IRON-MANGANESE ALLOY HAVING IMPROVED WELDABILITY

Abstract

The invention relates to an iron-manganese alloy, comprising in weight percentage: 25.0% = Mn = 32.0%, 7.0% <Cr < 14.0%, 0 = Ni = 2.5%, 0.05% = N = 0.30%, 0.1 = Si = 0.5%, opcionalmente 0.010% = tierras raras = 0.14%. El resto que es hierro y elementos residuales resultantes de la producción.

Description

IRON-MANGANESE ALLOY HAVING IMPROVED WELDABILITY Description of the Invention The present invention relates to an iron-manganese alloy proposed for use in the manufacture of welded parts and assemblies for applications where high dimensional stability is required under the effect of temperature variations, particularly at cryogenic temperatures. The alloy according to the invention is proposed more particularly for use in the field of electronics, as well as in cryogenic applications. The most commonly used alloys for these applications are iron-nickel alloys, and more specifically InvarsMR, which generally comprise approximately 36% nickel. These alloys have excellent dimensional stability properties, particularly at cryogenic temperatures, but they have the disadvantage of a relatively high cost, resulting primarily from their relatively high nickel content. Furthermore, the weldability of these alloys to other metals is not always entirely satisfactory, particularly in terms of the mechanical strength of heterogeneous welds. Therefore, in the context of the present invention, the aim is to provide an alloy suitable for the applications mentioned above and which, consequently, has particularly good cryogenic temperature properties, while being less expensive than invarMR. Iron-based alloys that also contain carbon and manganese are known to exist and are marketed by the Korean company Poseo. These steels comprise, by weight: 0.35% < C < 0.55% 22.0% < Mn < 26.0% 3.0% < Cr < 4.0% < Si < 0.3% the rest being iron and residual elements resulting from production. However, these alloys do not provide complete satisfaction. In fact, even if they are satisfactory from the point of view of their coefficient of thermal expansion and their resilience at room temperature and cryogenic temperature (-196°C), the inventors of the present invention have found that they have a high sensitivity to hot cracking and, consequently, relatively poor weldability. Furthermore, the inventors of the present invention have also observed that these steels have a high susceptibility to corrosion. However, good corrosion resistance is important for the aforementioned applications, particularly in the case of thin strips, especially to limit the risk of fatigue or tensile fracture of parts and structures manufactured from these alloys. Consequently, these alloys are not entirely satisfactory for the aforementioned applications. Accordingly, an object of the invention is to propose an alloy that can be used satisfactorily to manufacture welded parts and assemblies for applications in which high dimensional stability is required under the effect of temperature variations, for example, for cryogenic applications, while having a relatively low cost. For this purpose, the invention relates to an iron-manganese alloy comprising, by weight: 25.0% < Mn < 32.0% 7.0% < Cr < 14.0% < Ni < 2.5% 0.05% < N < 0.30% 0.1 < If <0.5% optionally 0.010% < rare earths < 0.14% the rest being iron and residual elements resulting from production. According to particular embodiments, the alloy according to the invention comprises one or more of the following characteristics, taken alone or in any technically feasible combination: The chromium content is between 8.5% and 11.5% by weight. The nickel content is between 0.5% and 2.5% by weight. The nitrogen content is between 0.15% and 0.25% by weight. Rare earth elements comprising one or more elements chosen from: lanthanum, cerium, trium, praseodymium, neodymium, samarium, and ytterbium. The iron-manganese alloy as described above has an average coefficient of thermal expansion (CTE) between -180°C and 0°C of less than or equal to 8.5 × 10'6 / °C. The iron-manganese alloy as described above has a Néel TNéei temperature greater than or equal to 40°C. The iron-manganese alloy described above, when produced in a thin strip less than or equal to 3 mm thick, exhibits at least one of the following characteristics: - a KCV resilience in a reduced test tube of 3 mm thickness and at a cryogenic temperature (-196°C) greater than or equal to 80 J / cm2, and for example greater than or equal to 100 J / cm2; - an elastic limit Rpo.2 at -196°C greater than or equal to 700 MPa; - an elastic limit Rpo.2 at room temperature (20°C) greater than or equal to 300 MPa. The iron-manganese alloy as described above is austenitic at cryogenic and room temperatures. The invention also relates to a manufacturing process for a strip made of an alloy as defined above, the process comprising the following successive steps: an alloy is produced as defined above; a semi-finished product of the alloy is formed; The semi-finished product is hot-rolled to obtain a hot strip; Optionally, the hot strip is cold rolled in one or more passes to obtain a cold strip. The invention also relates to a strip made of an iron-manganese alloy as defined above. The invention also relates to a manufacturing process for a wire made of an iron-manganese alloy as defined above, the process comprising the following steps: supplying a semi-finished product made of an iron-manganese alloy; hot transforming the semi-finished product to form an intermediate wire; and transforming the intermediate wire into a wire, having a diameter smaller than that of the intermediate wire, this transformation comprising a wire drawing step. The invention also relates to a wire made of an iron-manganese alloy as defined above. This wire is in particular a material filler wire or a wire proposed for the manufacture of bolts or screws; these bolts and screws are obtained in particular by cold stamping from this wire. The invention will be better understood by reading the following description provided only as an example. Throughout the description, the contents are given as a percentage by weight. The alloy according to the invention is an iron-manganese alloy comprising, by weight: 0.0% < Mn < 32.0% 0.0% <Cr< 14.0% < Ni < 2.5% 0.05% < N < 0.30% 0.1 < If <0.5% optionally 0.010% < rare earths < 0.14%< The rest are iron and residual elements resulting from production. This alloy is a high manganese austenitic steel. The alloy according to the invention is austenitic at room temperature and cryogenic temperature (-196°C). Residual elements resulting from production are elements present in the raw materials used to produce the alloy or originating from the equipment used in its production, such as the refractory materials in the furnaces. These residual elements have no metallurgical effect on the alloy. Residual elements comprise in particular one or more elements selected from: carbon (C), aluminum (Al), selenium (Se), sulfur (S), phosphorus (P), oxygen (O), cobalt (Co), copper (Cu), molybdenum (Mo), tin (Sn), niobium (Nb), vanadium (V), titanium (Ti) and lead (Pb). For each of the residual elements listed above, the maximum contents are preferably selected as follows, by weight: C < 0.05% by weight, and preferably C < 0.035% by weight, < Al < 0.02% by weight, and preferably Al < 0.005% by weight, οο / οηη / ίζηζ / Β / γι Se < 0.02% by weight, and preferably Se < 0.01% by weight, even more advantageously Se < 0.005% by weight, S < 0.005% by weight, and preferably S < 0.001% by weight, P < 0.04% by weight, and preferably P < 0.02% by weight, O < 0.005% by weight, and preferably O < 0.002% by weight, Co, Cu, Mo < 0.2% by weight each, Sn, Nb, V, Ti < 0.02% by weight each, Pb < 0.001% by weight. In particular, the selenium content is limited according to the intervals mentioned above in order to avoid hot cracking problems that could result from too high a presence of selenium in the alloy. The alloy according to the invention has in particular: - an average coefficient of thermal expansion (CTE) between -180°C and 0°C of 8.5x10⁶ / °C or less; and - a Néel TNéei temperature greater than or equal to 40°C, and, when produced in thin strips less than or equal to 3 mm thick, a KCV resilience in a reduced test tube 3 mm thick already at a cryogenic temperature (-196°C) greater than or equal to 80 J / cm2, and for example greater than or equal to 100 J / cm2; an elastic limit Rpo.2 at -196°C greater than or equal to 700 MPa; and an elastic limit Rpo.2 at room temperature (20°C) greater than or equal to 300 MPa. Therefore, this alloy has thermal expansion, resilience, and mechanical strength properties that are satisfactory for use in the applications mentioned above, particularly at cryogenic temperatures. The alloy according to the invention also