nickel-based alloy

Abstract

The present invention relates to a dispersion strengthened nickel-based alloy forming alumina comprising in weight percent (wt %): C 0.08 to 0.28; Si 0 to 1.50; Mn 0 to 0.50; Cr 15.0 to 20.0; Al 4.0 to 5.0; Fe 15.0 to 25.0; N 0.030 to 0.075; O 0 to 0.1; B 0 to 0.02; Y 0.01 to 0.1; at least one of Ta, Zr, Hf, Ti and Nb 1.0 to 2.7; balance Ni and normally occurring impurities; wherein the alloy fulfils the following requirements: (C+N) / (Ta+Zr+Hf+Nb+Ti) > 1.4 (values in at.%) [1]; Zr+Hf-N > 0.05 (values in at.%) [2]. The alloy of the present invention has excellent hot ductility.

Description

[0001] This invention relates to a nickel-based alloy that forms alumina and to a powder comprising the nickel-based alloy that forms the alumina. Furthermore, this invention relates to objects manufactured from the alloy or the powder and their uses. Background Technology

[0002] Nickel-based alloys with aluminum alloys are used in a variety of high-temperature applications, such as in heat treatment furnaces, because they form a stable and protective aluminum oxide on the surface, which provides very good oxidation resistance.

[0003] Objects made of nickel-based alloys that form aluminum oxides (such as wires or tubes) are known to be difficult to manufacture due to their poor hot ductility. A significant factor contributing to this is the formation of intermetallic phases during slow cooling / heating at temperatures below approximately 900°C (e.g., during heat treatment or hot working). These intermetallic phases make the alloy hard and brittle, thus difficult to machine.

[0004] The present invention aims to solve these problems. Summary of the Invention

[0005] Therefore, the present invention relates to a nickel-based alloy that meets specific requirements regarding carbon and carbide and nitride-forming elements, because the inventors have surprisingly discovered that, if these requirements are met, objects obtained from said alloy or powder made from said alloy, or after HIP (hot isostatic pressing), will ensure excellent hot ductility. This excellent hot ductility, in turn, will ensure that virtually no cracks form during the hot working manufacturing process when producing the object. Furthermore, the nickel-based alloy of the present invention will provide objects made of said alloy with excellent oxidation resistance at high temperatures and good creep strength.

[0006] Therefore, the present invention relates to a dispersion-hardening nickel-based alloy that forms alumina, the dispersion-hardening nickel-based alloy comprising, by weight percentage (wt%):

[0007] C 0.08 to 0.28;

[0008] Si 0 to 1.5;

[0009] Mn 0 to 0.50;

[0010] Cr 15.0 to 20.0;

[0011] Al 4.0 to 5.0;

[0012] Fe 15.0 to 25.0;

[0013] N 0.030 to 0.075;

[0014] O < 0.1;

[0015] B < 0.02;

[0016] Y 0.01 to 0.1;

[0017] At least one of Ta, Zr, Hf, Ti and Nb, at a concentration of 1.0 to 2.7;

[0018] The balance consists of Ni and commonly present impurities;

[0019] And the alloy described therein meets the following requirements:

[0020] (C+N) / (Ta+Zr+Hf+Nb+Ti)≥1.40 (value in atomic percent) [1];

[0021] Zr+Hf-N≥0.05 (value in atomic percent) [2].

[0022] The inventors have surprisingly discovered that if the nickel-based alloy is within the elemental range defined above or below, and additionally meets requirements [1] and [2], an object containing the alloy will ensure excellent hot ductility, meaning that the object can be hot-worked in further processes to obtain the desired product without cracking. Furthermore, the nickel-based alloy will have an austenitic microstructure and will have very good oxidation resistance, especially at high temperatures, such as above 900°C. In addition, the alloy will provide good creep resistance.

[0023] According to one embodiment, the alloy can be converted into powder and then used to manufacture objects. This powder can be used in HIP (Hybrid Injection Processing) or additive manufacturing processes such as 3D printing.

[0024] According to embodiments, the object defined above or below is a HIP-ed object, such as a component or product, which is an object obtained by a hot isostatic pressing process. According to embodiments, the object defined above or below has been obtained by using additive manufacturing.

