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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
• • 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
• • 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
  • C21D7/00—Modifying the physical properties of iron or steel by deformation
  • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
  • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
• • 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 by deformation combined with, or followed by, heat treatment
  • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
• • 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
  • C21D9/0068—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for particular articles not mentioned below
• • 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
  • C21D9/0075—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for rods of limited length
• • 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
  • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
• • 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
• • 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
  • C21D2221/00—Treating localised areas of an article
  • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
• • 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
  • C21D2261/00—Machining or cutting being involved
• • 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
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • 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
  • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
• • 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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
• • 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
  • C22C38/30—Ferrous alloys, e.g. steel alloys containing chromium with cobalt
• • 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
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• TITLE Non-magnetic timepieces and thermomechanical treatment process for obtaining such parts.
• the present invention relates to an austenitic alloy part, preferably a stainless steel alloy.
• This alloy can be used for the manufacture of non-magnetic parts.
• This alloy is suitable, in particular, for the manufacture of non-magnetic parts of revolution comprising a mechanical axis.
• the present invention also relates to a thermomechanical treatment process for the implementation of such non-magnetic parts composed of such an alloy.
• the present invention relates, for example, to timepieces and in particular, but not exclusively, to balances or balance shafts, anchor rods or even escapement pinions.
• timepieces and in particular the balance wheel, must have good resistance to shocks, to breakage, to deformation and to wear.
• the balance wheel is one of the most important timepieces in that it is the regulating organ.
• the pendulum moves back and forth regularly, oscillating around its axis.
• the balance shaft supports the spiral spring and includes a pivot at each of its two ends.
• timepieces are known, in particular balance shafts, made of steel, for example steels of the 20AP type and of the FINEMAC type.
• 20AP steel contains lead which is a toxic element to be banned.
• Another disadvantage is that these steels are likely to exhibit residual magnetization or remanence after being subjected to external magnetic fields. This residual magnetization disturbs the functioning of the parts of the regulating organs.
• Processes for manufacturing timepieces aimed at shaping the parts and improving their resistance to shocks, to breakage and to wear are known in the state of the prior art.
• processes for manufacturing timepieces from steel of the 20AP type and of the FINEMAC type are known.
• a disadvantage of these methods is that they require the implementation a quenching step followed by tempering aimed at relieving the mechanical stresses generated in the material during quenching.
• thermomechanical hardening treatment methods of the state of the art make the manufactured parts more fragile and therefore more likely to break during their use.
• An object of the invention is in particular:
• an austenitic alloy comprising, in mass percentage, iron between 50 and 85%, one or more gammagenic elements whose mass percentage or the sum of the mass percentages is between 8 and 38% and nitrogen at a mass percentage of less than 2%; said austenitic alloy has a crystallographic structure comprising a predominant cubic crystal structure, preferably face-centered cubic, and a presence of a hexagonal crystal structure, preferably compact hexagonal, and/or a presence of nitrogen atoms bordering or surrounding or enveloping or located around dislocations of the alloy, preferably around dislocations of the alloy.
• the nitrogen atoms have the effect of blocking the movement of said dislocations in the alloy and therefore of increasing the hardness of the alloy.
• the austenitic alloy does not contain nickel.
• the alloy comprises a mass percentage of nitrogen of less than 1.9%, more preferably 1.8%, more preferably 1.7%, more preferably 1.6%, so more preferably still 1.5%, particularly preferably 1.4%, most preferably 1.3%.
• the alloy comprises precipitates, or crystalline precipitates, of hexagonal crystallographic structure, preferably compact hexagonal.
• the presence of hexagonal crystal structure is comprised in, preferably constituted by, the precipitates.
• a Feret diameter of the precipitates is between 5 and 80 nm.
• the austenitic alloy may comprise nitrogen at a mass percentage greater than 0.1%, preferably greater than 0.3%.
• the gammagenic element(s) may comprise, in mass percentage, manganese between 8 to 30% and/or cobalt between 0 and 10%, preferably between 0 and 5% of cobalt, and/or carbon between 0.1 and 0.3%.
• the alloy may comprise one or more non-gamgenic elements whose mass percentage or the sum of the mass percentages is between 8 and 35% or between 10 and 35%, preferably between 13 and 35%, more preferably between 15 and 35 %, more preferably between 17 and 33%, so more preferably between 19 and 31% and most preferably between 20 and 30%.
• the mass percentage or the sum of the mass percentages of the non-gammagenic element(s) is less than 30%.
• the mass percentage or the sum of the mass percentages of the gammagenic element(s) is greater than 8%, preferably greater than 15%.
• the mass percentage or the sum of the mass percentages of the gammagenic element(s) is between 15 and 38%.
• the non-gammagenic element(s) may comprise, in mass percentage, chromium between 0 and 35% and/or molybdenum between 0 and 8% and/or silicon between 0 and 2% and/or titanium between 0 and 1% and/or niobium between 0 and 1% and/or tungsten between 0 and 1% and/or sulfur between 0 and 1.5%.
• the non-gammagenic element(s) comprise, in mass percentage, chromium between 8 and 35%, more preferably between 10 and 35%, more preferably between 12 and 35%, more preferably between 15 and 35%, more preferably between 17 and 33%, particularly advantageously between 19 and 31% and most preferably between 20 and 30%.
• the austenitic alloy comprises chromium in a mass percentage greater than 8%.
• the austenitic alloy comprises chromium, in mass percentage, between 8 and 35%, more preferably between 10 and 35%, more preferably between 12 and 35%, more preferably between 15 and 35% , more preferably between 17 and 33%, particularly advantageously between 19 and 31% and most preferably between 20 and 30%.
• the alloy comprises a work-hardened austenitic phase, denoted /work-hardened, whose lattice parameter is preferably 0.3635 nm, and a non-work-hardened austenitic phase, denoted /non-work-hardened, whose lattice parameter is , preferably 0.360 nm.
• the alloy according to the invention does not comprise martensite.
• the alloy according to the invention does not include ferrite.
• the alloy according to the invention may comprise a reformed or undeformed austenitic phase, the lattice parameter of which is preferably 0.360 nm, and a deformed austenitic phase, the lattice parameter of which is preferably 0, 3632 nm.
• the alloy comprises the reformed, or undeformed, austenitic phase.
• the work-hardened alloy does not comprise a deformed austenitic phase.
• the reformed austenitic phase is located on the dislocations or on the slip bands.
• the reformed austenitic phase is located at the grain boundaries.
• the alloy comprises nitride precipitates.
• the nitride precipitates help to immobilize the dislocations.
• the nitride precipitates contribute to increasing the hardness of the alloy.
• the nitride precipitates are intra and/or intergranular, that is to say located in the grains and/or in the grain boundaries.