has corrosion resistance characterized by a critical corrosion current in H₂SO₄ (2 mol / L⁻¹) strictly less than 230 mA / cm² and a pitting potential V in NaCl (0.02 mol / L⁻¹) strictly greater than 40 mV, the pitting potential being determined with reference to a reference potential, the hydrogen electrode (HEN). Therefore, the alloy according to the invention has corrosion resistance greater than or equal to that of lnvarMR-M93. It is noted in this context that lnvarMR-M93 is a material commonly used in the aforementioned applications, particularly at cryogenic temperatures. The alloy according to the invention also has a much higher corrosion resistance than that observed for the previous Fe-Mη alloys, which have a critical corrosion current in H2SO4 (2 mol / l-1) medium greater than approximately 350 mA / cm2 and a pitting potential V less than or equal to -200 mV with respect to the hydrogen electrode (HEN). The alloy according to the invention also has satisfactory weldability, and in particular good resistance to hot cracking. Specifically, as explained below, it has a crack length of less than or equal to 7 mm during a Varestraint test for 3% plastic deformation. Consequently, the alloy according to the invention has a much higher cracking resistance than that observed for prior Fe-Mη alloys. More specifically, in the alloy according to the invention, manganese, with a content of less than or equal to 32.0% by weight, makes it possible to obtain an average coefficient of thermal expansion of less than 8.5 x 10⁶ / °C between -180°C and 0°C. This coefficient of thermal expansion is satisfactory for the use of the alloy in the context of the contemplated applications, and particularly in the context of cryogenic applications. Furthermore, a manganese content of 25.0% or more by weight, combined with a chromium content of 14.0% or less by weight, allows for good dimensional stability of the alloy at both room and cryogenic temperatures (-196°C). Specifically, the Néel temperature of the alloy is therefore strictly above 40°C and is unlikely to be reached at typical operating temperatures. However, using the alloy at temperatures above the Néel temperature can lead to significant variations in the expansion of welded parts and assemblies at room temperature. In fact, the coefficient of expansion of the high-manganese steel described above is on the order of 8 × 10⁻⁶ / °C at temperatures below or equal to the Néel temperature, while it is on the order of 16 × 10⁻⁶ / °C at temperatures above the Néel temperature. Chromium, with a content of 14.0% or less by weight, allows for good KCV resilience in a test tube reduced to 3 mm in thickness at cryogenic temperature (-196°C), and in particular a KCV resilience at -196°C greater than or equal to 50 J / cm². Conversely, the inventors have found that a chromium content strictly greater than 14.0% by weight can result in very high brittleness of the alloy at cryogenic temperature. Furthermore, at a chromium content of 7.0% or higher by weight, chromium enables good weldability of the alloy. The inventors have found that weldability tends to degrade for chromium contents strictly below 7.0% by weight. Chromium also contributes to improving the alloy's corrosion resistance. Preferably, the chromium content is between 8.5% and 11.5% by weight. A chromium content in this range results in an even better compromise between a high Néel temperature and high corrosion resistance. Nickel, with a content of 2.5% or less by weight, allows for an average coefficient of thermal expansion between -180°C and 0°C of 8.5 × 10⁻⁶ / °C or less. This coefficient of thermal expansion is satisfactory for the alloy's intended applications. Conversely, the inventors have found that the coefficient of thermal expansion is likely to degrade for nickel contents significantly greater than 2.5% by weight. Preferably, the nickel content is between 0.5% and 2.5% by weight. In fact, a nickel content greater than or equal to 0.5% by weight further improves the alloy's resilience at cryogenic temperatures (-196°C). Nitrogen, at contents greater than or equal to 0.05% by weight, contributes to improved corrosion resistance. However, its content is limited to 0.30% by weight to maintain satisfactory weldability and resilience at cryogenic temperatures (-196°C). Preferably, the nitrogen content is between 0.15% and 0.25% by weight. A nitrogen content