US20240133004A1

US20240133004A1 - Iron alloys

Info

Publication number: US20240133004A1
Application number: US18/547,600
Authority: US
Inventors: Kevin Laws; Patrick Lars Joseph CONWAY; Lori Cheryl BASSMAN; Jackson Baker; Catherine Holland Frank; Douglas Anderson Raigosa; Stephanie Blankley; Natalie Rachel Krieger
Original assignee: Individual
Current assignee: Advanced Alloy Holdings Pty Ltd
Priority date: 2020-02-24
Filing date: 2021-02-24
Publication date: 2024-04-25
Also published as: WO2021168507A1; EP4298260A1

Abstract

The present disclosure relates generally to alloys, and in particular, to iron alloys.

Description

FIELD OF THE DISCLOSURE

BACKGROUND OF THE DISCLOSURE

Any discussion of the prior art throughout this specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
Since at least the early 20^thcentury, iron-chromium-based ‘Inox’ alloys or ‘stainless steels’ have been extensively used in commercial and domestic applications due in large part to their corrosion resistance and their mechanical and processing properties. Austenitic iron-chromium-nickel (Fe—Cr—Ni) stainless steels (300 Series) are among the most widely used, accounting for more than 60% of total world production. These stainless steels often contain 7-10 wt. % nickel to stabilize the face-centred cubic (fcc) austenite phase. However, in recent years, the market price for nickel has become higher and increasingly volatile.
A lower cost alternative to the 300 series are the 200 series stainless steels, which largely substitute nickel with the austenite-stabilising element, manganese. However, the corrosion resistance of these alloys may be notably reduced with increasing manganese content. Moreover, the 200 series alloys tend to be much harder/stronger than 300 series alloys, making them more difficult to work and machine into products.
Another lower-cost alternative to austenitic stainless steels are the ferritic stainless steels (400 series), which exhibit a body-centred cubic (bcc) crystal structure and are magnetic. These steels may have a chromium content from 11 to 30 wt. % and contain little to no nickel, therefore reducing production cost. However, the lack of nickel and increased chromium content can promote the formation of the detrimental brittle sigma phase at elevated temperatures (˜500-800° C.) and microstructural segregation into two bcc phases at moderate temperatures (200-500° C.). Consequently, their application is typically limited to room temperature service and they usually require very specific hot-working and heat treatments.

SUMMARY OF THE DISCLOSURE

In work leading to the present disclosure, the inventors developed a series of iron-chromium-manganese-aluminium (Fe—Cr—Mn-AI) alloys which maintain a bcc crystal structure, exhibit corrosion resistance, low thermal conductivity and offer processing advantages over known stainless steels.
In one aspect, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; and 1 to 10 at. % Al.
In some examples, the alloy comprises or consists of: 37.5 to 67.5 at. % Fe; 12.5 to 47.5 at. % Cr, 2.5 to 25 at. % Mn; and 2.5 to 7.5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 25 at. % Mn; and 2.5 to 7.5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 25 at. % Mn; and 4 to 6 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; and 2.5 to 7.5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; and 4 to 6 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 25 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 45 to 65 at. % Fe; 25 to 45 at. % Cr; 2.5 to 7.5 at. % Mn; and 2.5 to 7.5 at. % Al.
In some examples, the alloy comprises or consists of: 45 to 60 at. % Fe; 25 to 45 at. % Cr; 2.5 to 7.5 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 45 to 60 at. % Fe; 25 to 45 at. % Cr; 5 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 45 to 65 at. % Fe; 20 to 40 at. % Cr; 7.5 to 12.5 at. % Mn; and 2.5 to 7.5 at. % Al.
In some examples, the alloy comprises or consists of: 45 to 65 at. % Fe; 20 to 40 at. % Cr; 7.5 to 12.5 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 45 to 65 at. % Fe; 20 to 40 at. % Cr; 10 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 40 at. % Cr; 12.5 to 17.5 at. % Mn; and 2.5 to 7.5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 40 at. % Cr; 12.5 to 17.5 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 65 at. % Fe; 15 to 40 at. % Cr; 15 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 60 at. % Fe; 15 to 35 at. % Cr; 17.5 to 22.5 at. % Mn; and 2.5 to 7.5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 60 at. % Fe; 15 to 35 at. % Cr; 17.5 to 22.5 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of: 40 to 60 at. % Fe; 15 to 35 at. % Cr; 20 at. % Mn; and 5 at. % Al.
In some examples, the alloy comprises or consists of 90 to 97.5 at. % [Fe+Cr+Mn] and a balance of Al.
In some examples, the alloy consists of 90 to 95 at. % [Fe+Cr+Mn] and a balance of Al.
In some examples, the alloy consists of 95 at. % [Fe+Cr+Mn] and 5 at. % Al.
In some examples, the alloy consists of: 75 to 90 at. % [Fe+Cr]; 5 to 20 at. % Mn; and a balance of Al.
In some examples, the alloy consists of: 75 to 90 at. % [Fe+Cr]; 5 to 20 at. % Mn; and 5 at. % Al.
In some examples, the alloy consists of: 10 to 30 at. % [Mn+Al]; 15 to 45 at. % Cr; and a balance of Fe.
In some examples, the alloy consists of: 10 to 25 at. % [Mn+Al]; 15 to 45 at. % Cr; and a balance of Fe.
In a second aspect, the present disclosure comprises or consists of: 35 to 70 at. % Fe; 10 to 50 at. % Cr 1 to 25 at. % Mn; 1 to 10 at. % Al; and 0 to 3 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].
In some examples, the alloy of the second aspect comprises or consists of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; 1 to 10 at. % Al; and up to 3 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].
In some examples, the alloy of the second aspect comprises or consists of: 37.5 to 67.5 at. % Fe; 12.5 to 47.5 at. % Cr; 2.5 to 25 at. % Mn; 2.5 to 7.5 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].
In some examples, the alloy of the second aspect comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; 2.5 to 7.5 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].
In some examples, the alloy of the second aspect comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; 5 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].
In some examples, the alloy of the second aspect comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; 2.5 to 7.5 at. % Al; and up to 1 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].
In some examples, the alloy of the second aspect comprises or consists of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; 5 at. % Al; and up to 1 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].
In some examples, the alloy of the first aspect or the second aspect comprises at least 15 at. % Cr.
In some examples, the alloy of the first aspect or the second aspect comprises at least 40% at. % Fe.
In some examples, the alloy of the first aspect or the second aspect has an at. % ratio of Mn:Al of at least 1.
In some examples, the alloy of the first aspect or the second aspect has an at. % ratio of Fe:Cr of at least 1.
In some examples, the alloy of the first aspect or the second aspect has an at. % ratio of Fe:Mn is of least 2.
In some examples, the alloy of the first aspect or the second aspect has an ultimate tensile strength of between about 500 and 900 MPa.
In some examples, the alloy of the first aspect or the second aspect has a 0.2%-offset yield strength of between about 400 and 900 MPa.
In some examples, the alloy of the first aspect or the second aspect has an as-cast hardness (HV) of between about 175 and 280.
In some examples, the alloy of the first aspect or the second aspect has an as-cast hardness (HV) of between about 183 and 272.
In some examples, the alloy of the first aspect or the second aspect has a density of between about 6.9 and 7.38 g/cm³.
In some examples, the alloy of the first aspect or the second aspect has a density of between about 7.19 and 7.38 g/cm³.
In some examples, the alloy of the first aspect or the second aspect has a single phase body-centred cubic (bcc) crystal structure.
In some examples, the alloy of the first aspect or the second aspect has two phases with a bcc crystal structure.
In some examples, the alloy of the first aspect or the second aspect comprises at least about 90 vol. % bcc crystal structure.
In some examples, the alloy of the first aspect or the second aspect comprises 0 to 1 at. % incidental impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 : Tensile properties of alloys of the present disclosure. *indicates an addition of 0.2 at. % Ti to the overall alloy composition e.g. [Fe₆₅Cr₂₅Mn₅Al₅]_99.8Ti_0.2. **indicates an addition of 0.2 at. % Ti and 0.2 at. % Nb to the overall alloy composition e.g. [Fe₆₅Cr₂₅Mn₅Al₅]_99.6Ti_0.2Nb_0.2.

