Metal parts with low coefficient of thermal expansion and high mechanical strength

Abstract

The invention relates to metal parts for producing rubber articles such as bands for wheels, caterpillar tracks, conveyor belts or transmission belts, which are iron based and in particular based on an Fe-Ni alloy, having a low isobaric coefficient of thermal expansion for temperatures up to approximately 200°C, and to the production of such parts. The term coefficient of thermal expansion (CTE) is commonly used.

Description

[0001] Metal parts with low coefficient of thermal expansion and high mechanical resistance

[0002] Technical field of the invention

[0003] The present invention relates to metal parts intended for the manufacture of rubber articles such as tires for wheels, tracks, conveyor belts or transmission belts based on iron, in particular an Fe alloy. _ Ni, having a low coefficient of isobaric thermal expansion for temperatures up to about 200°C as well as the manufacture of such parts. It is commonly referred to as the coefficient of thermal expansion (CTE).

[0004] Prior art

[0005] The metal parts used in the manufacture of pneumatic or non-pneumatic tires, rubber tracks, vehicle wheels, i.e. having a mobility function and / or parts of pneumatic or non-pneumatic tires, rubber tracks or such wheels must meet numerous constraints, in particular good mechanical strength, so as not to deform during use and thus ensure an acceptable service life, and the lowest possible thermal expansion so as to control the geometry of the rubber object formed. It should be remembered that a pneumatic tire is understood to mean a tire capable of supporting a load, for example a vehicle, by means of a pressurized gas. A non-pneumatic tire is understood to mean a tire capable of supporting a load, for example a vehicle, by means other than a pressurized gas, for example by means of guy wires.

[0006] For example, a curing, or vulcanization, mold of the sector type for vehicle wheel tires mainly comprises two shells each ensuring the molding of one of the lateral sidewalls of the tire, a plurality of sectors ensuring the molding of the tread of said tire and movable radially between an open position and a closed position of the mold. The shells and the sectors define an interior space intended to be brought into contact with the unvulcanized tire blank. To form the tread patterns, sipes are fixed to the sectors of the mold and extend projecting into this interior space. For more details on a mold comprising such sipes, reference may for example be made to documents EP 1 758 743 and US 2002 / 0139164.

[0007] These elements must not only have sufficient mechanical resistance to not break during use and withstand the constraints linked to the shaping of the molded materials, but also deform as little as possible during the temperature cycles linked to the cooking (or crosslinking) of these materials.

[0008] The interest in manufacturing by selective fusion of superimposed layers of powder, more commonly known as powder bed fusion, lies mainly in the fact that this technique is well suited to the manufacturing of small and complex shaped elements, such as mold trim strips, which are difficult to manufacture using other processes.

[0009] When selective melting is performed by a laser beam, it is called sintering when the melting of the powder grains is partial, or laser melting. The laser melting technique consists of manufacturing the lamella layer by layer, by stacking the consolidated and fused powder layers on top of each other by the laser beam in a stacking direction. The term "powder" refers to a powder or a mixture of powders that are mainly metallic, but can also be mineral, for example ceramic.

[0010] The first layer is deposited and then fused directly onto the build plate. The other layers are then formed successively to obtain a stack from the first layer.

[0011] Generally, the manufacturing of a small element, such as a trim strip, is carried out horizontally on the manufacturing plate so that its length is substantially parallel to the manufacturing plate. This is referred to as horizontal manufacturing. This avoids having an excessively high strip height and thus reduces manufacturing time. Such elements must have good properties of fracture toughness and / or fatigue resistance to ensure their longevity of use, hence the importance of the alloy used in such manufacturing.

[0012] The i'e-Ni alloys of composition generally of the type 64Fe _36Ni alloys with low coefficients of thermal expansion for temperatures up to about 200°C are already known from the prior art. They are generally marketed under the name INVAR® 36. However, it would be interesting to improve the mechanical strength and hardness of such an alloy while maintaining the lowest possible coefficient of thermal expansion (CTE) and allowing their implementation by additive manufacturing.

[0013] It is already known to improve the mechanical resistance of INVAR® 36 by strengthening the alloy through the precipitation of multiple carbides and by strong deformation, particularly when cold.

[0014] This is the case of patent application WO03025239 which proposes reinforcement by carbides of Ti, Nb, V, Mo, Hf and Ta and the production of a very strongly cold deformed wire. The authors thus obtain a tensile strength Rm of up to 1300 MPa for a CET of 3.7 10' 6 / °C between 20 and 230°C. However, the alloys thus obtained cannot be implemented by additive manufacturing because their carbon content is too high and the presence of carbides thus hinders said additive manufacturing.

[0015] This is also the case for application RU2568541 which also proposes reinforcement with carbides of Nb, Ti, V, Mo, W, Zr in large quantities. The authors thus obtain a tensile strength Rm of up to 1900 MPa for a CET <7 10' 6 / °C between -196 and 327°C after forging and heat treatment. However, the alloys thus obtained cannot be implemented by additive manufacturing due to the presence of cobalt, which it is desirable to eliminate in the powder for health and safety reasons, in a content of at most 0.5% by weight.

[0016] Nakama et al. (Metallogr. Microstruct. Anal. 2, 383-387 (2013)) also propose reinforcement by precipitation of V or Ti or Zr or Nb or Ta carbides. The authors obtain a tensile strength Rm of up to 1010 Pa for a CET of 2.5 x 10' 6 / °C between 50 and 150°C after forging and heat treatment. However, the alloys thus obtained cannot be used by additive manufacturing because their carbon content is too high and the presence of carbides thus hinders said additive manufacturing.