within this range allows for an even better compromise between mechanical properties and corrosion resistance. Silicon, present in the alloy with a content of between 0.1% and 0.5% by weight, acts as a deoxidizer in the alloy. The alloy optionally comprises rare earth elements with a content of between 0.010% and 0.14% by weight. The rare earth elements are preferably selected from yttrium (Y), cerium (Ce), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), and ytterbium (Yb), or mixtures of one or more of these elements. According to one particular example, the rare earth elements comprise a mixture of cerium and lanthanum or yttrium, used alone or mixed with cerium and lanthanum. In particular, rare earths consist of lanthanum and / or trium, the sum of the lanthanum and trium contents being between 0.010% and 0.14% by weight. As a variant, rare earths consist of cerium, the cerium content being between 0.010% and 0.14% by weight. As an alternative, rare earth elements consist of a mixture of lanthanum, yttrium, neodymium, and praseodymium, with the sum of the lanthanum, yttrium, neodymium, and praseodymium contents ranging from 0.010% to 0.14% by weight. In this case, the rare earth elements are added, for example, in the form of Misch metal with a content of between 0.010% and 0.14% by weight. Misch metal contains lanthanum, yttrium, neodymium, and praseodymium in the following proportions: Ce: 50%, La: 25%, Nd: 20%, and Pr: 5%. The presence of rare earth elements, and more specifically a mixture of cerium and lanthanum or yttrium, in the contents mentioned above allows for obtaining an alloy that exhibits very good resistance to hot cracking and, consequently, even improved weldability. As an example, the rare earth content is between 150 ppm and 800 ppm. The alloy according to the invention can be produced by any suitable method known to those skilled in the art. By way of example, it is produced in an electric arc furnace and then refined in a ladle by conventional methods (decarburization, deoxidation, and desulfurization), which may include a reduced pressurization stage. Alternatively, the alloy according to the invention is produced in a vacuum furnace from low-residue raw materials. Hot or cold strips are then manufactured, for example, from the alloy produced in this way. As an example, the following process is used to manufacture these hot or cold strips. The alloy is poured in the form of semi-finished products such as ingots, remelting electrodes, slabs, in particular thin slabs with a thickness of less than 200 mm, in particular obtained by continuous pouring, or billets. When the alloy is poured in the form of a re-melting electrode, it is remelted advantageously in a vacuum or under electrically conductive slag in order to obtain better purity and more homogeneous semi-finished products. The semi-finished product obtained in this way will be hot-rolled at a temperature between 950°C and 1220°C to obtain a hot strip. The thickness of the hot strip is, in particular, between 2 mm and 6.5 mm. According to one method, hot rolling is preceded by a chemical homogenization heat treatment at a temperature between 950°C and 1220°C for a period of between 30 minutes and 24 hours. The chemical homogenization process is carried out, in particular, on the slab, especially the thin slab. The hot strip is cooled to room temperature to form a cooled strip, and then wound onto coils. Optionally, the cooled strip is then cold rolled to obtain a cold strip with a final thickness advantageously of between 0.5 mm and 2 mm. Cold rolling is carried out in one pass or in several successive passes. At its final thickness, the cold-rolled strip is optionally subjected to a recrystallization heat treatment in a static furnace for a period ranging from 10 minutes to several hours at a temperature exceeding 700°C. Alternatively, it undergoes a recrystallization heat treatment in a continuous annealing furnace for a duration ranging from a few seconds to approximately 1 minute, at a temperature exceeding 900°C in the furnace holding zone, and under a protected N2 / H2 (30% / 70%) atmosphere with a frost temperature between -50°C and -15°C. The frost temperature defines the partial pressure of water vapor contained in the heat treatment atmosphere. A recrystallization heat treatment can be performed under the same conditions during cold rolling, at an intermediate