Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/005—Heat treatment of ferrous alloys containing Mn
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0236—Cold rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0247—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
  • C21D8/0263—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/06—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/525—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length for wire, for rods
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite

Definitions

• the present invention relates to an iron-manganese alloy for use in manufacturing welded parts and assemblies for applications where high dimensional stability under temperature variations is required, particularly at cryogenic temperatures.
• the alloy according to the invention is more particularly intended to be used in the field of electronics, as well as in cryogenic applications.
• alloys for such applications are iron-nickel alloys, and more particularly Invars ® , generally comprising about 36% nickel.
• Such alloys have excellent dimensional stability properties, particularly at cryogenic temperatures, but have the disadvantage of a relatively high cost price resulting in particular from their relatively high nickel content.
• the weldability of these alloys on other metals is not always entirely satisfactory, particularly in terms of the mechanical strength of heterogeneous welds.
• Iron-based alloys also containing carbon and manganese are known, marketed by the Korean company Posco. These steels include, by weight: 0.35 % ⁇ C ⁇ 0.55 % 22.0 % ⁇ Mn ⁇ 26.0 % 3.0 % ⁇ Cr ⁇ 4.0 % 0 ⁇ If ⁇ 0.3 % the remainder being iron and residual elements resulting from the elaboration. However, these alloys do not give complete satisfaction.
• an object of the invention is to provide an alloy capable of being used satisfactorily for manufacturing welded parts and assemblies for applications in which high dimensional stability under the effect of temperature variations is required, for example for cryogenic applications, while having a relatively low cost price.
• the invention relates to an iron-manganese alloy comprising, by weight: 25.0 % ⁇ Mn ⁇ 32.0 % 7.0 % ⁇ Cr ⁇ 14.0 % 0 ⁇ Neither ⁇ 2.5 % 0.05 % ⁇ N ⁇ 0.30 % 0.1 ⁇ If ⁇ 0.5 % optionally 0.010% ⁇ rare earths ⁇ 0.14% the remainder being iron and residual elements resulting from the elaboration.
• the invention also relates to a strip made from an iron-manganese alloy as defined above.
• the invention also relates to a wire made from an iron-manganese alloy as defined above.
• This wire is in particular a material filler wire or a wire intended for the manufacture of bolts or screws, these bolts and screws being in particular obtained by cold heading from this wire.
• the alloy according to the invention is an iron-manganese alloy comprising, by weight: 25.0 % ⁇ Mn ⁇ 32.0 % 7.0 % ⁇ Cr ⁇ 14.0 % 0 ⁇ Neither ⁇ 2.5 % 0.05 % ⁇ N ⁇ 0.30 % 0.1 ⁇ If ⁇ 0.5 % optionally 0.010% ⁇ rare earths ⁇ 0.14% the remainder being iron and residual elements resulting from the elaboration.
• One such alloy is a high manganese austenitic steel.
• the alloy according to the invention is austenitic at room temperature and at cryogenic temperature (-196°C).
• Residual elements resulting from the elaboration are elements which are present in the raw materials used to elaborate the alloy or which come from the equipment used for its elaboration, for example from the refractories of the furnaces. These residual elements have no metallurgical effect on the alloy.
• the residual elements include in particular one or more elements chosen 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).
• the selenium content is limited within the ranges mentioned above in order to avoid hot cracking problems that could result from too high a presence of selenium in the alloy.
• this alloy exhibits satisfactory thermal expansion, resilience and mechanical strength properties for its use in the applications mentioned above, particularly at cryogenic temperatures.
• the alloy according to the invention also has a corrosion resistance characterized by a critical corrosion current in H 2 SO 4 medium (2 mol.l -1 ) strictly less than 230 mA/cm 2 and a pitting potential V in NaCl medium (0.02 mol.l -1 ) strictly greater than 40 mV, the pitting potential being determined by reference to a reference potential, the hydrogen electrode (ENH).
