, N and Zr is the following equation:

The ferrite alloy according to any one of claims 1 to 10, which satisfies the above condition. A coating comprising the ferrite alloy according to any one of claims 1 to 11. An object comprising the ferrite alloy according to any one of claims 1 to 12. Use of a ferrite alloy according to any one of claims 1 to 11 for producing coatings and/or claddings and/or objects. Use of a ferrite alloy according to any one of claims 1 to 11 for producing an object or coating for use in corrosive environments. Use of a ferrite alloy according to any one of claims 1 to 11 for producing an object or coating for use in a furnace or as a heating element. Ferrite alloys are exposed to salts, liquid lead, and other metals, as well as ash or high carbon content deposits, combustion atmospheres, atmospheres with low pO ₂ and/or high N ₂ and/or high carbon activity. Use of a ferrite alloy according to any one of claims 1 to 11 in an exposed environment.

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