[0025] The term "desired product" is intended to include, for example, wires, bars, hollow bars, hollow parts, strips, tubes, seamless tubes, bars, or plates, all of which can be produced during a hot working process without cracking issues. Examples of hot working processes are rolling, forging, and / or extrusion.

[0026] The nickel-based alloy according to the present invention is a dispersion-strengthened alloy. This effect is achieved by adding one or more elements selected from Ta, Zr, Hf, Ti, and Nb. These elements, together with C and / or N, and optionally added O, form dispersion-strengthened particles. Dispersion strengthening contributes to mechanical strength and provides excellent creep strength. Therefore, the alloy of the present invention will have excellent mechanical properties, especially at high temperatures.

[0027] The present invention also relates to a powder made from the alloy of the present invention, thereby having the same requirements (i.e., [1] and [2]) and range of alloying elements. This powder can be produced by means of powder metallurgy. Powder metallurgy manufacturing processes yield rapidly solidified materials in which brittle phases do not have time to form and do not develop large compositional changes due to segregation. Therefore, a mixture of rapidly solidified powders will result in a metallic body with a substantially homogeneous composition and substantially uniformly distributed, very small, dispersed particles.

[0028] Examples of suitable applications of the alloy of the present invention are: as structural materials for heat treatment furnaces, as rollers for roller hearth furnaces, as muffle tubes for annealing in a protective atmosphere, as structural materials for heating elements, as combustion chamber materials in gas turbines, as gas-to-gas heat exchangers, for example in the glass manufacturing industry or in gas turbines, as woven conveyor belts for heat treatment furnaces, as radiant tubes for heating in heat treatment furnaces, or as protective tubes for thermocouples. Detailed Implementation

[0029] The invention will now be described in more detail with reference to various exemplary embodiments. However, the invention is not limited to the exemplary embodiments discussed, but may vary within the scope of the appended claims.

[0030] Furthermore, unless otherwise expressly stated, the dispersion-strengthened nickel-based alloys described herein may exist in any possible form and / or state without departing from the invention.

[0031] As mentioned above, nickel-based alloys alloyed with aluminum are generally considered difficult to use for manufacturing objects and parts due to their poor hot ductility. Hot ductility is a very important factor in achieving ease of production. The inventors have surprisingly discovered that nickel-based alloys containing the alloying element range mentioned above or below and meeting the following requirements exhibit excellent hot ductility under HIP conditions and in hot working processes used in the manufacturing process:

[0032] (C+N) / (Ta+Zr+Hf+Nb+Ti)≥1.4 (value in atomic percent) [1];

[0033] Zr+Hf-N≥0.05 (value in atomic percent) [2],

[0034] Therefore, the alloys of the present invention can be processed into desired products with virtually no crack formation in the final products. Thus, without being bound by any theory, it is believed that these requirements will provide a balance between the elements that form carbides and nitrides, thereby ensuring that harmful brittle phases are not formed. Therefore, the inventors have been able to determine, through extensive research, which elements are essential in nickel-based alloys and to what extent they need to be controlled to ensure good hot ductility without affecting weldability, oxidation properties, and creep properties. According to embodiments, (C+N) / (Ta+Zr+Hf+Nb+Ti) is 1.50 to 1.75. According to embodiments, Zr+Hf-N is 0.18 to 0.38.

[0035] Hot isostatic pressing (HIP) is a process in which powder is subjected to elevated temperatures and pressures in an inert gas atmosphere. This transforms the powder into a bulk / object through a combination of plastic deformation, flow, and diffusion, eliminating internal cavities and micropores. Suitable process temperatures range from 900 to 1250°C, suitable pressures from 80 to 200 MPa, and suitable holding times from 1 to 3 hours.

[0036] When a range is described in this invention, unless otherwise expressly stated, such a range includes the corresponding end value of the range. Similarly, when an open range is described, unless otherwise expressly stated, the open range also includes the individual end value of the open range.

[0037] The importance of the different alloying elements in the nickel-based alloys described herein will be briefly discussed below. Unless otherwise expressly stated, all percentages of chemical composition are given in weight % (wt%). As described below, unless otherwise expressly stated, the upper and / or lower limits of individual elements in any composition described herein may be freely combined within the widest possible definition of the composition of the nickel-based alloy described in the claims.