[0017] The inventors surprisingly realized that it was possible to improve the mechanical resistance of mechanical parts while maintaining the lowest possible CET and allowing their manufacture by additive manufacturing. They thus realized that to achieve such a result (Rm-CET compromise) it was necessary to carry out precipitation hardening of the y" phase (gamma second) of the alloy while adjusting the Nb and Ni elements. Indeed, a fine intragranular precipitation is thus obtained which disrupts the magnetic ordering less than large precipitates and therefore increases the CET less. In addition, it is possible to simplify the heat treatment subsequent to additive manufacturing by not needing solution treatment at a very high temperature to obtain the desired hardening.Furthermore, all the additional Nb and Ni elements are found in the precipitates, without any remaining in solid solution in the austenite, which would be detrimental to the CET, and there remains 36% of Ni in substitution in the austenite after precipitation of all the possible y" phase (gamma second) in order to be in the optimal condition of CET. Carbon is also added to the composition in order to form some NbC carbides to limit the growth of the austenite grain during the heat treatment. However, the carbon content is limited to be able to be implemented by additive manufacturing.

[0018] Detailed description of the invention

[0019] The invention relates to a metal part for the manufacture of rubber articles based on an iron-based alloy composition comprising, advantageously consisting essentially of, in percentages by weight of the total composition ■

[0020] Nickel ■ 38.0 - 42.0, preferably 39.0 - 42.0

[0021] Niobium: 4.750 - 5.500, preferably 5.000 - 5.500; Carbon: 0.010 - 0.100, preferably 0.015 - 0.070; Cobalt: <0.400, preferably <0.100 Chromium ■ <0.500 Silicon: <0.500 Manganese ■ <0.500;

[0022] Iron ■ balance as well as unavoidable impurities.

[0023] The invention also relates to a method of manufacturing such a metal part comprising the following steps: ■

[0024] A - manufacturing an iron-based alloy powder having the composition of the alloy composition at the base of the metal part according to the invention according to the following steps ■ a) mixing of elementary or pre-alloyed raw materials, b) melting of the mixture obtained in step a), advantageously in a vacuum induction furnace, c) atomization with gas, advantageously with nitrogen, of the product obtained in step b) so as to obtain a powder, d) sieving or screening of the powder obtained in step c) so as to obtain a desired particle size fraction, e) recovery of the powder obtained.Bl - subjecting the powder obtained in step A) to an additive manufacturing process, advantageously chosen from the group consisting of selective laser powder bed melting (LBM), electron beam melting (EBM), laser powder projection melting such as Direct Additive Laser Construction or Direct Metal Deposition (DMD) and powder bed binder injection (MBJ), or to a hot isostatic compaction treatment with the aim of obtaining a part or.

[0025] B2 — subjecting the powder obtained in step A) to a laser melting process by powder projection such as Direct Additive Laser Construction or Direct Metal Deposition (DMD) followed by forging of the deposit made up of the melted powder,

[0026] C — subjecting the part obtained in step B1) or B2) to at least one thermal and / or physical and / or chemical treatment, advantageously chosen from the group consisting of a relaxation heat treatment, a hot isostatic compaction treatment if step B1) is not a hot isostatic compaction treatment, a solution treatment, an aging treatment, a finishing treatment such as a surface modification treatment or a deposit of a protective coating against corrosion and oxidation, and a mixture of these treatments,

[0027] D - recovery of the part thus obtained.

[0028] The invention also relates to a method for manufacturing such a metal part comprising the following steps: ■ i. mixing of elementary or pre-alloyed raw materials, ii. melting of the mixture obtained in step i), advantageously in a vacuum induction furnace, iii. optionally, homogenization by heat treatment of the ingot obtained in step ii), iv. transformation of the ingot obtained in any one of steps ii) or iii) by forging, v. recovery of the part thus obtained, vi.preferentially, subjecting the part obtained in step v) to at least one thermal and / or physical and / or chemical treatment, advantageously chosen from the group consisting of a relaxation thermal treatment, a hot isostatic compaction treatment, a solution treatment, an aging treatment, a finishing treatment such as a surface modification treatment or a deposit of a protective coating against corrosion and oxidation, and a mixture of these treatments.

[0029] The invention also relates to a metal part obtained by one of these methods, as well as to the use of a metal part according to the invention or obtained by a method according to the invention for the manufacture of pneumatic or non-pneumatic tires, rubber tracks, wheels for vehicles, i.e. having a mobility function and / or parts of pneumatic or non-pneumatic tires, rubber tracks or such wheels.

[0030] Definitions

[0031] In this document, unless expressly stated otherwise, all percentages (%) indicated are percentages (%) by mass.

[0032] The expression "composition based on" means a composition comprising the mixture and / or the in situ reaction product of the different constituents used, some of these constituents being able to react and / or being intended to react with each other, at least partially, during the different phases of manufacture of the composition. In the more specific case of a rubber composition, the composition may thus be in a totally or partially crosslinked state or in a non-crosslinked state.

[0033] The carbon-containing compounds mentioned in the description may be of fossil or bio-sourced origin. In the latter case, they may be, partially or totally, derived from biomass or obtained from renewable raw materials derived from biomass. This includes, in particular, polymers, plasticizers, fillers, etc.

[0034] Metal part

[0035] The present invention therefore relates to a metal part for the manufacture of rubber articles based on an iron-based alloy composition comprising, advantageously consisting essentially of, in particular consisting of, in percentages by weight of the total composition ■

[0036] Nickel ■ 38.0 - 42.0, preferably 39.0 - 42.0

[0037] Niobium: 4,750 - 5,500, preferably 5,000 - 5,500;

[0038] Carbon: 0.010 - 0.100, preferably 0.015 - 0.070;

[0039] Cobalt: <0.400, preferably <0.100

[0040] Chromium ■ <0.500

[0041] Silicon: <0.500

[0042] Manganese ■ <0.500;

[0043] Iron ■ balance as well as unavoidable impurities.