FIG. 2 : X-ray diffraction trace showing the bcc structure of an alloy after solution treatment at 850° C., and a week of heat treatment at 400° C. then quenching.

DETAILED DESCRIPTION

The term “about” is understood to refer to a range of +/−10%, preferably +/−5% or +/−1% or, more preferably, +/−0.1%.
Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising” will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Thus, in the context of this specification, the term “comprising” means “including principally, but not necessarily solely”.
Any numerical range recited herein is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of 1.0 to 5.0 is intended to include all sub-ranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 5.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 5.0, such as 2.1 to 4.5. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited herein is intended to include all higher numerical limitations subsumed therein.
The present disclosure provides alloys comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; and 1 to 10 at. % Al. It will be understood that the alloys described herein may comprise incidental impurities. Those skilled in the art will understand, for example, that carbon impurities may arise from iron smelting and raw materials, and that nitrogen impurities may arise from atmospheric nitrogen during melt processing. Nickel may also arise as an unavoidable impurity due to the recycling loop of stainless steels. Incidental silicon impurities may arise from scrap metal refinement loops. Cobalt is another potentially unavoidable impurity. Preferably, the incidental impurities do not exceed 1 at. %, or 0.5 at. %, or preferably, 0.1 at. %, or more preferably, 0.05 at. %.
In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25% Mn; and 1 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 70 at. % Fe; 15 to 50 at. % Cr; 1 to 25 at. % Mn; and 1 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr 1 to 25 at. % Mn; and 1 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr; 2 to 25 at. % Mn; and 2 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr; 5 to 25 at. % Mn; and 2 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr; 5 to 20 at. % Mn; and 2 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr; 5 to 20 at. % Mn; and 4 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr; 5 to 20 at. % Mn; and 4 to 8 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at % Fe; 15 to 55 at. % Cr; 5 to 20 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 20 to 55 at. % Cr; 1 to 25 at. % Mn; and 1 to 10 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 20 to 55 at. % Cr; 5 to 25 at. % Mn; and 1 to 10 at % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 20 to 55 at. % Cr; 5 to 25 at. % Mn; and 4 to 6 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 20 to 50 at. % Cr; 5 to 20 at. % Mn; and 4 to 6 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 70 at. % Fe; 15 to 50 at. % Cr 1 to 25 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr; 5 to 20 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at % Fe; 20 to 55 at. % Cr, 5 to 25 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr, 5 to 25 at. % Mn; and 4 to 6 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 55 at. % Cr; 5 to 22.5 at. % Mn; and 4 to 6 at. % Al. In some examples, the alloy of the present disclosure comprises 0 to 1 at. % incidental impurities. The incidental impurities may, for example, be Ni or Co.
In some examples, the present disclosure provides an alloy having 30 to 75 at. % Fe, such as 35 to 70 at. % Fe, 37 to 67 at. % Fe, 37 to 65 at. % Fe, 37 to 63 at. % Fe, 40 to 60 at. % Fe, 42 to 58 at. % Fe, 45 to 55 at. % Fe, or 47 to 52 at. % Fe. In some examples, the alloy comprises 45 to 50 at. % Fe, such as 50 to 55 at. % Fe, 55 to 60 at % Fe, or 60 to 65 at. % Fe. In some examples, the alloy comprises 40 to 65 at. % Fe, such as 45 to 65 at. % Fe, 50 to 65 at. % Fe, 55 to 65 at. % Fe, or 60 to 65 at. % Fe. In some example, the alloy comprises 40 to 60 at. % Fe, 40 to 55 at. % Fe, 40 to 50 at % Fe, or 40 to 45 at. % Fe.
In some examples, the Cr content of the presently disclosed alloys is greater than 10 at. %, such as greater than 11 at. %, or great than 12 at. %, greater than 13 at. %, greater than 14 at. %, such as at least 15 at. %, or at least 20 at. %, at least 25 at. %, at least 30 at. %, at least 35 at %, at least 40 at. %, or at least 45 at. %. In some examples, the present disclosure provides an alloy having 10 to 50 at % Cr, such as 12 to 47 at. % Cr, 15 to 45 at. % Cr, 17 to 43 at. % Cr, 20 to 40 at. % Cr, 22 to 38 at. % Cr, 25 to 35 at. % Cr, in 27 to 33 at. % Cr. In some examples, the alloy comprises 15 to 20 at % Cr, such as 20 to 25 at. % Cr, 25 to 30 at. % Cr, 35 to 40 at. % Cr, or 40 to 45 at. % Cr. In some examples, the alloy comprises 15 to 45 at. % Cr, such as 20 to 45 at. % Cr, 25 to 45 at. % Cr, 30 to 45 at % Cr, or 35 to 45 at. % Cr.
In some examples, the present disclosure provides an alloy having 1 to 25 at. % Mn, such as 2 to 23 at. % Mn, 5 to 20 at. % Mn, 7 to 18 at. % Mn or 10 to 15 at. % Mn. In some examples, the alloy comprises 5 to 20 at % Mn, such as 5 to 15 at. % Mn, or 5 to 10 at. % Mn. In some examples, the alloy comprises 10 to 20 at. % Mn or 15 to 20 at. % Mn.
In some examples, the present disclosure provides an alloy having 1 to 10 at. % Al, such as 2 to 9 at. % Al, 3 to 8 at. % Al, 4 to 7 at. % Al, 4 to 6 at. % Al, or 5 at. % Al. In some examples, the alloy comprises 1 to 9 at. % Al, 1 to 8 at. % Al, 1 to 7 at % Al, 1 to 6 at % Al, 1 to 5 at. % Al, 1 to 4 at. % Al, or 1 to 3 at. % Al. In some examples, the alloy comprises 2 to 10 at. % Al, 3 to 10 at. % Al, 4 to 10 at. % Al, 5 to 10 at. % Al, 6 to 10 at. % Al, 7 to 10 at. % Al, or 8 to 10 at. % Al.