thickness between the initial thickness (corresponding to the thickness of the hot strip) and the final thickness. The intermediate thickness is selected, for example, to be 1.5 mm when the final thickness of the cold strip is 0.7 mm. The alloy production process and the manufacturing of hot and cold strips of this alloy are provided as an example only. For this purpose, any other method of preparing the alloy according to the invention and of manufacturing finished products made from this alloy known to those skilled in the art may be used. The invention also relates to a strip, and in particular a hot or cold strip, made of the alloy as described above. In particular, the strip has a thickness less than or equal to 6.5 mm, and preferably less than or equal to 3 mm. This strip is, for example, a cold strip manufactured by the process described above or a hot strip obtained at the end of the hot rolling stage of the process described above. The invention also relates to a wire manufactured from the alloy described above. οο / οηη / ίζηζ / Β / γι More specifically, the wire is a material filler wire proposed for use in welding pieces together. As a variant, the wire proposed for the manufacture of bolts or screws, these bolts and screws are obtained in particular by cold stamping from this wire. As an example, this wire is manufactured by implementing a process that includes the following stages: supply of a semi-finished product made of an alloy as described above; hot processing of the semi-finished product to form an intermediate wire; and processing of the intermediate wire into a wire, having a diameter smaller than that of the intermediate wire, this processing comprising a wire drawing stage. The semi-finished product is, in particular, an ingot or a billet. These semi-finished products are preferably transformed by hot forming between 1050°C and 1220°C to form the intermediate wire. Specifically, during this hot rolling stage, the semi-finished products, particularly ingots or billets, are hot-rolled to reduce their cross-section, giving them, for example, a square cross-section with sides of approximately 100 mm to 200 mm. This results in a reduced-section semi-finished product. The length of this reduced-section semi-finished product is typically between 10 and 20 meters. Advantageously, the reduction of the cross-section of the semi-finished products is achieved through one or more successive hot-rolling passes. The reduced-section semi-finished products are then hot-rolled again to obtain wire. The wire can be, in particular, a wire rod. It has, for example, a diameter of between 5 mm and 21 mm, and specifically approximately 5.5 mm. Advantageously, during this stage, the wire is produced by hot rolling in a wire rolling mill. Evidence The inventors carried out laboratory pours of alloys having compositions as defined above, as well as of comparative alloys, which have different compositions from the composition described above. These alloys were produced in a vacuum and then hot-rolled to obtain strips with dimensions of 35 mm wide and 4 mm thick. These strips were then machined to obtain a surface free of hot oxidation. The alloy compositions of each of the tested strips are shown in Table 1 below. The inventors performed Varestraint tests on the resulting strips, in accordance with the European standard FD CEN ISO / TR 17641-3, under 3.2% plastic deformation, to evaluate their resistance to hot cracking. They measured the total length of cracks that developed during the test and classified the strips into three categories: Strips with a total crack length of 2 mm or less at the end of the test were considered to have excellent resistance to hot cracking; strips with a total crack length between 2 mm and 7 mm at the end of the test were considered to have good resistance to hot cracking; and strips with a total crack length strictly greater than 7 mm were considered to have insufficient resistance to hot cracking. The results of these tests are shown in the column titled “Varestraint Tests” in Table 1 below. This column indicates: “1”: strips that have excellent resistance to hot cracking; “2“: strips that have good resistance to hot cracking; “3”: strips that have insufficient resistance to hot cracking. Resistance to hot cracking is an important aspect of an alloy's weldability; the better the weldability, the better the crack resistance. The