• the alloy according to the invention thus has a corrosion resistance greater than or equal to that of Invar ® -M93. It should be noted in this context that Invar ® -M93 is a material usually used in the context of the applications mentioned above, in particular at cryogenic temperature.
• the alloy according to the invention also exhibits a corrosion resistance much higher than that observed for previous Fe- Mn alloys, which exhibit a critical corrosion current in H2SO4 medium (2 mol.l -1 ) greater than approximately 350mA/ cm2 and a pitting potential V less than or equal to -200 mV relative to the hydrogen electrode (ENH).
• the alloy according to the invention also has satisfactory weldability, and in particular good resistance to hot cracking. In particular, 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 resistance to cracking much higher than that observed for previous Fe-Mn alloys.
• manganese at 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 8.5.10 -6 /°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 applications envisaged, and in particular in the context of cryogenic applications.
• the manganese content greater than or equal to 25.0% by weight, combined with a chromium content less than or equal to 14.0% by weight, makes it possible to obtain good dimensional stability of the alloy at room temperature and at cryogenic temperature (-196°C).
• the Néel temperature of the alloy is then strictly greater than 40°C, and is not likely to be reached at the usual temperatures of use of the alloy.
• use of the alloy at temperatures higher than the Néel temperature risks generating significant variations in expansion of welded parts and assemblies at room temperature.
• the expansion coefficient of the high manganese steel described above is of the order of 8.10 -6 /°C at temperatures lower than or equal to the Néel temperature, while it is of the order of 16.10 -6 /°C for temperatures higher than the Néel temperature.
• Chromium at a content less than or equal to 14.0% by weight, makes it possible to obtain good KCV resilience on a reduced test piece of 3 mm thickness and at cryogenic temperature (-196°C), and in particular a KCV resilience at -196°C greater than or equal to 50 J/cm 2 .
• the inventors have found that a chromium content strictly greater than 14.0% by weight risks resulting in excessive brittleness of the alloy at cryogenic temperature.
• chromium makes it possible to obtain good weldability of the alloy.
• the inventors have found that weldability tends to deteriorate for chromium contents strictly less than 7.0% by weight. Chromium also contributes to improving the corrosion resistance of the alloy.
• 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 at a content less than or equal to 2.5% by weight, makes it possible to obtain an average coefficient of thermal expansion between -180°C and 0°C less than or equal to 8.5.10 -6 °/C. This coefficient of thermal expansion is satisfactory for the use of the alloy in the context of the envisaged applications. On the contrary, the inventors have found that the coefficient of thermal expansion risks degrading for nickel contents strictly greater than 2.5% by weight.
• the nickel content is between 0.5% and 2.5% by weight.
• a nickel content greater than or equal to 0.5% by weight makes it possible to further improve the resilience of the alloy at cryogenic temperature (-196°C).
• Nitrogen at contents greater than or equal to 0.05% by weight, helps to improve corrosion resistance. However, its content is limited to 0.30% by weight in order to maintain satisfactory weldability and resilience at cryogenic temperature (-196°C).
• the nitrogen content is between 0.15% and 0.25% by weight.
• a nitrogen content within this range makes it possible to obtain an even better compromise between mechanical properties and corrosion resistance.
• Silicon present in the alloy at a content of between 0.1% and 0.5% by weight, acts as a deoxidizer in the alloy.
• the alloy optionally comprises rare earths in a content of between 0.010% and 0.14% by weight.
• the rare earths 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.
• the rare earths comprise a mixture of cerium and lanthanum or yttrium, used alone or mixed with cerium and lanthanum.
• rare earths consist of lanthanum and/or yttrium, the sum of the lanthanum and yttrium contents being between 0.010% and 0.14% by weight.
• the rare earths consist of cerium, with the cerium content ranging from 0.010% to 0.14% by weight.