In some examples, the present disclosure provides an alloy comprising or consisting of: 65 at. % Fe; 25 at. % Cr; 5 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 60 at % Fe; 30 at. % Cr; 5 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 55 at. % Fe; 35 at. % Cr; 5 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 50 at % Fe; 40 at. % Cr; 5 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 45 at. % Fe; 45 at. % Cr; 5 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 65 at. % Fe; 20 at. % Cr; 10 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 60 at. % Fe; 25 at. % Cr; 10 at. % Mn; and 5 at % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 55 at. % Fe; 30 at. % Cr; 10 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 50 at. % Fe; 35 at. % Cr; 10 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 45 at. % Fe; 40 at. % Cr; 10 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 65 at. % Fe; 15 at. % Cr, 15 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 60 at. % Fe; 20 at. % Cr; 15 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 55 at. % Fe; 25 at. % Cr; 15 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 50 at. % Fe; 30 at. % Cr; 15 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 45 at. % Fe; 35 at. % Cr; 15 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 at. % Fe; 40 at. % Cr; 15 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 60 at. % Fe; 15 at. % Cr, 20 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 55 at. % Fe; 20 at. % Cr; 20 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 50 at. % Fe; 25 at. % Cr; 20 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 45 at. % Fe; 30 at. % Cr; 20 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 at. % Fe; 35 at. % Cr; 20 at. % Mn; and 5 at. % Al. In some examples, the present disclosure provides an alloy substantially as described in Table 1 or Table 2.
Elements such as titanium (Ti), niobium (Nb), vanadium (V), tungsten (W), zirconium (Zr), hafnium (Hf), tantalum (Ta) and molybdenum (Mo) may, in some examples, be added to the alloy in order to remove carbon and nitrogen impurities. These elements react with carbon and nitrogen, forming carbides and nitrides respectively, which can then be removed from the alloy, for example, by skimming from its molten surface. Molybdenum may also strengthen the alloy and improve its corrosion resistance. Boron (B) may also be added to remove impurities and/or to increase the grain boundary strength of the alloy. In that regard, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; 1 to 10 at. % Al; and 0 to 3 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo]. It will be understood that in such examples, the alloy may comprise any one or more elements selected from the group consisting of Ti, Nb, V, W, Zr, Hf, Ta, B and Mo, as long as the total content of those one or more elements combined does not exceed 3 at. % in the alloy. Preferably the alloy of the present disclosure comprises up to 2.75 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], such as up to 2.5 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], or up to 2 at. %[Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], up to 1.75 at. %[Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], up to 1.5 at. %[Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], up to 1.25 at. %[Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], up to 1 at. %[Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], up to 0.75 at. %[Ti+Nb+V+W+Zr+Hf+Ta+B+Mo], up to 0.5 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo] or up to 0.25 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo].
In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; 1 to 10 at. % Al; and up to 3 at. % [Ti+Nb+V+W+Zr+Hf+Ta+Mo]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; 1 to 10 at. % Al; and up to 3 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; 1 to 10 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 15 to 50 at. % Cr; 5 to 25 at. % Mn; 2.5 to 7.5 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 15 to 50 at. % Cr; 5 to 25 at. % Mn; 2.5 to 7.5 at. % Al; and up to 1 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 15 to 50 at. % Cr; 5 to 25 at. % Mn; 5 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+Ta+B+Mo]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 15 to 50 at. % Cr; 5 to 25 at. % Mn; 2.5 to 7.5 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 15 to 50 at. % Cr; 5 to 25 at. % Mn; 2.5 to 7.5 at. % Al; and up to 3 at. % Mo. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; 1 to 10 at. % Al; and up to 0.2 at. % Ti. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 70 at. % Fe; 10 to 50 at. % Cr; 1 to 25 at. % Mn; 1 to 10 at. % Al; and up to 0.4 at. % [Ti+Nb]. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 25 at. % Mn; 2.5 to 7.5 at. % Al; and up to 0.2 at. % Ti. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; 2.5 to 7.5 at. % Al; and up to 0.4 at. % [Ti+Nb]. In some examples, the present disclosure provides an alloy comprising or consisting of: 40 to 65 at. % Fe; 15 to 45 at. % Cr; 5 to 20 at. % Mn; 2.5 to 7.5 at. % Al; up to 0.2 at. % Ti; and up to 0.2 at. % Nb. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 15 to 50 at. % Cr; 5 to 25 at. % Mn; 2.5 to 7.5 at. % Al; and up to 1 at. % [Ti+Nb+V+W+Zr+Hf+B+Mo]. In some examples, the present disclosure provides an alloy comprising or consisting of: 35 to 65 at. % Fe; 15 to 50 at. % Cr; 5 to 25 at. % Mn; 5 at. % Al; and up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Mo].
In known ferritic steels, Fe and Cr can, in some instances, stabilise the sigma phase (˜Fe₅₀Cr₅₀) which is detrimental to both corrosion resistance and mechanical performance with respect to ductility and toughness. Moreover, at temperatures below about 500° C., the atomic bonding between Fe and Cr in Fe—Cr bcc (ferritic) alloys becomes repulsive, leading to Fe—Cr segregation and the formation of an Fe- and Cr-rich two phase alloy in a process commonly referred to as α′+α″ phase separation. This can lead to detrimental embrittlement, sometimes called 475° C. embrittlement or simply 475 embrittlement. The alloys of the present disclosure comprise specific combinations of Mn and Al, which largely destabilise or eradicate the detrimental sigma phase that exists in known ferritic stainless steels. The alloys may therefore be particularly useful in medium- to high-temperature applications (eg, >500° C.), and more amenable to economical thermomechanical processing routes