Ferritic iron-chromium-aluminum powder and seamless tubes manufactured from said powder

Abstract

The present disclosure relates to ferritic iron-chromium-aluminum (FeCrAl) powders, seamless tubes of which have a combination of good formability, shape stability, good oxidation resistance and creep resistance. The present disclosure also relates to seamless tubes comprising the FeCrAl alloy. The FeCrAl powder contains the following elements in weight percent: balance Fe and unavoidable impurities, Al 4.0-6.0, Y 0.01-0.10, Hf 0.05-0.25, O 0.01-0.04, Cr 19.0-23.0, Ta 0.01-0.40, Ti 0.01-0.15, C 0.01-0.05, N 0.01-0.10, Si max 0.50, Mn max 0.30, Zr 0.05-0.20, and satisfies the condition 2×[Y]-3×[O]<0, where the numbers [Y] and [O] are in atomic percent.

Description

[Technical field]

[0001] The present disclosure relates to ferritic iron-chromium-aluminum (FeCrAl) powders and articles constructed therefrom that have a combination of good formability, shape stability, oxidation resistance, and creep resistance. The present disclosure also relates to seamless tubes comprising FeCrAl alloys produced from the powders. [Background technology]

[0002] Iron-chromium-aluminum (FeCrAl) alloys, produced from FeCrAl powder with a chromium (Cr) content of 15-25% by weight and an aluminum (Al) content of 3-6% by weight, are well known for their ability to form a protective alpha-alumina (Al2O3), aluminum oxide scale when exposed to temperatures between 900 and 1300°C. These alloys are good for applications where good oxidation resistance is required.

[0003] However, although it is possible to obtain tubes of these powder compositions, the process of obtaining seamless tubes without cracks is very troublesome due to the moldability issue.

[0004] It is thus an aspect of the present disclosure to provide an FeCrAl powder that, when used in a method of manufacturing an object (e.g., a seamless tube), results in an object having a combination of good formability, form stability, oxidation resistance, and creep resistance, which reduces or even eliminates crack formation during the manufacturing process.

[0005] Summary of the Invention Thus, the present disclosure provides ferritic iron-chromium-aluminum (FeCrAl) powders having an optimized composition to provide objects (e.g., tubes, e.g., seamless tubes) with excellent mechanical properties, good creep strength, good oxidation resistance, and which are substantially free of crack formation during the manufacturing process. This is possible because the powders provide objects made from the powders with excellent ductility (e.g., both high and low temperature ductility), and therefore excellent formability.

[0006] The FeCrAl powder according to the present disclosure has the following composition (by weight): The balance is Fe and inevitable impurities. Al 4.0~6.0 Y 0.01~0.10 Hf 0.05~0.25 O 0.01~0.04 Cr 19.0~23.0 Ta 0.01~0.40 Ti 0.01~0.15 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn max 0.30 Zr 0.05~0.20 and satisfying the requirement 2×[Y]−3×[O]<0 (where the numbers of [Y] and [O] are in atomic % (at %)).

[0007] By satisfying these element ranges and the above requirements, an excess of yttrium relative to oxygen is avoided, which reduces the formation of unfavorable phases (e.g., Fe 17 Y2, which is detrimental to hot ductility), is avoided. Moreover, it has been found that if this requirement is met, the bodies obtained from the powder have excellent both hot and cold ductility.

[0008] Detailed Description The present disclosure provides a composition having the following composition (by weight): The balance is Fe and inevitable impurities. Al 4.0~6.0 Y 0.01~0.10 Hf 0.05~0.25 O 0.01~0.04 Cr 19.0~23.0 Ta 0.01~0.40 Ti 0.01~0.15 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn max 0.30 Zr 0.05~~0.20 and satisfies the requirement 2×[Y]−3×[O]<0 (where the numbers [Y] and [O] are in atomic %).

[0009] The present disclosure also provides a method for producing a composition comprising the following composition (by weight): The balance is Fe and inevitable impurities. Al 4.0~6.0 Y 0.01~0.10 Hf 0.05~0.25 O 0.01~0.03 Cr 19.0~23.0 Ta 0.01~0.20 Ti 0.01~0.10 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn max 0.30 Zr 0.05~0.20 and satisfies the requirement 2×[Y]−3×[O]<0 (where the numbers [Y] and [O] are in atomic %).

[0010] The present disclosure also provides a method for producing a composition comprising the following composition (by weight): The balance is Fe and inevitable impurities. Al 4.0~6.0 Y 0.01~0.10 Hf 0.05~0.25 O 0.01~0.04 Cr 19.0~23.0 Ta 0.01~0.40 Ti 0.01~0.15 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn max 0.30 Zr 0.05~0.20 and satisfies the requirement that 2×[Y]−3×[O]<0 (where the numbers [Y] and [O] are in atomic %).

