A new iron-chromium-aluminium powder and the use thereof

Abstract

An iron-chromium-aluminium, FeCrAl, powder comprising in weight%, wt%, C C equal to or less than 0.08, N 0.04 to 0.10, Cr 20.0 to 24.0, Al 4.0 to 6.0, Mo 2.0 to 4.0, Si equal to or less than 0.60, P equal to or less than 0.03, S equal to or less than 0.03, Ti 0.05 to 0.20, Zr 0.05 to 0.25, Nb 0.05 to 0.20, O equal to or less than 0.05, Y equal to or less than 0.10, balance Fe and normally occurring impurities up to at most 1.5 wt% in total.

Description

[0001] A new iron-chromium-aluminium powder and the use thereof

[0002] Technical field

[0003] The present disclosure relates to a new iron-chromium-aluminium (FeCrAl) powder and its use. More specifically, the present disclosure relates to an iron-chromium-aluminium powder suitable for being used for manufacturing components to be used in nuclear applications.

[0004] Background

[0005] FeCrAl alloys are of interest in the nuclear industry for their excellent corrosion and oxidation resistance and have been considered for nuclear applications such as accident tolerant fuel cladding, structural components for fast fission reactors, and within blanket structures of fusion power devices. However, as these alloys may have problems with absorption of neutrons and also to retain form stability, there is a need for a FeCrAl alloys avoiding these problems. Furthermore, even though several FeCrAl alloys are powder, the manufacturing processes for obtaining a final product are quite time consuming and complicated with low yield.

[0006] The present disclosure therefore provides a FeCrAl powder which will solve or at least reduce the problems mentioned above.

[0007] Brief description of the Figures

[0008] Figure 1 shows the results from sag testing of extruded tube samples at 1000 °C.

[0009] Summery

[0010] An aspect of the present disclosure is therefore to provide a FeCrAl powder which, when used for manufacturing a FeCrAl alloy or an object, will allow neutrons to pass through, i.e., it will have a low neutron absorption cross section.

[0011] Another aspect of the present disclosure is to provide a FeCrAl powder which will ensure that an alloy or an object made thereof will have high creep strength during long time exposure, i.e., it will have excellent form stability.

[0012] Yet another aspect of the present disclosure is to provide a FeCrAl powder, which will ensure that an alloy or an object made thereof will withstand high temperatures, e.g., temperatures around 700 to 1200 °C, during long time exposure while retaining its creep strength and corrosion resistance. Another aspect of the present disclosure is to provide a FeCrAl powder which will reduce the manufacturing problems with low yield and complicated process steps.

[0013] Another aspect of the present disclosure is to provide a FeCrAl alloy or FeCrAl component which contains all the elements in the ranges mentioned hereinabove or hereinafter.

[0014] Another aspect of the present disclosure relates to the use of the FeCrAl powder as defined hereinabove or hereinbelow for obtaining an FeCrAl alloy or a FeCrAl component.

[0015] Detailed description of the invention

[0016] The present disclosure provides an iron-chromium-aluminium, FeCrAl, powder comprising in weight%, wt%,

[0017] C equal to or less than 0.08,

[0018] N 0.04 to 0.10,

[0019] Cr 20.0 to 24.0,

[0020] Al 4.0 to 6.0,

[0021] Mo 2.0 to 4.0,

[0022] Si equal to or less than 0.60,

[0023] P equal to or less than 0.03,

[0024] S equal to or less than 0.03,

[0025] Ti 0.05 to 0.20,

[0026] Zr 0.05 to 0.25,

[0027] Nb 0.05 to 0.20 balance Fe and normally occurring impurities up to at most 1.5 wt% in total.

[0028] According to an embodiment, to further ensure that the present FeCrAl powder as defined hereinabove or hereinafter will provide the desired properties mentioned hereinabove or hereinafter, the powder fulfills the following requirement:

[0029] Hence, by ensuring that the present condition is fulfilled, the formation of brittle intermetallic phases will be avoided or essentially avoided during the manufacturing of the FeCrAl powder as the amounts, in atom percent of the reactive elements, are balanced with the amount, in atom percent, of carbon and nitrogen in the powder. In other words, the quotient between carbon and nitride and reactive elements available to form carbides or nitrides is between equal to or greater than 1 to equal to or less than 2 which means that there will be less of the elements Ti, Zr and Nb available for forming intermetallic phases during production and this in turn will ensure that objects or alloys obtained from the powder will have reduced or essentially no brittleness issues.