[0044] A metal part for the manufacture of rubber articles based on a particularly advantageous iron-based alloy composition according to the invention comprises, advantageously consists essentially of, in particular consists of, in percentages by weight of the total composition ■ Nickel: 39.0 - 42.0

[0045] Niobium: 5,000 - 5,500;

[0046] Carbon: 0.015 - 0.070;

[0047] Cobalt ■ <0.050

[0048] Chromium ■ <0.100 Silicon: <0.500 Manganese ■ <0.500; Iron ■ balance as well as unavoidable impurities.

[0049] In the context of the present invention the ranges "X - Y%", "X to Y" mean that the limits X and Y are included. The range "between X and Y" excludes the limits X and Y.

[0050] In the context of the present invention, the measurement uncertainties indicated are typical uncertainties.

[0051] In particular, unavoidable impurities, notably chosen from nitrogen (N), oxygen (O), hydrogen (H), sulfur (S), phosphorus (P), aluminum (Al), titanium (Ti), vanadium (V), molybdenum (Mo), calcium (Ca), copper (Cu), magnesium (Mg) and mixtures thereof, are kept at the lowest level. These impurities are generally due essentially to the manufacturing process and the quality of the furnace. Advantageously, the alloy composition at the base of the metal part according to the invention comprises at most 1.00% by weight of unavoidable impurities, advantageously at most 0.75% by weight, even more advantageously at most 0.50% by weight, relative to the total weight of the composition. Generally, the content of impurities in the alloy is measured with an absolute uncertainty of ±0.08%.

[0052] In particular, the alloy composition at the base of the metal part according to the invention comprises in percentages by weight of the total composition: ■

[0053] Nitrogen < 0.030, advantageously < 0.020, in particular < 0.010, and / or Oxygen < 0.040, advantageously < 0.035.

[0054] Limiting the nitrogen content limits the formation of nitrides in the alloy, which could be detrimental to the CET. The nitrogen content is measured with an absolute uncertainty of ±0.0012%. Limiting the oxygen content limits the formation of oxides, which could be detrimental to the CET and the ductility of the alloy. Such oxygen contents may seem surprising in light of conventional processes, but fractionating the metal into powder form induces a very high surface / volume ratio, which will tend to significantly increase the oxygen content of the alloy. This will increase further if the powder manufacturing process is not sufficiently controlled. The oxygen content is measured with an absolute uncertainty of ±0.0019%.

[0055] Advantageously, the hydrogen content of the alloy composition at the base of the metal part according to the invention < 0.0050% by weight of the total composition. Limiting the hydrogen content makes it possible to limit the embrittlement of the alloy. The hydrogen content is measured with an absolute uncertainty of ±0.0005%.

[0056] Advantageously, the sulfur content of the alloy composition at the base of the metal part according to the invention is <0.0150% by weight of the total composition, advantageously <0.0050% by weight of the total composition. Limiting the sulfur content makes it possible to limit the formation of low-melting phases such as F eS which would wet the grain boundaries, which is harmful to the alloy. Indeed, these phases have very low mechanical strength and their presence would therefore reduce the mechanical characteristics of the alloy. The sulfur content is measured with an absolute uncertainty of ±0.0001%.

[0057] Advantageously, the phosphorus content of the alloy composition at the base of the metal part according to the invention is <0.0150% by weight of the total composition, advantageously <0.0050% by weight of the total composition. Limiting the phosphorus content makes it possible to limit the formation of low-melting-point phases such as FesP which would accumulate in the grain boundaries and which are therefore harmful to the alloy by reducing its resilience. The phosphorus content is measured with an absolute uncertainty of ±0.0001%.

[0058] Advantageously, the aluminum content of the alloy composition at the base of the metal part according to the invention is <0.100% by weight of the total composition. Limiting the aluminum content makes it possible to limit the formation of possible intermetallic phases between Ni and Al, such as, for example, the y' (gamma prime) phase, which would result in the formation of precipitates potentially larger than the y” (gamma second) precipitates and which would reduce the Ni content in the austenite. This would result in an increase in the CET. The aluminum content is measured with an absolute uncertainty of ±0.005%. Advantageously, the titanium content of the alloy composition at the base of the metal part according to the invention is <0.100% by weight of the total composition.Limiting the titanium content limits the formation of possible intermetallic phases between Ni and Ti, such as the y' (gamma prime) phase or the i] (eta) phase, which would result in the formation of precipitates potentially larger than the y” (gamma second) precipitates and would reduce the Ni content in the austenite. This would result in an increase in the CET. The titanium content is measured with an absolute uncertainty of ±0.005%.

[0059] Advantageously, the vanadium content of the alloy composition at the base of the metal part according to the invention is <0.100% by weight of the total composition. Limiting the vanadium content makes it possible to limit the formation of coarse vanadium carbides which would have a detrimental impact on the CET. The vanadium content is measured with an absolute uncertainty of ±0.007%.

[0060] Advantageously, the molybdenum content of the alloy composition at the base of the metal part according to the invention is <0.020% by weight of the total composition. Limiting the molybdenum content makes it possible to limit the formation of coarse molybdenum carbides which would have a detrimental impact on the CET. The molybdenum content is measured with an absolute uncertainty of ±0.003%.

[0061] Advantageously, the calcium content of the alloy composition at the base of the metal part according to the invention is <0.015% by weight of the total composition. Limiting the calcium content makes it possible to limit the formation of inclusions harmful to the alloy. The calcium content is measured with an absolute uncertainty of ±0.005%.