[0011] The present disclosure also provides a method for producing a composition comprising the following composition (by weight): The balance is Fe and inevitable impurities. Al 4.0~6.0 Y 0.01~0.10 Hf 0.05~0.25 O 0.01~0.03 Cr 19.0~23.0 Ta 0.01~0.20 Ti 0.01~0.10 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn max 0.30 Zr 0.05~0.20 and satisfies the requirement that 2×[Y]−3×[O]<0 (where the numbers [Y] and [O] are in atomic %).

[0012] The object may be a tube, for example a seamless tube.

[0013] The inventors have surprisingly found that it is essential that the requirement 2×[Y]-3×[O]<0 is met, because when this requirement is met together with the above elemental ranges, there is an excess of oxygen relative to yttrium, which ensures that the object, or the object produced from said powder, has good ductility both at low and high temperatures. This makes it very easy to produce the object, for example a seamless tube, because it has a combination of good formability and shape stability, and furthermore, the object obtained is substantially crack-free and has good oxidation and creep resistance.

[0014] The alloying elements according to the present disclosure are described in more detail below. "Weight %" and "wt%" are used interchangeably. Also, the listing of properties or contributions stated for specific elements should not be considered exhaustive.

[0015] Iron (Fe) The primary function of the iron in the FeCrAl powder is to provide the balance of the composition.

[0016] 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. chromium oxide formation 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 Cr content is 19-23 wt%, such as 20-22 wt%.

[0017] 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 reduces the electrical resistance and the ability to form an Al2O3 layer, which reduces the oxidation 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.

[0018] Titanium (Ti) 0.01 to 0.15% by weight Titanium is added to bond with liberated carbon or nitrogen, and its content is 0.01 to 0.15% by weight, for example, 0.01 to 0.10% by weight.

[0019] 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 0.02-0.08 wt.%, for example 0.02-0.06 wt.%.

[0020] 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 high temperature creep strength. Too little Zr increases the risk of forming undesirable carbides. Zirconium is therefore preferably present in an amount of at least 0.05 wt.%, such as at least 0.08 wt.%, for example at least 0.10 wt.%. 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 wt.%, for example at most 0.17 wt.%.

[0021] Yttrium (Y) 0.01 to 0.10% by weight Yttrium is added to improve oxidation resistance. However, too much yttrium content leads to hot embrittlement. Moreover, too much yttrium content promotes the formation of yttrium oxide clusters, which leads to brittleness and therefore poor formability at high and low temperatures. As a result, the maximum yttrium content is set to 0.10 wt%, such as max. 0.07 wt%, such as max. 0.06 wt%, such as max. 0.05 wt%.

[0022] Carbon (C) 0.01~0.05% by weight Carbon is added to increase strength through precipitation hardening. Too much carbon can make the material difficult to form and can also adversely affect corrosion resistance. Therefore, the maximum amount is 0.05% by weight.

[0023] Silicon (Si) ≦0.50% by weight Silicon is present at levels of ≦0.50 wt. % to increase electrical resistivity and improve corrosion resistance, however above this level it increases hardness and becomes brittle at low temperatures.

[0024] Oxygen (O) 0.01 to 0.04% by weight The oxygen is present in the form of oxides. The maximum permitted amount is ≦0.04 wt.%. According to some embodiments, the maximum oxygen content is ≦0.03 wt.%. The inventors have surprisingly found that an excess of oxygen relative to Y reduces the formation of brittle phases, thereby improving the high temperature ductility.

[0025] Hafnium (Hf) 0.05-0.30% by weight Hafnium is included in the powder to combine with free nitrogen or carbon, the absence of which would have a detrimental effect on corrosion resistance. According to some embodiments, the Hf content is 0.05-0.30 wt%, for example 0.05-0.25 wt%, for example 0.15-0.25 wt%.

[0026] Tantalum (Ta) 0.01 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 Ta content is 0.01 to 0.20 wt%, for example 0.01 to 0.20 wt%.

[0027] Manganese (Mn) 0.30% max by weight Manganese is an optional alloying element. Too much Mn content reduces the formation of the alumina layer. Therefore, the Mn content is set to a maximum of 0.30 wt.%.

[0028] Furthermore, the inventors have found that the powder according to the invention 2×Y-3×O<0 (where all values ​​are in atomic %) It has been found that it is also important to satisfy the condition: 2×Y-3×O<−0.10, e.g., <−0.15. This requirement is important because it results in an excess of oxygen relative to yttrium. This excess ensures good ductility at high and low temperatures. This further reduces the risk of yttrium oxide clusters and stringers forming in the object. According to an embodiment, 2×Y-3×O<−0.10, e.g., <−0.15.

[0029] 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.

[0030] 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.

