WO2024123229A1

WO2024123229A1 - Nickel-based alloy

Info

Publication number: WO2024123229A1
Application number: PCT/SE2023/051228
Authority: WO
Inventors: Martin ÖSTLUND; Thomas Helander; Mats HÄTTESTRAND; Mats Lundberg; Ulrika BORGGREN; Christina HARALDSSON
Original assignee: Alleima Emea AB
Current assignee: Alleima Emea AB
Priority date: 2022-12-07
Filing date: 2023-12-06
Publication date: 2024-06-13
Anticipated expiration: 2025-06-07
Also published as: SE546256C2; EP4630592A1; JP2025539887A; CN120265803A; SE2230398A1

Abstract

The present invention relates to a dispersion strengthened alumina forming nickel- based alloy comprising in percent by weight (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; and wherein said alloy fulfils the requirements of: (C+N)/(Ta+Zr+Hf+Nb+Ti) ≥ 1.4 (values in at%) [1]; Zr + Hf – N ≥ 0.05 (values in at%) [2]. The present alloy will have excelllent hot ductility.

Description

NICKEL-BASED ALLOY

The present disclosure relates to an alumina forming nickel-based alloy and to a powder comprising said alumina forming nickel-based alloy. Further, the present disclosure also relates to an object manufactured from said alloy or said powder and to the use thereof.

Background art

Nickel-based alloys alloyed with aluminium are used in a variety of high temperature applications, such as in heat treatment furnaces, as they will form a stable and protective aluminium oxide on the surface which will provide for a very good oxidation resistance.

Objects, such as wire or tube, of aluminium oxide forming nickel-based alloys are known to be difficult to manufacture due to their poor hot ductility. A strongly contributing factor to this is the intermetallic phases which are formed during slow cooling/heating at temperatures below approximately 900°C, such as during heat treatments or during hot working. These intermetallic phases make the alloy hard and brittle and consequently difficult to work.

The present disclosure aims at solving these problems.

Summary of the disclosure

The present disclosure therefore relates to a nickel-based alloy fulfilling certain requirements concerning carbon and carbide and nitride forming elements as the inventors have surprisingly found that if these requirements are fulfilled, an object obtained by said alloy or a powder made of said alloy or will after performed HIPing (hot isostatic pressure) be ensured to have excellent hot ductility. This excellent hot ductility will in turn ensure that essentially no cracks are formed during hot working manufacturing processes when producing the object. Additionally, the present nickel-based alloy will provide for that an object composed of said alloy will have excellent oxidation resistance at high temperatures and good creep strength. Hence, the present disclosure relates to an alumina forming dispersion hardening nickel-based alloy comprising in percent by weight (wt%)

C 0.08 to 0.28;

Si 0 to 1.5;

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 < 0.1

B < 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; and wherein said alloy fulfils the requirements of: (C+N)/(Ta+Zr+Hf+Nb+Ti) > 1 .40 (values in at%) [1]; Zr + Hf - N > 0.05 (values in at%) [2],

The inventors have surprisingly found that if a nickel-based alloy is within the element ranges defined hereinabove or hereinafter and additionally fulfils the requirements [1] and [2], an object comprising said alloy will be ensured to have excellent hot ductility meaning that it will be possible to hot work the object in further processes to obtain a desired product without formation of cracks. Additionally, the nickel-based alloy will have an austenitic micro structure and will have very good oxidation resistance, especially at high temperatures, such as above 900°C. Furthermore, the alloy will provide for good creep resistance.

According to embodiments, the alloy may be converted to a powder which is then used for manufacturing an object. The powder may be used in a HIP process or an additive manufacturing process, such as 3D printing.

According to embodiments, the object as defined hereinabove or hereinafter is a HIP:ed object, such as a component or a product, A HIP:ed object is an object obtained from a hot isostatic pressure process. According to embodiments, the object as defined hereinabove or hereinafter has been obtained by using additive manufacturing.

The term “desired product” is intended to for example include a wire, a bar, a hollow bar, a hollow, a strip, a tube, a seamless tube, a rod or a plate, all these forms will be able to be produced without having problems with cracking during a hot working process. Examples of hot working processes are rolling, forging and/or extrusion.

The nickel-based alloy according to the disclosure is a dispersion strengthened alloy. This effect is achieved due to the addition of one or more elements selected from the group consisting of Ta, Zr, Hf, Ti and Nb. These elements will form dispersion strengthening particles with C and/or N and optionally added O. The dispersion hardening contributes to the mechanical strength and provides excellent creep strength. Hence, the present alloy will have excellent mechanical properties, especially at high temperatures.