and welding processes. Moreover, a higher Mn content may reduce the extent and tendency of phase separation and subsequent embrittlement to a point where this effect is largely eradicated or negligible at moderate temperatures (eg, 200 to 500° C.) for extended time in service. In that regard, the alloy of the present disclosure is preferably a single phase alloy. In some examples, the alloy of the present disclosure comprises a bcc crystal structure. In some examples, the alloy of the present disclosure has a substantially single phase bcc crystal structure, excepting for incidental impurities. In some examples, the alloy of the present disclosure comprises at least about 75 vol. % bcc crystal structure, such as at least about 80 vol. % bcc crystal structure, or at least about 85 vol. % bcc crystal structure, at least about 90 vol. % bcc crystal structure, at least about 95 vol. % bcc crystal structure, at least about 96 vol. % bcc crystal structure, at least about 97 vol. % bcc crystal structure, at least about 98 vol. % bcc crystal structure, or at least about 99 vol. % bcc crystal structure. In some examples, the alloy of the present disclosure has a single phase bcc crystal structure. In some examples, the alloy of the present disclosure has two phases with a bcc crystal structure.
The present disclosure provides alloys comprising or consisting of: 5 to 30 at. % [Mn+Al]; 10 to 50 at. % Cr; and a balance of Fe. In some examples, the present disclosure provides an alloy comprising or consisting of: 10 to 25 at. % [Mn+Al]; 15 to 45 at. % Cr; and a balance of Fe. In some examples, the present disclosure provides an alloy comprising or consisting of: 10 to 15 at. % [Mn+Al]; 20 to 45 at. % Cr; and a balance of Fe. In some examples, the present disclosure provides an alloy comprising or consisting of: 20 to 25 at. % [Mn+Al]; 15 to 40 at. % Cr; and a balance of Fe. In some examples, the present disclosure provides an alloy comprising or consisting of: 10 to 25 at. % [Mn+Al]; 15 to 45 at. % Cr; and a balance of Fe, wherein the at. % ratio of Mn:Al is at least about 1. In some examples, the present disclosure provides an alloy comprising or consisting of: 10 to 25 at. % [Mn+Al]; 15 to 45 at. % Cr; and a balance of Fe, wherein the at. % ratio of Mn:Al is at least about 1, and wherein the at. % ratio of Fe:Cr is at least about 1. In some examples, the present disclosure provides an alloy comprising or consisting of: 10 to 25 at. % [Mn+Al]; 15 to 45 at. % Cr, and a balance of Fe, wherein the at. % ratio of Mn:Al is at least about 1, and wherein the alloy comprises at least 40 at. % Fe. In some examples, the present disclosure provides an alloy comprising or consisting of: 10 to 25 at. % [Mn+Al]; 15 to 45 at. % Cr; and a balance of Fe, wherein the at. % ratio of Fe:Cr is at least about 1, and wherein the alloy comprises at least 40 at. % Fe.
The alloys of the present disclosure preferably do not exhibit sigma transformation. It will be appreciated by those skilled in the art that, in the absence of the sigma phase and the minimisation of phase separation, the Cr-content in the presently described alloys may be higher compared to known stainless steels, thereby providing extended corrosion resistance without substantially degrading mechanical performance.
In some examples, the present disclosure provides an alloy comprising or consisting of: 70 to 95 at. % [Fe+Cr]; 2 to 25 at. % Mn; and a balance of Al. In such examples, Fe and Cr may be present in the alloy at any amount as long as their combined content is at least 70 at. % and no greater than 95 at. %. In some examples, the present disclosure provides an alloy comprising or consisting of: 75 to 95 at. % [Fe+Cr]; 2 to 20 at. % Mn; and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 70 to 90 at. % [Fe+Cr]; 5 to 25 at. % Mn; and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 75 to 90 at. % [Fe+Cr]; 5 to 20 at. % Mn; and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 80 to 90 at. % [Fe+Cr]; 5 to 15 at. % Mn; and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 75 to 90 at. % [Fe+Cr]; 5 to 25 at. % Mn; and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 75 to 90 at. % [Fe+Cr]; 5 to 22 at. % Mn; and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 70 to 95 at. % [Fe+Cr]; 2 to 25 at. % Mn; and a balance of Al, wherein the alloy comprises at least 15 at. % Cr. In some examples, the present disclosure provides an alloy comprising or consisting of: 70 to 90 at. % [Fe+Cr]; 5 to 25 at. % Mn; and a balance of Al, wherein the alloy comprises at least 15 at. % Cr. In some examples, the present disclosure provides an alloy comprising or consisting of: 80 to 90 at. % [Fe+Cr]; 5 to 15 at. % Mn; and a balance of Al, wherein the alloy comprises at least 15 at. % Cr. In some examples, the present disclosure provides an alloy comprising or consisting of: 75 to 90 at. % [Fe+Cr]; 5 to 20 at. % Mn; and a balance of Al, wherein the at. % ratio of Fe:Cr is at least 1. In some examples, the present disclosure provides an alloy comprising or consisting of: 75 to 90 at. % [Fe+Cr]; 5 to 20 at. % Mn; and a balance of Al, wherein the at. % ratio of Fe:Cr is at least 1, and wherein the alloy comprises at least 40 at. % Fe. 1. In some examples, the present disclosure provides an alloy comprising or consisting of: 75 to 90 at. % [Fe+Cr]; 5 to 20 at. % Mn; and a balance of Al, wherein the at. % ratio of Mn:Al is at least 1, and wherein the alloy comprises at least 40 at. % Fe.
In some examples, the present disclosure provides an alloy comprising or consisting of: 80 to 98 at. % [Fe+Cr+Mn] and a balance of AI. In some examples, the present disclosure provides an alloy comprising or consisting of: 80 to 95 at. % [Fe+Cr+Mn] and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 85 to 95 at. % [Fe+Cr+Mn] and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 90 to 95 at. % [Fe+Cr+Mn] and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 90 to 98 at. % [Fe+Cr+Mn] and a balance of Al. In some examples, the present disclosure provides an alloy comprising or consisting of: 80 to 98 at. % [Fe+Cr+Mn] and a balance of Al, wherein the alloy comprises at least 15 at. % Cr. In some examples, the present disclosure provides an alloy comprising or consisting of: 85 to 95 at. % [Fe+Cr+Mn] and a balance of Al, wherein the alloy comprises at least 15 at. % Cr. In some examples, the present disclosure provides an alloy comprising or consisting of: 90 to 98 at. % [Fe+Cr+Mn] and a balance of Al, wherein the alloy comprises at least 15 at. % Cr.
