SE548280C2

SE548280C2 - A ferritic alloy

Info

Publication number: SE548280C2
Application number: SE2450982A
Authority: SE
Inventors: Peter Szakalos
Original assignee: Blykalla Ab
Priority date: 2024-10-02
Filing date: 2024-10-02
Publication date: 2026-05-11
Also published as: WO2026075591A1; SE2450982A1

Abstract

The invention relates to a ferritic alloy comprising of in weight %: C 0.001 - 0.03, O ≤ 0.2, N ≤ 0.1, Si ≤ 1, Mn ≤ 1, Cr 9 - 12.0, A13.5 - 5, Ce La 0.01 - 0.2. Ni ≤ 3, Mo ≤ 3, W ≤ 3, Y ≤0.5, Ti ≤1, Zr ≤ 1, Nb ≤ 1, V ≤ 1, Hf ≤ 1, Ta ≤ 1, Th ≤ 1, B ≤ 0.05, Cu ≤ 0.5, REE ≤ 0.3 balance Fe apart from impurities, wherein the content of REE does not include the amount of Y, Ce, La but only the amount of the elements having atomic numbers 21 and 59-71 wherein the amounts of Ti+Zr+Nb+V+Hf+Ta+Th, C, N and O in atom % are balanced such that: (Ti+Zr+Nb+V+Hf+Ta+Th -xO - N)/C is ≥ 2, wherein x is 0.5, unless the content of Y is more than equal to 0.01 weight %, then x is 0.67.

Description

[0001] The invention relates to a ferritic alloy, in particular to an alloy of the type FeCrAl.

[0003] BACKGROUND OF THE INVENTION

[0004] Ferritic alloys of the type FeCrAl have been known for long and are used because of the protective alumina formation on the surface. Such alloys are known from WO2016092085 A1, WO2017182188A1, WO2018215065A1 and WO2021043913A1.

[0006] WO20 16/092085 Al is directed to a ferritic alloy wherein the content of the carbide forming elements (Reactive Elements) Ti, Zr, Nb, Hf, V, Ta and Th is balanced against the carbon content. According to the document, over-doping of RE will lead to the formation of intermetallic laves phase and a decrease of the oxidation resistance of the alloy. The document defines an quotient for RE, O, N and C.

[0008] WO202 1/043913 Al is directed to a welding material.

[0010] OBJECT OF THE INVENTION

[0011] It is an object of the present invention is to provide a new and alternative alloy to the FeCrAl alloys known in the art.

[0013] It would further be beneficial to at least to some extent meet one of more of the following, - reducing the risk of high temperature cracking in the production of the alloy

[0014] - providing a FeCrAl alloy having an improved weldability,

[0015] - providing an FeCrAl alloy with improved ductility.

[0016] - providing an FeCrAl alloy with good high temperature corrosion resistance, particularly in liquid lead

[0017] It would be highly desirable if all of them were met.

[0019] DETAILED DESCRIPTION

[0020] We suggest a ferritic alloy consisting of in weight %:

[0021] C 0.001 - 0.03

[0022] O ≤ 0.2

[0023] N ≤ 0.1

[0024] Si ≤ 1

[0025] Mn ≤ 1

[0026] Cr 9 - 12.0

[0027] Al 3.5 - 5

[0028] Ce La 0.01 - 0.2

[0029] Ni ≤ 3

[0030] Mo ≤ 3

[0031] W ≤ 3

[0032] Y ≤ 0.5

[0033] Ti ≤ 1

[0034] Zr ≤ 1

[0035] Nb ≤ 1

[0036] V ≤ 1

[0037] Hf ≤ 1

[0038] Ta ≤ 1

[0039] Th ≤ 1

[0040] B ≤ 0.05

[0041] Cu ≤ 0.5

[0042] REE ≤ 0.3

[0043] balance Fe apart from impurities, wherein the content of IEEE does not include the amount of Y, Ce, La but only the amount of the elements having atomic numbers 21 and 59-71.

