FeCrAl powder and objects made of said powder

Abstract

The present disclosure relates to a ferritic iron-chromium-aluminum (FeCrAl) powder having the following composition (balance Fe, and unavoidable impurities): Al 4.0~6.0 Y max 0.20 Hf 0.05~0.20 O 0.01~0.03 Cr 19.0~23.0 Ta 0.05~0.30 Ti 0.01~0.10 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn max 0.30 P max 0.01 S max 0.01 Zr 0.05~0.20 This results in the article or alloy thereof having superior creep strength.

Description

[Technical field]

[0001] The present disclosure relates to ferritic iron-chromium-aluminum alloy (FeCrAl) powders that provide bodies or alloys thereof with excellent creep strength. [Background technology]

[0002] Iron-chromium-aluminium (FeCrAl) alloys, produced from FeCrAl powders with chromium (Cr) content of 15-25% by weight and aluminium (Al) content of 3-6% by weight, are well known for their ability to form protective α-alumina (Al2O3) (aluminium oxide scale) when exposed to temperatures of 900-1300°C. These alloys are therefore very useful in applications where good oxidation resistance is required. However, while the powders provide products that perform well in high temperature applications, there is always a need for products with even higher creep resistance and good form stability, as these properties would result in longer service life.

[0003] Thus, aspects of the present disclosure provide FeCrAl powders that have these properties when used to manufacture alloys or articles thereof. Summary of the Invention

[0004] The present disclosure provides a ferritic iron-chromium-aluminium alloy (FeCrAl) powder composition optimized to provide a creep-resistant object. The present disclosure also provides an alloy or object (which may be selected from a tube, wire, strip, sheet, heating element or structural element) that is produced from the powder defined below and therefore exhibits excellent creep strength and shape stability. Furthermore, the powder according to the present disclosure can be used in conventional and additive manufacturing methods. The term "shape stability" means that the object essentially retains its shape (form) even when exposed to high temperatures.

[0005] The iron-chromium-aluminum alloy (FeCrAl) powder according to the present disclosure is characterized by having the following composition in weight percent (wt%): TIFF2024543066000001.tif151170

[0006] Detailed Description The present disclosure relates to an iron-chromium-aluminum alloy (FeCrAl) powder characterized by having the following composition in weight percent (wt%): TIFF2024543066000002.tif151170

[0007] The inventors have surprisingly found that the low yttrium and oxygen content, combined with the absence of any deliberate addition of molybdenum, results in bodies with superior creep resistance compared to conventional FeCrAl powders. This finding is quite surprising, as yttrium oxide is believed to contribute to creep strength, and thus reducing these elements should lead to a decrease in creep strength. However, bodies made from the powder have been shown to have improved creep strength.

[0008] The alloying elements of the powder (and thus the alloy and body(s)) are described in more detail below. The terms "weight %" and "wt%" are used interchangeably. Also, the listing of properties or contributions stated for specific elements should not be considered exhaustive.

[0009] Iron (Fe) The primary function of the iron is to provide the balance of the composition.

[0010] Chromium (Cr) 19.0-23.0% by weight Chromium is an important element since it improves the corrosion resistance and increases the tensile and yield strength. Chromium also facilitates the formation of Al2O3 at the surface due to the so-called third element effect (i.e. the formation of chromium oxides in the transitional oxidation stage). Too little chromium leads to loss of corrosion resistance. Therefore, chromium is preferably present in an amount of at least 19.0 wt.%, such as at least 20.0 wt.%. Too much chromium leads to α-α' decomposition and 475°C embrittlement, as well as an increase in the solid solution hardening effect on the ferritic structure. Therefore, the maximum chromium content is set to 23.0 wt.%, such as a maximum of 22.0 wt.%. According to some embodiments, the chromium content is between 19.0 and 23.0 wt.%, such as between 20.0 and 22.0 wt.%.

[0011] Aluminum (Al) 4.0-6.0% by weight Aluminum is an important element because, when exposed to oxygen at high temperatures, it forms a dense and thin Al2O3 layer on the surface, which protects the underlying surface from further oxidation. Aluminum also increases the electrical resistance. Too little aluminum leads to the loss of the ability to form an Al2O3 layer, which also reduces the electrical resistance. Aluminum is therefore preferably present in an amount of at least 4.0% by weight, such as at least 4.5% by weight. Too much aluminum leads to brittleness at low temperatures and promotes the formation of undesirable brittle aluminides. The maximum amount of aluminum is therefore set at 6.0% by weight, such as a maximum of 5.5% by weight. According to some embodiments, the Al content is between 4.0 and 6.0% by weight, such as between 4.5 and 5.5% by weight.