• the rare earths consist of a mixture of lanthanum, yttrium, neodymium and praseodymium, the sum of the contents of lanthanum, yttrium, neodymium and praseodymium being between 0.010% and 0.14% by weight.
• the rare earths are added, for example, in the form of Mischmetal at a content of between 0.010% and 0.14% by weight.
• the Mischmetal contains lanthanum, yttrium, neodymium and praseodymium in the following proportions: Ce: 50%, La: 25%, Nd: 20% and Pr: 5%.
• rare earths and more particularly of a mixture of cerium and lanthanum or yttrium, at the contents mentioned above, makes it possible to obtain an alloy with very good resistance to hot cracking and, consequently, even better weldability.
• 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.
• the alloy according to the invention is produced in a vacuum furnace from low-residue raw materials.
• hot or cold strips are then produced from the alloy thus produced.
• the following process is used to manufacture such hot or cold strips.
• the alloy is cast 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 casting, or billets.
• the alloy When the alloy is cast in the form of a remelting electrode, it is advantageously remelted under vacuum or under electro-conductive slag in order to obtain better purity and more homogeneous semi-finished products.
• the semi-finished product thus obtained is then hot rolled at a temperature between 950°C and 1220°C to obtain a hot strip.
• the hot rolling is preceded by a chemical homogenization heat treatment at a temperature between 950°C and 1220°C for a duration between 30 minutes and 24 hours.
• the chemical homogenization process is notably carried out on the slab, in particular the thin slab.
• the hot strip is cooled to room temperature to form a chilled strip and then wound into coils.
• the cooled strip is then cold rolled to obtain a cold strip having a final thickness advantageously between 0.5 mm and 2 mm.
• Cold rolling is carried out in one pass or in several successive passes.
• the cold strip is optionally subjected to a recrystallization heat treatment in a static furnace for a period ranging from 10 minutes to several hours and at a temperature above 700°C.
• a recrystallization heat treatment in a continuous annealing furnace for a period ranging from a few seconds to approximately 1 minute, at a temperature above 900°C in the holding zone of the furnace, and under a protected atmosphere of the N2/H2 type (30%/70%) 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 carried out, 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 for example chosen to be equal to 1.5 mm when the final thickness of the cold strip is 0.7 mm.
• the invention also relates to a strip, and in particular a hot or cold strip, made from the alloy as described above.
• the strip has a thickness less than or equal to 6.5 mm, and preferably less than or equal to 3 mm.
• Such a 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 step of the process described above.
• the invention also relates to a wire made from the alloy described above.
• wire is a filler wire intended to be used to weld parts together.
• the wire intended is for the manufacture of bolts or screws, these bolts and screws being obtained in particular by cold heading from this wire.
• the semi-finished product is in particular an ingot or a billet.
• These semi-finished products are preferably transformed by hot transformation between 1050°C and 1220°C to form the intermediate wire.
• the semi-finished products i.e. in particular the ingots or billets
• the semi-finished products are hot transformed so as to reduce their section, by giving them, for example, a square section, of approximately 100 mm to 200 mm on each side.
• a semi-finished product of reduced section is thus obtained.
• the length of this semi-finished product of reduced section is in particular between 10 meters and 20 meters.
• the reduction of the section of the semi-finished products is carried out by one or more successive hot rolling passes.
• the semi-finished products of reduced section are then hot-processed again to obtain the wire.
• the wire may in particular be a wire rod.
• it has a diameter of between 5 mm and 21 mm, and in particular approximately equal to 5.5 mm.
• the wire is produced by hot rolling on a wire train.
• the inventors have made laboratory castings of alloys having compositions as defined above, as well as comparative alloys having compositions different from the composition described above.
• Hot crack resistance is an important aspect of the weldability of an alloy, the weldability being better the higher the crack resistance.