[0062] Advantageously, the copper content of the alloy composition at the base of the metal part according to the invention is <0.010% by weight of the total composition. Limiting the copper content makes it possible to limit the formation of Cu precipitates in the grain boundaries which could be harmful to the CET and to the mechanical properties of the alloy. The copper content is measured with an absolute uncertainty of ±0.002%.

[0063] Advantageously, the magnesium content of the alloy composition at the base of the metal part according to the invention is <0.015% by weight of the total composition. Limiting the magnesium content makes it possible to limit the formation of inclusions harmful to the alloy. The magnesium content is measured with an absolute uncertainty of ±0.005%. Preferably, the alloy composition at the base of the metal part according to the invention has an unavoidable impurity content chosen from nitrogen (N), oxygen (O), hydrogen (H), sulfur (S), phosphorus (P), aluminum (Al), titanium (Ti), vanadium (V), molybdenum (Mo), calcium (Ca), copper (Cu), magnesium (Mg) and mixtures thereof meeting at least one, preferably at least two, preferably at least three and preferably all of the following conditions: ■ nitrogen <0.030% by weight of the total composition; oxygen < 0.040% by weight of the total composition;hydrogen < 0.0050% by weight of the total composition; sulfur < 0.0150% by weight of the total composition; phosphorus < 0.0150% by weight of the total composition; aluminum < 0.100% by weight of the total composition; titanium < 0.100% by weight of the total composition; vanadium < 0.100% by weight of the total composition; molybdenum < 0.020% by weight of the total composition; calcium < 0.015% by weight of the total composition; copper < 0.010% by weight of the total composition; magnesium < 0.015% by weight of the total composition.;

[0064] The alloy composition at the base of the metal part according to the invention therefore comprises Nickel (Ni) in a content in % by weight relative to the total weight of the composition in the range 38.0 - 42.0, advantageously 39.0 - 42.0, even more advantageously 39.5 - 42.0. In fact, Nickel plays two roles in the alloy: the first is to give the alloy its invar character, i.e. low CET up to approximately 200°C, and the second is to participate in the hardening of the alloy by the formation of y” (second range) or 5 (delta) precipitates, both of composition NisNb. The minimum content of 38.0% nickel is necessary so that 36% of Ni remains in substitution in the austenite after precipitation of all the y" (gamma second) phase possible in order to be in the optimal CET condition. It is not desirable for the Ni content to exceed 42% because then there could be too much Ni substitution in the matrix, which would be detrimental to the CET.The nickel content is measured with an absolute uncertainty of ±0.3%.

[0065] The alloy composition at the base of the metal part according to the invention further comprises niobium (Nb) in a content in % by weight relative to the total weight of the composition in the range 4.750 - 5.500, advantageously 5.000 - 5.500, even more advantageously 5.100 - 5.300. Indeed, niobium mainly allows the formation of small precipitates of the hardening phase γ” (gamma second) in the intergranular state, very compatible with additive manufacturing in that it does not cause cracking problems and with the desired application because it allows the CET not to be greatly increased. Niobium also allows the formation of a small fraction of Nb carbides making it possible to hold the grain during heat treatment, in particular during solution treatment. It is necessary to have an Nb content greater than 4.750 to obtain the desired reinforcement.However, it is not desirable to go beyond 5,500 because this would degrade the CET too much and could induce the precipitation of unwanted phases. The niobium content is measured with an absolute uncertainty of ±0.005%.

[0066] The alloy composition at the base of the metal part according to the invention further comprises Carbon (C) in a content in % by weight relative to the total weight of the composition in the range 0.010 - 0.100, advantageously 0.015 - 0.070, even more advantageously 0.015 - 0.050. Indeed, carbon allows the precipitation at high temperature of Nb carbides which will play a role in blocking the growth of the grain during the heat treatment, in particular during solution treatment. In order to obtain high hardening and elastic limit, it is necessary to control the growth of the grain. It is necessary to have a carbon content of less than 0.100 to allow implementation by additive manufacturing. At this content, the carbon is found in the precipitates, without any remaining in solid solution in the austenite, which would be detrimental to the CET. Carbon content is measured with an absolute uncertainty of ±0.0015%.

[0067] The Cobalt (Co) content of the alloy composition at the base of the metal part according to the invention is <0.400% by weight relative to the total weight of the composition, advantageously <0.100% by weight relative to the total weight of the composition, more advantageously <0.050% by weight relative to the total weight of the composition. Indeed, the cobalt content must be as low as possible because cobalt poses HSE (Health, Safety, Environment) problems during the handling of powders for implementation by additive manufacturing. In an advantageous embodiment, the alloy composition at the base of the metal part only comprises cobalt as an unavoidable impurity. By "only comprises cobalt as an unavoidable impurity", it is meant that the cobalt content is as low as possible, and preferably less than or equal to the measurement tolerance.The alloy composition at the base of the metal part according to the invention can then be said to be "free" of cobalt. The cobalt content is measured with an absolute uncertainty of ±0.003%.

[0068] The Chromium (Cr) content of the alloy composition at the base of the metal part according to the invention is <0.500% by weight relative to the total weight of the composition, advantageously <0.100% by weight relative to the total weight of the composition. Indeed, the chromium content must be as low as possible because the chromium could form carbides during the heat treatment or end up as a solid substitution in the austenite, which would be detrimental to the CET. The chromium content is measured with an absolute uncertainty of ±0.0015%.

[0069] The Silicon (Si) content of the alloy composition at the base of the metal part according to the invention is <0.500% by weight relative to the total weight of the composition, advantageously <0.470% by weight relative to the total weight of the composition. Indeed, the silicon content must be as low as possible because this element is known to segregate in the liquid, which results in either the formation of oxides or the formation of low-melting-point phases which pose problems of implementation by additive manufacturing such as cracking. The silicon content is measured with an absolute uncertainty of ±0.0063%.