The present disclosure also relates to a powder manufactured from the present alloy and thereby having the same requirement, i.e. [1] and [2], and alloying element ranges. The powder may be produced by means of powder metallurgy. The powder metallurgical manufacturing process results in a rapidly solidified material wherein brittle phases will not have time to form, and no great compositional variations are developed due to segregation. A mixture of rapidly solidified powder will therefore render a metal body with essentially homogenous composition and an essentially even distribution of very small dispersion particles.

Examples of suitable applications for the present alloy are as a construction material for a heat treatment furnace, in a roller for a roller hearth furnace, as a muffle tube for annealing in protective atmosphere, as a construction material for heating elements, a combustion chamber material in gas turbines, as a gas-to-gas heat exchangers for example in the glass manufacturing industry or in gas turbines, as a transportation belt woven from wire intended for heat treatment furnaces, in a radiation tube for heating in a heat treatment furnace or as a protective tube for thermocouples. Detailed description

The invention will be described in more detail below with reference to various exemplifying embodiments. The invention is however not limited to the exemplifying embodiments discussed but may be varied within the scope of the appended claims.

Further, the herein described dispersed strengthening nickel-based alloy may be present in any possible form and/or condition without departing from the present disclosure, except where explicitly specified otherwise.

As mentioned above, nickel-based alloys alloyed with aluminium 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 enabling an easy production. The inventors have surprisingly found that a nickel-based alloy comprising the alloying elemental ranges mentioned hereinabove or hereinafter and fulfilling 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], will have excellent hot ductility in HIP:ed condition and also in hot working processes used in the manufacturing process. Thus, the present alloy can therefore be worked into a desired product with essentially no formation of cracks within the final product. Hence, without being bound to any theory, it is believed that these requirements will provide for a balance between the carbide and nitride forming elements and thereforeensure that no deleterious brittle phases are formed. Thus, the inventors have through extensive research been able to identify which elements are necessary and to which extent these are necessary to control in a nickel-based alloy in order to ensure good hot ductility without affecting weldability, oxidation and creep properties. According to embodiments, (C+N)/(Ta+Zr+Hf+Nb+Ti) is of 1.50 to 1.75. According to embodiments Zr + Hf - N is of 0.18 to 0.38.

Hot Isostatic Pressing (HIP) is a process which exposes powder to elevated heat and pressure in an inert gas atmosphere. This will convert the powder into a body/an object as well as eliminate the internal cavities and micro-porosities by a combination of plastic deformation, flow and diffusion bonding. Suitable process temperature is from 900 to 1250 °C and suitable pressure is 80 to 200 MPa and a suitable holding time is 1 to 3 hours.

When ranges are disclosed in the present disclosure, such ranges include the respective end values of the range, unless explicitly disclosed otherwise. Similarly, when an open range is disclosed, the open range also include the single end value of the open range, unless explicitly disclosed otherwise.

In the following, the importance of the different alloying elements of the herein described nickel-based alloy will be briefly discussed. All percentages for the chemical composition are given in weight% (wt%), unless explicitly disclosed otherwise. Any herein disclosed upper and/or lower limit of the individual elements of the composition, as specified below, can be freely combined within the broadest limits of the composition of the nickel-based alloy set out in the claims, unless explicitly disclosed otherwise.

Carbon

Carbon in free form will take interstitial locations in the crystal structure and thereby lock the mobility of dislocations 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 micro structure with finely dispersed carbides, these carbides provide obstacles for the dislocation movement and have effect even at higher temperatures. Carbon is an essential element to improve the creep strength. Too high contents of C will however lead to the alloy becoming difficult to cold work due to deteriorated ductility at lower temperatures, such as below 300°C. The content of carbon is therefore 0.08 to 0.28 weight%. According to embodiments the content of carbon is 0.15 to 0.28 weight%, such as 0.20 to 0.28 weight%.

Silicon

Silicon may be present in contents up to 1 .5 wt%. Too high levels of Si may lead to increased risk for precipitations of nickel silicides, which will have an embrittling effect on this type of alloy. According to embodiments, the Si content is no more than 1 .0 wt%. According to embodiments, the content of Si of no more than 0.30 wt%. According to embodiments, the content of Si is equal to or greater than 0.001 wt%.

Manganese

Manganese is present as an impurity. It is likely that up to 0.50 wt% can be allowed without negatively influencing the properties. According to embodiments, Mn is an impurity, and the content is up to 0.05 wt%. According to embodiments, the content of Mn is equal to or greater than 0.001 wt%.

