Nickel-based alloy

Abstract

The present invention relates to an alumina-forming dispersion strengthened nickel-based alloy comprising, in weight percent (wt.%): C 0.08 to 0.28; 0 to 1.50% of Si; mn from 0 to 0.50; 15% to 20.0% of Cr; 4.0 to 5.0 of Al; 15.0 to 25.0% of Fe; n is from 0.030 to 0.075; o 0 to 0.1; b 0 to 0.02; y is from 0.01 to 0.1; 1.0 to 2.7 of at least one of Ta, Zr, Hf, Ti, and Nb; the balance being Ni and commonly existing impurities; wherein the alloy satisfies the following requirements: (C + N) / (Ta + Zr + Hf + Nb + Ti) > = 1.4 (in atomic% value) [1]; zr + Hf-N > = 0.05 (in atomic%) [2]. The alloy disclosed by the invention has excellent thermal-state ductility.

Description

[0001] The present invention relates to a nickel-based alloy that forms alumina and a powder comprising the nickel-based alloy that forms alumina. In addition, the present invention also relates to an object made of the alloy or the powder and its use. Background Art

[0002] Nickel-based alloys alloyed with aluminum are used in various high-temperature applications, such as in heat treatment furnaces, because they form stable and protective aluminum oxides on the surface, which will provide very good oxidation resistance.

[0003] It is known that objects (such as wires or tubes) made of nickel-based alloys that form aluminum oxides are difficult to manufacture due to their poor hot ductility. An important factor contributing to this is the intermetallic phases formed during slow cooling / heating at temperatures below about 900 °C (such as during heat treatment or hot working). These intermetallic phases make the alloy hard and brittle, and thus difficult to process.

[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 found that if these requirements are met, objects obtained from the alloy or powders made from the alloy, or after HIP (hot isostatic pressing), will ensure excellent hot ductility. This excellent hot ductility, in turn, will ensure that cracks are substantially not formed during the hot working manufacturing process when producing objects. In addition, the nickel-based alloy of the present invention will provide excellent oxidation resistance at high temperatures and good creep strength for objects composed of the alloy.

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

[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 1.0 to 2.7;

[0018] The balance is Ni and impurities normally present;

[0019] And wherein the alloy meets the following requirements:

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

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

[0022] The inventors have surprisingly found that if a nickel-based alloy is within the element ranges defined above or below, and additionally meets requirements [1] and [2], then an object comprising the alloy will ensure excellent hot ductility, which means that the object can be hot-worked in a further process to obtain the desired product without forming cracks. In addition, 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 an embodiment, the alloy can be converted into powder and then used to manufacture an object. The powder can be used in a HIP process or an additive manufacturing process such as 3D printing.

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

[0025] The term "desired product" is intended to include, for example, wire, rod, hollow rod, hollow piece, strip, tube, seamless tube, bar, or plate, all of which forms will be able to be produced during a hot working process without cracking problems. 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 will form dispersion-strengthening particles with C and / or N and optionally added O. 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, thus having the same requirements (i.e., [1] and [2]) and alloying element ranges. The powder can be produced by means of powder metallurgy. The powder metallurgy manufacturing process results in a rapidly solidified material, where brittle phases do not have time to form and large compositional variations do not develop due to segregation. Therefore, a mixture of rapidly solidified powders will give the metal body a substantially uniform composition and very small dispersion particles that are substantially uniformly distributed.

[0028] Examples of suitable applications of the alloy of the present invention are: as a structural material for heat treatment furnaces, in the rolls of roller hearth furnaces, as muffle tubes for annealing under a protective atmosphere, as a structural material for heating elements, as a combustion chamber material in gas turbines, as a gas-to-gas heat exchanger, for example, in the glass manufacturing industry or in gas turbines, as a wire woven conveyor belt for heat treatment furnaces, as a radiant tube for heating in heat treatment furnaces, or as a protective tube for thermocouples. Detailed Description

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

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

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

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

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

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

[0035] Hot isostatic pressing (HIP) is a process in which powders are subjected to elevated temperature and pressure in an inert gas atmosphere. This converts the powders into a bulk / object by plastic deformation, flow and diffusion bonding, and eliminates internal cavities and micropores. The suitable process temperature is from 900 to 1250 °C, the suitable pressure is from 80 to 200 MPa, and the suitable holding time is from 1 to 3 hours.

[0036] When within the ranges described in the present invention, unless otherwise expressly stated, such ranges include the corresponding end values of the range. Similarly, when an open range is described, unless otherwise expressly stated, the open range also includes the individual end values of the open range.