[0038] carbon

[0039] Free carbon occupies interstitial sites in the crystal structure, thereby locking dislocation mobility at temperatures up to approximately 400-500°C. Carbon also forms carbides with other elements in the alloy, such as Ta, Ti, Hf, Zr, and Nb. In a microstructure with finely dispersed carbides, these carbides provide an impediment to dislocation movement, effective even at higher temperatures. Carbon is an essential element for improving creep strength. However, excessively high C content can cause the alloy to become difficult to cold work at lower temperatures (e.g., below 300°C) due to deterioration in ductility. Therefore, the carbon content is 0.08 to 0.28% by weight. According to embodiments, the carbon content is 0.15 to 0.28% by weight, for example, 0.20 to 0.28% by weight.

[0040] silicon

[0041] Silicon may be present in a maximum content of 1.5% by weight. Excessive Si levels may increase the risk of nickel silicide precipitation, which can have an embrittlement effect on this type of alloy. According to one embodiment, the Si content does not exceed 1.0% by weight. According to another embodiment, the Si content does not exceed 0.30% by weight. According to yet another embodiment, the Si content is equal to or greater than 0.001% by weight.

[0042] manganese

[0043] Manganese is present as an impurity. It can be permitted at a maximum of 0.50% by weight without negatively impacting performance. According to one embodiment, Mn is an impurity and its content is at most 0.05% by weight. According to another embodiment, the content of Mn is equal to or greater than 0.001% by weight.

[0044] chromium

[0045] The chromium content should be at least 15.0% by weight to ensure sufficient oxidation resistance of the oxide at high temperatures. However, nickel-based alloys containing 4.0% by weight of Al should not contain more than about 20.0% by weight of Cr, as this higher content will increase the risk of brittle phase formation. According to embodiments, the Cr content is 15.0 to 20.0% by weight, for example, 17.0 to 19.0% by weight.

[0046] aluminum

[0047] Aluminum is an element that produces a dense and protective oxide scale. Therefore, the alloy of the present invention contains at least 4.0% by weight of Al, which ensures sufficient oxidation resistance at high temperatures and complete oxide coverage of the surface. When the Al content exceeds 5.0% by weight, there is a risk of significant deterioration in hot ductility; therefore, the maximum Al content is 5.0% by weight. According to embodiments, the Al content is 4.0 to 4.5% by weight.

[0048] iron

[0049] According to the present invention, a relatively high Fe content in nickel-based alloys that form aluminum oxides can have a positive effect. The addition of Fe creates a metallic structure that is energy-unfavorable for the formation of brittle γ' phases, which in turn poses a risk of the alloy becoming hard and brittle. Therefore, the nickel-based alloy contains at least 15.0% by weight of Fe. However, a high iron content can lead to the formation of unwanted phases. Therefore, the alloy contains no more than 25.0% by weight of Fe. According to embodiments, the iron content is 17.0 to 23.0% by weight, for example 18.0 to 21.0% by weight, for example 18.0 to 20.0% by weight, for example 19.0 to 20.0% by weight.

[0050] nickel

[0051] The alloy according to the invention is nickel-based. Nickel is an alloying element that stabilizes the austenitic structure, thereby counteracting the formation of some brittle intermetallic phases (e.g., σ phase). The austenitic structure is advantageous, for example, when welding is involved. The austenitic structure also contributes to creep strength at high temperatures. Ni is the balance alloying element.

[0052] nitrogen

[0053] In the same manner as with C, free nitrogen occupies interstitial sites in the crystal structure, thereby locking dislocation mobility at temperatures up to approximately 400 to 500 °C. Nitrogen also forms nitrides and / or carbonitrides with other elements such as Ta, Ti, Hf, Zr, and Nb. In the finely dispersed microstructure of these particles, they impede dislocation movement, especially at higher temperatures. Therefore, nitrogen is added to improve creep strength. However, when nitrogen is added to aluminum alloys, the formation of aluminum nitrides can be problematic if added carelessly; therefore, the nitrogen content is 0.030 to 0.075% by weight. According to an embodiment, the nitrogen content is 0.040 to 0.060% by weight.