[0030] An additional positive effect of the present requirement is that the formed carbides of the reactive elements are homogenously distributed throughout the bulk of FeCrAl alloy as defined hereinabove or hereinafter as well as any object made of the present powder and thus will contribute to the mechanical strength by dispersion hardening.

[0031] The principles and advantages of the present FeCrAl powder and the selection of the ranges of the alloying elements which renders the unexpected superiority can be described as follows below. The present disclosure is however not limited to the exemplifying embodiments discussed but may be varied within the scope of the appended claims. Upper and lower limits of the individual elements of the composition can be freely combined within the broadest limits set out in the claims, unless explicitly disclosed otherwise. Additionally, 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.

[0032] Carbon (C)

[0033] Carbon may be included in the FeCrAl powder as defined hereinabove or hereinafter to increase strength by precipitation hardening. To achieve sufficient strength in the alloy, carbon may be present in an amount of at least 0.02 wt%. At too high levels, carbon will result in difficulties to form components and also have a negative effect on the corrosion resistance. The highest level is therefore set to equal to or less than 0.08 wt%. The content of C of the present FeCrAl powder may also be of 0.02 to 0.05 wt%, such as of 0.02 to 0.04 wt%.

[0034] Nitrogen (N)

[0035] Nitrogen is included in the FeCrAl powder as defined hereinabove or hereinafter to increase strength by precipitation hardening. At too high levels, nitrogen will result in difficulties in forming the alloy thereof to an object and may also have a negative effect on the corrosion resistance. Therefore, the highest content of N is 0.10 wt%. In order to obtain the desired effects, the content of nitrogen must be at least 0.04 wt%. The content of N of the present FeCrAl powder may also be of 0.04 to 0.08 wt%, such as of 0.05 to 0.07 wt%.

[0036] Silicon (Si)

[0037] Silicon may be present as an impurity but may also be added. In order to avoid embrittlement, the highest Si content allowed is equal to or less than 0.60 wt%. According to embodiments, the content of Si may equal to or less than 0.50 wt%, such as 0.10 to 0.50 wt%.

[0038] Chromium (Cr)

[0039] Chromium promotes the formation of the AI2O3 layer through the so-called third element effect, i.e., by formation of chromium oxide in the transient oxidation stage. In order to obtain this effect, chromium shall therefore be present in an amount of at least 20 wt%. However, if the content of Cr is above 24 wt%, there will be problems with brittleness. Further, the content of Cr may also be in the range of 20.5 to 23.5 wt%, such as of 21 to 23 wt%.

[0040] Aluminum (Al)

[0041] Aluminum is an important element as aluminum, when exposed to oxygen at high temperature, will form the dense and thin oxide AI2O3, which will protect from corrosion. The amount of aluminum should be at least 4.0 wt% to ensure that the AI2O3 layer is formed, and that sufficient aluminum is present to heal the AI2O3 layer when damaged. However, aluminum has a negative impact on the formability and the amount of aluminum should not exceed 6.0 wt%. Further, the content of Al may also be of 4.0 to 5.0 wt%; such as of 4.1 to 4.9 wt%.

[0042] Molybdenum (Mo)

[0043] Molybdenum is added in order to increase hot strength and corrosion resistance. Mo is therefore added in an amount of 2.0 to 4.0 wt%, such as 2.5 to 3.5 wt%, such as of 2.6 to 3.4 wt%. If the content of Mo is too high, i.e., above 4.0 wt%, it will have a negative effect on oxidation resistance.

[0044] Oxygen (O)

[0045] Oxygen may be added to achieve a precipitation hardening effect. The maximum content of oxygen is equal to or less than up to 0.05 wt%, such as of 0.02 to 0.05 wt%, such as 0.02 to 0.04 wt%. At too high levels, i.e., above 0.05 wt%, oxygen will result in brittleness after hot isostatic pressing (HIP) to a billet.

[0046] Titanium (Ti)

[0047] Titanium is added in order to improve the oxidation properties by balancing the diffusion of metal ions and oxygen, which will govern the kinetics of the oxide growth process. Titanium is also added in order to form particles with N and C and thereby bind these elements. If the Ti content is too high, there may be a problem with oxidation resistance. The content of Ti is of 0.05 to 0.20 wt%, such as of 0.07 to 0.15 wt%.