[0070] The Manganese (Mn) content of the alloy composition at the base of the metal part according to the invention is <0.500% by weight relative to the total weight of the composition, advantageously <0.400% by weight relative to the total weight of the composition. Indeed, the manganese content must be as low as possible because this element can induce the formation of oxides or carbides harmful to the CET. The manganese content is measured with an absolute uncertainty of ±0.009%.

[0071] In particular, the alloy composition at the base of the metal part according to the present invention can be chosen from one of the 2 examples indicated in tables 1 and 3 of the example part below.

[0072] The metal part according to the invention can be manufactured from an iron-based alloy composition in the form of powder, a forged part, a rolled part or wire, advantageously a powder, in particular intended for additive manufacturing, or a forged part.

[0073] In an advantageous embodiment, the metal part according to the invention can be manufactured from an alloy composition in the form of a wire, used as such or in the form of cables made up of the wire or intended for shaping by wire deposition, according to the different possible processes (by arc, plasma, electron beam or laser).In another advantageous embodiment, the metal part according to the invention can be manufactured from an alloy composition in the form of a powder, intended for shaping by additive manufacturing, advantageously chosen from the group consisting of selective laser powder bed melting (LBM), electron beam melting (EBM), laser powder projection melting such as Direct Additive Laser Construction (CLAD®) or Direct Metal Deposition (DMD) and binder injection on a powder bed (Metal Binder Jetting or MBJ), more particularly it is selective laser powder bed melting (LBM).

[0074] The powder preferably at the base of the metal part according to the invention has a particle size distribution (number diameter) in the range 10 to 60 μm, in particular if it is intended for the manufacture of the part by selective laser powder bed fusion (LBM). Traditionally for this type of particle size cuts, the lower limit of 10 μm, characterized by the D10 in number is controlled by laser diffraction (ASTM B822-17), and the upper cut characterized by the D90 in number of 60 μm is controlled by sieving. The practice of particle size cut control according to the current ASTM B214-16 or ISO 2591'1 of 1988 standard allows control of cuts up to 45 μm by sieving. Below this limit, control by sieve is no longer permitted according to the standard and the characterization is done by the value of the D10 in number of the distribution measured by laser diffraction.

[0075] The metal part according to the invention is preferably chosen from baking molds, injection molds and the constituent elements of these molds. Indeed, its mechanical properties make it particularly suitable for these uses which undergo numerous heating / cooling cycles.

[0076] Manufacturing process

[0077] The present invention further relates to a method for manufacturing a metal part for the manufacture of rubber articles according to the invention made of an iron-based alloy, comprising the following steps :

[0078] A - manufacturing an iron-based alloy powder having the composition of the alloy composition at the base of the metal part according to the invention, advantageously using the following method ■ a- mixing of elementary or pre-alloyed raw materials, b- melting of the mixture obtained in step a), advantageously in a vacuum induction furnace (VIM), c- gas atomization, advantageously with nitrogen, of the product obtained in step b) so as to obtain a powder, advantageously predominantly spherical (i.e. without a vill angle), d- sieving or screening of the powder obtained in step c), advantageously under an inert atmosphere, so as to obtain a desired particle size fraction, e- recovery of the powder obtained.

[0079] The powder particle size is thus adapted according to the additive manufacturing technology or powder deposition process envisaged. The particle size ranges used for the different additive manufacturing or powder deposition processes vary depending on the technology, the equipment and the intended applications. In general, if all applications are combined, the powder used for these processes will have more or less broad number particle size distributions between 5 and 150 |im (as indicated above, the lower limit of 5 pm, characterized by the D10 by number, is controlled by laser diffraction (ASTM B822-17), and the upper cut of 150 pm, characterized by the D90 by number, is controlled by sieving).

[0080] B1 - subjecting the powder obtained in step A) to an additive manufacturing process, advantageously chosen from the group consisting of selective laser powder bed melting (LBM), electron beam melting (EBM), laser powder projection melting such as Direct Additive Laser Construction (CLAD®) or Direct Metal Deposition (DMD) and powder bed binder injection (MBJ), or to a hot isostatic compaction (HIC) treatment with the aim of obtaining a part or

[0081] B2 — subjecting the powder obtained in step A) to a laser melting process by powder projection such as Direct Additive Laser Construction (CLAD®) or Direct Metal Deposition (DMD) followed by forging of the deposit made up of the melted powder,

[0082] C — subjecting the part obtained in step B1) or B2) to at least one thermal and / or physical and / or chemical treatment, advantageously chosen from the group consisting of a relaxation heat treatment, a hot isostatic compaction (HIC) treatment, if step B1) is not a hot isostatic compaction (HIC) treatment, a solution treatment, an aging treatment, a finishing treatment such as a surface modification treatment or a deposition of a protective coating against corrosion and oxidation, and a mixture of these treatments,

[0083] D - recovery of the part thus obtained. The additive manufacturing processes that can be used in the context of the present invention, in particular such as selective laser powder bed melting (LBM), electron beam melting (EBM), laser melting by powder projection such as Direct Additive Laser Construction (CLAD®) or Direct Metal Deposition (DMD) and binder injection on powder bed (MB J), are well known to those skilled in the art.

[0084] In an advantageous embodiment, step B1) consists of an additive manufacturing process which comprises the layer-by-layer manufacturing of the part by using an energy source (laser or electron beam) which melts a thin layer of the superalloy powder according to the invention. A second layer of superalloy powder according to the invention is then deposited and then melted. This process is repeated until the final part is obtained. This is advantageously selective laser powder bed melting (LBM).