Chromium

The content of chromium should be at least 15.0 wt% in order to ensure that an oxide with sufficient oxidation resistance at high temperatures is obtained. A nickel-based alloy comprising 4.0 wt% Al should however not comprise more than about 20.0 wt% Cr as higher contents increases the risk of formation of brittle phases. According to embodiments, the Cr content is from 15.0 to 20.0 wt%, such as 17.0 to 19.0 wt%.

Aluminium

Aluminium is an element which generates a dense and protective oxide scale. The present alloy comprises therefore at least 4.0 wt% Al, which ensures a sufficient oxidation resistance at high temperatures and that the oxide covers the surface entirely. At Al contents above 5.0 wt%, there is a risk that the hot ductility is considerably deteriorated, the maximum Al content is therefore 5.0 wt%, According to embodiments, the content of Al is between 4.0 to 4.5 wt%

Iron

It has been shown in accordance with the present disclosure that relatively high contents of Fe in an aluminium oxide forming nickel-based alloy can have positive effects. Additions of Fe generate a metallic structure which is energetically unfavourable for the formation of embrittling y’, which in turn to the risk of the alloy becoming hard and brittle. Therefore, the nickel-based alloy comprises at least 15.0 wt% Fe. High contents of iron may however lead to formation of unwanted phases. Therefore, the alloy does not comprise more than 25.0. wt% Fe. According to 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%.

Nickel

The alloy according to the disclosure is nickel-based. Nickel is an alloying element which stabilises an austenitic structure and thereby counteracts formation of some brittle intermetallic phases, such as o-phase. The austenitic structure is beneficial for example when it comes to welding. The austenitic structure also contributes to good creep strength at high temperatures. Ni is the balance alloying element.

Nitrogen

In the same way as C, free N will take interstitial locations in the crystal structure and thereby lock the dislocation mobility at temperatures up to approximately 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 where these particles are finely dispersed, they confer obstacles for the dislocation mobility, especially at higher temperatures. Therefore, N is added in order to improve the creep strength. However, when adding N to aluminium alloyed alloys, if not added with caution, formation of aluminium nitrides will be a problem, therefore the content of N is 0.030 to 0.075 wt%. According to embodiments, the content of N is 0.040 to 0.060 wt%.

Oxygen

Oxygen may be present in the present alloy up to 0.1 wt%.

Oxygen may contribute to increasing the creep strength of the alloy by forming small oxide dispersions together with Zr, Hf, Ta and Ti, which, when they are finely distributed in the alloy, will improve the creep strength. These oxide dispersions have higher dissolution temperature than corresponding carbides and nitrides, whereby oxygen is a preferred addition for use at high temperatures. Oxygen may also form dispersions with Al, the elements in group 3 of the periodic table, Sc, Y and La as well as the fourteen lanthanides, and in the same manner as with the above identified elements thereby contribute to higher creep strength of the alloy. According to embodiments, the nickel-based alloy comprises 20 to1000 ppm O, such as 50 to300 ppm O. Tantalum, Hafnium, Zirconium, Titanium and Niobium

The elements Ta, Hf and Zr form very small and stable particles with carbon and nitrogen. It is these particles which, if they are finely dispersed in the structure, help to lock dislocation movement and thereby increase the creep strength, i.e. , provide the dispersion strengthening. It is also possible to accomplish this effect with addition of Ti. Niobium also forms stable dispersions with C and or N and can therefore suitably be added to the present. Due to the above, the combined content of Ta, Zr, Hf, Ti and Nb is 1 .0 to 2.7 wt%. According to embodiments, the combined content of Ta, Zr, Hf, Ti and Nb is 1 .4 to 2.3 wt%, such as 1 .6 to 2.0 wt%.

Even though the combined conent is as mentioned above. There are some limitations of the content of each the elements, according to embodiments, the content of Hf may be 0.3 to 0.7 wt% and according to another embodiment, the content of Zr may be 0.3 to 0.7 wt% and according to embodiments, the content of Ta may be 0.3 to 0.7 wt% and according to embodiments, the content of Nb may be 0.3 to 0.7 wt%.

Yttrium (Y)

Y affects the oxidation properties by doping of the formed oxide. Excess alloying of this element often gives an oxide which tends to spall of the surface and a too low addition of these elements tends to give an oxide with weaker adhesion to the metal surface. Excess alloying of Y also deteriorates the hot ductility. Hence, the content of Y is therefore restricted to 0.10 wt%. According to embodiments, the content of Yttrium is 0.005 to 0.10 wt%.