• the nitride precipitates are located at the level of the dislocations, preferably at the level of the slip bands.
• the nitride precipitates are uniformly distributed within the alloy.
• a size of the nitride precipitates is less than 300 nm, preferably 250 nm, more preferably 200 nm, more preferably 150 nm and even more preferably 100 nm.
• the size of the nitride precipitates of the alloy and/or the uniform distribution of the nitride precipitates in the alloy has the effect of increasing the hardness of the alloy.
• the nitride precipitates comprise chromium nitrides, more preferably chromium CrzN heminirides.
• the alloy comprises an austenitic phase having a nitrogen concentration of less than or equal to 0.6%, preferably 0.5%, more preferably 0.4% and more preferably 0.3%.
• the alloy comprises an austenitic phase having a nitrogen concentration greater than or equal to 0.7%, preferably 0.8%, more preferably 0.9%, more preferably 1% and most preferably 1.1%.
• the austenitic phase having a nitrogen concentration of less than or equal to 0.6%, preferably 0.5%, more preferably 0.4% and more preferably 0.3% is the austenitic phase reformed.
• the austenitic phase having a nitrogen concentration greater than or equal to 0.7%, preferably 0.8%, more preferably 0.9%, more preferably 1% and more preferably between all at 1.1% is the deformed austenitic phase.
• the reformed austenitic phase comprises a superstructure.
• superstructure an ordered crystalline structure obtained by the effect of temperature, preferably by heating, on a disordered structure.
• the reformed austenitic phase comprises a disordered phase, denoted y', and a phase comprising a superstructure, denoted y".
• the y' phase does not comprise a superstructure.
• the y' phase is a minority within of the reformed austenitic phase.
• the y′′ phase predominates within the reformed austenitic phase.
• the superstructure helps to immobilize the dislocations.
• the superstructure contributes to increasing the hardness of the alloy.
• a ratio between the deformed austenitic phase and the reformed austenitic phase is greater than 25%, preferably 35%, more preferably 45% and more preferably 50%.
• a ratio between the deformed austenitic phase and the reformed austenitic phase is greater than 60%, preferably 70%, more preferably 80% and more preferably 90%.
• a grain size of the alloy is less than 5 ⁇ m, more preferably less than 1 ⁇ m.
• the grain size of the alloy is less than 900 nm, more preferably less than 800 nm, more preferably less than 700 nm, even more preferably less than 600 nm and most preferably less than 600 nm. 500nm. It can be understood by “size of the grains of the alloy”, the size of each of the grains constituting the alloy. Such a grain size of the alloy according to the invention has the effect of increasing the hardness of the alloy.
• non-magnetic part comprising an austenitic alloy, preferably made of or composed of, an austenitic alloy according to the invention.
• the non-magnetic part is a mechanical part.
• the non-magnetic part can be a part of revolution.
• the non-magnetic part can be oblong, conical, frustoconical or cylindrical.
• At least part of a surface of the non-magnetic part can have a hardness greater than or equal to 700 HV where HV is the Vickers hardness.
• the surface of the non-magnetic part can be an external surface of the magnetic part.
• the arithmetic roughness of at least part of the surface of the non-magnetic part corresponding to at least part of the surface of the work-hardened and smoothed mechanical part is less than 0.4 ⁇ m, more preferably than 0.3 ⁇ m, more preferably 0.2 ⁇ m, more preferably 0.1 ⁇ m, particularly advantageously 0.05 ⁇ m and most preferably 0.025 ⁇ m.
• the non-magnetic part may include a surface layer.
• the non-magnetic part may comprise a surface layer extending radially, from the at least part of the surface towards the inside of the non-magnetic part, over a distance, referred to as the thickness of the surface layer, of less than 30 ⁇ m.
• the thickness of the surface layer can be defined as the dimension or magnitude of the surface layer in the direction extending radially from the at least part of the surface of the non-magnetic part towards the interior of the non-magnetic part.
• the thickness of the surface layer is less than 25 ⁇ m, more preferably 20 ⁇ m, more preferably 15 ⁇ m, more preferably 10 ⁇ m, more preferably 8 ⁇ m, more preferably more preferably still at 7 ⁇ m, particularly advantageously at 6 ⁇ m and most preferably at 5 ⁇ m.
• the non-magnetic part may comprise a central part extending from the surface layer towards the inside of the non-magnetic part, said central part having a hardness less than or equal to 600 HV and/or a work hardening rate of less than 85%.
• the central part can extend from an interface or a surface separating the surface layer from the central part towards the inside of the non-magnetic part.
• the surface layer may comprise a hardness gradient, and/or respectively a strain hardening rate gradient, along the direction extending radially from the surface of the at least part of the non-magnetic part towards the inside of the part non-magnetic, said hardness gradient having a value greater than or equal to 100 HV and/or respectively said strain hardening rate gradient having a value greater than 14%.
• hardness gradient having a value greater than or equal to 100 HV is understood to mean a variation in hardness between the surface of at least part of the non-magnetic part and the central part greater than or equal to 100 HV or a difference between the hardness of the surface of the at least part of the non-magnetic part and the hardness of the central part which is greater than or equal to 100 HV.
• the term “gradient in hardening rate having a value greater than 14%” is understood to mean a variation in hardening rate between the surface of at least a part of the non-magnetic part and the upper central part or equal to 14% or a difference between the hardening rate of the surface of the at least part of the non-magnetic part and the hardening rate of the central part which is greater than or equal to 14%.
• the hardness gradient of the surface layer is greater than 125 HV, more preferably than 150 HV, preferably 175 HV, more preferably 200 HV, even more preferably 225 HV and most preferably at 250 HV and/or the hardening rate of the layer surface area is greater than 18%, more preferably 21%, more preferably 25%, more preferably 29%, more preferably 32% and most preferably 35% .
• the hardness and/or the hardening rate of the surface layer decreases along the direction extending from the surface of the non-magnetic part towards the inside of the non-magnetic part.
• the at least part of the surface of the non-magnetic part constitutes a part of revolution of the non-magnetic part.
• the surface of the at least part of the surface of the non-magnetic part is a surface of revolution.
• the at least part of the surface of the non-magnetic part is a surface defining or delimiting a friction zone of the non-magnetic part.
• the at least part of the surface of the non-magnetic part comprises or constitutes an end, a crest, a summit or, preferably, a pivot or a pivot zone of the non-magnetic part.
• non-magnetic a material whose relative permeability is less than 10, preferably less than 7, more preferably less than 5, more preferably less than 4, more preferably less than 3, more preferably less than 2. , more preferably 1.1, particularly preferably 1.05 and most preferably 1.01.