In some the examples, the present disclosure provides an alloy having an at. % ratio of Mn:Al of at least about 1. In some examples, the at. % ratio of Mn:Al is at least about 1.1, such as at least about 1.25, or at least about 1.5, or at least about 1.75, or at least about 2, or at least about 2.25, or at least about 2.5, or at least about 2.75, or at least about 3, or at least about 3.25, or at least about 3.5, or at least about 3.75, or at least about 4. In some examples, the at. % ratio of Mn:Al is between about 1 and 5, such as between about 1 and 4.5 or between about 1 and 4.
In some the examples, the present disclosure provides an alloy having an at. % ratio of Fe:Cr of at least about 1. In some examples, the at. % ratio of Fe:Cr is at least about 1.1, such as at least about 1.25, or at least about 1.5, or at least about 1.75, or at least about 2, or at least about 2.25, or at least about 2.5, or at least about 2.75, or at least about 3, or at least about 3.25, or at least about 3.5, or at least about 3.75, or at least about 4, such as at least about 4.25. In some examples, the at. % ratio of Fe:Cr is between about 1 and 5, such as between about 1.23 and 5, or between about 1.25 and 4.75, or between about 1.5 and 4.75, or between about 1.5 and 4.5, or between about 1.5 and 4.3.
In some the examples, the present disclosure provides an alloy having an at. % ratio of Fe:Mn of at least about 1.5, such as at least about 1.75, or at least about 2, at least about 2.5, at least about 3, at least about 3.3, at least about 3.6, at least about 4, at least about 4.5, at least about 5, at least about 5.5, at least about 6, at least about 6.5, at least about 7, at least about 8, at least about 8.5, at least about 9, at least about 9.5, at least about 10, at least about 10.5, at least about 11, at least about 11.5, at least about 12, at least about 12.5, or at least about 13. In some examples, the at. % ratio of Fe:Mn is between about 1.5 and 14, or between about 2 and 13, between about 2.25 and 13, between about 2.5 and 13, between about 2.5 and 12, between about 2.75 and 13, between about 2.75 and 12, between about 2.6 and 13, or between about 2.75 and 11.
In some examples, the present disclosure provides an alloy having an ultimate tensile strength of between about 300 and 1,000 MPa, such as between about 400 and 1,000 MPa, or between about 450 and 1,000 MPa, between about 500 and 1,000 MPa, between about 500 and 950 MPa, between about 500 and 900 MPa, between about 510 and 880 MPa, between about 510 and 865 MPa, between about 520 and 865 MPa, or between about 538 and 865 MPa. The strength of the alloy may be increased by increasing Cr and Mn content.
In some examples, the present disclosure provides an alloy having a 0.2%-offset yield strength of between about 300 and 1,000 MPa, such as between about 400 and 1,000 MPa, or between about 400 and 950 MPa, between about 425 and 900 MPa, or between about 425 and 850 MPa.
In some examples, the present disclosure provides an alloy having a hardness (HV) (solution treated at 850° C.) of between about 165 and 300, such as between about 165 and 295, or between about 175 and 295, between about 180 and 295, between about 180 and 290, between about 180 and 285, between about 180 and 280, between about 180 and 276, between about 182 and 276, between about 185 and 276, between about 188 and 276, between about 193 and 276, between about 196 and 276, between about 203 and 276 or between about 204 and 276. Preferably, the alloy has a hardness (solution treated at 850° C.) of between 180 and 276.
In some examples, the present disclosure provides an alloy having an as-cast hardness (HV) of between about 200 and about 272, or between about 210 and about 260, or between about 220 and about 240, or between about 220 and about 270, or between about 220 and about 260, or between about 220 and about 250, or between about 183 and about 272, or between about 183 and about 250, or between about 183 and about 240, or between about 190 and about 230. Preferably, the alloy has an as-cast hardness of between about 183 and about 272.
The alloys of the present disclosure may have a density which is lower than that of 200, 300 and 400 series stainless steels. As such, they may produce lighter weight materials, and from a production/cost standpoint, they may provide more material volume per kilogram, or inversely, may be lighter per unit length of product. In some examples, the present disclosure provides an alloy having a density of between about 6.9 and about 7.38 g/cm³, or between about 7.0 and about 7.38 g/cm³, or between about 7.05 and about 7.36 g/cm³, or between about 7.1 and about 7.36 g/cm³, or between about 7.15 and about 7.35 g/cm³, or between about 7.22 and about 7.35 g/cm³Preferably, the alloy has a density of between about 7.19 and 7.38 g/cm³.
The alloys described herein maintain a bcc crystal structure, and may exhibit similar processing advantages to stainless steels as well as high corrosion resistance, particularly with higher chromium contents. In some examples, the alloys of the present disclosure have a bcc microstructure. The alloys of the present disclosure may be useful in the production of mechanical fixing devices such as screws, nuts, bolts, plumbing fixtures (machined, forged or cast), domestic whitegoods, nuclear fuel tubes/cladding, pipes, such as steam pipes, construction and cladding components, motor vehicle exhaust systems, hot liquid transfer and cooling interchangers, domestic and industrial civil construction materials, such as press or roll-formed structural beams, sheets or rods, including weldable products or those intended for down-stream fabrication. The alloys described herein may also exhibit hard ferro magnetic properties and may be suitable for electromagnetic devices.