[0012] Titanium (Ti) 0.01 to 0.10% by weight Titanium is added to combine with free carbon or nitrogen. According to one embodiment, the Ti content is 0.01 to 0.06 wt %.

[0013] Nitrogen (N) 0.01 to 0.10% by weight Nitrogen is included to increase strength through precipitation hardening. Too high a nitrogen level can adversely affect corrosion resistance. Thus, the maximum amount of nitrogen is 0.10 wt.%. According to the present disclosure, the N content is 0.01-0.10 wt.%, for example 0.01-0.07 wt.%.

[0014] Zirconium (Zr) 0.05-0.20% by weight Zirconium is an important element since it reduces the activity of C and N by the formation of ZrC or ZrN precipitates. Zirconium can also improve the high temperature creep strength of the manufactured object. Too little Zr increases the risk of undesired chromium carbide and / or aluminum nitride formation. Zirconium is therefore preferably present in an amount of at least 0.05% by weight, such as at least 0.07% by weight, for example at least 0.10% by weight. On the other hand, too high a content of zirconium can have a detrimental effect on the formation of Al2O3. For these reasons, the maximum content of zirconium is set at 0.20% by weight, for example at most 0.15% by weight.

[0015] Yttrium (Y) max 0.20% by weight Yttrium is an optional element in the powder. Its addition improves the oxidation resistance of the manufactured object. However, too much yttrium added leads to hot embrittlement. As a result, the maximum yttrium content is set to max. 0.20 wt.%, for example max. 0.15 wt.%.

[0016] Carbon (C) 0.01~0.05% by weight Carbon is added to increase strength by precipitation hardening. Too high a carbon level can lead to forming difficulties due to the formation of chromium carbides and can also adversely affect corrosion resistance. The maximum amount of carbon is therefore 0.05% by weight in the powder according to the invention.

[0017] Silicon (Si) 0.50% by weight max Silicon is present at levels up to 0.50% by weight to increase electrical resistivity and improve corrosion resistance, however above this level it increases hardness and becomes brittle at low temperatures.

[0018] Oxygen (O) 0.01 to 0.03% by weight The oxygen is present in the form of oxides. The inventors have surprisingly found that by lowering the oxygen content, objects manufactured with the powders defined above or below have a very low creep rate and thus also a high dimensional stability, compared to conventional FeCrAl alloys. The maximum permissible content is 0.03 wt.%. Thus, according to some embodiments, the oxygen content is between 0.01 and 0.03 wt.%, for example between 0.01 and 0.02 wt.%.

[0019] Hafnium (Hf) 0.05-0.50% by weight Hafnium is included to bond with free nitrogen or carbon, and the absence of hafnium may adversely affect corrosion resistance. According to some embodiments, the content of Hf is 0.05 to 0.50 wt%, for example, 0.10 to 0.30 wt%, for example, 0.10 to 0.20 wt%.

[0020] Tantalum (Ta) 0.05 to 0.30% by weight Tantalum is included to bond with free nitrogen or carbon, and the absence of tantalum may adversely affect corrosion resistance. According to some embodiments, the content of each element is 0.05 to 0.30 wt%, for example 0.15 to 0.25 wt%.

[0021] Manganese (Mn) 0.30% max by weight Manganese is an optional alloying element. Too much Mn content will prevent the formation of the alumina layer. Therefore, the Mn content is set to max 0.30 wt%, for example max 0.20 wt%.

[0022] According to some embodiments, the powder or object may contain trace fractions of one or more of the following impurity elements (by way of example only and not limitation): magnesium (Mg), nickel (Ni), cerium (Ce), calcium (Ca), phosphorus (P), tungsten (W), cobalt (Co), sulfur (S), molybdenum (Mo), niobium (Nb), vanadium (V), and copper (Cu), by which is meant elements that are present due to the manufacturing method and / or due to the materials used in the manufacturing process, but in amounts so small that they do not affect the properties.