• a hardness, and/or respectively the hardening rate, of the at least part of the surface of the non-magnetic part, corresponding to the at least part of the work-hardened and heated mechanical part is greater or equal to 700 HV, preferably 750 HV, more preferably 800 HV, preferably 850 HV, more preferably 900 HV, even more preferably 950 HV and so as to the most preferred advantage is 1000 HV where HV is the Vickers hardness and/or respectively is greater than 100%, preferably 107%, more preferably 114%, more preferably 121%, more preferably preferably 128%, more preferably 135% and most preferably 142%.
• a maximum resistance of the non-magnetic part is greater than 2200 MPa, more preferably greater than 2500 MPa.
• an elongation at break of the non-magnetic part is greater than 1.5%, preferably greater than 2.5%.
• the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the work-hardened and heated mechanical part can comprise a friction zone of the non-magnetic part or part of a mechanical axis of the non-magnetic part.
• the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the at least part of the work-hardened and heated mechanical part can comprise a friction zone of a mechanical axis of the non-magnetic part.
• the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the work-hardened and heated mechanical part can comprise a pivot of the mechanical axis of the non-magnetic part.
• the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the work-hardened and heated mechanical part can be an outer surface defining or delimiting the whole of the mechanical axis and/or a end portion of the mechanical shaft and/or may comprise an outer surface defining or delimiting the pivot of the mechanical shaft.
• a diameter, for example maximum or average, of the part of the non-magnetic part comprising the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the work-hardened and heated mechanical part can be less to 2 mm, preferably to 1 mm.
• the diameter of the part of the non-magnetic part comprising the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the work-hardened and heated mechanical part is less than 0.9 mm, more preferably 0.8 mm, more preferably 0.7 mm, more preferably 0.6 mm and most preferably less than 0.5 mm .
• the diameter of the part of the non-magnetic part comprising the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the work-hardened and heated mechanical part is less than 0, 4mm, more preferably 0.3mm, more preferably 0.2mm and most preferably less than 0.1mm.
• a diameter of the pivot of the mechanical shaft may be less than 0.1 mm, more preferably 0.08 mm, more preferably 0.06 mm, even more preferably 0.04 mm and most preferably less than 0.03 mm
• the non-magnetic part is a timepiece.
• the timepiece is a balance wheel or balance shaft, an anchor rod or an escapement pinion.
• non-magnetic part according to the invention is also proposed, for its non-magnetic and/or hardness and/or tribological properties and/or breaking strength and/or resilience.
• non-magnetic part as a mechanical part or as a timepiece is also proposed.
• - a step of heating the mechanical part or part of the mechanical part comprising the at least part of the surface of the part or the at least part of the surface of the work-hardened mechanical part to a temperature comprised between 350°C and 700°C to harden the work-hardened part(s) of the mechanical part.
• the part or parts of the hardened mechanical part comprise at least a part of the surface of the mechanical part.
• the part or parts of the hardened mechanical part that is to say work-hardened and heated, can comprise one or more parts work-hardened prior to the implementation of the process.
• the method does not include a step implemented subsequent to the heating step.
• hardened mechanical part is understood to mean the mechanical part obtained after implementation of the surface hardening step.
• the surface hardening step is implemented by machining at least part of the surface of the mechanical part.
• Surface hardening can also be carried out by rolling.
• a machining step can be performed prior to the rolling step.
• the surface hardening step and therefore the machining used to implement the surface hardening step, does not aim to remove or remove material from the mechanical part from the at least part of the surface of the mechanical part.
• the surface hardening step and therefore the machining used to implement the surface hardening step, does not remove or remove material from the mechanical part from the at least one part of the surface of the mechanical part.
• Machining can be turning.
• Machining can be bar turning.
• the method does not include quenching of the mechanical part.
• the method does not include stress relief annealing for the relaxation of mechanical stresses.
• stress relief annealing a step of heating to a temperature below 350°C.
• the purpose of stress relief annealing is to eliminate the residual stresses accumulated during the manufacture of the part.
• the heating step is implemented on the mechanical part as a whole.
• the obtaining step may consist of obtaining the mechanical part.
• the surface of the mechanical part is an external surface of the mechanical part.
• the mechanical part can be a part of revolution.
• the mechanical part can be oblong, conical, frustoconical or cylindrical.
• the at least part of the surface of the mechanical part can constitute a part of revolution of the mechanical part.
• the at least part of the surface of the mechanical part can be a surface of revolution.
• the term work hardening can be understood to mean a relative variation in length and/or section, in the zone of plastic deformation, of an object.
• the relative variation can be defined with respect to an initial state of the object, here the mechanical part, in which it is not hardened.
• At least part of the surface of the work-hardened mechanical part or the mechanical part as a whole is heated to a temperature between 350° C. and 700° C., more preferably still between 400°C and 680°C, more preferably between 450°C and 650°C and even more preferably between 500°C and 600°C.
• At least part of the surface of the work-hardened mechanical part or the mechanical part as a whole is heated to a temperature above 350° C., more preferably still at 400° C., more preferably at 450°C and even more preferably at 500°C and at a temperature below 700°C, more preferably at 680°C, more preferably at 650°C and even more preferably at 600°C.
• the mechanical part is composed of an austenitic alloy comprising iron between 50 and 85%, one or more gammagenic elements whose mass percentage or the sum of the mass percentages is between 8 and 38% and nitrogen at a mass percentage of less than 2%, preferably a mass percentage of nitrogen greater than 0.1%.
• the chemical element composition of the mechanical part is identical to that of the austenitic alloy according to the invention.
• the austenitic alloy does not contain nickel.
• the surface hardening step induces surface hardening of the part of the mechanical part comprising at least a part of the surface of the mechanical part.
• the work hardening rate of at least a part of the surface of the non-magnetic part corresponding to the at least part of the surface of the hardened mechanical part, obtained by implementing the step of work hardening is greater than 100%, preferably 107%, more preferably 114%, more preferably 121%, more preferably 128%, even more preferably 135% and most preferably 142%.
• the surface layer after heating, may have a hardness gradient, along the direction extending radially from the surface of the at least part of the non-magnetic part towards the inside of the non-magnetic part, of a value greater than or equal to 100 HV.
• the at least part of the surface of the non-magnetic part corresponding to the at least part of the surface of the work-hardened and heated mechanical part can have a hardness greater than or equal to 700 HV.
• the surface layer has a work hardening rate gradient, along the direction extending radially from the surface of the at least part of the hardened mechanical part towards the inside of the hardened mechanical part, greater than 14 or 18%, more preferably 21%, more preferably 25%, more preferably 29%, more preferably 32% and most preferably 35%.
• a work hardening depth, relative to at least a portion of the surface of the work hardened mechanical part, obtained by implementing the surface work hardening step may be less than 30 ⁇ m, preferably less than 25 ⁇ m , more preferably 20 ⁇ m, more preferably 15 ⁇ m, more preferably 10 ⁇ m, more preferably 8 ⁇ m, even more preferably 7 ⁇ m, particularly advantageously 6 pm and most preferably at 5 pm.