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

[0038] Carbon

[0039] Free carbon will occupy interstitial positions in the crystal structure, thereby locking the mobility of dislocations at temperatures up to about 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 obstacle to dislocation movement, even at higher temperatures. Carbon is an essential element for improving creep strength. However, too high a content of C will cause the alloy to be difficult to cold work due to deteriorated ductility at lower temperatures (such as below 300 °C). Therefore, the content of carbon is from 0.08 to 0.28 wt%. According to an embodiment, the content of carbon is from 0.15 to 0.28 wt%, for example from 0.20 to 0.28 wt%.

[0040] Silicon

[0041] Silicon may be present in a content of up to 1.5% by weight. Too high a level of Si may lead to an increased risk of nickel silicide precipitation, which will have a embrittling effect on this type of alloy. According to an embodiment, the Si content does not exceed 1.0% by weight. According to an embodiment, the content of Si does not exceed 0.30% by weight. According to an embodiment, the content of Si is equal to or greater than 0.001% by weight.

[0042] Manganese

[0043] Manganese is present as an impurity. It may be allowed to be up to 0.50% by weight without having a negative impact on the properties. According to an embodiment, Mn is an impurity and the content is at most 0.05% by weight. According to an embodiment, the content of Mn is equal to or greater than 0.001% by weight.

[0044] Chromium

[0045] The content of chromium should be at least 15.0% by weight to ensure obtaining an oxide with sufficient oxidation resistance at high temperatures. However, a nickel-based alloy containing 4.0% by weight of Al should not contain more than about 20.0% by weight of Cr, because a higher content will increase the risk of formation of brittle phases. According to an embodiment, 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 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 the oxide completely covers the surface. When the Al content is higher than 5.0% by weight, there is a risk of significant deterioration of hot ductility, so the maximum Al content is 5.0% by weight. According to an embodiment, the content of Al is 4.0 to 4.5% by weight.

[0048] Iron

[0049] According to the present invention, in a nickel-based alloy in which aluminum oxide is formed, a relatively high content of Fe can have a positive effect. Adding Fe produces a metal structure that is energetically unfavorable for the formation of brittle γ', which in turn poses a risk of the alloy becoming hard and brittle. Therefore, the nickel-based alloy contains at least 15.0 wt% of Fe. However, a high content of iron may lead to the formation of unwanted phases. Therefore, the alloy contains no more than 25.0 wt% of Fe. According to an embodiment, the iron content is 17.0 to 23.0 wt%, such as 18.0 to 21.0 wt%, such as 18.0 to 20.0 wt%, such as 19.0 to 20.0 wt%.

[0050] Nickel

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

[0052] Nitrogen

[0053] In the same way as C, free N will occupy interstitial positions in the crystal structure, thereby locking the dislocation mobility at temperatures up to about 400 to 500 °C. Nitrogen will also form nitrides and / or carbonitrides with other elements (such as Ta, Ti, Hf, Zr, and Nb). In a microstructure in which these particles are finely dispersed, they impede dislocation movement, especially at higher temperatures. Therefore, N is added to improve the creep strength. However, when N is added to an alloy alloyed with aluminum, if not added carefully, the formation of aluminum nitride will be a problem, so the content of N is 0.030 to 0.075 wt%. According to an embodiment, the content of N is 0.040 to 0.060 wt%.

[0054] Oxygen

[0055] Oxygen can be present in the alloy of the present invention at a maximum of 0.1 wt%.

[0056] Oxygen can contribute to improving the creep strength of an alloy by forming small oxide dispersoids together with Zr, Hf, Ta, and Ti, which, when finely distributed in the alloy, will improve the creep strength. The dissolution temperatures of these oxide dispersoids are higher than those of the corresponding carbides and nitrides, so oxygen is preferably added for high-temperature applications. Oxygen can also form dispersoids with Al, Group 3 elements of the periodic table, Sc, Y, and La, as well as the fourteen lanthanide elements, and form dispersoids in the same way as the elements identified above, thus contributing to a higher creep strength of the alloy. According to an embodiment, the nickel-based alloy contains 20 to 1000 ppm of O, for example, 50 to 300 ppm of 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 microstructure, they contribute to locking the movement of dislocations, thereby increasing the creep strength, i.e., providing dispersion strengthening. Adding Ti can also achieve such an effect. Niobium also forms stable dispersoids with C and / or N, so it can be suitably added to the present invention. Based on the above, the combined content of Ta, Zr, Hf, Ti, and Nb is 1.0 to 2.7 wt%. According to an embodiment, the combined content of Ta, Zr, Hf, Ti, and Nb is 1.4 to 2.3 wt%, for example, 1.6 to 2.0 wt%.

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

[0060] Yttrium (Y)

[0061] Y affects the oxidation performance by doping the formed oxides. Excessive alloying of this element usually causes the oxides to tend to spall from the surface, and too low addition of these elements tends to result in weak adhesion of the oxides to the metal surface. Excessive alloying of Y also deteriorates the hot ductility. Therefore, the content of Y is limited to 0.10 wt%. According to an embodiment, the content of yttrium is 0.005 to 0.10 wt%.