Boron (B)

Addition of B has been shown to improve the hot ductility in nickel-based alloys. However, too high content of B will reduce the melting point and thereby reduce the hot workability by reducing the temperature range in which the material can be worked. Too high content of B may also deteriorate the desired high temperature properties. The powder may comprise B in a content of up to 0.02 wt%. According to embodiments, B is 0.0001 to 0.02 wt% Additionally, one of Ca or Mg may be added to improve the hot ductility of the material during production process. Preferably, the calcium content is at most 0.05 wt%, suitably equal to or less than 0.01 wt%. The content of Mg may suitably be at most 0.05 wt%.

The nickel-based alloy according to the disclosure may also comprise normally occurring impurities as a result of the raw material used or the selected manufacturing process. Examples of impurities are S and P. The herein described alloy may, in addition to the elements already specified and discussed above, comprise up to at most 0.8 wt% in total of normally occurring impurities. In the present disclosure, normally occurring impurities are considered to be impurities resulting from the manufacturing process and/or the raw material used. The amount of normally occurring impurities may according to embodiments suitably be equal to or less than 0.6 wt% in total or alternatively equal to or less than 0.5 wt% in total.

Moreover, the alloy, the powder or the object as defined hereinabove or hereinafter may comprise or consist of the elements as defined hereinabove or hereinafter herein, in any of the ranges mentioned herein.

The products, such as components, manufactured from the powder as defined hereinabove or hereinafter are foremost intended for use at high temperatures. Examples of applications are construction materials for heat treatment furnaces, rollers for roller hearth furnaces, muffle tubes for annealing in protective atmosphere, construction material for heating elements, combustion chamber material in gas turbines, gas-to-gas heat exchangers for example in the glass manufacturing industry or in gas turbines, tubular reactors in high temperature processes, transportation belts of woven wires intended for heat treatment furnaces, radiation tubes for heating of heat treatment furnaces or protective tubes for thermocouples.

The present invention is described by the following non-limiting examples. Examples

The different powders were produced by means of gas atomization in which virgin raw material were melted and poured through a ceramic nozzle after which the melt stream was subjected nitrogen gas at high flow rates. The gas flow breaks up the melt stream into small droplets which solidifies rapidly into spherical powder particles. The powders were filled into welded sheet metal canisters which were degassed, sealed and subjected to Hot Isostatic Pressing (HIP). In the HIP process the filled powder canisters were subjected to high temperature (1150°C) at high pressure in an argon atmosphere (100 MPa) for a 3 hour long holding time. This process results in densification of the powder filled canister to a full density body. The HIPed body was then subjected to hot rolling in several passes with a total reduction of 70%. From the hot rolled material, specimens for Gleeble hot ductility tensile testing were extracted in the rolling direction.

The composition of the manufactured powders are shown in Table 1 below

Hot ductility tests were performed accordingly in a Gleeble system: Tensile test specimens were heated to a set temperature with a specific heating profile/rate which is measured by thermocouples. The set temperature can be reached by heating to desired temperature (ONH), or by cooling from a higher temperature (ONC). After a specified holding time at the desired temperature tensile tests are conducted. The area reduction of the tensile specimen at the fracture point is then measured which provides a measurement of the hot ductility. The result of the tests is shown in Table 2 below.

Hot ductility testing in a Gleeble-system constitutes a measure of a materials ability to withstand deformation at high temperature without formation of cracks, i.e. hot ductility. As can be seen from Table 2, the heats that fulfill all requirements as defined hereinabove or hereinafter show good hot ductility in form of high area reduction values at elevated high temperatures in the Gleeble test results. It should be noted that an area reduction > 50% at 1150°C and > 35% at 1050°C from the Gleeble test results is required for a heat to be regarded as having good hot ductility. Table 1 All Heats within the invention is marked with a "*", the balance is Nickel and unavoidable impurities

Heat Heat Heat Heat l* Heat 2* Heat 3* Heat 4* Heat 5* Heat 6* Heat 7* Heat 8 Heat 9 10* 11* 12*

C (wt%) 0,24 0.24 0.23 0.23 0.23 0.23 0.18 0.28 0.17 0.21 0.10 0.09

Si (wt%) <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 0.02 0.02 <0.01 <0.01 0.10 0.16