• the work hardening depth corresponds to or is equal to the thickness of the surface layer of the non-magnetic part.
• the step of heating the at least part of the surface of the mechanical part is, preferably, carried out directly after the step of the surface hardening of the mechanical part.
• the method does not include heating, preferably no step heating, of the surface layer of the non-magnetic part, formed during the surface hardening step, to a temperature greater than 700°C, preferably 680°C, more preferably 650°C, more preferred at 600°C.
• - can be implemented for a period of between 10 minutes and 400 hours, preferably between 20 minutes and 4 hours, more preferably between 30 minutes and 2 hours, more preferably for a period of 1 hour, and /Where
• - may include a temperature gradient of between 4°C/min and 400°C/min, preferably a gradient of 50°C/min, and/or
• - can be implemented under ambient conditions or in a controlled atmosphere.
• the temperature gradient is implemented during the rise and/or during the fall in temperature.
• the controlled atmosphere can be a neutral atmosphere.
• the neutral atmosphere can be an atmosphere containing no reactive species, for example no oxidizing or corrosive species.
• the controlled atmosphere can be nitrogen or a rare gas, for example argon.
• the step of obtaining the mechanical part can comprise a step of turning at least a part of a bar turning to form the mechanical part of which at least part of a surface of the part mechanism having a hardness greater than 350 HV, where HV is the Vickers hardness, and/or a strain hardening rate greater than 50%.
• the step of obtaining the mechanical part can comprise a step of hardening at least part of a raw bar to form the mechanical part, at least part of a surface of the part mechanism having a hardness greater than 350 HV, where HV is the Vickers hardness, and/or a work hardening rate greater than 50%.
• the raw bar can be:
• non work-hardened bar in other words an annealed bar
• the step of obtaining the mechanical part can comprise a step of turning at least part of a bar turning bar followed by a step of hardening the at least one turned part of the free-cutting bar, or the free-cutting bar as a whole, to form the mechanical part, of which at least part of a surface of the mechanical part has a hardness greater than 350 HV, where HV is the Vickers hardness, and /or a hardening rate greater than 50%.
• the step of obtaining the mechanical part can comprise a step of hardening at least part of a raw bar, or of the raw bar as a whole, followed by a step of turning of at least a part of the raw bar work-hardened to form the mechanical part, of which at least part of a surface of the mechanical part has a hardness greater than 350 HV, where HV is the Vickers hardness, and/or a hardening rate greater than 50%.
• the raw bar can be:
• non work-hardened bar in other words an annealed bar
• the at least part of the raw bar, before hardening comprises a surface having, preferably, a hardness greater than or equal to 250 HV, preferably 280 HV and/or a hardness rate work hardening greater than or equal to 0%, more preferably equal to 0%.
• the at least part of the raw bar, before hardening comprises a surface having, preferably, a hardness of between 250 and 300 HV and/or a hardening rate equal to 0%. .
• the step for obtaining may comprise a step consisting in obtaining the raw bar, at least part of which comprises a surface having a hardness greater than or equal to 250 HV, preferably 280 HV and /or a hardening rate greater than or equal to 0%, more preferably equal to 0.
• the step of obtaining can comprise a step consisting in procuring the raw bar of which at least one part comprises a surface having a hardness of between 250 and 300 HV and/or a hardening rate equal to 0%.
• the at least part of the raw bar, before work hardening comprises a surface having, preferably, a hardness greater than or equal to 350 HV, preferably 400 HV and/ or a hardening rate greater than or equal to 20%, preferably still greater than 30%.
• the at least part of the raw bar, before work hardening comprises a surface having, preferably, a hardness of between 350 HV and 400 HV and/or a rate of work hardening between 20% and 30%.
• the step for obtaining may comprise a step consisting in obtaining the raw bar, at least part of which comprises a surface having a hardness greater than or equal to 350 HV, preferably at 400 HV and/or a hardening rate greater than or equal to 20%, preferably still greater than 30%.
• the step for obtaining may comprise a step consisting in obtaining the raw bar, at least part of which comprises a surface having a hardness of between 350 HV and 400 HV and/ or a hardening rate of between 20% and 30%.
• the at least part of the free-cutting bar, before free-cutting preferably has a hardness greater than or equal to 325 HV, more preferably 350 HV, preferably 375 HV and more preferably 400 HV and/or a hardening rate greater than or equal to 15%, more preferably 20%, more preferably 25% and more preferably 30.
• the at least part of the free-cutting bar, before free-cutting preferably has a hardness of between 350 and 400 HV and/or a hardening rate of between 20 and 30 %.
• the step for obtaining may comprise a step consisting in obtaining a bar turning bar of which at least a part has a hardness greater than or equal to 325 HV, preferably 350 HV, of more preferably at 375 HV and more preferably at 400 and/or a strain hardening rate greater than or equal to 15%, more preferably at 20%, more preferably at 25% and more preferably at 30 %.
• the step for obtaining may comprise a step consisting in procuring the bar turning bar, at least a part of which has a hardness of between 350 and 400 HV and/or a hardening rate of between 20 and 30%.
• the bar turning bar is preferably a bar calibrated in diameter.
• the bar turning is preferably a bar calibrated in diameter and hardened, preferably hardened by drawing.
• the bar turning and/or the bar turning and/or the raw bar and/or the hardened raw bar can be a bar of revolution, and/or
• the bar turning and/or the bar turning and/or the raw bar and/or the hardened raw bar can be oblong in shape;
• the bar turning and/or the bar turning and/or the raw bar and/or the work-hardened raw bar can have a cylindrical shape, such as a rod or a tube, and/or
• the at least part of the free-cut bar can be the whole of the free-cut bar and/or the at least part of the raw bar can be the whole of the raw bar, and/or
• the free-cutting step may comprise the formation of a surface of revolution, on the free-cut bar, defining or delimiting a part of the free-cut bar, and/or
• the bar-cutting step may include a modification of the shape of at least part of the bar-cut bar, and/or
• the bar-cutting step may include a reduction in diameter of at least part of the bar-cut bar, and/or
• the reduction in the diameter of the at least part of the free-cutting bar can comprise a variation of the diameter along the at least part of the free-cutting bar, and/or
• the bar turning, before turning, and/or the raw bar, before turning, and/or the work-hardened raw bar, before turning preferably has a hardness of less than 60%, more preferably than 50%.
• the turning step is a machining step.
• the purpose of the bar-cutting step is to remove or remove material from at least part of the bar-turning bar and/or from the raw bar and/or from the work-hardened raw bar.
• the hardening step implemented during the step for obtaining the mechanical part and the surface hardening step are two distinct steps.