[0085] In an advantageous embodiment, step C) of the method according to the invention consists of a solution treatment between 1050°C and 1150°C, advantageously between 1050°C and 1100°C, in particular 1050°C, for 1 hour to 4 hours, advantageously for 1 hour, followed by an aging treatment between 600°C and 700°C, advantageously between 600°C and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours, or a direct aging treatment between 600°C and 700°C, advantageously between 600°C and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours, without solution treatment. Such treatment conditions make it possible to maximize the hardness of the metal part.

[0086] In a particularly advantageous embodiment, step C) of the method according to the invention consists of a direct aging treatment between 600°C and 700°C, advantageously between 600 and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours, without solution treatment. Such treatment conditions make it possible to maximize the hardness of the metal part if it is not desired to carry out a high-temperature heat treatment.

[0087] In another advantageous embodiment, step C) of the method according to the invention consists of a solution treatment between 900°C and 1000°C, advantageously between 900°C and 950°C, in particular 950°C, for 30 min to 1 hour, followed by an aging treatment between 600°C and 700°C, advantageously between 600°C and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours. Such treatment conditions make it possible to maximize the elongation at break of the metal part. The present invention further relates to a method for manufacturing a metal part for the manufacture of rubber articles according to the invention made of an iron-based alloy comprising the following steps: :i- mixture of elementary or pre-alloyed raw materials, ii- melting of the mixture obtained in step i), advantageously in a vacuum induction furnace (VIM), iii- optionally, homogenization by heat treatment of the ingot obtained in step ii), advantageously at a temperature of 1240°C for 4 hours, iv transformation of the ingot obtained in any one of steps ii) or iii) by forging, in particular hot, advantageously with a deformation rate of 80 to 90%, v. recovery of the metal part thus obtained.

[0088] In an advantageous embodiment, the method according to the invention comprises an additional step vi) of subjecting the part obtained in step v) to at least one thermal and / or physical and / or chemical treatment, advantageously chosen from the group consisting of a relaxation heat treatment, a hot isostatic compaction treatment, a solution treatment, an aging treatment, a finishing treatment such as a surface modification treatment or a deposition of a protective coating against corrosion and oxidation, and a mixture of these treatments.

[0089] In an advantageous embodiment, step vi) of the method according to the invention consists of a solution treatment between 1050°C and 1150°C, advantageously between 1050°C and 1100°C, in particular 1050°C, for 1 hour to 4 hours, advantageously for 1 hour, followed by an aging treatment between 600°C and 700°C, advantageously between 600°C and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours, or a direct aging treatment between 600°C and 700°C, advantageously between 600°C and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours, without solution treatment. Such treatment conditions make it possible to maximize the hardness of the metal part.

[0090] In a particularly advantageous embodiment, step vi) of the method according to the invention consists of a direct aging treatment between 600°C and 700°C, advantageously between 600 and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours, without solution treatment. Such treatment conditions make it possible to maximize the hardness of the metal part if it is not desired to carry out a high-temperature heat treatment. In another advantageous embodiment, step vi) of the process according to the invention consists of a solution treatment between 900°C and 1000°C, advantageously between 900°C and 950°C, in particular 950°C, for 30 min to 1 hour, followed by an aging treatment between 600°C and 700°C, advantageously between 600°C and 650°C, in particular 600°C, for 5 hours to 10 hours, advantageously for 5 hours.Such processing conditions allow to maximize the elongation at break of the metal part.

[0091] The present invention further relates to a metal part for the manufacture of rubber articles according to the invention made of an iron-based alloy obtained from an alloy powder, advantageously capable of being obtained using the method of the invention.

[0092] Advantageously, the metal part according to the invention is characterized in that ■ its linear expansion coefficient is less than 3.5 10' 6 / °C, preferably less than 3.4 10' 6 / °C, more preferably < 3.3 10' 6 / °C between 30°C and 200°C according to standard ASTM E 228-17 (2017) and / or it has a tensile strength greater than 1000Pa, advantageously greater than or equal to 1100Pa according to standard ISO6892-1 (2019) and / or it has an HV30 hardness greater than 350HV, in particular greater than 360HV, more particularly greater than 370HV, even more particularly greater than 375HV, according to standard ISO 6507-1 (2018).

[0093] The present invention finally relates to the use of a metal part according to the invention or obtained by one of the methods according to the invention for the manufacture of pneumatic or non-pneumatic tires, rubber tracks, wheels for vehicles, i.e. having a mobility function and / or parts of pneumatic or non-pneumatic tires, rubber tracks or such wheels.

[0094] The present invention will be better understood upon reading the description of the following examples which are given for non-limiting information purposes.

[0095] In the examples, unless otherwise indicated, all percentages are by weight, temperature is in degrees Celsius, and pressure is atmospheric pressure.

[0096] Metallic compositions are determined by measuring the infrared absorption and thermal conductivity of flue gases (LECO) and by inductively coupled plasma (ICP) mass spectrometry. Examples

[0097] Various metal parts are manufactured from iron-based alloys with compositions shown in Tables 1 and 3. Property measurements are listed in Tables 2 and 4.

[0098] Table 1 shows an example 1 of an iron-based alloy for a metal part according to the present invention, strengthened by the precipitation of γ” (gamma second) phase in an amount capable of properly hardening the alloy. A standard Invar 36 type alloy, without hardening elements, with the same levels of residuals was produced as a reference, as well as four counter-example alloys.

[0099] Counterexample 1 is an iron-based alloy reinforced by the y” phase (gamma second) in a content lower than that of the alloy of a part according to the invention (the Nb content is less than 4.75 as a percentage by weight of the total composition).

[0100] Counterexample 2 is an iron-based alloy strengthened by the precipitation of molybdenum carbides, with a Mo content of 3.97 weight percent and a C content of 0.236 weight percent.