• Invar ® -M93 has the following composition, in percentage by weight: 35 % ⁇ Neither ⁇ 36.5 % 0.2 % ⁇ Mn ⁇ 0.4 % 0.02 ⁇ C ⁇ 0.04 % 0.15 % ⁇ If ⁇ 0.25 % optionally 0 ⁇ Co ⁇ 20 % 0 ⁇ You ⁇ 0.5 % 0.01 % ⁇ Cr ⁇ 0.5 % the remainder being iron and residual elements resulting from the elaboration.
• the inventors also carried out resilience tests at -196°C on a reduced specimen (thickness - 3.5 mm) and measured the impact breaking energy of the strip (denoted KCV), in accordance with standard NF EN ISO 148-1. The breaking energy is expressed in J/cm 2 . It reflects the resilience of the strip. The results of these tests are summarized in the column entitled "KCV at -196°C" in Table 1 below.
• the average coefficient of thermal expansion is determined by measuring the length variation in micrometers between -180°C and 0°C of a 50 mm long test piece at 0°C.
• the average coefficient of thermal expansion is then obtained by applying the following formula: 1 L 0 ⁇ L 0 ⁇ L 1 T 0 ⁇ T 1 where L 0 - L 1 represents the length variation in micrometers between 0°C and -180°C, L 0 represents the length of the specimen at 0°C, T 0 is equal to 0°C and T 1 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 dUdT.
• the Néel temperature corresponds to the temperature of change in slope of this curve.
• mini means N ⁇ 0.03% by weight. At these levels, nitrogen is considered a residual element.
• mini means that the alloy includes 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.
• these strips have a corrosion resistance greater than or equal to that of invar M93, an average coefficient of thermal expansion CTE 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/cm 2 and an elastic limit Rp 0.2 at -196°C greater than or equal to 700 MPa.
• the strips made from the alloy according to the invention therefore have thermal expansion, resilience and mechanical resistance properties which are satisfactory for their use in applications for which high dimensional stability under the effect of temperature variations is required, in particular at cryogenic temperature.
• the alloys according to tests numbered 1 to 5 have a chromium content strictly less than 7.0% by weight. It is noted that the corresponding strips have poor resistance to hot cracking, and therefore unsatisfactory weldability. Furthermore, tests 1 and 3 show that this poor resistance to hot cracking is not compensated by the addition of carbon, even at relatively high contents.
• the alloy according to test 11 has a chromium content strictly greater than 14.0% by weight. It is observed that the corresponding strips have significant brittleness at cryogenic temperature, resulting in a KCV resilience strictly less than 50 J/cm 2 . It is also observed that this alloy 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 CTE between -180°C and 0°C strictly greater than 8.5.10 -6 /°C.
• the strips corresponding to tests 14, 17, 19 and 20 which comprise rare earths in proportions of between 0.010% and 0.14% by weight, have excellent resistance to hot cracking, with crack lengths of less than 2 mm.
• the strips corresponding to tests 18 and 21 have a rare earth content strictly greater than 0.14% by weight, and it is observed that these strips have degraded weldability.
• homogeneous welds were produced by butt welding together two coupons taken from a strip made of the iron-manganese alloy according to example 16 of table 1. Heterogeneous welds were also produced by butt welding a coupon taken from a strip made of the alloy according to example 16 of table 1 to a coupon taken from a strip made of Invar ® M93 or to a coupon taken from a strip made of 304L stainless steel.
• homogeneous welds were produced by butt welding together two coupons taken from strips made of Invar ® M93 and heterogeneous welds by butt welding together a coupon taken from a strip made of Invar ® M93 and a coupon taken from a strip made of 304L stainless steel.
• the alloy according to the invention can be advantageously used in any application in which good dimensional stability, associated with good corrosion resistance and good weldability are desired, in particular in the cryogenic field or in the electronics field.
• the alloys according to the invention can be advantageously used for the manufacture of welded assemblies intended for applications in which high dimensional stability under the effect of temperature variations is required, in particular at cryogenic temperature.

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