Mn (wt%) <0.01 <0.01 <0.01 <0.01 <0.01 0.01 0.07 <0.010 0.01 0.01 0.11 0.09

Cr (wt%) 18.5 18.3 18.2 18.4 18.4 17.7 18.4 17.3 18.3 18.4 18.2 18.3

Ti (wt%) <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 0.02 0.28 <0.01 <0.01 0.05 <0.02

Al (wt%) 4.2 4.3 4.4 4.2 4.2 4.4 4.4 4.4 4.4 4.3 4.7 4.6

B (wt%) <0.0004 <0.0004 0.0007 0.0007 0.0007 0.0013 <0.0004 <0.0004 <0.0004 <0.0004 <0.0004 <0.0004

Fe (wt%) 19.4 19.4 19.6 19.6 19.9 19.1 19.3 18.5 19.7 20.0 20.0 19.7

Ta (wt%) 0.55 0.37 0.68 0.55 0.37 0.56 0.45 0.44 0.55 0.59 0.48 0.39

Nb (wt%) 0.40 0.27 0.53 0.43 0.30 0.44 <0.02 0.38 0.45 0.44 <0.02 <0.02

Zr (wt%) 0.45 0.59 0.34 0.44 0.58 0.36 0.34 0.34 0.41 0.46 0.40 0.25

Y (wt%) 0.02 0.02 0.01 0.01 0.02 0.05 0.05 0.01 0.04 0.08 0.03 0.08

Hf (wt%) 0.44 0.57 0.31 0.41 0.54 0.49 0.35 0.23 0.43 0.49 0.23 0.39

O (wt%) 0.008 0.008 0.009 0.007 0.008 0.009 0.03 0.012 0.008 0.0132 0.0109 0.0164

N (wt%) 0.065 0.052 0.052 0.05 0.057 0.053 0.064 0.061 0.055 0.055 0.057 0.046

Ta+Zr+Hf+Ti+Nb (wt%) 1.84 1.80 1.86 1.83 1.79 1.85 1.16 1.67 1.84 1.98 1.16 1.03

(C+N)/(Ta+Zr+Hf+Nb+

Ti) (at%) 1.67 1.62 1.53 1.54 1.58 1.58 2.22 1.59 1.22 1.36 1.28 1.36

Zr+Hf-N (at%) 0.15 0.32 0.09 0.19 0.29 0.16 0.06 0.04 0.16 0.21 0.09 0.09

Table 2 Gleeble data relating to hot ductility

A is area reduction

Claims

1 . A dispersion strengthened alumina forming nickel-based alloy comprising in percent by weight (wt%)

C 0.08 to 0.28;

Si Oto 1.50;

Mn Oto 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 O 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; and wherein said alloy fulfils the requirements of: (C+N)/(Ta+Zr+Hf+Nb+Ti) > 1.4 (values in at%) [1];

Zr + Hf - N > 0.05 (values in at%) [2],

2. The dispersion strengthened alumina forming nickel-based alloy according to claim 1 , wherein the content of C is 0.15 to 0.28 wt%, such as 0.20 to 0.28 wt% C.

3. The dispersion strengthened alumina forming nickel-based alloy according to claim 1 or 2, wherein the content of Si is of no more than 0.30 wt%.

4. The dispersion strengthened alumina forming nickel-based alloy according to anyone of claims 1 to 3, wherein Mn is an impurity, and the content thereof is up to 0.05 wt%. The dispersion strengthened alumina forming nickel-based alloy according to anyone of claims 1 to 4, wherein the content of Cr is 17.0 to 19.0 wt%. The dispersion strengthened alumina forming nickel-based alloy according to anyone of claims 1 to 5, wherein the content of Fe is 18.0 to 21 . wt%, such as 18.0 to 20.0 wt%. The dispersion strengthened alumina forming nickel-based alloy according to anyone of claims 1 to 6, wherein the content of oxygen is 20 to 1000 ppm , such as 50 to 300 ppm O. The dispersion strengthened alumina forming nickel-based alloy according to anyone of claims 1 to 7, the combined content of Ta, Zr, Hf, Ti and Nb is 1 .4 to 2.3 wt%, such as 1 .6 to 2.0 wt%. A powder composed of a dispersion strengthened alumina forming nickel- based alloy according to anyone of claims 1 to 8. An object made from a dispersion strengthened alumina forming nickel- based alloy or a powder according to anyone of claims 1 to 9. The object according to claim 10, wherein said object is a HIP:ed object. The object according to claim 10 or claim 11 , wherein said object is in the form of a tube, a hollow, a bloom, a bar, a rod, a strip, a plate or a wire.