• the hardening step and/or the surface hardening step according to the invention is carried out cold, that is to say at a temperature below 50° C., more preferably still below 30° C. , more preferably at room temperature or at standard temperature.
• the work hardening step increases the work hardening rate of at least a part of the free-cut bar and/or the free-cut bar and/or the raw bar by at least 10%, preferably still at least 15% and preferably at least 20%.
• a difference between the at least part of the bar turning and/or the bar turning and/or the raw bar, before work hardening, and the at least part of the bar turning work hardened and/ or of the work-hardened turned bar and/or of the work-hardened raw bar, after work-hardening is preferably greater than 10%, more preferably greater than 15% and more preferably greater than 20%.
• the work hardening step of at least a part of the raw bar or of the at least a part of the free-cutting bar or of the at least one turned part of the free-cutting bar is a step of stretching to reduce a diameter of the at least a part of the raw bar or of the at least a part of the bar turning or of the at least a turned part of the bar turning.
• the method includes a smoothing step to reduce the roughness of at least part of the surface of the mechanical part.
• the smoothing step can comprise a modification of the shape of at least part of the surface of the mechanical part.
• the smoothing step can be a turning step.
• the smoothing step can be implemented on all or part, for example on at least one part of the surface of the mechanical part, of the mechanical part.
• the smoothing step does not have the objective of significantly reducing the diameter of at least part of the surface of the mechanical part.
• the smoothing step does not significantly reduce the diameter of at least part of the surface of the mechanical part.
• the smoothing step is considered as machining according to the invention.
• the smoothing step and the surface hardening step are implemented simultaneously during the same and/or single step.
• the smoothing step and the surface hardening step can be implemented simultaneously during the same turning step.
• the turning step can be a rolling or burnishing step.
• the turning step can be implemented on the entire mechanical part or on at least part of the surface of the mechanical part.
• the surface hardening step and the smoothing step can constitute one and the same and/or single rolling or burnishing step.
• the revolving part and/or the timepiece and/or the non-magnetic part and/or the mechanical part and/or the at least part of the surface of the non-magnetic part corresponding to the at least one part of the surface of the work-hardened and heated mechanical part and/or the free-cutting bar and/or the raw bar has a composition of chemical elements identical to that of the austenitic alloy according to the invention.
• the method and its conditions of implementation have the effects of:
• a quantity of reformed, or undeformed, austenitic phase in the part preferably depends on the duration of the heating step.
• a hardening rate greater than or equal to 30% is preferable in order to make the superstructure appear within the reformed or undeformed austenitic phase during the heating step.
• a strain hardening rate greater than or equal to 40%, more preferably 50% is preferable to make the superstructure appear within the reformed or undeformed austenitic phase during the heating step. It has been observed that a work hardening rate of 25% does not make it possible to obtain this superstructure, regardless of the duration of the heating step.
• a nitrogen concentration of the reformed austenitic phase of the non-magnetic part obtained by the process is lower than the nitrogen concentration of the mechanical part.
• a nitrogen concentration of the deformed austenitic phase is greater than the reformed austenitic phase.
• the nitrogen concentration of the deformed austenitic phase is equal or approximately equal to the nitrogen concentration of the mechanical part.
• the process causes nitrogen depletion of the austenitic phase of the mechanical part located in the zones close to the dislocations, preferably and in particular at the level of the slip bands.
• the process causes the precipitation of nitrides.
• the nitride precipitates and the nitrogen depletion of the austenitic phase of the mechanical part are generated during the heating step.
• Austenitic alloy preferably according to the invention, obtained or capable of being obtained by the process according to the invention.
• the alloy according to the invention and/or the non-magnetic part according to the invention is preferably implemented by the method according to the invention.
• the method according to the invention is particularly suitable, preferably even specially designed, to implement the alloy according to the invention and/or the non-magnetic part according to the invention.
• any characteristic of the method according to the invention can be integrated into the alloy according to the invention and/or into the non-magnetic part according to the invention and vice versa.
• FIGURE 1 shows scanning electron microscopy images of a balance shaft
• FIGURE 2 is a diagram illustrating the hardness of 20AP and FINEMAC steel bars before and after implementation of the state-of-the-art hardened timepiece manufacturing process for an applied load of 0.5 kg ,
• FIGURE 3 illustrates the evolution of the induced moment in an annealed 316L steel part 513, in a work-hardened 316L steel part 511, in an annealed nickel-free Al alloy 514 and in a work-hardened Al nickel-free alloy 512 as a function of the field applied magnetic,
• FIGURE 4 illustrates an enlargement of curves 511, 512 and 514 of Figure 3
• FIGURES 5a and 5b are, respectively, scanning electron microscopy images of a turned part and respectively of a turned and smoothed part
• FIGURE 6 is a diagram representing the hardness, for an applied load of 1 kg, of raw bars in Al alloys work hardened at a work hardening rate of 85% and the hardness 612 of raw bars in A2 alloys work hardened at a work hardening rate of work hardening of 85% depending on the heating temperature and for a heating time of one hour,
• FIGURE 7 illustrates the evolution of hardness, for an applied load of 1 kg, as a function of the work hardening rate of bars made of the Al alloy for different heating temperatures of the bar
• FIGURE 8 illustrates the evolution of the hardness, for an applied load of 1 kg, of a bar composed of Al alloy work hardened at a work hardening rate of 85% as a function of the heating time, for a heating temperature 575°C,
• FIGURES 9a and 9b show, respectively, the equivalent hardness HV1 measured at the surface and at different depths in an Al alloy bar hardened by stretching then heated to a temperature of 525°C and respectively in an Al alloy bar hardened by stretching then superficially hardened by machining then heated to a temperature of 525°C
• - FIGURE 10 shows images and a crystallographic analysis by transmission electron microscopy in bright field mode taken on a part manufactured by the method according to the invention
• FIGURE 11 is a graph illustrating the evolution of the hardness of a non-magnetic part, obtained by the method according to the invention, as a function of the hardening rate of the mechanical part, from which the non-magnetic part is obtained , and the duration of the heating step,
• FIGURE 12 is a scanning electron microscopy image of a section of a non-magnetic part according to the invention on which the surface layer and the central part of the non-magnetic part are visible,
• FIGURE 13 is a scanning electron microscopy image of a cross-section of the surface part of a non-magnetic part according to the invention on which the structure of the hardened and then heated surface layer is visible,
• FIGURE 14 is a scanning electron microscopy image in backscattered electron diffraction mode on a thin layer of a section of the surface part of a non-magnetic part according to the invention on which are visible the reformed austenitic domains, the superstructures and nitride precipitates.
• variants of the invention may in particular be considered comprising only a selection of characteristics described, isolated from the other characteristics described (even if this selection is isolated within a sentence including these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art.