[0101] Counterexample 3 is an iron-based alloy strengthened by the precipitation of molybdenum and niobium carbides, with weight percentage contents of 3.95 in Mo, 0.475 in Nb and 0.212 in C. These Mo, Nb and C contents are within the windows claimed by patent application WO03025239 with a Mo content of 1.5 to 6, an Nb content less than or equal to 0.5 and a C content of 0.2 to 0.4.

[0102] Counterexample 4 is an iron-based alloy strengthened by the precipitation of vanadium carbides, with a V content of 0.899 and a C content of 0.204. These V and C contents are very close to those of invar—V from the publication Nakama et al. (Metallogr. Microstruct. Anal. (2 (2013) 383-387), with a V content of 0.8 and a C content of 0.203.

[0103] [Table 1]

[0104] Table 2 shows the results of maximum mechanical strength, Rm (according to ISO 6892-R2019) at room temperature, Vickers hardness HV30 (according to ISO 6507-02018) at room temperature, and coefficient of thermal expansion between 30 and 200°C (CET) measured according to ASTM E228. _17(2017) for example 1, the invar 36 reference and the 4 counterexamples after the following implementation ■ vacuum furnace elaboration (VIM) of 6kg ingots, homogenization at 1240°C for 4 hours, hot forging by drawing with a pestle with a deformation rate between 80 and 90% followed by air cooling and heat treatment. The final heat treatment is different depending on the alloys, and the results reported are the best obtained. Example 1 underwent aging at 600°C for 5 h followed by air cooling, counter-examples 1, 2 and 3 underwent precipitation aging at 650°C for 5 h followed by air cooling, the reference alloy Invar 36 underwent treatment at 1100°C for 1 h followed by water cooling, and counter-example 4 underwent solution treatment at 1250°C for 1 h followed by water cooling and aging at 650°C for 5 h followed by air cooling.The y” phase precipitation (gamma second) strengthening strategy used to strengthen the alloy allows to obtain the best hardening for a limited increase in the CET, compared to the reference Invar 36 and to the 4 counter-examples produced with the same residual levels and iso-transformation range. In addition, the low hardness level of counter-example 1, with a Nb content of 2.81, shows that it is necessary to have a Nb content higher than 4.75 to obtain the desired strengthening. On the other hand, it is not desirable to go beyond 5.5 because this would degrade the CET too much and could induce the precipitation of unwanted phases.

[0105] Furthermore, these results show the strong influence of the transformation range, and in particular of the cold spinning or drawing steps in the hardening. Indeed, counter-example 3, whose Mo, Nb and C contents are within the windows claimed by patent WO03025239, has an Rm equal to 795MPa against 1300MPa for the wire produced according to patent WO03025239. Comparison of the results obtained for counter-example 4, with an Rm equal to 794MPa to that of the publication by Nakama et al. (Metallogr. Microstruct. Anal. 2 (2013) 383-387), with an Rm of 1010MPa after cold transformation steps, confirms this contribution of the transformation in the hardening.

[0106] It appears that at the same transformation range, the alloy strengthening strategy with a Ni rate between 38.0 and 42.0, an Nb rate between 4.750 and 5.500 and a C rate between 0.010 and 0.100 provides the best compromise between hardening and low CET.

[0107] [Table 2]

[0108] Example 1, in another test, was heat treated by solution treatment at 1050°C for 1 h followed by water cooling and then aging at 600°C for 5 h followed by air cooling, after forging. In this case, the Rm is equal to 1129 MPa, the elongation to 15.5%, the hardness HV30 measured according to ISO 6507-1 : 2018 at 378HV and the CET between 30°C and 200°C is 3.09xl0' 6 / °C. The CET is also measured on this sample between 30°C and 100°C, between 30°C and 300°C and between 30°C and 400°C. The results obtained are respectively 2.47xlO' 6 / °C, 5, 16xlO' 6 / °C and 7.49xlO' 6 / °C. Thus, the CET remains low even for a temperature range of 30°C to 400°C.

[0109] Table 3 shows the composition of an example 2 of an iron-based alloy for a metal part according to the present invention and of a counter-example 5 reinforced by the precipitation of vanadium carbides produced under vacuum then gas atomized in powder form, sieved, shaped by the additive manufacturing process of laser fusion on powder bed with a layer thickness of 50 pm and a lasing strategy at + / - 45 0 (i.e. a 90° rotation between each successive layer) then heat treated at 1050°C for 1h followed by air cooling then aged at 600°C for 5h followed by air cooling for example 2 and at 650°C for 5h followed by air cooling for counter-example 5.

[0110] [Table 3] Table 4 shows the Vickers HV30 hardnesses obtained for example 2 and counter-example 5 after obtaining parts by the laser powder bed fusion process and the heat treatment indicated above.

[0111] [Table 4] Example 2 of the alloy according to the invention, produced by powder processing and additive manufacturing, confirms the level of hardness obtained for example 1 by the forged route. Counter-example 5 confirms that the hardening achieved by reinforcement by precipitation of vanadium carbides does not allow such a high level of hardness to be obtained.

[0112] Table 5 shows the tensile strengths Rm and the elongations at break A% obtained after different heat treatments carried out on a metal part based on the alloy of example 2. The index "H" corresponds to a test carried out on a test piece manufactured horizontally, while the index "V" corresponds to a test carried out on a test piece manufactured vertically. It can be seen that it is possible to modulate the heat treatment to obtain a metal part by promoting its hardness or its elongation at break.