[0023] Additionally, the FeCrAl powders or bodies defined above or below may include the alloying elements recited herein, in any of the ranges recited herein. According to one embodiment, the powders or bodies consist of all of the alloying elements recited herein, in any of the ranges recited herein.

[0024] Furthermore, the alloy or object as defined above or below may comprise or consist of the alloying elements of the FeCrAl powder as defined above or below in any range mentioned herein. The object obtained from the FeCrAl powder as defined above or below works well at high temperatures, for example at temperatures up to 1250° C. Furthermore, the object has good high-temperature corrosion resistance and is highly resistant to oxidation, sulfidation and carburization. Furthermore, the object has good high-temperature creep strength and shape stability.

[0025] The object may be selected from a tube, or a strip, or a sheet, or a wire, or a heating element, or a structural element. The object is particularly useful as an electrical heating element or as an object in high temperature applications.

[0026] The FeCrAl powders defined above or below can be produced by various methods, for example: Directly by gas atomization Heating a powder containing all alloying elements in the ranges mentioned above or below, Mixing powders containing all alloying elements in the ranges mentioned above or below, The present invention can be produced by, but is not limited to, the following methods.

[0027] The invention is further illustrated by the following non-limiting examples. EXAMPLES

[0028] Three powders (Table 1) with the chemical compositions (wt%) listed in Table 1 were produced by nitrogen gas atomization and then sieved into appropriate fractions to obtain powders with particle sizes less than 750 μm. Alloy 1 is an example of an alloy according to the invention within the scope of this disclosure, while Alloy 2 and Alloy 3 are reference alloys.

[0029] TIFF2024543066000003.tif221170

[0030] The three powders (see Table 1) were HIP-treated by holding them at 1150°C and a pressure of 100 MPa for 3 hours. A specimen for mechanical testing that had only been HIP-treated was taken out and the outer dimensions were A cylindrical extrusion billet of 138×450 mm was machined. The extrusion billet was then hot worked into a tube by a conventional extrusion process, and several sample pieces were taken from the extrusion tube.

[0031] Creep test samples were machined from the as-HIPed specimens and from the extruded tube specimens. Creep tests were performed uniaxially in air at 1100°C and 8.0 MPa tensile load to determine the secondary creep rate. The creep test results are shown in Table 2. As can be seen from the results in Table 2, the creep strength of the objects made from the powder according to the present invention has a low secondary creep rate and a long time to fracture. Thus, the objects made from the powder according to the present invention will have good mechanical stability and will not deform at high temperatures when exposed to load.

[0032] TIFF2024543066000005.tif88170

Claims

1. A powder having the following elements in weight percent: The balance is Fe and unavoidable impurities Al 4.0 to 6.0 Y maximum 0.20 Hf 0.05~0.20 O 0.01~0.03 Cr 19.0~23.0 Ta 0.05~0.30 Ti 0.01~0.10 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn maximum 0.30 P maximum 0.01 S max 0.01 Zr 0.05-0.

20.

2. 2. The powder according to claim 1, wherein the Cr content is 20 to 22 wt. %.

3. 2. The powder according to claim 1, wherein the Y content is up to 0.16% by weight.

4. 2. The powder according to claim 1, wherein the O content is 0.01 to 0.02 wt %.

5. 2. The powder according to claim 1, wherein the Hf content is 0.10 to 0.20 wt. %.

6. 2. The powder according to claim 1, wherein the Ta content is 0.15 to 0.25 wt. %.

7. 2. The powder according to claim 1, wherein the Ti content is 0.01 to 0.05 wt. %.

8. 2. The powder according to claim 1, wherein the Zr content is 0.10 to 0.15 wt. %.

9. 9. An object or alloy made from the powder of any one of claims 1 to 8.

10. 10. The object of claim 9, which is a tube, or a strip, or a wire, or a heating element, or a structural element.

11. 10. The article of claim 9, wherein the secondary creep rate is less than 8.0E-09 [1 / s] in the HIPed condition when measured uniaxially under a load of 8.0 MPa in air at 1100°C.

12. 10. The article of claim 9, wherein the secondary creep rate, measured uniaxially under a load of 8.0 MPa in air at 1100°C, is less than 7.0E-08 [1 / s] in the hot extruded condition.

13. The object of claim 9 , wherein a method for manufacturing the object comprises an additive manufacturing process and / or a HIP process.