[0048] Zirconium (Zr)

[0049] Zr is added in order to improve the oxidation properties by balancing the diffusion of metal ions and oxygen, which will govern the kinetics of the oxide growth process. Zirconium is also added in order to form particles with N and C and thereby bind these elements. If the Zr content is too high, there may be a problem with oxidation resistance. The content of Zr is of 0.05 to 0.25 wt%, such as 0.07 to 0.20 wt%.

[0050] Niobium (Nb)

[0051] Nb is added in order to improve the oxidation properties by balancing the diffusion of metal ions and oxygen, which will govern the kinetics of the oxide growth process. Niobium is also added in order to form particles with N and C and thereby bind these elements.

[0052] The content of Nb is of 0.01 to 0.20 wt%, such as 0.05 to 0.15.

[0053] Yttrium (Y)

[0054] Yttrium may be added to improve the adherence of the AI2O3 layer. If yttrium is added the content is equal to or less than 0.10 wt%, as above this content the formed yttrium oxides may cause embrittlement of the material. According to one embodiment, the content of yttrium is in impurity level such as less than 0.01 wt%. According to one embodiment, yttrium is purposively added and then in a range of 0.01 to 0.10 wt%.

[0055] The balance of FeCrAl powder as defined hereinabove or hereinafter is Fe and unavoidable impurities. The herein described powder may, in addition to the elements already specified and discussed above, comprise up to at most 1.5 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. Normally occurring impurities is herein intended to encompass both impurities and trace elements. The amount of normally occurring impurities may according to embodiments suitably be equal to or less than 1.5 wt% in total.

[0056] For example, the herein described powder may comprise normally occurring impurities of Manganese (Mn). The content of said element may be limited to at most 0.5 wt%, such as 0.05 to 0.2 wt%. Further, the herein described powder may comprise normally occurring impurities belonging to the group consisting of Cobalt (Co), Nickel (Ni) and Cupper (Cu). The content of elements belonging to said group may be limited to at most 0.7 wt% in total. Further, the herein described powder may comprise normally occurring impurities belonging to the group consisting of Tantalum (Ta) and Hafnium (Hf). The contents of elements belonging to this group are limited to at most 0.02 wt% each, such as at most 0.01 wt%. Further, the herein described powder may comprise normally occurring impurity of Vanadium (V). The content of V is limited to at most 0.07 wt%.

[0057] The present disclosure also relates to a FeCrAl alloy comprising the elements in the ranges as defined hereinabove or hereafter.

[0058] According to embodiments, the FeCrAl alloy or the FeCrAl powder comprises or consists of all the different alloying elements in any of the ranges mentioned hereinabove or hereinafter.

[0059] The present disclosure also relates to an object or a component of the FeCrAl powder as defined hereinabove or hereinafter or of the FeCrAl alloy as defined hereinabove or hereinafter.

[0060] The object may be a formed product, such as a component. Examples of such are a pipe, a tube, such as a seamless tube, such as a thin-walled tube or pipe, a bar, a hollow bar and a hollow. The present powder as defined hereinabove or hereinafter or the present alloy as defined hereinabove or hereinafter are especially usable for components to be used in nuclear applications as component obtained thereof will be form stable, ductile, have heat resistance, have low neutron absorption cross section, and easy to manufacture. Further examples are heat pipe which will transport heat from the reactor core or as a cladding tube.

[0061] The present disclosure also relates to a method for producing an object of the FeCrAl powder as defined hereinabove or hereinafter or the FeCrAl alloy as defined hereinabove or hereinafter, said method comprising:

[0062] Providing a powder as defined hereinabove or hereinafter;

[0063] Expose the powder to a high isostatic process (HIP) in order to obtain a billet, optionally hot working of the billet, optionally performing an additional hot working on the billet,

[0064] Examples of hot working are extrusion, hot rolling and forging, optionally cold working the hot worked tube,

[0065] Examples of cold working are cold rolling or cold drawing, optionally heat treating the cold worked tube.

[0066] Example of heat treating is annealing.

[0067] The present disclosure is further described by the following non-limiting Examples:

[0068] Examples

[0069] Powders with composition as of Table 1 were produced using gas atomization and then sieved to suitable fraction so that powders with particle size of less than 750 pm were obtained.