EXAMPLES

Nominal alloy composition ingots of volume 10.5 cm³were produced in an electric arc furnace (Edmund Buehler AM) from high purity primary elements iron, chromium, manganese, aluminium and, in some cases, high purity additions of titanium and niobium. A titanium-gettered argon atmosphere was produced via purging of the melting chamber with high purity argon (three times over) and then evacuating to the melting chamber to within the order of 10⁴mbar. The melting chamber was filled to 60% of atmospheric pressure with high purity argon. This was followed by melting a titanium getter. To ensure homogenous distribution of the small amounts of Ti and Nb, these elements were first formed into initial button-shaped ingots with approximately 10% of the required Fe by melting and inverting resultant ingots five times. This ingot was then melted with the required balance of Fe and the Cr and Mn to meet the nominal alloy composition, which was repeatedly melted and inverted at least three times. To reduce vaporisation, the Al balance was added after this initial alloy ingot was homogeneous. The complete composition was melted and inverted at least 5 more times to form the Fe—Cr—Mn—Al (+Ti,Nb) homogeneous ingot.
Alloyed ingots were mechanically cleaned/abraded to a lustrous finish, removing any surface oxide products. Castings were produced from the cleaned ingots in an electric arc furnace using copper moulds in a titanium-gettered argon atmosphere as described previously. Castings 6 mm in diameter×30 mm were produced independently for microstructural and hardness analysis, and these were sectioned into 3 mm long slices. Rectangular castings with a 16.5 mm by 11.7 mm cross section and length of 36-44 mm were produced for thermomechanical processing and tensile testing. The castings were mechanically abraded to remove surface defects then processed via hot rolling at 1000° C. in 0.25 mm increments to close any casting porosity or structural defects, to consolidate the material, and to refine and recrystallise the grain structure, essentially simulating industry processing. Samples were rolled from 11.7 mm thickness to 8 mm thickness. Samples were intermittently cooled and mechanically cleaned/abraded to remove any oxide scale and then returned to 1000° C. before the next rolling increment. The resulting ˜16 mm×8 mm×48-56 mm ingots were mechanically cleaned/abraded and then sectioned into two 8 mm×8 mm×36-44 mm samples. Samples were further hot rolled at 1000° C. along both perpendicular long faces in 0.25 mm increments, with reheating in a 1000° C. furnace between steps, to 7 mm square cross section billets/bars with final lengths of 65-75 mm.
Following the hot rolling process, the strips were heat treated in a vacuum furnace at 850° C. for 6 hours to produce the final processed alloys in a hot rolled plus annealed condition. The strips were cut to lengths of 62 mm and machined into cylindrical tensile specimens with 4 mm gauge diameter and 20 mm gauge length in accordance with ASTM E8M. Tensile testing was conducted in accordance with ASTM A370 using an Instron tensile testing machine, laser extension meter and associated computer and data logger. The tensile strain rate for all samples was 1 mm/min. Measured response sample load and laser extension of the gauge section were recorded using software produced by Bluehill. Representative engineering stress-strain data are provided in FIG. 1 , and characteristic mechanical properties are set out in Table 1.
Microstructural analysis was conducted on both as-cast and heat treated sections of the 6 mm diameter cylindrical castings. Samples were heat treated in a muffle furnace in evacuated quartz capsules for 850° C. for 6 hours for homogenization and then select samples were further heat treated at 350, 400, 450 and 500° C. for 7 days to confirm the absence of the sigma phase and the degree of any low-temperature phase separation (α′+α″). Hardness data is provided in Tables 1 and 2. Scanning electron microscopy including electron dispersive spectroscopy for composition analysis/confirmation was conducted on suitably prepared samples with a Hitachi S3400 electron microscope. X-ray diffraction was conducted on powdered samples with a PANalytical Empyrean 2 Co-sourceXRD to confirm a single phase bcc structure and absence of the sigma phase. FIG. 2 provides an x-ray diffraction trace showing the bcc structure of an alloy after homogenisation at 850° C. and a week at 400° C. Hardness testing was conducted using a Struers Durascan hardness testing machine with a 1 kg load and a 10 second dwell time. A minimum of 20 hardness indents were conducted for each sample. Density was measured using Archimedes' principle with a Mettler Toledo density test kit and Mettler Toledo 5-digit balance.

TABLE 1

Composition and mechanical properties of specific Fe—Cr—Mn—Al
alloys compared to 304, 316, 430, 455M2 and 1018 steels.

				Average
				Hardness
	0.2%-offset	Ultimate		(HV)
	Yield	Tensile	Tensile	(solution
	Strength	Strength	Elongation	treated	Density
Material/Alloy	(MPa)	(MPa)	(% range)	850° C.)	g/cm³