inventors also tested the corrosion resistance by performing potentiometric tests. For this purpose, the following tests were carried out: Evaluation of generalized corrosion by measuring the critical corrosion current of JaceroMn in H2SO4 medium (2 mol / H) and comparing this current with the measurement for lnvarMRM93 strips (lnvarM93 ~ 230mA / cm2); Evaluation of localized corrosion by measuring the pitting potential V in NaCl medium (0.02 mol / l'1) and comparing this potential V with that of lnvarMR-M93 (Vinvar M93 / Eenh ~ 40mV), where Eenh is the reference potential with respect to the hydrogen electrode. It is recalled that lnvarMR-M93 has the following composition, in percentage by weight: 35% < Ni < 36.5% 0.2% < Mn < 0.4% 0.02 < C < 0.04% 0.15 < If <0.25% optionally <Co<20% <Ti<0.5% 0.01% <Cr<0.5% el resto que son hierro y elementos residuales resultantes de la producción. If Jacero Mn < Jinvar M93 and Vacero μπ / EΕενη > Vinvar m9s / Eenh> the tested steel is considered more corrosion resistant than Invar M93. If Jacero Mn > Jinvar M93 or Vacero Мπ / ЕеНЗ < Vinvar m93 / Eenh, the tested steel is considered less corrosion resistant than lnvarMR-M93. The results of these tests are summarized in the column titled Corrosion Resistance in Table 1 below. In this column: The reference to “> Invar” corresponds to the bands for which Jacero Mn < Jlnvar M93 and Vacero Mn / EeNH > Vlnvar M93 / EeNH1; the reference to “< Invar” corresponds to the bands for which Jacero Mn > Jlnvar M93 or Vacero Mn / EeNH < Vlnvar M93 / EENH; and the reference to “~ Invar” corresponds to the bands for which Jacero Mn ~ Jlnvar M93 and Vacero Mn / EeNH > Vlnvar M93 / EENH. The inventors also conducted resilience tests at -196°C in a reduced-thickness test tube (-3.5 mm) and measured the impact breaking energy of the strip (denoted KCV), in accordance with EN ISO 148-1. Breaking energy is expressed in J / cm². It indicates the strength of the strip. The results of these tests are summarized in the column titled KCV at -196°C in Table 1 below. The inventors also performed dilatometric tests: from -180°C to 0°C in order to determine the average coefficient of thermal expansion of the alloy; and - from 20°C to 500°C in order to determine the Néel temperature (TNéei) of the alloy. The Néel temperature corresponds to the temperature above which an antiferromagnetic material becomes paramagnetic. More specifically, the average coefficient of thermal expansion is determined by measuring the change in length, in micrometers, between -180°C and 0°C of a 50 mm long test tube at 0°C. The average coefficient of thermal expansion is then obtained by applying the following formula: where Lo-Li represents the length variation in micrometers between 0°C and -180°C, Lo represents the length of the test tube at 0°C, To is equal to 0°C and Ti is equal to -180°C. The Néel temperature is determined by measuring L(T), where L is the length of the sample at temperature T, and then calculating the slope dL / dT. The Néel temperature corresponds to the temperature at which the slope of this curve changes. The results of these tests are indicated respectively in the columns titled CTE [180°C to 0°C] and TW in Table 1 below. Finally, the inventors conducted flat tensile mechanical tests at -196°C to measure the yield strength at 0.2% elongation, Rpo.2 at -196°C. The results of these tests are summarized in the column titled Rpo.2 at -196°C in Table 1 below. οο / οηη / ίζηζ / Β / γι Table 1: Alloy compositions and test results No. Fe Mn Cr Ni N Ce +La Y Si C Al Se SPO Otros Prueba de Vares traint Resistencia de corrosión KCVa196°C (J / cm2) Tde Néel (°C) CTE [180°Ca 0°C] (10'6 / °C) Rpo,2 a -196°C (MPa) 1 Bal. 25.0 3.6 0.18 mini mini mini 0.30 0.4 mini mini mini 3 < Invar ndndndnd 2 Bal. 25.0 3.6 0.18 mini mini mini 0.30 mini mini mini mini 3 < Invar ndndndnd 3 Bal. 23.0 6.5 0.18 mini mini mini 0.28 0.45 mini mini mini 3 < Invar nd 58 ndnd 4 Bal. 23.0 6.5 0.18 mini mini mini 0.28 mini mini mini mini 3 < Invar nd 60 ndnd 5 Bal. 28.0 6.5 2.1 0.1 mini mini 0.25 mmi mim mim mini 3 > Invar 120 88 8.5 710 6 Bal. 28.0 8.0 2.1 0.1 mini mini 0.25 mini mini mini mini 2 > Invar 122 72 8.4 740 7 Bal. 28.0 10.2 1.8 mini mini mini 0.30 mini mini mini mini 2 < Invar ndndndnd 8 Bal. 28.0 10.2 1.8 0.1 mini mini 0.30 mini mini mini mini 2 > Invar 125 62 8.3 760 9 Bal. 28.0 12.1 1.8 0.35 mini mini 0.30 mini mini mini mini 3 > Invar < 50 52 8.3 1220 10 Bal. 28.0 13.5 2.0 0.1 mini mini 0.28 mini mini mini mini 2 > Invar 120 42 8.3 815 11 Bal. 28.0 16.0 2.0 0.1 mini mini 0.28 mini mini mini mini 2 > Invar < 50 <40 9.2 1260 12 Bal. 27.8 10.1 0.3 0.15 mini mini 0.26 mini mini mini mini 2 > Invar 120 75 7.7 880 13 Bal. 27.8 10.1 2.8 0.15 mini mini 0.26 mini mini mini mini 2 > Invar ndnd 8.8 875 14 Bal. 22.0 9.9 2.0 0.15 0.015 mini 0.20 mini mini mini mini 1 > Invar 115 <40 8.1 690 15 Bal. 25.5 9.9 2.0 0.15 0.035 mini 0.20 mini mini mini mini 1 > Invar 122 51 8.3 815 16 Bal. 28.0 10.0 1.8 0.15 0.050 mini 0.25 mini mini mini mini 1 > Invar 95 61 8.3 880 17 Bal. 31.5 10.0 1.8 0.15 0.075 mini 0.25 mini mini mini mini 1 > Invar 105 70 8.4 1020 18 Bal. 31.5 10.0 1.8 0.15 0.150 mini 0.25 mini mini mini mini 3 > Invar 95 72 8.4 990 19 Bal. 28.0 9.5 1.9 0.2 mini 0.040 0.24 mini mini mini mini 1 > Invar 100 63 8.3 1010 20 Bal. 28.0 9.5 1.9 0.2 mini 0.080 0.24 mini mini mini mini 1 > Invar 105 64 8.4 980 21 Bal. 28.0 9.5 1.9 0.2 mini 0.200 0.24 mini mini mini mini 3 > Invar 85 63 8.3 1000. QQ / Qnn / Lznz / E / Yi In Table 1 above, “nd” means that the value considered has not been determined. Furthermore, the tests in accordance with the invention have been highlighted. In this table: For the elements C, Al, Se, S, P, O, “mini” means: C < 0.05% by weight, At < 0.02% by weight, Se < 0.001% by weight, S < 0.005% by weight, P < 0.04% by weight, O < 0.002% by weight, The elements marked Other include Co, Cu, Mo, Sn, Nb, V, Ti and Pb, and in this column mini means: Co, Cu, Mo < 0.2% by weight, Sn, Nb, V, Ti < 0.02% by weight, and Pb < 0.001% by weight. For nitrogen, mini means N < 0.03% by weight. In these concentrations, nitrogen is considered a residual element. For rare earth elements, i.e., Ce, La and Y, mini means that the alloy comprises at most traces of these elements, preferably a content of each of these elements less than or equal to 1 ppm. Tests numbered 6, 8, 10, 12, 15 to 17, 19 and 20 are in accordance with the invention. Strips made according to these tests are found to have good, or even excellent, resistance to hot cracking (cf. Varestraint test column), and consequently, good weldability. Furthermore, these strips have a corrosion resistance greater than or equal to that of Invar M93, an average coefficient of thermal expansion GTE between -180°C and 0°C less than or equal to 8.5 × 10'6 / °C, a Néel temperature greater than or equal to 40°C, a KCV resilience at -196°C greater than or equal to 80 J / cm2 and a yield strength Rpo.2 at -196°C greater than or equal to 700 MPa. Therefore, the strips made from the alloy according to the invention have satisfactory thermal expansion, resilience, and mechanical strength properties for use in applications requiring high dimensional stability under the effect of temperature variations, particularly at cryogenic temperatures. The alloys that passed tests 1 through 5 have a chromium content strictly below 7.0% by weight. The corresponding strips exhibit poor resistance to hot cracking and, consequently, unsatisfactory weldability. Furthermore, tests 1 and 3 show that this poor resistance to hot cracking is not compensated for by the addition of carbon, even at relatively high levels. The alloy tested in test 11 has a chromium content strictly greater than 14.0% by weight. The corresponding strips exhibit high brittleness at cryogenic temperatures, resulting in a KCV resilience strictly less than 50 J / cm². This alloy also has a Néel temperature strictly less than 40°C. The alloy, according to test number 13, has a nickel content strictly greater than 2.5% by weight. It is observed that the corresponding strips have an average coefficient of thermal expansion (GTE) between -180°C and 0°C strictly greater than 8.5 × 10⁶ / °C. A comparison of tests 7 and 8 shows that, all else being equal, increasing the nitrogen content improves corrosion resistance. Furthermore, the alloy in test 9, with a nitrogen content strictly exceeding 0.30% by weight, exhibits degraded weldability and KCV resilience at -196°C. Furthermore, as shown by the comparison of tests 14 and 15, the decrease in manganese content, all else being equal, results in a decrease in Néel temperature. It is also observed that the strips corresponding to tests 14, 17, 19, and 20, comprising rare earth elements in proportions between 0.010% and 0.14% by weight, have excellent resistance to hot