• This selection includes at least one feature, preferably functional without structural details, or with only part of the structural details if only this part is sufficient to confer a technical advantage or to differentiate the invention from the state of the prior art .
• the embodiment presented relates to the manufacture of a non-magnetic part of revolution 1.
• the part manufactured may be a clockwork balance 1 or balance pin 1 as shown in FIGURE 1.
• FIG. FIGURE 1 is presented an image of a conventional pendulum 1.
• a balance 1 is a part of revolution comprising an axis of revolution 2.
• Each of the two ends 112 of the balance 1 forms a pivot zone 112 intended to constitute a friction zone 112.
• the diameter, measured radially with respect to the axis of revolution 2, pivot zones 112 is about 60 ⁇ m.
• the usual process is known in the state of the art comprising the machining of a raw bar made of 20AP or FINEMAC steel followed by heat treatment of hardening.
• the hardening heat treatment includes heating to a temperature above 700°C, typically around 800°C, for 15 minutes followed by water quenching of the part followed by tempering at a temperature below 300°C, typically at 175° C for 30 minutes to adjust the hardness and relax the stresses generated during quenching.
• This hardening heat treatment is followed by a final step of smoothing the manufactured part, for example rolling aimed at improving the surface condition of the part.
• FIGURE 2 is presented a diagram illustrating the Vickers hardness (HV) measured on bars of 2 mm diameter in 20AP and FINEMAC steels before 441, 442 and after 443, 444 implementation of the heat treatment of hardening of the state art for an applied load of 0.5 kg.
• Bars 441 and 442 respectively illustrate the hardness of the raw bar of 20AP steel, before implementation of the state-of-the-art hardening heat treatment, and respectively the hardness of the raw bar of FINEMAC steel , before implementation of the hardening heat treatment. These measurements were obtained from the data (time-temperature) specified in the state of the art. Bars 443 and 444 respectively in FIG.
• the hardness values of the raw bars are around 300 HVo,s and the hardness of the balance bars is less than or equal to 700 HVo,s.
• the inventors observed that certain austenitic alloys can be used, counter-intuitively, when they are implemented under the conditions of the process according to the invention, for the manufacture of parts requiring machining and /or significant hardening. Indeed, austenitic alloys are known to be difficult to machine and are therefore not used when significant machining and/or several machining steps are required. According to the invention, the austenitic alloys chosen to constitute the timepiece comprise, in mass percentage, iron between 50 and 85%, one or more gammagenic elements whose mass percentage or the sum of the mass percentages is between 8 and 38%.
• FIGURES 3 and 4 illustrate the mass susceptibility of austenitic alloys, i.e. the evolution of the induced magnetic moment in emu/g as a function of the applied field in Teslas , and the residual magnetization of these austenitic alloys.
• the 316L alloy comprises, in mass percentage, between 16 and 19% chromium, between 9 and 13% nickel, between 1.5 and 3% molybdenum, less than 2% molybdenum, less than 0.01% Manganese, less than 0.03% carbon, less than 0.005% sulfur, less than 0.003% nitrogen, less than 0.002% oxygen and the balance iron.
• FIGURES 3 and 4 illustrate the evolution of the induced magnetic field of 316L after annealing 511 at a temperature of 1050° C. for 30 minutes and of 316L drawing 513 at a work hardening rate of 60%.
• the relative permeability, denoted pr , of 316L after 513 drawing at a work hardening rate of 60% is 8.8 and the relative permeability of 316L after 511 annealing at a temperature of 1050°C for 30 minutes is 1, 08, the relative permeability Note that the value of the residual magnetization is greater than ten emu/g for work-hardened 316L 513. These residual magnetization values are incompatible with applications in the watchmaking field and do not allow to use this type of alloy as a non-magnetic part and, in particular, as a timepiece.
• austenitic alloys are used, counter-intuitively and surprisingly, when they are used under the process conditions, for the manufacture of parts having good mechanical properties, in particular good impact resistance. , breakage, deformation and wear. Indeed, it is known that the heat treatments for hardening of the state of the art detailed above (heating at a temperature above 750°C followed by quenching and tempering) are not effective on austenitic alloys.
• an austenitic alloy comprising, in mass percentage, between 0.15 and 0.25% carbon, between 9.5 and 12.5% manganese, 16.5% chromium, between 0.45 and 0.55% nitrogen, 2.7 % molybdenum and the rest of iron
• an austenitic alloy comprising between 21 and 24% manganese, between 19 and 23% chromium between 0.5 and 1.5% molybdenum, 0.9% nitrogen, less than 0.08% carbon and the balance iron.
• the method according to the invention does not generate any significant change in the composition of the alloy making up the mechanical part or the raw bar used for implementing the method.
• the timepiece obtained, by implementing the method according to the invention comprises the same composition as that of the alloy making up the mechanical part or the raw bar used (Al and A2 according to the non-limiting embodiment present).
• FIGURES 3 and 4 The effect of work hardening on the residual magnetization of Al and 316L alloys is presented in FIGURES 3 and 4.
• Curves 512 and 514 represent the respective evolution of the magnetic moment induced in the Al alloy after annealing at a temperature of 1050°C for 30 minutes and drawing at a work hardening rate of 72%.
• the relative permeability, pr , of the Al alloy after drawing at a work hardening rate of 72% is 1.006
• the relative permeability, pr of the Al alloy after annealing at a temperature of 1050°C for 30 minutes is 1.002.
• the method comprises a step for obtaining a mechanical part of which at least part of a surface has a hardness greater than 350 HV.
• the mechanical part is a part of revolution, in particular a solid rod.
• the obtaining step is followed by a surface hardening step aimed at forming a surface layer extending radially from the surface of the mechanical part towards the axis of rotation (and of symmetry) of the mechanical part.
• the surface layer has a thickness typically less than 30 ⁇ m.
• the surface layer has a hardening rate gradient along the direction extending radially from the surface of the hardened mechanical part towards the inside of the hardened mechanical part.
• the variation in hardening rate along the thickness of the surface layer is greater than 18%. In other words, the difference between the hardening rate of the surface of the mechanical part and the hardening rate of the central part of the mechanical part is greater than 18%.
• the hardening rate of the surface of the hardened mechanical part is greater than 100%.
• the surface work hardening step is followed by a step of heating the work hardened mechanical part to a temperature between 350° C. and 700° C. to harden the work hardened parts of the mechanical part.
• the surface hardening step is a turning step which has the effect, in addition to surface hardening the mechanical part, of reducing the roughness of the surface of the mechanical part.
• FIGURE 5b is an image of one end of the raw bar turned, then surface hardened and simultaneously smoothed by rolling which is a particular turning method.
• the arithmetic roughness of the work-hardened and smoothed mechanical part obtained is of the order of 0.05 ⁇ m.