[0045] The importance of the separate elements and their interaction with each other as well as the limitations of the chemical ingredients of the claimed alloy are briefly explained in the following. All percentages for the chemical composition of the steel are given in weight % (wt. %) throughout the description. Upper and lower limits of the individual elements can be freely combined within the limits set out in the claims. The arithmetic precision of the numerical values can be increased by one or two digits for all values given in the present application. Hence, a value of given as e.g. 0.1 % can also be expressed as 0.10 or 0.100 %. The amounts of the microstructural constituents are given in volume % (vol. %).

[0046] C: 0.001 - 0.03 %

[0047] Carbon increase strength by precipitation hardening. The lower limit can be set to 0.001, 0.002, or 0.003 %. However, increasing carbon amounts strongly affect then oxidation and corrosion resistance, especially in liquid lead. Low carbon is also beneficial for some desired intermetallic phases that can improve creep resistance. The upper limit is therefore set to 0.03, 0.025, 0.02, 0.015, 0.01, 0.009, 0.008, 0.007, 0.006 or 0.005 %. A preferred range is 0.001 - 0.01%.

[0049] N: ≤ 0.1 %

[0050] Nitrogen can be present as an impurity up to 0.1 %. The upper limit may be set to 0.1 , 0.08, 0.05, or 0.01 %.

[0052] O: ≤ 0.2 %

[0053] In a powder metallurgical steel oxygen may be deliberately added to achieve a precipitation hardening effect. If added for this affect, the content may be 0.01 - 0.2 %. In conventional melt and cast metallurgy oxygen is only present as an impurity resulting from the production process. Preferably, the upper limit is 0.05, 0.02, 0.01, or 0.005 %.

[0055] Si: ≤ 1 %

[0057] Silicon is commonly used for deoxidation in the production of alloy. Presence of Si can improve oxidation and corrosion resistance, and the fluidity of the molten alloy. However, too much Si can affect workability negatively, and the upper limit is therefore set to 1 %. No deliberate addition is required. Optionally, the lower limit can be set to 0.01, 0.05, 0.1, or 0.2 %. The upper limit can be set to 1, 0.9, 0.8, 0.7, 0.6, 0.5, or 0.4 %. A preferred range is 0.1 — 0.8 %.

[0059] Mn: ≤ 1 %

[0061] Manganese may be present up to 1%. Optionally, the lower limit can be set to 0.01, 0.05, 0.1, or 0.2 %. The upper limit can be set to 1, 0.9, 0.8, 0.7, 0.6, 0.5, or 0.4 %. A preferred range is 0.1 - 0.8 %.

[0063] Cr: 9 - 12.0 %

[0064] Chromium is a ferrite stabilizer that should be present in an amount of at least 9 % to provide good oxidation and corrosion resistance, and to promote the formation of an alumina layer though a so called third element effect as known in the art. However, too much of Cr may cause so called 475 °C embitterment at elevated temperatures due to formation of chromium rich alpha prime phase. The upper amount is therefore limited to 12.0 %. A preferred range is 10 - 12.0 %.

[0066] A13.5 - 5 %

[0067] Aluminum is essential for the formation of a protective and self-healing alumina layer. When the alloy is exposed to oxygen at high temperature, a dense and thin alumina layer is formed, which protects the underlying surface from further oxidation. The amount should be at least 3.5 % to ensure an effective oxide layer. Too much of A1 may cause brittle A1 rich phases that can impact formability negatively. The upper limit is therefore set to 5 %. A preferred range is 3.8 - 4.5 %.

[0069] Ce La: 0.01 - 0.2 %

[0070] According to the invention Cerium and Lanthanum should be added individually or in combination in a total amount of up to 0.2 %. The addition of Ce and/or La has been found to refine the grain structure of the as-cast alloy. The refined grain structure is beneficial for ductility and makes forming and welding of the alloy much easier. This also makes it possible to use conventional melt metallurgy when producing the alloy with reduced risk of high temperature cracking after casting that can occur in steel ingots or slabs during cooling to room temperature. This could reduce or eliminate the need of hot charging between casting and hot rolling. The preferred amount of Ce is 0.02 - 0.08 %, more preferably 0.02 - 0.04 %. The preferred amount if Ce+ La is 0.02 - 0.1 %. Cerium and/or Lanthanum can e.g. be added as pure metals or a mischmetal.