304	215	505	70	129	8.00
316	240	550	60	155	8.03
430	310	517	22-30	183 (162)	7.80
455M2	350	520	30	170	7.75
1018 mild steel	370	440	15	126	7.85
Fe₆₅Cr₂₅Mn₅Al₅	375	460	32-37	—	7.36
Fe₆₅Cr₂₅Mn₅Al₅*	425	525	26-30	—	7.36
Fe₆₅Cr₂₅Mn₅Al₅**	400	485	23	181	7.36
Fe₆₀Cr₃₀Mn₅Al₅**	474	561	27-29	195	7.35
Fe₅₅Cr₃₅Mn₅Al₅**	548	582	2.6	210	7.31
Fe₅₀Cr₄₀Mn₅Al₅**	719	779	8.7	236	7.27
Fe₄₅Cr₄₅Mn₅Al₅				272	7.19
Fe₄₅Cr₄₅Mn₅Al₅*				274	7.19
Fe₄₅Cr₄₅Mn₅Al₅**	850	865	3.8	266	7.19
Fe₆₅Cr₂₀Mn₁₀Al₅				183	7.36
Fe₆₅Cr₂₀Mn₁₀Al₅**	425	510	28-32	180	7.36
Fe₆₀Cr₂₅Mn₁₀Al₅**	460	549	34	185	7.34
Fe₅₅Cr₃₀Mn₁₀Al₅**	527	597	23-31	203	7.32
Fe₅₀Cr₃₅Mn₁₀Al₅**	622	674	4.7	221	7.23
Fe₄₅Cr₄₀Mn₁₀Al₅				240	7.26
Fe₄₅Cr₄₀Mn₁₀Al₅*				241	7.26
Fe₄₅Cr₄₀Mn₁₀Al₅**	757	794	3.9	248	7.26
Fe₆₅Cr₁₅Mn₁₅Al₅				187	7.35
Fe₆₅Cr₁₅Mn₁₅Al₅**	425	538	34 (30)	188	7.35
Fe₆₀Cr₂₀Mn₁₅Al₅**	454	541	30	182	7.33
Fe₅₅Cr₂₅Mn₁₅Al₅**	473	534	6.8	196	7.26
Fe₅₀Cr₃₀Mn₁₅Al₅				223	7.26
Fe₅₀Cr₃₀Mn₁₅Al₅**	565	618	5.9	217	7.26
Fe₄₅Cr₃₅Mn₁₅Al₅				223	7.27
Fe₄₅Cr₃₅Mn₁₅Al₅**	690	731	4.7	232	7.27
Fe₄₀Cr₄₀Mn₁₅Al₅**				276	7.24
Fe₆₀Cr₁₅Mn₂₀Al₅**	490	558	29	186	7.38
Fe₅₅Cr₂₀Mn₂₀Al₅**	454	532	32	193	7.34
Fe₅₀Cr₂₅Mn₂₀Al₅**	489	588	24	204	7.31
Fe₄₅Cr₃₀Mn₂₀Al₅**	525	582	21	225	7.28
Fe₄₀Cr₃₅Mn₂₀Al₅**				259	7.25
Fe₅₀Cr₂₀Mn₂₅Al₅**	424	517	33		7.29
Fe₄₅Cr₂₅Mn₂₅Al₅**	523	591	22		7.25
Fe₄₀Cr₃₀Mn₂₅Al₅**					7.22

*indicates an addition of 0.2 at. % Ti to the overall alloy composition e.g. [Fe₆₅Cr₂₅Mn₅Al₅]_99.8Ti_0.2
**indicates an addition of 0.2 at. % Ti and 0.2 at. % Nb to the overall alloy composition e.g. [Fe₆₅Cr₂₅Mn₅Al₅]_99.6Ti_0.2Nb_0.2

TABLE 2

Composition and hardness of Fe—Cr—Mn—Al alloys with the addition
of 0.2 at. % Ti and 0.2 at. % Nb in the following conditions: as-
cast, solution treated (ST) at 850° C., slow cooled then heat
treated (HT) at 350, 400, 450 and 500° C. for 7 days and quenched
(Q), solution treated at 850° C. then slow cooled.

		ST +	ST +	ST +	ST +
		HT	HT	HT	HT	Solution
	As	350° C. +	400° C. +	450° C. +	500° C. +	treated
Alloy	Cast	Q	Q	Q	Q	850° C.

Fe₆₅Cr₂₅Mn₅Al₅	189	202	282	307	224	181
Fe₆₀Cr₃₀Mn₅Al₅	201	230	313	334	300	195
Fe₅₅Cr₃₅Mn₅Al₅	217	231	345	380	359	210
Fe₅₀Cr₄₀Mn₅Al₅	253	249	377	402	381	236
Fe₄₅Cr₄₅Mn₅Al₅	272	314	392	429	448	266
Fe₆₅Cr₂₀Mn₁₀Al₅	183	202	237	211	202	180
Fe₆₀Cr₂₅Mn₁₀Al₅	191	225	280	282	198	185
Fe₅₅Cr₃₀Mn₁₀Al₅	200	220	311	316	217	203
Fe₅₀Cr₃₅Mn₁₀Al₅		256	358	368	251	221
Fe₄₅Cr₄₀Mn₁₀Al₅	251	261	385	393	318	248
Fe₆₅Cr₁₅Mn₁₅Al₅	189	208	196	207	191	188
Fe₆₀Cr₂₀Mn₁₅Al₅	188	220	203	195	190	182
Fe₅₅Cr₂₅Mn₁₅Al₅	190	241	222	217	202	196
Fe₅₀Cr₃₀Mn₁₅Al₅	211	251	301	241	224	217
Fe₄₅Cr₃₅Mn₁₅Al₅	239	275	342	319	269	232
Fe₆₀Cr₁₅Mn₂₀Al₅	186	197	185	179	178	186
Fe₅₅Cr₂₀Mn₂₀Al₅	193	222	199	192	186	193
Fe₅₀Cr₂₅Mn₂₀Al₅	204	235	219	209	205	204
Fe₄₅Cr₃₀Mn₂₀Al₅	225	261	279	255	230	225
Fe₄₀Cr₃₅Mn₂₀Al₅	259	305	334	326	266	259
Fe₅₀Cr₂₀Mn₂₅Al₅	187
Fe₄₅Cr₂₅Mn₂₅Al₅	210
Fe₄₀Cr₃₀Mn₂₅Al₅	224

It will be appreciated by those skilled in the art that the alloys of the present disclosure may be embodied in many other forms.

Claims

1. An alloy comprising or consisting of:

35 to 70 at. % Fe;

10 to 50 at. % Cr;

1 to 25 at. % Mn; and

1 to 10 at. % Al.

2. The alloy of claim 1 comprising or consisting of:

37.5 to 67.5 at. % Fe;

12.5 to 47.5 at. % Cr;

2.5 to 25 at. % Mn; and

2.5 to 7.5 at. % Al.

3. The alloy of claim 1 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 25 at. % Mn; and

2.5 to 7.5 at. % Al.

4. The alloy of claim 1 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 25 at. % Mn; and

4 to 6 at. % Al.

5. The alloy of claim 1 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 20 at. % Mn; and

2.5 to 7.5 at. % Al.

6. The alloy of claim 1 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 20 at. % Mn; and

4 to 6 at. % Al.

7. The alloy of claim 1 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 25 at. % Mn; and

5 at. % Al.

8. The alloy of claim 1 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 20 at. % Mn; and

5 at. % Al.

9. The alloy of claim 1 comprising or consisting of:

45 to 65 at. % Fe;

25 to 45 at. % Cr;

2.5 to 7.5 at. % Mn; and

2.5 to 7.5 at. % Al.