[0062] Boron (B)

[0063] It has been shown that the addition of B improves the hot workability of nickel-based alloys. However, too high a content of B will lower the melting point, thereby reducing the hot workability by narrowing the temperature range in which the material can be processed. Too high a content of B may also deteriorate the required high-temperature properties. The powder may contain B in a content of up to 0.02% by weight. According to an embodiment, B is from 0.0001% to 0.02% by weight.

[0064] In addition, one of Ca or Mg may be added to improve the hot workability of the material during production. Preferably, the calcium content is at most 0.05% by weight, suitably equal to or less than 0.01% by weight. The content of Mg may suitably be at most 0.05% by weight.

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

[0066] In addition, the alloys, powders or objects as defined above or below may contain or consist of the elements as defined above or below in any value within the ranges mentioned herein.

[0067] Products (such as components) made from the powders as defined above or below are mainly intended for use at high temperatures. Examples of applications are: structural materials for heat treatment furnaces, rolls 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, wire braided conveyor belts for heat treatment furnaces, radiant tubes for heating heat treatment furnaces or protective tubes for thermocouples.

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

[0069] Examples

[0070] Different powders are produced by gas atomization, in which the raw material is melted, poured through a ceramic nozzle, and then the melt stream is subjected to a high flow rate of nitrogen gas. The gas stream breaks up the melt stream into small droplets, which rapidly solidify into spherical powder particles. The powder is filled into a welded sheet metal can, which is degassed, sealed, and subjected to hot isostatic pressing (HIP). In the HIP process, the filled powder can is 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 filled can into a fully dense body. Then, the HIPed block is hot rolled in several passes with a total reduction of 70%. From the hot rolled material, specimens for Gleeble hot ductility tensile tests are extracted along the rolling direction.

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

[0072] The hot ductility tests were accordingly carried out in the Gleeble system:

[0073] The tensile test specimens were heated to a set temperature with a specific heating curve / rate, 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 was carried out. Then the area reduction at the fracture point of the tensile specimen was measured, which provides a measure of hot ductility. The results of the tests are shown in Table 2 below.

[0074] The hot ductility tests in the Gleeble system constitute a measure of the ability of the material to withstand deformation at high temperatures without forming cracks, i.e., hot ductility. As can be seen from Table 2, heating elements that meet all the requirements defined above or below show good hot ductility in the Gleeble test results in the form of high values of area reduction at elevated high temperatures. It should be noted that for a heating element to be considered to have good hot ductility, the area reduction at 1150 °C in the Gleeble test results should be ≥ 50% and the area reduction at 1050 °C should be ≥ 35%.

[0075]

[0076]

[0077]

Claims

1. A dispersion-strengthened nickel-based alloy for forming alumina, the 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 1.0 to 2.7; The balance being Ni and normally present impurities; Wherein the alloy meets the following requirements: (C + N) / (Ta + Zr + Hf + Nb + Ti) ≥ 1.4 (value in atomic%); [1] Zr + Hf - N ≥ 0.05 (value in atomic%); [2] 2. The dispersion-strengthened nickel-based alloy for forming alumina according to claim 1, wherein the content of C is 0.15 wt% to 0.28 wt%, such as C of 0.20 wt% to 0.28 wt%.

3. The dispersion-strengthened nickel-based alloy for forming alumina according to claim 1 or 2, wherein the content of Si does not exceed 0.30 wt%.

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

5. The dispersion-strengthened nickel-based alloy for forming alumina according to any one of claims 1 to 4, wherein the content of Cr is 17.0 wt% to 19.0 wt%.

6. The dispersion-strengthened nickel-based alloy for forming alumina according to any one of claims 1 to 5, wherein the content of Fe is 18.0 wt% to 21 wt%, such as Fe of 18.0 wt% to 20.0 wt%.

7. The dispersion-strengthened nickel-based alloy for forming alumina according to any one of claims 1 to 6, wherein the content of oxygen is 20 ppm to 1000 ppm, such as O of 50 ppm to 300 ppm.

8. The dispersion-strengthened nickel-based alloy for forming alumina according to any one of claims 1 to 7, the combined content of Ta, Zr, Hf, Ti and Nb is 1.4 wt% to 2.3 wt%, such as 1.6 wt% to 2.0 wt%.

9. A powder, the powder being composed of the dispersion-strengthened nickel-based alloy for forming alumina according to any one of claims 1 to 8.

10. An object, the object being made of the dispersion-strengthened nickel-based alloy or powder for forming alumina according to any one of claims 1 to 9.

11. The object according to claim 10, wherein the object is an object subjected to HIP.

12. The object according to claim 10 or claim 11, wherein the object is in the form of a tube, a hollow part, a block, a rod, a bar, a strip, a plate or a wire.

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