[0072] Ni: ≤ 3 %

[0073] Nickel may optionally be added for improved high temperature mechanical properties, such as hardness and yield strength, through the formation of nickel aluminides. The lower limit can therefore be set to 0, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.0 %. Too much Ni may suppress the formation of the protective alumina forming layer and can also affect ductility negatively. The upper limit can therefore be set to 3, 2.5, 2, 1.9, 1.8, 1.7, orl.6 %. A preferred range is 0.5 - 3 %, more preferred 0.8 - 2.0 %.

[0074] Mo: ≤ 3 %

[0075] Molybdenum can optionally be added to the alloy. Addition of Mo improves high temperature mechanical properties and the creep resistance. The lower amount of Mo can be set to 0, 0.1, 0.2, or 0.5 %. Too much Mo affect corrosion resistance negatively. The upper limit may be set to 3 or 2 %.

[0077] W: ≤ 3 %

[0079] Tungsten can optionally be added to the alloy. The effect of W is similar to that of Mo.

[0080] However, in liquid lead W has less negative effect to corrosion resistance than Mo and can therefore be a more preferred addition than Mo for such applications. Addition of W improves high temperature mechanical properties and the creep resistance. The lower amount of W can be set to 0, 0.1, 0.2, or 0.5 %. Too much W affect corrosion resistance negatively. The upper limit may be set to 3 or 2 %.

[0082] B: ≤ 0.05 %

[0083] Boron may optionally be added. The upper limit can be 0.05, 0.01, 0.005, or 0.001 %. If deliberately added a preferred range is 0.02 - 0.04 %.

[0085] Cu: ≤ 0.5 %

[0086] Cupper may have a positive effect on the formation of nickel aluminides. Cu may therefore optionally be added. Cu may also be present as an impurity from manufacturing of the alloy. The upper limit can be 0.5, 0.4, 0.3, 0.2 or 0.1 %.

[0088] Y: ≤ 0.5 %

[0090] Yttrium may be added in an amount up to 0.5 % to improve the adherence of the

[0091] alumina layer. If yttrium is added in amounts of more than or equal to 0.01 %, the formation of yttrium oxides will affect the x in the formula (Ti+Zr+Nb+V+Hf+Ta+Th -xO - N)/C described below, such that x is 0.5, unless the content of Y is more than equal to 0.01 %, then x is 0.67.

[0092] RE (Ti, Zr, Nb, V, Hf, Ta, Th)

[0093] Titanium, Zirconium, Niobium, Vanadium, Hafnium, Tantalum, and Thorium are reactive elements (RE) in the sense that they have high affinity to carbon, nitrogen and oxygen. These elements may be added to improve the oxidation properties of the alloy. Yttrium is usually considered to be a reactive element but is in the present disclosure discussed in a separated paragraph because it will not form as strong carbides as Ti, Zr, Nb, V, Hf, Ta, and Th.

[0095] The elements Ti, Zr, Nb, V, Hf, Ta, and Th are each limited to max 1 %. The lower limit can individually be set to 0, 0.01, or 0.1 %.

[0097] Preferably, the total content sum of RE should be 0.1 -2.0 %, more preferably 0.5- 1.5 %.

[0099] The quotient defined on page 15 in WO2016092085 is in the present application named the "RE/C" quotient. The "RE/C" quotient is calculated as follows:

[0100] (at%Ti at%Zr at%Nb at%V at%Hf at%Ta at%Th - x at%0 - at%N ) / at%C where x is 0.5, unless the content of Y is more than equal to 0.01 weight %, then x is 0.67. The "RE/C" quotient should be ≥ 2, preferably ≥ 3, more preferably ≥ 5, most preferably ≥ 10. By increasing the "RE/C" quotient oxidation and corrosion resistance is improved.