[0070] The powders were HIP:ed to extrusion billets by the following process: 5 h holding time at a temperature of about 1150°C and a pressure of about 100 MPa followed by a slow cooling and milled to final dimensions. The extrusions billets were extruded to hollows which were then cold worked. Table 1 The element compositions of the powder made. The balance is Fe and unavoidable impurities not mentioned in the table. The numbers are in wt%. Samples were taken from extruded tubes with outer diameter 33.4 mm, and wall thickness 3.1 mm, and cut to lengths of 1.50 m. The samples were tested by means of sag testing in order to show form stability and oxidation resistance. The test was performed by resting the two ends of tube samples on supports, separated by 1.42 m, for 50 hours while inside a furnace heated to 1000 °C. The amount of sag, i.e., downward deflection, of the tube at the center-point between the supports was then measured after the tube has cooled down. The results are shown in Table 2 and. A lower sag value corresponds to better form stability. The commercial alloy sold under the tradename Kanthal® APM has been included as an example of a tube material with good form stability. Thus, as can be seen from table 2, all the powders of the present invention showed good form stability. Further, the oxide formed on the surface of the tube samples during the sag testing was fully covering, thin, and adhesive on all tested samples, showing a good oxidation resistance. Table 2 Results from sag testing of extruded tube samples at 1000 °C.

Claims

CLAIMS1. An iron-chromium-aluminium, FeCrAl, powder comprising in weight%, wt%,C equal to or less than 0.08,N 0.04 to 0.10,Cr 20.0 to 24.0,Al 4.0 to 6.0,Mo 2.0 to 4.0,Si equal to or less than 0.60,P equal to or less than 0.03,S equal to or less than 0.03,Ti 0.05 to 0.20,Zr 0.05 to 0.25,Nb 0.05 to 0.20,O equal to or less than 0.05,Y equal to or less than 0.10, balance Fe and normally occurring impurities up to at most 1.5 wt% in total.

2. The FeCrAl powder according to claim 1, fulfilling the requirement of:

3. The FeCrAl powder according to claim 1 or claim 2, wherein the content of C is of 0.02 to 0.05 wt%.

4. The FeCrAl powder according to any one of claims 1 to 3, wherein the content of N is of 0.04 to 0.08 wt%.

5. The FeCrAl powder according to any one of claims 1 to 4, wherein the content of Al is of 4.0 to 5.5 wt%.

6. The FeCrAl powder according to any one of claims 1 to 5, wherein the content of Al is of 4.0 to 5.0 wt%.

7. The FeCrAl powder according to any one of claims 1 to 6, wherein the content of Cr is of 20.5 to 23.5 wt%.

8. The FeCrAl powder according to anyone of claims 1 to 7, wherein the content of Ti is of 0.07 to 0.15 wt%.

9. The FeCrAl powder according to anyone of claims 1 to 8, wherein the content of Zr is of 0.07 to 0.20 wt%.

10. The FeCrAl powder according to anyone of claims 1 to 9, wherein the content of Nb is of 0.05 to 0.15 wt%.

11. The FeCrAl powder according to any one of the preceding claims, wherein normally occurring impurity of Mn is limited to at most 0.5 wt% normally occurring impurities belonging to the group consisting of Co, Ni and Cu are limited to at most 0.7 wt% in total, normally occurring impurities belonging to the group consisting of Ta and Hf are limited to at most 0.02 wt% each, normally occurring impurity V is limited to at most 0.07 wt%.

12. A FeCrAl alloy comprising the elements according to any one of claims 1 to 11.

13. A FeCrAl component comprising the elements according to to any one of claims 1 to 11.

14. Use of the FeCrAl powder according to any one of claims 1 to 11 or the FeCrAl alloy of claim 12, in an alloy or in a component to be used in nuclear applications, wherein said component is a bar or a hollow bar or an extrusion billet or a pipe or a tube or a seamless tube, process tubing component or a piping component.

15. A method for producing an object of the FeCrAl alloy according to any one of claims 1 to 11 or the FeCrAl alloy of claim 12, said method comprising:Providing a powder as defined hereinabove or hereinafter;HIP:ing the powder to a billet, optionally hot working of the billet, optionally performing an additional hot working on the billet, optionally cold working the hot worked tube, - optionally heat treating the cold worked tube.

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