10. The alloy of claim 9 comprising or consisting of:

45 to 60 at. % Fe;

25 to 45 at. % Cr,

2.5 to 7.5 at. % Mn; and

5 at. % Al.

11. The alloy of claim 9 or claim 10 comprising or consisting of:

45 to 60 at. % Fe;

25 to 45 at. % Cr;

5 at. % Mn; and

5 at. % Al.

12. The alloy of claim 1 comprising or consisting of:

45 to 65 at. % Fe;

20 to 40 at. % Cr;

7.5 to 12.5 at. % Mn; and

2.5 to 7.5 at. % Al.

13. The alloy of claim 12 comprising or consisting of:

45 to 65 at. % Fe;

20 to 40 at. % Cr;

7.5 to 12.5 at. % Mn; and

5 at. % Al.

14. The alloy of claim 12 or claim 13 comprising or consisting of:

45 to 65 at. % Fe;

20 to 40 at. % Cr;

10 at. % Mn; and

5 at. % Al.

15. The alloy of claim 1 comprising or consisting of:

40 to 65 at. % Fe;

15 to 40 at. % Cr;

12.5 to 17.5 at. % Mn; and

2.5 to 7.5 at. % Al.

16. The alloy of claim 15 comprising or consisting of:

40 to 65 at. % Fe;

15 to 40 at. % Cr;

12.5 to 17.5 at. % Mn; and

5 at. % Al.

17. The alloy of claim 15 or claim 16 comprising or consisting of:

40 to 65 at. % Fe;

15 to 40 at. % Cr;

15 at. % Mn; and

5 at. % Al.

18. The alloy of claim 1 comprising or consisting of:

40 to 60 at. % Fe;

15 to 35 at. % Cr;

17.5 to 22.5 at. % Mn; and

2.5 to 7.5 at. % Al.

19. The alloy of claim 18 comprising or consisting of:

40 to 60 at. % Fe;

15 to 35 at. % Cr;

17.5 to 22.5 at. % Mn; and

5 at. % Al.

20. The alloy of claim 18 or claim 19 comprising or consisting of:

40 to 60 at. % Fe;

15 to 35 at. % Cr;

20 at. % Mn; and

5 at. % Al.

21. The alloy of any one of the preceding claims wherein the alloy consists of 90 to 97.5 at. % [Fe+Cr+Mn] and a balance of Al.

22. The alloy of any one of the preceding claims wherein the alloy consists of 90 to 95 at. % [Fe+Cr+Mn] and a balance of Al.

23. The alloy of any one of the preceding claims wherein the alloy consists of 95 at. % [Fe+Cr+Mn] and 5 at. % Al.

24. The alloy of any one of the preceding claims wherein the alloy consists of:

75 to 90 at. % [Fe+Cr];

5 to 20 at. % Mn; and

a balance of Al.

25. The alloy of any one of the preceding claims wherein the alloy consists of:

75 to 90 at. % [Fe+Cr];

5 to 20 at. % Mn; and

5 at. % Al.

26. The alloy of any one of the preceding claims wherein the alloy consists of:

10 to 30 at. % [Mn+Al];

15 to 45 at. % Cr; and

a balance of Fe.

27. The alloy of any one of the preceding claims wherein the alloy consists of:

10 to 25 at. % [Mn+Al];

15 to 45 at. % Cr; and

a balance of Fe.

28. An alloy comprising or consisting of:

35 to 70 at. % Fe;

10 to 50 at. % Cr,

1 to 25 at. % Mn;

1 to 10 at. % Al; and

0 to 3 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].

29. The alloy of claim 28 comprising or consisting of:

35 to 70 at. % Fe;

10 to 50 at. % Cr;

1 to 25 at. % Mn;

1 to 10 at. % Al; and

up to 3 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].

30. The alloy of claim 28 comprising or consisting of:

37.5 to 67.5 at. % Fe;

12.5 to 47.5 at. % Cr;

2.5 to 25 at. % Mn;

2.5 to 7.5 at. % Al; and

up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].

31. The alloy of claim 28 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 20 at. % Mn;

2.5 to 7.5 at. % Al; and

up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].

32. The alloy of claim 28 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 20 at. % Mn;

5 at. % Al; and

up to 2 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].

33. The alloy of claim 28 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 20 at. % Mn;

2.5 to 7.5 at. % Al; and

up to 1 at. % [Ti+Nb+V+W+Zr+Hf+B+Ta+Mo].

34. The alloy of claim 28 comprising or consisting of:

40 to 65 at. % Fe;

15 to 45 at. % Cr;

5 to 20 at. % Mn;

5 at. % Al; and

up to 1 at. % [Ti+Nb+V+W+Zr+Hf+B+Mo].

35. The alloy of any one of the preceding claims wherein the alloy comprises at least 15 at. % Cr.

36. The alloy of any one of the preceding claims wherein the alloy comprises at least 40% at. % Fe.

37. The alloy of any one of the preceding claims wherein the at. % ratio of Mn:Al is at least 1.

38. The alloy of any one of the preceding claims wherein the at. % ratio of Fe:Cr is at least 1.

39. The alloy of any one of the preceding claims wherein the at. % ratio of Fe:Mn is at least 2.

40. The alloy of any one of the preceding claims wherein the alloy has an ultimate tensile strength of between about 500 and 900 MPa.

41. The alloy of any one of the preceding claims wherein the alloy has a 0.2%-offset yield strength of between about 400 and 900 MPa.

42. The alloy of any one of the preceding claims wherein the alloy has an as-cast hardness (HV) of between about 175 and 280.

43. The alloy of any one of the preceding claims wherein the alloy has an as-cast hardness (HV) of between about 183 and 272.

44. The alloy of any one of the preceding claims wherein the alloy has a density of between about 6.9 and 7.38 g/cm³.

45. The alloy of any one of the preceding claims wherein the alloy has a density of between about 7.19 and 7.38 g/cm³.

46. The alloy of any one of the preceding claims wherein the alloy has a single phase body-centred cubic (bcc) crystal structure.

47. The alloy of any one of claims 1 to 45 wherein the alloy has two phases with a bcc crystal structure.

48. The alloy of any one of claims 1 to 45 wherein the alloy comprises at least about 90 vol. % bcc crystal structure.

49. The alloy of any one of the preceding claims wherein the alloy comprises 0 to 1 at. % incidental impurities.