• the step of obtaining the method comprises the manufacture of the mechanical part from a raw bar made of Al or A2 alloy.
• the step for obtaining comprises a step of cold working of at least part of the raw bar followed by a step of turning at least part of the hardened raw bar.
• the purpose of this hardening step is to increase the density of dislocations in the raw hardened bar, and therefore in the mechanical part.
• the work-hardened raw bar is called the free-turning bar and the bar turned, i.e. the raw bar work-hardened then cut, corresponds to the part mechanical.
• a turned end of the raw bar is shown in FIGURE 5a.
• the raw bar has the shape of a wire (or a tube or a rod) 2 to 4 mm in diameter, typically 3 mm, and has a hardness of the order of 280 HV. It should be noted that the raw bar, or the hardened raw bar, must not have too high a hardening rate, typically be less than 50%, so that the turning can be carried out correctly.
• the hardening step is a drawing step aimed at increasing the hardness of the raw bar.
• the hardening step, here drawing has the effect of hardening the raw bar at a hardening rate greater than 30%.
• the cutting step is carried out so as to obtain the particular shape of the balance shaft 1 as shown in FIGURE 1.
• the purpose of the cutting step is to to obtain a turned bar whose diameter varies between 20 to 60 ⁇ m at the ends 112, corresponding to the pivot zones 112 of the rocker arm 1, and 1.4 mm for the part 113 of work-hardened and turned raw bar having the highest diameter.
• the bar turning step further hardens the bar turning bar (the bar obtained after the drawing step) and substantially modifies the section of the bar turning.
• the mechanical part (work-hardened and turned bar) has a section which varies along its axis 2 of revolution.
• the heating step is implemented for a period of one hour at a temperature below 700° C. with a temperature rise ramp of 50° C./min under ambient conditions.
• the method according to the invention makes it possible to obtain mechanical properties similar or even better than those obtained by the heat treatments for hardening of the state of the art while eliminating the quenching step required in the heat treatments for hardening the 'state of the art.
• This heating step according to the invention is carried out at low temperature, in particular compared to the temperatures of the hardening heat treatments of the state of the art, there is therefore no stress concentration in the piece after the heating step according to the invention.
• the method according to the invention therefore does not require tempering after the heating step.
• FIGURE 6 is a diagram in which is presented the hardness 611 of raw bars in Al alloys work hardened at a work hardening rate of 85% and the hardness 612 of raw bars in A2 alloys work hardened at a work hardening rate of 85% in depending on the heating temperature.
• the heating time is one hour.
• a reduction in the effect of heating on the hardness 611, 612 is observed above 520° C. for the A2 alloy and above 650° C. for the Al alloy.
• the preferred temperature is between 450°C and 640°C and that the optimum temperature is between 500°C and 600°C.
• FIG. 7 represents the evolution of the hardness as a function of the work hardening rate of a bar with a diameter of 3 mm composed of the A2 alloy for different heating temperatures.
• the heating time is one hour.
• Work hardening was carried out by drawing a raw bar (not work hardened) in Al alloy. It can be seen that the greater the degree of work hardening of the bar before heating, the greater the hardening of the work hardened bar. Consequently, to obtain the hardness of the mechanical part as high as possible, it is advisable to work harden the part as much as possible before implementing the heating step, that is to say heating a part having a rate of work hardening as high as possible. Furthermore, this also implies that the heating step should preferably be carried out as the last step of the process.
• the evolution of the hardness HV1 of a bar composed of Al alloy work hardened at a work hardening rate of 85% is illustrated as a function of the heating time for an applied load of 1 kg.
• the bar is heated to a temperature of 575°C. It is noted that the hardness is maximum for times between 100 and 300 hours.
• the hardness is greater than 800 HV after 45 hours of heating and 700 HV after 3 hours of heating.
• the hardness obtained is a function of the hardening rate of the bar before heating and the hardness of the bar before heating. For a given heating temperature and time, the greater the work hardening rate of the bar before heating, the greater the hardness of the bar obtained after heating. Similarly, for a given heating temperature and time, at most the bar hardness before heating is high the greater the hardness of the bar obtained after heating.
• FIGURES 9a and 9b is illustrated the evolution of the hardness of bars in alloy A2 as a function of the depth of measurement of the hardness.
• the depth of measurement corresponds to the distance measured radially from the external surface of the bars in the direction of the axis of rotation (or the center) of the bar.
• the hardness indicated is an equivalent HV1 hardness, that is to say for a load of 1 kg, calculated from hardness measurements by Ultranonindentation with an indentation size of around 1.5 ⁇ m.
• FIGURE 9a is illustrated the evolution of the hardness of an A2 alloy raw bar work hardened at a rate of 30% by stretching then heated to a temperature of 525° C. for 1 hour.
• the hardness of the bar is constant and homogeneous over the entire depth explored.
• the hardness of the bar is around 600 HV1.
• FIGURE 9b are presented several series of measurements carried out on an Al alloy bar work hardened at a rate of 30% by stretching then superficially work hardened by machining then heated to a temperature of 525° C. for 1 hour.
• the work-hardened and heated part comprises a surface layer having a hardness gradient which decreases along the direction extending radially from the external surface of the part towards the central part of the part.
• the surface layer has a thickness of less than 20 ⁇ m
• the hardness of the surface of the work-hardened and heated part is greater than 700 HV1
• the central part has a hardness less than or equal to 400 HV1
• the hardness gradient in the surface layer is greater than 200 HV1.
• the surface hardening when it is followed by heating according to the invention, makes it possible to obtain a surface layer having a hardness gradient.
• This also demonstrates that the surface hardening generates the appearance of an average hardening rate gradient in the surface layer which is greater than 18%.
• the average rate of hardening of the central part is identical to that of the bar which is not superficially hardened (by machining), i.e. less than or equal to 85%, it is of the order of 30% depending on the embodiment.
• the average hardening rate of the surface is greater than 85%. Machining parameters are not optimal and more effective surface work hardening may be achieved.
• the part manufactured according to the method has such a hardness gradient makes it possible to obtain a surface hardness of the part which is much greater than the hardness of the central part of the part.
• the method therefore makes it possible to obtain a part whose central part retains a certain ductility and therefore gives the part better resistance to shocks, to rupture, to deformation than a part having a homogeneous and constant hardness over the whole. of the room.
• the method according to the invention makes it possible to modulate the hardness of the central part of the manufactured part according to the application by modulating the work hardening rate of the mechanical part resulting from the obtaining stage. It is thus possible to give the part better resistance to shocks, to rupture, to deformation by having a central part that is more ductile than the surface of the part.
• the step of obtaining the mechanical part includes work hardening of the part as a whole, for example by stretching, at a high work hardening rate, for example greater than or equal to 85% to further increase the hardness of the manufactured part.