[0031] Yet another aspect of the present disclosure is to provide a tube having good mechanical properties and substantially free of cracks (e.g. seamless tube), which can be produced by rolling. However, the powder as defined above or below can also be used to produce wires or sheets or strips etc.

[0032] 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.

[0033] The object, for example a tube or seamless tube, is manufactured by conventional methods, including hot and cold working steps. Prior to the hot and cold working steps, a billet is manufactured, for example by hot isostatic pressing (HIP).

[0034] Seamless tubes and other objects obtained from the FeCrAl powders defined above or below perform well at high temperatures up to 1250° C. Furthermore, the objects according to the invention have good high temperature corrosion resistance and are highly resistant to oxidation, sulfidation and carburization. In addition, the tubes have good high temperature creep strength and shape stability, high electrical resistance and ductility. The tubes are particularly useful as electric heating elements or as components in high temperature applications.

[0035] According to the present disclosure, the tube may be a hot worked tube or a hot worked and cold worked tube, for example a hot rolled and cold rolled tube.

[0036] The invention is further illustrated by the following non-limiting examples. EXAMPLES

[0037] Powders (Table 1A) having the chemical composition (wt%) set forth in Table 1 were produced by gas atomization and then sieved into appropriate fractions to obtain powders with particle sizes less than 750 μm. Powders 1 and 2 are powders within the scope of the present disclosure.

[0038] TIFF2024543844000001.tif175170

[0039] TIFF2024543844000002.tif49170

[0040] These powders (see Table 1A) were HIPed by holding at 1150°C and 100 MPa pressure for 3 hours, followed by slow cooling into extrusion billets with dimensions of 0121 mm, from which specimens were taken for use in the Gleeble test (see Table 2).

[0041] The Greeble test was performed as follows: The tensile specimen is heated to a set temperature with a specific heating profile / rate measured by a thermocouple in the Gleeble system (Gleeble instrument). The set temperature can be reached by heating to the desired temperature (ONH) or by cooling from high temperature (ONC). After holding at the desired temperature for a specific time, the tensile test is carried out by subjecting a cylindrical specimen with a reduced cross section of 40 mm in length to a tensile displacement rate of 50 mm / s. The area reduction of the tensile specimen at the break point is then measured, thereby measuring the hot ductility. The results are shown in Table 2.

[0042] TIFF2024543844000003.tif164170

[0043] High temperature tensile tests performed with the Gleeble system consistently show improved area reduction values ​​for all tested temperatures evaluated. Moreover, powders 1 and 2 according to the invention remain ductile even at significantly lower temperatures. From these results it can be concluded that the ductility of powders 1 and 2 according to the invention is significantly greater compared to the reference powder. This is very surprising, since without intending to be bound by any theory, it is believed that this is due to the relationship between yttrium and oxygen. Moreover, it is surprising that powders 1 and 2 according to the invention contain only traces of Mo as an impurity, yet still have good material properties.

Claims

1. The following elements in weight percent: The balance is Fe and inevitable impurities, Al 4.0 to 6.0 Y 0.01~0.10 Hf 0.05~0.25 O 0.01~0.04 Cr 19.0~23.0 Ta 0.01~0.40 Ti 0.01~0.15 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn maximum 0.30 Zr 0.05~0.20 and satisfying the requirement 2×[Y]−3×[O]<0, where the numbers [Y] and [O] are in atomic percent.

2. The balance is Fe and inevitable impurities, Al 4.0 to 6.0 Y 0.01~0.10 Hf 0.05~0.25 O 0.01~0.03 Cr 19.0~23.0 Ta 0.01~0.20 Ti 0.01~0.10 C 0.01~0.05 N 0.01~0.10 Si max 0.50 Mn maximum 0.30 Zr 0.05~0.20 2. The powder according to claim 1, having a composition of: and satisfying the requirement 2×[Y]−3×[O]<0, where the numbers [Y] and [O] are in atomic %.

3. 2. The powder of claim 1, wherein the Cr content is 20-22 wt.%.

4. 2. The powder of claim 1, wherein the Al content is between 4.5 and 5.5 wt.%.

5. 2. The powder of claim 1, wherein the Y content is at most 0.07% by weight, for example 0.05% by weight.

6. 2. The powder according to claim 1, wherein the N content is 0.02 to 0.08 wt.%, for example 0.02 to 0.06 wt.%.

7. 2. The powder of claim 1, wherein the Ta content is 0.01 to 0.20 wt. %, for example 0.01 to 0.10 wt. %.

8. 2. The powder of claim 1, wherein 2*[Y]-3*[O]<-0.10, for example <-0.

15.

9. 9. An object comprising an alloy having the elemental ranges of any one of claims 1 to 8.

10. The object of claim 9 , wherein the object is a tube, for example a seamless tube.