[0054] oxygen

[0055] Oxygen may be present in the alloys of the present invention at a maximum of 0.1% by weight.

[0056] Oxygen can contribute to improved creep strength of alloys by forming small oxide dispersions with Zr, Hf, Ta, and Ti, where fine distribution within the alloy enhances creep strength. These oxide dispersions have higher dissolution temperatures than their corresponding carbides and nitrides, thus oxygen is preferred for applications at high temperatures. Oxygen can also form dispersions with Al, Group 3 elements, Sc, Y, and La, and the fourteen lanthanides, and in the same manner as the elements identified above, thereby contributing to even higher creep strength in the alloy. According to embodiments, the nickel-based alloy contains 20 to 1000 ppm O, for example, 50 to 300 ppm O.

[0057] Tantalum, hafnium, zirconium, titanium and niobium

[0058] Elements Ta, Hf, and Zr form very small and stable particles with carbon and nitrogen. If these particles are finely dispersed in the tissue, they help to lock dislocation movement, thereby increasing creep strength, i.e., providing dispersion strengthening. Adding Ti can also achieve this effect. Niobium also forms stable dispersions with C and / or N, and therefore can be suitably added to this invention. Based on the foregoing, the combined content of Ta, Zr, Hf, Ti, and Nb is 1.0 to 2.7% by weight. According to embodiments, the combined content of Ta, Zr, Hf, Ti, and Nb is 1.4 to 2.3% by weight, for example, 1.6 to 2.0% by weight.

[0059] Although the combined content is as mentioned above, there are still some limitations on the content of each element. According to one embodiment, the content of Hf can be 0.3 to 0.7% by weight. According to another embodiment, the content of Zr can be 0.3 to 0.7% by weight. According to one embodiment, the content of Ta can be 0.3 to 0.7% by weight. According to one embodiment, the content of Nb can be 0.3 to 0.7% by weight.

[0060] Yttrium (Y)

[0061] Y influences oxidation properties through the oxides formed by doping. Excessive alloying of this element typically leads to a tendency for the oxide to spall from the surface, while insufficient addition tends to result in weak adhesion of the oxide to the metal surface. Excessive alloying of Y also degrades hot ductility. Therefore, the Y content is limited to 0.10% by weight. According to embodiments, the yttrium content is from 0.005 to 0.10% by weight.

[0062] Boron (B)

[0063] It has been shown that the addition of boron (B) improves the hot ductility of nickel-based alloys. However, excessively high B content will lower the melting point, thereby reducing hot workability by narrowing the temperature range at which the material can be processed. Excessively high B content may also degrade the desired high-temperature properties. The powder may contain B at a maximum content of 0.02% by weight. According to embodiments, B is from 0.0001% by weight to 0.02% by weight.

[0064] In addition, either Ca or Mg can be added to improve the thermal ductility of the material during the production process. Preferably, the calcium content is up to 0.05% by weight, suitable to be equal to or less than 0.01% by weight. The Mg content can be suitable to be up to 0.05% by weight.

[0065] The nickel-based alloys according to the invention may also contain impurities that are normally present due to the raw materials used or the selected manufacturing process. Examples of impurities are sulfur (S) and phosphorus (P). In addition to the elements specified and discussed above, the alloys described herein may also contain a total of up to 0.8% by weight of normally present impurities. In this invention, normally present impurities are considered to be impurities generated by the manufacturing process and / or the raw materials used. According to embodiments, the amount of normally present impurities may suitably be equal to or less than 0.6% by weight, or equal to or less than 0.5% by weight.

[0066] Furthermore, the alloy, powder, or object defined above or below may contain or consist of the elements defined above or below at any value within the range mentioned herein.

[0067] Products (e.g., components) manufactured from powder, as defined above or below, are primarily intended for use at high temperatures. Examples of applications include: structural materials for heat treatment furnaces, rollers for roller hearth furnaces, muffle tubes for annealing in a protective atmosphere, structural materials for heating elements, combustion chamber materials in gas turbines, gas-to-gas heat exchangers, such as in the glass manufacturing industry or gas turbines, tubular reactors in high-temperature processes, braided conveyor belts for heat treatment furnaces, radiant tubes for heating in heat treatment furnaces, or protective tubes for thermocouples.