• the process also makes it possible to obtain a part with very good surface hardness and therefore better resistance to shocks and wear.
• the surface work hardening step is implemented by means of turning making it possible to surface smooth and work harden the part, in particular rolling or burnishing, this saves considerable time and energy.
• using turning to implement the surface hardening step also makes it possible to take advantage of the work hardening of the part generated by the smoothing to further increase the hardness of the part after heating.
• the manufactured part comprises a predominant face-centered cubic crystalline structure and further comprises the presence of a compact hexagonal crystalline structure while the alloys Al and A2 composing the rolled mechanical part , before heating, comprised a single face-centered cubic crystal structure.
• this compact hexagonal crystallographic structure corresponds to the crystal structure of crystalline precipitates, within the face-centered cubic structure, whose Féret diameter is typically between 5 and 80 nm.
• the heating step implemented under the conditions of the process according to the invention induces a change in the crystalline structure of at least part of the grains of the austenitic alloy making up the mechanical part of a cubic structure. face centered towards a compact hexagonal structure.
• the advantages and effects of the alloy according to the invention, in particular with regard to the mechanical properties, are, at least in part, conferred by the modifications of the crystallographic structure observed.
• the inventors have also observed the presence of nitrogen atoms surrounding dislocations of the austenitic alloy making up the part manufactured by the process according to the invention.
• the advantages and effects of the alloy according to the invention are, at least in part, conferred by the reduction in the mobility of the dislocations in the manufactured part due to the presence of the atoms of nitrogens around the dislocations.
• FIGURES 11 to 14 The results presented in FIGURES 11 to 14 were obtained from non-magnetic parts obtained according to the method according to the invention.
• the mechanical parts used to obtain non-magnetic parts are bars with a diameter of 3.2 mm made of an alloy found under the trade names CHRONIFER® 108 and BIODUR® 108.
• the alloy of trade name CHRONIFER® 108 UNS S29108 is sold by the company KLEIN.
• CHRONIFER® 108 consists, in mass percentage, of manganese between 21 and 24%, of chromium between 19 and 23%, of molybdenum between 0.5 and 1.5%, of 0.9% of nitrogen, of 0 25% copper, carbon at a percentage by mass of less than 0.08%, silicon at a percentage by mass of less than 0.75%, phosphorus at a percentage by mass of less than 0.03%, sulfur at a percentage by mass less than 0.1%, of nickel at a mass percentage of less than 0.1% and of iron, the mass percentage of which completes the composition to obtain a total of 100%.
• the alloy with the trade name BIODUR® 108 is sold by the company CARPENTER.
• BIODUR® 108 is made up, in mass percentage, of manganese between 21 and 24%, of chromium between 19 and 23%, of molybdenum between 0.5 and 1.5%, of 0.9% of nitrogen, of 0 .01% sulphur, 0.25% copper, 0.1% nickel, 0.75% silicon, 0.08% carbon, 0.03% phosphorus and iron whose mass percentage completes the composition to obtain a total of 100%.
• Identical results were obtained for each of the CHRONIFER® 108 and BIODUR® 108 alloys.
• FIGURE 11 is illustrated the evolution of the hardness HV1 of a non-magnetic part obtained by the implementation of the method according to the invention.
• FIGURE 11 illustrates the effect of the hardening rate of the mechanical part as well as the effect of the heating time on the hardness of the non-magnetic part obtained. Three hardening rates were studied: 25%, 42% and 85%. It is noted that the greater the hardening rate of the mechanical part, the greater the hardness of the mechanical part obtained.
• the cold hardening step generates dislocations. These dislocations constitute sites of intra and intergranular germination of nitride precipitates. In addition, these dislocations make it possible to accelerate the precipitation of the nitride precipitates during the heating step. The dislocations therefore contribute to increasing the hardening of the alloy.
• the work hardening prior to the heat treatment makes it possible to obtain precipitation at temperatures necessarily lower than 700° C., preferably at temperatures lower than or equal to 650° C. Usually, this precipitation is observed at temperatures well above 700°C.
• work hardening prior to heat treatment makes it possible to obtain substantial precipitation for shorter heating times.
• FIGURE 12 the surface layer and the central part of the non-magnetic part are observed. These two parts are clearly visible and distinguishable. We also observe the presence of chromium nitride precipitates within the domains of reformed austenite.
• the method according to the invention thus makes it possible to obtain a non-magnetic part having a ductile central part and having a hard surface layer.
• FIGURE 13 illustrates the reformed austenitic domains 3, comprising the y' and y' phases, and the deformed austenitic domains 4, comprising the y phase.
• FIGURE 14 is illustrated the microstructure of the non-magnetic part obtained by the method according to the invention with work hardening at a work hardening rate of 85% followed by heating at 575° C. for 978 hours.
• work hardening at a work hardening rate of 85% followed by heating at 575° C. for 978 hours.
• the presence of precipitates 6 of Cr2No,9i nitrides is also observed.
• superstructures 7, of phase y are also observed.
• the grains of the alloy have a size of less than 1 ⁇ m. It is also noted that the size of the precipitates of nitrides 7 have a size of less than 100 nm.
• the step of obtaining the mechanical part includes:
• the non-magnetic part is a timepiece, and/or
• the non-magnetic part is an anchor rod or an escapement pinion, and/or
• the invention provides for the use of the non-magnetic part, for its non-magnetic and/or hardness and/or tribological and/or breaking strength properties, and/or
• the step of obtaining comprises a step of turning at least part of a bar turning followed by a work hardening step of at least one turned part of the bar turning to form the mechanical part
• the smoothing step is a burnishing or rolling step, and/or
• the austenitic alloy comprises chromium in a mass percentage greater than 8%, and/or
• the austenitic alloy comprises nitrogen at a mass percentage greater than 0.1%, and/or
• the gammagenic element(s) of the austenitic alloy comprise, in mass percentage, manganese between 8 to 30% and/or cobalt between 0 and 10%
• the austenitic alloy comprises one or more non-gamgenic elements whose mass percentage or the sum of the mass percentages is between 10 and 35%,
• the non-gammagenic element(s) of the austenitic alloy comprise, in mass percentage, chromium between 0 and 35% and/or molybdenum between 0 and 8% and/or silicon between 0 to 2% and/or titanium between 0 and X% and/or niobium between 0 and X% and/or tungsten between 0 and X% and/or sulfur between 0 and 1.5%, and/or
• the hardness gradient has a value greater than or equal to 100 HV, and/or
• the turning step is a rolling or burnishing step.

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• 2020
  • 2020-12-23 FR FR2014031A patent/FR3118064B1/fr active Active
• 2021
  • 2021-12-22 WO PCT/EP2021/087307 patent/WO2022136552A1/fr active Application Filing
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