[0102] Rare Earth Elements (REE) with atomic numbers 21 and 59-71 may optionally be present up to at most 0.3 %, preferably at most 0.1%. The amount of Yttrium, Lanthanum, and Cerium are defined separately.

[0104] Further optional restrictions of impurity elements:

[0105] P: ≤ 0.02 %

[0106] S: ≤ 0.01 %

[0108] The alloy can be produced by conventional steel manufacturing methods including the steps of primary steelmaking, secondary steelmaking, casting, and primary forming.

[0110] The alloy may also be manufactured by powder metallurgy in which casting is replaced by atomizing to form a powder, which can be used in different applications, such as sintering, Hot Isostatic Pressing, powder coating, additive manufacturing.

[0111] Six different steel alloy compositions were prepared in a vacuum furnace. One reference alloy R1 and five inventive alloys I1 - I5. The target values of respective element are shown in the table below. Actual values are within -10% of the target values. An ingot of size about 2 kg where cast for each alloy.

[0113] Table 1

[0115]

[0117] *oxygen and nitrogen levels are so low that they do not significantly affect the "RE/C" quotient in the Table 1. The "RE/C" quotient is calculated using [at %].

[0119] The reference alloy R1 did not contain Ce or La, and had a RE/C quotient of 1.8. I1 - I5 tested various amounts of alloying elements. The inventive samples I1 - I5 all a had visibly much finer grain structure than the reference sample R1. The addition of Ce contributed to a refinement of the microstructure. A finer microstructure is highly beneficial for ductility and weldability and reduces the risk of high temperature cracking when casting the alloy. The samples I2 - I5 containing nickel, showed that nickel aluminides were formed in the microstructure. All samples had a protective alumina layer.

[0120] INDUSTRIAL APPLICABILITY

[0121] The alloy is an alternative to FeCrAl alloys previously known in the art. It can particularly be useful as a corrosion resistance material at 300 - 800 °C in liquid lead and lead alloys.

Claims

1. A ferrite alloy consisting of in weight percent C 0.001 0.03 O ≤0.2 N ≤0.1 Si ≤ 1 Mn ≤ 1 Cr 0 Al 3.5-5 Cc La 0.01-0.2 Ni ≤3 Mo ≤3 W ≤3 Y ≤0.5 Ti ≤ 1 Zr ≤ 1 Nb ≤ 1 V ≤ 1 Hf ≤ 1 Ta ≤ 1 Th ≤ 1 B ≤0.05 Cu ≤0.5 REE ≤0.3 the balance Fe except impurities, where the content of REE does not include the amount of Y, Ce, La but only the amount of elements with atomic numbers 21 and 59-71 where the amounts of Ti+Zr+Nb+V+Hf+Ta+Th, C, N and O in atomic percent are balanced so that: (Ti+Zr+Nb+V+Hf+Ta+Th -xO - N)/C is ≥ 2 where x is 0.5, if the content of Y is not more than equal to 0.01 weight percent, then x is 0.67.

2. The alloy according to claim 1, wherein the amounts of Ti+Zr+Nb+V+Hf+Ta+Th, C, N and O in atomic percent are balanced such that: (Ti+Zr+Nb+V+Hf+Ta+Th -xO - N)/C is ≥ 3 where x is 0.5, unless the content of Y is more than equal to 0.01 weight percent, then x is 0.67.

3. The alloy according to claim 1 or 2, wherein the content of Ce is 0.02 0.08 wt%, and/or Ce+La is 0.02 0. 1 wt%.

4. The alloy according to any one of the preceding claims, wherein the content of Ni is 0.5-3 weight percent.

5. The alloy according to any one of the preceding claims, wherein the content of Ti+Zr+Nb+V+Hf+Ta+Th is 0.1-2.0 wt%.

6. The alloy according to any one of the preceding claims, wherein the content of C is < 0.015 wt%.

7. The alloy according to any one of the preceding claims, wherein the content of C is < 0.01 wt%.