cracking, with crack lengths of less than 2 mm. Conversely, the strips corresponding to tests 18 and 21 have a rare earth element content strictly greater than 0.14% by weight, and these strips are observed to have degraded weldability. The mechanical strength of a homogeneous weld between two parts made of iron-manganese alloy according to the invention, or of a heterogeneous weld between a part made of iron-manganese alloy according to the invention and a part made of a different alloy, and in particular stainless steel 304L and lnvarMRM93, was investigated by tensile tests. These tests were carried out using the alloy according to Example 16 of Table 1 as the iron-manganese alloy. More specifically, homogeneous welds were made by butt welding between two pieces removed from a strip made from the iron-manganese alloy according to example 16 in table 1. Heterogeneous welds were also made by butt welding a piece removed from a strip made of the alloy according to example 16 in table 1 to a piece removed from a strip made of lnvarMRM93 or to a coupon removed from a strip made of 304L stainless steel. In addition, for comparison, homogeneous butt welds were made between two pieces removed from strips made of lnvarMRM93 and heterogeneous butt welds were made between a piece removed from a strip made of lnvarMRM93 and a piece removed from a strip made of 304L stainless steel. QQ / Qnn / Lznz / E / Yi The results are presented in Table 2 below. Table 2: Results of the traction tests Nature of the butt weld Example 16- Example: 16 Example: 16- 304L Stainless Steel Example 16- Invar M93 Invar M93 Invar M93 304L Stainless Steel Invar M93 Mechanical strength Rm of the welded assembly at 25 °C (MPa) 615 475 425 410 330 The tensile tests were carried out at room temperature as is usual for welding qualification tests. These tests show that the alloy according to the invention has satisfactory weldability with stainless steel and invarMR. The alloy according to the invention can be advantageously used in any application where good dimensional stability is desired, associated with good corrosion resistance and good weldability, particularly in the cryogenic field or in the field of electronics. Given their properties, the alloys according to the invention can be advantageously used for the manufacture of welded assemblies proposed for applications where high dimensional stability is required under the effect of temperature variations, particularly at cryogenic temperatures.

Claims

1. An iron-manganese alloy comprising, by weight: 25.0% < Mn < 32.0% 7.0% < Cr < 14.0% 0 < Ni < 2.5% 0.05% < N < 0.30% 0.1 <S¡ < 0.5% opcionalmente 0.010% < tierras raras < 0.14% el resto que son hierro y elementos residuales resultantes de la producción.

2. The alloy according to claim 1, wherein the chromium content is between 8.5% and 11.5% by weight.

3. The alloy according to one of claims 1 or 2, wherein the nickel content is between 0.5% and 2.5% by weight.

4. The alloy according to any of the preceding claims, wherein the nitrogen content is between 0.15% and 0.25% by weight.

5. The alloy according to any of the preceding claims, wherein the rare earths comprise one or more elements selected from: lanthanum (La), cerium (Ce), triium (Y), praseodymium (Pr), neodymium (Nd), samarium (Sm) and ytterbium (Yb).

6. A manufacturing process for a strip made of an iron-manganese alloy according to any of the preceding claims, wherein the process comprises the following successive steps: an alloy is produced according to any of the preceding claims; a semi-finished product is formed from the alloy; the semi-finished product is hot-rolled to obtain a hot strip; optionally, the hot strip is cold-rolled in one or more passes to obtain a cold strip.

7. The strip made of an iron-manganese alloy according to any of claims 1 to 5.

8. The process of manufacturing a wire made of an iron-manganese alloy according to any one of claims 1 to 5, wherein the process comprises the following steps: supplying a semi-finished product made of an iron-manganese alloy according to any one of claims 1 to 5; hot-working the semi-finished product to form an intermediate wire; and transforming the intermediate wire into a wire, having a diameter smaller than that of the intermediate wire, this transformation comprising a wire drawing step.

9. A wire made of an iron-manganese alloy according to any of claims 1 to 5.