[0068] The present invention is described by way of the following non-limiting examples.

[0069] Example

[0070] Different powders are produced using a gas atomization method, in which the raw material is melted and poured through a ceramic nozzle, whereby the melt stream is subjected to a high flow rate of nitrogen. The gas flow breaks the melt stream into small droplets, which rapidly solidify into spherical powder particles. The powder is then filled into welded sheet metal cans, degassed, sealed, and subjected to hot isostatic pressing (HIP). In the HIP process, the filled powder cans are subjected to a high temperature (1150°C) and a high-pressure argon atmosphere (100 MPa) for a holding time of 3 hours. This process densifies the powder in the cans into a fully dense mass. The HIP-processed mass is then hot-rolled several times, with a total reduction of 70%. Specimens for the Gleeble hot ductility tensile test are extracted from the hot-rolled material along the rolling direction.

[0071] The composition of the manufactured powder is shown in Table 1 below.

[0072] The corresponding hot ductility test was conducted in the Gleeble system:

[0073] The tensile test specimen is heated to a set temperature according to a specific heating profile / rate, and the temperature is measured by a thermocouple. The set temperature can be reached by heating to the desired temperature (ONH) or by cooling from a higher temperature (ONC). After holding at the desired temperature for a specific time, a tensile test is performed. The reduction in area at the point of fracture is then measured, providing a measurement of hot ductility. The test results are shown in Table 2 below.

[0074] The hot ductility test in the Gleeble system constitutes a measure of a material's ability to withstand deformation at high temperatures without cracking; that is, hot ductility. As shown in Table 2, heated elements that meet all the requirements defined above or below exhibit good hot ductility in the Gleeble test results, manifested by a high value of area reduction at increasing temperatures. It should be noted that for a heated element to be considered to have good hot ductility, the area reduction at 1150°C must be ≥50% and the area reduction at 1050°C ≥35% in the Gleeble test results.

[0075]

[0076]

[0077]

Claims

1. A dispersion-strengthened nickel-based alloy forming alumina, said alloy comprising, by weight percentage (wt%): C 0.08 to 0.28; Si 0 to 1.50; Mn 0 to 0.50; Cr 15.0 to 20.0; Al 4.0 to 5.0; Fe 15.0 to 25.0; N 0.030 to 0.075; O 0 to 0.1; B 0 to 0.02; Y 0.01 to 0.1; At least one of Ta, Zr, Hf, Ti and Nb, at a concentration of 1.0 to 2.7; The balance consists of Ni and commonly present impurities; The alloy described herein meets the following requirements: (C+N) / (Ta+Zr+Hf+Nb+Ti)≥1.4 (value in atomic percent) [1]; Zr+Hf-N≥0.05 (value in atomic percent) [2].

2. The dispersion-strengthened nickel-based alloy for forming alumina according to claim 1, wherein the C content is from 0.15% to 0.28% by weight.

3. The dispersion-strengthened nickel-based alloy for forming alumina according to claim 1, wherein the C content is from 0.20% to 0.28% by weight.

4. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the Si content does not exceed 0.30% by weight.

5. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein Mn is an impurity and its content is at most 0.05 by weight.

6. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the Cr content is from 17.0% to 19.0% by weight.

7. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the Fe content is 18.0% to 21% by weight.

8. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the Fe content is from 18.0% to 20.0% by weight.

9. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the oxygen content is from 20 ppm to 1000 ppm.

10. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the oxygen content is from 50 ppm to 300 ppm.

11. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the combined content of Ta, Zr, Hf, Ti and Nb is from 1.4% to 2.3% by weight.

12. The dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 3, wherein the combined content of Ta, Zr, Hf, Ti and Nb is from 1.6% to 2.0% by weight.

13. A powder comprising a dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 12.

14. An object made of a dispersion-strengthened nickel-based alloy forming alumina according to any one of claims 1 to 12 or the powder according to claim 13.

15. The object of claim 14, wherein the object is a HIP-processed object.

16. The object according to claim 14 or claim 15, wherein the object is in the form of a tube, hollow part, block, rod, strip, belt, plate or filament.

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