[0113] [Table 5]

Claims

CLAIMS

1. Metal part for the manufacture of rubber articles based on an iron-based alloy composition comprising, advantageously consisting essentially of, in percentages by weight of the total composition ■ Nickel ■ 38.0 - 42.0, preferably 39.0 - 42.0 Niobium: 4,750 - 5,500, preferably 5,000 - 5,500; Carbon: 0.010 - 0.100, preferably 0.015 - 0.070; Cobalt: <0.400, preferably <0.100 Chromium ■ <0.500 Silicon: <0.500 Manganese ■ <0.500; Iron ■ balance as well as unavoidable impurities, at least one of the following conditions of content in percentage by weight of the total composition is met ■ nitrogen < 0.030% by weight of the total composition; oxygen < 0.040% by weight of the total composition; hydrogen < 0.0050% by weight of the total composition; sulfur < 0.0150% by weight of the total composition phosphorus < 0.0150% by weight of the total composition; aluminum < 0.100% by weight of the total composition titanium < 0.100% by weight of the total composition; vanadium < 0.100% by weight of the total composition molybdenum < 0.020% by weight of the total composition; calcium < 0.015% by weight of the total composition copper < 0.010% by weight of the total composition; magnesium < 0.015% by weight of the total composition.

2. Metal part according to claim 1, characterized in that the iron-based alloy comprises at most 1.00% by weight of unavoidable impurities, advantageously at most 0.50% by weight.

3. Metal part according to any one of claims 1 to 2, characterized in that the iron-based alloy comprises at most 0.050% by weight of cobalt relative to the total weight of the composition, preferably only comprising cobalt as an unavoidable impurity.

4. Metal part according to any one of claims 1 to 3 chosen from cooking molds, injection molds and the constituent elements of these molds.

5. A method of manufacturing a metal part according to any one of claims 1 to 4, comprising the following steps: ■ • A - manufacturing an iron-based alloy powder having the composition of the alloy composition at the base of the metal part according to any one of claims 1 to 4 according to the following steps ■ a) mixing of elementary or pre-alloyed raw materials, b) melting of the mixture obtained in step a), advantageously in a vacuum induction furnace, c) atomization with gas, advantageously with nitrogen, of the product obtained in step b) so as to obtain a powder, d) sieving or screening of the powder obtained in step c) so as to obtain a desired particle size fraction, e) recovery of the powder obtained. • B1 - subjecting the powder obtained in step A) to an additive manufacturing process, advantageously chosen from the group consisting of selective laser powder bed melting (LBM), electron beam melting (EBM), laser powder projection melting such as Direct Additive Laser Construction or Direct Metal Deposition (DMD) and powder bed binder injection (MBJ), or to a hot isostatic compaction treatment with the aim of obtaining a part or • B2 — subjecting the powder obtained in step A) to a laser melting process by powder projection such as Direct Additive Laser Construction or Direct Metal Deposition (DMD) followed by forging of the deposit made up of the melted powder, • C — subjecting the part obtained in step B1) or B2) to at least one thermal and / or physical and / or chemical treatment, advantageously chosen from the group consisting of a relaxation heat treatment, a hot isostatic compaction treatment if step B1) is not a hot isostatic compaction treatment, a solution treatment, an aging treatment, a finishing treatment such as a surface modification treatment or a deposit of a protective coating against corrosion and oxidation, and a mixture of these treatments, • D - recovery of the part thus obtained.

6. Method according to claim 5, characterized in that step B1) is a selective powder bed laser fusion (LBM).

7. Method according to any one of claims 5 or 6, characterized in that step C) consists of a solution treatment between 1050°C and 1150°C for 1 hour to 4 hours followed by an aging treatment between 600°C and 700°C for 5 hours to 10 hours, or a direct aging treatment between 600°C and 700°C for 5 hours to 10 hours without solution treatment.

8. Method according to any one of claims 5 or 6, characterized in that step C) consists of a solution treatment between 900°C and 1000°C, for 30 min to 1 hour, followed by an aging treatment between 600°C and 700°C, for 5 hours to 10 hours.

9. Method for manufacturing a metal part according to any one of claims 1 to 4, comprising the following steps: i. mixing of elementary or pre-alloyed raw materials, ii. melting of the mixture obtained in step i), advantageously in a vacuum induction furnace, iii. optionally, homogenization by heat treatment of the ingot obtained in step ii), iv. transformation of the ingot obtained in any one of steps ii) or iii) by forging, v. recovery of the part thus obtained, vi.preferentially, subjecting the part obtained in step v) to at least one thermal and / or physical and / or chemical treatment, advantageously chosen from the group consisting of a relaxation thermal treatment, a hot isostatic compaction treatment, a solution treatment, an aging treatment, a finishing treatment such as a surface modification treatment or a deposit of a protective coating against corrosion and oxidation, and a mixture of these treatments.

10. Method according to claim 9, characterized in that step vi) consists of a solution treatment between 1050°C and 1150°C for 1 hour to 4 hours followed by an aging treatment between 600°C and 700°C for 5 hours to 10 hours, or a direct aging treatment between 600°C and 700°C for 5 hours to 10 hours without solution treatment.

11. Method according to claim 9, characterized in that step vi) consists of a solution treatment between 900°C and 1000°C, for 30 min to 1 hour, followed by an aging treatment between 600°C and 700°C, for 5 hours to 10 hours.

12. Metal part according to any one of claims 1 to 4 or obtained by a method according to any one of claims 5 to 11, characterized in that ■ • its linear expansion coefficient is less than 3.5 10 _ 6 / °C between 30°C and 200°C according to ASTM E228-17 (2017) and / or • it has a tensile strength greater than 1000Pa according to standard ISO6892-R2019 and / or • it has an HV30 hardness greater than 350HV according to the ISO 6507-E2018 standard.

13. Use of a metal part according to any one of claims 1 to 4 or obtained by a process according to any one of claims 5 to 11 for the manufacture of pneumatic or non-pneumatic tires, rubber tracks, vehicle wheels and / or parts of pneumatic or non-pneumatic tires, rubber tracks or such wheels.

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